ALLIANT ENERGY CORP, 10-K filed on 2/20/2026
Annual Report
v3.25.4
Document And Entity Information - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Jan. 31, 2026
Jun. 30, 2025
Entity Information [Line Items]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2025    
Document Transition Report false    
Entity Registrant Name ALLIANT ENERGY CORP    
Entity Central Index Key 0000352541    
Entity Incorporation, State or Country Code WI    
Entity Address, Address Line One 4902 N. Biltmore Lane    
Entity Address, City or Town Madison    
Entity Address, State or Province WI    
Entity Address, Postal Zip Code 53718    
City Area Code 608    
Local Phone Number 458-3311    
Entity File Number 1-9894    
Entity Tax Identification Number 39-1380265    
Title of 12(b) Security Common Stock, $0.01 Par Value    
Trading Symbol LNT    
Security Exchange Name NASDAQ    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Large Accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
ICFR Auditor Attestation Flag true    
Financial Statement Error Correction false    
Entity Shell Company false    
Entity Public Float     $ 15,500.0
Entity Common Stock, Shares Outstanding   257,140,829  
Current Fiscal Year End Date --12-31    
Document Fiscal Year Focus 2025    
Document Fiscal Period Focus FY    
Amendment Flag false    
Documents Incorporated by Reference
Portions of the Proxy Statement relating to Alliant Energy Corporation’s 2026 Annual Meeting of Shareowners are, or will be upon filing with the Securities and Exchange Commission, incorporated by reference into Part III hereof.
    
Auditor Name Deloitte & Touche LLP    
Auditor Location Milwaukee, Wisconsin    
Auditor Firm ID 34    
IPL [Member]      
Entity Information [Line Items]      
Entity Registrant Name INTERSTATE POWER & LIGHT CO    
Entity Central Index Key 0000052485    
Entity Incorporation, State or Country Code IA    
Entity Address, Address Line One Alliant Energy Tower    
Entity Address, City or Town Cedar Rapids    
Entity Address, State or Province IA    
Entity Address, Postal Zip Code 52401    
City Area Code 319    
Local Phone Number 786-4411    
Entity File Number 1-4117    
Entity Tax Identification Number 42-0331370    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Non-accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
Financial Statement Error Correction false    
Entity Shell Company false    
Entity Public Float     0.0
Entity Common Stock, Shares Outstanding   13,370,788  
Auditor Name Deloitte & Touche LLP    
Auditor Location Milwaukee, Wisconsin    
Auditor Firm ID 34    
WPL [Member]      
Entity Information [Line Items]      
Entity Registrant Name WISCONSIN POWER & LIGHT CO    
Entity Central Index Key 0000107832    
Entity Incorporation, State or Country Code WI    
Entity Address, Address Line One 4902 N. Biltmore Lane    
Entity Address, City or Town Madison    
Entity Address, State or Province WI    
Entity Address, Postal Zip Code 53718    
City Area Code 608    
Local Phone Number 458-3311    
Entity File Number 0-337    
Entity Tax Identification Number 39-0714890    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Non-accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
Financial Statement Error Correction false    
Entity Shell Company false    
Entity Public Float     $ 0.0
Entity Common Stock, Shares Outstanding   13,236,601  
Auditor Name Deloitte & Touche LLP    
Auditor Location Milwaukee, Wisconsin    
Auditor Firm ID 34    
v3.25.4
Consolidated Statements Of Income - USD ($)
shares in Millions, $ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Revenues:      
Electric utility $ 3,697 $ 3,372 $ 3,345
Gas utility 525 465 540
Other utility 51 54 52
Non-utility 89 90 90
Total revenues 4,362 3,981 4,027
Operating expenses:      
Electric production fuel and purchased power 742 628 736
Electric transmission service 625 613 583
Cost of gas sold 263 224 299
Asset valuation charge for IPL's Lansing Generating Station 0 60 0
Other operation and maintenance 740 676 675
Depreciation and amortization 846 772 676
Taxes other than income taxes 121 122 115
Total operating expenses 3,337 3,095 3,084
Operating income (loss) 1,025 886 943
Other (income) and deductions:      
Interest expense 512 449 394
Equity income from unconsolidated investments, net (60) (61) (61)
Allowance for funds used during construction (89) (75) (100)
Other 1 (3) 3
Total other (income) and deductions 364 310 236
Income before income taxes 661 576 707
Income tax expense (benefit) (149) (114) 4
Net income attributable to common shareowners $ 810 $ 690 $ 703
Weighted average number of common shares outstanding:      
Basic (in shares) 257.0 256.5 253.0
Diluted (in shares) 257.8 256.8 253.3
Earnings per weighted average common share attributable to Alliant Energy common shareowners:      
Basic (in dollars per share) $ 3.15 $ 2.69 $ 2.78
Diluted (in dollars per share) $ 3.14 $ 2.69 $ 2.78
IPL [Member]      
Revenues:      
Electric utility $ 1,896 $ 1,747 $ 1,761
Gas utility 265 250 300
Other utility 47 49 49
Total revenues 2,208 2,046 2,110
Operating expenses:      
Electric production fuel and purchased power 283 269 282
Electric transmission service 422 417 420
Cost of gas sold 130 123 166
Asset valuation charge for IPL's Lansing Generating Station 0 60 0
Other operation and maintenance 373 358 353
Depreciation and amortization 463 404 388
Taxes other than income taxes 59 60 57
Total operating expenses 1,730 1,691 1,666
Operating income (loss) 478 355 444
Other (income) and deductions:      
Interest expense 211 177 155
Allowance for funds used during construction (56) (43) (21)
Other (7) (12) 2
Total other (income) and deductions 148 122 136
Income before income taxes 330 233 308
Income tax expense (benefit) (127) (129) (58)
Net income attributable to common shareowners 457 362 366
WPL [Member]      
Revenues:      
Electric utility 1,801 1,625 1,584
Gas utility 260 215 240
Other utility 4 5 3
Total revenues 2,065 1,845 1,827
Operating expenses:      
Electric production fuel and purchased power 459 359 455
Electric transmission service 203 196 163
Cost of gas sold 133 101 134
Other operation and maintenance 306 279 271
Depreciation and amortization 370 357 280
Taxes other than income taxes 55 56 52
Total operating expenses 1,526 1,348 1,355
Operating income (loss) 539 497 472
Other (income) and deductions:      
Interest expense 173 165 149
Allowance for funds used during construction (33) (32) (79)
Other 12 8 (3)
Total other (income) and deductions 152 141 67
Income before income taxes 387 356 405
Income tax expense (benefit) (14) 11 60
Net income attributable to common shareowners $ 401 $ 345 $ 345
v3.25.4
Consolidated Balance Sheets - USD ($)
$ in Millions
Dec. 31, 2025
Dec. 31, 2024
Current assets:    
Cash and cash equivalents $ 556 $ 81
Accounts receivable, less allowance for expected credit losses 476 427
Production fuel, at weighted average cost 46 54
Gas stored underground, at weighted average cost 49 55
Materials and supplies, at weighted average cost 193 186
Regulatory assets 155 210
Other 222 171
Total current assets 1,697 1,184
Property, plant and equipment, net 20,344 18,701
Investments:    
ATC Holdings 463 415
Other 231 224
Total investments 694 639
Other assets:    
Regulatory assets 2,119 2,064
Deferred charges and other 137 126
Total other assets 2,256 2,190
Total assets 24,991 22,714
Current liabilities:    
Current maturities of long-term debt 1,074 1,171
Commercial paper 88 558
Accounts payable 498 532
Accrued interest 124 112
Regulatory liabilities 88 69
Other 251 273
Total current liabilities 2,123 2,715
Long-term debt, net (excluding current portion) 10,954 8,677
Other liabilities:    
Deferred tax liabilities 2,310 2,188
Regulatory liabilities 1,113 959
Pension and other benefit obligations 173 224
Other 984 947
Total other liabilities 4,580 4,318
Commitments and contingencies (Note 16)
Common Stock, Shares, Issued 257,137,261 256,690,222
Common equity:    
Common stock $ 3 $ 3
Additional paid-in capital 3,101 3,060
Retained earnings 4,243 3,954
Accumulated other comprehensive income 1 1
Shares in deferred compensation trust - 367,338 and 372,116 shares at a weighted average cost of $39.05 and $36.56 per share (14) (14)
Total common equity 7,334 7,004
Total liabilities and equity 24,991 22,714
IPL [Member]    
Current assets:    
Cash and cash equivalents 7 29
Accounts receivable, less allowance for expected credit losses 185 192
Production fuel, at weighted average cost 18 30
Gas stored underground, at weighted average cost 24 25
Materials and supplies, at weighted average cost 111 113
Regulatory assets 59 77
Other 58 43
Total current assets 462 509
Property, plant and equipment, net 10,436 9,336
Other assets:    
Regulatory assets 1,557 1,509
Deferred charges and other 40 53
Total other assets 1,597 1,562
Total assets 12,495 11,407
Current liabilities:    
Current maturities of long-term debt 0 300
Commercial paper 88 50
Accounts payable 232 263
Accounts payable to associated companies 45 47
Accrued taxes 53 77
Accrued interest 47 48
Regulatory liabilities 41 54
Other 80 89
Total current liabilities 586 928
Long-term debt, net (excluding current portion) 4,680 3,790
Other liabilities:    
Deferred tax liabilities 1,278 1,179
Regulatory liabilities 545 492
Pension and other benefit obligations 30 46
Other 532 511
Total other liabilities 2,385 2,228
Commitments and contingencies (Note 16)
Common Stock, Shares, Issued 13,370,788 13,370,788
Common equity:    
Common stock $ 33 $ 33
Additional paid-in capital 3,497 3,212
Retained earnings 1,314 1,216
Total common equity 4,844 4,461
Total liabilities and equity 12,495 11,407
WPL [Member]    
Current assets:    
Cash and cash equivalents 37 51
Accounts receivable, less allowance for expected credit losses 273 220
Production fuel, at weighted average cost 28 24
Gas stored underground, at weighted average cost 25 30
Materials and supplies, at weighted average cost 81 69
Regulatory assets 96 133
Prepaid gross receipts tax 52 51
Other 59 57
Total current assets 651 635
Property, plant and equipment, net 9,363 8,861
Other assets:    
Regulatory assets 562 555
Deferred charges and other 79 55
Total other assets 641 610
Total assets 10,655 10,106
Current liabilities:    
Current maturities of long-term debt 0 0
Commercial paper 0 183
Accounts payable 197 209
Accrued interest 46 44
Regulatory liabilities 47 15
Other 105 94
Total current liabilities 395 545
Long-term debt, net (excluding current portion) 3,669 3,370
Other liabilities:    
Deferred tax liabilities 861 865
Regulatory liabilities 568 467
Pension and other benefit obligations 75 102
Other 712 656
Total other liabilities 2,216 2,090
Commitments and contingencies (Note 16)
Common Stock, Shares, Issued 13,236,601 13,236,601
Common equity:    
Common stock $ 66 $ 66
Additional paid-in capital 2,613 2,533
Retained earnings 1,696 1,502
Total common equity 4,375 4,101
Total liabilities and equity $ 10,655 $ 10,106
v3.25.4
Consolidated Balance Sheets (Parenthetical) - $ / shares
Dec. 31, 2025
Dec. 31, 2024
Common stock, par value (in dollars per share) $ 0.01 $ 0.01
Common stock, shares authorized (in shares) 480,000,000 480,000,000
Common stock, shares outstanding (in shares) 257,137,261 256,690,222
Shares in deferred compensation trust (in shares) 367,338 372,116
Shares in deferred compensation trust, weighted average cost per share (in dollars per share) $ 39.05 $ 36.56
IPL [Member]    
Common stock, par value (in dollars per share) $ 2.50 $ 2.50
Common stock, shares authorized (in shares) 24,000,000 24,000,000
Common stock, shares outstanding (in shares) 13,370,788 13,370,788
WPL [Member]    
Common stock, par value (in dollars per share) $ 5 $ 5
Common stock, shares authorized (in shares) 18,000,000 18,000,000
Common stock, shares outstanding (in shares) 13,236,601 13,236,601
v3.25.4
Consolidated Statements Of Cash Flows - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Cash flows from operating activities:      
Net income $ 810 $ 690 $ 703
Adjustments to reconcile net income to net cash flows from operating activities:      
Depreciation and amortization 846 772 676
Deferred tax expense (benefit) and tax credits (158) (117) 14
Asset valuation charge for IPL's Lansing Generating Station 0 60 0
Other 27 (22) (39)
Other changes in assets and liabilities:      
Accounts receivable (652) (547) (414)
Derivative assets 6 13 149
Accounts payable 14 96 (122)
Regulatory liabilities 140 (103) (149)
Deferred income taxes 252 259 84
Other (116) 66 (35)
Net cash flows from operating activities 1,169 1,167 867
Cash flows from (used for) investing activities:      
Utility construction and acquisition expenditures (2,277) (2,052) (1,731)
Other construction and acquisition expenditures (206) (197) (123)
Cash receipts on sold receivables 628 593 453
Proceeds from sales of partial ownership interests in West Riverside 0 123 120
Other (41) (14) (120)
Net cash flows from (used for) investing activities (1,896) (1,547) (1,401)
Cash flows from (used for) financing activities:      
Common stock dividends (521) (492) (456)
Proceeds from issuance of common stock, net 23 23 246
Proceeds from issuance of long-term debt 2,470 1,613 1,455
Payments to retire long-term debt (300) (809) (508)
Net change in commercial paper (470) 83 (167)
Other 0 (20) 3
Net cash flows from (used for) financing activities 1,202 398 573
Net increase (decrease) in cash, cash equivalents and restricted cash 475 18 39
Cash, cash equivalents and restricted cash at beginning of period 81 63 24
Cash, cash equivalents and restricted cash at end of period 556 81 63
Supplemental cash flows information:      
Interest (500) (434) (378)
Income taxes, net 266 197 88
Significant non-cash investing and financing activities:      
Accrued capital expenditures 178 224 364
Beneficial interest obtained in exchange for securitized accounts receivable 126 163 216
Federal [Member]      
Supplemental cash flows information:      
Income taxes, net 271 202 82
Iowa State [Member]      
Supplemental cash flows information:      
Income taxes, net (5) (5) 6
Indemnification Agreement [Member] | Renewable Tax Credits Transferred [Member]      
Supplemental cash flows information:      
Proceeds from renewable tax credits transferred to other corporate taxpayers 285 216 98
IPL [Member]      
Cash flows from operating activities:      
Net income 457 362 366
Adjustments to reconcile net income to net cash flows from operating activities:      
Depreciation and amortization 463 404 388
Deferred tax expense (benefit) and tax credits (96) (91) 8
Asset valuation charge for IPL's Lansing Generating Station 0 60 0
Other (25) (12) (10)
Other changes in assets and liabilities:      
Accounts receivable (599) (544) (437)
Regulatory assets (72) (2) 58
Derivative assets 4 6 84
Regulatory liabilities 20 (61) (92)
Deferred income taxes 194 178 36
Other (60) 57 (140)
Net cash flows from operating activities 286 357 261
Cash flows from (used for) investing activities:      
Utility construction and acquisition expenditures (1,473) (1,224) (712)
Cash receipts on sold receivables 628 593 453
Other (14) (53) (67)
Net cash flows from (used for) investing activities (859) (684) (326)
Cash flows from (used for) financing activities:      
Common stock dividends (359) (200) (280)
Capital contributions from parent 285 325 80
Proceeds from issuance of long-term debt 888 643 296
Payments to retire long-term debt (300) (500) 0
Net change in commercial paper 38 50 0
Other (1) (15) 7
Net cash flows from (used for) financing activities 551 303 103
Net increase (decrease) in cash, cash equivalents and restricted cash (22) (24) 38
Cash, cash equivalents and restricted cash at beginning of period 29 53 15
Cash, cash equivalents and restricted cash at end of period 7 29 53
Supplemental cash flows information:      
Interest (212) (169) (150)
Income taxes, net 139 175 117
Significant non-cash investing and financing activities:      
Accrued capital expenditures 98 128 140
Beneficial interest obtained in exchange for securitized accounts receivable 126 163 216
IPL [Member] | Federal [Member]      
Supplemental cash flows information:      
Income taxes, net 142 164 98
IPL [Member] | Iowa State [Member]      
Supplemental cash flows information:      
Income taxes, net (3) 11 19
IPL [Member] | Indemnification Agreement [Member] | Renewable Tax Credits Transferred [Member]      
Supplemental cash flows information:      
Proceeds from renewable tax credits transferred to other corporate taxpayers 140 117 76
WPL [Member]      
Cash flows from operating activities:      
Net income 401 345 345
Adjustments to reconcile net income to net cash flows from operating activities:      
Depreciation and amortization 370 357 280
Other (63) (51) (47)
Other changes in assets and liabilities:      
Accounts receivable (56) (5) 23
Regulatory assets 43 72 (34)
Regulatory liabilities 120 (41) (57)
Deferred income taxes 40 84 50
Other (19) 0 18
Net cash flows from operating activities 836 761 578
Cash flows from (used for) investing activities:      
Utility construction and acquisition expenditures (804) (828) (1,019)
Proceeds from sales of partial ownership interests in West Riverside 0 123 120
Other (23) (19) (47)
Net cash flows from (used for) investing activities (827) (724) (946)
Cash flows from (used for) financing activities:      
Common stock dividends (207) (196) (184)
Capital contributions from parent 80 55 245
Proceeds from issuance of long-term debt 296 297 297
Net change in commercial paper (183) (135) 28
Other (9) (14) (16)
Net cash flows from (used for) financing activities (23) 7 370
Net increase (decrease) in cash, cash equivalents and restricted cash (14) 44 2
Cash, cash equivalents and restricted cash at beginning of period 51 7 5
Cash, cash equivalents and restricted cash at end of period 37 51 7
Supplemental cash flows information:      
Interest (176) (163) (146)
Income taxes, net 109 14 (50)
Significant non-cash investing and financing activities:      
Accrued capital expenditures 71 87 217
WPL [Member] | Federal [Member]      
Supplemental cash flows information:      
Income taxes, net 124 41 (25)
WPL [Member] | State Taxes - Wisconsin [Member]      
Supplemental cash flows information:      
Income taxes, net (15) (27) (25)
WPL [Member] | Indemnification Agreement [Member] | Renewable Tax Credits Transferred [Member]      
Supplemental cash flows information:      
Proceeds from renewable tax credits transferred to other corporate taxpayers $ 145 $ 99 $ 22
v3.25.4
Consolidated Statements of Common Equity - USD ($)
$ in Millions
Total
IPL [Member]
WPL [Member]
Common Stock [Member]
Common Stock [Member]
IPL [Member]
Common Stock [Member]
WPL [Member]
Additional Paid-in Capital [Member]
Additional Paid-in Capital [Member]
IPL [Member]
Additional Paid-in Capital [Member]
WPL [Member]
Retained Earnings [Member]
Retained Earnings [Member]
IPL [Member]
Retained Earnings [Member]
WPL [Member]
Accumulated Other Comprehensive Income (Loss) [Member]
Shares in Deferred Compensation Trust [Member]
Beginning balance at Dec. 31, 2022       $ 3 $ 33 $ 66 $ 2,777 $ 2,807 $ 2,233 $ 3,509 $ 968 $ 1,192 $ 0 $ (13)
Beginning balance at Dec. 31, 2022 $ 6,276 $ 3,808 $ 3,491                      
Increase (Decrease) in Shareowners' Equity [Roll Forward]                            
Net Income 703 366 345             703 366 345    
Common stock dividends (456) (280) (184)             (456) (280) (184)    
At-the-market offering program, net and Shareowner Direct Plan issuances 246           246              
Capital contributions from parent   80 245         80 245          
Equity-based compensation plans and other 7           7              
Other comprehensive income (loss), net of tax 1                       1  
Ending balance at Dec. 31, 2023       3 33 66 3,030 2,887 2,478 3,756 1,054 1,353 1 (13)
Ending balance at Dec. 31, 2023 6,777 3,974 3,897                      
Increase (Decrease) in Shareowners' Equity [Roll Forward]                            
Net Income 690 362 345             690 362 345    
Common stock dividends (492) (200) (196)             (492) (200) (196)    
At-the-market offering program, net and Shareowner Direct Plan issuances 23           23              
Capital contributions from parent   325 55         325 55          
Equity-based compensation plans and other 6           7             (1)
Ending balance at Dec. 31, 2024 7,004 4,461 4,101 3 33 66 3,060 3,212 2,533 3,954 1,216 1,502 1 (14)
Ending balance at Dec. 31, 2024 7,004 4,461 4,101                      
Increase (Decrease) in Shareowners' Equity [Roll Forward]                            
Net Income 810 457 401             810 457 401    
Common stock dividends (521) (359) (207)             (521) (359) (207)    
At-the-market offering program, net and Shareowner Direct Plan issuances 23           23              
Capital contributions from parent   285 80         285 80          
Equity-based compensation plans and other 18           18              
Ending balance at Dec. 31, 2025 7,334 4,844 4,375 $ 3 $ 33 $ 66 $ 3,101 $ 3,497 $ 2,613 $ 4,243 $ 1,314 $ 1,696 $ 1 $ (14)
Ending balance at Dec. 31, 2025 $ 7,334 $ 4,844 $ 4,375                      
v3.25.4
Consolidated Statements of Common Equity (Parenthetical) - $ / shares
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Statement of Stockholders' Equity [Abstract]      
Common stock dividends (in dollars per share) $ 2.03 $ 1.92 $ 1.81
v3.25.4
Summary Of Significant Accounting Policies
 12 Months Ended
Dec. 31, 2025
Statement [Line Items]  
Summary Of Significant Accounting Policies SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES(a) General -
Description of Business - Alliant Energy’s financial statements include the accounts of Alliant Energy and its consolidated subsidiaries. Alliant Energy is a Midwest U.S. energy holding company, whose primary wholly-owned subsidiaries are IPL, WPL, AEF and Corporate Services.

IPL’s financial statements include the accounts of IPL and its consolidated subsidiaries, including IPL SPE LLC, which is used for IPL’s sales of accounts receivable program. IPL is a direct subsidiary of Alliant Energy and is a public utility engaged principally in the generation and distribution of electricity and the distribution and transportation of natural gas to retail customers in select markets in Iowa. IPL also sells electricity to wholesale customers in Illinois and Iowa. In July 2025, IPL’s wholesale power agreement with Southern Minnesota Energy Cooperative expired. IPL provided steam from its Prairie Creek Generating Station to high-pressure steam customers in Cedar Rapids, Iowa through 2025.

WPL’s financial statements include the accounts of WPL and its consolidated subsidiaries. WPL is a direct subsidiary of Alliant Energy and is a public utility engaged principally in the generation and distribution of electricity and the distribution and transportation of natural gas to retail customers in select markets in Wisconsin. WPL also sells electricity to wholesale customers in Wisconsin.

AEF is comprised of Travero, ATI, corporate venture investments, a non-utility wind farm, the Sheboygan Falls Energy Facility and other non-utility holdings. Travero includes a short-line rail freight service in Iowa; a Mississippi River barge, rail and truck freight terminal in Illinois; freight brokerage services; and a rail-served warehouse in Iowa. ATI, a wholly-owned subsidiary of AEF, holds all of Alliant Energy’s interest in ATC Holdings. Corporate venture investments includes various minority ownership interests in regional and national venture funds, including a global coalition of energy companies working together to help identify and research innovative technologies and business models within the emerging energy economy. The non-utility wind farm includes a 50% cash equity ownership interest in a 225 MW wind farm located in Oklahoma. The Sheboygan Falls Energy Facility is a 347 MW, simple-cycle, natural gas-fired EGU near Sheboygan Falls, Wisconsin, which is currently leased to WPL through 2044.

Corporate Services is the subsidiary formed to provide administrative services to Alliant Energy and its subsidiaries.

Basis of Presentation - The financial statements reflect investments in controlled subsidiaries on a consolidated basis and Alliant Energy’s, IPL’s and WPL’s proportionate shares of jointly-owned utility EGUs. Unconsolidated investments that Alliant Energy and WPL do not control are accounted for under the equity method of accounting. Under the equity method of accounting, Alliant Energy and WPL initially record the investment at cost, and adjust the carrying amount of the investment to recognize their respective share of the earnings or losses of the investee. Dividends received from an investee reduce the carrying amount of the equity investment. Investments that do not meet the criteria for consolidation or the equity method of accounting are accounted for under the cost method.

All intercompany balances and transactions, other than certain transactions affecting the rate-making process at IPL and WPL, have been eliminated from the financial statements. Such transactions not eliminated include costs that are recoverable from customers through rate-making processes. The financial statements are prepared in conformity with GAAP, which give recognition to the rate-making practices of FERC and state commissions having regulatory jurisdiction.

Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes.

Use of Estimates - The preparation of the financial statements requires management to make estimates and assumptions that affect: (a) the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements; and (b) the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
(b) Regulatory Assets and Regulatory Liabilities - Alliant Energy, IPL and WPL are subject to regulation by FERC and state regulatory commissions in their service territories. As a result, Alliant Energy, IPL and WPL are subject to GAAP provisions for regulated operations, which provide that rate-regulated public utilities record certain costs and credits allowed in the rate-making process in different periods than for non-utility entities. Regulatory assets generally represent incurred costs that have been deferred as such costs are probable of recovery in future customer rates. Regulatory liabilities generally represent obligations to make refunds to customers or amounts collected in rates for which the related costs have not yet been incurred. Amounts recorded as regulatory assets or regulatory liabilities are generally recognized in the income statements at the time they are reflected in rates.(c) Income Taxes - The liability method of accounting is followed for deferred taxes, which requires the establishment of deferred tax assets and liabilities, as appropriate, for temporary differences between the tax basis of assets and liabilities and the amounts reported in the financial statements. Deferred taxes are recorded using currently enacted tax rates and estimates of state apportionment. Changes in deferred tax assets and liabilities associated with certain property-related differences at IPL are accounted for differently than other subsidiaries of Alliant Energy due to rate-making practices in Iowa. Rate-making practices in Iowa do not allow the impact of certain deferred tax expenses (benefits) to be included in the determination of retail rates. Based on these rate-making practices, deferred tax expense (benefit) related to these property-related differences at IPL is not recorded in the income statement but instead recorded to regulatory assets or regulatory liabilities until these temporary differences reverse. In Wisconsin, the PSCW allows rate recovery of deferred tax expense on all temporary differences.
The flow-through method of accounting is used for investment tax credits. Certain federal investment tax credits related to utility property, plant and equipment are subject to statutory tax normalization rules limiting how they may be treated in rate-making. As appropriate to reflect the rate-making practices, investment tax credits are deferred and amortized over the book depreciable lives of the related property or other period prescribed by rate regulation.

Alliant Energy files a consolidated federal income tax return and a combined return in Wisconsin, which include Alliant Energy and its subsidiaries. Alliant Energy subsidiaries with a presence in Iowa file as part of a consolidated return in Iowa.

Alliant Energy allocates consolidated income tax expense to its subsidiaries that are members of the group that file a consolidated or combined income tax return. IPL and WPL use the separate return approach for calculating their income tax provisions and related deferred tax assets and liabilities. IPL and WPL are assumed to file separate tax returns with the federal and state taxing authorities, except that net operating losses (and other current or deferred tax attributes) are characterized as realized (or realizable) by IPL and WPL when those tax attributes are realized (or realizable) by the consolidated tax return group of Alliant Energy (even if IPL and WPL would not otherwise have realized the attributes on a stand-alone basis).

IPL and WPL have entered into agreements to transfer renewable tax credits from certain wind, solar and energy storage facilities to other corporate taxpayers in exchange for cash. Alliant Energy, IPL and WPL have elected to record transfers of renewable tax credits as part of income taxes, and cash received from the transfer of renewable tax credits is recorded in cash flows from operating activities. Renewable tax credits subject to future transfer are recorded at expected realizable value. Renewable tax credits are derecognized when control of the tax credits is transferred to other corporate taxpayers. Beginning October 1, 2024, IPL’s renewable energy rider was discontinued, and production tax credits, excluding production tax credits from the refurbishment of existing wind farms, are credited to IPL’s retail electric customers through its fuel-related cost recovery mechanism. Investment tax credits resulting from IPL’s renewable generation and energy storage projects that are not yet included in base rates may be utilized to offset any revenue deficiency on an annual basis up to IPL’s return on common equity threshold; any remaining investment tax credits, net of the cost of transferability, that are not used to offset any revenue deficiency, will be deferred by IPL and carried forward to offset any potential revenue deficiency in future years. At WPL, pursuant to escrow treatment approved by the PSCW, the difference between actual renewable tax credits and the amount of renewable tax credits collected from customers as electric revenues is recognized in “Income taxes” in Alliant Energy’s and WPL’s income statements. An offsetting amount is recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until reflected in future billings to customers. Refer to Note 16(d) for further discussion of the indemnification requirements.
(d) Cash, Cash Equivalents and Restricted Cash - Cash and cash equivalents include short-term liquid investments that have original maturities of less than 90 days. At December 31, 2025, Alliant Energy’s and WPL’s cash and cash equivalents included $411 million and $25 million, respectively, of money market fund investments, with weighted average interest rates of 4%. At December 31, 2025 and 2024, Alliant Energy’s restricted cash was not material.(e) Property, Plant and Equipment -
Utility Plant -
General - Utility plant is recorded at the original cost of acquisition or construction, which includes material, labor, contractor services, AFUDC and allocable overheads, such as supervision, engineering, certain administrative costs directly related to construction, benefits, certain taxes and transportation. Repairs, replacements and renewals of items of property determined to be less than a unit of property or that do not increase the property’s life or functionality are charged to maintenance expense. Property, plant and equipment that is probable of being retired early is classified as plant anticipated to be retired early. Generally, ordinary retirements of utility plant and salvage value are netted and charged to accumulated depreciation upon removal from utility plant accounts and no gain or loss is recognized consistent with rate-making principles. However, if regulators have approved recovery of the remaining net book value of property, plant and equipment that is retired early, or such approval by regulators is probable, the remaining net book value is reclassified from property, plant and equipment to regulatory assets upon retirement.
Depreciation - IPL and WPL use a combination of remaining life and straight-line depreciation methods as approved by their respective regulatory commissions. The composite or group method of depreciation is used, in which a single depreciation rate is applied to the gross investment in a particular class of property. This method pools similar assets and then depreciates each group as a whole. Periodic depreciation studies are performed to determine the appropriate group lives, net salvage, estimated cost of removal and group depreciation rates. These depreciation studies are subject to review and approval by IPL’s and WPL’s respective regulatory commissions. Depreciation expense is included within the recoverable cost of service component of rates collected from customers. The average rates of depreciation for electric, gas and other properties, consistent with current rate-making practices, were as follows:
IPLWPL
202520242023202520242023
Electric - generation3.5%3.3%3.3%3.4%3.4%3.0%
Electric - distribution2.9%2.8%2.8%2.7%2.7%2.7%
Electric - other3.6%5.2%5.6%4.2%6.1%6.3%
Gas3.3%3.3%3.3%2.4%2.5%2.5%
Other5.6%4.6%6.2%4.5%4.4%4.6%

AFUDC - AFUDC represents costs to finance construction additions, including a return on equity component and cost of debt component as required by regulatory accounting. AFUDC for IPL’s construction projects is calculated in accordance with FERC guidelines. AFUDC for WPL’s retail and wholesale jurisdiction construction projects is calculated in accordance with PSCW and FERC guidelines, respectively. The AFUDC rates, computed in accordance with the prescribed regulatory formula, were as follows:
202520242023
IPL7.1%7.0%7.0%
WPL (retail jurisdiction)7.4%7.4%7.4%
WPL (wholesale jurisdiction)6.6%7.1%7.1%

In accordance with their respective regulatory commission decisions, IPL applies its AFUDC rates to 100% of applicable CWIP balances, and WPL generally applies its AFUDC rates to 50% of applicable CWIP balances and the remaining 50% of applicable CWIP balances earns a return on such balances as part of its rate base. WPL may be authorized to apply its AFUDC rates to 100% of the retail portion of the CWIP balances for construction projects requiring a CA or CPCN that were approved by the PSCW after its then most recent rate order. Beginning January 1, 2026, the PSCW also authorized an AFUDC applied to 100% of the retail portion of CWIP balances related to construction activity on capital projects requiring PSCW approval and are impacted by federal law changes.

Non-utility and Other Property -
General - Non-utility property is recorded at the original cost of acquisition or construction, which includes material, labor and contractor services. Repairs, replacements and renewals of items of property determined to be less than a unit of property or that do not increase the property’s life or functionality are charged to maintenance expense. Upon retirement or sale of non-utility property, the original cost and related accumulated depreciation are removed from the accounts and any gain or loss is included in the income statements.

Costs related to software developed or obtained for internal use are capitalized and amortized on a straight-line basis over the estimated useful life of the related software. If software is retired prior to being fully amortized, the remaining book value is recorded as a loss in the income statements.
(f) Revenue Recognition -
Utility - Revenues from Alliant Energy’s utility business are primarily from electric and gas sales to customers. Utility revenues are recognized over time as services are rendered or commodities are delivered to customers, and include billed and unbilled components. The billed component is based on the reading of customers’ meters, which occurs on a systematic basis throughout each reporting period and represents the fair value of the services provided or commodities delivered. The unbilled component is recorded at the end of each reporting period based on estimated amounts of energy delivered to customers but not yet billed.

IPL and WPL accrue revenues from their wholesale customers to the extent that the actual net revenue requirements calculated in accordance with FERC-approved formula rates for the reporting period are higher or lower than the amounts billed to wholesale customers during such period. Regulatory assets or regulatory liabilities are recorded as the offset for these accrued revenues under formulaic rate-making programs. As of December 31, 2025, the related amounts accrued for IPL and WPL were not material.
IPL and WPL participate in bid/offer-based wholesale energy and ancillary services markets operated by MISO. The MISO transactions are grouped together, resulting in a net supply to or net purchase from MISO for each hour of each day. The net supply to MISO is recorded as bulk power sales in “Electric utility revenues” and the net purchase from MISO is recorded in “Electric production fuel and purchased power” in the income statements.

Non-utility - Revenues from Alliant Energy’s non-utility businesses are primarily from its Travero business and are recognized over time as services are rendered to customers.

Taxes Collected from Customers - Sales or various other taxes collected by certain of Alliant Energy’s subsidiaries on behalf of other agencies are recorded on a net basis and are not included in revenues.

Other - Alliant Energy, IPL and WPL do not disclose the value of unsatisfied performance obligations for: (i) contracts with an original expected length of one year or less; and (ii) contracts for which revenue is recognized at the amount to which they have the right to invoice for services performed.
(g) Utility Cost Recovery Mechanisms -
Electric Production Fuel and Purchased Power (Fuel-related Costs) - Fuel-related costs are incurred to generate and purchase electricity to meet the demand of IPL’s and WPL’s electric customers. These fuel-related costs include the cost of fossil fuels (primarily natural gas and coal) used to produce electricity at their EGUs, and electricity purchased from MISO wholesale energy markets and under PPAs. These fuel-related costs are recorded in “Electric production fuel and purchased power” in the income statements.

IPL Retail - The cost recovery mechanisms for IPL’s retail electric customers provide for monthly adjustments to their electric rates for changes in fuel-related costs. Changes in the under-/over-collection of these costs are recognized in “Electric production fuel and purchased power” in Alliant Energy’s and IPL’s income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers.

WPL Retail - The cost recovery mechanism for WPL’s retail electric customers is based on forecasts of certain fuel-related costs expected to be incurred during forward-looking test periods and fuel monitoring ranges determined by the PSCW during each retail electric rate proceeding or in a separate fuel cost plan approval proceeding. If WPL’s actual fuel-related costs fall outside these fuel monitoring ranges, WPL is authorized to defer the incremental under-/over-collection of fuel-related costs that are outside the approved ranges. Deferral of under-collections are reduced to the extent actual return on common equity earned by WPL during the fuel cost plan year exceeds the most recently authorized return on common equity. Deferred amounts for fuel-related costs outside the approved fuel monitoring ranges are recognized in “Electric production fuel and purchased power” in Alliant Energy’s and WPL’s income statements. The cumulative effects of these deferred amounts are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until they are reflected in future billings to customers.

IPL and WPL Wholesale - The cost recovery mechanisms for IPL’s and WPL’s wholesale electric customers provide for subsequent adjustments to their electric rates for changes in fuel-related costs. Changes in the under-/over-collection of these costs are recognized in “Electric production fuel and purchased power” in the income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers.

Electric Capacity - PPAs help meet the electricity demand of IPL’s and WPL’s customers. Certain PPAs include minimum payments for IPL’s and WPL’s rights to electric generating capacity, which are charged each period to “Electric production fuel and purchased power” in the income statements. Purchased electric capacity expenses are recovered from IPL’s and WPL’s retail electric customers through changes in base rates determined during periodic rate proceedings. Purchased electric capacity expenses are recovered from IPL’s and WPL’s wholesale electric customers through annual changes in base rates determined by a formula rate structure. Electric capacity revenues are refunded to IPL's retail electric customers through changes in base rates determined during periodic rate proceedings, and to IPL and WPL's wholesale electric customers through annual changes in base rates determined by a formula rate structure. Electric capacity revenues are refunded to WPL's retail electric customers through its fuel cost recovery mechanism.

Electric Transmission Service - Costs incurred for the transmission of electricity to meet the demands of IPL’s and WPL’s customers are charged to “Electric transmission service” in the income statements.

IPL Retail - Electric transmission service expense is recovered from IPL’s retail electric customers through a transmission cost rider. This cost recovery mechanism provides for periodic adjustments to electric rates charged to retail electric customers for changes in electric transmission service expense. Changes in the under-/over-collection of these costs are recognized in “Electric transmission service” in Alliant Energy’s and IPL’s income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers.
WPL Retail - Electric transmission service expense is recovered from WPL’s retail electric customers through changes in base rates determined during periodic rate proceedings. Pursuant to escrow accounting treatment approved by the PSCW, the difference between actual electric transmission service expense incurred and the amount of electric transmission service costs collected from customers as electric revenues is recognized in “Electric transmission service” in Alliant Energy’s and WPL’s income statements. An offsetting amount is recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until reflected in future billings to customers.

IPL and WPL Wholesale - IPL and WPL arrange transmission service for the majority of their respective wholesale electric customers. Electric transmission service expense is allocated to and recovered from these customers based on a load ratio share computation.

Cost of Gas Sold - Costs are incurred for the purchase, transportation and storage of natural gas to serve IPL’s and WPL’s gas customers and the costs associated with the natural gas delivered to customers are charged to “Cost of gas sold” in the income statements. The tariffs for IPL’s and WPL’s retail gas customers provide for subsequent adjustments to their rates periodically for changes in the cost of gas sold. Changes in the under-/over-collection of these costs are also recognized in “Cost of gas sold” in the income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers.

Energy Efficiency Costs - Costs incurred to fund energy efficiency programs and initiatives that help customers reduce their energy usage are charged to “Other operation and maintenance” in the income statements. Energy efficiency costs incurred by IPL are recovered from its retail electric and gas customers through energy efficiency and demand response cost recovery factor tariffs, which are revised annually and include a reconciliation to eliminate any under-/over-collection of energy efficiency costs from prior periods. Pursuant to escrow accounting treatment approved by the PSCW, the difference between actual energy efficiency costs incurred by WPL and the amount collected from its retail electric and gas customers is recovered through changes in base rates determined during periodic rate proceedings, and reconciliations eliminate any under-/over-collection of energy efficiency costs from prior periods. Changes in the under-/over-collection of energy efficiency costs for IPL and WPL are recognized in “Other operation and maintenance” in the income statements. The cumulative effects of the under-/over-collection of these costs for IPL and WPL are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers.

Renewable Energy Rider - IPL utilized a renewable energy rider prior to its discontinuation on October 1, 2024, effective with the IUC’s order for IPL’s retail electric rate review for the October 2024 through September 2025 Test Period. Prior to October 1, 2024, IPL recovered a return of, as well as earned a return on, its wind generation placed in service in 2019 and 2020 from its retail electric customers through the renewable energy rider. Other applicable costs and tax benefits associated with this wind generation, excluding operation and maintenance expenses, were also included in the rider. This cost recovery mechanism provided for annual adjustments to electric rates charged to IPL’s retail electric customers for actual renewable energy costs and tax benefits. Changes in the under-/over-collection of these costs were recognized in “Electric utility revenue” in Alliant Energy’s and IPL’s income statements. The cumulative effects of the under-/over-collection of these costs for IPL is recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers. Refer to Note 1(c) for further discussion of the treatment of IPL’s renewable tax credits for rate-making purposes.
(h) Financial Instruments - Financial instruments are periodically used for risk management purposes to mitigate exposures to fluctuations in certain commodity prices, transmission congestion costs and interest rates. The fair value of those financial instruments that are determined to be derivatives are recorded as assets or liabilities on the balance sheets. Certain commodity purchase and sales contracts qualified for and were designated under the normal purchase and sale exception, and were accounted for on the accrual basis of accounting. Alliant Energy, IPL and WPL have elected to not net the fair value amounts of derivatives subject to a master netting arrangement by counterparty. Alliant Energy, IPL and WPL do not offset fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) against fair value amounts recognized for derivative instruments that are executed with the same counterparty under the same master netting arrangement. Refer to Note 2 for discussion of the recognition of regulatory assets and regulatory liabilities related to the unrealized losses and gains on commodity derivative instruments. Refer to Notes 14, 15 and 16(f) for further discussion of derivatives and related credit risk.(i) Asset Impairments -
Property, Plant and Equipment of Regulated Operations - Property, plant and equipment of regulated operations are reviewed for possible impairment whenever events or changes in circumstances indicate all or a portion of the carrying value of the assets may be disallowed for rate-making purposes. If IPL or WPL are disallowed recovery of any portion of, or are only allowed a partial return on, the carrying value of their regulated property, plant and equipment that is under construction, has been recently completed or is probable of abandonment, or conclude it is probable recovery or a full return will be disallowed, then an impairment charge is recognized.
Property, Plant and Equipment of Non-utility Operations - Property, plant and equipment of non-utility operations are reviewed for possible impairment whenever events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Impairment is indicated if the carrying value of an asset exceeds its undiscounted future cash flows. If an impairment is indicated, a charge is recognized equal to the amount the carrying value exceeds the asset’s fair value. Refer to Note 17 for discussion of an asset valuation charge at Alliant Energy’s non-utility holdings in 2025.

Unconsolidated Equity Investments - If events or circumstances indicate the carrying value of investments accounted for under the equity method of accounting exceeds fair value and the decline in value is other than temporary, potential impairment is assessed. If an impairment is indicated, a charge is recognized equal to the amount the carrying value exceeds the investment’s fair value.
(j) Asset Retirement Obligations - The fair value of a legal obligation associated with the retirement of an asset is recorded as a liability when an asset is placed in service, when a legal obligation is subsequently identified or when sufficient information becomes available to determine a reasonable estimate of the fair value of future retirement costs. When an ARO is recorded as a liability, an equivalent amount is added to the asset cost. The fair value of AROs at inception is determined using discounted cash flows analyses. The liability is accreted to its present value and the capitalized cost is depreciated over the useful life of the related asset. Accretion and depreciation expenses related to AROs for IPL’s and WPL’s regulated operations are recorded to regulatory assets on the balance sheets. Revisions in estimated cash flows for IPL’s and WPL’s regulated operations are recorded as an increase or decrease to the ARO liability, with an offset to the asset cost, unless the asset is already retired and then the offset is recorded to regulatory assets or regulatory liabilities on the balance sheets. Upon regulatory approval to recover IPL’s AROs expenditures, its regulatory assets are amortized to depreciation and amortization expenses in Alliant Energy’s and IPL’s income statements over the same time period the ARO expenditures are recovered from IPL’s customers. WPL’s regulatory assets related to AROs are recovered as a component of depreciation rates pursuant to PSCW and FERC orders. Upon settlement of the ARO liability, an entity settles the obligation for its recorded amount or incurs a gain or loss. Any gains or losses related to AROs for IPL’s and WPL’s regulated operations are recorded to regulatory liabilities or regulatory assets on the balance sheets. Refer to Note 13 for details of an ARO charge for steam assets at IPL in 2024.(k) Debt Issuance and Retirement Costs - Debt issuance costs and debt premiums or discounts are presented on the balance sheets as a direct adjustment to the carrying amount of the related debt liability, and are deferred and amortized over the expected life of each debt issue, considering maturity dates and, if applicable, redemption rights held by us or by others. Alliant Energy’s non-utility businesses and Corporate Services record to interest expense in the period of retirement any unamortized debt issuance costs and debt premiums or discounts on debt retired early.(l) Current Expected Credit Losses Estimates - Current expected credit losses are estimated for trade and other receivables and credit exposures on guarantees of the performance by third parties. The current expected credit losses for short-term trade receivables are based on estimates of losses resulting from the inability of customers to make required payments. The methodology used to estimate losses is based on historical write-offs, regional economic conditions, significant events that could impact collectability, such as significant weather related matters and related regulatory actions, and actual and forecasted changes to the accounts receivable aging portfolio and write-offs. The current expected credit losses related to guarantees of the performance by third parties are estimated using both quantitative and qualitative information, which utilizes potential outcomes in a range of possible estimated amounts.(m) Variable Interest Entities - An entity is considered a VIE if its equity investors do not have sufficient equity at risk for the entity to finance its activities without additional subordinated financial support from other parties, the entity is structured with disproportionate voting rights and substantially all of the entity’s activities are conducted on behalf of the investor with disproportionately fewer voting rights, or its equity investors lack any of the following characteristics: (1) power, through voting rights or similar rights, to direct the activities of the entity that most significantly impact the entity’s economic performance; (2) the obligation to absorb expected losses of the entity; or (3) the right to receive expected benefits of the entity. The primary beneficiary of a VIE is required to consolidate the VIE. The financial statements do not reflect any consolidation of VIEs.(n) Leases - The determination of whether an arrangement qualifies as a lease occurs at the inception of the arrangement. Arrangements that qualify as leases are classified as either operating or finance. Operating and finance lease liabilities represent obligations to make payments arising from the lease. Operating and finance lease assets represent the right to use an underlying asset for the lease term and are recognized at the lease commencement date based on the present value of the lease payments over the lease term. Leases with initial terms less than 12 months are not recognized as leases. For operating leases, an incremental borrowing rate, as determined at the lease commencement date, is used to determine the present value of the lease payments. For finance leases, the rate implicit in the lease, if known, is used to determine the present value of the lease payments. If the rate implicit in the lease is not known, the incremental borrowing rate, as determined at the lease commencement date, is used to determine the present value of the lease payments. Lease terms include options to extend or terminate the lease when it is reasonably certain that the option will be exercised. Operating lease expense is recognized on a straight-line basis over the expected lease term. Finance lease expense is comprised of depreciation and amortization, and interest expenses. Finance lease assets are accounted for as operating leases for rate-making purposes.
IPL [Member]  
Statement [Line Items]  
Summary Of Significant Accounting Policies SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES(a) General -
Description of Business - Alliant Energy’s financial statements include the accounts of Alliant Energy and its consolidated subsidiaries. Alliant Energy is a Midwest U.S. energy holding company, whose primary wholly-owned subsidiaries are IPL, WPL, AEF and Corporate Services.

IPL’s financial statements include the accounts of IPL and its consolidated subsidiaries, including IPL SPE LLC, which is used for IPL’s sales of accounts receivable program. IPL is a direct subsidiary of Alliant Energy and is a public utility engaged principally in the generation and distribution of electricity and the distribution and transportation of natural gas to retail customers in select markets in Iowa. IPL also sells electricity to wholesale customers in Illinois and Iowa. In July 2025, IPL’s wholesale power agreement with Southern Minnesota Energy Cooperative expired. IPL provided steam from its Prairie Creek Generating Station to high-pressure steam customers in Cedar Rapids, Iowa through 2025.

WPL’s financial statements include the accounts of WPL and its consolidated subsidiaries. WPL is a direct subsidiary of Alliant Energy and is a public utility engaged principally in the generation and distribution of electricity and the distribution and transportation of natural gas to retail customers in select markets in Wisconsin. WPL also sells electricity to wholesale customers in Wisconsin.

AEF is comprised of Travero, ATI, corporate venture investments, a non-utility wind farm, the Sheboygan Falls Energy Facility and other non-utility holdings. Travero includes a short-line rail freight service in Iowa; a Mississippi River barge, rail and truck freight terminal in Illinois; freight brokerage services; and a rail-served warehouse in Iowa. ATI, a wholly-owned subsidiary of AEF, holds all of Alliant Energy’s interest in ATC Holdings. Corporate venture investments includes various minority ownership interests in regional and national venture funds, including a global coalition of energy companies working together to help identify and research innovative technologies and business models within the emerging energy economy. The non-utility wind farm includes a 50% cash equity ownership interest in a 225 MW wind farm located in Oklahoma. The Sheboygan Falls Energy Facility is a 347 MW, simple-cycle, natural gas-fired EGU near Sheboygan Falls, Wisconsin, which is currently leased to WPL through 2044.

Corporate Services is the subsidiary formed to provide administrative services to Alliant Energy and its subsidiaries.

Basis of Presentation - The financial statements reflect investments in controlled subsidiaries on a consolidated basis and Alliant Energy’s, IPL’s and WPL’s proportionate shares of jointly-owned utility EGUs. Unconsolidated investments that Alliant Energy and WPL do not control are accounted for under the equity method of accounting. Under the equity method of accounting, Alliant Energy and WPL initially record the investment at cost, and adjust the carrying amount of the investment to recognize their respective share of the earnings or losses of the investee. Dividends received from an investee reduce the carrying amount of the equity investment. Investments that do not meet the criteria for consolidation or the equity method of accounting are accounted for under the cost method.

All intercompany balances and transactions, other than certain transactions affecting the rate-making process at IPL and WPL, have been eliminated from the financial statements. Such transactions not eliminated include costs that are recoverable from customers through rate-making processes. The financial statements are prepared in conformity with GAAP, which give recognition to the rate-making practices of FERC and state commissions having regulatory jurisdiction.

Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes.

Use of Estimates - The preparation of the financial statements requires management to make estimates and assumptions that affect: (a) the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements; and (b) the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
(b) Regulatory Assets and Regulatory Liabilities - Alliant Energy, IPL and WPL are subject to regulation by FERC and state regulatory commissions in their service territories. As a result, Alliant Energy, IPL and WPL are subject to GAAP provisions for regulated operations, which provide that rate-regulated public utilities record certain costs and credits allowed in the rate-making process in different periods than for non-utility entities. Regulatory assets generally represent incurred costs that have been deferred as such costs are probable of recovery in future customer rates. Regulatory liabilities generally represent obligations to make refunds to customers or amounts collected in rates for which the related costs have not yet been incurred. Amounts recorded as regulatory assets or regulatory liabilities are generally recognized in the income statements at the time they are reflected in rates.(c) Income Taxes - The liability method of accounting is followed for deferred taxes, which requires the establishment of deferred tax assets and liabilities, as appropriate, for temporary differences between the tax basis of assets and liabilities and the amounts reported in the financial statements. Deferred taxes are recorded using currently enacted tax rates and estimates of state apportionment. Changes in deferred tax assets and liabilities associated with certain property-related differences at IPL are accounted for differently than other subsidiaries of Alliant Energy due to rate-making practices in Iowa. Rate-making practices in Iowa do not allow the impact of certain deferred tax expenses (benefits) to be included in the determination of retail rates. Based on these rate-making practices, deferred tax expense (benefit) related to these property-related differences at IPL is not recorded in the income statement but instead recorded to regulatory assets or regulatory liabilities until these temporary differences reverse. In Wisconsin, the PSCW allows rate recovery of deferred tax expense on all temporary differences.
The flow-through method of accounting is used for investment tax credits. Certain federal investment tax credits related to utility property, plant and equipment are subject to statutory tax normalization rules limiting how they may be treated in rate-making. As appropriate to reflect the rate-making practices, investment tax credits are deferred and amortized over the book depreciable lives of the related property or other period prescribed by rate regulation.

Alliant Energy files a consolidated federal income tax return and a combined return in Wisconsin, which include Alliant Energy and its subsidiaries. Alliant Energy subsidiaries with a presence in Iowa file as part of a consolidated return in Iowa.

Alliant Energy allocates consolidated income tax expense to its subsidiaries that are members of the group that file a consolidated or combined income tax return. IPL and WPL use the separate return approach for calculating their income tax provisions and related deferred tax assets and liabilities. IPL and WPL are assumed to file separate tax returns with the federal and state taxing authorities, except that net operating losses (and other current or deferred tax attributes) are characterized as realized (or realizable) by IPL and WPL when those tax attributes are realized (or realizable) by the consolidated tax return group of Alliant Energy (even if IPL and WPL would not otherwise have realized the attributes on a stand-alone basis).

IPL and WPL have entered into agreements to transfer renewable tax credits from certain wind, solar and energy storage facilities to other corporate taxpayers in exchange for cash. Alliant Energy, IPL and WPL have elected to record transfers of renewable tax credits as part of income taxes, and cash received from the transfer of renewable tax credits is recorded in cash flows from operating activities. Renewable tax credits subject to future transfer are recorded at expected realizable value. Renewable tax credits are derecognized when control of the tax credits is transferred to other corporate taxpayers. Beginning October 1, 2024, IPL’s renewable energy rider was discontinued, and production tax credits, excluding production tax credits from the refurbishment of existing wind farms, are credited to IPL’s retail electric customers through its fuel-related cost recovery mechanism. Investment tax credits resulting from IPL’s renewable generation and energy storage projects that are not yet included in base rates may be utilized to offset any revenue deficiency on an annual basis up to IPL’s return on common equity threshold; any remaining investment tax credits, net of the cost of transferability, that are not used to offset any revenue deficiency, will be deferred by IPL and carried forward to offset any potential revenue deficiency in future years. At WPL, pursuant to escrow treatment approved by the PSCW, the difference between actual renewable tax credits and the amount of renewable tax credits collected from customers as electric revenues is recognized in “Income taxes” in Alliant Energy’s and WPL’s income statements. An offsetting amount is recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until reflected in future billings to customers. Refer to Note 16(d) for further discussion of the indemnification requirements.
(d) Cash, Cash Equivalents and Restricted Cash - Cash and cash equivalents include short-term liquid investments that have original maturities of less than 90 days. At December 31, 2025, Alliant Energy’s and WPL’s cash and cash equivalents included $411 million and $25 million, respectively, of money market fund investments, with weighted average interest rates of 4%. At December 31, 2025 and 2024, Alliant Energy’s restricted cash was not material.(e) Property, Plant and Equipment -
Utility Plant -
General - Utility plant is recorded at the original cost of acquisition or construction, which includes material, labor, contractor services, AFUDC and allocable overheads, such as supervision, engineering, certain administrative costs directly related to construction, benefits, certain taxes and transportation. Repairs, replacements and renewals of items of property determined to be less than a unit of property or that do not increase the property’s life or functionality are charged to maintenance expense. Property, plant and equipment that is probable of being retired early is classified as plant anticipated to be retired early. Generally, ordinary retirements of utility plant and salvage value are netted and charged to accumulated depreciation upon removal from utility plant accounts and no gain or loss is recognized consistent with rate-making principles. However, if regulators have approved recovery of the remaining net book value of property, plant and equipment that is retired early, or such approval by regulators is probable, the remaining net book value is reclassified from property, plant and equipment to regulatory assets upon retirement.
Depreciation - IPL and WPL use a combination of remaining life and straight-line depreciation methods as approved by their respective regulatory commissions. The composite or group method of depreciation is used, in which a single depreciation rate is applied to the gross investment in a particular class of property. This method pools similar assets and then depreciates each group as a whole. Periodic depreciation studies are performed to determine the appropriate group lives, net salvage, estimated cost of removal and group depreciation rates. These depreciation studies are subject to review and approval by IPL’s and WPL’s respective regulatory commissions. Depreciation expense is included within the recoverable cost of service component of rates collected from customers. The average rates of depreciation for electric, gas and other properties, consistent with current rate-making practices, were as follows:
IPLWPL
202520242023202520242023
Electric - generation3.5%3.3%3.3%3.4%3.4%3.0%
Electric - distribution2.9%2.8%2.8%2.7%2.7%2.7%
Electric - other3.6%5.2%5.6%4.2%6.1%6.3%
Gas3.3%3.3%3.3%2.4%2.5%2.5%
Other5.6%4.6%6.2%4.5%4.4%4.6%

AFUDC - AFUDC represents costs to finance construction additions, including a return on equity component and cost of debt component as required by regulatory accounting. AFUDC for IPL’s construction projects is calculated in accordance with FERC guidelines. AFUDC for WPL’s retail and wholesale jurisdiction construction projects is calculated in accordance with PSCW and FERC guidelines, respectively. The AFUDC rates, computed in accordance with the prescribed regulatory formula, were as follows:
202520242023
IPL7.1%7.0%7.0%
WPL (retail jurisdiction)7.4%7.4%7.4%
WPL (wholesale jurisdiction)6.6%7.1%7.1%

In accordance with their respective regulatory commission decisions, IPL applies its AFUDC rates to 100% of applicable CWIP balances, and WPL generally applies its AFUDC rates to 50% of applicable CWIP balances and the remaining 50% of applicable CWIP balances earns a return on such balances as part of its rate base. WPL may be authorized to apply its AFUDC rates to 100% of the retail portion of the CWIP balances for construction projects requiring a CA or CPCN that were approved by the PSCW after its then most recent rate order. Beginning January 1, 2026, the PSCW also authorized an AFUDC applied to 100% of the retail portion of CWIP balances related to construction activity on capital projects requiring PSCW approval and are impacted by federal law changes.

Non-utility and Other Property -
General - Non-utility property is recorded at the original cost of acquisition or construction, which includes material, labor and contractor services. Repairs, replacements and renewals of items of property determined to be less than a unit of property or that do not increase the property’s life or functionality are charged to maintenance expense. Upon retirement or sale of non-utility property, the original cost and related accumulated depreciation are removed from the accounts and any gain or loss is included in the income statements.

Costs related to software developed or obtained for internal use are capitalized and amortized on a straight-line basis over the estimated useful life of the related software. If software is retired prior to being fully amortized, the remaining book value is recorded as a loss in the income statements.
(f) Revenue Recognition -
Utility - Revenues from Alliant Energy’s utility business are primarily from electric and gas sales to customers. Utility revenues are recognized over time as services are rendered or commodities are delivered to customers, and include billed and unbilled components. The billed component is based on the reading of customers’ meters, which occurs on a systematic basis throughout each reporting period and represents the fair value of the services provided or commodities delivered. The unbilled component is recorded at the end of each reporting period based on estimated amounts of energy delivered to customers but not yet billed.

IPL and WPL accrue revenues from their wholesale customers to the extent that the actual net revenue requirements calculated in accordance with FERC-approved formula rates for the reporting period are higher or lower than the amounts billed to wholesale customers during such period. Regulatory assets or regulatory liabilities are recorded as the offset for these accrued revenues under formulaic rate-making programs. As of December 31, 2025, the related amounts accrued for IPL and WPL were not material.
IPL and WPL participate in bid/offer-based wholesale energy and ancillary services markets operated by MISO. The MISO transactions are grouped together, resulting in a net supply to or net purchase from MISO for each hour of each day. The net supply to MISO is recorded as bulk power sales in “Electric utility revenues” and the net purchase from MISO is recorded in “Electric production fuel and purchased power” in the income statements.

Non-utility - Revenues from Alliant Energy’s non-utility businesses are primarily from its Travero business and are recognized over time as services are rendered to customers.

Taxes Collected from Customers - Sales or various other taxes collected by certain of Alliant Energy’s subsidiaries on behalf of other agencies are recorded on a net basis and are not included in revenues.

Other - Alliant Energy, IPL and WPL do not disclose the value of unsatisfied performance obligations for: (i) contracts with an original expected length of one year or less; and (ii) contracts for which revenue is recognized at the amount to which they have the right to invoice for services performed.
(g) Utility Cost Recovery Mechanisms -
Electric Production Fuel and Purchased Power (Fuel-related Costs) - Fuel-related costs are incurred to generate and purchase electricity to meet the demand of IPL’s and WPL’s electric customers. These fuel-related costs include the cost of fossil fuels (primarily natural gas and coal) used to produce electricity at their EGUs, and electricity purchased from MISO wholesale energy markets and under PPAs. These fuel-related costs are recorded in “Electric production fuel and purchased power” in the income statements.

IPL Retail - The cost recovery mechanisms for IPL’s retail electric customers provide for monthly adjustments to their electric rates for changes in fuel-related costs. Changes in the under-/over-collection of these costs are recognized in “Electric production fuel and purchased power” in Alliant Energy’s and IPL’s income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers.

WPL Retail - The cost recovery mechanism for WPL’s retail electric customers is based on forecasts of certain fuel-related costs expected to be incurred during forward-looking test periods and fuel monitoring ranges determined by the PSCW during each retail electric rate proceeding or in a separate fuel cost plan approval proceeding. If WPL’s actual fuel-related costs fall outside these fuel monitoring ranges, WPL is authorized to defer the incremental under-/over-collection of fuel-related costs that are outside the approved ranges. Deferral of under-collections are reduced to the extent actual return on common equity earned by WPL during the fuel cost plan year exceeds the most recently authorized return on common equity. Deferred amounts for fuel-related costs outside the approved fuel monitoring ranges are recognized in “Electric production fuel and purchased power” in Alliant Energy’s and WPL’s income statements. The cumulative effects of these deferred amounts are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until they are reflected in future billings to customers.

IPL and WPL Wholesale - The cost recovery mechanisms for IPL’s and WPL’s wholesale electric customers provide for subsequent adjustments to their electric rates for changes in fuel-related costs. Changes in the under-/over-collection of these costs are recognized in “Electric production fuel and purchased power” in the income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers.

Electric Capacity - PPAs help meet the electricity demand of IPL’s and WPL’s customers. Certain PPAs include minimum payments for IPL’s and WPL’s rights to electric generating capacity, which are charged each period to “Electric production fuel and purchased power” in the income statements. Purchased electric capacity expenses are recovered from IPL’s and WPL’s retail electric customers through changes in base rates determined during periodic rate proceedings. Purchased electric capacity expenses are recovered from IPL’s and WPL’s wholesale electric customers through annual changes in base rates determined by a formula rate structure. Electric capacity revenues are refunded to IPL's retail electric customers through changes in base rates determined during periodic rate proceedings, and to IPL and WPL's wholesale electric customers through annual changes in base rates determined by a formula rate structure. Electric capacity revenues are refunded to WPL's retail electric customers through its fuel cost recovery mechanism.

Electric Transmission Service - Costs incurred for the transmission of electricity to meet the demands of IPL’s and WPL’s customers are charged to “Electric transmission service” in the income statements.

IPL Retail - Electric transmission service expense is recovered from IPL’s retail electric customers through a transmission cost rider. This cost recovery mechanism provides for periodic adjustments to electric rates charged to retail electric customers for changes in electric transmission service expense. Changes in the under-/over-collection of these costs are recognized in “Electric transmission service” in Alliant Energy’s and IPL’s income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers.
WPL Retail - Electric transmission service expense is recovered from WPL’s retail electric customers through changes in base rates determined during periodic rate proceedings. Pursuant to escrow accounting treatment approved by the PSCW, the difference between actual electric transmission service expense incurred and the amount of electric transmission service costs collected from customers as electric revenues is recognized in “Electric transmission service” in Alliant Energy’s and WPL’s income statements. An offsetting amount is recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until reflected in future billings to customers.

IPL and WPL Wholesale - IPL and WPL arrange transmission service for the majority of their respective wholesale electric customers. Electric transmission service expense is allocated to and recovered from these customers based on a load ratio share computation.

Cost of Gas Sold - Costs are incurred for the purchase, transportation and storage of natural gas to serve IPL’s and WPL’s gas customers and the costs associated with the natural gas delivered to customers are charged to “Cost of gas sold” in the income statements. The tariffs for IPL’s and WPL’s retail gas customers provide for subsequent adjustments to their rates periodically for changes in the cost of gas sold. Changes in the under-/over-collection of these costs are also recognized in “Cost of gas sold” in the income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers.

Energy Efficiency Costs - Costs incurred to fund energy efficiency programs and initiatives that help customers reduce their energy usage are charged to “Other operation and maintenance” in the income statements. Energy efficiency costs incurred by IPL are recovered from its retail electric and gas customers through energy efficiency and demand response cost recovery factor tariffs, which are revised annually and include a reconciliation to eliminate any under-/over-collection of energy efficiency costs from prior periods. Pursuant to escrow accounting treatment approved by the PSCW, the difference between actual energy efficiency costs incurred by WPL and the amount collected from its retail electric and gas customers is recovered through changes in base rates determined during periodic rate proceedings, and reconciliations eliminate any under-/over-collection of energy efficiency costs from prior periods. Changes in the under-/over-collection of energy efficiency costs for IPL and WPL are recognized in “Other operation and maintenance” in the income statements. The cumulative effects of the under-/over-collection of these costs for IPL and WPL are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers.

Renewable Energy Rider - IPL utilized a renewable energy rider prior to its discontinuation on October 1, 2024, effective with the IUC’s order for IPL’s retail electric rate review for the October 2024 through September 2025 Test Period. Prior to October 1, 2024, IPL recovered a return of, as well as earned a return on, its wind generation placed in service in 2019 and 2020 from its retail electric customers through the renewable energy rider. Other applicable costs and tax benefits associated with this wind generation, excluding operation and maintenance expenses, were also included in the rider. This cost recovery mechanism provided for annual adjustments to electric rates charged to IPL’s retail electric customers for actual renewable energy costs and tax benefits. Changes in the under-/over-collection of these costs were recognized in “Electric utility revenue” in Alliant Energy’s and IPL’s income statements. The cumulative effects of the under-/over-collection of these costs for IPL is recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers. Refer to Note 1(c) for further discussion of the treatment of IPL’s renewable tax credits for rate-making purposes.
(h) Financial Instruments - Financial instruments are periodically used for risk management purposes to mitigate exposures to fluctuations in certain commodity prices, transmission congestion costs and interest rates. The fair value of those financial instruments that are determined to be derivatives are recorded as assets or liabilities on the balance sheets. Certain commodity purchase and sales contracts qualified for and were designated under the normal purchase and sale exception, and were accounted for on the accrual basis of accounting. Alliant Energy, IPL and WPL have elected to not net the fair value amounts of derivatives subject to a master netting arrangement by counterparty. Alliant Energy, IPL and WPL do not offset fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) against fair value amounts recognized for derivative instruments that are executed with the same counterparty under the same master netting arrangement. Refer to Note 2 for discussion of the recognition of regulatory assets and regulatory liabilities related to the unrealized losses and gains on commodity derivative instruments. Refer to Notes 14, 15 and 16(f) for further discussion of derivatives and related credit risk.(i) Asset Impairments -
Property, Plant and Equipment of Regulated Operations - Property, plant and equipment of regulated operations are reviewed for possible impairment whenever events or changes in circumstances indicate all or a portion of the carrying value of the assets may be disallowed for rate-making purposes. If IPL or WPL are disallowed recovery of any portion of, or are only allowed a partial return on, the carrying value of their regulated property, plant and equipment that is under construction, has been recently completed or is probable of abandonment, or conclude it is probable recovery or a full return will be disallowed, then an impairment charge is recognized.
Property, Plant and Equipment of Non-utility Operations - Property, plant and equipment of non-utility operations are reviewed for possible impairment whenever events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Impairment is indicated if the carrying value of an asset exceeds its undiscounted future cash flows. If an impairment is indicated, a charge is recognized equal to the amount the carrying value exceeds the asset’s fair value. Refer to Note 17 for discussion of an asset valuation charge at Alliant Energy’s non-utility holdings in 2025.

Unconsolidated Equity Investments - If events or circumstances indicate the carrying value of investments accounted for under the equity method of accounting exceeds fair value and the decline in value is other than temporary, potential impairment is assessed. If an impairment is indicated, a charge is recognized equal to the amount the carrying value exceeds the investment’s fair value.
(j) Asset Retirement Obligations - The fair value of a legal obligation associated with the retirement of an asset is recorded as a liability when an asset is placed in service, when a legal obligation is subsequently identified or when sufficient information becomes available to determine a reasonable estimate of the fair value of future retirement costs. When an ARO is recorded as a liability, an equivalent amount is added to the asset cost. The fair value of AROs at inception is determined using discounted cash flows analyses. The liability is accreted to its present value and the capitalized cost is depreciated over the useful life of the related asset. Accretion and depreciation expenses related to AROs for IPL’s and WPL’s regulated operations are recorded to regulatory assets on the balance sheets. Revisions in estimated cash flows for IPL’s and WPL’s regulated operations are recorded as an increase or decrease to the ARO liability, with an offset to the asset cost, unless the asset is already retired and then the offset is recorded to regulatory assets or regulatory liabilities on the balance sheets. Upon regulatory approval to recover IPL’s AROs expenditures, its regulatory assets are amortized to depreciation and amortization expenses in Alliant Energy’s and IPL’s income statements over the same time period the ARO expenditures are recovered from IPL’s customers. WPL’s regulatory assets related to AROs are recovered as a component of depreciation rates pursuant to PSCW and FERC orders. Upon settlement of the ARO liability, an entity settles the obligation for its recorded amount or incurs a gain or loss. Any gains or losses related to AROs for IPL’s and WPL’s regulated operations are recorded to regulatory liabilities or regulatory assets on the balance sheets. Refer to Note 13 for details of an ARO charge for steam assets at IPL in 2024.(k) Debt Issuance and Retirement Costs - Debt issuance costs and debt premiums or discounts are presented on the balance sheets as a direct adjustment to the carrying amount of the related debt liability, and are deferred and amortized over the expected life of each debt issue, considering maturity dates and, if applicable, redemption rights held by us or by others. Alliant Energy’s non-utility businesses and Corporate Services record to interest expense in the period of retirement any unamortized debt issuance costs and debt premiums or discounts on debt retired early.(l) Current Expected Credit Losses Estimates - Current expected credit losses are estimated for trade and other receivables and credit exposures on guarantees of the performance by third parties. The current expected credit losses for short-term trade receivables are based on estimates of losses resulting from the inability of customers to make required payments. The methodology used to estimate losses is based on historical write-offs, regional economic conditions, significant events that could impact collectability, such as significant weather related matters and related regulatory actions, and actual and forecasted changes to the accounts receivable aging portfolio and write-offs. The current expected credit losses related to guarantees of the performance by third parties are estimated using both quantitative and qualitative information, which utilizes potential outcomes in a range of possible estimated amounts.(m) Variable Interest Entities - An entity is considered a VIE if its equity investors do not have sufficient equity at risk for the entity to finance its activities without additional subordinated financial support from other parties, the entity is structured with disproportionate voting rights and substantially all of the entity’s activities are conducted on behalf of the investor with disproportionately fewer voting rights, or its equity investors lack any of the following characteristics: (1) power, through voting rights or similar rights, to direct the activities of the entity that most significantly impact the entity’s economic performance; (2) the obligation to absorb expected losses of the entity; or (3) the right to receive expected benefits of the entity. The primary beneficiary of a VIE is required to consolidate the VIE. The financial statements do not reflect any consolidation of VIEs.(n) Leases - The determination of whether an arrangement qualifies as a lease occurs at the inception of the arrangement. Arrangements that qualify as leases are classified as either operating or finance. Operating and finance lease liabilities represent obligations to make payments arising from the lease. Operating and finance lease assets represent the right to use an underlying asset for the lease term and are recognized at the lease commencement date based on the present value of the lease payments over the lease term. Leases with initial terms less than 12 months are not recognized as leases. For operating leases, an incremental borrowing rate, as determined at the lease commencement date, is used to determine the present value of the lease payments. For finance leases, the rate implicit in the lease, if known, is used to determine the present value of the lease payments. If the rate implicit in the lease is not known, the incremental borrowing rate, as determined at the lease commencement date, is used to determine the present value of the lease payments. Lease terms include options to extend or terminate the lease when it is reasonably certain that the option will be exercised. Operating lease expense is recognized on a straight-line basis over the expected lease term. Finance lease expense is comprised of depreciation and amortization, and interest expenses. Finance lease assets are accounted for as operating leases for rate-making purposes.
WPL [Member]  
Statement [Line Items]  
Summary Of Significant Accounting Policies SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES(a) General -
Description of Business - Alliant Energy’s financial statements include the accounts of Alliant Energy and its consolidated subsidiaries. Alliant Energy is a Midwest U.S. energy holding company, whose primary wholly-owned subsidiaries are IPL, WPL, AEF and Corporate Services.

IPL’s financial statements include the accounts of IPL and its consolidated subsidiaries, including IPL SPE LLC, which is used for IPL’s sales of accounts receivable program. IPL is a direct subsidiary of Alliant Energy and is a public utility engaged principally in the generation and distribution of electricity and the distribution and transportation of natural gas to retail customers in select markets in Iowa. IPL also sells electricity to wholesale customers in Illinois and Iowa. In July 2025, IPL’s wholesale power agreement with Southern Minnesota Energy Cooperative expired. IPL provided steam from its Prairie Creek Generating Station to high-pressure steam customers in Cedar Rapids, Iowa through 2025.

WPL’s financial statements include the accounts of WPL and its consolidated subsidiaries. WPL is a direct subsidiary of Alliant Energy and is a public utility engaged principally in the generation and distribution of electricity and the distribution and transportation of natural gas to retail customers in select markets in Wisconsin. WPL also sells electricity to wholesale customers in Wisconsin.

AEF is comprised of Travero, ATI, corporate venture investments, a non-utility wind farm, the Sheboygan Falls Energy Facility and other non-utility holdings. Travero includes a short-line rail freight service in Iowa; a Mississippi River barge, rail and truck freight terminal in Illinois; freight brokerage services; and a rail-served warehouse in Iowa. ATI, a wholly-owned subsidiary of AEF, holds all of Alliant Energy’s interest in ATC Holdings. Corporate venture investments includes various minority ownership interests in regional and national venture funds, including a global coalition of energy companies working together to help identify and research innovative technologies and business models within the emerging energy economy. The non-utility wind farm includes a 50% cash equity ownership interest in a 225 MW wind farm located in Oklahoma. The Sheboygan Falls Energy Facility is a 347 MW, simple-cycle, natural gas-fired EGU near Sheboygan Falls, Wisconsin, which is currently leased to WPL through 2044.

Corporate Services is the subsidiary formed to provide administrative services to Alliant Energy and its subsidiaries.

Basis of Presentation - The financial statements reflect investments in controlled subsidiaries on a consolidated basis and Alliant Energy’s, IPL’s and WPL’s proportionate shares of jointly-owned utility EGUs. Unconsolidated investments that Alliant Energy and WPL do not control are accounted for under the equity method of accounting. Under the equity method of accounting, Alliant Energy and WPL initially record the investment at cost, and adjust the carrying amount of the investment to recognize their respective share of the earnings or losses of the investee. Dividends received from an investee reduce the carrying amount of the equity investment. Investments that do not meet the criteria for consolidation or the equity method of accounting are accounted for under the cost method.

All intercompany balances and transactions, other than certain transactions affecting the rate-making process at IPL and WPL, have been eliminated from the financial statements. Such transactions not eliminated include costs that are recoverable from customers through rate-making processes. The financial statements are prepared in conformity with GAAP, which give recognition to the rate-making practices of FERC and state commissions having regulatory jurisdiction.

Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes.

Use of Estimates - The preparation of the financial statements requires management to make estimates and assumptions that affect: (a) the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements; and (b) the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
(b) Regulatory Assets and Regulatory Liabilities - Alliant Energy, IPL and WPL are subject to regulation by FERC and state regulatory commissions in their service territories. As a result, Alliant Energy, IPL and WPL are subject to GAAP provisions for regulated operations, which provide that rate-regulated public utilities record certain costs and credits allowed in the rate-making process in different periods than for non-utility entities. Regulatory assets generally represent incurred costs that have been deferred as such costs are probable of recovery in future customer rates. Regulatory liabilities generally represent obligations to make refunds to customers or amounts collected in rates for which the related costs have not yet been incurred. Amounts recorded as regulatory assets or regulatory liabilities are generally recognized in the income statements at the time they are reflected in rates.(c) Income Taxes - The liability method of accounting is followed for deferred taxes, which requires the establishment of deferred tax assets and liabilities, as appropriate, for temporary differences between the tax basis of assets and liabilities and the amounts reported in the financial statements. Deferred taxes are recorded using currently enacted tax rates and estimates of state apportionment. Changes in deferred tax assets and liabilities associated with certain property-related differences at IPL are accounted for differently than other subsidiaries of Alliant Energy due to rate-making practices in Iowa. Rate-making practices in Iowa do not allow the impact of certain deferred tax expenses (benefits) to be included in the determination of retail rates. Based on these rate-making practices, deferred tax expense (benefit) related to these property-related differences at IPL is not recorded in the income statement but instead recorded to regulatory assets or regulatory liabilities until these temporary differences reverse. In Wisconsin, the PSCW allows rate recovery of deferred tax expense on all temporary differences.
The flow-through method of accounting is used for investment tax credits. Certain federal investment tax credits related to utility property, plant and equipment are subject to statutory tax normalization rules limiting how they may be treated in rate-making. As appropriate to reflect the rate-making practices, investment tax credits are deferred and amortized over the book depreciable lives of the related property or other period prescribed by rate regulation.

Alliant Energy files a consolidated federal income tax return and a combined return in Wisconsin, which include Alliant Energy and its subsidiaries. Alliant Energy subsidiaries with a presence in Iowa file as part of a consolidated return in Iowa.

Alliant Energy allocates consolidated income tax expense to its subsidiaries that are members of the group that file a consolidated or combined income tax return. IPL and WPL use the separate return approach for calculating their income tax provisions and related deferred tax assets and liabilities. IPL and WPL are assumed to file separate tax returns with the federal and state taxing authorities, except that net operating losses (and other current or deferred tax attributes) are characterized as realized (or realizable) by IPL and WPL when those tax attributes are realized (or realizable) by the consolidated tax return group of Alliant Energy (even if IPL and WPL would not otherwise have realized the attributes on a stand-alone basis).

IPL and WPL have entered into agreements to transfer renewable tax credits from certain wind, solar and energy storage facilities to other corporate taxpayers in exchange for cash. Alliant Energy, IPL and WPL have elected to record transfers of renewable tax credits as part of income taxes, and cash received from the transfer of renewable tax credits is recorded in cash flows from operating activities. Renewable tax credits subject to future transfer are recorded at expected realizable value. Renewable tax credits are derecognized when control of the tax credits is transferred to other corporate taxpayers. Beginning October 1, 2024, IPL’s renewable energy rider was discontinued, and production tax credits, excluding production tax credits from the refurbishment of existing wind farms, are credited to IPL’s retail electric customers through its fuel-related cost recovery mechanism. Investment tax credits resulting from IPL’s renewable generation and energy storage projects that are not yet included in base rates may be utilized to offset any revenue deficiency on an annual basis up to IPL’s return on common equity threshold; any remaining investment tax credits, net of the cost of transferability, that are not used to offset any revenue deficiency, will be deferred by IPL and carried forward to offset any potential revenue deficiency in future years. At WPL, pursuant to escrow treatment approved by the PSCW, the difference between actual renewable tax credits and the amount of renewable tax credits collected from customers as electric revenues is recognized in “Income taxes” in Alliant Energy’s and WPL’s income statements. An offsetting amount is recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until reflected in future billings to customers. Refer to Note 16(d) for further discussion of the indemnification requirements.
(d) Cash, Cash Equivalents and Restricted Cash - Cash and cash equivalents include short-term liquid investments that have original maturities of less than 90 days. At December 31, 2025, Alliant Energy’s and WPL’s cash and cash equivalents included $411 million and $25 million, respectively, of money market fund investments, with weighted average interest rates of 4%. At December 31, 2025 and 2024, Alliant Energy’s restricted cash was not material.(e) Property, Plant and Equipment -
Utility Plant -
General - Utility plant is recorded at the original cost of acquisition or construction, which includes material, labor, contractor services, AFUDC and allocable overheads, such as supervision, engineering, certain administrative costs directly related to construction, benefits, certain taxes and transportation. Repairs, replacements and renewals of items of property determined to be less than a unit of property or that do not increase the property’s life or functionality are charged to maintenance expense. Property, plant and equipment that is probable of being retired early is classified as plant anticipated to be retired early. Generally, ordinary retirements of utility plant and salvage value are netted and charged to accumulated depreciation upon removal from utility plant accounts and no gain or loss is recognized consistent with rate-making principles. However, if regulators have approved recovery of the remaining net book value of property, plant and equipment that is retired early, or such approval by regulators is probable, the remaining net book value is reclassified from property, plant and equipment to regulatory assets upon retirement.
Depreciation - IPL and WPL use a combination of remaining life and straight-line depreciation methods as approved by their respective regulatory commissions. The composite or group method of depreciation is used, in which a single depreciation rate is applied to the gross investment in a particular class of property. This method pools similar assets and then depreciates each group as a whole. Periodic depreciation studies are performed to determine the appropriate group lives, net salvage, estimated cost of removal and group depreciation rates. These depreciation studies are subject to review and approval by IPL’s and WPL’s respective regulatory commissions. Depreciation expense is included within the recoverable cost of service component of rates collected from customers. The average rates of depreciation for electric, gas and other properties, consistent with current rate-making practices, were as follows:
IPLWPL
202520242023202520242023
Electric - generation3.5%3.3%3.3%3.4%3.4%3.0%
Electric - distribution2.9%2.8%2.8%2.7%2.7%2.7%
Electric - other3.6%5.2%5.6%4.2%6.1%6.3%
Gas3.3%3.3%3.3%2.4%2.5%2.5%
Other5.6%4.6%6.2%4.5%4.4%4.6%

AFUDC - AFUDC represents costs to finance construction additions, including a return on equity component and cost of debt component as required by regulatory accounting. AFUDC for IPL’s construction projects is calculated in accordance with FERC guidelines. AFUDC for WPL’s retail and wholesale jurisdiction construction projects is calculated in accordance with PSCW and FERC guidelines, respectively. The AFUDC rates, computed in accordance with the prescribed regulatory formula, were as follows:
202520242023
IPL7.1%7.0%7.0%
WPL (retail jurisdiction)7.4%7.4%7.4%
WPL (wholesale jurisdiction)6.6%7.1%7.1%

In accordance with their respective regulatory commission decisions, IPL applies its AFUDC rates to 100% of applicable CWIP balances, and WPL generally applies its AFUDC rates to 50% of applicable CWIP balances and the remaining 50% of applicable CWIP balances earns a return on such balances as part of its rate base. WPL may be authorized to apply its AFUDC rates to 100% of the retail portion of the CWIP balances for construction projects requiring a CA or CPCN that were approved by the PSCW after its then most recent rate order. Beginning January 1, 2026, the PSCW also authorized an AFUDC applied to 100% of the retail portion of CWIP balances related to construction activity on capital projects requiring PSCW approval and are impacted by federal law changes.

Non-utility and Other Property -
General - Non-utility property is recorded at the original cost of acquisition or construction, which includes material, labor and contractor services. Repairs, replacements and renewals of items of property determined to be less than a unit of property or that do not increase the property’s life or functionality are charged to maintenance expense. Upon retirement or sale of non-utility property, the original cost and related accumulated depreciation are removed from the accounts and any gain or loss is included in the income statements.

Costs related to software developed or obtained for internal use are capitalized and amortized on a straight-line basis over the estimated useful life of the related software. If software is retired prior to being fully amortized, the remaining book value is recorded as a loss in the income statements.
(f) Revenue Recognition -
Utility - Revenues from Alliant Energy’s utility business are primarily from electric and gas sales to customers. Utility revenues are recognized over time as services are rendered or commodities are delivered to customers, and include billed and unbilled components. The billed component is based on the reading of customers’ meters, which occurs on a systematic basis throughout each reporting period and represents the fair value of the services provided or commodities delivered. The unbilled component is recorded at the end of each reporting period based on estimated amounts of energy delivered to customers but not yet billed.

IPL and WPL accrue revenues from their wholesale customers to the extent that the actual net revenue requirements calculated in accordance with FERC-approved formula rates for the reporting period are higher or lower than the amounts billed to wholesale customers during such period. Regulatory assets or regulatory liabilities are recorded as the offset for these accrued revenues under formulaic rate-making programs. As of December 31, 2025, the related amounts accrued for IPL and WPL were not material.
IPL and WPL participate in bid/offer-based wholesale energy and ancillary services markets operated by MISO. The MISO transactions are grouped together, resulting in a net supply to or net purchase from MISO for each hour of each day. The net supply to MISO is recorded as bulk power sales in “Electric utility revenues” and the net purchase from MISO is recorded in “Electric production fuel and purchased power” in the income statements.

Non-utility - Revenues from Alliant Energy’s non-utility businesses are primarily from its Travero business and are recognized over time as services are rendered to customers.

Taxes Collected from Customers - Sales or various other taxes collected by certain of Alliant Energy’s subsidiaries on behalf of other agencies are recorded on a net basis and are not included in revenues.

Other - Alliant Energy, IPL and WPL do not disclose the value of unsatisfied performance obligations for: (i) contracts with an original expected length of one year or less; and (ii) contracts for which revenue is recognized at the amount to which they have the right to invoice for services performed.
(g) Utility Cost Recovery Mechanisms -
Electric Production Fuel and Purchased Power (Fuel-related Costs) - Fuel-related costs are incurred to generate and purchase electricity to meet the demand of IPL’s and WPL’s electric customers. These fuel-related costs include the cost of fossil fuels (primarily natural gas and coal) used to produce electricity at their EGUs, and electricity purchased from MISO wholesale energy markets and under PPAs. These fuel-related costs are recorded in “Electric production fuel and purchased power” in the income statements.

IPL Retail - The cost recovery mechanisms for IPL’s retail electric customers provide for monthly adjustments to their electric rates for changes in fuel-related costs. Changes in the under-/over-collection of these costs are recognized in “Electric production fuel and purchased power” in Alliant Energy’s and IPL’s income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers.

WPL Retail - The cost recovery mechanism for WPL’s retail electric customers is based on forecasts of certain fuel-related costs expected to be incurred during forward-looking test periods and fuel monitoring ranges determined by the PSCW during each retail electric rate proceeding or in a separate fuel cost plan approval proceeding. If WPL’s actual fuel-related costs fall outside these fuel monitoring ranges, WPL is authorized to defer the incremental under-/over-collection of fuel-related costs that are outside the approved ranges. Deferral of under-collections are reduced to the extent actual return on common equity earned by WPL during the fuel cost plan year exceeds the most recently authorized return on common equity. Deferred amounts for fuel-related costs outside the approved fuel monitoring ranges are recognized in “Electric production fuel and purchased power” in Alliant Energy’s and WPL’s income statements. The cumulative effects of these deferred amounts are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until they are reflected in future billings to customers.

IPL and WPL Wholesale - The cost recovery mechanisms for IPL’s and WPL’s wholesale electric customers provide for subsequent adjustments to their electric rates for changes in fuel-related costs. Changes in the under-/over-collection of these costs are recognized in “Electric production fuel and purchased power” in the income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers.

Electric Capacity - PPAs help meet the electricity demand of IPL’s and WPL’s customers. Certain PPAs include minimum payments for IPL’s and WPL’s rights to electric generating capacity, which are charged each period to “Electric production fuel and purchased power” in the income statements. Purchased electric capacity expenses are recovered from IPL’s and WPL’s retail electric customers through changes in base rates determined during periodic rate proceedings. Purchased electric capacity expenses are recovered from IPL’s and WPL’s wholesale electric customers through annual changes in base rates determined by a formula rate structure. Electric capacity revenues are refunded to IPL's retail electric customers through changes in base rates determined during periodic rate proceedings, and to IPL and WPL's wholesale electric customers through annual changes in base rates determined by a formula rate structure. Electric capacity revenues are refunded to WPL's retail electric customers through its fuel cost recovery mechanism.

Electric Transmission Service - Costs incurred for the transmission of electricity to meet the demands of IPL’s and WPL’s customers are charged to “Electric transmission service” in the income statements.

IPL Retail - Electric transmission service expense is recovered from IPL’s retail electric customers through a transmission cost rider. This cost recovery mechanism provides for periodic adjustments to electric rates charged to retail electric customers for changes in electric transmission service expense. Changes in the under-/over-collection of these costs are recognized in “Electric transmission service” in Alliant Energy’s and IPL’s income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers.
WPL Retail - Electric transmission service expense is recovered from WPL’s retail electric customers through changes in base rates determined during periodic rate proceedings. Pursuant to escrow accounting treatment approved by the PSCW, the difference between actual electric transmission service expense incurred and the amount of electric transmission service costs collected from customers as electric revenues is recognized in “Electric transmission service” in Alliant Energy’s and WPL’s income statements. An offsetting amount is recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until reflected in future billings to customers.

IPL and WPL Wholesale - IPL and WPL arrange transmission service for the majority of their respective wholesale electric customers. Electric transmission service expense is allocated to and recovered from these customers based on a load ratio share computation.

Cost of Gas Sold - Costs are incurred for the purchase, transportation and storage of natural gas to serve IPL’s and WPL’s gas customers and the costs associated with the natural gas delivered to customers are charged to “Cost of gas sold” in the income statements. The tariffs for IPL’s and WPL’s retail gas customers provide for subsequent adjustments to their rates periodically for changes in the cost of gas sold. Changes in the under-/over-collection of these costs are also recognized in “Cost of gas sold” in the income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers.

Energy Efficiency Costs - Costs incurred to fund energy efficiency programs and initiatives that help customers reduce their energy usage are charged to “Other operation and maintenance” in the income statements. Energy efficiency costs incurred by IPL are recovered from its retail electric and gas customers through energy efficiency and demand response cost recovery factor tariffs, which are revised annually and include a reconciliation to eliminate any under-/over-collection of energy efficiency costs from prior periods. Pursuant to escrow accounting treatment approved by the PSCW, the difference between actual energy efficiency costs incurred by WPL and the amount collected from its retail electric and gas customers is recovered through changes in base rates determined during periodic rate proceedings, and reconciliations eliminate any under-/over-collection of energy efficiency costs from prior periods. Changes in the under-/over-collection of energy efficiency costs for IPL and WPL are recognized in “Other operation and maintenance” in the income statements. The cumulative effects of the under-/over-collection of these costs for IPL and WPL are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers.

Renewable Energy Rider - IPL utilized a renewable energy rider prior to its discontinuation on October 1, 2024, effective with the IUC’s order for IPL’s retail electric rate review for the October 2024 through September 2025 Test Period. Prior to October 1, 2024, IPL recovered a return of, as well as earned a return on, its wind generation placed in service in 2019 and 2020 from its retail electric customers through the renewable energy rider. Other applicable costs and tax benefits associated with this wind generation, excluding operation and maintenance expenses, were also included in the rider. This cost recovery mechanism provided for annual adjustments to electric rates charged to IPL’s retail electric customers for actual renewable energy costs and tax benefits. Changes in the under-/over-collection of these costs were recognized in “Electric utility revenue” in Alliant Energy’s and IPL’s income statements. The cumulative effects of the under-/over-collection of these costs for IPL is recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers. Refer to Note 1(c) for further discussion of the treatment of IPL’s renewable tax credits for rate-making purposes.
(h) Financial Instruments - Financial instruments are periodically used for risk management purposes to mitigate exposures to fluctuations in certain commodity prices, transmission congestion costs and interest rates. The fair value of those financial instruments that are determined to be derivatives are recorded as assets or liabilities on the balance sheets. Certain commodity purchase and sales contracts qualified for and were designated under the normal purchase and sale exception, and were accounted for on the accrual basis of accounting. Alliant Energy, IPL and WPL have elected to not net the fair value amounts of derivatives subject to a master netting arrangement by counterparty. Alliant Energy, IPL and WPL do not offset fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) against fair value amounts recognized for derivative instruments that are executed with the same counterparty under the same master netting arrangement. Refer to Note 2 for discussion of the recognition of regulatory assets and regulatory liabilities related to the unrealized losses and gains on commodity derivative instruments. Refer to Notes 14, 15 and 16(f) for further discussion of derivatives and related credit risk.(i) Asset Impairments -
Property, Plant and Equipment of Regulated Operations - Property, plant and equipment of regulated operations are reviewed for possible impairment whenever events or changes in circumstances indicate all or a portion of the carrying value of the assets may be disallowed for rate-making purposes. If IPL or WPL are disallowed recovery of any portion of, or are only allowed a partial return on, the carrying value of their regulated property, plant and equipment that is under construction, has been recently completed or is probable of abandonment, or conclude it is probable recovery or a full return will be disallowed, then an impairment charge is recognized.
Property, Plant and Equipment of Non-utility Operations - Property, plant and equipment of non-utility operations are reviewed for possible impairment whenever events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Impairment is indicated if the carrying value of an asset exceeds its undiscounted future cash flows. If an impairment is indicated, a charge is recognized equal to the amount the carrying value exceeds the asset’s fair value. Refer to Note 17 for discussion of an asset valuation charge at Alliant Energy’s non-utility holdings in 2025.

Unconsolidated Equity Investments - If events or circumstances indicate the carrying value of investments accounted for under the equity method of accounting exceeds fair value and the decline in value is other than temporary, potential impairment is assessed. If an impairment is indicated, a charge is recognized equal to the amount the carrying value exceeds the investment’s fair value.
(j) Asset Retirement Obligations - The fair value of a legal obligation associated with the retirement of an asset is recorded as a liability when an asset is placed in service, when a legal obligation is subsequently identified or when sufficient information becomes available to determine a reasonable estimate of the fair value of future retirement costs. When an ARO is recorded as a liability, an equivalent amount is added to the asset cost. The fair value of AROs at inception is determined using discounted cash flows analyses. The liability is accreted to its present value and the capitalized cost is depreciated over the useful life of the related asset. Accretion and depreciation expenses related to AROs for IPL’s and WPL’s regulated operations are recorded to regulatory assets on the balance sheets. Revisions in estimated cash flows for IPL’s and WPL’s regulated operations are recorded as an increase or decrease to the ARO liability, with an offset to the asset cost, unless the asset is already retired and then the offset is recorded to regulatory assets or regulatory liabilities on the balance sheets. Upon regulatory approval to recover IPL’s AROs expenditures, its regulatory assets are amortized to depreciation and amortization expenses in Alliant Energy’s and IPL’s income statements over the same time period the ARO expenditures are recovered from IPL’s customers. WPL’s regulatory assets related to AROs are recovered as a component of depreciation rates pursuant to PSCW and FERC orders. Upon settlement of the ARO liability, an entity settles the obligation for its recorded amount or incurs a gain or loss. Any gains or losses related to AROs for IPL’s and WPL’s regulated operations are recorded to regulatory liabilities or regulatory assets on the balance sheets. Refer to Note 13 for details of an ARO charge for steam assets at IPL in 2024.(k) Debt Issuance and Retirement Costs - Debt issuance costs and debt premiums or discounts are presented on the balance sheets as a direct adjustment to the carrying amount of the related debt liability, and are deferred and amortized over the expected life of each debt issue, considering maturity dates and, if applicable, redemption rights held by us or by others. Alliant Energy’s non-utility businesses and Corporate Services record to interest expense in the period of retirement any unamortized debt issuance costs and debt premiums or discounts on debt retired early.(l) Current Expected Credit Losses Estimates - Current expected credit losses are estimated for trade and other receivables and credit exposures on guarantees of the performance by third parties. The current expected credit losses for short-term trade receivables are based on estimates of losses resulting from the inability of customers to make required payments. The methodology used to estimate losses is based on historical write-offs, regional economic conditions, significant events that could impact collectability, such as significant weather related matters and related regulatory actions, and actual and forecasted changes to the accounts receivable aging portfolio and write-offs. The current expected credit losses related to guarantees of the performance by third parties are estimated using both quantitative and qualitative information, which utilizes potential outcomes in a range of possible estimated amounts.(m) Variable Interest Entities - An entity is considered a VIE if its equity investors do not have sufficient equity at risk for the entity to finance its activities without additional subordinated financial support from other parties, the entity is structured with disproportionate voting rights and substantially all of the entity’s activities are conducted on behalf of the investor with disproportionately fewer voting rights, or its equity investors lack any of the following characteristics: (1) power, through voting rights or similar rights, to direct the activities of the entity that most significantly impact the entity’s economic performance; (2) the obligation to absorb expected losses of the entity; or (3) the right to receive expected benefits of the entity. The primary beneficiary of a VIE is required to consolidate the VIE. The financial statements do not reflect any consolidation of VIEs.(n) Leases - The determination of whether an arrangement qualifies as a lease occurs at the inception of the arrangement. Arrangements that qualify as leases are classified as either operating or finance. Operating and finance lease liabilities represent obligations to make payments arising from the lease. Operating and finance lease assets represent the right to use an underlying asset for the lease term and are recognized at the lease commencement date based on the present value of the lease payments over the lease term. Leases with initial terms less than 12 months are not recognized as leases. For operating leases, an incremental borrowing rate, as determined at the lease commencement date, is used to determine the present value of the lease payments. For finance leases, the rate implicit in the lease, if known, is used to determine the present value of the lease payments. If the rate implicit in the lease is not known, the incremental borrowing rate, as determined at the lease commencement date, is used to determine the present value of the lease payments. Lease terms include options to extend or terminate the lease when it is reasonably certain that the option will be exercised. Operating lease expense is recognized on a straight-line basis over the expected lease term. Finance lease expense is comprised of depreciation and amortization, and interest expenses. Finance lease assets are accounted for as operating leases for rate-making purposes.
v3.25.4
Regulatory Matters
 12 Months Ended
Dec. 31, 2025
Regulatory Matters [Line Items]  
Regulatory Matters REGULATORY MATTERS
Regulatory Assets - Alliant Energy, IPL and WPL assess whether IPL’s and WPL’s regulatory assets are probable of future recovery by considering factors such as applicable regulations, recent orders by the applicable regulatory agencies, historical treatment of similar costs by the applicable regulatory agencies and regulatory environment changes. Based on these assessments, Alliant Energy, IPL and WPL believe the regulatory assets recognized as of December 31, 2025 are probable of future recovery. However, no assurance can be made that IPL and WPL will recover all of these regulatory assets in future rates. If future recovery of a regulatory asset ceases to be probable, the regulatory asset will be charged to expense. At December 31, regulatory assets were comprised of the following items (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Tax-related$1,089 $989 $949 $870 $140 $119 
AROs455 401 312 281 143 120 
Pension and OPEB costs274 315 136 157 138 158 
Assets retired early158 180 149 168 9 12 
Non-service pension and OPEB costs57 51 21 19 36 32 
Derivatives52 60 12 15 40 45 
WPL’s Western Wisconsin gas distribution expansion investments39 42 — — 39 42 
Commodity cost recovery10 68 3 2 7 66 
Other140 168 34 74 106 94 
$2,274 $2,274 $1,616 $1,586 $658 $688 

At December 31, 2025, IPL and WPL had $165 million and $28 million, respectively, of regulatory assets that were not earning a return on investment. IPL’s regulatory assets that were not earning a return consisted primarily of the retired Lansing Generating Station, retired analog electric meters, and costs for certain construction projects. WPL’s regulatory assets that were not earning a return consisted primarily of amounts related to the retail portion of under-collected electric transmission service expenses and costs for certain construction projects. The other regulatory assets reported in the above table either earn a return or the cash has not yet been expended, in which case the assets are offset by liabilities that also do not incur a carrying cost.

Tax-related - IPL and WPL record regulatory assets for certain temporary differences (primarily related to utility property, plant and equipment at IPL) that result in a decrease in current rates charged to customers and an increase in future rates charged to customers based on the timing of income tax expense that is used to determine such rates. These temporary differences for IPL include the impacts of qualifying deductions for repairs expenditures, allocation of mixed service costs, and Iowa accelerated tax depreciation, which all contribute to lower current income tax expense during the first part of an asset’s useful life and higher current income tax expense during the latter part of an asset’s useful life. Conversely, cost of removal obligations contribute to higher current income tax expense during the first part of an asset’s useful life and lower current income tax expense during the latter part of an asset’s useful life. These regulatory assets will be recovered from customers in the future when these temporary differences reverse resulting in additional current income tax expense used to determine customers’ rates.

AROs - Alliant Energy, IPL and WPL believe it is probable that certain differences between expenses accrued for AROs related to their utility operations and expenses recovered currently in rates will be recoverable in future rates, and are deferring the differences as regulatory assets. Refer to Note 13 for discussion of the recognition of additional ARO regulatory assets in 2024, substantially resulting from the enactment of the revised CCR Rule.

Pension and other postretirement benefits costs - The IUC, PSCW and FERC have authorized IPL and WPL to record the previously unrecognized net actuarial gains and losses, and prior service costs and credits, as regulatory assets in lieu of accumulated other comprehensive loss on the balance sheets, as these amounts are expected to be recovered in future rates. These regulatory assets will be increased or decreased as the net actuarial gains or losses, and prior service costs or credits, are subsequently amortized and recognized as a component of net periodic benefit costs. Regulatory assets are also increased or decreased as a result of the annual defined benefit plan measurement process. Pension and OPEB costs are included within the recoverable cost of service component of rates charged to IPL’s and WPL’s retail and wholesale customers, which are based upon pension and OPEB costs determined in accordance with GAAP and are calculated in accordance with IPL’s and WPL’s respective regulatory jurisdictions.
Assets retired early - IPL and WPL have retired various natural gas- and coal-fired EGUs, and IPL has retired certain analog electric meters. As a result, the remaining net book value of these assets was reclassified from property, plant and equipment to a regulatory asset on their respective balance sheets. Details regarding the recovery of the remaining net book value of these assets from IPL’s and WPL’s customers are as follows (dollars in millions):
EntityAssetRetirement Date
Regulatory Asset Balance as of Dec. 31, 2025
RecoveryRegulatory Approval
IPLLansing2023$123Return of (IUC and FERC) and return on (FERC) remaining net book value through 2037 (a)IUC and FERC (b)
IPLAnalog electric meters201910Return of remaining net book value through 2028IUC and FERC
IPLSutherland Units 1 and 3201711Return of and return on remaining net book value through 2027 (a)IUC and FERC
IPLM.L. Kapp Unit 220185Return of and return on remaining net book value through 2029 (a)IUC and FERC
WPLEdgewater Unit 420189Return of and return on remaining net book value through 2028PSCW and FERC

(a)The remaining regulatory asset balances include differences between expected and actual cost of removal obligations.
(b)IPL was previously allowed a full recovery of and a full return on the Lansing Generating Station from both its retail and wholesale customers. The IUC’s September 2024 order for IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period includes a return of the remaining net book value of Lansing, but does not include a return on the remaining net book value of Lansing, effective October 1, 2024. As a result, the return on the remaining net book value is no longer recoverable from IPL’s retail electric customers, and a pre-tax non-cash charge of $60 million was recorded to “Asset valuation charge for IPL’s Lansing Generating Station” in Alliant Energy’s and IPL’s income statements in 2024, with a corresponding decrease in Alliant Energy’s and IPL’s assets retired early regulatory assets.

Non-service pension and OPEB costs - Non-service pension and OPEB costs are recorded to regulatory assets to reflect the impacts of rate-making, and are recovered from IPL’s and WPL’s electric and gas customers through depreciation expense based on the depreciation rates for plant in-service.

Derivatives - In accordance with IPL’s and WPL’s fuel and natural gas recovery mechanisms, prudently incurred costs from derivative instruments are recoverable from customers in the future after any losses are realized, and gains from derivative instruments are refundable to customers in the future after any gains are realized. Based on these recovery mechanisms, the changes in the fair value of derivative liabilities/assets resulted in comparable changes to regulatory assets/liabilities on the balance sheets. Refer to Note 14 for discussion of changes in Alliant Energy’s, IPL’s and WPL’s derivative liabilities/assets during 2025, which resulted in comparable changes to regulatory assets/liabilities on the balance sheets.

WPL’s Western Wisconsin gas distribution expansion investments - WPL made contributions in aid of construction to a third party for investments as part of its Western Wisconsin gas distribution expansion project. Pursuant to authorization by the PSCW, Alliant Energy and WPL have recorded a regulatory asset for these costs, and are authorized by the PSCW to recover these amounts from WPL’s retail gas customers in base rates from 2021 through the end of 2040.

Commodity cost recovery - Refer to Note 1(g) for details of IPL’s and WPL’s commodity cost recovery mechanisms. The cost recovery mechanism for WPL’s retail electric customers is based on forecasts of certain fuel-related costs expected to be incurred during forward-looking test periods and fuel monitoring ranges determined by the PSCW during each retail electric rate proceeding or in a separate fuel cost plan approval proceeding. In 2022, WPL’s actual fuel-related costs fell outside these fuel monitoring ranges, resulting in a $117 million deferral as of December 31, 2022, which WPL substantially collected from October 2023 through December 2025 from its retail electric customers, plus interest ($12 million, $50 million and $52 million was collected in 2023, 2024 and 2025, respectively). In 2023, WPL’s actual fuel-related costs fell outside these fuel monitoring ranges, resulting in a $34 million regulatory liability as of December 31, 2023, which was refunded in 2024 to its retail electric customers, plus interest.

Regulatory Liabilities - At December 31, regulatory liabilities were comprised of the following items (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Tax-related$690$582$304$286$386$296
Cost of removal obligations366347217205149142
Derivatives475326292124
Other984639265920
$1,201$1,028$586$546$615$482
Tax-related regulatory liabilities reduce revenue requirement calculations utilized in IPL’s and WPL’s respective rate proceedings. Cost of removal obligations, to the extent expensed through depreciation rates, reduce rate base. A significant portion of the remaining regulatory liabilities is not used to adjust revenue requirement calculations.

Tax-related - Alliant Energy’s, IPL’s and WPL’s tax-related regulatory liabilities are primarily related to excess deferred tax benefits resulting from the remeasurement of accumulated deferred income taxes caused by the Tax Cuts and Jobs Act. The majority of these benefits related to accelerated depreciation are subject to tax normalization rules. These rules limit the rate at which these tax benefits are allowed to be passed on to customers. Additionally, Alliant Energy’s, IPL’s and WPL’s tax-related regulatory liabilities include tax benefits resulting from investment tax credits for IPL’s and WPL’s energy storage facilities and WPL’s Cassville solar facility. Refer to Note 1(c) for details related to the regulatory treatment of IPL’s and WPL’s investment tax credits.

Cost of removal obligations - Alliant Energy, IPL and WPL collect in rates future removal costs for many assets that do not have associated AROs or that have removal costs in addition to AROs. Alliant Energy, IPL and WPL record a regulatory liability for the amounts collected in rates for these future removal costs and reduce the regulatory liability for amounts spent on removal activities. Cash payments related to cost of removal obligations are included in “Other” in cash flows used for investing activities.

Rate Reviews -

WPL’s Retail Electric and Gas Rate Reviews (2024/2025 Forward-looking Test Period) - In December 2023, the PSCW issued an order authorizing annual base rate increases of $49 million and $13 million for WPL’s retail electric and gas customers, respectively, effective January 1, 2024, for the 2024 forward-looking Test Period. The PSCW’s order also authorized WPL to implement an additional $60 million increase in annual rates for its retail electric customers, effective January 1, 2025, for the 2025 forward-looking Test Period. The key drivers for the annual base rate increases include revenue requirement impacts of increasing electric and gas rate base, including investments in solar generation and energy storage. In addition, the PSCW’s order extended, with certain modifications, an earnings sharing mechanism through the end of 2025. The PSCW also authorized WPL to defer the incremental under-/over-collection of solar and energy storage renewable tax credits that are outside of the approved amounts, which are included in the tax-related lines of the regulatory assets and regulatory liabilities tables above. Refer to Note 3 for discussion of PSCW orders approving deferral of, and the deferral of a return on, incremental solar generation construction costs in 2024 and 2025.

WPL’s Retail Electric and Gas Rate Reviews (2026/2027 Forward-looking Test Period) - In December 2025, the PSCW issued an order authorizing annual base rate increases of $69 million and $7 million for WPL’s retail electric and gas customers, respectively, effective January 1, 2026, for the 2026 forward-looking Test Period. The PSCW’s order also authorized WPL to implement an additional $75 million and $5 million increase in annual rates for its retail electric and gas customers, respectively, effective January 1, 2027, for the 2027 forward-looking Test Period.

IPL’s Retail Electric and Gas Rate Reviews (October 2024 through September 2025 Forward-looking Test Period) - In September 2024, the IUC issued an order authorizing annual base rate increases of $185 million for IPL’s retail electric customers, with customers receiving partially offsetting credits for the first 12 months through a tax benefit rider, and $10 million for IPL’s retail gas customers, for the October 2024 through September 2025 forward-looking Test Period. Rate changes were effective October 1, 2024. The IUC’s order also reflects the following:
•Electric earnings sharing mechanism beginning in calendar year 2025, where IPL would apply excess earnings to the remaining net book value of IPL’s highest earning asset with advance ratemaking principles (currently the Emery Generation Station) based on its authorized return on common equity;
•Investment tax credits resulting from renewable generation and energy storage projects may be utilized to offset any revenue deficiency on an annual basis up to IPL’s return on common equity threshold; any remaining investment tax credits, net of the cost of transferability, that are not used to offset any revenue deficiency, will be deferred by IPL and carried forward to offset any revenue deficiency in future years; and
•Discontinuation of the renewable energy rider.
IPL [Member]  
Regulatory Matters [Line Items]  
Regulatory Matters REGULATORY MATTERS
Regulatory Assets - Alliant Energy, IPL and WPL assess whether IPL’s and WPL’s regulatory assets are probable of future recovery by considering factors such as applicable regulations, recent orders by the applicable regulatory agencies, historical treatment of similar costs by the applicable regulatory agencies and regulatory environment changes. Based on these assessments, Alliant Energy, IPL and WPL believe the regulatory assets recognized as of December 31, 2025 are probable of future recovery. However, no assurance can be made that IPL and WPL will recover all of these regulatory assets in future rates. If future recovery of a regulatory asset ceases to be probable, the regulatory asset will be charged to expense. At December 31, regulatory assets were comprised of the following items (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Tax-related$1,089 $989 $949 $870 $140 $119 
AROs455 401 312 281 143 120 
Pension and OPEB costs274 315 136 157 138 158 
Assets retired early158 180 149 168 9 12 
Non-service pension and OPEB costs57 51 21 19 36 32 
Derivatives52 60 12 15 40 45 
WPL’s Western Wisconsin gas distribution expansion investments39 42 — — 39 42 
Commodity cost recovery10 68 3 2 7 66 
Other140 168 34 74 106 94 
$2,274 $2,274 $1,616 $1,586 $658 $688 

At December 31, 2025, IPL and WPL had $165 million and $28 million, respectively, of regulatory assets that were not earning a return on investment. IPL’s regulatory assets that were not earning a return consisted primarily of the retired Lansing Generating Station, retired analog electric meters, and costs for certain construction projects. WPL’s regulatory assets that were not earning a return consisted primarily of amounts related to the retail portion of under-collected electric transmission service expenses and costs for certain construction projects. The other regulatory assets reported in the above table either earn a return or the cash has not yet been expended, in which case the assets are offset by liabilities that also do not incur a carrying cost.

Tax-related - IPL and WPL record regulatory assets for certain temporary differences (primarily related to utility property, plant and equipment at IPL) that result in a decrease in current rates charged to customers and an increase in future rates charged to customers based on the timing of income tax expense that is used to determine such rates. These temporary differences for IPL include the impacts of qualifying deductions for repairs expenditures, allocation of mixed service costs, and Iowa accelerated tax depreciation, which all contribute to lower current income tax expense during the first part of an asset’s useful life and higher current income tax expense during the latter part of an asset’s useful life. Conversely, cost of removal obligations contribute to higher current income tax expense during the first part of an asset’s useful life and lower current income tax expense during the latter part of an asset’s useful life. These regulatory assets will be recovered from customers in the future when these temporary differences reverse resulting in additional current income tax expense used to determine customers’ rates.

AROs - Alliant Energy, IPL and WPL believe it is probable that certain differences between expenses accrued for AROs related to their utility operations and expenses recovered currently in rates will be recoverable in future rates, and are deferring the differences as regulatory assets. Refer to Note 13 for discussion of the recognition of additional ARO regulatory assets in 2024, substantially resulting from the enactment of the revised CCR Rule.

Pension and other postretirement benefits costs - The IUC, PSCW and FERC have authorized IPL and WPL to record the previously unrecognized net actuarial gains and losses, and prior service costs and credits, as regulatory assets in lieu of accumulated other comprehensive loss on the balance sheets, as these amounts are expected to be recovered in future rates. These regulatory assets will be increased or decreased as the net actuarial gains or losses, and prior service costs or credits, are subsequently amortized and recognized as a component of net periodic benefit costs. Regulatory assets are also increased or decreased as a result of the annual defined benefit plan measurement process. Pension and OPEB costs are included within the recoverable cost of service component of rates charged to IPL’s and WPL’s retail and wholesale customers, which are based upon pension and OPEB costs determined in accordance with GAAP and are calculated in accordance with IPL’s and WPL’s respective regulatory jurisdictions.
Assets retired early - IPL and WPL have retired various natural gas- and coal-fired EGUs, and IPL has retired certain analog electric meters. As a result, the remaining net book value of these assets was reclassified from property, plant and equipment to a regulatory asset on their respective balance sheets. Details regarding the recovery of the remaining net book value of these assets from IPL’s and WPL’s customers are as follows (dollars in millions):
EntityAssetRetirement Date
Regulatory Asset Balance as of Dec. 31, 2025
RecoveryRegulatory Approval
IPLLansing2023$123Return of (IUC and FERC) and return on (FERC) remaining net book value through 2037 (a)IUC and FERC (b)
IPLAnalog electric meters201910Return of remaining net book value through 2028IUC and FERC
IPLSutherland Units 1 and 3201711Return of and return on remaining net book value through 2027 (a)IUC and FERC
IPLM.L. Kapp Unit 220185Return of and return on remaining net book value through 2029 (a)IUC and FERC
WPLEdgewater Unit 420189Return of and return on remaining net book value through 2028PSCW and FERC

(a)The remaining regulatory asset balances include differences between expected and actual cost of removal obligations.
(b)IPL was previously allowed a full recovery of and a full return on the Lansing Generating Station from both its retail and wholesale customers. The IUC’s September 2024 order for IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period includes a return of the remaining net book value of Lansing, but does not include a return on the remaining net book value of Lansing, effective October 1, 2024. As a result, the return on the remaining net book value is no longer recoverable from IPL’s retail electric customers, and a pre-tax non-cash charge of $60 million was recorded to “Asset valuation charge for IPL’s Lansing Generating Station” in Alliant Energy’s and IPL’s income statements in 2024, with a corresponding decrease in Alliant Energy’s and IPL’s assets retired early regulatory assets.

Non-service pension and OPEB costs - Non-service pension and OPEB costs are recorded to regulatory assets to reflect the impacts of rate-making, and are recovered from IPL’s and WPL’s electric and gas customers through depreciation expense based on the depreciation rates for plant in-service.

Derivatives - In accordance with IPL’s and WPL’s fuel and natural gas recovery mechanisms, prudently incurred costs from derivative instruments are recoverable from customers in the future after any losses are realized, and gains from derivative instruments are refundable to customers in the future after any gains are realized. Based on these recovery mechanisms, the changes in the fair value of derivative liabilities/assets resulted in comparable changes to regulatory assets/liabilities on the balance sheets. Refer to Note 14 for discussion of changes in Alliant Energy’s, IPL’s and WPL’s derivative liabilities/assets during 2025, which resulted in comparable changes to regulatory assets/liabilities on the balance sheets.
Commodity cost recovery - Refer to Note 1(g) for details of IPL’s and WPL’s commodity cost recovery mechanisms. The cost recovery mechanism for WPL’s retail electric customers is based on forecasts of certain fuel-related costs expected to be incurred during forward-looking test periods and fuel monitoring ranges determined by the PSCW during each retail electric rate proceeding or in a separate fuel cost plan approval proceeding. In 2022, WPL’s actual fuel-related costs fell outside these fuel monitoring ranges, resulting in a $117 million deferral as of December 31, 2022, which WPL substantially collected from October 2023 through December 2025 from its retail electric customers, plus interest ($12 million, $50 million and $52 million was collected in 2023, 2024 and 2025, respectively). In 2023, WPL’s actual fuel-related costs fell outside these fuel monitoring ranges, resulting in a $34 million regulatory liability as of December 31, 2023, which was refunded in 2024 to its retail electric customers, plus interest.

Regulatory Liabilities - At December 31, regulatory liabilities were comprised of the following items (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Tax-related$690$582$304$286$386$296
Cost of removal obligations366347217205149142
Derivatives475326292124
Other984639265920
$1,201$1,028$586$546$615$482
Tax-related regulatory liabilities reduce revenue requirement calculations utilized in IPL’s and WPL’s respective rate proceedings. Cost of removal obligations, to the extent expensed through depreciation rates, reduce rate base. A significant portion of the remaining regulatory liabilities is not used to adjust revenue requirement calculations.

Tax-related - Alliant Energy’s, IPL’s and WPL’s tax-related regulatory liabilities are primarily related to excess deferred tax benefits resulting from the remeasurement of accumulated deferred income taxes caused by the Tax Cuts and Jobs Act. The majority of these benefits related to accelerated depreciation are subject to tax normalization rules. These rules limit the rate at which these tax benefits are allowed to be passed on to customers. Additionally, Alliant Energy’s, IPL’s and WPL’s tax-related regulatory liabilities include tax benefits resulting from investment tax credits for IPL’s and WPL’s energy storage facilities and WPL’s Cassville solar facility. Refer to Note 1(c) for details related to the regulatory treatment of IPL’s and WPL’s investment tax credits.

Cost of removal obligations - Alliant Energy, IPL and WPL collect in rates future removal costs for many assets that do not have associated AROs or that have removal costs in addition to AROs. Alliant Energy, IPL and WPL record a regulatory liability for the amounts collected in rates for these future removal costs and reduce the regulatory liability for amounts spent on removal activities. Cash payments related to cost of removal obligations are included in “Other” in cash flows used for investing activities.

Rate Reviews -
IPL’s Retail Electric and Gas Rate Reviews (October 2024 through September 2025 Forward-looking Test Period) - In September 2024, the IUC issued an order authorizing annual base rate increases of $185 million for IPL’s retail electric customers, with customers receiving partially offsetting credits for the first 12 months through a tax benefit rider, and $10 million for IPL’s retail gas customers, for the October 2024 through September 2025 forward-looking Test Period. Rate changes were effective October 1, 2024. The IUC’s order also reflects the following:
•Electric earnings sharing mechanism beginning in calendar year 2025, where IPL would apply excess earnings to the remaining net book value of IPL’s highest earning asset with advance ratemaking principles (currently the Emery Generation Station) based on its authorized return on common equity;
•Investment tax credits resulting from renewable generation and energy storage projects may be utilized to offset any revenue deficiency on an annual basis up to IPL’s return on common equity threshold; any remaining investment tax credits, net of the cost of transferability, that are not used to offset any revenue deficiency, will be deferred by IPL and carried forward to offset any revenue deficiency in future years; and
•Discontinuation of the renewable energy rider.
WPL [Member]  
Regulatory Matters [Line Items]  
Regulatory Matters REGULATORY MATTERS
Regulatory Assets - Alliant Energy, IPL and WPL assess whether IPL’s and WPL’s regulatory assets are probable of future recovery by considering factors such as applicable regulations, recent orders by the applicable regulatory agencies, historical treatment of similar costs by the applicable regulatory agencies and regulatory environment changes. Based on these assessments, Alliant Energy, IPL and WPL believe the regulatory assets recognized as of December 31, 2025 are probable of future recovery. However, no assurance can be made that IPL and WPL will recover all of these regulatory assets in future rates. If future recovery of a regulatory asset ceases to be probable, the regulatory asset will be charged to expense. At December 31, regulatory assets were comprised of the following items (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Tax-related$1,089 $989 $949 $870 $140 $119 
AROs455 401 312 281 143 120 
Pension and OPEB costs274 315 136 157 138 158 
Assets retired early158 180 149 168 9 12 
Non-service pension and OPEB costs57 51 21 19 36 32 
Derivatives52 60 12 15 40 45 
WPL’s Western Wisconsin gas distribution expansion investments39 42 — — 39 42 
Commodity cost recovery10 68 3 2 7 66 
Other140 168 34 74 106 94 
$2,274 $2,274 $1,616 $1,586 $658 $688 

At December 31, 2025, IPL and WPL had $165 million and $28 million, respectively, of regulatory assets that were not earning a return on investment. IPL’s regulatory assets that were not earning a return consisted primarily of the retired Lansing Generating Station, retired analog electric meters, and costs for certain construction projects. WPL’s regulatory assets that were not earning a return consisted primarily of amounts related to the retail portion of under-collected electric transmission service expenses and costs for certain construction projects. The other regulatory assets reported in the above table either earn a return or the cash has not yet been expended, in which case the assets are offset by liabilities that also do not incur a carrying cost.

Tax-related - IPL and WPL record regulatory assets for certain temporary differences (primarily related to utility property, plant and equipment at IPL) that result in a decrease in current rates charged to customers and an increase in future rates charged to customers based on the timing of income tax expense that is used to determine such rates. These temporary differences for IPL include the impacts of qualifying deductions for repairs expenditures, allocation of mixed service costs, and Iowa accelerated tax depreciation, which all contribute to lower current income tax expense during the first part of an asset’s useful life and higher current income tax expense during the latter part of an asset’s useful life. Conversely, cost of removal obligations contribute to higher current income tax expense during the first part of an asset’s useful life and lower current income tax expense during the latter part of an asset’s useful life. These regulatory assets will be recovered from customers in the future when these temporary differences reverse resulting in additional current income tax expense used to determine customers’ rates.

AROs - Alliant Energy, IPL and WPL believe it is probable that certain differences between expenses accrued for AROs related to their utility operations and expenses recovered currently in rates will be recoverable in future rates, and are deferring the differences as regulatory assets. Refer to Note 13 for discussion of the recognition of additional ARO regulatory assets in 2024, substantially resulting from the enactment of the revised CCR Rule.

Pension and other postretirement benefits costs - The IUC, PSCW and FERC have authorized IPL and WPL to record the previously unrecognized net actuarial gains and losses, and prior service costs and credits, as regulatory assets in lieu of accumulated other comprehensive loss on the balance sheets, as these amounts are expected to be recovered in future rates. These regulatory assets will be increased or decreased as the net actuarial gains or losses, and prior service costs or credits, are subsequently amortized and recognized as a component of net periodic benefit costs. Regulatory assets are also increased or decreased as a result of the annual defined benefit plan measurement process. Pension and OPEB costs are included within the recoverable cost of service component of rates charged to IPL’s and WPL’s retail and wholesale customers, which are based upon pension and OPEB costs determined in accordance with GAAP and are calculated in accordance with IPL’s and WPL’s respective regulatory jurisdictions.
Assets retired early - IPL and WPL have retired various natural gas- and coal-fired EGUs, and IPL has retired certain analog electric meters. As a result, the remaining net book value of these assets was reclassified from property, plant and equipment to a regulatory asset on their respective balance sheets. Details regarding the recovery of the remaining net book value of these assets from IPL’s and WPL’s customers are as follows (dollars in millions):
EntityAssetRetirement Date
Regulatory Asset Balance as of Dec. 31, 2025
RecoveryRegulatory Approval
IPLLansing2023$123Return of (IUC and FERC) and return on (FERC) remaining net book value through 2037 (a)IUC and FERC (b)
IPLAnalog electric meters201910Return of remaining net book value through 2028IUC and FERC
IPLSutherland Units 1 and 3201711Return of and return on remaining net book value through 2027 (a)IUC and FERC
IPLM.L. Kapp Unit 220185Return of and return on remaining net book value through 2029 (a)IUC and FERC
WPLEdgewater Unit 420189Return of and return on remaining net book value through 2028PSCW and FERC

(a)The remaining regulatory asset balances include differences between expected and actual cost of removal obligations.
(b)IPL was previously allowed a full recovery of and a full return on the Lansing Generating Station from both its retail and wholesale customers. The IUC’s September 2024 order for IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period includes a return of the remaining net book value of Lansing, but does not include a return on the remaining net book value of Lansing, effective October 1, 2024. As a result, the return on the remaining net book value is no longer recoverable from IPL’s retail electric customers, and a pre-tax non-cash charge of $60 million was recorded to “Asset valuation charge for IPL’s Lansing Generating Station” in Alliant Energy’s and IPL’s income statements in 2024, with a corresponding decrease in Alliant Energy’s and IPL’s assets retired early regulatory assets.

Non-service pension and OPEB costs - Non-service pension and OPEB costs are recorded to regulatory assets to reflect the impacts of rate-making, and are recovered from IPL’s and WPL’s electric and gas customers through depreciation expense based on the depreciation rates for plant in-service.

Derivatives - In accordance with IPL’s and WPL’s fuel and natural gas recovery mechanisms, prudently incurred costs from derivative instruments are recoverable from customers in the future after any losses are realized, and gains from derivative instruments are refundable to customers in the future after any gains are realized. Based on these recovery mechanisms, the changes in the fair value of derivative liabilities/assets resulted in comparable changes to regulatory assets/liabilities on the balance sheets. Refer to Note 14 for discussion of changes in Alliant Energy’s, IPL’s and WPL’s derivative liabilities/assets during 2025, which resulted in comparable changes to regulatory assets/liabilities on the balance sheets.

WPL’s Western Wisconsin gas distribution expansion investments - WPL made contributions in aid of construction to a third party for investments as part of its Western Wisconsin gas distribution expansion project. Pursuant to authorization by the PSCW, Alliant Energy and WPL have recorded a regulatory asset for these costs, and are authorized by the PSCW to recover these amounts from WPL’s retail gas customers in base rates from 2021 through the end of 2040.

Commodity cost recovery - Refer to Note 1(g) for details of IPL’s and WPL’s commodity cost recovery mechanisms. The cost recovery mechanism for WPL’s retail electric customers is based on forecasts of certain fuel-related costs expected to be incurred during forward-looking test periods and fuel monitoring ranges determined by the PSCW during each retail electric rate proceeding or in a separate fuel cost plan approval proceeding. In 2022, WPL’s actual fuel-related costs fell outside these fuel monitoring ranges, resulting in a $117 million deferral as of December 31, 2022, which WPL substantially collected from October 2023 through December 2025 from its retail electric customers, plus interest ($12 million, $50 million and $52 million was collected in 2023, 2024 and 2025, respectively). In 2023, WPL’s actual fuel-related costs fell outside these fuel monitoring ranges, resulting in a $34 million regulatory liability as of December 31, 2023, which was refunded in 2024 to its retail electric customers, plus interest.

Regulatory Liabilities - At December 31, regulatory liabilities were comprised of the following items (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Tax-related$690$582$304$286$386$296
Cost of removal obligations366347217205149142
Derivatives475326292124
Other984639265920
$1,201$1,028$586$546$615$482
Tax-related regulatory liabilities reduce revenue requirement calculations utilized in IPL’s and WPL’s respective rate proceedings. Cost of removal obligations, to the extent expensed through depreciation rates, reduce rate base. A significant portion of the remaining regulatory liabilities is not used to adjust revenue requirement calculations.

Tax-related - Alliant Energy’s, IPL’s and WPL’s tax-related regulatory liabilities are primarily related to excess deferred tax benefits resulting from the remeasurement of accumulated deferred income taxes caused by the Tax Cuts and Jobs Act. The majority of these benefits related to accelerated depreciation are subject to tax normalization rules. These rules limit the rate at which these tax benefits are allowed to be passed on to customers. Additionally, Alliant Energy’s, IPL’s and WPL’s tax-related regulatory liabilities include tax benefits resulting from investment tax credits for IPL’s and WPL’s energy storage facilities and WPL’s Cassville solar facility. Refer to Note 1(c) for details related to the regulatory treatment of IPL’s and WPL’s investment tax credits.

Cost of removal obligations - Alliant Energy, IPL and WPL collect in rates future removal costs for many assets that do not have associated AROs or that have removal costs in addition to AROs. Alliant Energy, IPL and WPL record a regulatory liability for the amounts collected in rates for these future removal costs and reduce the regulatory liability for amounts spent on removal activities. Cash payments related to cost of removal obligations are included in “Other” in cash flows used for investing activities.

Rate Reviews -

WPL’s Retail Electric and Gas Rate Reviews (2024/2025 Forward-looking Test Period) - In December 2023, the PSCW issued an order authorizing annual base rate increases of $49 million and $13 million for WPL’s retail electric and gas customers, respectively, effective January 1, 2024, for the 2024 forward-looking Test Period. The PSCW’s order also authorized WPL to implement an additional $60 million increase in annual rates for its retail electric customers, effective January 1, 2025, for the 2025 forward-looking Test Period. The key drivers for the annual base rate increases include revenue requirement impacts of increasing electric and gas rate base, including investments in solar generation and energy storage. In addition, the PSCW’s order extended, with certain modifications, an earnings sharing mechanism through the end of 2025. The PSCW also authorized WPL to defer the incremental under-/over-collection of solar and energy storage renewable tax credits that are outside of the approved amounts, which are included in the tax-related lines of the regulatory assets and regulatory liabilities tables above. Refer to Note 3 for discussion of PSCW orders approving deferral of, and the deferral of a return on, incremental solar generation construction costs in 2024 and 2025.

WPL’s Retail Electric and Gas Rate Reviews (2026/2027 Forward-looking Test Period) - In December 2025, the PSCW issued an order authorizing annual base rate increases of $69 million and $7 million for WPL’s retail electric and gas customers, respectively, effective January 1, 2026, for the 2026 forward-looking Test Period. The PSCW’s order also authorized WPL to implement an additional $75 million and $5 million increase in annual rates for its retail electric and gas customers, respectively, effective January 1, 2027, for the 2027 forward-looking Test Period.
v3.25.4
Property, Plant and Equipment
 12 Months Ended
Dec. 31, 2025
Property, Plant and Equipment [Line Items]  
Property, Plant and Equipment PROPERTY, PLANT AND EQUIPMENT
At December 31, details of property, plant and equipment on the balance sheets were as follows (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Utility:
Electric plant:
Generation and energy storage in service (a)(b)$12,757 $11,156 $6,251 $5,924 $6,506 $5,232 
Distribution in service8,418 7,811 4,691 4,344 3,727 3,467 
Other in service572 595 369 385 203 210 
Anticipated to be retired early (c)— 784 — — — 784 
Total electric plant21,747 20,346 11,311 10,653 10,436 9,693 
Gas plant in service1,938 1,863 1,020 981 918 882 
Other plant in service752 734 456456 296 278 
Accumulated depreciation (c)(6,690)(6,229)(3,574)(3,360)(3,116)(2,869)
Net plant17,747 16,714 9,213 8,730 8,534 7,984 
Leased Sheboygan Falls Energy Facility, net (d)— — — — 110 74 
Leased land for solar generation, net190 189 52 53 138 136 
Construction work in progress (e)1,742 1,215 1,166 548 576 667 
Other, net10 5 5 5 5 — 
Total utility19,689 18,123 10,436 9,336 9,363 8,861 
Non-utility and other:
Non-utility Generation, net (f)146 103 — — — — 
Corporate Services and other, net (g)509475 — — — — 
Total non-utility and other655 578 — — — — 
Total property, plant and equipment$20,344 $18,701 $10,436 $9,336 $9,363 $8,861 

(a)Construction costs associated with WPL’s approximately 1,100 MW of new solar generation exceeded the construction cost estimates previously approved by the PSCW by approximately $205 million. In 2024, the PSCW issued orders approving deferral of, and the deferral of a return on, the incremental solar generation construction costs in 2024 and 2025. In December 2025, the PSCW issued an order for the 2026/2027 forward-looking Test Period, which includes a full return of and on these solar generation construction costs from WPL’s retail electric customers. As a result, Alliant Energy and WPL concluded that there was not a probable disallowance of the higher rate base amounts as of December 31, 2025.
(b)WPL’s Grant County (100 MW) and Wood County (75 MW) energy storage facilities, and IPL’s Wever (99 MW) energy storage facility, were placed in service in 2025.
(c)WPL previously received approval from MISO to retire the coal-fired Columbia Units 1 and 2. As of December 31, 2024, WPL planned to cease coal operations at Columbia Units 1 and 2 by the end of 2029, and Alliant Energy and WPL concluded that Columbia Units 1 and 2 met the criteria to be considered probable of abandonment. WPL currently plans to continue coal operations at Columbia Units 1 and 2 at least through 2029 as well as evaluate the potential conversion of Columbia Unit 1 and/or Unit 2 to natural gas. As a result, as of December 31, 2025, Alliant Energy and WPL concluded that Columbia Units 1 and 2 no longer meet the criteria to be considered probable of abandonment.
(d)Less accumulated amortization of $120 million and $116 million for WPL as of December 31, 2025 and 2024, respectively. Refer to Note 9 for discussion of WPL’s remeasurement of this lease in 2025. For Alliant Energy, the leased Sheboygan Falls Energy Facility is eliminated upon consolidation and is included in the “Non-utility Generation, net” line within Alliant Energy’s consolidated property, plant and equipment.
(e)Alliant Energy’s and IPL’s CWIP balances were higher as of December 31, 2025, compared to December 31, 2024, primarily due to IPL’s energy storage and natural gas-fired generation projects.
(f)Less accumulated depreciation of $81 million and $78 million for Alliant Energy as of December 31, 2025 and 2024, respectively.
(g)Less accumulated depreciation of $305 million and $289 million for Alliant Energy as of December 31, 2025 and 2024, respectively.
AFUDC - AFUDC represents costs to finance construction additions, including a return on equity component and cost of debt component as required by regulatory accounting. The concurrent credit for the amount of AFUDC capitalized is recorded as “Allowance for funds used during construction” in the income statements. The amount of AFUDC generated by equity and debt components was as follows (in millions):
Alliant EnergyIPLWPL
202520242023202520242023202520242023
Equity$63$54$74$39$31$15$24$23$59
Debt262126171269920
$89$75$100$56$43$21$33$32$79

Non-utility and Other - The non-utility and other property, plant and equipment recorded on Alliant Energy’s balance sheets include the following:

Non-utility Generation - The Sheboygan Falls Energy Facility was placed in service in 2005 and is depreciated using the straight-line method over a 45-year period.

Corporate Services and Other - Property, plant and equipment related to Corporate Services include computer software, and the corporate headquarters building located in Madison, Wisconsin. The majority of the software is amortized over a 5-year period. Other property, plant and equipment include Travero assets (a short-line rail freight service in Iowa; a Mississippi River barge, rail and truck freight terminal in Illinois; and a rail-served warehouse in Iowa). All Corporate Services and Other property, plant and equipment are depreciated using the straight-line method over periods ranging from 5 to 30 years.
IPL [Member]  
Property, Plant and Equipment [Line Items]  
Property, Plant and Equipment PROPERTY, PLANT AND EQUIPMENT
At December 31, details of property, plant and equipment on the balance sheets were as follows (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Utility:
Electric plant:
Generation and energy storage in service (a)(b)$12,757 $11,156 $6,251 $5,924 $6,506 $5,232 
Distribution in service8,418 7,811 4,691 4,344 3,727 3,467 
Other in service572 595 369 385 203 210 
Anticipated to be retired early (c)— 784 — — — 784 
Total electric plant21,747 20,346 11,311 10,653 10,436 9,693 
Gas plant in service1,938 1,863 1,020 981 918 882 
Other plant in service752 734 456456 296 278 
Accumulated depreciation (c)(6,690)(6,229)(3,574)(3,360)(3,116)(2,869)
Net plant17,747 16,714 9,213 8,730 8,534 7,984 
Leased Sheboygan Falls Energy Facility, net (d)— — — — 110 74 
Leased land for solar generation, net190 189 52 53 138 136 
Construction work in progress (e)1,742 1,215 1,166 548 576 667 
Other, net10 5 5 5 5 — 
Total utility19,689 18,123 10,436 9,336 9,363 8,861 
Non-utility and other:
Non-utility Generation, net (f)146 103 — — — — 
Corporate Services and other, net (g)509475 — — — — 
Total non-utility and other655 578 — — — — 
Total property, plant and equipment$20,344 $18,701 $10,436 $9,336 $9,363 $8,861 

(a)Construction costs associated with WPL’s approximately 1,100 MW of new solar generation exceeded the construction cost estimates previously approved by the PSCW by approximately $205 million. In 2024, the PSCW issued orders approving deferral of, and the deferral of a return on, the incremental solar generation construction costs in 2024 and 2025. In December 2025, the PSCW issued an order for the 2026/2027 forward-looking Test Period, which includes a full return of and on these solar generation construction costs from WPL’s retail electric customers. As a result, Alliant Energy and WPL concluded that there was not a probable disallowance of the higher rate base amounts as of December 31, 2025.
(b)WPL’s Grant County (100 MW) and Wood County (75 MW) energy storage facilities, and IPL’s Wever (99 MW) energy storage facility, were placed in service in 2025.
(c)WPL previously received approval from MISO to retire the coal-fired Columbia Units 1 and 2. As of December 31, 2024, WPL planned to cease coal operations at Columbia Units 1 and 2 by the end of 2029, and Alliant Energy and WPL concluded that Columbia Units 1 and 2 met the criteria to be considered probable of abandonment. WPL currently plans to continue coal operations at Columbia Units 1 and 2 at least through 2029 as well as evaluate the potential conversion of Columbia Unit 1 and/or Unit 2 to natural gas. As a result, as of December 31, 2025, Alliant Energy and WPL concluded that Columbia Units 1 and 2 no longer meet the criteria to be considered probable of abandonment.
(d)Less accumulated amortization of $120 million and $116 million for WPL as of December 31, 2025 and 2024, respectively. Refer to Note 9 for discussion of WPL’s remeasurement of this lease in 2025. For Alliant Energy, the leased Sheboygan Falls Energy Facility is eliminated upon consolidation and is included in the “Non-utility Generation, net” line within Alliant Energy’s consolidated property, plant and equipment.
(e)Alliant Energy’s and IPL’s CWIP balances were higher as of December 31, 2025, compared to December 31, 2024, primarily due to IPL’s energy storage and natural gas-fired generation projects.
(f)Less accumulated depreciation of $81 million and $78 million for Alliant Energy as of December 31, 2025 and 2024, respectively.
(g)Less accumulated depreciation of $305 million and $289 million for Alliant Energy as of December 31, 2025 and 2024, respectively.
AFUDC - AFUDC represents costs to finance construction additions, including a return on equity component and cost of debt component as required by regulatory accounting. The concurrent credit for the amount of AFUDC capitalized is recorded as “Allowance for funds used during construction” in the income statements. The amount of AFUDC generated by equity and debt components was as follows (in millions):
Alliant EnergyIPLWPL
202520242023202520242023202520242023
Equity$63$54$74$39$31$15$24$23$59
Debt262126171269920
$89$75$100$56$43$21$33$32$79
WPL [Member]  
Property, Plant and Equipment [Line Items]  
Property, Plant and Equipment PROPERTY, PLANT AND EQUIPMENT
At December 31, details of property, plant and equipment on the balance sheets were as follows (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Utility:
Electric plant:
Generation and energy storage in service (a)(b)$12,757 $11,156 $6,251 $5,924 $6,506 $5,232 
Distribution in service8,418 7,811 4,691 4,344 3,727 3,467 
Other in service572 595 369 385 203 210 
Anticipated to be retired early (c)— 784 — — — 784 
Total electric plant21,747 20,346 11,311 10,653 10,436 9,693 
Gas plant in service1,938 1,863 1,020 981 918 882 
Other plant in service752 734 456456 296 278 
Accumulated depreciation (c)(6,690)(6,229)(3,574)(3,360)(3,116)(2,869)
Net plant17,747 16,714 9,213 8,730 8,534 7,984 
Leased Sheboygan Falls Energy Facility, net (d)— — — — 110 74 
Leased land for solar generation, net190 189 52 53 138 136 
Construction work in progress (e)1,742 1,215 1,166 548 576 667 
Other, net10 5 5 5 5 — 
Total utility19,689 18,123 10,436 9,336 9,363 8,861 
Non-utility and other:
Non-utility Generation, net (f)146 103 — — — — 
Corporate Services and other, net (g)509475 — — — — 
Total non-utility and other655 578 — — — — 
Total property, plant and equipment$20,344 $18,701 $10,436 $9,336 $9,363 $8,861 

(a)Construction costs associated with WPL’s approximately 1,100 MW of new solar generation exceeded the construction cost estimates previously approved by the PSCW by approximately $205 million. In 2024, the PSCW issued orders approving deferral of, and the deferral of a return on, the incremental solar generation construction costs in 2024 and 2025. In December 2025, the PSCW issued an order for the 2026/2027 forward-looking Test Period, which includes a full return of and on these solar generation construction costs from WPL’s retail electric customers. As a result, Alliant Energy and WPL concluded that there was not a probable disallowance of the higher rate base amounts as of December 31, 2025.
(b)WPL’s Grant County (100 MW) and Wood County (75 MW) energy storage facilities, and IPL’s Wever (99 MW) energy storage facility, were placed in service in 2025.
(c)WPL previously received approval from MISO to retire the coal-fired Columbia Units 1 and 2. As of December 31, 2024, WPL planned to cease coal operations at Columbia Units 1 and 2 by the end of 2029, and Alliant Energy and WPL concluded that Columbia Units 1 and 2 met the criteria to be considered probable of abandonment. WPL currently plans to continue coal operations at Columbia Units 1 and 2 at least through 2029 as well as evaluate the potential conversion of Columbia Unit 1 and/or Unit 2 to natural gas. As a result, as of December 31, 2025, Alliant Energy and WPL concluded that Columbia Units 1 and 2 no longer meet the criteria to be considered probable of abandonment.
(d)Less accumulated amortization of $120 million and $116 million for WPL as of December 31, 2025 and 2024, respectively. Refer to Note 9 for discussion of WPL’s remeasurement of this lease in 2025. For Alliant Energy, the leased Sheboygan Falls Energy Facility is eliminated upon consolidation and is included in the “Non-utility Generation, net” line within Alliant Energy’s consolidated property, plant and equipment.
(e)Alliant Energy’s and IPL’s CWIP balances were higher as of December 31, 2025, compared to December 31, 2024, primarily due to IPL’s energy storage and natural gas-fired generation projects.
(f)Less accumulated depreciation of $81 million and $78 million for Alliant Energy as of December 31, 2025 and 2024, respectively.
(g)Less accumulated depreciation of $305 million and $289 million for Alliant Energy as of December 31, 2025 and 2024, respectively.
AFUDC - AFUDC represents costs to finance construction additions, including a return on equity component and cost of debt component as required by regulatory accounting. The concurrent credit for the amount of AFUDC capitalized is recorded as “Allowance for funds used during construction” in the income statements. The amount of AFUDC generated by equity and debt components was as follows (in millions):
Alliant EnergyIPLWPL
202520242023202520242023202520242023
Equity$63$54$74$39$31$15$24$23$59
Debt262126171269920
$89$75$100$56$43$21$33$32$79
v3.25.4
Jointly-Owned Electric Utility Plant
 12 Months Ended
Dec. 31, 2025
Jointly Owned Electric Utility Plant [Line Items]  
Jointly-Owned Electric Utility Plant JOINTLY-OWNED ELECTRIC UTILITY PLANT
Under joint ownership agreements with other utilities, IPL and WPL have undivided ownership interests in jointly-owned EGUs. Each of the respective owners is responsible for the financing of its portion of the construction costs. IPL’s and WPL’s shares of expenses from jointly-owned EGUs are included in the corresponding operating expenses (e.g., electric production fuel, other operation and maintenance, etc.) in the income statements. Information relative to IPL’s and WPL’s ownership interest in these jointly-owned EGUs at December 31, 2025 was as follows (dollars in millions):
OwnershipElectricAccumulated ProvisionConstruction
Interest %Plantfor DepreciationWork in Progress
IPL
Ottumwa Unit 148.0%$662$302$7
George Neal Unit 425.7%2011134
George Neal Unit 328.0%192894
Louisa Unit 14.0%44241
1,09952816
WPL
Columbia Units 1-2 and Energy Storage System53.5%8684074
West Riverside Energy Center and Solar Facility56.6%456717
Forward Wind Energy Center42.6%11858—
1,44253611
Alliant Energy$2,541$1,064$27
IPL [Member]  
Jointly Owned Electric Utility Plant [Line Items]  
Jointly-Owned Electric Utility Plant JOINTLY-OWNED ELECTRIC UTILITY PLANT
Under joint ownership agreements with other utilities, IPL and WPL have undivided ownership interests in jointly-owned EGUs. Each of the respective owners is responsible for the financing of its portion of the construction costs. IPL’s and WPL’s shares of expenses from jointly-owned EGUs are included in the corresponding operating expenses (e.g., electric production fuel, other operation and maintenance, etc.) in the income statements. Information relative to IPL’s and WPL’s ownership interest in these jointly-owned EGUs at December 31, 2025 was as follows (dollars in millions):
OwnershipElectricAccumulated ProvisionConstruction
Interest %Plantfor DepreciationWork in Progress
IPL
Ottumwa Unit 148.0%$662$302$7
George Neal Unit 425.7%2011134
George Neal Unit 328.0%192894
Louisa Unit 14.0%44241
1,09952816
WPL
Columbia Units 1-2 and Energy Storage System53.5%8684074
West Riverside Energy Center and Solar Facility56.6%456717
Forward Wind Energy Center42.6%11858—
1,44253611
Alliant Energy$2,541$1,064$27
WPL [Member]  
Jointly Owned Electric Utility Plant [Line Items]  
Jointly-Owned Electric Utility Plant JOINTLY-OWNED ELECTRIC UTILITY PLANT
Under joint ownership agreements with other utilities, IPL and WPL have undivided ownership interests in jointly-owned EGUs. Each of the respective owners is responsible for the financing of its portion of the construction costs. IPL’s and WPL’s shares of expenses from jointly-owned EGUs are included in the corresponding operating expenses (e.g., electric production fuel, other operation and maintenance, etc.) in the income statements. Information relative to IPL’s and WPL’s ownership interest in these jointly-owned EGUs at December 31, 2025 was as follows (dollars in millions):
OwnershipElectricAccumulated ProvisionConstruction
Interest %Plantfor DepreciationWork in Progress
IPL
Ottumwa Unit 148.0%$662$302$7
George Neal Unit 425.7%2011134
George Neal Unit 328.0%192894
Louisa Unit 14.0%44241
1,09952816
WPL
Columbia Units 1-2 and Energy Storage System53.5%8684074
West Riverside Energy Center and Solar Facility56.6%456717
Forward Wind Energy Center42.6%11858—
1,44253611
Alliant Energy$2,541$1,064$27
v3.25.4
Receivables
 12 Months Ended
Dec. 31, 2025
Receivables [Line Items]  
Receivables RECEIVABLES(a) Accounts Receivable - Details for accounts receivable included on the balance sheets as of December 31 were as follows (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Customer$139 $113 $— $— $126 $98 
Unbilled utility revenues117 101 — — 117 101 
Deferred proceeds126 163 126 163 — — 
Other104 58 59 29 39 29 
Allowance for expected credit losses(10)(8)— — (9)(8)
$476 $427 $185 $192 $273 $220 
In 2025, gross write-offs for accounts receivable were as follows (in millions):
Originated in 2023
Originated in 2024
Originated in 2025
Alliant Energy$1$12$16
IPL189
WPL—47
(b) Sales of Accounts Receivable - IPL maintains a Receivables Agreement whereby it may sell its customer accounts receivables, unbilled revenues and certain other accounts receivables to a third party through wholly-owned and consolidated special purpose entities. In March 2024, IPL amended and extended through March 2026 the purchase commitment from the third party to which it sells its receivables. IPL pays a monthly fee to the third party that varies based on interest rates, limits on cash proceeds and cash amounts received from the third party. Deferred proceeds represent IPL’s interest in the receivables sold to the third party. At IPL’s request, deferred proceeds are paid to IPL from collections of receivables, after paying any required expenses incurred by the third party and the collection agent. Corporate Services acts as collection agent for the third party and receives a fee for collection services. The Receivables Agreement can be terminated by the third party if arrears or write-offs exceed certain levels. The transfers of receivables meet the criteria for sale accounting established by the transfer of financial assets accounting rules. IPL believes that the allowance for expected credit losses related to its sales of receivables is a reasonable approximation of credit risk of the customers that generated the receivables. Refer to Note 15 for discussion of the fair value of deferred proceeds.
Under the Receivables Agreement, IPL has the right to receive cash proceeds, up to a certain limit, from the third party in exchange for the receivables sold. The limit on cash proceeds fluctuates between $5 million and $110 million, which IPL may change periodically throughout the year. As of December 31, 2025, the limit on cash proceeds was $110 million and IPL had no available capacity under its sales of accounts receivable program. Cash proceeds are used by IPL to meet short-term financing needs, and cannot exceed the current limit or amount of receivables available for sale, whichever is less. IPL’s maximum and average outstanding aggregate cash proceeds (based on daily outstanding balances) related to the sales of accounts receivable program were as follows (in millions):
MaximumAverage
202520242023202520242023
Outstanding aggregate cash proceeds$110$110$110$57$31$51

As of December 31, the attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions):
20252024
Customer accounts receivable$147$137
Unbilled utility revenues104108
Receivables sold to third party251245
Less: cash proceeds11070
Deferred proceeds141175
Less: allowance for expected credit losses1512
Fair value of deferred proceeds$126$163
Outstanding receivables past due$21$21

Additional attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions):
202520242023
Collections$2,279$2,090$2,233 
Write-offs, net of recoveries121212 
IPL [Member]  
Receivables [Line Items]  
Receivables RECEIVABLES(a) Accounts Receivable - Details for accounts receivable included on the balance sheets as of December 31 were as follows (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Customer$139 $113 $— $— $126 $98 
Unbilled utility revenues117 101 — — 117 101 
Deferred proceeds126 163 126 163 — — 
Other104 58 59 29 39 29 
Allowance for expected credit losses(10)(8)— — (9)(8)
$476 $427 $185 $192 $273 $220 
In 2025, gross write-offs for accounts receivable were as follows (in millions):
Originated in 2023
Originated in 2024
Originated in 2025
Alliant Energy$1$12$16
IPL189
WPL—47
(b) Sales of Accounts Receivable - IPL maintains a Receivables Agreement whereby it may sell its customer accounts receivables, unbilled revenues and certain other accounts receivables to a third party through wholly-owned and consolidated special purpose entities. In March 2024, IPL amended and extended through March 2026 the purchase commitment from the third party to which it sells its receivables. IPL pays a monthly fee to the third party that varies based on interest rates, limits on cash proceeds and cash amounts received from the third party. Deferred proceeds represent IPL’s interest in the receivables sold to the third party. At IPL’s request, deferred proceeds are paid to IPL from collections of receivables, after paying any required expenses incurred by the third party and the collection agent. Corporate Services acts as collection agent for the third party and receives a fee for collection services. The Receivables Agreement can be terminated by the third party if arrears or write-offs exceed certain levels. The transfers of receivables meet the criteria for sale accounting established by the transfer of financial assets accounting rules. IPL believes that the allowance for expected credit losses related to its sales of receivables is a reasonable approximation of credit risk of the customers that generated the receivables. Refer to Note 15 for discussion of the fair value of deferred proceeds.
Under the Receivables Agreement, IPL has the right to receive cash proceeds, up to a certain limit, from the third party in exchange for the receivables sold. The limit on cash proceeds fluctuates between $5 million and $110 million, which IPL may change periodically throughout the year. As of December 31, 2025, the limit on cash proceeds was $110 million and IPL had no available capacity under its sales of accounts receivable program. Cash proceeds are used by IPL to meet short-term financing needs, and cannot exceed the current limit or amount of receivables available for sale, whichever is less. IPL’s maximum and average outstanding aggregate cash proceeds (based on daily outstanding balances) related to the sales of accounts receivable program were as follows (in millions):
MaximumAverage
202520242023202520242023
Outstanding aggregate cash proceeds$110$110$110$57$31$51

As of December 31, the attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions):
20252024
Customer accounts receivable$147$137
Unbilled utility revenues104108
Receivables sold to third party251245
Less: cash proceeds11070
Deferred proceeds141175
Less: allowance for expected credit losses1512
Fair value of deferred proceeds$126$163
Outstanding receivables past due$21$21

Additional attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions):
202520242023
Collections$2,279$2,090$2,233 
Write-offs, net of recoveries121212 
WPL [Member]  
Receivables [Line Items]  
Receivables RECEIVABLES(a) Accounts Receivable - Details for accounts receivable included on the balance sheets as of December 31 were as follows (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Customer$139 $113 $— $— $126 $98 
Unbilled utility revenues117 101 — — 117 101 
Deferred proceeds126 163 126 163 — — 
Other104 58 59 29 39 29 
Allowance for expected credit losses(10)(8)— — (9)(8)
$476 $427 $185 $192 $273 $220 
In 2025, gross write-offs for accounts receivable were as follows (in millions):
Originated in 2023
Originated in 2024
Originated in 2025
Alliant Energy$1$12$16
IPL189
WPL—47
v3.25.4
Investments
 12 Months Ended
Dec. 31, 2025
Schedule of Equity Method Investments [Line Items]  
Investments INVESTMENTS
Unconsolidated Equity Investments - Alliant Energy’s unconsolidated investments accounted for under the equity method of accounting are as follows (in millions):
Ownership Interest atCarrying Value at December 31,Equity (Income) / Loss
December 31, 202520252024202520242023
ATC Holdings
16%, 20%
$463$415($59)($57)($49)
Non-utility wind farm in Oklahoma50%112107(9)(6)(7)
Corporate venture investmentsVarious7678103(2)
OtherVarious2323(2)(1)(3)
$674$623($60)($61)($61)
Summary aggregate financial information from the financial statements of these holdings is as follows (in millions):
Alliant Energy
202520242023
Revenues$1,080$1,005$898
Operating income482433384
Net income91434370
As of December 31:
Current assets254223
Non-current assets10,8189,930
Current liabilities879524
Non-current liabilities4,2433,933
Noncontrolling interest184221

ATC Holdings - As of December 31, 2025, Alliant Energy has a 16% ownership interest in ATC and a 20% ownership interest in ATC Holdco LLC, collectively referred to as ATC Holdings. ATC is an independent, for-profit, transmission-only company. ATC Holdco LLC holds an interest in Duke-American Transmission Company, LLC, which holds a note receivable related to previously owned electric transmission infrastructure in North America.

Non-utility Wind Farm in Oklahoma - The non-utility wind farm located in Oklahoma provides electricity to a third-party under a long-term PPA, and has both cash and tax equity ownership. Alliant Energy does not maintain or operate the wind farm, and provided a parent guarantee of its subsidiary’s indemnification obligations under the operating agreement and PPA. Refer to Note 16(d) for discussion of the guarantee.

Corporate Venture Investments - Alliant Energy has various minority ownership interests in regional and national venture funds, including a global coalition of energy companies working together to help identify and research innovative technologies and business models within the emerging energy economy.
v3.25.4
Common Equity
 12 Months Ended
Dec. 31, 2025
Schedule of Common Equity [Line Items]  
Common Equity COMMON EQUITY
Common Share Activity - A summary of Alliant Energy’s common stock activity was as follows:
202520242023
Shares outstanding, January 1256,690,222 256,096,848 251,134,966 
At-the-market offering program— — 4,372,561 
Shareowner Direct Plan360,662 439,107 454,987 
Equity-based compensation plans86,377 154,267 134,334 
Shares outstanding, December 31257,137,261 256,690,222 256,096,848 

At December 31, 2025, Alliant Energy had a total of 11 million shares available for issuance in the aggregate, pursuant to its 2020 OIP, Shareowner Direct Plan and 401(k) Savings Plan.

At-the-Market Offering Program - In December 2022, Alliant Energy filed a prospectus supplement to sell up to $225 million of its common stock through an at-the-market offering program. In 2023, Alliant Energy issued 4,372,561 shares of common stock through this program and received cash proceeds of $223 million, net of $2 million in commissions and fees. The proceeds from the issuances of common stock were used for general corporate purposes. This at-the-market offering program has expired.

In May 2025, Alliant Energy filed a prospectus supplement and executed a related distribution agreement, under which it may sell up to $1.3 billion in aggregate of its common stock through 2028 through an at-the-market offering program that includes an equity forward sales component. Alliant Energy expects to use proceeds from the issuance of common stock for general corporate purposes.
Alliant Energy entered into forward sale agreements under its at-the-market offering program with various counterparties who, for the quarter and year ended December 31, 2025, borrowed and sold an aggregate of 3,831,429 and 14,595,532 shares of Alliant Energy common stock at an aggregate gross sales price of $258 million and $944 million, including approximately $2 million and $7 million in commissions, respectively, to the counterparties payable by Alliant Energy when the forward sale agreements are settled. Alliant Energy has not yet received any proceeds from this program and no amounts have been or will be recorded in equity on Alliant Energy’s balance sheets until the forward sale agreements settle. Alliant Energy currently expects to settle the forward sale agreements in 2026 and 2027 through physical delivery of shares of common stock in exchange for cash proceeds at the then-applicable forward sale price; however, Alliant Energy may elect cash settlement or net share settlement for all or a portion of the obligations under the forward sale agreements. As of December 31, 2025, the weighted-average forward price, net of commissions, was $64.44 per share and is subject to daily adjustment based on a floating interest rate factor and decreased by other fixed amounts specified in the forward sale agreements. As of December 31, 2025, Alliant Energy could have settled all of its outstanding forward sale agreements under the at-the-market offering program with physical delivery of 14,595,532 shares of Alliant Energy common stock to the counterparties in exchange for cash of $941 million.

Alliant Energy has concluded that the forward sale agreements meet the derivative scope exception for certain contracts involving an entity’s own equity. Until settlement of the forward sale agreements, Alliant Energy’s EPS dilution resulting from the agreements, if any, is determined using the treasury stock method. Share dilution occurs when the average market price of Alliant Energy stock during the reporting period is higher than the forward sale price as of the end of the reporting period. As of December 31, 2025, 569,944 incremental shares were included in the calculation of diluted EPS related to the securities under the forward sale agreements.

Shareowner Direct Plan - Alliant Energy satisfies its requirements under the Shareowner Direct Plan (dividend reinvestment and stock purchase plan) by acquiring Alliant Energy common stock through original issue, rather than on the open market.
v3.25.4
Debt
 12 Months Ended
Dec. 31, 2025
Debt Instrument [Line Items]  
Debt DEBT(a) Short-term Debt - Alliant Energy and its subsidiaries maintain committed bank lines of credit to provide short-term borrowing flexibility and back-stop liquidity for commercial paper outstanding. At December 31, 2025, the short-term borrowing capacity under a single credit facility agreement, which expires in December 2030, totaled $1.3 billion ($550 million for Alliant Energy at the parent company level, $350 million for IPL and $400 million for WPL). Subject to certain conditions, Alliant Energy (at the parent company level), IPL and WPL may each reallocate and change its sublimit up to $1 billion, $400 million and $500 million, respectively, within the $1.3 billion total commitment. Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper and borrowings under the single credit facility classified as short-term debt was as follows (dollars in millions):
Alliant EnergyIPLWPL
December 31202520242025202420252024
Amount outstanding$88$558$88$50$—$183
Weighted average interest rates3.8%4.5%3.8%4.6%N/A4.5%
Available credit facility capacity$1,212$742$262$250$400$217
Alliant EnergyIPLWPL
For the year ended202520242025202420252024
Maximum amount outstanding (based on daily outstanding balances)$741$632$141$80$297$390
Average amount outstanding (based on daily outstanding balances)$349$327$25$1$176$70
Weighted average interest rates4.5%5.3%4.6%5.1%4.5%5.4%
(b) Long-Term Debt - Long-term debt, net as of December 31 was as follows (dollars in millions):
20252024
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Senior Debentures (a):
4.1%, due 2028
$500 $500 $— $500 $500 $— 
3.6%, due 2029
300 300 — 300 300 — 
2.3%, due 2030
400 400 — 400 400 — 
5.7%, due 2033
300 300 — 300 300 — 
6.45%, due 2033
100 100 — 100 100 — 
4.95%, due 2034
350 350 — 350 350 — 
6.3%, due 2034
125 125 — 125 125 — 
5.6%, due 2035 (b)
600 600 — — — — 
6.25%, due 2039
300 300 — 300 300 — 
4.7%, due 2043
250 250 — 250 250 — 
3.7%, due 2046
300 300 — 300 300 — 
3.5%, due 2049
300 300 — 300 300 — 
3.1%, due 2051
300 300 — 300 300 — 
5.45%, due 2054
300 300 — 300 300 — 
5.6%, due 2055 (b)
300 300 — — — — 
3.4%, (Retired in 2025)
— — — 250 250 — 
5.5%, (Retired in 2025)
— — — 50 50 — 
4,725 4,725 — 4,125 4,125 — 
Debentures (a):
3.05%, due 2027
300 — 300 300 — 300 
3%, due 2029
350 — 350 350 — 350 
1.95%, due 2031
300 — 300 300 — 300 
3.95%, due 2032
600 — 600 600 — 600 
4.95%, due 2033
300 — 300 300 — 300 
5.375%, due 2034
300 — 300 300 — 300 
6.25%, due 2034
100 — 100 100 — 100 
6.375%, due 2037
300 — 300 300 — 300 
7.6%, due 2038
250 — 250 250 — 250 
4.1%, due 2044
250 — 250 250 — 250 
3.65%, due 2050
350 — 350 350 — 350 
5.7%, due 2055 (c)
300 — 300 — — — 
3,700 — 3,700 3,400 — 3,400 
Other:
AEF term loan credit agreement through March 2026, 5% at December 31, 2025 (with Alliant Energy as guarantor) (d)
300 — — — — — 
AEF 1.4% senior notes, due 2026 (with Alliant Energy as guarantor) (a)
200 — — 200 — — 
Alliant Energy 3.875% convertible senior notes, due 2026 (e)
575 — — 575 — — 
AEF 5.4% senior notes, due 2027 (with Alliant Energy as guarantor) (a)
375 — — 375 — — 
Alliant Energy 3.25% convertible senior notes, due 2028 (e)
575 — — — — — 
AEF 4.25% senior notes, due 2028 (with Alliant Energy as guarantor) (a)
300 — — 300 — — 
AEF 5.95% senior notes, due 2029 (with Alliant Energy as guarantor) (a)
300 — — 300 — — 
AEF 3.6% senior notes, due 2032 (with Alliant Energy as guarantor) (a)
350 — — 350 — — 
Alliant Energy 5.75% junior subordinated notes, due 2056 (f)
725 — — — — — 
AEF term loan credit agreement, 6% at December 31, 2024 (with Alliant Energy as guarantor) (Retired in 2025) (d)
— — — 300 — — 
3,700 — — 2,400 — — 
Subtotal12,125 4,725 3,700 9,925 4,125 3,400 
Current maturities(1,074)— — (1,171)(300)— 
Unamortized debt issuance costs(70)(30)(21)(55)(25)(20)
Unamortized debt (discount) and premium, net(27)(15)(10)(22)(10)(10)
Long-term debt, net (g)$10,954 $4,680 $3,669 $8,677 $3,790 $3,370 
(a)Contains optional redemption provisions which, if elected by the issuer at its sole discretion, could require material redemption premium payments by the issuer. The redemption premium payments under these optional redemption provisions are variable and dependent on applicable U.S. Treasury rates at the time of redemption.
(b)In May 2025, IPL issued $600 million of 5.6% senior debentures due 2035. A portion of the net proceeds was used for the retirement of IPL’s $50 million 5.5% senior debentures and $250 million 3.4% senior debentures. The remainder of the proceeds were used to reduce cash amounts received from its sale of accounts receivable program and commercial paper classified as long-term debt, and for general corporate purposes. In September 2025, IPL issued $300 million of 5.6% senior debentures due 2055. The net proceeds were used to reduce cash amounts received from its sale of accounts receivable program, to reduce outstanding commercial paper, and for general corporate purposes.
(c)In December 2025, WPL issued $300 million of 5.7% debentures due 2055. The net proceeds were used to reduce outstanding commercial paper and for general corporate purposes.
(d)In March 2025, AEF entered into a $300 million variable rate term loan credit agreement, which amended and restated the term loan credit agreement that expired in March 2025, and retired the $300 million variable rate term loan set forth therein, which was classified as a non-cash financing activity. AEF’s restated agreement includes an option to increase the amount outstanding with one or more additional term loans in an aggregate amount not to exceed $100 million. Refer to Note 14 for information on AEF’s related interest rate swap. In January 2026, AEF retired its $300 million term loan.
(e)Refer to “Convertible Senior Notes” below for additional information.
(f)In September 2025, Alliant Energy issued $725 million of junior subordinated notes due 2056. The interest rate will reset every 5 years beginning April 1, 2031, to equal the then-current five-year U.S. Treasury rate plus a spread of 2.077%, provided the interest rate will not reset below 5.75%. The net proceeds were used to reduce outstanding commercial paper, retire long term debt and for general corporate purposes. Long term debt to be retired includes AEF’s $300 million variable rate term loan which was retired in January 2026, AEF’s $200 million of 1.4% senior notes and Alliant Energy’s $575 million of 3.875% convertible senior notes, each of which matures in March 2026 and is expected to be retired at or prior to maturity. Alliant Energy has the option to redeem the notes prior to maturity upon the occurrence of certain events and during specified periods, at redemption prices specified in the governing agreements.
(g)There were no significant sinking fund requirements related to the outstanding long-term debt.

Convertible Senior Notes
2026 Notes - In March 2023, Alliant Energy issued $575 million of 3.875% convertible senior notes (the 2026 Notes), which are senior unsecured obligations, and used the net proceeds from the issuance for general corporate purposes. The 2026 Notes will mature on March 15, 2026 unless earlier converted or repurchased. Alliant Energy may not redeem the 2026 Notes prior to the maturity date. Holders could have converted their 2026 Notes at their option at any time prior to the close of business on the business day immediately preceding December 15, 2025 only under the following circumstances:

•during any calendar quarter commencing after the calendar quarter ending on June 30, 2023 (and only during such calendar quarter), if the last reported sale price of Alliant Energy’s common stock for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter is greater than or equal to 130% of the conversion price on each applicable trading day during such period;
•during the 5 business day period after any 10 consecutive trading day period (the “measurement period”) in which the trading price (as defined in the related Indenture) per $1,000 principal amount of 2026 Notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price of Alliant Energy’s common stock and the conversion rate on each such trading day; or
•upon the occurrence of specified corporate events.

On or after December 15, 2025 until the close of business on the business day immediately preceding the maturity date, holders may convert all or any portion of their 2026 Notes at any time, regardless of the foregoing circumstances. Upon conversion of the 2026 Notes, Alliant Energy will pay cash up to the aggregate principal amount of the 2026 Notes to be converted and deliver shares of its common stock, in respect of the remainder, if any, of its conversion obligation in excess of the aggregate principal amount of the 2026 Notes being converted.

The initial conversion rate is 15.5461 shares of common stock per $1,000 principal amount of 2026 Notes (equivalent to an initial conversion price of approximately $64.32 per share of Alliant Energy’s common stock). The conversion rate is subject to adjustment in some events but will not be adjusted for any accrued and unpaid interest. In addition, following certain corporate events that occur prior to the maturity date, Alliant Energy will, in certain circumstances, increase the conversion rate for a holder who elects to convert its 2026 Notes in connection with such a corporate event.

If Alliant Energy undergoes a fundamental change (as defined in the related Indenture), then, subject to certain conditions, holders of the 2026 Notes may require Alliant Energy to repurchase for cash all or any portion of its 2026 Notes at a fundamental change repurchase price equal to 100% of the principal amount of the 2026 Notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date.
As of December 31, 2025 and 2024, the 2026 Notes were classified on Alliant Energy’s balance sheets as “Current maturities of long-term debt”. As of December 31, 2025 and 2024, the net carrying amount of the 2026 Notes was $574 million and $571 million, with unamortized debt issuance costs of $1 million and $4 million, and the estimated fair value (Level 2) of the 2026 Notes was $599 million and $591 million. As of December 31, 2025, there were 407,821 shares of Alliant Energy’s common stock related to the potential conversion of the 2026 Notes included in diluted EPS based on Alliant Energy’s average stock prices and the relevant terms of the 2026 Notes.

2028 Notes - In May 2025, Alliant Energy issued $575 million of 3.25% convertible senior notes (the 2028 Notes), which are senior unsecured obligations, and used the net proceeds from the issuance to reduce Alliant Energy’s outstanding commercial paper and for general corporate purposes. The 2028 Notes will mature on May 30, 2028 unless earlier converted or repurchased, and no sinking fund is provided for the 2028 Notes. Alliant Energy may not redeem the 2028 Notes prior to the maturity date. Holders may convert their 2028 Notes at their option at any time prior to the close of business on the business day immediately preceding March 1, 2028 only under the following circumstances:

•during any calendar quarter commencing after the calendar quarter ending on September 30, 2025 (and only during such calendar quarter), if the last reported sale price of Alliant Energy’s common stock for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter is greater than or equal to 130% of the conversion price on each applicable trading day during such period;
•during the 5 business day period after any 10 consecutive trading day period (the “measurement period”) in which the trading price (as defined in the related Indenture) per $1,000 principal amount of 2028 Notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price of Alliant Energy’s common stock and the conversion rate on each such trading day; or
•upon the occurrence of specified corporate events.

On or after March 1, 2028 until the close of business on the business day immediately preceding the maturity date, holders may convert all or any portion of their 2028 Notes at any time, regardless of the foregoing circumstances. Upon conversion of the 2028 Notes, Alliant Energy will pay cash up to the aggregate principal amount of the 2028 Notes to be converted and pay or deliver, as the case may be, cash, shares of its common stock or a combination of cash and shares of its common stock, at its election, in respect of the remainder, if any, of its conversion obligation in excess of the aggregate principal amount of the 2028 Notes being converted.

The initial conversion rate is 13.1773 shares of common stock per $1,000 principal amount of 2028 Notes (equivalent to an initial conversion price of approximately $75.89 per share of Alliant Energy’s common stock). The conversion rate is subject to adjustment in some events but will not be adjusted for any accrued and unpaid interest. In addition, following certain corporate events that occur prior to the maturity date, Alliant Energy will, in certain circumstances, increase the conversion rate for a holder who elects to convert its 2028 Notes in connection with such a corporate event.

If Alliant Energy undergoes a fundamental change (as defined in the related Indenture), then, subject to certain conditions, holders of the 2028 Notes may require Alliant Energy to repurchase for cash all or any portion of its 2028 Notes at a fundamental change repurchase price equal to 100% of the principal amount of the 2028 Notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date.

As of December 31, 2025, the conditions allowing holders of the 2028 Notes to convert their 2028 Notes were not met, and the 2028 Notes were classified as “Long-term debt, net” on Alliant Energy’s balance sheet. As of December 31, 2025, the net carrying amount was $569 million, with unamortized debt issuance costs of $6 million, and the estimated fair value (Level 2) was $587 million for the 2028 Notes. As of December 31, 2025, there were no shares of Alliant Energy’s common stock related to the potential conversion of the 2028 Notes included in diluted EPS based on Alliant Energy’s average stock prices and the relevant terms of the 2028 Notes.

Five-Year Schedule of Long-term Debt Maturities - At December 31, 2025, long-term debt maturities for 2026 through 2030 were as follows (in millions):
20262027202820292030
IPL$—$—$500$300$400
WPL—300—350—
AEF500375300300—
Alliant Energy parent company575—575——
Alliant Energy$1,075$675$1,375$950$400

Fair Value of Long-term Debt - Refer to Note 15 for information on the fair value of long-term debt outstanding.
IPL [Member]  
Debt Instrument [Line Items]  
Debt DEBT(a) Short-term Debt - Alliant Energy and its subsidiaries maintain committed bank lines of credit to provide short-term borrowing flexibility and back-stop liquidity for commercial paper outstanding. At December 31, 2025, the short-term borrowing capacity under a single credit facility agreement, which expires in December 2030, totaled $1.3 billion ($550 million for Alliant Energy at the parent company level, $350 million for IPL and $400 million for WPL). Subject to certain conditions, Alliant Energy (at the parent company level), IPL and WPL may each reallocate and change its sublimit up to $1 billion, $400 million and $500 million, respectively, within the $1.3 billion total commitment. Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper and borrowings under the single credit facility classified as short-term debt was as follows (dollars in millions):
Alliant EnergyIPLWPL
December 31202520242025202420252024
Amount outstanding$88$558$88$50$—$183
Weighted average interest rates3.8%4.5%3.8%4.6%N/A4.5%
Available credit facility capacity$1,212$742$262$250$400$217
Alliant EnergyIPLWPL
For the year ended202520242025202420252024
Maximum amount outstanding (based on daily outstanding balances)$741$632$141$80$297$390
Average amount outstanding (based on daily outstanding balances)$349$327$25$1$176$70
Weighted average interest rates4.5%5.3%4.6%5.1%4.5%5.4%
(b) Long-Term Debt - Long-term debt, net as of December 31 was as follows (dollars in millions):
20252024
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Senior Debentures (a):
4.1%, due 2028
$500 $500 $— $500 $500 $— 
3.6%, due 2029
300 300 — 300 300 — 
2.3%, due 2030
400 400 — 400 400 — 
5.7%, due 2033
300 300 — 300 300 — 
6.45%, due 2033
100 100 — 100 100 — 
4.95%, due 2034
350 350 — 350 350 — 
6.3%, due 2034
125 125 — 125 125 — 
5.6%, due 2035 (b)
600 600 — — — — 
6.25%, due 2039
300 300 — 300 300 — 
4.7%, due 2043
250 250 — 250 250 — 
3.7%, due 2046
300 300 — 300 300 — 
3.5%, due 2049
300 300 — 300 300 — 
3.1%, due 2051
300 300 — 300 300 — 
5.45%, due 2054
300 300 — 300 300 — 
5.6%, due 2055 (b)
300 300 — — — — 
3.4%, (Retired in 2025)
— — — 250 250 — 
5.5%, (Retired in 2025)
— — — 50 50 — 
4,725 4,725 — 4,125 4,125 — 
Debentures (a):
3.05%, due 2027
300 — 300 300 — 300 
3%, due 2029
350 — 350 350 — 350 
1.95%, due 2031
300 — 300 300 — 300 
3.95%, due 2032
600 — 600 600 — 600 
4.95%, due 2033
300 — 300 300 — 300 
5.375%, due 2034
300 — 300 300 — 300 
6.25%, due 2034
100 — 100 100 — 100 
6.375%, due 2037
300 — 300 300 — 300 
7.6%, due 2038
250 — 250 250 — 250 
4.1%, due 2044
250 — 250 250 — 250 
3.65%, due 2050
350 — 350 350 — 350 
5.7%, due 2055 (c)
300 — 300 — — — 
3,700 — 3,700 3,400 — 3,400 
Other:
AEF term loan credit agreement through March 2026, 5% at December 31, 2025 (with Alliant Energy as guarantor) (d)
300 — — — — — 
AEF 1.4% senior notes, due 2026 (with Alliant Energy as guarantor) (a)
200 — — 200 — — 
Alliant Energy 3.875% convertible senior notes, due 2026 (e)
575 — — 575 — — 
AEF 5.4% senior notes, due 2027 (with Alliant Energy as guarantor) (a)
375 — — 375 — — 
Alliant Energy 3.25% convertible senior notes, due 2028 (e)
575 — — — — — 
AEF 4.25% senior notes, due 2028 (with Alliant Energy as guarantor) (a)
300 — — 300 — — 
AEF 5.95% senior notes, due 2029 (with Alliant Energy as guarantor) (a)
300 — — 300 — — 
AEF 3.6% senior notes, due 2032 (with Alliant Energy as guarantor) (a)
350 — — 350 — — 
Alliant Energy 5.75% junior subordinated notes, due 2056 (f)
725 — — — — — 
AEF term loan credit agreement, 6% at December 31, 2024 (with Alliant Energy as guarantor) (Retired in 2025) (d)
— — — 300 — — 
3,700 — — 2,400 — — 
Subtotal12,125 4,725 3,700 9,925 4,125 3,400 
Current maturities(1,074)— — (1,171)(300)— 
Unamortized debt issuance costs(70)(30)(21)(55)(25)(20)
Unamortized debt (discount) and premium, net(27)(15)(10)(22)(10)(10)
Long-term debt, net (g)$10,954 $4,680 $3,669 $8,677 $3,790 $3,370 
(a)Contains optional redemption provisions which, if elected by the issuer at its sole discretion, could require material redemption premium payments by the issuer. The redemption premium payments under these optional redemption provisions are variable and dependent on applicable U.S. Treasury rates at the time of redemption.
(b)In May 2025, IPL issued $600 million of 5.6% senior debentures due 2035. A portion of the net proceeds was used for the retirement of IPL’s $50 million 5.5% senior debentures and $250 million 3.4% senior debentures. The remainder of the proceeds were used to reduce cash amounts received from its sale of accounts receivable program and commercial paper classified as long-term debt, and for general corporate purposes. In September 2025, IPL issued $300 million of 5.6% senior debentures due 2055. The net proceeds were used to reduce cash amounts received from its sale of accounts receivable program, to reduce outstanding commercial paper, and for general corporate purposes.
(c)In December 2025, WPL issued $300 million of 5.7% debentures due 2055. The net proceeds were used to reduce outstanding commercial paper and for general corporate purposes.
(d)In March 2025, AEF entered into a $300 million variable rate term loan credit agreement, which amended and restated the term loan credit agreement that expired in March 2025, and retired the $300 million variable rate term loan set forth therein, which was classified as a non-cash financing activity. AEF’s restated agreement includes an option to increase the amount outstanding with one or more additional term loans in an aggregate amount not to exceed $100 million. Refer to Note 14 for information on AEF’s related interest rate swap. In January 2026, AEF retired its $300 million term loan.
(e)Refer to “Convertible Senior Notes” below for additional information.
(f)In September 2025, Alliant Energy issued $725 million of junior subordinated notes due 2056. The interest rate will reset every 5 years beginning April 1, 2031, to equal the then-current five-year U.S. Treasury rate plus a spread of 2.077%, provided the interest rate will not reset below 5.75%. The net proceeds were used to reduce outstanding commercial paper, retire long term debt and for general corporate purposes. Long term debt to be retired includes AEF’s $300 million variable rate term loan which was retired in January 2026, AEF’s $200 million of 1.4% senior notes and Alliant Energy’s $575 million of 3.875% convertible senior notes, each of which matures in March 2026 and is expected to be retired at or prior to maturity. Alliant Energy has the option to redeem the notes prior to maturity upon the occurrence of certain events and during specified periods, at redemption prices specified in the governing agreements.
(g)There were no significant sinking fund requirements related to the outstanding long-term debt.

Convertible Senior Notes
2026 Notes - In March 2023, Alliant Energy issued $575 million of 3.875% convertible senior notes (the 2026 Notes), which are senior unsecured obligations, and used the net proceeds from the issuance for general corporate purposes. The 2026 Notes will mature on March 15, 2026 unless earlier converted or repurchased. Alliant Energy may not redeem the 2026 Notes prior to the maturity date. Holders could have converted their 2026 Notes at their option at any time prior to the close of business on the business day immediately preceding December 15, 2025 only under the following circumstances:

•during any calendar quarter commencing after the calendar quarter ending on June 30, 2023 (and only during such calendar quarter), if the last reported sale price of Alliant Energy’s common stock for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter is greater than or equal to 130% of the conversion price on each applicable trading day during such period;
•during the 5 business day period after any 10 consecutive trading day period (the “measurement period”) in which the trading price (as defined in the related Indenture) per $1,000 principal amount of 2026 Notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price of Alliant Energy’s common stock and the conversion rate on each such trading day; or
•upon the occurrence of specified corporate events.

On or after December 15, 2025 until the close of business on the business day immediately preceding the maturity date, holders may convert all or any portion of their 2026 Notes at any time, regardless of the foregoing circumstances. Upon conversion of the 2026 Notes, Alliant Energy will pay cash up to the aggregate principal amount of the 2026 Notes to be converted and deliver shares of its common stock, in respect of the remainder, if any, of its conversion obligation in excess of the aggregate principal amount of the 2026 Notes being converted.

The initial conversion rate is 15.5461 shares of common stock per $1,000 principal amount of 2026 Notes (equivalent to an initial conversion price of approximately $64.32 per share of Alliant Energy’s common stock). The conversion rate is subject to adjustment in some events but will not be adjusted for any accrued and unpaid interest. In addition, following certain corporate events that occur prior to the maturity date, Alliant Energy will, in certain circumstances, increase the conversion rate for a holder who elects to convert its 2026 Notes in connection with such a corporate event.

If Alliant Energy undergoes a fundamental change (as defined in the related Indenture), then, subject to certain conditions, holders of the 2026 Notes may require Alliant Energy to repurchase for cash all or any portion of its 2026 Notes at a fundamental change repurchase price equal to 100% of the principal amount of the 2026 Notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date.
As of December 31, 2025 and 2024, the 2026 Notes were classified on Alliant Energy’s balance sheets as “Current maturities of long-term debt”. As of December 31, 2025 and 2024, the net carrying amount of the 2026 Notes was $574 million and $571 million, with unamortized debt issuance costs of $1 million and $4 million, and the estimated fair value (Level 2) of the 2026 Notes was $599 million and $591 million. As of December 31, 2025, there were 407,821 shares of Alliant Energy’s common stock related to the potential conversion of the 2026 Notes included in diluted EPS based on Alliant Energy’s average stock prices and the relevant terms of the 2026 Notes.

2028 Notes - In May 2025, Alliant Energy issued $575 million of 3.25% convertible senior notes (the 2028 Notes), which are senior unsecured obligations, and used the net proceeds from the issuance to reduce Alliant Energy’s outstanding commercial paper and for general corporate purposes. The 2028 Notes will mature on May 30, 2028 unless earlier converted or repurchased, and no sinking fund is provided for the 2028 Notes. Alliant Energy may not redeem the 2028 Notes prior to the maturity date. Holders may convert their 2028 Notes at their option at any time prior to the close of business on the business day immediately preceding March 1, 2028 only under the following circumstances:

•during any calendar quarter commencing after the calendar quarter ending on September 30, 2025 (and only during such calendar quarter), if the last reported sale price of Alliant Energy’s common stock for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter is greater than or equal to 130% of the conversion price on each applicable trading day during such period;
•during the 5 business day period after any 10 consecutive trading day period (the “measurement period”) in which the trading price (as defined in the related Indenture) per $1,000 principal amount of 2028 Notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price of Alliant Energy’s common stock and the conversion rate on each such trading day; or
•upon the occurrence of specified corporate events.

On or after March 1, 2028 until the close of business on the business day immediately preceding the maturity date, holders may convert all or any portion of their 2028 Notes at any time, regardless of the foregoing circumstances. Upon conversion of the 2028 Notes, Alliant Energy will pay cash up to the aggregate principal amount of the 2028 Notes to be converted and pay or deliver, as the case may be, cash, shares of its common stock or a combination of cash and shares of its common stock, at its election, in respect of the remainder, if any, of its conversion obligation in excess of the aggregate principal amount of the 2028 Notes being converted.

The initial conversion rate is 13.1773 shares of common stock per $1,000 principal amount of 2028 Notes (equivalent to an initial conversion price of approximately $75.89 per share of Alliant Energy’s common stock). The conversion rate is subject to adjustment in some events but will not be adjusted for any accrued and unpaid interest. In addition, following certain corporate events that occur prior to the maturity date, Alliant Energy will, in certain circumstances, increase the conversion rate for a holder who elects to convert its 2028 Notes in connection with such a corporate event.

If Alliant Energy undergoes a fundamental change (as defined in the related Indenture), then, subject to certain conditions, holders of the 2028 Notes may require Alliant Energy to repurchase for cash all or any portion of its 2028 Notes at a fundamental change repurchase price equal to 100% of the principal amount of the 2028 Notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date.

As of December 31, 2025, the conditions allowing holders of the 2028 Notes to convert their 2028 Notes were not met, and the 2028 Notes were classified as “Long-term debt, net” on Alliant Energy’s balance sheet. As of December 31, 2025, the net carrying amount was $569 million, with unamortized debt issuance costs of $6 million, and the estimated fair value (Level 2) was $587 million for the 2028 Notes. As of December 31, 2025, there were no shares of Alliant Energy’s common stock related to the potential conversion of the 2028 Notes included in diluted EPS based on Alliant Energy’s average stock prices and the relevant terms of the 2028 Notes.

Five-Year Schedule of Long-term Debt Maturities - At December 31, 2025, long-term debt maturities for 2026 through 2030 were as follows (in millions):
20262027202820292030
IPL$—$—$500$300$400
WPL—300—350—
AEF500375300300—
Alliant Energy parent company575—575——
Alliant Energy$1,075$675$1,375$950$400

Fair Value of Long-term Debt - Refer to Note 15 for information on the fair value of long-term debt outstanding.
WPL [Member]  
Debt Instrument [Line Items]  
Debt DEBT(a) Short-term Debt - Alliant Energy and its subsidiaries maintain committed bank lines of credit to provide short-term borrowing flexibility and back-stop liquidity for commercial paper outstanding. At December 31, 2025, the short-term borrowing capacity under a single credit facility agreement, which expires in December 2030, totaled $1.3 billion ($550 million for Alliant Energy at the parent company level, $350 million for IPL and $400 million for WPL). Subject to certain conditions, Alliant Energy (at the parent company level), IPL and WPL may each reallocate and change its sublimit up to $1 billion, $400 million and $500 million, respectively, within the $1.3 billion total commitment. Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper and borrowings under the single credit facility classified as short-term debt was as follows (dollars in millions):
Alliant EnergyIPLWPL
December 31202520242025202420252024
Amount outstanding$88$558$88$50$—$183
Weighted average interest rates3.8%4.5%3.8%4.6%N/A4.5%
Available credit facility capacity$1,212$742$262$250$400$217
Alliant EnergyIPLWPL
For the year ended202520242025202420252024
Maximum amount outstanding (based on daily outstanding balances)$741$632$141$80$297$390
Average amount outstanding (based on daily outstanding balances)$349$327$25$1$176$70
Weighted average interest rates4.5%5.3%4.6%5.1%4.5%5.4%
(b) Long-Term Debt - Long-term debt, net as of December 31 was as follows (dollars in millions):
20252024
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Senior Debentures (a):
4.1%, due 2028
$500 $500 $— $500 $500 $— 
3.6%, due 2029
300 300 — 300 300 — 
2.3%, due 2030
400 400 — 400 400 — 
5.7%, due 2033
300 300 — 300 300 — 
6.45%, due 2033
100 100 — 100 100 — 
4.95%, due 2034
350 350 — 350 350 — 
6.3%, due 2034
125 125 — 125 125 — 
5.6%, due 2035 (b)
600 600 — — — — 
6.25%, due 2039
300 300 — 300 300 — 
4.7%, due 2043
250 250 — 250 250 — 
3.7%, due 2046
300 300 — 300 300 — 
3.5%, due 2049
300 300 — 300 300 — 
3.1%, due 2051
300 300 — 300 300 — 
5.45%, due 2054
300 300 — 300 300 — 
5.6%, due 2055 (b)
300 300 — — — — 
3.4%, (Retired in 2025)
— — — 250 250 — 
5.5%, (Retired in 2025)
— — — 50 50 — 
4,725 4,725 — 4,125 4,125 — 
Debentures (a):
3.05%, due 2027
300 — 300 300 — 300 
3%, due 2029
350 — 350 350 — 350 
1.95%, due 2031
300 — 300 300 — 300 
3.95%, due 2032
600 — 600 600 — 600 
4.95%, due 2033
300 — 300 300 — 300 
5.375%, due 2034
300 — 300 300 — 300 
6.25%, due 2034
100 — 100 100 — 100 
6.375%, due 2037
300 — 300 300 — 300 
7.6%, due 2038
250 — 250 250 — 250 
4.1%, due 2044
250 — 250 250 — 250 
3.65%, due 2050
350 — 350 350 — 350 
5.7%, due 2055 (c)
300 — 300 — — — 
3,700 — 3,700 3,400 — 3,400 
Other:
AEF term loan credit agreement through March 2026, 5% at December 31, 2025 (with Alliant Energy as guarantor) (d)
300 — — — — — 
AEF 1.4% senior notes, due 2026 (with Alliant Energy as guarantor) (a)
200 — — 200 — — 
Alliant Energy 3.875% convertible senior notes, due 2026 (e)
575 — — 575 — — 
AEF 5.4% senior notes, due 2027 (with Alliant Energy as guarantor) (a)
375 — — 375 — — 
Alliant Energy 3.25% convertible senior notes, due 2028 (e)
575 — — — — — 
AEF 4.25% senior notes, due 2028 (with Alliant Energy as guarantor) (a)
300 — — 300 — — 
AEF 5.95% senior notes, due 2029 (with Alliant Energy as guarantor) (a)
300 — — 300 — — 
AEF 3.6% senior notes, due 2032 (with Alliant Energy as guarantor) (a)
350 — — 350 — — 
Alliant Energy 5.75% junior subordinated notes, due 2056 (f)
725 — — — — — 
AEF term loan credit agreement, 6% at December 31, 2024 (with Alliant Energy as guarantor) (Retired in 2025) (d)
— — — 300 — — 
3,700 — — 2,400 — — 
Subtotal12,125 4,725 3,700 9,925 4,125 3,400 
Current maturities(1,074)— — (1,171)(300)— 
Unamortized debt issuance costs(70)(30)(21)(55)(25)(20)
Unamortized debt (discount) and premium, net(27)(15)(10)(22)(10)(10)
Long-term debt, net (g)$10,954 $4,680 $3,669 $8,677 $3,790 $3,370 
(a)Contains optional redemption provisions which, if elected by the issuer at its sole discretion, could require material redemption premium payments by the issuer. The redemption premium payments under these optional redemption provisions are variable and dependent on applicable U.S. Treasury rates at the time of redemption.
(b)In May 2025, IPL issued $600 million of 5.6% senior debentures due 2035. A portion of the net proceeds was used for the retirement of IPL’s $50 million 5.5% senior debentures and $250 million 3.4% senior debentures. The remainder of the proceeds were used to reduce cash amounts received from its sale of accounts receivable program and commercial paper classified as long-term debt, and for general corporate purposes. In September 2025, IPL issued $300 million of 5.6% senior debentures due 2055. The net proceeds were used to reduce cash amounts received from its sale of accounts receivable program, to reduce outstanding commercial paper, and for general corporate purposes.
(c)In December 2025, WPL issued $300 million of 5.7% debentures due 2055. The net proceeds were used to reduce outstanding commercial paper and for general corporate purposes.
(d)In March 2025, AEF entered into a $300 million variable rate term loan credit agreement, which amended and restated the term loan credit agreement that expired in March 2025, and retired the $300 million variable rate term loan set forth therein, which was classified as a non-cash financing activity. AEF’s restated agreement includes an option to increase the amount outstanding with one or more additional term loans in an aggregate amount not to exceed $100 million. Refer to Note 14 for information on AEF’s related interest rate swap. In January 2026, AEF retired its $300 million term loan.
(e)Refer to “Convertible Senior Notes” below for additional information.
(f)In September 2025, Alliant Energy issued $725 million of junior subordinated notes due 2056. The interest rate will reset every 5 years beginning April 1, 2031, to equal the then-current five-year U.S. Treasury rate plus a spread of 2.077%, provided the interest rate will not reset below 5.75%. The net proceeds were used to reduce outstanding commercial paper, retire long term debt and for general corporate purposes. Long term debt to be retired includes AEF’s $300 million variable rate term loan which was retired in January 2026, AEF’s $200 million of 1.4% senior notes and Alliant Energy’s $575 million of 3.875% convertible senior notes, each of which matures in March 2026 and is expected to be retired at or prior to maturity. Alliant Energy has the option to redeem the notes prior to maturity upon the occurrence of certain events and during specified periods, at redemption prices specified in the governing agreements.
(g)There were no significant sinking fund requirements related to the outstanding long-term debt.

Convertible Senior Notes
2026 Notes - In March 2023, Alliant Energy issued $575 million of 3.875% convertible senior notes (the 2026 Notes), which are senior unsecured obligations, and used the net proceeds from the issuance for general corporate purposes. The 2026 Notes will mature on March 15, 2026 unless earlier converted or repurchased. Alliant Energy may not redeem the 2026 Notes prior to the maturity date. Holders could have converted their 2026 Notes at their option at any time prior to the close of business on the business day immediately preceding December 15, 2025 only under the following circumstances:

•during any calendar quarter commencing after the calendar quarter ending on June 30, 2023 (and only during such calendar quarter), if the last reported sale price of Alliant Energy’s common stock for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter is greater than or equal to 130% of the conversion price on each applicable trading day during such period;
•during the 5 business day period after any 10 consecutive trading day period (the “measurement period”) in which the trading price (as defined in the related Indenture) per $1,000 principal amount of 2026 Notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price of Alliant Energy’s common stock and the conversion rate on each such trading day; or
•upon the occurrence of specified corporate events.

On or after December 15, 2025 until the close of business on the business day immediately preceding the maturity date, holders may convert all or any portion of their 2026 Notes at any time, regardless of the foregoing circumstances. Upon conversion of the 2026 Notes, Alliant Energy will pay cash up to the aggregate principal amount of the 2026 Notes to be converted and deliver shares of its common stock, in respect of the remainder, if any, of its conversion obligation in excess of the aggregate principal amount of the 2026 Notes being converted.

The initial conversion rate is 15.5461 shares of common stock per $1,000 principal amount of 2026 Notes (equivalent to an initial conversion price of approximately $64.32 per share of Alliant Energy’s common stock). The conversion rate is subject to adjustment in some events but will not be adjusted for any accrued and unpaid interest. In addition, following certain corporate events that occur prior to the maturity date, Alliant Energy will, in certain circumstances, increase the conversion rate for a holder who elects to convert its 2026 Notes in connection with such a corporate event.

If Alliant Energy undergoes a fundamental change (as defined in the related Indenture), then, subject to certain conditions, holders of the 2026 Notes may require Alliant Energy to repurchase for cash all or any portion of its 2026 Notes at a fundamental change repurchase price equal to 100% of the principal amount of the 2026 Notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date.
As of December 31, 2025 and 2024, the 2026 Notes were classified on Alliant Energy’s balance sheets as “Current maturities of long-term debt”. As of December 31, 2025 and 2024, the net carrying amount of the 2026 Notes was $574 million and $571 million, with unamortized debt issuance costs of $1 million and $4 million, and the estimated fair value (Level 2) of the 2026 Notes was $599 million and $591 million. As of December 31, 2025, there were 407,821 shares of Alliant Energy’s common stock related to the potential conversion of the 2026 Notes included in diluted EPS based on Alliant Energy’s average stock prices and the relevant terms of the 2026 Notes.

2028 Notes - In May 2025, Alliant Energy issued $575 million of 3.25% convertible senior notes (the 2028 Notes), which are senior unsecured obligations, and used the net proceeds from the issuance to reduce Alliant Energy’s outstanding commercial paper and for general corporate purposes. The 2028 Notes will mature on May 30, 2028 unless earlier converted or repurchased, and no sinking fund is provided for the 2028 Notes. Alliant Energy may not redeem the 2028 Notes prior to the maturity date. Holders may convert their 2028 Notes at their option at any time prior to the close of business on the business day immediately preceding March 1, 2028 only under the following circumstances:

•during any calendar quarter commencing after the calendar quarter ending on September 30, 2025 (and only during such calendar quarter), if the last reported sale price of Alliant Energy’s common stock for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on, and including, the last trading day of the immediately preceding calendar quarter is greater than or equal to 130% of the conversion price on each applicable trading day during such period;
•during the 5 business day period after any 10 consecutive trading day period (the “measurement period”) in which the trading price (as defined in the related Indenture) per $1,000 principal amount of 2028 Notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price of Alliant Energy’s common stock and the conversion rate on each such trading day; or
•upon the occurrence of specified corporate events.

On or after March 1, 2028 until the close of business on the business day immediately preceding the maturity date, holders may convert all or any portion of their 2028 Notes at any time, regardless of the foregoing circumstances. Upon conversion of the 2028 Notes, Alliant Energy will pay cash up to the aggregate principal amount of the 2028 Notes to be converted and pay or deliver, as the case may be, cash, shares of its common stock or a combination of cash and shares of its common stock, at its election, in respect of the remainder, if any, of its conversion obligation in excess of the aggregate principal amount of the 2028 Notes being converted.

The initial conversion rate is 13.1773 shares of common stock per $1,000 principal amount of 2028 Notes (equivalent to an initial conversion price of approximately $75.89 per share of Alliant Energy’s common stock). The conversion rate is subject to adjustment in some events but will not be adjusted for any accrued and unpaid interest. In addition, following certain corporate events that occur prior to the maturity date, Alliant Energy will, in certain circumstances, increase the conversion rate for a holder who elects to convert its 2028 Notes in connection with such a corporate event.

If Alliant Energy undergoes a fundamental change (as defined in the related Indenture), then, subject to certain conditions, holders of the 2028 Notes may require Alliant Energy to repurchase for cash all or any portion of its 2028 Notes at a fundamental change repurchase price equal to 100% of the principal amount of the 2028 Notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date.

As of December 31, 2025, the conditions allowing holders of the 2028 Notes to convert their 2028 Notes were not met, and the 2028 Notes were classified as “Long-term debt, net” on Alliant Energy’s balance sheet. As of December 31, 2025, the net carrying amount was $569 million, with unamortized debt issuance costs of $6 million, and the estimated fair value (Level 2) was $587 million for the 2028 Notes. As of December 31, 2025, there were no shares of Alliant Energy’s common stock related to the potential conversion of the 2028 Notes included in diluted EPS based on Alliant Energy’s average stock prices and the relevant terms of the 2028 Notes.

Five-Year Schedule of Long-term Debt Maturities - At December 31, 2025, long-term debt maturities for 2026 through 2030 were as follows (in millions):
20262027202820292030
IPL$—$—$500$300$400
WPL—300—350—
AEF500375300300—
Alliant Energy parent company575—575——
Alliant Energy$1,075$675$1,375$950$400

Fair Value of Long-term Debt - Refer to Note 15 for information on the fair value of long-term debt outstanding.
v3.25.4
Leases
 12 Months Ended
Dec. 31, 2025
Leases [Line Items]  
Operating Leases LEASES
Operating Leases - Alliant Energy’s, IPL’s and WPL’s operating leases primarily include leases of space on telecommunication towers and leases of property. Operating lease details are as follows (dollars in millions):
December 31, 2025December 31, 2024
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net$21$11$9$22$12$9
Other current liabilities$2$1$1$2$1$1
Other liabilities1910820118
Total operating lease liabilities$21$11$9$22$12$9
Weighted average remaining lease term10 years10 years11 years11 years11 years12 years
Weighted average discount rate4%4%4%4%4%4%

Finance Leases - WPL is currently leasing the Sheboygan Falls Energy Facility from AEF’s Non-utility Generation business. WPL is responsible for the operation of the EGU and has exclusive rights to its output. In 2024, WPL renewed this financing lease through 2044. There are no lease renewal periods remaining. In 2025, WPL’s rent payments increased following the completion of certain enhancements to the Sheboygan Falls Energy Facility, resulting in a lease modification and remeasurement. For Alliant Energy, the leased Sheboygan Falls Energy Facility is eliminated upon consolidation and therefore is not reflected in Alliant Energy’s amounts below.

Related to their investments in solar generation, IPL and WPL entered into various land lease agreements with unaffiliated parties that have commenced. The leases have various terms with optional renewal periods that are assumed to be extended through the end of the estimated useful lives of the solar generating facilities. The leases do not contain purchase options and are fixed lease payments.

Finance lease details are as follows (dollars in millions):
December 31, 2025December 31, 2024
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net:
Sheboygan Falls Energy FacilityN/AN/A$110N/AN/A$74
Leased land for solar generation$190$52138$189$53136
$190$52$248$189$53$210
Other current liabilities:
Sheboygan Falls Energy FacilityN/AN/A$4N/AN/A$7
$—$—$4$—$—$7
Other liabilities:
Sheboygan Falls Energy FacilityN/AN/A$106N/AN/A$71
Leased land for solar generation1905213818953136
1905224418953207
Total finance lease liabilities$190$52$248$189$53$214
Weighted average remaining lease term30 years27 years26 years31 years28 years28 years
Weighted average discount rate5%5%6%5%5%5%
Alliant EnergyIPLWPL
202520242023202520242023202520242023
Depreciation and amortization expenses$— $— $1 $— $— $— $2 $4 $6 
Interest expense9 8 6 3 2 1 11 10 8 
Total finance lease expense$9 $8 $7 $3 $2 $1 $13 $14 $14 

Finance lease liabilities arising from obtaining leased assets, which represent non-cash financing activities, were as follows (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Finance lease liabilities arising from obtaining leased assets
$1 $20 $— $20 $39 $— 
Expected Maturities - As of December 31, 2025, expected maturities of lease liabilities were as follows (in millions):
20262027202820292030ThereafterTotalLess: amount representing interestPresent value of minimum lease payments
Operating Leases:
Alliant Energy$3 $3 $3 $3 $2 $13$27$6$21
IPL2 1 1 1 1 814311
WPL1 1 1 1 1 71239
Finance Leases:
Alliant Energy9 10 10 10 10 328377187190
IPL3 3 3 3 3 871025052
WPL18 18 19 19 19 386479231248
Finance Leases LEASES
Operating Leases - Alliant Energy’s, IPL’s and WPL’s operating leases primarily include leases of space on telecommunication towers and leases of property. Operating lease details are as follows (dollars in millions):
December 31, 2025December 31, 2024
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net$21$11$9$22$12$9
Other current liabilities$2$1$1$2$1$1
Other liabilities1910820118
Total operating lease liabilities$21$11$9$22$12$9
Weighted average remaining lease term10 years10 years11 years11 years11 years12 years
Weighted average discount rate4%4%4%4%4%4%

Finance Leases - WPL is currently leasing the Sheboygan Falls Energy Facility from AEF’s Non-utility Generation business. WPL is responsible for the operation of the EGU and has exclusive rights to its output. In 2024, WPL renewed this financing lease through 2044. There are no lease renewal periods remaining. In 2025, WPL’s rent payments increased following the completion of certain enhancements to the Sheboygan Falls Energy Facility, resulting in a lease modification and remeasurement. For Alliant Energy, the leased Sheboygan Falls Energy Facility is eliminated upon consolidation and therefore is not reflected in Alliant Energy’s amounts below.

Related to their investments in solar generation, IPL and WPL entered into various land lease agreements with unaffiliated parties that have commenced. The leases have various terms with optional renewal periods that are assumed to be extended through the end of the estimated useful lives of the solar generating facilities. The leases do not contain purchase options and are fixed lease payments.

Finance lease details are as follows (dollars in millions):
December 31, 2025December 31, 2024
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net:
Sheboygan Falls Energy FacilityN/AN/A$110N/AN/A$74
Leased land for solar generation$190$52138$189$53136
$190$52$248$189$53$210
Other current liabilities:
Sheboygan Falls Energy FacilityN/AN/A$4N/AN/A$7
$—$—$4$—$—$7
Other liabilities:
Sheboygan Falls Energy FacilityN/AN/A$106N/AN/A$71
Leased land for solar generation1905213818953136
1905224418953207
Total finance lease liabilities$190$52$248$189$53$214
Weighted average remaining lease term30 years27 years26 years31 years28 years28 years
Weighted average discount rate5%5%6%5%5%5%
Alliant EnergyIPLWPL
202520242023202520242023202520242023
Depreciation and amortization expenses$— $— $1 $— $— $— $2 $4 $6 
Interest expense9 8 6 3 2 1 11 10 8 
Total finance lease expense$9 $8 $7 $3 $2 $1 $13 $14 $14 

Finance lease liabilities arising from obtaining leased assets, which represent non-cash financing activities, were as follows (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Finance lease liabilities arising from obtaining leased assets
$1 $20 $— $20 $39 $— 
Expected Maturities - As of December 31, 2025, expected maturities of lease liabilities were as follows (in millions):
20262027202820292030ThereafterTotalLess: amount representing interestPresent value of minimum lease payments
Operating Leases:
Alliant Energy$3 $3 $3 $3 $2 $13$27$6$21
IPL2 1 1 1 1 814311
WPL1 1 1 1 1 71239
Finance Leases:
Alliant Energy9 10 10 10 10 328377187190
IPL3 3 3 3 3 871025052
WPL18 18 19 19 19 386479231248
IPL [Member]  
Leases [Line Items]  
Operating Leases LEASES
Operating Leases - Alliant Energy’s, IPL’s and WPL’s operating leases primarily include leases of space on telecommunication towers and leases of property. Operating lease details are as follows (dollars in millions):
December 31, 2025December 31, 2024
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net$21$11$9$22$12$9
Other current liabilities$2$1$1$2$1$1
Other liabilities1910820118
Total operating lease liabilities$21$11$9$22$12$9
Weighted average remaining lease term10 years10 years11 years11 years11 years12 years
Weighted average discount rate4%4%4%4%4%4%

Finance Leases - WPL is currently leasing the Sheboygan Falls Energy Facility from AEF’s Non-utility Generation business. WPL is responsible for the operation of the EGU and has exclusive rights to its output. In 2024, WPL renewed this financing lease through 2044. There are no lease renewal periods remaining. In 2025, WPL’s rent payments increased following the completion of certain enhancements to the Sheboygan Falls Energy Facility, resulting in a lease modification and remeasurement. For Alliant Energy, the leased Sheboygan Falls Energy Facility is eliminated upon consolidation and therefore is not reflected in Alliant Energy’s amounts below.

Related to their investments in solar generation, IPL and WPL entered into various land lease agreements with unaffiliated parties that have commenced. The leases have various terms with optional renewal periods that are assumed to be extended through the end of the estimated useful lives of the solar generating facilities. The leases do not contain purchase options and are fixed lease payments.

Finance lease details are as follows (dollars in millions):
December 31, 2025December 31, 2024
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net:
Sheboygan Falls Energy FacilityN/AN/A$110N/AN/A$74
Leased land for solar generation$190$52138$189$53136
$190$52$248$189$53$210
Other current liabilities:
Sheboygan Falls Energy FacilityN/AN/A$4N/AN/A$7
$—$—$4$—$—$7
Other liabilities:
Sheboygan Falls Energy FacilityN/AN/A$106N/AN/A$71
Leased land for solar generation1905213818953136
1905224418953207
Total finance lease liabilities$190$52$248$189$53$214
Weighted average remaining lease term30 years27 years26 years31 years28 years28 years
Weighted average discount rate5%5%6%5%5%5%
Alliant EnergyIPLWPL
202520242023202520242023202520242023
Depreciation and amortization expenses$— $— $1 $— $— $— $2 $4 $6 
Interest expense9 8 6 3 2 1 11 10 8 
Total finance lease expense$9 $8 $7 $3 $2 $1 $13 $14 $14 

Finance lease liabilities arising from obtaining leased assets, which represent non-cash financing activities, were as follows (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Finance lease liabilities arising from obtaining leased assets
$1 $20 $— $20 $39 $— 
Expected Maturities - As of December 31, 2025, expected maturities of lease liabilities were as follows (in millions):
20262027202820292030ThereafterTotalLess: amount representing interestPresent value of minimum lease payments
Operating Leases:
Alliant Energy$3 $3 $3 $3 $2 $13$27$6$21
IPL2 1 1 1 1 814311
WPL1 1 1 1 1 71239
Finance Leases:
Alliant Energy9 10 10 10 10 328377187190
IPL3 3 3 3 3 871025052
WPL18 18 19 19 19 386479231248
Finance Leases LEASES
Operating Leases - Alliant Energy’s, IPL’s and WPL’s operating leases primarily include leases of space on telecommunication towers and leases of property. Operating lease details are as follows (dollars in millions):
December 31, 2025December 31, 2024
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net$21$11$9$22$12$9
Other current liabilities$2$1$1$2$1$1
Other liabilities1910820118
Total operating lease liabilities$21$11$9$22$12$9
Weighted average remaining lease term10 years10 years11 years11 years11 years12 years
Weighted average discount rate4%4%4%4%4%4%

Finance Leases - WPL is currently leasing the Sheboygan Falls Energy Facility from AEF’s Non-utility Generation business. WPL is responsible for the operation of the EGU and has exclusive rights to its output. In 2024, WPL renewed this financing lease through 2044. There are no lease renewal periods remaining. In 2025, WPL’s rent payments increased following the completion of certain enhancements to the Sheboygan Falls Energy Facility, resulting in a lease modification and remeasurement. For Alliant Energy, the leased Sheboygan Falls Energy Facility is eliminated upon consolidation and therefore is not reflected in Alliant Energy’s amounts below.

Related to their investments in solar generation, IPL and WPL entered into various land lease agreements with unaffiliated parties that have commenced. The leases have various terms with optional renewal periods that are assumed to be extended through the end of the estimated useful lives of the solar generating facilities. The leases do not contain purchase options and are fixed lease payments.

Finance lease details are as follows (dollars in millions):
December 31, 2025December 31, 2024
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net:
Sheboygan Falls Energy FacilityN/AN/A$110N/AN/A$74
Leased land for solar generation$190$52138$189$53136
$190$52$248$189$53$210
Other current liabilities:
Sheboygan Falls Energy FacilityN/AN/A$4N/AN/A$7
$—$—$4$—$—$7
Other liabilities:
Sheboygan Falls Energy FacilityN/AN/A$106N/AN/A$71
Leased land for solar generation1905213818953136
1905224418953207
Total finance lease liabilities$190$52$248$189$53$214
Weighted average remaining lease term30 years27 years26 years31 years28 years28 years
Weighted average discount rate5%5%6%5%5%5%
Alliant EnergyIPLWPL
202520242023202520242023202520242023
Depreciation and amortization expenses$— $— $1 $— $— $— $2 $4 $6 
Interest expense9 8 6 3 2 1 11 10 8 
Total finance lease expense$9 $8 $7 $3 $2 $1 $13 $14 $14 

Finance lease liabilities arising from obtaining leased assets, which represent non-cash financing activities, were as follows (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Finance lease liabilities arising from obtaining leased assets
$1 $20 $— $20 $39 $— 
Expected Maturities - As of December 31, 2025, expected maturities of lease liabilities were as follows (in millions):
20262027202820292030ThereafterTotalLess: amount representing interestPresent value of minimum lease payments
Operating Leases:
Alliant Energy$3 $3 $3 $3 $2 $13$27$6$21
IPL2 1 1 1 1 814311
WPL1 1 1 1 1 71239
Finance Leases:
Alliant Energy9 10 10 10 10 328377187190
IPL3 3 3 3 3 871025052
WPL18 18 19 19 19 386479231248
WPL [Member]  
Leases [Line Items]  
Operating Leases LEASES
Operating Leases - Alliant Energy’s, IPL’s and WPL’s operating leases primarily include leases of space on telecommunication towers and leases of property. Operating lease details are as follows (dollars in millions):
December 31, 2025December 31, 2024
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net$21$11$9$22$12$9
Other current liabilities$2$1$1$2$1$1
Other liabilities1910820118
Total operating lease liabilities$21$11$9$22$12$9
Weighted average remaining lease term10 years10 years11 years11 years11 years12 years
Weighted average discount rate4%4%4%4%4%4%

Finance Leases - WPL is currently leasing the Sheboygan Falls Energy Facility from AEF’s Non-utility Generation business. WPL is responsible for the operation of the EGU and has exclusive rights to its output. In 2024, WPL renewed this financing lease through 2044. There are no lease renewal periods remaining. In 2025, WPL’s rent payments increased following the completion of certain enhancements to the Sheboygan Falls Energy Facility, resulting in a lease modification and remeasurement. For Alliant Energy, the leased Sheboygan Falls Energy Facility is eliminated upon consolidation and therefore is not reflected in Alliant Energy’s amounts below.

Related to their investments in solar generation, IPL and WPL entered into various land lease agreements with unaffiliated parties that have commenced. The leases have various terms with optional renewal periods that are assumed to be extended through the end of the estimated useful lives of the solar generating facilities. The leases do not contain purchase options and are fixed lease payments.

Finance lease details are as follows (dollars in millions):
December 31, 2025December 31, 2024
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net:
Sheboygan Falls Energy FacilityN/AN/A$110N/AN/A$74
Leased land for solar generation$190$52138$189$53136
$190$52$248$189$53$210
Other current liabilities:
Sheboygan Falls Energy FacilityN/AN/A$4N/AN/A$7
$—$—$4$—$—$7
Other liabilities:
Sheboygan Falls Energy FacilityN/AN/A$106N/AN/A$71
Leased land for solar generation1905213818953136
1905224418953207
Total finance lease liabilities$190$52$248$189$53$214
Weighted average remaining lease term30 years27 years26 years31 years28 years28 years
Weighted average discount rate5%5%6%5%5%5%
Alliant EnergyIPLWPL
202520242023202520242023202520242023
Depreciation and amortization expenses$— $— $1 $— $— $— $2 $4 $6 
Interest expense9 8 6 3 2 1 11 10 8 
Total finance lease expense$9 $8 $7 $3 $2 $1 $13 $14 $14 

Finance lease liabilities arising from obtaining leased assets, which represent non-cash financing activities, were as follows (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Finance lease liabilities arising from obtaining leased assets
$1 $20 $— $20 $39 $— 
Expected Maturities - As of December 31, 2025, expected maturities of lease liabilities were as follows (in millions):
20262027202820292030ThereafterTotalLess: amount representing interestPresent value of minimum lease payments
Operating Leases:
Alliant Energy$3 $3 $3 $3 $2 $13$27$6$21
IPL2 1 1 1 1 814311
WPL1 1 1 1 1 71239
Finance Leases:
Alliant Energy9 10 10 10 10 328377187190
IPL3 3 3 3 3 871025052
WPL18 18 19 19 19 386479231248
Finance Leases LEASES
Operating Leases - Alliant Energy’s, IPL’s and WPL’s operating leases primarily include leases of space on telecommunication towers and leases of property. Operating lease details are as follows (dollars in millions):
December 31, 2025December 31, 2024
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net$21$11$9$22$12$9
Other current liabilities$2$1$1$2$1$1
Other liabilities1910820118
Total operating lease liabilities$21$11$9$22$12$9
Weighted average remaining lease term10 years10 years11 years11 years11 years12 years
Weighted average discount rate4%4%4%4%4%4%

Finance Leases - WPL is currently leasing the Sheboygan Falls Energy Facility from AEF’s Non-utility Generation business. WPL is responsible for the operation of the EGU and has exclusive rights to its output. In 2024, WPL renewed this financing lease through 2044. There are no lease renewal periods remaining. In 2025, WPL’s rent payments increased following the completion of certain enhancements to the Sheboygan Falls Energy Facility, resulting in a lease modification and remeasurement. For Alliant Energy, the leased Sheboygan Falls Energy Facility is eliminated upon consolidation and therefore is not reflected in Alliant Energy’s amounts below.

Related to their investments in solar generation, IPL and WPL entered into various land lease agreements with unaffiliated parties that have commenced. The leases have various terms with optional renewal periods that are assumed to be extended through the end of the estimated useful lives of the solar generating facilities. The leases do not contain purchase options and are fixed lease payments.

Finance lease details are as follows (dollars in millions):
December 31, 2025December 31, 2024
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net:
Sheboygan Falls Energy FacilityN/AN/A$110N/AN/A$74
Leased land for solar generation$190$52138$189$53136
$190$52$248$189$53$210
Other current liabilities:
Sheboygan Falls Energy FacilityN/AN/A$4N/AN/A$7
$—$—$4$—$—$7
Other liabilities:
Sheboygan Falls Energy FacilityN/AN/A$106N/AN/A$71
Leased land for solar generation1905213818953136
1905224418953207
Total finance lease liabilities$190$52$248$189$53$214
Weighted average remaining lease term30 years27 years26 years31 years28 years28 years
Weighted average discount rate5%5%6%5%5%5%
Alliant EnergyIPLWPL
202520242023202520242023202520242023
Depreciation and amortization expenses$— $— $1 $— $— $— $2 $4 $6 
Interest expense9 8 6 3 2 1 11 10 8 
Total finance lease expense$9 $8 $7 $3 $2 $1 $13 $14 $14 

Finance lease liabilities arising from obtaining leased assets, which represent non-cash financing activities, were as follows (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Finance lease liabilities arising from obtaining leased assets
$1 $20 $— $20 $39 $— 
Expected Maturities - As of December 31, 2025, expected maturities of lease liabilities were as follows (in millions):
20262027202820292030ThereafterTotalLess: amount representing interestPresent value of minimum lease payments
Operating Leases:
Alliant Energy$3 $3 $3 $3 $2 $13$27$6$21
IPL2 1 1 1 1 814311
WPL1 1 1 1 1 71239
Finance Leases:
Alliant Energy9 10 10 10 10 328377187190
IPL3 3 3 3 3 871025052
WPL18 18 19 19 19 386479231248
v3.25.4
Revenues
 12 Months Ended
Dec. 31, 2025
Disaggregation of Revenue [Line Items]  
Revenues REVENUES
Revenues from Alliant Energy’s, IPL’s and WPL’s utility businesses are primarily from electric and gas sales provided to customers based on approved tariffs or specific contracts with customers. IPL’s and WPL’s primary performance obligations under such arrangements are to deliver electricity and gas, and their customers simultaneously receive and consume the electricity and gas. For such arrangements, revenues are recognized equivalent to the value of the electricity or gas supplied during each period, including amounts billed during each period and changes in amounts estimated to be billed at the end of each period. IPL and WPL apply the right to invoice method to measure progress towards completing performance obligations to transfer electricity and gas to their customers.

IPL provides retail electric and gas service to customers in Iowa, and WPL provides retail and wholesale electric and retail gas service to customers in Wisconsin. IPL also provides electricity to wholesale customers in Illinois and Iowa. IPL’s wholesale power agreement with Southern Minnesota Energy Cooperative expired in July 2025. IPL provided steam from its Prairie Creek Generating Station to high-pressure steam customers in Iowa through 2025.

IPL’s and WPL’s retail electric and gas revenues include sales to residential, commercial and industrial customers. IPL’s and WPL’s retail electric and gas customer prices are based on IPL’s and WPL’s cost of service and are determined through general rate review proceedings and various tariff filings with the IUC and PSCW, respectively. Such tariff-based services provide electricity or gas to customers without a defined contractual term.

IPL and WPL have wholesale electric market-based rate authority from FERC allowing them to participate in wholesale energy markets (e.g. MISO) and transact directly with third parties. This authority from FERC allows sales of electricity referred to as bulk power sales based on current market values. FERC also allows IPL and WPL to enter into power supply agreements with municipalities and rural electric cooperatives with defined contractual terms, which include standard pricing mechanisms that are detailed in current tariffs accepted by FERC through wholesale rate review proceedings.

Revenues from Alliant Energy’s non-utility business customers are primarily from its Travero business, which includes a short-line rail freight service in Iowa; a Mississippi River barge, rail and truck freight terminal in Illinois; freight brokerage services; and a rail-served warehouse in Iowa.
Disaggregation of revenues from contracts with customers is provided for each reportable segment (IPL and WPL), as well as by customer class within electric and gas sales, as follows (in millions):
Alliant EnergyIPLWPL
202520242023202520242023202520242023
Electric Utility:
Retail - residential$1,339 $1,236 $1,220 $661 $640 $641 $678 $596 $579 
Retail - commercial932 821 820 609 525 519 323 296 301 
Retail - industrial1,034 952 968 531 497 501 503 455 467 
Wholesale184 200 213 39 61 62 145 139 151 
Bulk power and other208 163 124 56 24 38 152 139 86 
Total Electric Utility3,697 3,372 3,345 1,896 1,747 1,761 1,801 1,625 1,584 
Gas Utility:
Retail - residential306 275 316 155 148 176 151 127 140 
Retail - commercial153 133 163 72 68 86 81 65 77 
Retail - industrial13 11 16 7 7 11 6 4 5 
Transportation/other53 46 45 31 27 27 22 19 18 
Total Gas Utility525 465 540 265 250 300 260 215 240 
Other Utility:
Steam37 40 45 37 40 45 — — — 
Other utility14 14 7 10 9 4 4 5 3 
Total Other Utility51 54 52 47 49 49 4 5 3 
Non-Utility and Other:
Travero and other89 90 90 — — — — — — 
Total Non-Utility and Other89 90 90 — — — — — — 
Total revenues$4,362 $3,981 $4,027 $2,208 $2,046 $2,110 $2,065 $1,845 $1,827 
IPL [Member]  
Disaggregation of Revenue [Line Items]  
Revenues REVENUES
Revenues from Alliant Energy’s, IPL’s and WPL’s utility businesses are primarily from electric and gas sales provided to customers based on approved tariffs or specific contracts with customers. IPL’s and WPL’s primary performance obligations under such arrangements are to deliver electricity and gas, and their customers simultaneously receive and consume the electricity and gas. For such arrangements, revenues are recognized equivalent to the value of the electricity or gas supplied during each period, including amounts billed during each period and changes in amounts estimated to be billed at the end of each period. IPL and WPL apply the right to invoice method to measure progress towards completing performance obligations to transfer electricity and gas to their customers.

IPL provides retail electric and gas service to customers in Iowa, and WPL provides retail and wholesale electric and retail gas service to customers in Wisconsin. IPL also provides electricity to wholesale customers in Illinois and Iowa. IPL’s wholesale power agreement with Southern Minnesota Energy Cooperative expired in July 2025. IPL provided steam from its Prairie Creek Generating Station to high-pressure steam customers in Iowa through 2025.

IPL’s and WPL’s retail electric and gas revenues include sales to residential, commercial and industrial customers. IPL’s and WPL’s retail electric and gas customer prices are based on IPL’s and WPL’s cost of service and are determined through general rate review proceedings and various tariff filings with the IUC and PSCW, respectively. Such tariff-based services provide electricity or gas to customers without a defined contractual term.

IPL and WPL have wholesale electric market-based rate authority from FERC allowing them to participate in wholesale energy markets (e.g. MISO) and transact directly with third parties. This authority from FERC allows sales of electricity referred to as bulk power sales based on current market values. FERC also allows IPL and WPL to enter into power supply agreements with municipalities and rural electric cooperatives with defined contractual terms, which include standard pricing mechanisms that are detailed in current tariffs accepted by FERC through wholesale rate review proceedings.

Revenues from Alliant Energy’s non-utility business customers are primarily from its Travero business, which includes a short-line rail freight service in Iowa; a Mississippi River barge, rail and truck freight terminal in Illinois; freight brokerage services; and a rail-served warehouse in Iowa.
Disaggregation of revenues from contracts with customers is provided for each reportable segment (IPL and WPL), as well as by customer class within electric and gas sales, as follows (in millions):
Alliant EnergyIPLWPL
202520242023202520242023202520242023
Electric Utility:
Retail - residential$1,339 $1,236 $1,220 $661 $640 $641 $678 $596 $579 
Retail - commercial932 821 820 609 525 519 323 296 301 
Retail - industrial1,034 952 968 531 497 501 503 455 467 
Wholesale184 200 213 39 61 62 145 139 151 
Bulk power and other208 163 124 56 24 38 152 139 86 
Total Electric Utility3,697 3,372 3,345 1,896 1,747 1,761 1,801 1,625 1,584 
Gas Utility:
Retail - residential306 275 316 155 148 176 151 127 140 
Retail - commercial153 133 163 72 68 86 81 65 77 
Retail - industrial13 11 16 7 7 11 6 4 5 
Transportation/other53 46 45 31 27 27 22 19 18 
Total Gas Utility525 465 540 265 250 300 260 215 240 
Other Utility:
Steam37 40 45 37 40 45 — — — 
Other utility14 14 7 10 9 4 4 5 3 
Total Other Utility51 54 52 47 49 49 4 5 3 
Non-Utility and Other:
Travero and other89 90 90 — — — — — — 
Total Non-Utility and Other89 90 90 — — — — — — 
Total revenues$4,362 $3,981 $4,027 $2,208 $2,046 $2,110 $2,065 $1,845 $1,827 
WPL [Member]  
Disaggregation of Revenue [Line Items]  
Revenues REVENUES
Revenues from Alliant Energy’s, IPL’s and WPL’s utility businesses are primarily from electric and gas sales provided to customers based on approved tariffs or specific contracts with customers. IPL’s and WPL’s primary performance obligations under such arrangements are to deliver electricity and gas, and their customers simultaneously receive and consume the electricity and gas. For such arrangements, revenues are recognized equivalent to the value of the electricity or gas supplied during each period, including amounts billed during each period and changes in amounts estimated to be billed at the end of each period. IPL and WPL apply the right to invoice method to measure progress towards completing performance obligations to transfer electricity and gas to their customers.

IPL provides retail electric and gas service to customers in Iowa, and WPL provides retail and wholesale electric and retail gas service to customers in Wisconsin. IPL also provides electricity to wholesale customers in Illinois and Iowa. IPL’s wholesale power agreement with Southern Minnesota Energy Cooperative expired in July 2025. IPL provided steam from its Prairie Creek Generating Station to high-pressure steam customers in Iowa through 2025.

IPL’s and WPL’s retail electric and gas revenues include sales to residential, commercial and industrial customers. IPL’s and WPL’s retail electric and gas customer prices are based on IPL’s and WPL’s cost of service and are determined through general rate review proceedings and various tariff filings with the IUC and PSCW, respectively. Such tariff-based services provide electricity or gas to customers without a defined contractual term.

IPL and WPL have wholesale electric market-based rate authority from FERC allowing them to participate in wholesale energy markets (e.g. MISO) and transact directly with third parties. This authority from FERC allows sales of electricity referred to as bulk power sales based on current market values. FERC also allows IPL and WPL to enter into power supply agreements with municipalities and rural electric cooperatives with defined contractual terms, which include standard pricing mechanisms that are detailed in current tariffs accepted by FERC through wholesale rate review proceedings.

Revenues from Alliant Energy’s non-utility business customers are primarily from its Travero business, which includes a short-line rail freight service in Iowa; a Mississippi River barge, rail and truck freight terminal in Illinois; freight brokerage services; and a rail-served warehouse in Iowa.
Disaggregation of revenues from contracts with customers is provided for each reportable segment (IPL and WPL), as well as by customer class within electric and gas sales, as follows (in millions):
Alliant EnergyIPLWPL
202520242023202520242023202520242023
Electric Utility:
Retail - residential$1,339 $1,236 $1,220 $661 $640 $641 $678 $596 $579 
Retail - commercial932 821 820 609 525 519 323 296 301 
Retail - industrial1,034 952 968 531 497 501 503 455 467 
Wholesale184 200 213 39 61 62 145 139 151 
Bulk power and other208 163 124 56 24 38 152 139 86 
Total Electric Utility3,697 3,372 3,345 1,896 1,747 1,761 1,801 1,625 1,584 
Gas Utility:
Retail - residential306 275 316 155 148 176 151 127 140 
Retail - commercial153 133 163 72 68 86 81 65 77 
Retail - industrial13 11 16 7 7 11 6 4 5 
Transportation/other53 46 45 31 27 27 22 19 18 
Total Gas Utility525 465 540 265 250 300 260 215 240 
Other Utility:
Steam37 40 45 37 40 45 — — — 
Other utility14 14 7 10 9 4 4 5 3 
Total Other Utility51 54 52 47 49 49 4 5 3 
Non-Utility and Other:
Travero and other89 90 90 — — — — — — 
Total Non-Utility and Other89 90 90 — — — — — — 
Total revenues$4,362 $3,981 $4,027 $2,208 $2,046 $2,110 $2,065 $1,845 $1,827 
v3.25.4
Income Taxes
 12 Months Ended
Dec. 31, 2025
Income Tax [Line Items]  
Income Taxes INCOME TAXES
Income Tax Expense (Benefit) - The components of “Income tax expense (benefit)” in the income statements were as follows (in millions):
Alliant EnergyIPLWPL
202520242023202520242023202520242023
Current tax expense (benefit):
Federal$10$13($3)($21)($19)($44)$38$37$48
State(1)(10)(6)(10)(19)(21)182325
Deferred tax expense (benefit):
Federal5960100363887302410
State3315362(17)171673
Production tax credits(208)(177)(121)(133)(108)(95)(75)(69)(26)
Investment tax credits(42)(15)(1)(1)(4)(1)(41)(11)—
Provision recorded as a change in accrued interest——(1)——(1)———
($149)($114)$4($127)($129)($58)($14)$11$60

Income Tax Rates - The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income before income taxes. In 2024, Alliant Energy’s and IPL’s effective income tax rates were impacted by the pre-tax non-cash charge of $60 million for IPL’s Lansing Generating Station discussed in Note 2. In the fourth quarter of 2025, Alliant Energy, IPL and WPL retrospectively adopted the Financial Accounting Standards Board’s (FASB) accounting standard for improvements to income tax disclosures. Previously reported information for prior periods has been recast to conform with current period presentation.
Alliant Energy202520242023
AmountTax RateAmountTax RateAmountTax Rate
Statutory federal income tax rate$139 21%$121 21%$149 21%
State income taxes, net of federal benefits (primarily from state income taxes in Iowa and Wisconsin)22341213
Tax credits:
Production tax credits(206)(31)(171)(30)(121)(17)
Investment tax credits(156)(24)(42)(7)(3)—
Research and development credits(2)—(6)(1)——
Tax credit regulatory deferrals (Refer to Note 1(c) and Note 2)
112172032—
Other credits(1)—————
Nontaxable or nondeductible items412—(2)—
Other adjustments:
Effect of rate-making on property-related differences (Refer to Note 1(c) and Note 2)
(37)(6)(33)(6)(27)(4)
Amortization of excess deferred taxes (Refer to Note 2)
(24)(4)(13)(2)(13)(2)
Other ——41(2)—
Total income tax expense (benefit) and overall income tax rate($149)(23%)($114)(20%)$41%
IPL202520242023
AmountTax RateAmountTax RateAmountTax Rate
Statutory federal income tax rate$69 21%$49 21%$65 21%
State income taxes, net of federal benefits (primarily from state income taxes in Iowa)(10)(3)(27)(12)(5)(2)
Tax credits:
Production tax credits(133)(40)(108)(46)(95)(31)
Investment tax credits(43)(13)(8)(4)(2)(1)
Tax credit regulatory deferrals (Refer to Note 1(c) and Note 2)
4213411—
Other credits(1)—(1)———
Nontaxable or nondeductible items1—(1)—(1)—
Other adjustments:
Effect of rate-making on property-related differences (Refer to Note 1(c) and Note 2)
(30)(9)(24)(10)(16)(5)
Amortization of excess deferred taxes (Refer to Note 2)
(22)(7)(13)(5)(5)(1)
Total income tax expense (benefit) and overall income tax rate($127)(38%)($129)(55%)($58)(19%)
WPL202520242023
AmountTax RateAmountTax RateAmountTax Rate
Statutory federal income tax rate$81 21%$75 21%$85 21%
State income taxes, net of federal benefits (primarily from state income taxes in Wisconsin)277237225
Tax credits:
Production tax credits(73)(19)(63)(18)(26)(6)
Investment tax credits(114)(29)(34)(10)(1)—
Tax credit regulatory deferrals (Refer to Note 1(c) and Note 2)
70181741—
Other credits——(1)———
Nontaxable or nondeductible items1—(1)—(2)—
Other adjustments:
Effect of rate-making on property-related differences (Refer to Note 1(c) and Note 2)
(6)(2)(5)(1)(12)(4)
Amortization of excess deferred taxes (Refer to Note 2)
————(7)(1)
Total income tax expense (benefit) and overall income tax rate($14)(4%)$11 3%$60 15%

Deferred Tax Assets and Liabilities - The deferred tax assets and liabilities included on the balance sheets at December 31 arise from the following temporary differences (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Deferred tax liabilities:
Property$2,828 $2,596 $1,666 $1,521 $1,060 $999 
ATC Holdings139 135 — — — — 
Other167 178 112 120 62 66 
Total deferred tax liabilities3,134 2,909 1,778 1,641 1,122 1,065 
Deferred tax assets:
Federal credit carryforwards669 605 455 426 199 166 
Net operating losses carryforwards - state19 20 1 1 — — 
Other143 98 48 37 65 34 
Subtotal deferred tax assets831 723 504 464 264 200 
Valuation allowances(7)(2)(4)(2)(3)— 
Total deferred tax assets824 721 500 462 261 200 
Total deferred tax liabilities, net$2,310 $2,188 $1,278 $1,179 $861 $865 

Carryforwards - At December 31, 2025, carryforwards and expiration dates were estimated as follows (in millions):
Range of Expiration DatesAlliant EnergyIPLWPL
State net operating losses2025-2045$311$7$1
Federal tax credits2034-2045669455199

State Income Tax Apportionment - Deferred tax assets and liabilities are recorded for temporary differences between the tax basis of assets and liabilities and the amounts reported in the financial statements. Deferred taxes are recorded using currently enacted tax rates and estimates of state income tax apportionment. Estimates of state income tax apportionment are supported by historical data and reasonable projections. Alliant Energy currently expects an increase in total state income tax apportionment primarily due to an increase in projected electric utility revenues driven by demand for energy from commercial and industrial customers, including demand from IPL’s and WPL’s executed electric service agreements with customers who expect to build data centers in their service territories. Alliant Energy parent company’s deferred tax assets were remeasured to reflect an increase in estimated total state income tax apportionment, which resulted in a charge of $8 million recorded to income tax expense in Alliant Energy’s income statement and an increase in deferred tax liabilities on Alliant Energy’s balance sheet in 2025.

Uncertain Tax Positions - At December 31, 2025, 2024 and 2023, there were no uncertain tax positions or penalties accrued related to uncertain tax positions. As of December 31, 2025, no material changes to unrecognized tax benefits are expected during the next 12 months.
Open tax years - Tax years that remain subject to the statute of limitations in the major jurisdictions for each of Alliant Energy, IPL and WPL are as follows:
Consolidated federal income tax returns (a)2022-2024
Consolidated Iowa income tax returns (b)2022-2024
Wisconsin combined tax returns (c)2021-2024

(a)The 2022 federal tax return is effectively settled as a result of participation in the IRS Compliance Assurance Program, which allows Alliant Energy and the IRS to work together to resolve issues related to Alliant Energy’s current tax year before filing its federal income tax return. The statute of limitations for these federal tax returns expires three years from each filing date.
(b)The statute of limitations for these Iowa tax returns expires three years from each filing date.
(c)The statute of limitations for these Wisconsin combined tax returns expires four years from each filing date.

Iowa Tax Reform - Pursuant to Iowa tax reform enacted in 2022, annually, and by each November 1, the Iowa Department of Revenue will establish corporate income tax rates for the next tax year based on net corporate income tax receipts for the prior tax year, and reduce such rates if the minimum receipt threshold is met. These corporate income tax rate reductions are currently expected to occur over a period of several years, with a target corporate income tax rate of 5.5%, compared to the 9.8% Iowa corporate income tax rate in effect at the time the Iowa tax reform was enacted. In 2023, the Iowa Department of Revenue announced an Iowa corporate income tax rate of 7.1% effective January 1, 2024.

Deferred tax assets and liabilities are measured at the enacted tax rate expected to be applied when temporary differences are to be realized or settled. Given the announcement of the new Iowa corporate income tax rate, Alliant Energy’s and IPL’s deferred tax liabilities were remeasured in 2023 based upon the new rate effective January 1, 2024, which resulted in a $74 million reduction of Alliant Energy’s and IPL’s tax-related regulatory assets and a corresponding decrease in their deferred tax liabilities in 2023. In addition, Iowa tax reform made Iowa state income taxes fully deductible for the purpose of determining Iowa state income tax obligations beginning with the 2023 tax year. Alliant Energy reflected the deduction of the additional Iowa state income taxes in its 2023 Iowa state income tax return filed in 2024, which resulted in a $26 million reduction of Alliant Energy’s and IPL’s tax-related regulatory assets and a corresponding decrease in their deferred tax liabilities in 2024. The reductions in tax-related regulatory assets are expected to provide cost benefits to IPL’s customers in the future.

Alliant Energy parent company’s deferred tax assets were remeasured based upon the new rate effective January 1, 2024, and the deduction of Iowa state income taxes included in Alliant Energy’s 2023 Iowa state income tax return filed in 2024, which resulted in charges of $10 million and $11 million recorded to income tax expense in Alliant Energy’s income statements and an increase in deferred income tax liabilities on Alliant Energy’s balance sheets in 2023 and 2024, respectively. Alliant Energy is currently unable to predict with certainty the timing or amount of any future rate reductions.
IPL [Member]  
Income Tax [Line Items]  
Income Taxes INCOME TAXES
Income Tax Expense (Benefit) - The components of “Income tax expense (benefit)” in the income statements were as follows (in millions):
Alliant EnergyIPLWPL
202520242023202520242023202520242023
Current tax expense (benefit):
Federal$10$13($3)($21)($19)($44)$38$37$48
State(1)(10)(6)(10)(19)(21)182325
Deferred tax expense (benefit):
Federal5960100363887302410
State3315362(17)171673
Production tax credits(208)(177)(121)(133)(108)(95)(75)(69)(26)
Investment tax credits(42)(15)(1)(1)(4)(1)(41)(11)—
Provision recorded as a change in accrued interest——(1)——(1)———
($149)($114)$4($127)($129)($58)($14)$11$60

Income Tax Rates - The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income before income taxes. In 2024, Alliant Energy’s and IPL’s effective income tax rates were impacted by the pre-tax non-cash charge of $60 million for IPL’s Lansing Generating Station discussed in Note 2. In the fourth quarter of 2025, Alliant Energy, IPL and WPL retrospectively adopted the Financial Accounting Standards Board’s (FASB) accounting standard for improvements to income tax disclosures. Previously reported information for prior periods has been recast to conform with current period presentation.
Alliant Energy202520242023
AmountTax RateAmountTax RateAmountTax Rate
Statutory federal income tax rate$139 21%$121 21%$149 21%
State income taxes, net of federal benefits (primarily from state income taxes in Iowa and Wisconsin)22341213
Tax credits:
Production tax credits(206)(31)(171)(30)(121)(17)
Investment tax credits(156)(24)(42)(7)(3)—
Research and development credits(2)—(6)(1)——
Tax credit regulatory deferrals (Refer to Note 1(c) and Note 2)
112172032—
Other credits(1)—————
Nontaxable or nondeductible items412—(2)—
Other adjustments:
Effect of rate-making on property-related differences (Refer to Note 1(c) and Note 2)
(37)(6)(33)(6)(27)(4)
Amortization of excess deferred taxes (Refer to Note 2)
(24)(4)(13)(2)(13)(2)
Other ——41(2)—
Total income tax expense (benefit) and overall income tax rate($149)(23%)($114)(20%)$41%
IPL202520242023
AmountTax RateAmountTax RateAmountTax Rate
Statutory federal income tax rate$69 21%$49 21%$65 21%
State income taxes, net of federal benefits (primarily from state income taxes in Iowa)(10)(3)(27)(12)(5)(2)
Tax credits:
Production tax credits(133)(40)(108)(46)(95)(31)
Investment tax credits(43)(13)(8)(4)(2)(1)
Tax credit regulatory deferrals (Refer to Note 1(c) and Note 2)
4213411—
Other credits(1)—(1)———
Nontaxable or nondeductible items1—(1)—(1)—
Other adjustments:
Effect of rate-making on property-related differences (Refer to Note 1(c) and Note 2)
(30)(9)(24)(10)(16)(5)
Amortization of excess deferred taxes (Refer to Note 2)
(22)(7)(13)(5)(5)(1)
Total income tax expense (benefit) and overall income tax rate($127)(38%)($129)(55%)($58)(19%)
WPL202520242023
AmountTax RateAmountTax RateAmountTax Rate
Statutory federal income tax rate$81 21%$75 21%$85 21%
State income taxes, net of federal benefits (primarily from state income taxes in Wisconsin)277237225
Tax credits:
Production tax credits(73)(19)(63)(18)(26)(6)
Investment tax credits(114)(29)(34)(10)(1)—
Tax credit regulatory deferrals (Refer to Note 1(c) and Note 2)
70181741—
Other credits——(1)———
Nontaxable or nondeductible items1—(1)—(2)—
Other adjustments:
Effect of rate-making on property-related differences (Refer to Note 1(c) and Note 2)
(6)(2)(5)(1)(12)(4)
Amortization of excess deferred taxes (Refer to Note 2)
————(7)(1)
Total income tax expense (benefit) and overall income tax rate($14)(4%)$11 3%$60 15%

Deferred Tax Assets and Liabilities - The deferred tax assets and liabilities included on the balance sheets at December 31 arise from the following temporary differences (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Deferred tax liabilities:
Property$2,828 $2,596 $1,666 $1,521 $1,060 $999 
ATC Holdings139 135 — — — — 
Other167 178 112 120 62 66 
Total deferred tax liabilities3,134 2,909 1,778 1,641 1,122 1,065 
Deferred tax assets:
Federal credit carryforwards669 605 455 426 199 166 
Net operating losses carryforwards - state19 20 1 1 — — 
Other143 98 48 37 65 34 
Subtotal deferred tax assets831 723 504 464 264 200 
Valuation allowances(7)(2)(4)(2)(3)— 
Total deferred tax assets824 721 500 462 261 200 
Total deferred tax liabilities, net$2,310 $2,188 $1,278 $1,179 $861 $865 

Carryforwards - At December 31, 2025, carryforwards and expiration dates were estimated as follows (in millions):
Range of Expiration DatesAlliant EnergyIPLWPL
State net operating losses2025-2045$311$7$1
Federal tax credits2034-2045669455199

State Income Tax Apportionment - Deferred tax assets and liabilities are recorded for temporary differences between the tax basis of assets and liabilities and the amounts reported in the financial statements. Deferred taxes are recorded using currently enacted tax rates and estimates of state income tax apportionment. Estimates of state income tax apportionment are supported by historical data and reasonable projections. Alliant Energy currently expects an increase in total state income tax apportionment primarily due to an increase in projected electric utility revenues driven by demand for energy from commercial and industrial customers, including demand from IPL’s and WPL’s executed electric service agreements with customers who expect to build data centers in their service territories. Alliant Energy parent company’s deferred tax assets were remeasured to reflect an increase in estimated total state income tax apportionment, which resulted in a charge of $8 million recorded to income tax expense in Alliant Energy’s income statement and an increase in deferred tax liabilities on Alliant Energy’s balance sheet in 2025.

Uncertain Tax Positions - At December 31, 2025, 2024 and 2023, there were no uncertain tax positions or penalties accrued related to uncertain tax positions. As of December 31, 2025, no material changes to unrecognized tax benefits are expected during the next 12 months.
Open tax years - Tax years that remain subject to the statute of limitations in the major jurisdictions for each of Alliant Energy, IPL and WPL are as follows:
Consolidated federal income tax returns (a)2022-2024
Consolidated Iowa income tax returns (b)2022-2024
Wisconsin combined tax returns (c)2021-2024

(a)The 2022 federal tax return is effectively settled as a result of participation in the IRS Compliance Assurance Program, which allows Alliant Energy and the IRS to work together to resolve issues related to Alliant Energy’s current tax year before filing its federal income tax return. The statute of limitations for these federal tax returns expires three years from each filing date.
(b)The statute of limitations for these Iowa tax returns expires three years from each filing date.
(c)The statute of limitations for these Wisconsin combined tax returns expires four years from each filing date.

Iowa Tax Reform - Pursuant to Iowa tax reform enacted in 2022, annually, and by each November 1, the Iowa Department of Revenue will establish corporate income tax rates for the next tax year based on net corporate income tax receipts for the prior tax year, and reduce such rates if the minimum receipt threshold is met. These corporate income tax rate reductions are currently expected to occur over a period of several years, with a target corporate income tax rate of 5.5%, compared to the 9.8% Iowa corporate income tax rate in effect at the time the Iowa tax reform was enacted. In 2023, the Iowa Department of Revenue announced an Iowa corporate income tax rate of 7.1% effective January 1, 2024.

Deferred tax assets and liabilities are measured at the enacted tax rate expected to be applied when temporary differences are to be realized or settled. Given the announcement of the new Iowa corporate income tax rate, Alliant Energy’s and IPL’s deferred tax liabilities were remeasured in 2023 based upon the new rate effective January 1, 2024, which resulted in a $74 million reduction of Alliant Energy’s and IPL’s tax-related regulatory assets and a corresponding decrease in their deferred tax liabilities in 2023. In addition, Iowa tax reform made Iowa state income taxes fully deductible for the purpose of determining Iowa state income tax obligations beginning with the 2023 tax year. Alliant Energy reflected the deduction of the additional Iowa state income taxes in its 2023 Iowa state income tax return filed in 2024, which resulted in a $26 million reduction of Alliant Energy’s and IPL’s tax-related regulatory assets and a corresponding decrease in their deferred tax liabilities in 2024. The reductions in tax-related regulatory assets are expected to provide cost benefits to IPL’s customers in the future.

Alliant Energy parent company’s deferred tax assets were remeasured based upon the new rate effective January 1, 2024, and the deduction of Iowa state income taxes included in Alliant Energy’s 2023 Iowa state income tax return filed in 2024, which resulted in charges of $10 million and $11 million recorded to income tax expense in Alliant Energy’s income statements and an increase in deferred income tax liabilities on Alliant Energy’s balance sheets in 2023 and 2024, respectively. Alliant Energy is currently unable to predict with certainty the timing or amount of any future rate reductions.
WPL [Member]  
Income Tax [Line Items]  
Income Taxes INCOME TAXES
Income Tax Expense (Benefit) - The components of “Income tax expense (benefit)” in the income statements were as follows (in millions):
Alliant EnergyIPLWPL
202520242023202520242023202520242023
Current tax expense (benefit):
Federal$10$13($3)($21)($19)($44)$38$37$48
State(1)(10)(6)(10)(19)(21)182325
Deferred tax expense (benefit):
Federal5960100363887302410
State3315362(17)171673
Production tax credits(208)(177)(121)(133)(108)(95)(75)(69)(26)
Investment tax credits(42)(15)(1)(1)(4)(1)(41)(11)—
Provision recorded as a change in accrued interest——(1)——(1)———
($149)($114)$4($127)($129)($58)($14)$11$60

Income Tax Rates - The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income before income taxes. In 2024, Alliant Energy’s and IPL’s effective income tax rates were impacted by the pre-tax non-cash charge of $60 million for IPL’s Lansing Generating Station discussed in Note 2. In the fourth quarter of 2025, Alliant Energy, IPL and WPL retrospectively adopted the Financial Accounting Standards Board’s (FASB) accounting standard for improvements to income tax disclosures. Previously reported information for prior periods has been recast to conform with current period presentation.
Alliant Energy202520242023
AmountTax RateAmountTax RateAmountTax Rate
Statutory federal income tax rate$139 21%$121 21%$149 21%
State income taxes, net of federal benefits (primarily from state income taxes in Iowa and Wisconsin)22341213
Tax credits:
Production tax credits(206)(31)(171)(30)(121)(17)
Investment tax credits(156)(24)(42)(7)(3)—
Research and development credits(2)—(6)(1)——
Tax credit regulatory deferrals (Refer to Note 1(c) and Note 2)
112172032—
Other credits(1)—————
Nontaxable or nondeductible items412—(2)—
Other adjustments:
Effect of rate-making on property-related differences (Refer to Note 1(c) and Note 2)
(37)(6)(33)(6)(27)(4)
Amortization of excess deferred taxes (Refer to Note 2)
(24)(4)(13)(2)(13)(2)
Other ——41(2)—
Total income tax expense (benefit) and overall income tax rate($149)(23%)($114)(20%)$41%
IPL202520242023
AmountTax RateAmountTax RateAmountTax Rate
Statutory federal income tax rate$69 21%$49 21%$65 21%
State income taxes, net of federal benefits (primarily from state income taxes in Iowa)(10)(3)(27)(12)(5)(2)
Tax credits:
Production tax credits(133)(40)(108)(46)(95)(31)
Investment tax credits(43)(13)(8)(4)(2)(1)
Tax credit regulatory deferrals (Refer to Note 1(c) and Note 2)
4213411—
Other credits(1)—(1)———
Nontaxable or nondeductible items1—(1)—(1)—
Other adjustments:
Effect of rate-making on property-related differences (Refer to Note 1(c) and Note 2)
(30)(9)(24)(10)(16)(5)
Amortization of excess deferred taxes (Refer to Note 2)
(22)(7)(13)(5)(5)(1)
Total income tax expense (benefit) and overall income tax rate($127)(38%)($129)(55%)($58)(19%)
WPL202520242023
AmountTax RateAmountTax RateAmountTax Rate
Statutory federal income tax rate$81 21%$75 21%$85 21%
State income taxes, net of federal benefits (primarily from state income taxes in Wisconsin)277237225
Tax credits:
Production tax credits(73)(19)(63)(18)(26)(6)
Investment tax credits(114)(29)(34)(10)(1)—
Tax credit regulatory deferrals (Refer to Note 1(c) and Note 2)
70181741—
Other credits——(1)———
Nontaxable or nondeductible items1—(1)—(2)—
Other adjustments:
Effect of rate-making on property-related differences (Refer to Note 1(c) and Note 2)
(6)(2)(5)(1)(12)(4)
Amortization of excess deferred taxes (Refer to Note 2)
————(7)(1)
Total income tax expense (benefit) and overall income tax rate($14)(4%)$11 3%$60 15%

Deferred Tax Assets and Liabilities - The deferred tax assets and liabilities included on the balance sheets at December 31 arise from the following temporary differences (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Deferred tax liabilities:
Property$2,828 $2,596 $1,666 $1,521 $1,060 $999 
ATC Holdings139 135 — — — — 
Other167 178 112 120 62 66 
Total deferred tax liabilities3,134 2,909 1,778 1,641 1,122 1,065 
Deferred tax assets:
Federal credit carryforwards669 605 455 426 199 166 
Net operating losses carryforwards - state19 20 1 1 — — 
Other143 98 48 37 65 34 
Subtotal deferred tax assets831 723 504 464 264 200 
Valuation allowances(7)(2)(4)(2)(3)— 
Total deferred tax assets824 721 500 462 261 200 
Total deferred tax liabilities, net$2,310 $2,188 $1,278 $1,179 $861 $865 

Carryforwards - At December 31, 2025, carryforwards and expiration dates were estimated as follows (in millions):
Range of Expiration DatesAlliant EnergyIPLWPL
State net operating losses2025-2045$311$7$1
Federal tax credits2034-2045669455199

State Income Tax Apportionment - Deferred tax assets and liabilities are recorded for temporary differences between the tax basis of assets and liabilities and the amounts reported in the financial statements. Deferred taxes are recorded using currently enacted tax rates and estimates of state income tax apportionment. Estimates of state income tax apportionment are supported by historical data and reasonable projections. Alliant Energy currently expects an increase in total state income tax apportionment primarily due to an increase in projected electric utility revenues driven by demand for energy from commercial and industrial customers, including demand from IPL’s and WPL’s executed electric service agreements with customers who expect to build data centers in their service territories. Alliant Energy parent company’s deferred tax assets were remeasured to reflect an increase in estimated total state income tax apportionment, which resulted in a charge of $8 million recorded to income tax expense in Alliant Energy’s income statement and an increase in deferred tax liabilities on Alliant Energy’s balance sheet in 2025.

Uncertain Tax Positions - At December 31, 2025, 2024 and 2023, there were no uncertain tax positions or penalties accrued related to uncertain tax positions. As of December 31, 2025, no material changes to unrecognized tax benefits are expected during the next 12 months.
Open tax years - Tax years that remain subject to the statute of limitations in the major jurisdictions for each of Alliant Energy, IPL and WPL are as follows:
Consolidated federal income tax returns (a)2022-2024
Consolidated Iowa income tax returns (b)2022-2024
Wisconsin combined tax returns (c)2021-2024

(a)The 2022 federal tax return is effectively settled as a result of participation in the IRS Compliance Assurance Program, which allows Alliant Energy and the IRS to work together to resolve issues related to Alliant Energy’s current tax year before filing its federal income tax return. The statute of limitations for these federal tax returns expires three years from each filing date.
(b)The statute of limitations for these Iowa tax returns expires three years from each filing date.
(c)The statute of limitations for these Wisconsin combined tax returns expires four years from each filing date.

Iowa Tax Reform - Pursuant to Iowa tax reform enacted in 2022, annually, and by each November 1, the Iowa Department of Revenue will establish corporate income tax rates for the next tax year based on net corporate income tax receipts for the prior tax year, and reduce such rates if the minimum receipt threshold is met. These corporate income tax rate reductions are currently expected to occur over a period of several years, with a target corporate income tax rate of 5.5%, compared to the 9.8% Iowa corporate income tax rate in effect at the time the Iowa tax reform was enacted. In 2023, the Iowa Department of Revenue announced an Iowa corporate income tax rate of 7.1% effective January 1, 2024.

Deferred tax assets and liabilities are measured at the enacted tax rate expected to be applied when temporary differences are to be realized or settled. Given the announcement of the new Iowa corporate income tax rate, Alliant Energy’s and IPL’s deferred tax liabilities were remeasured in 2023 based upon the new rate effective January 1, 2024, which resulted in a $74 million reduction of Alliant Energy’s and IPL’s tax-related regulatory assets and a corresponding decrease in their deferred tax liabilities in 2023. In addition, Iowa tax reform made Iowa state income taxes fully deductible for the purpose of determining Iowa state income tax obligations beginning with the 2023 tax year. Alliant Energy reflected the deduction of the additional Iowa state income taxes in its 2023 Iowa state income tax return filed in 2024, which resulted in a $26 million reduction of Alliant Energy’s and IPL’s tax-related regulatory assets and a corresponding decrease in their deferred tax liabilities in 2024. The reductions in tax-related regulatory assets are expected to provide cost benefits to IPL’s customers in the future.

Alliant Energy parent company’s deferred tax assets were remeasured based upon the new rate effective January 1, 2024, and the deduction of Iowa state income taxes included in Alliant Energy’s 2023 Iowa state income tax return filed in 2024, which resulted in charges of $10 million and $11 million recorded to income tax expense in Alliant Energy’s income statements and an increase in deferred income tax liabilities on Alliant Energy’s balance sheets in 2023 and 2024, respectively. Alliant Energy is currently unable to predict with certainty the timing or amount of any future rate reductions.
v3.25.4
Benefit Plans
 12 Months Ended
Dec. 31, 2025
Statement [Line Items]  
Benefit Plans BENEFIT PLANS(a) Pension and Other Postretirement Benefits Plans - Retirement benefits are provided to substantially all employees through various qualified and non-qualified non-contributory defined benefit pension plans (currently closed to new hires), and/or through defined contribution plans (including 401(k) savings plans). Benefits of the non-contributory defined benefit pension plans are based on the plan participant’s years of service, age and compensation. Benefits of the defined contribution plans are based on the plan participant’s years of service, age, compensation and contributions. Certain defined benefit postretirement health care and life benefits are provided to eligible retirees. In general, the retiree health care plans consist of fixed benefit subsidy structures and the retiree life insurance plans are non-contributory.
IPL and WPL account for their participation in Alliant Energy and Corporate Services sponsored plans as multiple-employer plans. For IPL and WPL, amounts below represent the amounts for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans.

Assumptions - The weighted-average assumptions for defined benefit pension and OPEB plans at the measurement date of December 31 were as follows:
Defined Benefit Pension PlansOPEB Plans
Alliant Energy202520242023202520242023
Discount rate for benefit obligations5.52%5.65%5.36%5.40%5.62%5.40%
Discount rate for net periodic cost5.65%5.36%5.54%5.62%5.40%5.53%
Expected rate of return on plan assets7.60%7.73%7.80%6.37%6.22%6.50%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan5.60%6.24%10.75%N/AN/AN/A
Rate of compensation increase3.75%-4.50%3.50%-4.50%3.30%-4.50%N/AN/AN/A
Qualified Defined Benefit Pension PlanOPEB Plans
IPL202520242023202520242023
Discount rate for benefit obligations5.56%5.66%5.35%5.38%5.61%5.40%
Discount rate for net periodic cost5.66%5.35%5.55%5.61%5.40%5.53%
Expected rate of return on plan assets7.60%7.60%7.80%6.70%6.60%6.90%
Rate of compensation increase4.00%3.75%3.30%N/AN/AN/A
Qualified Defined Benefit Pension PlanOPEB Plans
WPL202520242023202520242023
Discount rate for benefit obligations5.56%5.66%5.35%5.38%5.61%5.40%
Discount rate for net periodic cost5.66%5.35%5.54%5.61%5.40%5.53%
Expected rate of return on plan assets7.60%7.80%7.80%5.75%5.61%5.65%
Rate of compensation increase3.75%3.50%3.30%N/AN/AN/A

Expected rate of return on plan assets - The expected rate of return on plan assets is based on projected asset class returns using target allocations. A forward-looking building blocks approach is used, and historical returns, survey information and capital market information are analyzed to support the expected rate of return on plan assets assumption. Refer to “Investment Strategy for Plan Assets” below for additional information related to investment strategy and mix of assets for the pension and OPEB plans.

Life Expectancy - The life expectancy assumption is used in determining the benefit obligation and net periodic benefit cost for defined benefit pension and OPEB plans. This assumption utilizes base mortality tables that were released in 2019 by the Society of Actuaries and mortality projection tables that were released in 2021 by the Society of Actuaries.

Net Periodic Benefit Costs - The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans are included below (in millions). The service cost component of net periodic benefit costs is included in “Other operation and maintenance” expenses in the income statements and all other components of net periodic benefit costs are included in “Other (income) and deductions” in the income statements or regulatory assets on the balance sheets.
Alliant EnergyDefined Benefit Pension PlansOPEB Plans
202520242023202520242023
Service cost$4 $5 $5 $1 $2 $2 
Interest cost46 45 47 8 8 9 
Expected return on plan assets (a)(53)(55)(53)(4)(5)(5)
Amortization of prior service credit (b)— (1)(1)— — — 
Amortization of actuarial loss (c)22 24 28 — — 1 
$19 $18 $26 $5 $5 $7 
IPLDefined Benefit Pension PlansOPEB Plans
202520242023202520242023
Service cost$3 $3 $3 $1 $1 $1 
Interest cost20 20 21 3 3 3 
Expected return on plan assets (a)(25)(26)(26)(4)(4)(3)
Amortization of actuarial loss (c)9 9 11 — — 1 
$7 $6 $9 $— $— $2 
WPLDefined Benefit Pension PlansOPEB Plans
202520242023202520242023
Service cost$1 $2 $2 $1 $1 $1 
Interest cost20 20 20 3 3 3 
Expected return on plan assets (a)(23)(23)(22)(1)(1)(1)
Amortization of actuarial loss (c)11 11 13 — — 1 
$9 $10 $13 $3 $3 $4 

(a)The expected return on plan assets is based on the expected rate of return on plan assets and the fair value approach to the market-related value of plan assets.
(b)Unrecognized prior service credits for the OPEB plans are amortized over the average future service period to full eligibility of the participants of each plan.
(c)Unrecognized net actuarial gains or losses in excess of 10% of the greater of the plans’ benefit obligations or assets are amortized over the average future service lives of plan participants, except for the Alliant Energy Cash Balance Pension Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits.
Benefit Plan Assets and Obligations - A reconciliation of the funded status of qualified and non-qualified defined benefit pension and OPEB plans to the amounts recognized on the balance sheets at December 31 was as follows (in millions):
Defined Benefit Pension PlansOPEB Plans
Alliant Energy2025202420252024
Change in benefit obligation:
Net benefit obligation at January 1$841 $876 $148 $160 
Service cost4 5 1 2 
Interest cost46 45 8 8 
Plan participants’ contributions— — 4 3 
Actuarial (gain) loss17 (19)6 (7)
Gross benefits paid(84)(66)(21)(18)
Net benefit obligation at December 31824 841 146 148 
Change in plan assets:
Fair value of plan assets at January 1715 732 80 83 
Actual return on plan assets93 38 7 5 
Employer contributions23 11 8 7 
Plan participants’ contributions— — 4 3 
Gross benefits paid(84)(66)(21)(18)
Fair value of plan assets at December 31747 715 78 80 
Under funded status at December 31($77)($126)($68)($68)
Defined Benefit Pension PlansOPEB Plans
Alliant Energy2025202420252024
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $18 $17 
Current liabilities(5)(3)(6)(7)
Pension and other benefit obligations(72)(123)(80)(78)
Net amounts recognized at December 31($77)($126)($68)($68)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$267 $312 $7 $4 
Prior service credit(1)(2)— — 
$266 $310 $7 $4 
Defined Benefit Pension PlansOPEB Plans
IPL2025202420252024
Change in benefit obligation:
Net benefit obligation at January 1$372 $387 $59 $65 
Service cost3 3 1 1 
Interest cost20 20 3 3 
Plan participants’ contributions— — 2 1 
Actuarial (gain) loss6 (8)3 (3)
Gross benefits paid(38)(30)(9)(8)
Net benefit obligation at December 31363 372 59 59 
Change in plan assets:
Fair value of plan assets at January 1340 352 59 61 
Actual return on plan assets43 18 6 4 
Employer contributions1 — 2 1 
Plan participants’ contributions— — 2 1 
Gross benefits paid(38)(30)(9)(8)
Fair value of plan assets at December 31346 340 60 59 
(Under) Over funded status at December 31($17)($32)$1 $— 
Defined Benefit Pension PlansOPEB Plans
IPL2025202420252024
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $14 $13 
Current liabilities— (1)(1)(1)
Pension and other benefit obligations(17)(31)(12)(12)
Net amounts recognized at December 31($17)($32)$1 $— 
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$105 $126 $7 $7 
Prior service credit— (1)— — 
$105 $125 $7 $7 
Defined Benefit Pension PlansOPEB Plans
WPL2025202420252024
Change in benefit obligation:
Net benefit obligation at January 1$365 $381 $56 $61 
Service cost1 2 1 1 
Interest cost20 20 3 3 
Plan participants’ contributions— — 1 1 
Actuarial (gain) loss 9 (8)2 (3)
Gross benefits paid(33)(30)(8)(7)
Net benefit obligation at December 31362 365 55 56 
Change in plan assets:
Fair value of plan assets at January 1303 306 13 14 
Actual return on plan assets41 17 2 — 
Employer contributions16 10 6 5 
Plan participants’ contributions— — 1 1 
Gross benefits paid(33)(30)(8)(7)
Fair value of plan assets at December 31327 303 14 13 
Under funded status at December 31($35)($62)($41)($43)
Defined Benefit Pension PlansOPEB Plans
WPL2025202420252024
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $4 $4 
Current liabilities— — (5)(6)
Pension and other benefit obligations(35)(62)(40)(41)
Net amounts recognized at December 31($35)($62)($41)($43)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$115 $135 $1 $— 

Accumulated benefit obligations, aggregate amounts applicable to defined benefit pension and OPEB plans with accumulated benefit obligations in excess of plan assets, as well as defined benefit pension plans with projected benefit obligations in excess of plan assets as of the December 31 measurement date are as follows (in millions):
Defined Benefit Pension PlansOPEB Plans
Alliant Energy2025202420252024
Accumulated benefit obligations$805 $824 $146 $148 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations805 824 146 148 
Fair value of plan assets747 715 78 80 
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations824 841 N/AN/A
Fair value of plan assets747 715 N/AN/A
Defined Benefit Pension PlansOPEB Plans
IPL2025202420252024
Accumulated benefit obligations$353 $362 $59 $59 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations353 362 N/AN/A
Fair value of plan assets346 340 N/AN/A
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations363 372 N/AN/A
Fair value of plan assets346 340 N/AN/A
Defined Benefit Pension PlansOPEB Plans
WPL2025202420252024
Accumulated benefit obligations$354 $358 $55 $56 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations354 358 55 56 
Fair value of plan assets327 303 14 13 
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations362 365 N/AN/A
Fair value of plan assets327 303 N/AN/A

In addition to the amounts recognized in regulatory assets in the above tables for IPL and WPL, regulatory assets were recognized for amounts associated with Corporate Services employees participating in other Alliant Energy sponsored benefit plans that were allocated to IPL and WPL at December 31 as follows (in millions):
IPLWPL
2025202420252024
Regulatory assets$23$25$21$22

Estimated Future Employer Contributions and Benefit Payments - Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2026 is as follows (in millions):
Alliant EnergyIPLWPL
Defined benefit pension plans (a)$23$3$13
OPEB plans715

(a)Alliant Energy sponsors several non-qualified defined benefit pension plans that cover certain current and former key employees of IPL and WPL. Alliant Energy allocates pension costs to IPL and WPL for these plans. In addition, IPL and WPL amounts reflect funding for their non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans.

Expected benefit payments for the qualified and non-qualified defined benefit plans, which reflect expected future service, as appropriate, are as follows (in millions):
Alliant Energy202620272028202920302031 - 2035
Defined benefit pension benefits$75 $75 $75 $74 $69 $320
OPEB16 15 15 14 14 61
$91 $90 $90 $88 $83 $381
IPL202620272028202920302031 - 2035
Defined benefit pension benefits$34 $33 $33 $32 $32 $143
OPEB6 6 6 6 6 24
$40 $39 $39 $38 $38 $167
WPL202620272028202920302031 - 2035
Defined benefit pension benefits$32 $31 $31 $31 $30 $142
OPEB6 6 5 5 5 23
$38 $37 $36 $36 $35 $165

Investment Strategy for Plan Assets - Investment strategies for defined benefit pension and OPEB plan assets combine preservation of principal and prudent risk-taking to protect the integrity of plan assets, in order to meet the obligations to plan participants while minimizing benefit costs over the long term. Investment risk of plan assets is mitigated through an asset mix, which is governed by allocation targets. The asset allocation is monitored regularly, and appropriate steps are taken as needed to rebalance the assets within the prescribed ranges.
Defined Benefit Pension Plan Assets - Defined benefit pension plan assets have a long-term investment time horizon and are classified into return-seeking and liability-hedging portfolios. The return-seeking portfolio includes: public equities with different market capitalization, investment style and geography; liquid alternative securities, which include hedge fund strategies; and fixed income investments, which include, but are not limited to, high-yield bonds, emerging market debt, bank loans and private credit bonds. The liability-hedging portfolio includes: fixed-income investments including investment grade instruments of government and corporate issuers, as well as private placements and securitized assets; and fixed income derivative contracts for liability and interest rate hedging positions. At December 31, 2025, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows:
Target RangeActual
AllocationAllocation
Public equity securities32%-44%40%
Liquid alternative securities0%-11%5%
Return-seeking fixed income securities4%-16%7%
Liability-hedging fixed income securities (including cash and equivalents)41%-54%48%

Other Postretirement Benefits Plan Assets - OPEB plan assets are comprised of specific assets within certain defined benefit pension plans (401(h) assets) as well as assets held in VEBA trusts. For asset pools with a long-term investment time horizon, investments include public equities with different market capitalization, investment style and geography, and fixed income securities including investment grade instruments of government and corporate issuers. At December 31, 2025, the current target ranges and actual allocations for assets with a long-term investment horizon were as follows:
Target RangeActual
AllocationAllocation
Cash and equivalents0%-5%3%
Public equity securities0%-40%26%
Fixed income securities34%-100%71%

Fair Value Measurements - Fair value measurement accounting establishes three levels of fair value hierarchy that prioritize the inputs to valuation techniques used to measure fair value. Refer to Note 15 for discussion of levels within the fair value hierarchy. Level 1 items include investments in securities held in registered investment companies, which are valued at the closing price reported in the active market in which the securities are traded. Level 2 items include cash and equivalents consisting of money market fund investments and cash collateral supporting derivative financial instruments. Certain investments that are measured at fair value using the net asset value practical expedient have not been classified in the fair value hierarchy. These fair value amounts are included below to reconcile the fair value hierarchy to the respective total plan assets.

At December 31, the fair values of qualified and non-qualified defined benefit pension plan assets were as follows (in millions):
20252024
FairLevelLevelLevelFairLevelLevelLevel
Alliant EnergyValue123Value123
Cash and equivalents$71 $— $71 $— $49 $— $49 $— 
Assets measured at net asset value676 667 
Due to brokers, net (pending trades with brokers)— (1)
Total pension plan assets$747 $715 
20252024
FairLevelLevelLevelFairLevelLevelLevel
IPLValue123Value123
Cash and equivalents$31 $— $31 $— $21 $— $21 $— 
Assets measured at net asset value315 319 
Total pension plan assets$346 $340 
20252024
FairLevelLevelLevelFairLevelLevelLevel
WPLValue123Value123
Cash and equivalents$32 $— $32 $— $22 $— $22 $— 
Assets measured at net asset value295 281 
Total pension plan assets$327 $303 
At December 31, the fair values of OPEB plan assets were as follows (in millions):
20252024
FairLevelLevelLevelFairLevelLevelLevel
Alliant EnergyValue123Value123
Cash and equivalents$7 $— $7 $— $8 $— $8 $— 
Equity securities19 19 — — 20 20 — — 
Fixed income securities52 52 — — 52 52 — — 
Total OPEB plan assets$78 $71 $7 $— $80 $72 $8 $— 
20252024
FairLevelLevelLevelFairLevelLevelLevel
IPLValue123Value123
Cash and equivalents$3 $— $3 $— $1 $— $1 $— 
Equity securities17 17 — — 18 18 — — 
Fixed income securities40 40 — — 40 40 — — 
Total OPEB plan assets$60 $57 $3 $— $59 $58 $1 $— 
20252024
FairLevelLevelLevelFairLevelLevelLevel
WPLValue123Value123
Equity securities$2 $2 — — $2 $2 — — 
Fixed income securities12 12 — — 11 11 — — 
Total OPEB plan assets$14 $14 $— $— $13 $13 $— $— 

For the various defined benefit pension and OPEB plans, Alliant Energy common stock represented less than 1% of the assets directly held in the plans at December 31, 2025 and 2024, respectively.

401(k) Savings Plans - A significant number of employees participate in defined contribution retirement plans (401(k) savings plans). Alliant Energy common stock directly held by participants represented 7% of total assets in the 401(k) savings plans at December 31, 2025 and 2024. Costs related to the 401(k) savings plans, which are partially based on the participants’ contributions and include allocated costs associated with Corporate Services employees for IPL and WPL, were as follows (in millions):
Alliant EnergyIPLWPL
202520242023202520242023202520242023
401(k) costs$30 $31 $30 $14 $14 $14 $14 $15 $14 

Restructuring and Voluntary Employee Separation Charges - In 2024, Alliant Energy announced restructuring activities, including offering certain employees a voluntary separation package. Approximately 5% of total Alliant Energy employees accepted the package, and as a result of the restructuring activities, Alliant Energy, IPL and WPL recorded pre-tax charges of $29 million, $14 million and $13 million, respectively, in 2024. These charges were primarily recorded in “Other operation and maintenance” expenses in the income statements.
(b) Equity-based Compensation Plans - In 2020, Alliant Energy’s shareowners approved the 2020 OIP, which permits the grant of shares of Alliant Energy common stock, restricted stock, restricted stock units, performance shares, performance units, and other stock-based or cash-based awards to key employees. At December 31, 2025, performance shares and restricted stock units were outstanding under the 2020 OIP, and 7 million shares of Alliant Energy common stock remained available for grants under the 2020 OIP. Alliant Energy satisfies share payouts related to equity awards through the issuance of new shares of its common stock. Nonvested awards generally do not have non-forfeitable rights to dividends or dividend equivalents when dividends are paid to common shareowners. A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards was as follows (in millions):
Alliant EnergyIPLWPL
202520242023202520242023202520242023
Compensation expense$22$12$12$11$6$6$10$5$5
Income tax benefits333222111

As of December 31, 2025, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $14 million, $7 million and $6 million, respectively, which is expected to be recognized over a weighted average period of between one year and two years. Share-based compensation expense is recognized on a straight-line basis over the requisite service periods and is recorded in “Other operation and maintenance” in the income statements. As of December 31, 2025, 725,647 shares were included in the calculation of diluted EPS related to the nonvested equity awards.
Performance Shares (Total Shareowner Return Metric) - Payouts of certain performance shares are contingent upon achievement over a three-year period of specified performance criteria, which currently is total shareowner return relative to an investor-owned utility peer group. Performance shares grants are to be paid out in shares of Alliant Energy common stock and are accounted for as equity awards. The fair value of each of these performance shares is based on the fair value of the underlying common stock on the grant date and the probability of satisfying the market condition contained in the agreement during a three-year performance period. The actual number of these performance shares that will be paid out upon vesting is dependent upon actual performance and may range from zero to 200% of the target number of shares. If minimum performance targets are not met during the performance period, these performance shares are forfeited. Compensation expense is recorded ratably over the performance period based on the fair value of the awards at the grant date. A summary of the performance shares activity, with amounts representing the target number of awards, was as follows:
202520242023
SharesWeighted
Average Grant
Date Fair Value		SharesWeighted
Average Grant
Date Fair Value		SharesWeighted
Average Grant
Date Fair Value
Nonvested awards, January 1289,399$51.31233,954$52.60190,273$54.13
Granted105,89666.52127,87446.04108,71255.68
Vested——(47,497)46.19(53,431)64.04
Forfeited(73,918)54.14(24,932)46.16(11,600)53.88
Nonvested awards, December 31321,37755.67289,39951.31233,95452.60

Restricted Stock Units - Payouts of restricted stock units are based on the expiration of a three-year time-vesting period. Restricted stock unit grants are to be paid out in shares of Alliant Energy common stock and are accounted for as equity awards. The fair value of each of these restricted stock units is based on the closing market price of one share of Alliant Energy common stock on the grant date of the award. Compensation expense is recorded ratably over the performance period based on the fair value of the awards on the grant date. A summary of the restricted stock units activity was as follows:
202520242023
UnitsWeighted
Average Grant
Date Fair Value		UnitsWeighted
Average Grant
Date Fair Value		UnitsWeighted
Average Grant
Date Fair Value
Nonvested awards, January 1289,148$51.85234,259$52.58198,275$54.53
Granted102,24061.73129,85448.69106,12452.77
Vested(63,789)56.70(71,441)48.65(55,345)59.40
Forfeited(14,215)51.13(3,524)48.40(14,795)54.53
Nonvested awards, December 31313,38454.06289,14851.85234,25952.58

Performance Shares (Net Income, Environmental and Workforce Composition Metrics) (certain awards formerly granted as Performance Restricted Stock Units) - Payouts of certain performance shares are contingent upon achievement over a three-year period of specific performance criteria, which currently is specified growth of cumulative consolidated net income from continuing operations, as well as environmental and workforce composition metrics. Performance shares grants are to be paid out in shares of Alliant Energy common stock and are accounted for as equity awards. The fair value of each of these performance shares is based on the closing market price of one share of Alliant Energy common stock on the grant date of the award. The actual number of these performance shares that will be paid out upon vesting is dependent upon actual performance and may range from zero to 200% of the target number of shares under each award type. If minimum performance targets are not met during the performance period, these performance shares are forfeited. Compensation expense is recorded ratably over the performance period based on a probability assessment of payouts for the awards at each reporting period. A summary of the performance shares activity, with amounts representing the target number of awards, was as follows:
202520242023
SharesWeighted Average Grant Date Fair ValueSharesWeighted Average Grant Date Fair ValueSharesWeighted Average Grant Date Fair Value
Nonvested awards, January 1330,700$51.81257,639$52.76199,874$54.74
Granted118,88361.63146,14348.55124,21752.71
Vested(68,233)56.74(67,852)48.66(53,431)59.36
Forfeited(16,225)53.05(5,230)48.40(13,021)55.47
Nonvested awards, December 31365,12554.03330,70051.81257,63952.76
(c) Deferred Compensation Plan - Alliant Energy maintains a DCP under which certain key employees may defer up to 80% of base salary and short-term cash incentive compensation and members of its Board of Directors may elect to defer all or part of their retainer and committee fees. Key employees who have made the maximum allowed contribution to the Alliant Energy 401(k) Savings Plan may receive an additional credit to the DCP. Key employees and Board of Directors members may elect to have their deferrals credited to a company stock account, an interest account, equity accounts or mutual fund accounts based on certain benchmark funds.
Company Stock Account - The DCP does not permit reallocation of deferrals credited to the company stock account and all distributions from participants’ company stock accounts are made in the form of shares of Alliant Energy common stock. The deferred compensation obligations for participants’ company stock accounts are recorded in “Additional paid-in capital” and the shares of Alliant Energy common stock held in a rabbi trust to satisfy this obligation are recorded in “Shares in deferred compensation trust” on Alliant Energy’s balance sheets. At December 31, the carrying value of the deferred compensation obligation for the company stock account and the shares in the deferred compensation trust based on the historical value of the shares of Alliant Energy common stock contributed to the rabbi trust, and the fair market value of the shares held in the rabbi trust, were as follows (in millions):
20252024
Carrying value$14$14
Fair market value2422

Interest, Equity and Mutual Fund Accounts - Distributions from participants’ interest, equity and mutual fund accounts are in the form of cash payments. The deferred compensation obligations for participants’ interest, equity and mutual fund accounts are recorded in “Pension and other benefit obligations” on the balance sheets. At December 31, 2025 and 2024, the carrying value of Alliant Energy’s deferred compensation obligations for participants’ interest, equity and mutual fund accounts, which approximates fair market value, was $22 million and $23 million, respectively.
IPL [Member]  
Statement [Line Items]  
Benefit Plans BENEFIT PLANS(a) Pension and Other Postretirement Benefits Plans - Retirement benefits are provided to substantially all employees through various qualified and non-qualified non-contributory defined benefit pension plans (currently closed to new hires), and/or through defined contribution plans (including 401(k) savings plans). Benefits of the non-contributory defined benefit pension plans are based on the plan participant’s years of service, age and compensation. Benefits of the defined contribution plans are based on the plan participant’s years of service, age, compensation and contributions. Certain defined benefit postretirement health care and life benefits are provided to eligible retirees. In general, the retiree health care plans consist of fixed benefit subsidy structures and the retiree life insurance plans are non-contributory.
IPL and WPL account for their participation in Alliant Energy and Corporate Services sponsored plans as multiple-employer plans. For IPL and WPL, amounts below represent the amounts for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans.

Assumptions - The weighted-average assumptions for defined benefit pension and OPEB plans at the measurement date of December 31 were as follows:
Defined Benefit Pension PlansOPEB Plans
Alliant Energy202520242023202520242023
Discount rate for benefit obligations5.52%5.65%5.36%5.40%5.62%5.40%
Discount rate for net periodic cost5.65%5.36%5.54%5.62%5.40%5.53%
Expected rate of return on plan assets7.60%7.73%7.80%6.37%6.22%6.50%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan5.60%6.24%10.75%N/AN/AN/A
Rate of compensation increase3.75%-4.50%3.50%-4.50%3.30%-4.50%N/AN/AN/A
Qualified Defined Benefit Pension PlanOPEB Plans
IPL202520242023202520242023
Discount rate for benefit obligations5.56%5.66%5.35%5.38%5.61%5.40%
Discount rate for net periodic cost5.66%5.35%5.55%5.61%5.40%5.53%
Expected rate of return on plan assets7.60%7.60%7.80%6.70%6.60%6.90%
Rate of compensation increase4.00%3.75%3.30%N/AN/AN/A
Qualified Defined Benefit Pension PlanOPEB Plans
WPL202520242023202520242023
Discount rate for benefit obligations5.56%5.66%5.35%5.38%5.61%5.40%
Discount rate for net periodic cost5.66%5.35%5.54%5.61%5.40%5.53%
Expected rate of return on plan assets7.60%7.80%7.80%5.75%5.61%5.65%
Rate of compensation increase3.75%3.50%3.30%N/AN/AN/A

Expected rate of return on plan assets - The expected rate of return on plan assets is based on projected asset class returns using target allocations. A forward-looking building blocks approach is used, and historical returns, survey information and capital market information are analyzed to support the expected rate of return on plan assets assumption. Refer to “Investment Strategy for Plan Assets” below for additional information related to investment strategy and mix of assets for the pension and OPEB plans.

Life Expectancy - The life expectancy assumption is used in determining the benefit obligation and net periodic benefit cost for defined benefit pension and OPEB plans. This assumption utilizes base mortality tables that were released in 2019 by the Society of Actuaries and mortality projection tables that were released in 2021 by the Society of Actuaries.

Net Periodic Benefit Costs - The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans are included below (in millions). The service cost component of net periodic benefit costs is included in “Other operation and maintenance” expenses in the income statements and all other components of net periodic benefit costs are included in “Other (income) and deductions” in the income statements or regulatory assets on the balance sheets.
Alliant EnergyDefined Benefit Pension PlansOPEB Plans
202520242023202520242023
Service cost$4 $5 $5 $1 $2 $2 
Interest cost46 45 47 8 8 9 
Expected return on plan assets (a)(53)(55)(53)(4)(5)(5)
Amortization of prior service credit (b)— (1)(1)— — — 
Amortization of actuarial loss (c)22 24 28 — — 1 
$19 $18 $26 $5 $5 $7 
IPLDefined Benefit Pension PlansOPEB Plans
202520242023202520242023
Service cost$3 $3 $3 $1 $1 $1 
Interest cost20 20 21 3 3 3 
Expected return on plan assets (a)(25)(26)(26)(4)(4)(3)
Amortization of actuarial loss (c)9 9 11 — — 1 
$7 $6 $9 $— $— $2 
WPLDefined Benefit Pension PlansOPEB Plans
202520242023202520242023
Service cost$1 $2 $2 $1 $1 $1 
Interest cost20 20 20 3 3 3 
Expected return on plan assets (a)(23)(23)(22)(1)(1)(1)
Amortization of actuarial loss (c)11 11 13 — — 1 
$9 $10 $13 $3 $3 $4 

(a)The expected return on plan assets is based on the expected rate of return on plan assets and the fair value approach to the market-related value of plan assets.
(b)Unrecognized prior service credits for the OPEB plans are amortized over the average future service period to full eligibility of the participants of each plan.
(c)Unrecognized net actuarial gains or losses in excess of 10% of the greater of the plans’ benefit obligations or assets are amortized over the average future service lives of plan participants, except for the Alliant Energy Cash Balance Pension Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits.
Benefit Plan Assets and Obligations - A reconciliation of the funded status of qualified and non-qualified defined benefit pension and OPEB plans to the amounts recognized on the balance sheets at December 31 was as follows (in millions):
Defined Benefit Pension PlansOPEB Plans
Alliant Energy2025202420252024
Change in benefit obligation:
Net benefit obligation at January 1$841 $876 $148 $160 
Service cost4 5 1 2 
Interest cost46 45 8 8 
Plan participants’ contributions— — 4 3 
Actuarial (gain) loss17 (19)6 (7)
Gross benefits paid(84)(66)(21)(18)
Net benefit obligation at December 31824 841 146 148 
Change in plan assets:
Fair value of plan assets at January 1715 732 80 83 
Actual return on plan assets93 38 7 5 
Employer contributions23 11 8 7 
Plan participants’ contributions— — 4 3 
Gross benefits paid(84)(66)(21)(18)
Fair value of plan assets at December 31747 715 78 80 
Under funded status at December 31($77)($126)($68)($68)
Defined Benefit Pension PlansOPEB Plans
Alliant Energy2025202420252024
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $18 $17 
Current liabilities(5)(3)(6)(7)
Pension and other benefit obligations(72)(123)(80)(78)
Net amounts recognized at December 31($77)($126)($68)($68)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$267 $312 $7 $4 
Prior service credit(1)(2)— — 
$266 $310 $7 $4 
Defined Benefit Pension PlansOPEB Plans
IPL2025202420252024
Change in benefit obligation:
Net benefit obligation at January 1$372 $387 $59 $65 
Service cost3 3 1 1 
Interest cost20 20 3 3 
Plan participants’ contributions— — 2 1 
Actuarial (gain) loss6 (8)3 (3)
Gross benefits paid(38)(30)(9)(8)
Net benefit obligation at December 31363 372 59 59 
Change in plan assets:
Fair value of plan assets at January 1340 352 59 61 
Actual return on plan assets43 18 6 4 
Employer contributions1 — 2 1 
Plan participants’ contributions— — 2 1 
Gross benefits paid(38)(30)(9)(8)
Fair value of plan assets at December 31346 340 60 59 
(Under) Over funded status at December 31($17)($32)$1 $— 
Defined Benefit Pension PlansOPEB Plans
IPL2025202420252024
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $14 $13 
Current liabilities— (1)(1)(1)
Pension and other benefit obligations(17)(31)(12)(12)
Net amounts recognized at December 31($17)($32)$1 $— 
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$105 $126 $7 $7 
Prior service credit— (1)— — 
$105 $125 $7 $7 
Defined Benefit Pension PlansOPEB Plans
WPL2025202420252024
Change in benefit obligation:
Net benefit obligation at January 1$365 $381 $56 $61 
Service cost1 2 1 1 
Interest cost20 20 3 3 
Plan participants’ contributions— — 1 1 
Actuarial (gain) loss 9 (8)2 (3)
Gross benefits paid(33)(30)(8)(7)
Net benefit obligation at December 31362 365 55 56 
Change in plan assets:
Fair value of plan assets at January 1303 306 13 14 
Actual return on plan assets41 17 2 — 
Employer contributions16 10 6 5 
Plan participants’ contributions— — 1 1 
Gross benefits paid(33)(30)(8)(7)
Fair value of plan assets at December 31327 303 14 13 
Under funded status at December 31($35)($62)($41)($43)
Defined Benefit Pension PlansOPEB Plans
WPL2025202420252024
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $4 $4 
Current liabilities— — (5)(6)
Pension and other benefit obligations(35)(62)(40)(41)
Net amounts recognized at December 31($35)($62)($41)($43)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$115 $135 $1 $— 

Accumulated benefit obligations, aggregate amounts applicable to defined benefit pension and OPEB plans with accumulated benefit obligations in excess of plan assets, as well as defined benefit pension plans with projected benefit obligations in excess of plan assets as of the December 31 measurement date are as follows (in millions):
Defined Benefit Pension PlansOPEB Plans
Alliant Energy2025202420252024
Accumulated benefit obligations$805 $824 $146 $148 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations805 824 146 148 
Fair value of plan assets747 715 78 80 
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations824 841 N/AN/A
Fair value of plan assets747 715 N/AN/A
Defined Benefit Pension PlansOPEB Plans
IPL2025202420252024
Accumulated benefit obligations$353 $362 $59 $59 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations353 362 N/AN/A
Fair value of plan assets346 340 N/AN/A
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations363 372 N/AN/A
Fair value of plan assets346 340 N/AN/A
Defined Benefit Pension PlansOPEB Plans
WPL2025202420252024
Accumulated benefit obligations$354 $358 $55 $56 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations354 358 55 56 
Fair value of plan assets327 303 14 13 
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations362 365 N/AN/A
Fair value of plan assets327 303 N/AN/A

In addition to the amounts recognized in regulatory assets in the above tables for IPL and WPL, regulatory assets were recognized for amounts associated with Corporate Services employees participating in other Alliant Energy sponsored benefit plans that were allocated to IPL and WPL at December 31 as follows (in millions):
IPLWPL
2025202420252024
Regulatory assets$23$25$21$22

Estimated Future Employer Contributions and Benefit Payments - Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2026 is as follows (in millions):
Alliant EnergyIPLWPL
Defined benefit pension plans (a)$23$3$13
OPEB plans715

(a)Alliant Energy sponsors several non-qualified defined benefit pension plans that cover certain current and former key employees of IPL and WPL. Alliant Energy allocates pension costs to IPL and WPL for these plans. In addition, IPL and WPL amounts reflect funding for their non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans.

Expected benefit payments for the qualified and non-qualified defined benefit plans, which reflect expected future service, as appropriate, are as follows (in millions):
Alliant Energy202620272028202920302031 - 2035
Defined benefit pension benefits$75 $75 $75 $74 $69 $320
OPEB16 15 15 14 14 61
$91 $90 $90 $88 $83 $381
IPL202620272028202920302031 - 2035
Defined benefit pension benefits$34 $33 $33 $32 $32 $143
OPEB6 6 6 6 6 24
$40 $39 $39 $38 $38 $167
WPL202620272028202920302031 - 2035
Defined benefit pension benefits$32 $31 $31 $31 $30 $142
OPEB6 6 5 5 5 23
$38 $37 $36 $36 $35 $165

Investment Strategy for Plan Assets - Investment strategies for defined benefit pension and OPEB plan assets combine preservation of principal and prudent risk-taking to protect the integrity of plan assets, in order to meet the obligations to plan participants while minimizing benefit costs over the long term. Investment risk of plan assets is mitigated through an asset mix, which is governed by allocation targets. The asset allocation is monitored regularly, and appropriate steps are taken as needed to rebalance the assets within the prescribed ranges.
Defined Benefit Pension Plan Assets - Defined benefit pension plan assets have a long-term investment time horizon and are classified into return-seeking and liability-hedging portfolios. The return-seeking portfolio includes: public equities with different market capitalization, investment style and geography; liquid alternative securities, which include hedge fund strategies; and fixed income investments, which include, but are not limited to, high-yield bonds, emerging market debt, bank loans and private credit bonds. The liability-hedging portfolio includes: fixed-income investments including investment grade instruments of government and corporate issuers, as well as private placements and securitized assets; and fixed income derivative contracts for liability and interest rate hedging positions. At December 31, 2025, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows:
Target RangeActual
AllocationAllocation
Public equity securities32%-44%40%
Liquid alternative securities0%-11%5%
Return-seeking fixed income securities4%-16%7%
Liability-hedging fixed income securities (including cash and equivalents)41%-54%48%

Other Postretirement Benefits Plan Assets - OPEB plan assets are comprised of specific assets within certain defined benefit pension plans (401(h) assets) as well as assets held in VEBA trusts. For asset pools with a long-term investment time horizon, investments include public equities with different market capitalization, investment style and geography, and fixed income securities including investment grade instruments of government and corporate issuers. At December 31, 2025, the current target ranges and actual allocations for assets with a long-term investment horizon were as follows:
Target RangeActual
AllocationAllocation
Cash and equivalents0%-5%3%
Public equity securities0%-40%26%
Fixed income securities34%-100%71%

Fair Value Measurements - Fair value measurement accounting establishes three levels of fair value hierarchy that prioritize the inputs to valuation techniques used to measure fair value. Refer to Note 15 for discussion of levels within the fair value hierarchy. Level 1 items include investments in securities held in registered investment companies, which are valued at the closing price reported in the active market in which the securities are traded. Level 2 items include cash and equivalents consisting of money market fund investments and cash collateral supporting derivative financial instruments. Certain investments that are measured at fair value using the net asset value practical expedient have not been classified in the fair value hierarchy. These fair value amounts are included below to reconcile the fair value hierarchy to the respective total plan assets.

At December 31, the fair values of qualified and non-qualified defined benefit pension plan assets were as follows (in millions):
20252024
FairLevelLevelLevelFairLevelLevelLevel
Alliant EnergyValue123Value123
Cash and equivalents$71 $— $71 $— $49 $— $49 $— 
Assets measured at net asset value676 667 
Due to brokers, net (pending trades with brokers)— (1)
Total pension plan assets$747 $715 
20252024
FairLevelLevelLevelFairLevelLevelLevel
IPLValue123Value123
Cash and equivalents$31 $— $31 $— $21 $— $21 $— 
Assets measured at net asset value315 319 
Total pension plan assets$346 $340 
20252024
FairLevelLevelLevelFairLevelLevelLevel
WPLValue123Value123
Cash and equivalents$32 $— $32 $— $22 $— $22 $— 
Assets measured at net asset value295 281 
Total pension plan assets$327 $303 
At December 31, the fair values of OPEB plan assets were as follows (in millions):
20252024
FairLevelLevelLevelFairLevelLevelLevel
Alliant EnergyValue123Value123
Cash and equivalents$7 $— $7 $— $8 $— $8 $— 
Equity securities19 19 — — 20 20 — — 
Fixed income securities52 52 — — 52 52 — — 
Total OPEB plan assets$78 $71 $7 $— $80 $72 $8 $— 
20252024
FairLevelLevelLevelFairLevelLevelLevel
IPLValue123Value123
Cash and equivalents$3 $— $3 $— $1 $— $1 $— 
Equity securities17 17 — — 18 18 — — 
Fixed income securities40 40 — — 40 40 — — 
Total OPEB plan assets$60 $57 $3 $— $59 $58 $1 $— 
20252024
FairLevelLevelLevelFairLevelLevelLevel
WPLValue123Value123
Equity securities$2 $2 — — $2 $2 — — 
Fixed income securities12 12 — — 11 11 — — 
Total OPEB plan assets$14 $14 $— $— $13 $13 $— $— 

For the various defined benefit pension and OPEB plans, Alliant Energy common stock represented less than 1% of the assets directly held in the plans at December 31, 2025 and 2024, respectively.

401(k) Savings Plans - A significant number of employees participate in defined contribution retirement plans (401(k) savings plans). Alliant Energy common stock directly held by participants represented 7% of total assets in the 401(k) savings plans at December 31, 2025 and 2024. Costs related to the 401(k) savings plans, which are partially based on the participants’ contributions and include allocated costs associated with Corporate Services employees for IPL and WPL, were as follows (in millions):
Alliant EnergyIPLWPL
202520242023202520242023202520242023
401(k) costs$30 $31 $30 $14 $14 $14 $14 $15 $14 

Restructuring and Voluntary Employee Separation Charges - In 2024, Alliant Energy announced restructuring activities, including offering certain employees a voluntary separation package. Approximately 5% of total Alliant Energy employees accepted the package, and as a result of the restructuring activities, Alliant Energy, IPL and WPL recorded pre-tax charges of $29 million, $14 million and $13 million, respectively, in 2024. These charges were primarily recorded in “Other operation and maintenance” expenses in the income statements.
(b) Equity-based Compensation Plans - In 2020, Alliant Energy’s shareowners approved the 2020 OIP, which permits the grant of shares of Alliant Energy common stock, restricted stock, restricted stock units, performance shares, performance units, and other stock-based or cash-based awards to key employees. At December 31, 2025, performance shares and restricted stock units were outstanding under the 2020 OIP, and 7 million shares of Alliant Energy common stock remained available for grants under the 2020 OIP. Alliant Energy satisfies share payouts related to equity awards through the issuance of new shares of its common stock. Nonvested awards generally do not have non-forfeitable rights to dividends or dividend equivalents when dividends are paid to common shareowners. A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards was as follows (in millions):
Alliant EnergyIPLWPL
202520242023202520242023202520242023
Compensation expense$22$12$12$11$6$6$10$5$5
Income tax benefits333222111

As of December 31, 2025, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $14 million, $7 million and $6 million, respectively, which is expected to be recognized over a weighted average period of between one year and two years. Share-based compensation expense is recognized on a straight-line basis over the requisite service periods and is recorded in “Other operation and maintenance” in the income statements. As of December 31, 2025, 725,647 shares were included in the calculation of diluted EPS related to the nonvested equity awards.
Performance Shares (Total Shareowner Return Metric) - Payouts of certain performance shares are contingent upon achievement over a three-year period of specified performance criteria, which currently is total shareowner return relative to an investor-owned utility peer group. Performance shares grants are to be paid out in shares of Alliant Energy common stock and are accounted for as equity awards. The fair value of each of these performance shares is based on the fair value of the underlying common stock on the grant date and the probability of satisfying the market condition contained in the agreement during a three-year performance period. The actual number of these performance shares that will be paid out upon vesting is dependent upon actual performance and may range from zero to 200% of the target number of shares. If minimum performance targets are not met during the performance period, these performance shares are forfeited. Compensation expense is recorded ratably over the performance period based on the fair value of the awards at the grant date. A summary of the performance shares activity, with amounts representing the target number of awards, was as follows:
202520242023
SharesWeighted
Average Grant
Date Fair Value		SharesWeighted
Average Grant
Date Fair Value		SharesWeighted
Average Grant
Date Fair Value
Nonvested awards, January 1289,399$51.31233,954$52.60190,273$54.13
Granted105,89666.52127,87446.04108,71255.68
Vested——(47,497)46.19(53,431)64.04
Forfeited(73,918)54.14(24,932)46.16(11,600)53.88
Nonvested awards, December 31321,37755.67289,39951.31233,95452.60

Restricted Stock Units - Payouts of restricted stock units are based on the expiration of a three-year time-vesting period. Restricted stock unit grants are to be paid out in shares of Alliant Energy common stock and are accounted for as equity awards. The fair value of each of these restricted stock units is based on the closing market price of one share of Alliant Energy common stock on the grant date of the award. Compensation expense is recorded ratably over the performance period based on the fair value of the awards on the grant date. A summary of the restricted stock units activity was as follows:
202520242023
UnitsWeighted
Average Grant
Date Fair Value		UnitsWeighted
Average Grant
Date Fair Value		UnitsWeighted
Average Grant
Date Fair Value
Nonvested awards, January 1289,148$51.85234,259$52.58198,275$54.53
Granted102,24061.73129,85448.69106,12452.77
Vested(63,789)56.70(71,441)48.65(55,345)59.40
Forfeited(14,215)51.13(3,524)48.40(14,795)54.53
Nonvested awards, December 31313,38454.06289,14851.85234,25952.58

Performance Shares (Net Income, Environmental and Workforce Composition Metrics) (certain awards formerly granted as Performance Restricted Stock Units) - Payouts of certain performance shares are contingent upon achievement over a three-year period of specific performance criteria, which currently is specified growth of cumulative consolidated net income from continuing operations, as well as environmental and workforce composition metrics. Performance shares grants are to be paid out in shares of Alliant Energy common stock and are accounted for as equity awards. The fair value of each of these performance shares is based on the closing market price of one share of Alliant Energy common stock on the grant date of the award. The actual number of these performance shares that will be paid out upon vesting is dependent upon actual performance and may range from zero to 200% of the target number of shares under each award type. If minimum performance targets are not met during the performance period, these performance shares are forfeited. Compensation expense is recorded ratably over the performance period based on a probability assessment of payouts for the awards at each reporting period. A summary of the performance shares activity, with amounts representing the target number of awards, was as follows:
202520242023
SharesWeighted Average Grant Date Fair ValueSharesWeighted Average Grant Date Fair ValueSharesWeighted Average Grant Date Fair Value
Nonvested awards, January 1330,700$51.81257,639$52.76199,874$54.74
Granted118,88361.63146,14348.55124,21752.71
Vested(68,233)56.74(67,852)48.66(53,431)59.36
Forfeited(16,225)53.05(5,230)48.40(13,021)55.47
Nonvested awards, December 31365,12554.03330,70051.81257,63952.76
WPL [Member]  
Statement [Line Items]  
Benefit Plans BENEFIT PLANS(a) Pension and Other Postretirement Benefits Plans - Retirement benefits are provided to substantially all employees through various qualified and non-qualified non-contributory defined benefit pension plans (currently closed to new hires), and/or through defined contribution plans (including 401(k) savings plans). Benefits of the non-contributory defined benefit pension plans are based on the plan participant’s years of service, age and compensation. Benefits of the defined contribution plans are based on the plan participant’s years of service, age, compensation and contributions. Certain defined benefit postretirement health care and life benefits are provided to eligible retirees. In general, the retiree health care plans consist of fixed benefit subsidy structures and the retiree life insurance plans are non-contributory.
IPL and WPL account for their participation in Alliant Energy and Corporate Services sponsored plans as multiple-employer plans. For IPL and WPL, amounts below represent the amounts for their plan participants covered under plans they sponsor, as well as amounts directly assigned to them related to certain participants in the Alliant Energy and Corporate Services sponsored plans.

Assumptions - The weighted-average assumptions for defined benefit pension and OPEB plans at the measurement date of December 31 were as follows:
Defined Benefit Pension PlansOPEB Plans
Alliant Energy202520242023202520242023
Discount rate for benefit obligations5.52%5.65%5.36%5.40%5.62%5.40%
Discount rate for net periodic cost5.65%5.36%5.54%5.62%5.40%5.53%
Expected rate of return on plan assets7.60%7.73%7.80%6.37%6.22%6.50%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan5.60%6.24%10.75%N/AN/AN/A
Rate of compensation increase3.75%-4.50%3.50%-4.50%3.30%-4.50%N/AN/AN/A
Qualified Defined Benefit Pension PlanOPEB Plans
IPL202520242023202520242023
Discount rate for benefit obligations5.56%5.66%5.35%5.38%5.61%5.40%
Discount rate for net periodic cost5.66%5.35%5.55%5.61%5.40%5.53%
Expected rate of return on plan assets7.60%7.60%7.80%6.70%6.60%6.90%
Rate of compensation increase4.00%3.75%3.30%N/AN/AN/A
Qualified Defined Benefit Pension PlanOPEB Plans
WPL202520242023202520242023
Discount rate for benefit obligations5.56%5.66%5.35%5.38%5.61%5.40%
Discount rate for net periodic cost5.66%5.35%5.54%5.61%5.40%5.53%
Expected rate of return on plan assets7.60%7.80%7.80%5.75%5.61%5.65%
Rate of compensation increase3.75%3.50%3.30%N/AN/AN/A

Expected rate of return on plan assets - The expected rate of return on plan assets is based on projected asset class returns using target allocations. A forward-looking building blocks approach is used, and historical returns, survey information and capital market information are analyzed to support the expected rate of return on plan assets assumption. Refer to “Investment Strategy for Plan Assets” below for additional information related to investment strategy and mix of assets for the pension and OPEB plans.

Life Expectancy - The life expectancy assumption is used in determining the benefit obligation and net periodic benefit cost for defined benefit pension and OPEB plans. This assumption utilizes base mortality tables that were released in 2019 by the Society of Actuaries and mortality projection tables that were released in 2021 by the Society of Actuaries.

Net Periodic Benefit Costs - The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans are included below (in millions). The service cost component of net periodic benefit costs is included in “Other operation and maintenance” expenses in the income statements and all other components of net periodic benefit costs are included in “Other (income) and deductions” in the income statements or regulatory assets on the balance sheets.
Alliant EnergyDefined Benefit Pension PlansOPEB Plans
202520242023202520242023
Service cost$4 $5 $5 $1 $2 $2 
Interest cost46 45 47 8 8 9 
Expected return on plan assets (a)(53)(55)(53)(4)(5)(5)
Amortization of prior service credit (b)— (1)(1)— — — 
Amortization of actuarial loss (c)22 24 28 — — 1 
$19 $18 $26 $5 $5 $7 
IPLDefined Benefit Pension PlansOPEB Plans
202520242023202520242023
Service cost$3 $3 $3 $1 $1 $1 
Interest cost20 20 21 3 3 3 
Expected return on plan assets (a)(25)(26)(26)(4)(4)(3)
Amortization of actuarial loss (c)9 9 11 — — 1 
$7 $6 $9 $— $— $2 
WPLDefined Benefit Pension PlansOPEB Plans
202520242023202520242023
Service cost$1 $2 $2 $1 $1 $1 
Interest cost20 20 20 3 3 3 
Expected return on plan assets (a)(23)(23)(22)(1)(1)(1)
Amortization of actuarial loss (c)11 11 13 — — 1 
$9 $10 $13 $3 $3 $4 

(a)The expected return on plan assets is based on the expected rate of return on plan assets and the fair value approach to the market-related value of plan assets.
(b)Unrecognized prior service credits for the OPEB plans are amortized over the average future service period to full eligibility of the participants of each plan.
(c)Unrecognized net actuarial gains or losses in excess of 10% of the greater of the plans’ benefit obligations or assets are amortized over the average future service lives of plan participants, except for the Alliant Energy Cash Balance Pension Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits.
Benefit Plan Assets and Obligations - A reconciliation of the funded status of qualified and non-qualified defined benefit pension and OPEB plans to the amounts recognized on the balance sheets at December 31 was as follows (in millions):
Defined Benefit Pension PlansOPEB Plans
Alliant Energy2025202420252024
Change in benefit obligation:
Net benefit obligation at January 1$841 $876 $148 $160 
Service cost4 5 1 2 
Interest cost46 45 8 8 
Plan participants’ contributions— — 4 3 
Actuarial (gain) loss17 (19)6 (7)
Gross benefits paid(84)(66)(21)(18)
Net benefit obligation at December 31824 841 146 148 
Change in plan assets:
Fair value of plan assets at January 1715 732 80 83 
Actual return on plan assets93 38 7 5 
Employer contributions23 11 8 7 
Plan participants’ contributions— — 4 3 
Gross benefits paid(84)(66)(21)(18)
Fair value of plan assets at December 31747 715 78 80 
Under funded status at December 31($77)($126)($68)($68)
Defined Benefit Pension PlansOPEB Plans
Alliant Energy2025202420252024
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $18 $17 
Current liabilities(5)(3)(6)(7)
Pension and other benefit obligations(72)(123)(80)(78)
Net amounts recognized at December 31($77)($126)($68)($68)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$267 $312 $7 $4 
Prior service credit(1)(2)— — 
$266 $310 $7 $4 
Defined Benefit Pension PlansOPEB Plans
IPL2025202420252024
Change in benefit obligation:
Net benefit obligation at January 1$372 $387 $59 $65 
Service cost3 3 1 1 
Interest cost20 20 3 3 
Plan participants’ contributions— — 2 1 
Actuarial (gain) loss6 (8)3 (3)
Gross benefits paid(38)(30)(9)(8)
Net benefit obligation at December 31363 372 59 59 
Change in plan assets:
Fair value of plan assets at January 1340 352 59 61 
Actual return on plan assets43 18 6 4 
Employer contributions1 — 2 1 
Plan participants’ contributions— — 2 1 
Gross benefits paid(38)(30)(9)(8)
Fair value of plan assets at December 31346 340 60 59 
(Under) Over funded status at December 31($17)($32)$1 $— 
Defined Benefit Pension PlansOPEB Plans
IPL2025202420252024
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $14 $13 
Current liabilities— (1)(1)(1)
Pension and other benefit obligations(17)(31)(12)(12)
Net amounts recognized at December 31($17)($32)$1 $— 
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$105 $126 $7 $7 
Prior service credit— (1)— — 
$105 $125 $7 $7 
Defined Benefit Pension PlansOPEB Plans
WPL2025202420252024
Change in benefit obligation:
Net benefit obligation at January 1$365 $381 $56 $61 
Service cost1 2 1 1 
Interest cost20 20 3 3 
Plan participants’ contributions— — 1 1 
Actuarial (gain) loss 9 (8)2 (3)
Gross benefits paid(33)(30)(8)(7)
Net benefit obligation at December 31362 365 55 56 
Change in plan assets:
Fair value of plan assets at January 1303 306 13 14 
Actual return on plan assets41 17 2 — 
Employer contributions16 10 6 5 
Plan participants’ contributions— — 1 1 
Gross benefits paid(33)(30)(8)(7)
Fair value of plan assets at December 31327 303 14 13 
Under funded status at December 31($35)($62)($41)($43)
Defined Benefit Pension PlansOPEB Plans
WPL2025202420252024
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $4 $4 
Current liabilities— — (5)(6)
Pension and other benefit obligations(35)(62)(40)(41)
Net amounts recognized at December 31($35)($62)($41)($43)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$115 $135 $1 $— 

Accumulated benefit obligations, aggregate amounts applicable to defined benefit pension and OPEB plans with accumulated benefit obligations in excess of plan assets, as well as defined benefit pension plans with projected benefit obligations in excess of plan assets as of the December 31 measurement date are as follows (in millions):
Defined Benefit Pension PlansOPEB Plans
Alliant Energy2025202420252024
Accumulated benefit obligations$805 $824 $146 $148 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations805 824 146 148 
Fair value of plan assets747 715 78 80 
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations824 841 N/AN/A
Fair value of plan assets747 715 N/AN/A
Defined Benefit Pension PlansOPEB Plans
IPL2025202420252024
Accumulated benefit obligations$353 $362 $59 $59 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations353 362 N/AN/A
Fair value of plan assets346 340 N/AN/A
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations363 372 N/AN/A
Fair value of plan assets346 340 N/AN/A
Defined Benefit Pension PlansOPEB Plans
WPL2025202420252024
Accumulated benefit obligations$354 $358 $55 $56 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations354 358 55 56 
Fair value of plan assets327 303 14 13 
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations362 365 N/AN/A
Fair value of plan assets327 303 N/AN/A

In addition to the amounts recognized in regulatory assets in the above tables for IPL and WPL, regulatory assets were recognized for amounts associated with Corporate Services employees participating in other Alliant Energy sponsored benefit plans that were allocated to IPL and WPL at December 31 as follows (in millions):
IPLWPL
2025202420252024
Regulatory assets$23$25$21$22

Estimated Future Employer Contributions and Benefit Payments - Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2026 is as follows (in millions):
Alliant EnergyIPLWPL
Defined benefit pension plans (a)$23$3$13
OPEB plans715

(a)Alliant Energy sponsors several non-qualified defined benefit pension plans that cover certain current and former key employees of IPL and WPL. Alliant Energy allocates pension costs to IPL and WPL for these plans. In addition, IPL and WPL amounts reflect funding for their non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans.

Expected benefit payments for the qualified and non-qualified defined benefit plans, which reflect expected future service, as appropriate, are as follows (in millions):
Alliant Energy202620272028202920302031 - 2035
Defined benefit pension benefits$75 $75 $75 $74 $69 $320
OPEB16 15 15 14 14 61
$91 $90 $90 $88 $83 $381
IPL202620272028202920302031 - 2035
Defined benefit pension benefits$34 $33 $33 $32 $32 $143
OPEB6 6 6 6 6 24
$40 $39 $39 $38 $38 $167
WPL202620272028202920302031 - 2035
Defined benefit pension benefits$32 $31 $31 $31 $30 $142
OPEB6 6 5 5 5 23
$38 $37 $36 $36 $35 $165

Investment Strategy for Plan Assets - Investment strategies for defined benefit pension and OPEB plan assets combine preservation of principal and prudent risk-taking to protect the integrity of plan assets, in order to meet the obligations to plan participants while minimizing benefit costs over the long term. Investment risk of plan assets is mitigated through an asset mix, which is governed by allocation targets. The asset allocation is monitored regularly, and appropriate steps are taken as needed to rebalance the assets within the prescribed ranges.
Defined Benefit Pension Plan Assets - Defined benefit pension plan assets have a long-term investment time horizon and are classified into return-seeking and liability-hedging portfolios. The return-seeking portfolio includes: public equities with different market capitalization, investment style and geography; liquid alternative securities, which include hedge fund strategies; and fixed income investments, which include, but are not limited to, high-yield bonds, emerging market debt, bank loans and private credit bonds. The liability-hedging portfolio includes: fixed-income investments including investment grade instruments of government and corporate issuers, as well as private placements and securitized assets; and fixed income derivative contracts for liability and interest rate hedging positions. At December 31, 2025, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows:
Target RangeActual
AllocationAllocation
Public equity securities32%-44%40%
Liquid alternative securities0%-11%5%
Return-seeking fixed income securities4%-16%7%
Liability-hedging fixed income securities (including cash and equivalents)41%-54%48%

Other Postretirement Benefits Plan Assets - OPEB plan assets are comprised of specific assets within certain defined benefit pension plans (401(h) assets) as well as assets held in VEBA trusts. For asset pools with a long-term investment time horizon, investments include public equities with different market capitalization, investment style and geography, and fixed income securities including investment grade instruments of government and corporate issuers. At December 31, 2025, the current target ranges and actual allocations for assets with a long-term investment horizon were as follows:
Target RangeActual
AllocationAllocation
Cash and equivalents0%-5%3%
Public equity securities0%-40%26%
Fixed income securities34%-100%71%

Fair Value Measurements - Fair value measurement accounting establishes three levels of fair value hierarchy that prioritize the inputs to valuation techniques used to measure fair value. Refer to Note 15 for discussion of levels within the fair value hierarchy. Level 1 items include investments in securities held in registered investment companies, which are valued at the closing price reported in the active market in which the securities are traded. Level 2 items include cash and equivalents consisting of money market fund investments and cash collateral supporting derivative financial instruments. Certain investments that are measured at fair value using the net asset value practical expedient have not been classified in the fair value hierarchy. These fair value amounts are included below to reconcile the fair value hierarchy to the respective total plan assets.

At December 31, the fair values of qualified and non-qualified defined benefit pension plan assets were as follows (in millions):
20252024
FairLevelLevelLevelFairLevelLevelLevel
Alliant EnergyValue123Value123
Cash and equivalents$71 $— $71 $— $49 $— $49 $— 
Assets measured at net asset value676 667 
Due to brokers, net (pending trades with brokers)— (1)
Total pension plan assets$747 $715 
20252024
FairLevelLevelLevelFairLevelLevelLevel
IPLValue123Value123
Cash and equivalents$31 $— $31 $— $21 $— $21 $— 
Assets measured at net asset value315 319 
Total pension plan assets$346 $340 
20252024
FairLevelLevelLevelFairLevelLevelLevel
WPLValue123Value123
Cash and equivalents$32 $— $32 $— $22 $— $22 $— 
Assets measured at net asset value295 281 
Total pension plan assets$327 $303 
At December 31, the fair values of OPEB plan assets were as follows (in millions):
20252024
FairLevelLevelLevelFairLevelLevelLevel
Alliant EnergyValue123Value123
Cash and equivalents$7 $— $7 $— $8 $— $8 $— 
Equity securities19 19 — — 20 20 — — 
Fixed income securities52 52 — — 52 52 — — 
Total OPEB plan assets$78 $71 $7 $— $80 $72 $8 $— 
20252024
FairLevelLevelLevelFairLevelLevelLevel
IPLValue123Value123
Cash and equivalents$3 $— $3 $— $1 $— $1 $— 
Equity securities17 17 — — 18 18 — — 
Fixed income securities40 40 — — 40 40 — — 
Total OPEB plan assets$60 $57 $3 $— $59 $58 $1 $— 
20252024
FairLevelLevelLevelFairLevelLevelLevel
WPLValue123Value123
Equity securities$2 $2 — — $2 $2 — — 
Fixed income securities12 12 — — 11 11 — — 
Total OPEB plan assets$14 $14 $— $— $13 $13 $— $— 

For the various defined benefit pension and OPEB plans, Alliant Energy common stock represented less than 1% of the assets directly held in the plans at December 31, 2025 and 2024, respectively.

401(k) Savings Plans - A significant number of employees participate in defined contribution retirement plans (401(k) savings plans). Alliant Energy common stock directly held by participants represented 7% of total assets in the 401(k) savings plans at December 31, 2025 and 2024. Costs related to the 401(k) savings plans, which are partially based on the participants’ contributions and include allocated costs associated with Corporate Services employees for IPL and WPL, were as follows (in millions):
Alliant EnergyIPLWPL
202520242023202520242023202520242023
401(k) costs$30 $31 $30 $14 $14 $14 $14 $15 $14 

Restructuring and Voluntary Employee Separation Charges - In 2024, Alliant Energy announced restructuring activities, including offering certain employees a voluntary separation package. Approximately 5% of total Alliant Energy employees accepted the package, and as a result of the restructuring activities, Alliant Energy, IPL and WPL recorded pre-tax charges of $29 million, $14 million and $13 million, respectively, in 2024. These charges were primarily recorded in “Other operation and maintenance” expenses in the income statements.
(b) Equity-based Compensation Plans - In 2020, Alliant Energy’s shareowners approved the 2020 OIP, which permits the grant of shares of Alliant Energy common stock, restricted stock, restricted stock units, performance shares, performance units, and other stock-based or cash-based awards to key employees. At December 31, 2025, performance shares and restricted stock units were outstanding under the 2020 OIP, and 7 million shares of Alliant Energy common stock remained available for grants under the 2020 OIP. Alliant Energy satisfies share payouts related to equity awards through the issuance of new shares of its common stock. Nonvested awards generally do not have non-forfeitable rights to dividends or dividend equivalents when dividends are paid to common shareowners. A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards was as follows (in millions):
Alliant EnergyIPLWPL
202520242023202520242023202520242023
Compensation expense$22$12$12$11$6$6$10$5$5
Income tax benefits333222111

As of December 31, 2025, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $14 million, $7 million and $6 million, respectively, which is expected to be recognized over a weighted average period of between one year and two years. Share-based compensation expense is recognized on a straight-line basis over the requisite service periods and is recorded in “Other operation and maintenance” in the income statements. As of December 31, 2025, 725,647 shares were included in the calculation of diluted EPS related to the nonvested equity awards.
Performance Shares (Total Shareowner Return Metric) - Payouts of certain performance shares are contingent upon achievement over a three-year period of specified performance criteria, which currently is total shareowner return relative to an investor-owned utility peer group. Performance shares grants are to be paid out in shares of Alliant Energy common stock and are accounted for as equity awards. The fair value of each of these performance shares is based on the fair value of the underlying common stock on the grant date and the probability of satisfying the market condition contained in the agreement during a three-year performance period. The actual number of these performance shares that will be paid out upon vesting is dependent upon actual performance and may range from zero to 200% of the target number of shares. If minimum performance targets are not met during the performance period, these performance shares are forfeited. Compensation expense is recorded ratably over the performance period based on the fair value of the awards at the grant date. A summary of the performance shares activity, with amounts representing the target number of awards, was as follows:
202520242023
SharesWeighted
Average Grant
Date Fair Value		SharesWeighted
Average Grant
Date Fair Value		SharesWeighted
Average Grant
Date Fair Value
Nonvested awards, January 1289,399$51.31233,954$52.60190,273$54.13
Granted105,89666.52127,87446.04108,71255.68
Vested——(47,497)46.19(53,431)64.04
Forfeited(73,918)54.14(24,932)46.16(11,600)53.88
Nonvested awards, December 31321,37755.67289,39951.31233,95452.60

Restricted Stock Units - Payouts of restricted stock units are based on the expiration of a three-year time-vesting period. Restricted stock unit grants are to be paid out in shares of Alliant Energy common stock and are accounted for as equity awards. The fair value of each of these restricted stock units is based on the closing market price of one share of Alliant Energy common stock on the grant date of the award. Compensation expense is recorded ratably over the performance period based on the fair value of the awards on the grant date. A summary of the restricted stock units activity was as follows:
202520242023
UnitsWeighted
Average Grant
Date Fair Value		UnitsWeighted
Average Grant
Date Fair Value		UnitsWeighted
Average Grant
Date Fair Value
Nonvested awards, January 1289,148$51.85234,259$52.58198,275$54.53
Granted102,24061.73129,85448.69106,12452.77
Vested(63,789)56.70(71,441)48.65(55,345)59.40
Forfeited(14,215)51.13(3,524)48.40(14,795)54.53
Nonvested awards, December 31313,38454.06289,14851.85234,25952.58

Performance Shares (Net Income, Environmental and Workforce Composition Metrics) (certain awards formerly granted as Performance Restricted Stock Units) - Payouts of certain performance shares are contingent upon achievement over a three-year period of specific performance criteria, which currently is specified growth of cumulative consolidated net income from continuing operations, as well as environmental and workforce composition metrics. Performance shares grants are to be paid out in shares of Alliant Energy common stock and are accounted for as equity awards. The fair value of each of these performance shares is based on the closing market price of one share of Alliant Energy common stock on the grant date of the award. The actual number of these performance shares that will be paid out upon vesting is dependent upon actual performance and may range from zero to 200% of the target number of shares under each award type. If minimum performance targets are not met during the performance period, these performance shares are forfeited. Compensation expense is recorded ratably over the performance period based on a probability assessment of payouts for the awards at each reporting period. A summary of the performance shares activity, with amounts representing the target number of awards, was as follows:
202520242023
SharesWeighted Average Grant Date Fair ValueSharesWeighted Average Grant Date Fair ValueSharesWeighted Average Grant Date Fair Value
Nonvested awards, January 1330,700$51.81257,639$52.76199,874$54.74
Granted118,88361.63146,14348.55124,21752.71
Vested(68,233)56.74(67,852)48.66(53,431)59.36
Forfeited(16,225)53.05(5,230)48.40(13,021)55.47
Nonvested awards, December 31365,12554.03330,70051.81257,63952.76
v3.25.4
Asset Retirement Obligations
 12 Months Ended
Dec. 31, 2025
Schedule of Asset Retirement Obligations [Line Items]  
Asset Retirement Obligations (AROs) ASSET RETIREMENT OBLIGATIONS
Recognized AROs relate to legal obligations for the removal, closure, dismantlement and management of several assets including, but not limited to, active and inactive ash landfills, ash ponds, wind farms, groundwater, solar facilities, above ground storage tanks and energy storage facilities. Recognized AROs also include legal obligations for the management and final disposition of asbestos and polychlorinated biphenyls. AROs are recorded in “Other current liabilities” and “Other liabilities” on the balance sheets. Refer to Note 2 for information regarding regulatory assets related to AROs. A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Balance, January 1$663 $246 $350 $148 $313 $98 
Revisions in estimated cash flows(1)(3)— (1)(1)(2)
Liabilities settled(5)(8)(2)(6)(3)(2)
Liabilities incurred (a)16 409 3 201 13 208 
Accretion expense31 19 16 8 15 11 
Balance, December 31$704 $663 $367 $350 $337 $313 

(a)In 2024, substantially due to the enactment of the revised CCR Rule, which significantly expands the scope of regulation to include coal ash ponds at sites that no longer produce electricity and inactive landfills, including some IPL and WPL facilities, Alliant Energy, IPL and WPL initially recorded additional AROs, additional ARO regulatory assets for EGUs no longer in operation, additional property, plant and equipment for EGUs still in operation, and a pre-tax non-cash charge of $20 million recorded to “Other operation and maintenance” in Alliant Energy’s and IPL’s income statements for the portion allocated to IPL’s steam business for IPL’s Prairie Creek Generating Station and the retired Sixth Street Generating Station as established in prior rate reviews. The amounts initially recorded in 2024 are expected to be adjusted in the future as additional information is obtained for the specific site closure plans, including the determination of whether or not individual sites are considered legal obligations and the acceptance and approval of compliance approaches, which could change management assumptions and result in a material change to the recorded amounts.
IPL [Member]  
Schedule of Asset Retirement Obligations [Line Items]  
Asset Retirement Obligations (AROs) ASSET RETIREMENT OBLIGATIONS
Recognized AROs relate to legal obligations for the removal, closure, dismantlement and management of several assets including, but not limited to, active and inactive ash landfills, ash ponds, wind farms, groundwater, solar facilities, above ground storage tanks and energy storage facilities. Recognized AROs also include legal obligations for the management and final disposition of asbestos and polychlorinated biphenyls. AROs are recorded in “Other current liabilities” and “Other liabilities” on the balance sheets. Refer to Note 2 for information regarding regulatory assets related to AROs. A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Balance, January 1$663 $246 $350 $148 $313 $98 
Revisions in estimated cash flows(1)(3)— (1)(1)(2)
Liabilities settled(5)(8)(2)(6)(3)(2)
Liabilities incurred (a)16 409 3 201 13 208 
Accretion expense31 19 16 8 15 11 
Balance, December 31$704 $663 $367 $350 $337 $313 

(a)In 2024, substantially due to the enactment of the revised CCR Rule, which significantly expands the scope of regulation to include coal ash ponds at sites that no longer produce electricity and inactive landfills, including some IPL and WPL facilities, Alliant Energy, IPL and WPL initially recorded additional AROs, additional ARO regulatory assets for EGUs no longer in operation, additional property, plant and equipment for EGUs still in operation, and a pre-tax non-cash charge of $20 million recorded to “Other operation and maintenance” in Alliant Energy’s and IPL’s income statements for the portion allocated to IPL’s steam business for IPL’s Prairie Creek Generating Station and the retired Sixth Street Generating Station as established in prior rate reviews. The amounts initially recorded in 2024 are expected to be adjusted in the future as additional information is obtained for the specific site closure plans, including the determination of whether or not individual sites are considered legal obligations and the acceptance and approval of compliance approaches, which could change management assumptions and result in a material change to the recorded amounts.
WPL [Member]  
Schedule of Asset Retirement Obligations [Line Items]  
Asset Retirement Obligations (AROs) ASSET RETIREMENT OBLIGATIONS
Recognized AROs relate to legal obligations for the removal, closure, dismantlement and management of several assets including, but not limited to, active and inactive ash landfills, ash ponds, wind farms, groundwater, solar facilities, above ground storage tanks and energy storage facilities. Recognized AROs also include legal obligations for the management and final disposition of asbestos and polychlorinated biphenyls. AROs are recorded in “Other current liabilities” and “Other liabilities” on the balance sheets. Refer to Note 2 for information regarding regulatory assets related to AROs. A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Balance, January 1$663 $246 $350 $148 $313 $98 
Revisions in estimated cash flows(1)(3)— (1)(1)(2)
Liabilities settled(5)(8)(2)(6)(3)(2)
Liabilities incurred (a)16 409 3 201 13 208 
Accretion expense31 19 16 8 15 11 
Balance, December 31$704 $663 $367 $350 $337 $313 

(a)In 2024, substantially due to the enactment of the revised CCR Rule, which significantly expands the scope of regulation to include coal ash ponds at sites that no longer produce electricity and inactive landfills, including some IPL and WPL facilities, Alliant Energy, IPL and WPL initially recorded additional AROs, additional ARO regulatory assets for EGUs no longer in operation, additional property, plant and equipment for EGUs still in operation, and a pre-tax non-cash charge of $20 million recorded to “Other operation and maintenance” in Alliant Energy’s and IPL’s income statements for the portion allocated to IPL’s steam business for IPL’s Prairie Creek Generating Station and the retired Sixth Street Generating Station as established in prior rate reviews. The amounts initially recorded in 2024 are expected to be adjusted in the future as additional information is obtained for the specific site closure plans, including the determination of whether or not individual sites are considered legal obligations and the acceptance and approval of compliance approaches, which could change management assumptions and result in a material change to the recorded amounts.
v3.25.4
Derivative Instruments
 12 Months Ended
Dec. 31, 2025
Derivative [Line Items]  
Derivative Instruments DERIVATIVE INSTRUMENTS
Commodity Derivatives -
Purpose - Derivative instruments were utilized for risk management purposes to mitigate pricing volatility for fuel used to supply natural gas-fired EGUs, natural gas supplied to retail customers, and purchased electricity, as well as optimize the value of natural gas pipeline capacity and electric generation, which may include swap, physical forward and option contracts. In addition, FTRs help manage transmission congestion costs in the MISO market. Risk policies are maintained that govern the use of such derivative instruments.
Notional Amounts - As of December 31, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands):
ElectricityFTRsNatural GasDiesel Fuel
MWhsYearsMWhsYearsDthsYearsGallonsYears
2025
Alliant Energy1,682 202611,332 2026140,731 2026-2032— N/A
IPL634 20264,482 202660,773 2026-2030— N/A
WPL1,048 20266,850 202679,958 2026-2032— N/A
2024
Alliant Energy1,422 2025-202610,232 2025147,894 2025-20322,520 2025
IPL383 2025-20263,551 202561,489 2025-2030— N/A
WPL1,039 2025-20266,681 202586,405 2025-20322,520 2025

Financial Statement Presentation - Derivative instruments are recorded at fair value each reporting date on the balance sheet as assets or liabilities. At December 31, based on the maturities of the underlying contracts, the fair values of current derivative assets are included in “Other current assets,” non-current derivative assets are included in “Deferred charges and other,” current derivative liabilities are included in “Other current liabilities” and non-current derivative liabilities are included in “Other liabilities” on the balance sheets as follows (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Current derivative assets$49$41$33$29$16$12
Non-current derivative assets20341119915
Current derivative liabilities25269111615
Non-current derivative liabilities2632222430

Based on IPL’s and WPL’s cost recovery mechanisms, the changes in the fair value of derivative liabilities/assets resulted in comparable changes to regulatory assets/liabilities on the balance sheets.

Credit Risk-related Contingent Features - Various agreements contain credit risk-related contingent features, including requirements to maintain certain credit ratings and/or limitations on liability positions under the agreements based on credit ratings. Certain of these agreements with credit risk-related contingency features are accounted for as derivative instruments. In the event of a material change in creditworthiness or if liability positions exceed certain contractual limits, credit support may need to be provided up to the amount of exposure under the contracts, or the contracts may need to be unwound and underlying liability positions paid. At December 31, 2025 and 2024, the aggregate fair value of all derivative instruments with credit risk-related contingent features in a net liability position was not materially different than amounts that would be required to be posted as credit support to counterparties by Alliant Energy, IPL or WPL if the most restrictive credit risk-related contingent features for derivative agreements in a net liability position were triggered.

Balance Sheet Offsetting - The fair value amounts of derivative instruments subject to a master netting arrangement are not netted by counterparty on the balance sheets. However, if the fair value amounts of derivative instruments by counterparty were netted, derivative assets and derivative liabilities related to commodity contracts would have been presented on the balance sheets at December 31 as follows:
Alliant EnergyIPLWPL
GrossGrossGross
(as reported)Net(as reported)Net(as reported)Net
2025
Derivative assets$69$59$44$40$25$19
Derivative liabilities51411174034
2024
Derivative assets756448432721
Derivative liabilities58471384539

Fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) are not offset against fair value amounts recognized for derivative instruments executed with the same counterparty under the same master netting arrangement.

Interest Rate Derivative - In January 2023, AEF entered into a $300 million interest rate swap maturing in January 2026 to mitigate interest rate risk. Under the terms of the swap, AEF exchanged a variable interest rate for a fixed interest rate of 3.93% on a portion of its variable-rate term loan borrowings. In 2025, 2024 and 2023, $1 million, $4 million and $3 million, respectively, of reductions to interest expense were recorded in Alliant Energy’s income statements related to the interest rate swap.
In October 2025, AEC entered into a $300 million forward starting interest rate swap maturing in March 2028 to mitigate forecasted interest rate risk. Under the terms of the swap, AEC exchanged a variable interest rate for a fixed interest rate of 3.10% on a portion of its forecasted variable-rate term loan borrowings expected to be issued in 2026. The related interest rate derivative was valued based on quoted prices that utilize current market interest rate forecasts. As of December 31, 2025, $1 million of non-current interest rate derivative assets was recorded in “Deferred charges and other” on Alliant Energy’s balance sheet. This interest rate derivative was designated as a cash flow hedge, with changes in fair value recorded as other comprehensive income. As of December 31, 2025, accumulated other comprehensive income included $1 million of income related to the interest rate swap. In 2025, there were no increases or reductions to interest expense recorded in Alliant Energy’s income statement related to the interest rate swap.
IPL [Member]  
Derivative [Line Items]  
Derivative Instruments DERIVATIVE INSTRUMENTS
Commodity Derivatives -
Purpose - Derivative instruments were utilized for risk management purposes to mitigate pricing volatility for fuel used to supply natural gas-fired EGUs, natural gas supplied to retail customers, and purchased electricity, as well as optimize the value of natural gas pipeline capacity and electric generation, which may include swap, physical forward and option contracts. In addition, FTRs help manage transmission congestion costs in the MISO market. Risk policies are maintained that govern the use of such derivative instruments.
Notional Amounts - As of December 31, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands):
ElectricityFTRsNatural GasDiesel Fuel
MWhsYearsMWhsYearsDthsYearsGallonsYears
2025
Alliant Energy1,682 202611,332 2026140,731 2026-2032— N/A
IPL634 20264,482 202660,773 2026-2030— N/A
WPL1,048 20266,850 202679,958 2026-2032— N/A
2024
Alliant Energy1,422 2025-202610,232 2025147,894 2025-20322,520 2025
IPL383 2025-20263,551 202561,489 2025-2030— N/A
WPL1,039 2025-20266,681 202586,405 2025-20322,520 2025

Financial Statement Presentation - Derivative instruments are recorded at fair value each reporting date on the balance sheet as assets or liabilities. At December 31, based on the maturities of the underlying contracts, the fair values of current derivative assets are included in “Other current assets,” non-current derivative assets are included in “Deferred charges and other,” current derivative liabilities are included in “Other current liabilities” and non-current derivative liabilities are included in “Other liabilities” on the balance sheets as follows (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Current derivative assets$49$41$33$29$16$12
Non-current derivative assets20341119915
Current derivative liabilities25269111615
Non-current derivative liabilities2632222430

Based on IPL’s and WPL’s cost recovery mechanisms, the changes in the fair value of derivative liabilities/assets resulted in comparable changes to regulatory assets/liabilities on the balance sheets.

Credit Risk-related Contingent Features - Various agreements contain credit risk-related contingent features, including requirements to maintain certain credit ratings and/or limitations on liability positions under the agreements based on credit ratings. Certain of these agreements with credit risk-related contingency features are accounted for as derivative instruments. In the event of a material change in creditworthiness or if liability positions exceed certain contractual limits, credit support may need to be provided up to the amount of exposure under the contracts, or the contracts may need to be unwound and underlying liability positions paid. At December 31, 2025 and 2024, the aggregate fair value of all derivative instruments with credit risk-related contingent features in a net liability position was not materially different than amounts that would be required to be posted as credit support to counterparties by Alliant Energy, IPL or WPL if the most restrictive credit risk-related contingent features for derivative agreements in a net liability position were triggered.

Balance Sheet Offsetting - The fair value amounts of derivative instruments subject to a master netting arrangement are not netted by counterparty on the balance sheets. However, if the fair value amounts of derivative instruments by counterparty were netted, derivative assets and derivative liabilities related to commodity contracts would have been presented on the balance sheets at December 31 as follows:
Alliant EnergyIPLWPL
GrossGrossGross
(as reported)Net(as reported)Net(as reported)Net
2025
Derivative assets$69$59$44$40$25$19
Derivative liabilities51411174034
2024
Derivative assets756448432721
Derivative liabilities58471384539

Fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) are not offset against fair value amounts recognized for derivative instruments executed with the same counterparty under the same master netting arrangement.
WPL [Member]  
Derivative [Line Items]  
Derivative Instruments DERIVATIVE INSTRUMENTS
Commodity Derivatives -
Purpose - Derivative instruments were utilized for risk management purposes to mitigate pricing volatility for fuel used to supply natural gas-fired EGUs, natural gas supplied to retail customers, and purchased electricity, as well as optimize the value of natural gas pipeline capacity and electric generation, which may include swap, physical forward and option contracts. In addition, FTRs help manage transmission congestion costs in the MISO market. Risk policies are maintained that govern the use of such derivative instruments.
Notional Amounts - As of December 31, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands):
ElectricityFTRsNatural GasDiesel Fuel
MWhsYearsMWhsYearsDthsYearsGallonsYears
2025
Alliant Energy1,682 202611,332 2026140,731 2026-2032— N/A
IPL634 20264,482 202660,773 2026-2030— N/A
WPL1,048 20266,850 202679,958 2026-2032— N/A
2024
Alliant Energy1,422 2025-202610,232 2025147,894 2025-20322,520 2025
IPL383 2025-20263,551 202561,489 2025-2030— N/A
WPL1,039 2025-20266,681 202586,405 2025-20322,520 2025

Financial Statement Presentation - Derivative instruments are recorded at fair value each reporting date on the balance sheet as assets or liabilities. At December 31, based on the maturities of the underlying contracts, the fair values of current derivative assets are included in “Other current assets,” non-current derivative assets are included in “Deferred charges and other,” current derivative liabilities are included in “Other current liabilities” and non-current derivative liabilities are included in “Other liabilities” on the balance sheets as follows (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Current derivative assets$49$41$33$29$16$12
Non-current derivative assets20341119915
Current derivative liabilities25269111615
Non-current derivative liabilities2632222430

Based on IPL’s and WPL’s cost recovery mechanisms, the changes in the fair value of derivative liabilities/assets resulted in comparable changes to regulatory assets/liabilities on the balance sheets.

Credit Risk-related Contingent Features - Various agreements contain credit risk-related contingent features, including requirements to maintain certain credit ratings and/or limitations on liability positions under the agreements based on credit ratings. Certain of these agreements with credit risk-related contingency features are accounted for as derivative instruments. In the event of a material change in creditworthiness or if liability positions exceed certain contractual limits, credit support may need to be provided up to the amount of exposure under the contracts, or the contracts may need to be unwound and underlying liability positions paid. At December 31, 2025 and 2024, the aggregate fair value of all derivative instruments with credit risk-related contingent features in a net liability position was not materially different than amounts that would be required to be posted as credit support to counterparties by Alliant Energy, IPL or WPL if the most restrictive credit risk-related contingent features for derivative agreements in a net liability position were triggered.

Balance Sheet Offsetting - The fair value amounts of derivative instruments subject to a master netting arrangement are not netted by counterparty on the balance sheets. However, if the fair value amounts of derivative instruments by counterparty were netted, derivative assets and derivative liabilities related to commodity contracts would have been presented on the balance sheets at December 31 as follows:
Alliant EnergyIPLWPL
GrossGrossGross
(as reported)Net(as reported)Net(as reported)Net
2025
Derivative assets$69$59$44$40$25$19
Derivative liabilities51411174034
2024
Derivative assets756448432721
Derivative liabilities58471384539

Fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) are not offset against fair value amounts recognized for derivative instruments executed with the same counterparty under the same master netting arrangement.
v3.25.4
Fair Value Measurements
 12 Months Ended
Dec. 31, 2025
Statement [Line Items]  
Fair Value Measurements FAIR VALUE MEASUREMENTS
Valuation Hierarchy - Fair value measurement accounting establishes three levels of fair value hierarchy that prioritize the inputs to valuation techniques used to measure fair value. Level 1 pricing inputs are quoted prices available in active markets for identical assets or liabilities as of the reporting date. Level 2 pricing inputs are quoted prices for similar assets or liabilities in active markets or quoted prices for identical or similar assets or liabilities in markets that are not active as of the reporting date. Level 3 pricing inputs are unobservable inputs for assets or liabilities for which little or no market data exist and require significant management judgment or estimation.

The fair value hierarchy gives the highest priority to quoted prices in active markets (Level 1) and the lowest priority to unobservable data (Level 3). In some cases, the inputs used to measure fair value might fall in different levels of the fair value hierarchy. The lowest level input that is significant to a fair value measurement in its entirety determines the applicable level in the fair value hierarchy. Assessing the significance of a particular input to the fair value measurement in its entirety requires judgment, considering factors specific to the asset or liability.

Valuation Techniques -
Derivative assets and derivative liabilities - Swap, option and physical forward commodity contracts were non-exchange-based derivative instruments and were valued using indicative price quotations from a pricing vendor that provides daily exchange forward price settlements, from broker or dealer quotations, from market publications or from on-line exchanges. The indicative price quotations reflected the average of the bid-ask mid-point prices and were obtained from sources believed to provide the most liquid market for the commodity. A portion of these indicative price quotations were corroborated using quoted prices for similar assets or liabilities in active markets and categorized derivative instruments based on such indicative price quotations as Level 2. Commodity contracts that were valued using indicative price quotations based on significant assumptions such as seasonal or monthly shaping and indicative price quotations that could not be readily corroborated were categorized as Level 3. Swap, option and physical forward commodity contracts were predominately at liquid trading points. FTRs were valued using auction prices and were categorized as Level 3. Refer to Note 14 for additional details of derivative assets and derivative liabilities.

Deferred proceeds (sales of receivables) - The fair value of IPL’s deferred proceeds related to its sales of accounts receivable program was calculated each reporting date using the cost approach valuation technique. The fair value represents the carrying amount of receivables sold less the allowance for expected credit losses associated with the receivables sold and cash amounts received from the receivables sold due to the short-term nature of the collection period. These inputs were considered unobservable and deferred proceeds were categorized as Level 3. Deferred proceeds represent IPL’s maximum exposure to loss related to the receivables sold. Refer to Note 5(b) for additional information regarding deferred proceeds.

Long-term debt (including current maturities) - The fair value of long-term debt instruments was based on a discounted cash flow methodology using observable data from comparably traded securities with similar credit profiles, and was classified as Level 2. Refer to Note 8(b) for additional information regarding long-term debt.
Fair Value of Financial Instruments - The carrying amounts of current assets and current liabilities approximate fair value because of the short maturity of such financial instruments. Carrying amounts and related estimated fair values of other financial instruments at December 31 were as follows (in millions):
Alliant Energy20252024
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$411 $411 $— $— $411 $52 $52 $— $— $52 
Commodity derivatives69 — 36 33 69 75 — 48 27 75 
Interest rate derivatives1 — 1 — 1 1 — 1 — 1 
Deferred proceeds126 — — 126 126 163 — — 163 163 
Liabilities:
Commodity derivatives51 — 50 1 51 58 — 56 2 58 
Long-term debt (incl. current maturities)12,028 — 11,748 — 11,748 9,848 — 9,577 — 9,577 
IPL20252024
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$— $— $— $— $— $9 $9 $— $— $9 
Commodity derivatives44 — 18 26 44 48 — 26 22 48 
Deferred proceeds126 — — 126 126 163 — — 163 163 
Liabilities:
Commodity derivatives11 — 10 1 11 13 — 11 2 13 
Long-term debt (incl. current maturities)4,680 — 4,445 — 4,445 4,090 — 3,736 — 3,736 
WPL20252024
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$25 $25 $— $— $25 $43 $43 $— $— $43 
Commodity derivatives25 — 18 7 25 27 — 22 5 27 
Liabilities:
Commodity derivatives40 — 40 — 40 45 — 45 — 45 
Long-term debt3,669 — 3,575 — 3,575 3,370 — 3,170 — 3,170 

Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions):
Alliant EnergyCommodity Contract Derivative
Assets and (Liabilities), netDeferred Proceeds
2025202420252024
Beginning balance, January 1$25$24$163$216
Total net gains (losses) included in changes in net assets (realized/unrealized)11(3)——
Purchases5059——
Sales(3)(3)——
Settlements (a)(51)(52)(37)(53)
Ending balance, December 31$32$25$126$163
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31$11($3)$—$—
IPLCommodity Contract Derivative
Assets and (Liabilities), netDeferred Proceeds
2025202420252024
Beginning balance, January 1$20$19$163$216
Total net gains (losses) included in changes in net assets (realized/unrealized)5(4)——
Purchases4045——
Sales(2)(2)——
Settlements (a)(38)(38)(37)(53)
Ending balance, December 31$25$20$126$163
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31$5($4)$—$—
WPLCommodity Contract Derivative
Assets and (Liabilities), net
20252024
Beginning balance, January 1$5$5
Total net gains included in changes in net assets (realized/unrealized)61
Purchases1014
Sales(1)(1)
Settlements(13)(14)
Ending balance, December 31$7$5
The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at December 31$6$1

(a)Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for expected credit losses associated with the receivables sold and cash amounts received from the receivables sold.

Commodity Contracts - The fair value of FTRs and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets at December 31 as follows (in millions):
Alliant EnergyIPLWPL
Excluding FTRsFTRsExcluding FTRsFTRsExcluding FTRsFTRs
2025$3$29$3$22$—$7
2024—25—20—5
IPL [Member]  
Statement [Line Items]  
Fair Value Measurements FAIR VALUE MEASUREMENTS
Valuation Hierarchy - Fair value measurement accounting establishes three levels of fair value hierarchy that prioritize the inputs to valuation techniques used to measure fair value. Level 1 pricing inputs are quoted prices available in active markets for identical assets or liabilities as of the reporting date. Level 2 pricing inputs are quoted prices for similar assets or liabilities in active markets or quoted prices for identical or similar assets or liabilities in markets that are not active as of the reporting date. Level 3 pricing inputs are unobservable inputs for assets or liabilities for which little or no market data exist and require significant management judgment or estimation.

The fair value hierarchy gives the highest priority to quoted prices in active markets (Level 1) and the lowest priority to unobservable data (Level 3). In some cases, the inputs used to measure fair value might fall in different levels of the fair value hierarchy. The lowest level input that is significant to a fair value measurement in its entirety determines the applicable level in the fair value hierarchy. Assessing the significance of a particular input to the fair value measurement in its entirety requires judgment, considering factors specific to the asset or liability.

Valuation Techniques -
Derivative assets and derivative liabilities - Swap, option and physical forward commodity contracts were non-exchange-based derivative instruments and were valued using indicative price quotations from a pricing vendor that provides daily exchange forward price settlements, from broker or dealer quotations, from market publications or from on-line exchanges. The indicative price quotations reflected the average of the bid-ask mid-point prices and were obtained from sources believed to provide the most liquid market for the commodity. A portion of these indicative price quotations were corroborated using quoted prices for similar assets or liabilities in active markets and categorized derivative instruments based on such indicative price quotations as Level 2. Commodity contracts that were valued using indicative price quotations based on significant assumptions such as seasonal or monthly shaping and indicative price quotations that could not be readily corroborated were categorized as Level 3. Swap, option and physical forward commodity contracts were predominately at liquid trading points. FTRs were valued using auction prices and were categorized as Level 3. Refer to Note 14 for additional details of derivative assets and derivative liabilities.

Deferred proceeds (sales of receivables) - The fair value of IPL’s deferred proceeds related to its sales of accounts receivable program was calculated each reporting date using the cost approach valuation technique. The fair value represents the carrying amount of receivables sold less the allowance for expected credit losses associated with the receivables sold and cash amounts received from the receivables sold due to the short-term nature of the collection period. These inputs were considered unobservable and deferred proceeds were categorized as Level 3. Deferred proceeds represent IPL’s maximum exposure to loss related to the receivables sold. Refer to Note 5(b) for additional information regarding deferred proceeds.

Long-term debt (including current maturities) - The fair value of long-term debt instruments was based on a discounted cash flow methodology using observable data from comparably traded securities with similar credit profiles, and was classified as Level 2. Refer to Note 8(b) for additional information regarding long-term debt.
Fair Value of Financial Instruments - The carrying amounts of current assets and current liabilities approximate fair value because of the short maturity of such financial instruments. Carrying amounts and related estimated fair values of other financial instruments at December 31 were as follows (in millions):
Alliant Energy20252024
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$411 $411 $— $— $411 $52 $52 $— $— $52 
Commodity derivatives69 — 36 33 69 75 — 48 27 75 
Interest rate derivatives1 — 1 — 1 1 — 1 — 1 
Deferred proceeds126 — — 126 126 163 — — 163 163 
Liabilities:
Commodity derivatives51 — 50 1 51 58 — 56 2 58 
Long-term debt (incl. current maturities)12,028 — 11,748 — 11,748 9,848 — 9,577 — 9,577 
IPL20252024
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$— $— $— $— $— $9 $9 $— $— $9 
Commodity derivatives44 — 18 26 44 48 — 26 22 48 
Deferred proceeds126 — — 126 126 163 — — 163 163 
Liabilities:
Commodity derivatives11 — 10 1 11 13 — 11 2 13 
Long-term debt (incl. current maturities)4,680 — 4,445 — 4,445 4,090 — 3,736 — 3,736 
WPL20252024
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$25 $25 $— $— $25 $43 $43 $— $— $43 
Commodity derivatives25 — 18 7 25 27 — 22 5 27 
Liabilities:
Commodity derivatives40 — 40 — 40 45 — 45 — 45 
Long-term debt3,669 — 3,575 — 3,575 3,370 — 3,170 — 3,170 

Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions):
Alliant EnergyCommodity Contract Derivative
Assets and (Liabilities), netDeferred Proceeds
2025202420252024
Beginning balance, January 1$25$24$163$216
Total net gains (losses) included in changes in net assets (realized/unrealized)11(3)——
Purchases5059——
Sales(3)(3)——
Settlements (a)(51)(52)(37)(53)
Ending balance, December 31$32$25$126$163
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31$11($3)$—$—
IPLCommodity Contract Derivative
Assets and (Liabilities), netDeferred Proceeds
2025202420252024
Beginning balance, January 1$20$19$163$216
Total net gains (losses) included in changes in net assets (realized/unrealized)5(4)——
Purchases4045——
Sales(2)(2)——
Settlements (a)(38)(38)(37)(53)
Ending balance, December 31$25$20$126$163
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31$5($4)$—$—
WPLCommodity Contract Derivative
Assets and (Liabilities), net
20252024
Beginning balance, January 1$5$5
Total net gains included in changes in net assets (realized/unrealized)61
Purchases1014
Sales(1)(1)
Settlements(13)(14)
Ending balance, December 31$7$5
The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at December 31$6$1

(a)Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for expected credit losses associated with the receivables sold and cash amounts received from the receivables sold.

Commodity Contracts - The fair value of FTRs and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets at December 31 as follows (in millions):
Alliant EnergyIPLWPL
Excluding FTRsFTRsExcluding FTRsFTRsExcluding FTRsFTRs
2025$3$29$3$22$—$7
2024—25—20—5
WPL [Member]  
Statement [Line Items]  
Fair Value Measurements FAIR VALUE MEASUREMENTS
Valuation Hierarchy - Fair value measurement accounting establishes three levels of fair value hierarchy that prioritize the inputs to valuation techniques used to measure fair value. Level 1 pricing inputs are quoted prices available in active markets for identical assets or liabilities as of the reporting date. Level 2 pricing inputs are quoted prices for similar assets or liabilities in active markets or quoted prices for identical or similar assets or liabilities in markets that are not active as of the reporting date. Level 3 pricing inputs are unobservable inputs for assets or liabilities for which little or no market data exist and require significant management judgment or estimation.

The fair value hierarchy gives the highest priority to quoted prices in active markets (Level 1) and the lowest priority to unobservable data (Level 3). In some cases, the inputs used to measure fair value might fall in different levels of the fair value hierarchy. The lowest level input that is significant to a fair value measurement in its entirety determines the applicable level in the fair value hierarchy. Assessing the significance of a particular input to the fair value measurement in its entirety requires judgment, considering factors specific to the asset or liability.

Valuation Techniques -
Derivative assets and derivative liabilities - Swap, option and physical forward commodity contracts were non-exchange-based derivative instruments and were valued using indicative price quotations from a pricing vendor that provides daily exchange forward price settlements, from broker or dealer quotations, from market publications or from on-line exchanges. The indicative price quotations reflected the average of the bid-ask mid-point prices and were obtained from sources believed to provide the most liquid market for the commodity. A portion of these indicative price quotations were corroborated using quoted prices for similar assets or liabilities in active markets and categorized derivative instruments based on such indicative price quotations as Level 2. Commodity contracts that were valued using indicative price quotations based on significant assumptions such as seasonal or monthly shaping and indicative price quotations that could not be readily corroborated were categorized as Level 3. Swap, option and physical forward commodity contracts were predominately at liquid trading points. FTRs were valued using auction prices and were categorized as Level 3. Refer to Note 14 for additional details of derivative assets and derivative liabilities.

Deferred proceeds (sales of receivables) - The fair value of IPL’s deferred proceeds related to its sales of accounts receivable program was calculated each reporting date using the cost approach valuation technique. The fair value represents the carrying amount of receivables sold less the allowance for expected credit losses associated with the receivables sold and cash amounts received from the receivables sold due to the short-term nature of the collection period. These inputs were considered unobservable and deferred proceeds were categorized as Level 3. Deferred proceeds represent IPL’s maximum exposure to loss related to the receivables sold. Refer to Note 5(b) for additional information regarding deferred proceeds.

Long-term debt (including current maturities) - The fair value of long-term debt instruments was based on a discounted cash flow methodology using observable data from comparably traded securities with similar credit profiles, and was classified as Level 2. Refer to Note 8(b) for additional information regarding long-term debt.
Fair Value of Financial Instruments - The carrying amounts of current assets and current liabilities approximate fair value because of the short maturity of such financial instruments. Carrying amounts and related estimated fair values of other financial instruments at December 31 were as follows (in millions):
Alliant Energy20252024
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$411 $411 $— $— $411 $52 $52 $— $— $52 
Commodity derivatives69 — 36 33 69 75 — 48 27 75 
Interest rate derivatives1 — 1 — 1 1 — 1 — 1 
Deferred proceeds126 — — 126 126 163 — — 163 163 
Liabilities:
Commodity derivatives51 — 50 1 51 58 — 56 2 58 
Long-term debt (incl. current maturities)12,028 — 11,748 — 11,748 9,848 — 9,577 — 9,577 
IPL20252024
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$— $— $— $— $— $9 $9 $— $— $9 
Commodity derivatives44 — 18 26 44 48 — 26 22 48 
Deferred proceeds126 — — 126 126 163 — — 163 163 
Liabilities:
Commodity derivatives11 — 10 1 11 13 — 11 2 13 
Long-term debt (incl. current maturities)4,680 — 4,445 — 4,445 4,090 — 3,736 — 3,736 
WPL20252024
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$25 $25 $— $— $25 $43 $43 $— $— $43 
Commodity derivatives25 — 18 7 25 27 — 22 5 27 
Liabilities:
Commodity derivatives40 — 40 — 40 45 — 45 — 45 
Long-term debt3,669 — 3,575 — 3,575 3,370 — 3,170 — 3,170 

Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions):
Alliant EnergyCommodity Contract Derivative
Assets and (Liabilities), netDeferred Proceeds
2025202420252024
Beginning balance, January 1$25$24$163$216
Total net gains (losses) included in changes in net assets (realized/unrealized)11(3)——
Purchases5059——
Sales(3)(3)——
Settlements (a)(51)(52)(37)(53)
Ending balance, December 31$32$25$126$163
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31$11($3)$—$—
IPLCommodity Contract Derivative
Assets and (Liabilities), netDeferred Proceeds
2025202420252024
Beginning balance, January 1$20$19$163$216
Total net gains (losses) included in changes in net assets (realized/unrealized)5(4)——
Purchases4045——
Sales(2)(2)——
Settlements (a)(38)(38)(37)(53)
Ending balance, December 31$25$20$126$163
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31$5($4)$—$—
WPLCommodity Contract Derivative
Assets and (Liabilities), net
20252024
Beginning balance, January 1$5$5
Total net gains included in changes in net assets (realized/unrealized)61
Purchases1014
Sales(1)(1)
Settlements(13)(14)
Ending balance, December 31$7$5
The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at December 31$6$1

(a)Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for expected credit losses associated with the receivables sold and cash amounts received from the receivables sold.

Commodity Contracts - The fair value of FTRs and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets at December 31 as follows (in millions):
Alliant EnergyIPLWPL
Excluding FTRsFTRsExcluding FTRsFTRsExcluding FTRsFTRs
2025$3$29$3$22$—$7
2024—25—20—5
v3.25.4
Commitments And Contingencies
 12 Months Ended
Dec. 31, 2025
Statement [Line Items]  
Commitments And Contingencies COMMITMENTS AND CONTINGENCIES(a) Capital Purchase Commitments - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects, including IPL’s and WPL’s expansion of energy storage, improvements at the natural gas-fired Neenah Energy Facility and Sheboygan Falls Energy Facility, and repowering projects at WPL’s Bent Tree Energy Facility. At December 31, 2025, Alliant Energy’s, IPL’s, and WPL’s minimum future commitments in 2026 for these projects were $459 million, $302 million, and $155 million, respectively.(b) Other Purchase Commitments - Various commodity supply, transportation and storage contracts help meet obligations to provide electricity and natural gas to utility customers. In addition, there are various purchase commitments associated with other goods and services. At December 31, 2025, the related minimum future commitments, excluding amounts for purchased power commitments that do not have minimum thresholds but require payment when electricity is generated by the provider and amounts for future commitments to deliver power to electric customers that do not have current minimum thresholds but will be billed for requirements when power is provided, were as follows (in millions):
Alliant Energy20262027202820292030ThereafterTotal
Natural gas$271$191$163$145$103$245$1,118
Coal764228———146
Other (a)571684317105
$404$249$199$149$106$262$1,369
IPL20262027202820292030ThereafterTotal
Natural gas$149$105$85$70$31$52$492
Coal341410———58
Other (a)2422221648
$207$121$97$72$33$68$598
WPL20262027202820292030ThereafterTotal
Natural gas$122$86$78$75$72$193$626
Coal422818———88
Other (a)251————26
$189$115$96$75$72$193$740

(a)Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2025.
(c) Legal Proceedings - Alliant Energy, IPL and WPL are involved in legal and administrative proceedings before various courts and agencies with respect to matters arising in the ordinary course of business. Although unable to predict the outcome of these matters, Alliant Energy, IPL and WPL believe that appropriate reserves have been established and final disposition of these actions will not have a material effect on their financial condition or results of operations.(d) Guarantees and Indemnifications -
Whiting Petroleum Corporation (Whiting Petroleum) - In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum, an independent oil and gas company. Alliant Energy Resources, LLC, as the successor to a predecessor entity that owned Whiting Petroleum, and a wholly-owned subsidiary of AEF, has guaranteed the partnership obligations of an affiliate of Whiting Petroleum under multiple general partnership agreements in the oil and gas industry. The guarantees do not include a maximum limit. Based on information made available to Alliant Energy by Whiting Petroleum, the Whiting Petroleum affiliate holds an approximate 6% share in the partnerships, and currently known obligations include costs associated with the future abandonment of certain facilities owned by the partnerships. The general partnerships were formed under California law, and Alliant Energy Resources, LLC may need to perform under the guarantees if the affiliate of Whiting Petroleum is unable to meet its partnership obligations.

Whiting Petroleum previously completed bankruptcy proceedings and business combinations, which substantially reduce the likelihood that Alliant Energy will be obligated to make any payments under these guarantees. As of December 31, 2025, the currently known partnership obligations for the abandonment obligations are estimated at $92 million, which represents Alliant Energy’s currently estimated maximum exposure under the guarantees. Alliant Energy is not currently aware of, nor does it currently expect to incur in the future, any material liabilities related to these guarantees and therefore has not recognized any material liabilities related to these guarantees as of December 31, 2025 and 2024.

Non-utility Wind Farm in Oklahoma - In 2017, a wholly-owned subsidiary of AEF acquired a cash equity ownership interest in a non-utility wind farm located in Oklahoma. The wind farm provides electricity to a third-party under a long-term PPA. Alliant Energy provided a parent guarantee of its subsidiary’s indemnification obligations under the related operating agreement and PPA. Alliant Energy’s obligations under the operating agreement were $35 million as of December 31, 2025 and will reduce annually until expiring in July 2047. Alliant Energy’s obligations under the PPA are subject to a maximum limit of $17 million and expire in December 2031, subject to potential extension. Alliant Energy is not aware of any material liabilities related to this guarantee that it is probable that it will be obligated to pay and therefore has not recognized any material liabilities related to this guarantee as of December 31, 2025 and 2024.

Transfers of Renewable Tax Credits - IPL and WPL have entered into agreements to transfer renewable tax credits from certain wind, solar and energy storage facilities to other corporate taxpayers in exchange for cash. As of December 31, 2025, IPL and WPL provided indemnifications associated with $333 million and $266 million, respectively, of proceeds for renewable tax credits transferred to other corporate taxpayers in the event of an adverse interpretation of tax law, including whether the related tax credits meet the qualification requirements. Alliant Energy, IPL and WPL believe the likelihood of having to make any material cash payments under these indemnifications is remote.

Electric Transmission Infrastructure - IPL and WPL have entered into agreements with their respective electric transmission service providers related to the construction of infrastructure necessary for the data centers that are expected to be built in IPL’s and WPL’s service territories by certain of their customers. If these construction projects were to be terminated prior to the infrastructure being placed in service by the electric transmission service providers, then IPL or WPL must reimburse their respective provider for the related costs incurred to-date. As of December 31, 2025, IPL’s and WPL’s related guarantees were approximately $130 million and $55 million, respectively. Alliant Energy, IPL and WPL are not aware of any material liabilities related to these guarantees that it is probable that they will be obligated to pay and therefore have not recognized any material liabilities related to these guarantees as of December 31, 2025.
(e) Environmental Matters - Alliant Energy, IPL and WPL are subject to environmental regulations as a result of their current and past operations. These regulations are designed to protect public health and the environment and have resulted in compliance, remediation, containment and monitoring obligations, which are recorded as current and non-current environmental liabilities. Substantially all of the environmental liabilities recorded on the balance sheets relate to MGP sites.
Manufactured Gas Plant Sites - IPL and WPL have current or previous ownership interests in various sites that are previously associated with the production of gas for which IPL and WPL have, or may have in the future, liability for investigation, remediation and monitoring costs. IPL and WPL are working pursuant to the requirements of various federal and state agencies to investigate, mitigate, prevent and remediate, where necessary, the environmental impacts to property, including natural resources, at and around these former MGP sites in order to protect public health and the environment. At December 31, 2025, estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, which are not discounted, were as follows (in millions):
Alliant EnergyIPLWPL
Range of estimated future costs$7 -$29$5 -$18$2 -$11
Current and non-current environmental liabilities$12$8$4

IPL Consent Decree - In 2015, the U.S. District Court for the Northern District of Iowa approved a Consent Decree that IPL entered into with the EPA, the Sierra Club, the State of Iowa and Linn County in Iowa, thereby resolving potential CAA issues associated with emissions from IPL’s coal-fired generating facilities in Iowa. IPL has completed all of the requirements under the Consent Decree. Alliant Energy and IPL currently expect to recover material costs incurred by IPL related to compliance with the terms of the Consent Decree from IPL’s electric customers.

Other Environmental Contingencies - In addition to the environmental liabilities discussed above, various environmental rules are monitored that may have a significant impact on future operations. Several of these environmental rules are subject to legal challenges, reconsideration and/or other uncertainties. Given uncertainties regarding the outcome, timing and compliance plans for these environmental matters, the complete financial impact of each of these rules is not able to be determined; however, future capital investments and/or modifications to EGUs and electric and gas distribution systems to comply with certain of these rules could be significant. Specific current, proposed or potential environmental matters include, among others: CSAPR, Effluent Limitation Guidelines, CCR Rule, and various legislation and EPA regulations to monitor and regulate the emission of GHG, including the CAA.
(f) Credit Risk - IPL provides retail electric and gas services in Iowa and wholesale electric service in Illinois and Iowa. WPL provides retail electric and gas services and wholesale electric service in Wisconsin. The geographic concentration of IPL’s and WPL’s customers did not contribute significantly to overall credit risk exposure. In addition, as a result of a large customer base, IPL and WPL did not have any significant credit risk concentration for receivables arising from the sale of electricity or gas services.
Alliant Energy, IPL and WPL are subject to credit risk related to the ability of counterparties to meet their contractual payment obligations, including reimbursement of generation and transmission costs from large load growth customers, or the potential non-performance of counterparties to deliver contracted commodities and other goods or services at the contracted price. Credit policies are maintained to mitigate credit risk. These credit policies include evaluation of the financial condition of certain counterparties, use of credit risk-related contingent provisions in certain agreements that require credit support from counterparties not meeting specific criteria, different counterparties to reduce concentrations of credit risk and the use of standardized agreements that facilitate the netting of cash flows associated with certain counterparties. Based on these credit policies and different counterparties, as well as utility cost recovery mechanisms, it is unlikely that counterparty non-performance would have a material effect on financial condition or results of operations. However, there is no assurance that these items will protect against all losses from counterparty non-performance.

Refer to Notes 5(a) and 14 for details of allowances for expected credit losses and credit risk-related contingent features, respectively.
(g) Collective Bargaining Agreements - At December 31, 2025, employees covered by collective bargaining agreements represented 58%, 74% and 86% of total employees of Alliant Energy, IPL and WPL, respectively. In May 2026, WPL’s collective bargaining agreement with International Brotherhood of Electrical Workers Local 965 expires, representing 29% and 86% of total employees of Alliant Energy and WPL, respectively.
IPL [Member]  
Statement [Line Items]  
Commitments And Contingencies COMMITMENTS AND CONTINGENCIES(a) Capital Purchase Commitments - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects, including IPL’s and WPL’s expansion of energy storage, improvements at the natural gas-fired Neenah Energy Facility and Sheboygan Falls Energy Facility, and repowering projects at WPL’s Bent Tree Energy Facility. At December 31, 2025, Alliant Energy’s, IPL’s, and WPL’s minimum future commitments in 2026 for these projects were $459 million, $302 million, and $155 million, respectively.(b) Other Purchase Commitments - Various commodity supply, transportation and storage contracts help meet obligations to provide electricity and natural gas to utility customers. In addition, there are various purchase commitments associated with other goods and services. At December 31, 2025, the related minimum future commitments, excluding amounts for purchased power commitments that do not have minimum thresholds but require payment when electricity is generated by the provider and amounts for future commitments to deliver power to electric customers that do not have current minimum thresholds but will be billed for requirements when power is provided, were as follows (in millions):
Alliant Energy20262027202820292030ThereafterTotal
Natural gas$271$191$163$145$103$245$1,118
Coal764228———146
Other (a)571684317105
$404$249$199$149$106$262$1,369
IPL20262027202820292030ThereafterTotal
Natural gas$149$105$85$70$31$52$492
Coal341410———58
Other (a)2422221648
$207$121$97$72$33$68$598
WPL20262027202820292030ThereafterTotal
Natural gas$122$86$78$75$72$193$626
Coal422818———88
Other (a)251————26
$189$115$96$75$72$193$740

(a)Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2025.
(c) Legal Proceedings - Alliant Energy, IPL and WPL are involved in legal and administrative proceedings before various courts and agencies with respect to matters arising in the ordinary course of business. Although unable to predict the outcome of these matters, Alliant Energy, IPL and WPL believe that appropriate reserves have been established and final disposition of these actions will not have a material effect on their financial condition or results of operations.(d) Guarantees and Indemnifications -
Whiting Petroleum Corporation (Whiting Petroleum) - In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum, an independent oil and gas company. Alliant Energy Resources, LLC, as the successor to a predecessor entity that owned Whiting Petroleum, and a wholly-owned subsidiary of AEF, has guaranteed the partnership obligations of an affiliate of Whiting Petroleum under multiple general partnership agreements in the oil and gas industry. The guarantees do not include a maximum limit. Based on information made available to Alliant Energy by Whiting Petroleum, the Whiting Petroleum affiliate holds an approximate 6% share in the partnerships, and currently known obligations include costs associated with the future abandonment of certain facilities owned by the partnerships. The general partnerships were formed under California law, and Alliant Energy Resources, LLC may need to perform under the guarantees if the affiliate of Whiting Petroleum is unable to meet its partnership obligations.

Whiting Petroleum previously completed bankruptcy proceedings and business combinations, which substantially reduce the likelihood that Alliant Energy will be obligated to make any payments under these guarantees. As of December 31, 2025, the currently known partnership obligations for the abandonment obligations are estimated at $92 million, which represents Alliant Energy’s currently estimated maximum exposure under the guarantees. Alliant Energy is not currently aware of, nor does it currently expect to incur in the future, any material liabilities related to these guarantees and therefore has not recognized any material liabilities related to these guarantees as of December 31, 2025 and 2024.

Non-utility Wind Farm in Oklahoma - In 2017, a wholly-owned subsidiary of AEF acquired a cash equity ownership interest in a non-utility wind farm located in Oklahoma. The wind farm provides electricity to a third-party under a long-term PPA. Alliant Energy provided a parent guarantee of its subsidiary’s indemnification obligations under the related operating agreement and PPA. Alliant Energy’s obligations under the operating agreement were $35 million as of December 31, 2025 and will reduce annually until expiring in July 2047. Alliant Energy’s obligations under the PPA are subject to a maximum limit of $17 million and expire in December 2031, subject to potential extension. Alliant Energy is not aware of any material liabilities related to this guarantee that it is probable that it will be obligated to pay and therefore has not recognized any material liabilities related to this guarantee as of December 31, 2025 and 2024.

Transfers of Renewable Tax Credits - IPL and WPL have entered into agreements to transfer renewable tax credits from certain wind, solar and energy storage facilities to other corporate taxpayers in exchange for cash. As of December 31, 2025, IPL and WPL provided indemnifications associated with $333 million and $266 million, respectively, of proceeds for renewable tax credits transferred to other corporate taxpayers in the event of an adverse interpretation of tax law, including whether the related tax credits meet the qualification requirements. Alliant Energy, IPL and WPL believe the likelihood of having to make any material cash payments under these indemnifications is remote.

Electric Transmission Infrastructure - IPL and WPL have entered into agreements with their respective electric transmission service providers related to the construction of infrastructure necessary for the data centers that are expected to be built in IPL’s and WPL’s service territories by certain of their customers. If these construction projects were to be terminated prior to the infrastructure being placed in service by the electric transmission service providers, then IPL or WPL must reimburse their respective provider for the related costs incurred to-date. As of December 31, 2025, IPL’s and WPL’s related guarantees were approximately $130 million and $55 million, respectively. Alliant Energy, IPL and WPL are not aware of any material liabilities related to these guarantees that it is probable that they will be obligated to pay and therefore have not recognized any material liabilities related to these guarantees as of December 31, 2025.
(e) Environmental Matters - Alliant Energy, IPL and WPL are subject to environmental regulations as a result of their current and past operations. These regulations are designed to protect public health and the environment and have resulted in compliance, remediation, containment and monitoring obligations, which are recorded as current and non-current environmental liabilities. Substantially all of the environmental liabilities recorded on the balance sheets relate to MGP sites.
Manufactured Gas Plant Sites - IPL and WPL have current or previous ownership interests in various sites that are previously associated with the production of gas for which IPL and WPL have, or may have in the future, liability for investigation, remediation and monitoring costs. IPL and WPL are working pursuant to the requirements of various federal and state agencies to investigate, mitigate, prevent and remediate, where necessary, the environmental impacts to property, including natural resources, at and around these former MGP sites in order to protect public health and the environment. At December 31, 2025, estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, which are not discounted, were as follows (in millions):
Alliant EnergyIPLWPL
Range of estimated future costs$7 -$29$5 -$18$2 -$11
Current and non-current environmental liabilities$12$8$4

IPL Consent Decree - In 2015, the U.S. District Court for the Northern District of Iowa approved a Consent Decree that IPL entered into with the EPA, the Sierra Club, the State of Iowa and Linn County in Iowa, thereby resolving potential CAA issues associated with emissions from IPL’s coal-fired generating facilities in Iowa. IPL has completed all of the requirements under the Consent Decree. Alliant Energy and IPL currently expect to recover material costs incurred by IPL related to compliance with the terms of the Consent Decree from IPL’s electric customers.

Other Environmental Contingencies - In addition to the environmental liabilities discussed above, various environmental rules are monitored that may have a significant impact on future operations. Several of these environmental rules are subject to legal challenges, reconsideration and/or other uncertainties. Given uncertainties regarding the outcome, timing and compliance plans for these environmental matters, the complete financial impact of each of these rules is not able to be determined; however, future capital investments and/or modifications to EGUs and electric and gas distribution systems to comply with certain of these rules could be significant. Specific current, proposed or potential environmental matters include, among others: CSAPR, Effluent Limitation Guidelines, CCR Rule, and various legislation and EPA regulations to monitor and regulate the emission of GHG, including the CAA.
(f) Credit Risk - IPL provides retail electric and gas services in Iowa and wholesale electric service in Illinois and Iowa. WPL provides retail electric and gas services and wholesale electric service in Wisconsin. The geographic concentration of IPL’s and WPL’s customers did not contribute significantly to overall credit risk exposure. In addition, as a result of a large customer base, IPL and WPL did not have any significant credit risk concentration for receivables arising from the sale of electricity or gas services.
Alliant Energy, IPL and WPL are subject to credit risk related to the ability of counterparties to meet their contractual payment obligations, including reimbursement of generation and transmission costs from large load growth customers, or the potential non-performance of counterparties to deliver contracted commodities and other goods or services at the contracted price. Credit policies are maintained to mitigate credit risk. These credit policies include evaluation of the financial condition of certain counterparties, use of credit risk-related contingent provisions in certain agreements that require credit support from counterparties not meeting specific criteria, different counterparties to reduce concentrations of credit risk and the use of standardized agreements that facilitate the netting of cash flows associated with certain counterparties. Based on these credit policies and different counterparties, as well as utility cost recovery mechanisms, it is unlikely that counterparty non-performance would have a material effect on financial condition or results of operations. However, there is no assurance that these items will protect against all losses from counterparty non-performance.

Refer to Notes 5(a) and 14 for details of allowances for expected credit losses and credit risk-related contingent features, respectively.
(g) Collective Bargaining Agreements - At December 31, 2025, employees covered by collective bargaining agreements represented 58%, 74% and 86% of total employees of Alliant Energy, IPL and WPL, respectively. In May 2026, WPL’s collective bargaining agreement with International Brotherhood of Electrical Workers Local 965 expires, representing 29% and 86% of total employees of Alliant Energy and WPL, respectively.
WPL [Member]  
Statement [Line Items]  
Commitments And Contingencies COMMITMENTS AND CONTINGENCIES(a) Capital Purchase Commitments - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects, including IPL’s and WPL’s expansion of energy storage, improvements at the natural gas-fired Neenah Energy Facility and Sheboygan Falls Energy Facility, and repowering projects at WPL’s Bent Tree Energy Facility. At December 31, 2025, Alliant Energy’s, IPL’s, and WPL’s minimum future commitments in 2026 for these projects were $459 million, $302 million, and $155 million, respectively.(b) Other Purchase Commitments - Various commodity supply, transportation and storage contracts help meet obligations to provide electricity and natural gas to utility customers. In addition, there are various purchase commitments associated with other goods and services. At December 31, 2025, the related minimum future commitments, excluding amounts for purchased power commitments that do not have minimum thresholds but require payment when electricity is generated by the provider and amounts for future commitments to deliver power to electric customers that do not have current minimum thresholds but will be billed for requirements when power is provided, were as follows (in millions):
Alliant Energy20262027202820292030ThereafterTotal
Natural gas$271$191$163$145$103$245$1,118
Coal764228———146
Other (a)571684317105
$404$249$199$149$106$262$1,369
IPL20262027202820292030ThereafterTotal
Natural gas$149$105$85$70$31$52$492
Coal341410———58
Other (a)2422221648
$207$121$97$72$33$68$598
WPL20262027202820292030ThereafterTotal
Natural gas$122$86$78$75$72$193$626
Coal422818———88
Other (a)251————26
$189$115$96$75$72$193$740

(a)Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2025.
(c) Legal Proceedings - Alliant Energy, IPL and WPL are involved in legal and administrative proceedings before various courts and agencies with respect to matters arising in the ordinary course of business. Although unable to predict the outcome of these matters, Alliant Energy, IPL and WPL believe that appropriate reserves have been established and final disposition of these actions will not have a material effect on their financial condition or results of operations.(d) Guarantees and Indemnifications -
Whiting Petroleum Corporation (Whiting Petroleum) - In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum, an independent oil and gas company. Alliant Energy Resources, LLC, as the successor to a predecessor entity that owned Whiting Petroleum, and a wholly-owned subsidiary of AEF, has guaranteed the partnership obligations of an affiliate of Whiting Petroleum under multiple general partnership agreements in the oil and gas industry. The guarantees do not include a maximum limit. Based on information made available to Alliant Energy by Whiting Petroleum, the Whiting Petroleum affiliate holds an approximate 6% share in the partnerships, and currently known obligations include costs associated with the future abandonment of certain facilities owned by the partnerships. The general partnerships were formed under California law, and Alliant Energy Resources, LLC may need to perform under the guarantees if the affiliate of Whiting Petroleum is unable to meet its partnership obligations.

Whiting Petroleum previously completed bankruptcy proceedings and business combinations, which substantially reduce the likelihood that Alliant Energy will be obligated to make any payments under these guarantees. As of December 31, 2025, the currently known partnership obligations for the abandonment obligations are estimated at $92 million, which represents Alliant Energy’s currently estimated maximum exposure under the guarantees. Alliant Energy is not currently aware of, nor does it currently expect to incur in the future, any material liabilities related to these guarantees and therefore has not recognized any material liabilities related to these guarantees as of December 31, 2025 and 2024.

Non-utility Wind Farm in Oklahoma - In 2017, a wholly-owned subsidiary of AEF acquired a cash equity ownership interest in a non-utility wind farm located in Oklahoma. The wind farm provides electricity to a third-party under a long-term PPA. Alliant Energy provided a parent guarantee of its subsidiary’s indemnification obligations under the related operating agreement and PPA. Alliant Energy’s obligations under the operating agreement were $35 million as of December 31, 2025 and will reduce annually until expiring in July 2047. Alliant Energy’s obligations under the PPA are subject to a maximum limit of $17 million and expire in December 2031, subject to potential extension. Alliant Energy is not aware of any material liabilities related to this guarantee that it is probable that it will be obligated to pay and therefore has not recognized any material liabilities related to this guarantee as of December 31, 2025 and 2024.

Transfers of Renewable Tax Credits - IPL and WPL have entered into agreements to transfer renewable tax credits from certain wind, solar and energy storage facilities to other corporate taxpayers in exchange for cash. As of December 31, 2025, IPL and WPL provided indemnifications associated with $333 million and $266 million, respectively, of proceeds for renewable tax credits transferred to other corporate taxpayers in the event of an adverse interpretation of tax law, including whether the related tax credits meet the qualification requirements. Alliant Energy, IPL and WPL believe the likelihood of having to make any material cash payments under these indemnifications is remote.

Electric Transmission Infrastructure - IPL and WPL have entered into agreements with their respective electric transmission service providers related to the construction of infrastructure necessary for the data centers that are expected to be built in IPL’s and WPL’s service territories by certain of their customers. If these construction projects were to be terminated prior to the infrastructure being placed in service by the electric transmission service providers, then IPL or WPL must reimburse their respective provider for the related costs incurred to-date. As of December 31, 2025, IPL’s and WPL’s related guarantees were approximately $130 million and $55 million, respectively. Alliant Energy, IPL and WPL are not aware of any material liabilities related to these guarantees that it is probable that they will be obligated to pay and therefore have not recognized any material liabilities related to these guarantees as of December 31, 2025.
(e) Environmental Matters - Alliant Energy, IPL and WPL are subject to environmental regulations as a result of their current and past operations. These regulations are designed to protect public health and the environment and have resulted in compliance, remediation, containment and monitoring obligations, which are recorded as current and non-current environmental liabilities. Substantially all of the environmental liabilities recorded on the balance sheets relate to MGP sites.
Manufactured Gas Plant Sites - IPL and WPL have current or previous ownership interests in various sites that are previously associated with the production of gas for which IPL and WPL have, or may have in the future, liability for investigation, remediation and monitoring costs. IPL and WPL are working pursuant to the requirements of various federal and state agencies to investigate, mitigate, prevent and remediate, where necessary, the environmental impacts to property, including natural resources, at and around these former MGP sites in order to protect public health and the environment. At December 31, 2025, estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, which are not discounted, were as follows (in millions):
Alliant EnergyIPLWPL
Range of estimated future costs$7 -$29$5 -$18$2 -$11
Current and non-current environmental liabilities$12$8$4

IPL Consent Decree - In 2015, the U.S. District Court for the Northern District of Iowa approved a Consent Decree that IPL entered into with the EPA, the Sierra Club, the State of Iowa and Linn County in Iowa, thereby resolving potential CAA issues associated with emissions from IPL’s coal-fired generating facilities in Iowa. IPL has completed all of the requirements under the Consent Decree. Alliant Energy and IPL currently expect to recover material costs incurred by IPL related to compliance with the terms of the Consent Decree from IPL’s electric customers.

Other Environmental Contingencies - In addition to the environmental liabilities discussed above, various environmental rules are monitored that may have a significant impact on future operations. Several of these environmental rules are subject to legal challenges, reconsideration and/or other uncertainties. Given uncertainties regarding the outcome, timing and compliance plans for these environmental matters, the complete financial impact of each of these rules is not able to be determined; however, future capital investments and/or modifications to EGUs and electric and gas distribution systems to comply with certain of these rules could be significant. Specific current, proposed or potential environmental matters include, among others: CSAPR, Effluent Limitation Guidelines, CCR Rule, and various legislation and EPA regulations to monitor and regulate the emission of GHG, including the CAA.
(f) Credit Risk - IPL provides retail electric and gas services in Iowa and wholesale electric service in Illinois and Iowa. WPL provides retail electric and gas services and wholesale electric service in Wisconsin. The geographic concentration of IPL’s and WPL’s customers did not contribute significantly to overall credit risk exposure. In addition, as a result of a large customer base, IPL and WPL did not have any significant credit risk concentration for receivables arising from the sale of electricity or gas services.
Alliant Energy, IPL and WPL are subject to credit risk related to the ability of counterparties to meet their contractual payment obligations, including reimbursement of generation and transmission costs from large load growth customers, or the potential non-performance of counterparties to deliver contracted commodities and other goods or services at the contracted price. Credit policies are maintained to mitigate credit risk. These credit policies include evaluation of the financial condition of certain counterparties, use of credit risk-related contingent provisions in certain agreements that require credit support from counterparties not meeting specific criteria, different counterparties to reduce concentrations of credit risk and the use of standardized agreements that facilitate the netting of cash flows associated with certain counterparties. Based on these credit policies and different counterparties, as well as utility cost recovery mechanisms, it is unlikely that counterparty non-performance would have a material effect on financial condition or results of operations. However, there is no assurance that these items will protect against all losses from counterparty non-performance.

Refer to Notes 5(a) and 14 for details of allowances for expected credit losses and credit risk-related contingent features, respectively.
(g) Collective Bargaining Agreements - At December 31, 2025, employees covered by collective bargaining agreements represented 58%, 74% and 86% of total employees of Alliant Energy, IPL and WPL, respectively. In May 2026, WPL’s collective bargaining agreement with International Brotherhood of Electrical Workers Local 965 expires, representing 29% and 86% of total employees of Alliant Energy and WPL, respectively.
v3.25.4
Segments Of Business
 12 Months Ended
Dec. 31, 2025
Segment Reporting Information [Line Items]  
Segments Of Business SEGMENTS OF BUSINESS
Alliant Energy - Alliant Energy’s two reportable segments as of December 31, 2025 are:
•IPL - is a utility primarily serving electric and natural gas customers in Iowa, and is its own reportable segment as shown in the tables below.
•WPL - is a utility serving electric and natural gas customers in Wisconsin, and is its own reportable segment as shown in the tables below.

Other, which is not a reportable segment of Alliant Energy, includes the operations of AEF and its subsidiaries, Corporate Services, the Alliant Energy parent company, and any Alliant Energy parent company consolidating adjustments. AEF is comprised of Alliant Energy’s interest in ATC Holdings, Travero, a non-utility wind farm, corporate venture investments, the Sheboygan Falls Energy Facility and other non-utility holdings. The “Other” columns are included in the tables below to reconcile to consolidated amounts. Prior to December 31, 2024, reportable segments for Alliant Energy’s, IPL’s, and WPL’s utility business were electric operations, gas operations, and other. In the fourth quarter of 2024, Alliant Energy, IPL and WPL adopted the FASB’s accounting standard for improvements to reportable segment disclosures. Previously reported information for prior periods has been recast to conform with the current period presentation.

Alliant Energy’s chief operating decision maker (CODM) is its President and CEO, and IPL’s and WPL’s CODM is their CEO. The CODM uses net income generated from IPL’s and WPL’s operations to assess segment performance, make operating decisions, and allocate resources. Alliant Energy’s administrative support services are directly charged to the applicable segment where practicable. In all other cases, administrative support services are allocated to the applicable segment based on services agreements. There was no single customer whose revenues were 10% or more of Alliant Energy’s, IPL’s and WPL’s respective consolidated revenues. All of Alliant Energy’s, IPL’s and WPL’s operations and assets are located in the U.S. Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s reportable segments, which represents the services provided to their customers, and reconciliation to consolidated amounts, was as follows (in millions):
Utility
TotalAlliant
ReportableEnergy
2025IPLWPLSegmentsOtherConsolidated
Electric utility revenues$1,896 $1,801 $3,697 N/A$3,697
Gas utility revenues265 260 525 N/A525
Other revenues47 4 51 $89140
Total revenues2,208 2,065 4,273 894,362
Electric production fuel and purchased power expense283 459 742 N/A742
Electric transmission service expense422 203 625 N/A625
Cost of gas sold expense130 133 263 N/A263
Other operation and maintenance expense (a)373 306 679 61740
Other segment items:
Depreciation and amortization expense463 370 833 13846
Interest expense211173384128512
Equity income from unconsolidated investments, net— (2)(2)(58)(60)
Income tax benefit(127)(14)(141)(8)(149)
Other (b)(4)3632 133
Net income (loss)457401858(48)810
Total assets12,495 10,655 23,150 1,84124,991
Investments in equity method subsidiaries5 19 24 650674
Construction and acquisition expenditures1,473 804 2,277 2062,483
Utility
TotalAlliant
ReportableEnergy
2024
IPLWPLSegmentsOtherConsolidated
Electric utility revenues$1,747 $1,625 $3,372 N/A$3,372
Gas utility revenues250 215 465 N/A465
Other revenues49 5 54 $90144
Total revenues2,046 1,845 3,891 903,981
Electric production fuel and purchased power expense269 359 628 N/A628
Electric transmission service expense417 196 613 N/A613
Cost of gas sold expense123 101 224 N/A224
Asset valuation charge for IPL’s Lansing Generating Station60 — 60 N/A60
Other operation and maintenance expense358 279 637 39676
Other segment items:
Depreciation and amortization expense404 357 761 11772
Interest expense177 165 342 107449
Equity income from unconsolidated investments, net— (2)(2)(59)(61)
Income tax expense (benefit)(129)11 (118)4(114)
Other (b)5 34 39 544
Net income (loss)362 345 707 (17)690
Total assets11,407 10,106 21,513 1,20122,714
Investments in equity method subsidiaries5 17 22 601623
Construction and acquisition expenditures1,224 828 2,052 1972,249
Utility
TotalAlliant
ReportableEnergy
2023 (amounts may not foot due to rounding)
IPLWPLSegmentsOtherConsolidated
Electric utility revenues$1,761 $1,584 $3,345 N/A$3,345
Gas utility revenues300 240 540 N/A540
Other revenues49 3 52 $90142
Total revenues2,110 1,827 3,937 904,027
Electric production fuel and purchased power expense282 455 737 N/A736
Electric transmission service expense420 163 583 N/A583
Cost of gas sold expense166 134 300 N/A299
Other operation and maintenance expense353 271 624 51675
Other segment items:
Depreciation and amortization expense388 280 668 8676
Interest expense155 149 304 90394
Equity income from unconsolidated investments, net— (3)(3)(58)(61)
Income tax expense (benefit)(58)60 2 24
Other (b)38 (27)11 518
Net income (loss)366 345 711 (8)703
Total assets10,489 9,634 20,123 1,11421,237
Investments in equity method subsidiaries5 16 21 564585
Construction and acquisition expenditures712 1,019 1,731 1231,854

(a)Alliant Energy’s non-utility holdings include Travero’s wind turbine blade recycling services, which commenced commercial operations in 2024, and whose assets are primarily included in “Property, plant and equipment, net” on Alliant Energy’s balance sheets. Alliant Energy suspended production of Travero’s wind turbine blade recycling services in November 2025 based on a review of strategic options, and as a result, a pre-tax non-cash asset valuation charge of $16 million was recorded to “Other operation and maintenance” in Alliant Energy’s income statement in 2025.
(b)Other segment items for each reportable segment include AFUDC, taxes other than income taxes, interest income, and other miscellaneous income and deductions.
IPL [Member]  
Segment Reporting Information [Line Items]  
Segments Of Business SEGMENTS OF BUSINESS
Alliant Energy - Alliant Energy’s two reportable segments as of December 31, 2025 are:
•IPL - is a utility primarily serving electric and natural gas customers in Iowa, and is its own reportable segment as shown in the tables below.
•WPL - is a utility serving electric and natural gas customers in Wisconsin, and is its own reportable segment as shown in the tables below.

Other, which is not a reportable segment of Alliant Energy, includes the operations of AEF and its subsidiaries, Corporate Services, the Alliant Energy parent company, and any Alliant Energy parent company consolidating adjustments. AEF is comprised of Alliant Energy’s interest in ATC Holdings, Travero, a non-utility wind farm, corporate venture investments, the Sheboygan Falls Energy Facility and other non-utility holdings. The “Other” columns are included in the tables below to reconcile to consolidated amounts. Prior to December 31, 2024, reportable segments for Alliant Energy’s, IPL’s, and WPL’s utility business were electric operations, gas operations, and other. In the fourth quarter of 2024, Alliant Energy, IPL and WPL adopted the FASB’s accounting standard for improvements to reportable segment disclosures. Previously reported information for prior periods has been recast to conform with the current period presentation.

Alliant Energy’s chief operating decision maker (CODM) is its President and CEO, and IPL’s and WPL’s CODM is their CEO. The CODM uses net income generated from IPL’s and WPL’s operations to assess segment performance, make operating decisions, and allocate resources. Alliant Energy’s administrative support services are directly charged to the applicable segment where practicable. In all other cases, administrative support services are allocated to the applicable segment based on services agreements. There was no single customer whose revenues were 10% or more of Alliant Energy’s, IPL’s and WPL’s respective consolidated revenues. All of Alliant Energy’s, IPL’s and WPL’s operations and assets are located in the U.S. Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s reportable segments, which represents the services provided to their customers, and reconciliation to consolidated amounts, was as follows (in millions):
Utility
TotalAlliant
ReportableEnergy
2025IPLWPLSegmentsOtherConsolidated
Electric utility revenues$1,896 $1,801 $3,697 N/A$3,697
Gas utility revenues265 260 525 N/A525
Other revenues47 4 51 $89140
Total revenues2,208 2,065 4,273 894,362
Electric production fuel and purchased power expense283 459 742 N/A742
Electric transmission service expense422 203 625 N/A625
Cost of gas sold expense130 133 263 N/A263
Other operation and maintenance expense (a)373 306 679 61740
Other segment items:
Depreciation and amortization expense463 370 833 13846
Interest expense211173384128512
Equity income from unconsolidated investments, net— (2)(2)(58)(60)
Income tax benefit(127)(14)(141)(8)(149)
Other (b)(4)3632 133
Net income (loss)457401858(48)810
Total assets12,495 10,655 23,150 1,84124,991
Investments in equity method subsidiaries5 19 24 650674
Construction and acquisition expenditures1,473 804 2,277 2062,483
Utility
TotalAlliant
ReportableEnergy
2024
IPLWPLSegmentsOtherConsolidated
Electric utility revenues$1,747 $1,625 $3,372 N/A$3,372
Gas utility revenues250 215 465 N/A465
Other revenues49 5 54 $90144
Total revenues2,046 1,845 3,891 903,981
Electric production fuel and purchased power expense269 359 628 N/A628
Electric transmission service expense417 196 613 N/A613
Cost of gas sold expense123 101 224 N/A224
Asset valuation charge for IPL’s Lansing Generating Station60 — 60 N/A60
Other operation and maintenance expense358 279 637 39676
Other segment items:
Depreciation and amortization expense404 357 761 11772
Interest expense177 165 342 107449
Equity income from unconsolidated investments, net— (2)(2)(59)(61)
Income tax expense (benefit)(129)11 (118)4(114)
Other (b)5 34 39 544
Net income (loss)362 345 707 (17)690
Total assets11,407 10,106 21,513 1,20122,714
Investments in equity method subsidiaries5 17 22 601623
Construction and acquisition expenditures1,224 828 2,052 1972,249
Utility
TotalAlliant
ReportableEnergy
2023 (amounts may not foot due to rounding)
IPLWPLSegmentsOtherConsolidated
Electric utility revenues$1,761 $1,584 $3,345 N/A$3,345
Gas utility revenues300 240 540 N/A540
Other revenues49 3 52 $90142
Total revenues2,110 1,827 3,937 904,027
Electric production fuel and purchased power expense282 455 737 N/A736
Electric transmission service expense420 163 583 N/A583
Cost of gas sold expense166 134 300 N/A299
Other operation and maintenance expense353 271 624 51675
Other segment items:
Depreciation and amortization expense388 280 668 8676
Interest expense155 149 304 90394
Equity income from unconsolidated investments, net— (3)(3)(58)(61)
Income tax expense (benefit)(58)60 2 24
Other (b)38 (27)11 518
Net income (loss)366 345 711 (8)703
Total assets10,489 9,634 20,123 1,11421,237
Investments in equity method subsidiaries5 16 21 564585
Construction and acquisition expenditures712 1,019 1,731 1231,854

(a)Alliant Energy’s non-utility holdings include Travero’s wind turbine blade recycling services, which commenced commercial operations in 2024, and whose assets are primarily included in “Property, plant and equipment, net” on Alliant Energy’s balance sheets. Alliant Energy suspended production of Travero’s wind turbine blade recycling services in November 2025 based on a review of strategic options, and as a result, a pre-tax non-cash asset valuation charge of $16 million was recorded to “Other operation and maintenance” in Alliant Energy’s income statement in 2025.
(b)Other segment items for each reportable segment include AFUDC, taxes other than income taxes, interest income, and other miscellaneous income and deductions.
WPL [Member]  
Segment Reporting Information [Line Items]  
Segments Of Business SEGMENTS OF BUSINESS
Alliant Energy - Alliant Energy’s two reportable segments as of December 31, 2025 are:
•IPL - is a utility primarily serving electric and natural gas customers in Iowa, and is its own reportable segment as shown in the tables below.
•WPL - is a utility serving electric and natural gas customers in Wisconsin, and is its own reportable segment as shown in the tables below.

Other, which is not a reportable segment of Alliant Energy, includes the operations of AEF and its subsidiaries, Corporate Services, the Alliant Energy parent company, and any Alliant Energy parent company consolidating adjustments. AEF is comprised of Alliant Energy’s interest in ATC Holdings, Travero, a non-utility wind farm, corporate venture investments, the Sheboygan Falls Energy Facility and other non-utility holdings. The “Other” columns are included in the tables below to reconcile to consolidated amounts. Prior to December 31, 2024, reportable segments for Alliant Energy’s, IPL’s, and WPL’s utility business were electric operations, gas operations, and other. In the fourth quarter of 2024, Alliant Energy, IPL and WPL adopted the FASB’s accounting standard for improvements to reportable segment disclosures. Previously reported information for prior periods has been recast to conform with the current period presentation.

Alliant Energy’s chief operating decision maker (CODM) is its President and CEO, and IPL’s and WPL’s CODM is their CEO. The CODM uses net income generated from IPL’s and WPL’s operations to assess segment performance, make operating decisions, and allocate resources. Alliant Energy’s administrative support services are directly charged to the applicable segment where practicable. In all other cases, administrative support services are allocated to the applicable segment based on services agreements. There was no single customer whose revenues were 10% or more of Alliant Energy’s, IPL’s and WPL’s respective consolidated revenues. All of Alliant Energy’s, IPL’s and WPL’s operations and assets are located in the U.S. Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s reportable segments, which represents the services provided to their customers, and reconciliation to consolidated amounts, was as follows (in millions):
Utility
TotalAlliant
ReportableEnergy
2025IPLWPLSegmentsOtherConsolidated
Electric utility revenues$1,896 $1,801 $3,697 N/A$3,697
Gas utility revenues265 260 525 N/A525
Other revenues47 4 51 $89140
Total revenues2,208 2,065 4,273 894,362
Electric production fuel and purchased power expense283 459 742 N/A742
Electric transmission service expense422 203 625 N/A625
Cost of gas sold expense130 133 263 N/A263
Other operation and maintenance expense (a)373 306 679 61740
Other segment items:
Depreciation and amortization expense463 370 833 13846
Interest expense211173384128512
Equity income from unconsolidated investments, net— (2)(2)(58)(60)
Income tax benefit(127)(14)(141)(8)(149)
Other (b)(4)3632 133
Net income (loss)457401858(48)810
Total assets12,495 10,655 23,150 1,84124,991
Investments in equity method subsidiaries5 19 24 650674
Construction and acquisition expenditures1,473 804 2,277 2062,483
Utility
TotalAlliant
ReportableEnergy
2024
IPLWPLSegmentsOtherConsolidated
Electric utility revenues$1,747 $1,625 $3,372 N/A$3,372
Gas utility revenues250 215 465 N/A465
Other revenues49 5 54 $90144
Total revenues2,046 1,845 3,891 903,981
Electric production fuel and purchased power expense269 359 628 N/A628
Electric transmission service expense417 196 613 N/A613
Cost of gas sold expense123 101 224 N/A224
Asset valuation charge for IPL’s Lansing Generating Station60 — 60 N/A60
Other operation and maintenance expense358 279 637 39676
Other segment items:
Depreciation and amortization expense404 357 761 11772
Interest expense177 165 342 107449
Equity income from unconsolidated investments, net— (2)(2)(59)(61)
Income tax expense (benefit)(129)11 (118)4(114)
Other (b)5 34 39 544
Net income (loss)362 345 707 (17)690
Total assets11,407 10,106 21,513 1,20122,714
Investments in equity method subsidiaries5 17 22 601623
Construction and acquisition expenditures1,224 828 2,052 1972,249
Utility
TotalAlliant
ReportableEnergy
2023 (amounts may not foot due to rounding)
IPLWPLSegmentsOtherConsolidated
Electric utility revenues$1,761 $1,584 $3,345 N/A$3,345
Gas utility revenues300 240 540 N/A540
Other revenues49 3 52 $90142
Total revenues2,110 1,827 3,937 904,027
Electric production fuel and purchased power expense282 455 737 N/A736
Electric transmission service expense420 163 583 N/A583
Cost of gas sold expense166 134 300 N/A299
Other operation and maintenance expense353 271 624 51675
Other segment items:
Depreciation and amortization expense388 280 668 8676
Interest expense155 149 304 90394
Equity income from unconsolidated investments, net— (3)(3)(58)(61)
Income tax expense (benefit)(58)60 2 24
Other (b)38 (27)11 518
Net income (loss)366 345 711 (8)703
Total assets10,489 9,634 20,123 1,11421,237
Investments in equity method subsidiaries5 16 21 564585
Construction and acquisition expenditures712 1,019 1,731 1231,854

(a)Alliant Energy’s non-utility holdings include Travero’s wind turbine blade recycling services, which commenced commercial operations in 2024, and whose assets are primarily included in “Property, plant and equipment, net” on Alliant Energy’s balance sheets. Alliant Energy suspended production of Travero’s wind turbine blade recycling services in November 2025 based on a review of strategic options, and as a result, a pre-tax non-cash asset valuation charge of $16 million was recorded to “Other operation and maintenance” in Alliant Energy’s income statement in 2025.
(b)Other segment items for each reportable segment include AFUDC, taxes other than income taxes, interest income, and other miscellaneous income and deductions.
v3.25.4
Related Parties
 12 Months Ended
Dec. 31, 2025
Related Party Transaction [Line Items]  
Related Parties RELATED PARTIES
Service Agreements - Pursuant to service agreements, IPL and WPL receive various administrative and general services from an affiliate, Corporate Services. These services are billed to IPL and WPL at cost based on expenses incurred by Corporate Services for the benefit of IPL and WPL, respectively. These costs consisted primarily of employee compensation and benefits, fees associated with various professional services, depreciation and amortization of property, plant and equipment, and a return on net assets. Corporate Services also acts as agent on behalf of IPL and WPL pursuant to the service agreements. As agent, Corporate Services enters into energy, capacity, ancillary services, and transmission sale and purchase transactions within MISO. Corporate Services assigns such sales and purchases among IPL and WPL based on statements received from MISO. The amounts billed for services provided, sales credited and purchases were as follows (in millions):
IPLWPL
202520242023202520242023
Corporate Services billings$194$183$181$189$171$163
Sales credited27—111318455
Purchases billed416430431755435

As of December 31, net intercompany payables to Corporate Services were as follows (in millions):
20252024
IPL$135$135
WPL8464

ATC - Pursuant to various agreements, WPL receives a range of transmission services from ATC. WPL provides operation, maintenance, and construction services to ATC. WPL and ATC also bill each other for use of shared facilities owned by each party. The related amounts billed between the parties were as follows (in millions):
202520242023
ATC billings to WPL$162$152$159
WPL billings to ATC271620

As of December 31, 2025 and 2024, WPL owed ATC net amounts of $10 million and $10 million, respectively.

WPL’s Sheboygan Falls Energy Facility Lease - Refer to Note 9 for discussion of WPL’s Sheboygan Falls Energy Facility lease.
IPL [Member]  
Related Party Transaction [Line Items]  
Related Parties RELATED PARTIES
Service Agreements - Pursuant to service agreements, IPL and WPL receive various administrative and general services from an affiliate, Corporate Services. These services are billed to IPL and WPL at cost based on expenses incurred by Corporate Services for the benefit of IPL and WPL, respectively. These costs consisted primarily of employee compensation and benefits, fees associated with various professional services, depreciation and amortization of property, plant and equipment, and a return on net assets. Corporate Services also acts as agent on behalf of IPL and WPL pursuant to the service agreements. As agent, Corporate Services enters into energy, capacity, ancillary services, and transmission sale and purchase transactions within MISO. Corporate Services assigns such sales and purchases among IPL and WPL based on statements received from MISO. The amounts billed for services provided, sales credited and purchases were as follows (in millions):
IPLWPL
202520242023202520242023
Corporate Services billings$194$183$181$189$171$163
Sales credited27—111318455
Purchases billed416430431755435

As of December 31, net intercompany payables to Corporate Services were as follows (in millions):
20252024
IPL$135$135
WPL8464
WPL [Member]  
Related Party Transaction [Line Items]  
Related Parties RELATED PARTIES
Service Agreements - Pursuant to service agreements, IPL and WPL receive various administrative and general services from an affiliate, Corporate Services. These services are billed to IPL and WPL at cost based on expenses incurred by Corporate Services for the benefit of IPL and WPL, respectively. These costs consisted primarily of employee compensation and benefits, fees associated with various professional services, depreciation and amortization of property, plant and equipment, and a return on net assets. Corporate Services also acts as agent on behalf of IPL and WPL pursuant to the service agreements. As agent, Corporate Services enters into energy, capacity, ancillary services, and transmission sale and purchase transactions within MISO. Corporate Services assigns such sales and purchases among IPL and WPL based on statements received from MISO. The amounts billed for services provided, sales credited and purchases were as follows (in millions):
IPLWPL
202520242023202520242023
Corporate Services billings$194$183$181$189$171$163
Sales credited27—111318455
Purchases billed416430431755435

As of December 31, net intercompany payables to Corporate Services were as follows (in millions):
20252024
IPL$135$135
WPL8464

ATC - Pursuant to various agreements, WPL receives a range of transmission services from ATC. WPL provides operation, maintenance, and construction services to ATC. WPL and ATC also bill each other for use of shared facilities owned by each party. The related amounts billed between the parties were as follows (in millions):
202520242023
ATC billings to WPL$162$152$159
WPL billings to ATC271620

As of December 31, 2025 and 2024, WPL owed ATC net amounts of $10 million and $10 million, respectively.

WPL’s Sheboygan Falls Energy Facility Lease - Refer to Note 9 for discussion of WPL’s Sheboygan Falls Energy Facility lease.
v3.25.4
Condensed Parent Company Financial Statements
 12 Months Ended
Dec. 31, 2025
Condensed Financial Information Disclosure [Abstract]  
Condensed Parent Company Financial Statements
SCHEDULE I - CONDENSED PARENT COMPANY FINANCIAL STATEMENTS
ALLIANT ENERGY CORPORATION (Parent Company Only)Year Ended December 31,
CONDENSED STATEMENTS OF INCOME202520242023
(in millions)
Operating expenses$4 $3 $3 
Operating loss(4)(3)(3)
Other (income) and deductions:
Equity earnings from consolidated subsidiaries(863)(734)(742)
Interest expense57 40 34 
Other(3)5 4 
Total other (income) and deductions(809)(689)(704)
Income before income taxes805 686 701 
Income tax benefit(6)(3)(5)
Net income$811 $689 $706 
Refer to accompanying Notes to Condensed Financial Statements.

ALLIANT ENERGY CORPORATION (Parent Company Only)December 31,
CONDENSED BALANCE SHEETS20252024
(in millions)
ASSETS
Current assets:
Cash and cash equivalents$512 $— 
Notes receivable from affiliated companies114 103 
Income tax refunds receivable12 12 
Other6 2 
Total current assets644 117 
Investments:
Investments in consolidated subsidiaries9,784 9,123 
Other1 1 
Total investments9,785 9,124 
Other assets102 84 
Total assets$10,531 $9,325 
LIABILITIES AND EQUITY
Current liabilities:
Current maturities of long-term debt$574 $571 
Commercial paper— 325 
Notes payable to affiliated companies1,300 1,401 
Other21 10 
Total current liabilities1,895 2,307 
Long-term debt, net (excluding current portion)1,286 — 
Other liabilities4 3 
Common equity:
Common stock and additional paid-in capital3,104 3,063 
Retained earnings4,255 3,965 
Accumulated other comprehensive income1 1 
Shares in deferred compensation trust(14)(14)
Total common equity7,346 7,015 
Total liabilities and equity$10,531 $9,325 
Refer to accompanying Notes to Condensed Financial Statements.
ALLIANT ENERGY CORPORATION (Parent Company Only)Year Ended December 31,
CONDENSED STATEMENTS OF CASH FLOWS202520242023
(in millions)
Net cash flows from operating activities$529 $355 $445 
Cash flows used for investing activities:
Capital contributions to consolidated subsidiaries(365)(380)(325)
Net change in notes receivable from and payable to affiliates(113)326 (281)
Net cash flows used for investing activities(478)(54)(606)
Cash flows from (used for) financing activities:
Common stock dividends(521)(492)(456)
Proceeds from issuance of common stock, net23 23 246 
Proceeds from issuance of long-term debt1,286 — 565 
Net change in commercial paper(325)168 (195)
Other(2)— 1 
Net cash flows from (used for) financing activities461 (301)161 
Net increase (decrease) in cash, cash equivalents and restricted cash512 — — 
Cash, cash equivalents and restricted cash at beginning of period— — — 
Cash, cash equivalents and restricted cash at end of period$512 $— $— 
Supplemental cash flows information:
Cash (paid) received during the period for:
Interest($45)($40)($27)
Income taxes, net:
Federal$4 $11 $8 
State - Iowa— (15)(13)
State - Wisconsin— 12 27 
Total income taxes, net$4 $8 $22 
Refer to accompanying Notes to Condensed Financial Statements.

ALLIANT ENERGY CORPORATION (Parent Company Only)
NOTES TO CONDENSED FINANCIAL STATEMENTS

Pursuant to rules and regulations of the SEC, the Condensed Financial Statements of Alliant Energy Corporation (Parent Company Only) do not reflect all of the information and notes normally included with financial statements prepared in accordance with GAAP. Therefore, these Condensed Financial Statements should be read in conjunction with the Financial Statements and related Notes included in the combined 2025 Form 10-K, Part II, Item 8, which is incorporated herein by reference.

In the Condensed Financial Statements of Alliant Energy Corporation (Parent Company Only), investments in subsidiaries are accounted for using the equity method.

NOTE: All other schedules are omitted because they are not applicable or not required, or because that required information is shown either in the financial statements or in the notes thereto.
v3.25.4
Insider Trading Arrangements
 3 Months Ended
Dec. 31, 2025
Trading Arrangements, by Individual  
Rule 10b5-1 Arrangement Adopted false
Non-Rule 10b5-1 Arrangement Adopted false
Rule 10b5-1 Arrangement Terminated false
Non-Rule 10b5-1 Arrangement Terminated false
v3.25.4
Cybersecurity Risk Management and Strategy Disclosure
 12 Months Ended
Dec. 31, 2025
Cybersecurity Risk Management, Strategy, and Governance [Line Items]  
Cybersecurity Risk Management Processes for Assessing, Identifying, and Managing Threats [Text Block]
Cybersecurity risks are identified as key risks through the enterprise risk management (ERM) program. These risks could include use of malicious code, employee theft or misuse, advanced persistent threats, vulnerabilities, fraud attempts, and phishing attacks that could cause, among others, an operations or information technology system failure, or breach or loss of sensitive information. The potential impact of cybersecurity risks on our business operations, results of operations or financial condition is discussed in the “Risks Related to Business Operations” section of Item 1A “Risk Factors.” We have not had any material cybersecurity breaches or incidents and have not incurred any material expenses, penalties or settlement costs related to any cybersecurity breaches or incidents. However, measures that we take to avoid, detect, mitigate or recover from cybersecurity breaches or incidents may be insufficient or become ineffective, and there are no assurances that cybersecurity breaches or incidents will not impact our business operations and strategy, results of operations and financial condition.
We maintain a cybersecurity program that includes development and implementation of policies, procedures and tools designed to help ensure availability of critical operations, information technology and telecommunication systems and safeguard sensitive information. The cybersecurity program is assessed against industry standards, including the National Institute of Standards and Technology Cybersecurity Framework. This assessment is conducted by a third party periodically and internally at least annually. We are also required to comply with cybersecurity standards under the North American Electric Reliability Corporation (NERC) Critical Infrastructure Protection and by the Department of Homeland Security Transportation Security Administration. We also periodically collaborate with federal and state law enforcement experts, external assessors, consultants, industry peers and other third parties in connection with understanding market and threat conditions used to identify, assess and mitigate cybersecurity risks.

The cybersecurity program includes:
•a dedicated cybersecurity team;
•operations, information technology and telecommunication systems implemented with segmentation and multiple levels of access controls;
•a security operations center that continuously monitors information technology and telecommunications systems;
•an incident response team composed of individuals from the information technology, operations, accounting, finance, legal, and communications departments, as needed, which is activated to respond to cybersecurity incidents;
•periodic drills and exercises to address risks and prepare for extraordinary scenarios, including industry collaboration on incident preparation, such as GridEx drills hosted by NERC, participation in a full activation drill at least annually, and several tabletop drills during the year;
•periodic drills with the full executive team, including the Chief Executive Officer (CEO), Chief Financial Officer (CFO), Chief Accounting Officer (CAO), Chief Information Officer (CIO) and General Counsel;
•periodic information security awareness training and phishing simulations for employees and contractors who access our networks;
•periodic security assessments of evolving risks and threats that lead to strengthening of cybersecurity measures;
•implementation of automation solutions to strengthen detection and response capabilities; and
•maintenance of cyber liability insurance.

We also address cybersecurity risks associated with third-party service providers, including those in our supply chain or who have access to our customer and employee data or our information technology systems. Third-party risks are included in the ERM program and the cybersecurity program. Diligence is performed on third parties that have access to information technology systems, data or facilities that house such systems or data. High-risk vendors are identified and continually monitored for cybersecurity threat risks. Additionally, third parties that have access to information technology systems, data or facilities that house such systems or data, agree by contract to manage their cybersecurity risks, provide notification in the event of a cybersecurity incident, and be subject to cybersecurity audits.
Cybersecurity Risk Management Processes Integrated [Flag] true
Cybersecurity Risk Management Processes Integrated [Text Block]
The cybersecurity program includes:
•a dedicated cybersecurity team;
•operations, information technology and telecommunication systems implemented with segmentation and multiple levels of access controls;
•a security operations center that continuously monitors information technology and telecommunications systems;
•an incident response team composed of individuals from the information technology, operations, accounting, finance, legal, and communications departments, as needed, which is activated to respond to cybersecurity incidents;
•periodic drills and exercises to address risks and prepare for extraordinary scenarios, including industry collaboration on incident preparation, such as GridEx drills hosted by NERC, participation in a full activation drill at least annually, and several tabletop drills during the year;
•periodic drills with the full executive team, including the Chief Executive Officer (CEO), Chief Financial Officer (CFO), Chief Accounting Officer (CAO), Chief Information Officer (CIO) and General Counsel;
•periodic information security awareness training and phishing simulations for employees and contractors who access our networks;
•periodic security assessments of evolving risks and threats that lead to strengthening of cybersecurity measures;
•implementation of automation solutions to strengthen detection and response capabilities; and
•maintenance of cyber liability insurance.
Cybersecurity Risk Management Third Party Engaged [Flag] true
Cybersecurity Risk Third Party Oversight and Identification Processes [Flag] true
Cybersecurity Risk Materially Affected or Reasonably Likely to Materially Affect Registrant [Flag] false
Cybersecurity Risk Board of Directors Oversight [Text Block] The Board retains direct oversight of cybersecurity matters to best utilize the experiences and expertise of all Board members. Management, including the CIO, provides reports approximately quarterly to the Board regarding risks, threats, the threat landscape, assessments of and improvements to the cybersecurity program, and internal response preparedness. The Audit Committee provides oversight of policies on risk assessment, controls, and accounting risk exposure, reviews cybersecurity disclosures in filings with the Securities and Exchange Commission, and reviews internal audit reports related to cybersecurity processes. The Operations Committee provides focused oversight of operational and capital‑related cybersecurity and technology matters.
Cybersecurity Risk Board Committee or Subcommittee Responsible for Oversight [Text Block] The full Board of Directors is responsible for oversight of our key cybersecurity risks.
Cybersecurity Risk Process for Informing Board Committee or Subcommittee Responsible for Oversight [Text Block] Management, including the CIO, provides reports approximately quarterly to the Board regarding risks, threats, the threat landscape, assessments of and improvements to the cybersecurity program, and internal response preparedness.
Cybersecurity Risk Role of Management [Text Block]
Our cybersecurity program is overseen by our Senior Vice President and CIO, who has nearly four decades of experience in information technology, including two decades as a CIO, having previously held CIO roles with other organizations, as well as experience in the utility sector. The CIO oversees a team dedicated to the support of cybersecurity tools and the overall cybersecurity program. The CIO reports to the Executive Vice President and Chief Strategy Officer. The CIO provides periodic briefs regarding prevention, detection, mitigation and remediation of cybersecurity incidents, as well as risks, threats and the threat landscape to the Board and executive management, including the CEO, CFO and CAO. These briefs are used to help continuously improve our cybersecurity program and to inform risk assessments as part of the ERM program.
Cybersecurity Risk Management Positions or Committees Responsible [Flag] true
Cybersecurity Risk Management Positions or Committees Responsible [Text Block] Our cybersecurity program is overseen by our Senior Vice President and CIO
Cybersecurity Risk Management Expertise of Management Responsible [Text Block] Our cybersecurity program is overseen by our Senior Vice President and CIO, who has nearly four decades of experience in information technology, including two decades as a CIO, having previously held CIO roles with other organizations, as well as experience in the utility sector.
Cybersecurity Risk Process for Informing Management or Committees Responsible [Text Block] The CIO provides periodic briefs regarding prevention, detection, mitigation and remediation of cybersecurity incidents, as well as risks, threats and the threat landscape to the Board and executive management, including the CEO, CFO and CAO. These briefs are used to help continuously improve our cybersecurity program and to inform risk assessments as part of the ERM program.
Cybersecurity Risk Management Positions or Committees Responsible Report to Board [Flag] true
v3.25.4
Summary Of Significant Accounting Policies (Policy)
 12 Months Ended
Dec. 31, 2025
Property, Plant and Equipment [Line Items]  
General, Basis of Presentation The financial statements reflect investments in controlled subsidiaries on a consolidated basis and Alliant Energy’s, IPL’s and WPL’s proportionate shares of jointly-owned utility EGUs. Unconsolidated investments that Alliant Energy and WPL do not control are accounted for under the equity method of accounting. Under the equity method of accounting, Alliant Energy and WPL initially record the investment at cost, and adjust the carrying amount of the investment to recognize their respective share of the earnings or losses of the investee. Dividends received from an investee reduce the carrying amount of the equity investment. Investments that do not meet the criteria for consolidation or the equity method of accounting are accounted for under the cost method.All intercompany balances and transactions, other than certain transactions affecting the rate-making process at IPL and WPL, have been eliminated from the financial statements. Such transactions not eliminated include costs that are recoverable from customers through rate-making processes.
General, Basis of Accounting The financial statements are prepared in conformity with GAAP, which give recognition to the rate-making practices of FERC and state commissions having regulatory jurisdiction.
General, Reclassification
Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes.
General, Use of Estimates The preparation of the financial statements requires management to make estimates and assumptions that affect: (a) the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements; and (b) the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
Regulatory Assets and Regulatory Liabilities Alliant Energy, IPL and WPL are subject to regulation by FERC and state regulatory commissions in their service territories. As a result, Alliant Energy, IPL and WPL are subject to GAAP provisions for regulated operations, which provide that rate-regulated public utilities record certain costs and credits allowed in the rate-making process in different periods than for non-utility entities. Regulatory assets generally represent incurred costs that have been deferred as such costs are probable of recovery in future customer rates. Regulatory liabilities generally represent obligations to make refunds to customers or amounts collected in rates for which the related costs have not yet been incurred. Amounts recorded as regulatory assets or regulatory liabilities are generally recognized in the income statements at the time they are reflected in rates.
Income Taxes The liability method of accounting is followed for deferred taxes, which requires the establishment of deferred tax assets and liabilities, as appropriate, for temporary differences between the tax basis of assets and liabilities and the amounts reported in the financial statements. Deferred taxes are recorded using currently enacted tax rates and estimates of state apportionment. Changes in deferred tax assets and liabilities associated with certain property-related differences at IPL are accounted for differently than other subsidiaries of Alliant Energy due to rate-making practices in Iowa. Rate-making practices in Iowa do not allow the impact of certain deferred tax expenses (benefits) to be included in the determination of retail rates. Based on these rate-making practices, deferred tax expense (benefit) related to these property-related differences at IPL is not recorded in the income statement but instead recorded to regulatory assets or regulatory liabilities until these temporary differences reverse. In Wisconsin, the PSCW allows rate recovery of deferred tax expense on all temporary differences.
The flow-through method of accounting is used for investment tax credits. Certain federal investment tax credits related to utility property, plant and equipment are subject to statutory tax normalization rules limiting how they may be treated in rate-making. As appropriate to reflect the rate-making practices, investment tax credits are deferred and amortized over the book depreciable lives of the related property or other period prescribed by rate regulation.

Alliant Energy files a consolidated federal income tax return and a combined return in Wisconsin, which include Alliant Energy and its subsidiaries. Alliant Energy subsidiaries with a presence in Iowa file as part of a consolidated return in Iowa.

Alliant Energy allocates consolidated income tax expense to its subsidiaries that are members of the group that file a consolidated or combined income tax return. IPL and WPL use the separate return approach for calculating their income tax provisions and related deferred tax assets and liabilities. IPL and WPL are assumed to file separate tax returns with the federal and state taxing authorities, except that net operating losses (and other current or deferred tax attributes) are characterized as realized (or realizable) by IPL and WPL when those tax attributes are realized (or realizable) by the consolidated tax return group of Alliant Energy (even if IPL and WPL would not otherwise have realized the attributes on a stand-alone basis).
IPL and WPL have entered into agreements to transfer renewable tax credits from certain wind, solar and energy storage facilities to other corporate taxpayers in exchange for cash. Alliant Energy, IPL and WPL have elected to record transfers of renewable tax credits as part of income taxes, and cash received from the transfer of renewable tax credits is recorded in cash flows from operating activities. Renewable tax credits subject to future transfer are recorded at expected realizable value. Renewable tax credits are derecognized when control of the tax credits is transferred to other corporate taxpayers. Beginning October 1, 2024, IPL’s renewable energy rider was discontinued, and production tax credits, excluding production tax credits from the refurbishment of existing wind farms, are credited to IPL’s retail electric customers through its fuel-related cost recovery mechanism. Investment tax credits resulting from IPL’s renewable generation and energy storage projects that are not yet included in base rates may be utilized to offset any revenue deficiency on an annual basis up to IPL’s return on common equity threshold; any remaining investment tax credits, net of the cost of transferability, that are not used to offset any revenue deficiency, will be deferred by IPL and carried forward to offset any potential revenue deficiency in future years. At WPL, pursuant to escrow treatment approved by the PSCW, the difference between actual renewable tax credits and the amount of renewable tax credits collected from customers as electric revenues is recognized in “Income taxes” in Alliant Energy’s and WPL’s income statements. An offsetting amount is recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until reflected in future billings to customers.
Cash, Cash Equivalents and Restricted Cash Cash and cash equivalents include short-term liquid investments that have original maturities of less than 90 days. At December 31, 2025, Alliant Energy’s and WPL’s cash and cash equivalents included $411 million and $25 million, respectively, of money market fund investments, with weighted average interest rates of 4%. At December 31, 2025 and 2024, Alliant Energy’s restricted cash was not material.
Property, Plant and Equipment
Utility Plant -
General - Utility plant is recorded at the original cost of acquisition or construction, which includes material, labor, contractor services, AFUDC and allocable overheads, such as supervision, engineering, certain administrative costs directly related to construction, benefits, certain taxes and transportation. Repairs, replacements and renewals of items of property determined to be less than a unit of property or that do not increase the property’s life or functionality are charged to maintenance expense. Property, plant and equipment that is probable of being retired early is classified as plant anticipated to be retired early. Generally, ordinary retirements of utility plant and salvage value are netted and charged to accumulated depreciation upon removal from utility plant accounts and no gain or loss is recognized consistent with rate-making principles. However, if regulators have approved recovery of the remaining net book value of property, plant and equipment that is retired early, or such approval by regulators is probable, the remaining net book value is reclassified from property, plant and equipment to regulatory assets upon retirement.
Non-utility and Other Property -
General - Non-utility property is recorded at the original cost of acquisition or construction, which includes material, labor and contractor services. Repairs, replacements and renewals of items of property determined to be less than a unit of property or that do not increase the property’s life or functionality are charged to maintenance expense. Upon retirement or sale of non-utility property, the original cost and related accumulated depreciation are removed from the accounts and any gain or loss is included in the income statements.

Costs related to software developed or obtained for internal use are capitalized and amortized on a straight-line basis over the estimated useful life of the related software. If software is retired prior to being fully amortized, the remaining book value is recorded as a loss in the income statements.
Depreciation IPL and WPL use a combination of remaining life and straight-line depreciation methods as approved by their respective regulatory commissions. The composite or group method of depreciation is used, in which a single depreciation rate is applied to the gross investment in a particular class of property. This method pools similar assets and then depreciates each group as a whole. Periodic depreciation studies are performed to determine the appropriate group lives, net salvage, estimated cost of removal and group depreciation rates. These depreciation studies are subject to review and approval by IPL’s and WPL’s respective regulatory commissions. Depreciation expense is included within the recoverable cost of service component of rates collected from customers. The average rates of depreciation for electric, gas and other properties, consistent with current rate-making practices, were as follows:
IPLWPL
202520242023202520242023
Electric - generation3.5%3.3%3.3%3.4%3.4%3.0%
Electric - distribution2.9%2.8%2.8%2.7%2.7%2.7%
Electric - other3.6%5.2%5.6%4.2%6.1%6.3%
Gas3.3%3.3%3.3%2.4%2.5%2.5%
Other5.6%4.6%6.2%4.5%4.4%4.6%
AFUDC AFUDC represents costs to finance construction additions, including a return on equity component and cost of debt component as required by regulatory accounting. AFUDC for IPL’s construction projects is calculated in accordance with FERC guidelines. AFUDC for WPL’s retail and wholesale jurisdiction construction projects is calculated in accordance with PSCW and FERC guidelines, respectively. The AFUDC rates, computed in accordance with the prescribed regulatory formula, were as follows:
202520242023
IPL7.1%7.0%7.0%
WPL (retail jurisdiction)7.4%7.4%7.4%
WPL (wholesale jurisdiction)6.6%7.1%7.1%

In accordance with their respective regulatory commission decisions, IPL applies its AFUDC rates to 100% of applicable CWIP balances, and WPL generally applies its AFUDC rates to 50% of applicable CWIP balances and the remaining 50% of applicable CWIP balances earns a return on such balances as part of its rate base. WPL may be authorized to apply its AFUDC rates to 100% of the retail portion of the CWIP balances for construction projects requiring a CA or CPCN that were approved by the PSCW after its then most recent rate order. Beginning January 1, 2026, the PSCW also authorized an AFUDC applied to 100% of the retail portion of CWIP balances related to construction activity on capital projects requiring PSCW approval and are impacted by federal law changes.
Revenue Recognition
Utility - Revenues from Alliant Energy’s utility business are primarily from electric and gas sales to customers. Utility revenues are recognized over time as services are rendered or commodities are delivered to customers, and include billed and unbilled components. The billed component is based on the reading of customers’ meters, which occurs on a systematic basis throughout each reporting period and represents the fair value of the services provided or commodities delivered. The unbilled component is recorded at the end of each reporting period based on estimated amounts of energy delivered to customers but not yet billed.

IPL and WPL accrue revenues from their wholesale customers to the extent that the actual net revenue requirements calculated in accordance with FERC-approved formula rates for the reporting period are higher or lower than the amounts billed to wholesale customers during such period. Regulatory assets or regulatory liabilities are recorded as the offset for these accrued revenues under formulaic rate-making programs. As of December 31, 2025, the related amounts accrued for IPL and WPL were not material.
IPL and WPL participate in bid/offer-based wholesale energy and ancillary services markets operated by MISO. The MISO transactions are grouped together, resulting in a net supply to or net purchase from MISO for each hour of each day. The net supply to MISO is recorded as bulk power sales in “Electric utility revenues” and the net purchase from MISO is recorded in “Electric production fuel and purchased power” in the income statements.

Non-utility - Revenues from Alliant Energy’s non-utility businesses are primarily from its Travero business and are recognized over time as services are rendered to customers.

Taxes Collected from Customers - Sales or various other taxes collected by certain of Alliant Energy’s subsidiaries on behalf of other agencies are recorded on a net basis and are not included in revenues.

Other - Alliant Energy, IPL and WPL do not disclose the value of unsatisfied performance obligations for: (i) contracts with an original expected length of one year or less; and (ii) contracts for which revenue is recognized at the amount to which they have the right to invoice for services performed.
Utility Cost Recovery Mechanisms
Electric Production Fuel and Purchased Power (Fuel-related Costs) - Fuel-related costs are incurred to generate and purchase electricity to meet the demand of IPL’s and WPL’s electric customers. These fuel-related costs include the cost of fossil fuels (primarily natural gas and coal) used to produce electricity at their EGUs, and electricity purchased from MISO wholesale energy markets and under PPAs. These fuel-related costs are recorded in “Electric production fuel and purchased power” in the income statements.

IPL Retail - The cost recovery mechanisms for IPL’s retail electric customers provide for monthly adjustments to their electric rates for changes in fuel-related costs. Changes in the under-/over-collection of these costs are recognized in “Electric production fuel and purchased power” in Alliant Energy’s and IPL’s income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers.

WPL Retail - The cost recovery mechanism for WPL’s retail electric customers is based on forecasts of certain fuel-related costs expected to be incurred during forward-looking test periods and fuel monitoring ranges determined by the PSCW during each retail electric rate proceeding or in a separate fuel cost plan approval proceeding. If WPL’s actual fuel-related costs fall outside these fuel monitoring ranges, WPL is authorized to defer the incremental under-/over-collection of fuel-related costs that are outside the approved ranges. Deferral of under-collections are reduced to the extent actual return on common equity earned by WPL during the fuel cost plan year exceeds the most recently authorized return on common equity. Deferred amounts for fuel-related costs outside the approved fuel monitoring ranges are recognized in “Electric production fuel and purchased power” in Alliant Energy’s and WPL’s income statements. The cumulative effects of these deferred amounts are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until they are reflected in future billings to customers.

IPL and WPL Wholesale - The cost recovery mechanisms for IPL’s and WPL’s wholesale electric customers provide for subsequent adjustments to their electric rates for changes in fuel-related costs. Changes in the under-/over-collection of these costs are recognized in “Electric production fuel and purchased power” in the income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers.

Electric Capacity - PPAs help meet the electricity demand of IPL’s and WPL’s customers. Certain PPAs include minimum payments for IPL’s and WPL’s rights to electric generating capacity, which are charged each period to “Electric production fuel and purchased power” in the income statements. Purchased electric capacity expenses are recovered from IPL’s and WPL’s retail electric customers through changes in base rates determined during periodic rate proceedings. Purchased electric capacity expenses are recovered from IPL’s and WPL’s wholesale electric customers through annual changes in base rates determined by a formula rate structure. Electric capacity revenues are refunded to IPL's retail electric customers through changes in base rates determined during periodic rate proceedings, and to IPL and WPL's wholesale electric customers through annual changes in base rates determined by a formula rate structure. Electric capacity revenues are refunded to WPL's retail electric customers through its fuel cost recovery mechanism.

Electric Transmission Service - Costs incurred for the transmission of electricity to meet the demands of IPL’s and WPL’s customers are charged to “Electric transmission service” in the income statements.

IPL Retail - Electric transmission service expense is recovered from IPL’s retail electric customers through a transmission cost rider. This cost recovery mechanism provides for periodic adjustments to electric rates charged to retail electric customers for changes in electric transmission service expense. Changes in the under-/over-collection of these costs are recognized in “Electric transmission service” in Alliant Energy’s and IPL’s income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers.
WPL Retail - Electric transmission service expense is recovered from WPL’s retail electric customers through changes in base rates determined during periodic rate proceedings. Pursuant to escrow accounting treatment approved by the PSCW, the difference between actual electric transmission service expense incurred and the amount of electric transmission service costs collected from customers as electric revenues is recognized in “Electric transmission service” in Alliant Energy’s and WPL’s income statements. An offsetting amount is recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until reflected in future billings to customers.

IPL and WPL Wholesale - IPL and WPL arrange transmission service for the majority of their respective wholesale electric customers. Electric transmission service expense is allocated to and recovered from these customers based on a load ratio share computation.

Cost of Gas Sold - Costs are incurred for the purchase, transportation and storage of natural gas to serve IPL’s and WPL’s gas customers and the costs associated with the natural gas delivered to customers are charged to “Cost of gas sold” in the income statements. The tariffs for IPL’s and WPL’s retail gas customers provide for subsequent adjustments to their rates periodically for changes in the cost of gas sold. Changes in the under-/over-collection of these costs are also recognized in “Cost of gas sold” in the income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers.

Energy Efficiency Costs - Costs incurred to fund energy efficiency programs and initiatives that help customers reduce their energy usage are charged to “Other operation and maintenance” in the income statements. Energy efficiency costs incurred by IPL are recovered from its retail electric and gas customers through energy efficiency and demand response cost recovery factor tariffs, which are revised annually and include a reconciliation to eliminate any under-/over-collection of energy efficiency costs from prior periods. Pursuant to escrow accounting treatment approved by the PSCW, the difference between actual energy efficiency costs incurred by WPL and the amount collected from its retail electric and gas customers is recovered through changes in base rates determined during periodic rate proceedings, and reconciliations eliminate any under-/over-collection of energy efficiency costs from prior periods. Changes in the under-/over-collection of energy efficiency costs for IPL and WPL are recognized in “Other operation and maintenance” in the income statements. The cumulative effects of the under-/over-collection of these costs for IPL and WPL are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers.
Renewable Energy Rider - IPL utilized a renewable energy rider prior to its discontinuation on October 1, 2024, effective with the IUC’s order for IPL’s retail electric rate review for the October 2024 through September 2025 Test Period. Prior to October 1, 2024, IPL recovered a return of, as well as earned a return on, its wind generation placed in service in 2019 and 2020 from its retail electric customers through the renewable energy rider. Other applicable costs and tax benefits associated with this wind generation, excluding operation and maintenance expenses, were also included in the rider. This cost recovery mechanism provided for annual adjustments to electric rates charged to IPL’s retail electric customers for actual renewable energy costs and tax benefits. Changes in the under-/over-collection of these costs were recognized in “Electric utility revenue” in Alliant Energy’s and IPL’s income statements. The cumulative effects of the under-/over-collection of these costs for IPL is recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers.
Financial Instruments Financial instruments are periodically used for risk management purposes to mitigate exposures to fluctuations in certain commodity prices, transmission congestion costs and interest rates. The fair value of those financial instruments that are determined to be derivatives are recorded as assets or liabilities on the balance sheets. Certain commodity purchase and sales contracts qualified for and were designated under the normal purchase and sale exception, and were accounted for on the accrual basis of accounting. Alliant Energy, IPL and WPL have elected to not net the fair value amounts of derivatives subject to a master netting arrangement by counterparty. Alliant Energy, IPL and WPL do not offset fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) against fair value amounts recognized for derivative instruments that are executed with the same counterparty under the same master netting arrangement.
Asset Impairments
Property, Plant and Equipment of Regulated Operations - Property, plant and equipment of regulated operations are reviewed for possible impairment whenever events or changes in circumstances indicate all or a portion of the carrying value of the assets may be disallowed for rate-making purposes. If IPL or WPL are disallowed recovery of any portion of, or are only allowed a partial return on, the carrying value of their regulated property, plant and equipment that is under construction, has been recently completed or is probable of abandonment, or conclude it is probable recovery or a full return will be disallowed, then an impairment charge is recognized.
Property, Plant and Equipment of Non-utility Operations - Property, plant and equipment of non-utility operations are reviewed for possible impairment whenever events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Impairment is indicated if the carrying value of an asset exceeds its undiscounted future cash flows. If an impairment is indicated, a charge is recognized equal to the amount the carrying value exceeds the asset’s fair value. Refer to Note 17 for discussion of an asset valuation charge at Alliant Energy’s non-utility holdings in 2025.

Unconsolidated Equity Investments - If events or circumstances indicate the carrying value of investments accounted for under the equity method of accounting exceeds fair value and the decline in value is other than temporary, potential impairment is assessed. If an impairment is indicated, a charge is recognized equal to the amount the carrying value exceeds the investment’s fair value.
Asset Retirement Obligations The fair value of a legal obligation associated with the retirement of an asset is recorded as a liability when an asset is placed in service, when a legal obligation is subsequently identified or when sufficient information becomes available to determine a reasonable estimate of the fair value of future retirement costs. When an ARO is recorded as a liability, an equivalent amount is added to the asset cost. The fair value of AROs at inception is determined using discounted cash flows analyses. The liability is accreted to its present value and the capitalized cost is depreciated over the useful life of the related asset. Accretion and depreciation expenses related to AROs for IPL’s and WPL’s regulated operations are recorded to regulatory assets on the balance sheets. Revisions in estimated cash flows for IPL’s and WPL’s regulated operations are recorded as an increase or decrease to the ARO liability, with an offset to the asset cost, unless the asset is already retired and then the offset is recorded to regulatory assets or regulatory liabilities on the balance sheets. Upon regulatory approval to recover IPL’s AROs expenditures, its regulatory assets are amortized to depreciation and amortization expenses in Alliant Energy’s and IPL’s income statements over the same time period the ARO expenditures are recovered from IPL’s customers. WPL’s regulatory assets related to AROs are recovered as a component of depreciation rates pursuant to PSCW and FERC orders. Upon settlement of the ARO liability, an entity settles the obligation for its recorded amount or incurs a gain or loss. Any gains or losses related to AROs for IPL’s and WPL’s regulated operations are recorded to regulatory liabilities or regulatory assets on the balance sheets.
Debt Issuance and Retirement Costs Debt issuance costs and debt premiums or discounts are presented on the balance sheets as a direct adjustment to the carrying amount of the related debt liability, and are deferred and amortized over the expected life of each debt issue, considering maturity dates and, if applicable, redemption rights held by us or by others. Alliant Energy’s non-utility businesses and Corporate Services record to interest expense in the period of retirement any unamortized debt issuance costs and debt premiums or discounts on debt retired early.
Current Expected Credit Losses Estimates Current expected credit losses are estimated for trade and other receivables and credit exposures on guarantees of the performance by third parties. The current expected credit losses for short-term trade receivables are based on estimates of losses resulting from the inability of customers to make required payments. The methodology used to estimate losses is based on historical write-offs, regional economic conditions, significant events that could impact collectability, such as significant weather related matters and related regulatory actions, and actual and forecasted changes to the accounts receivable aging portfolio and write-offs. The current expected credit losses related to guarantees of the performance by third parties are estimated using both quantitative and qualitative information, which utilizes potential outcomes in a range of possible estimated amounts.
Variable Interest Entities An entity is considered a VIE if its equity investors do not have sufficient equity at risk for the entity to finance its activities without additional subordinated financial support from other parties, the entity is structured with disproportionate voting rights and substantially all of the entity’s activities are conducted on behalf of the investor with disproportionately fewer voting rights, or its equity investors lack any of the following characteristics: (1) power, through voting rights or similar rights, to direct the activities of the entity that most significantly impact the entity’s economic performance; (2) the obligation to absorb expected losses of the entity; or (3) the right to receive expected benefits of the entity. The primary beneficiary of a VIE is required to consolidate the VIE. The financial statements do not reflect any consolidation of VIEs.
Leases The determination of whether an arrangement qualifies as a lease occurs at the inception of the arrangement. Arrangements that qualify as leases are classified as either operating or finance. Operating and finance lease liabilities represent obligations to make payments arising from the lease. Operating and finance lease assets represent the right to use an underlying asset for the lease term and are recognized at the lease commencement date based on the present value of the lease payments over the lease term. Leases with initial terms less than 12 months are not recognized as leases. For operating leases, an incremental borrowing rate, as determined at the lease commencement date, is used to determine the present value of the lease payments. For finance leases, the rate implicit in the lease, if known, is used to determine the present value of the lease payments. If the rate implicit in the lease is not known, the incremental borrowing rate, as determined at the lease commencement date, is used to determine the present value of the lease payments. Lease terms include options to extend or terminate the lease when it is reasonably certain that the option will be exercised. Operating lease expense is recognized on a straight-line basis over the expected lease term. Finance lease expense is comprised of depreciation and amortization, and interest expenses. Finance lease assets are accounted for as operating leases for rate-making purposes.
IPL [Member]  
Property, Plant and Equipment [Line Items]  
General, Basis of Presentation The financial statements reflect investments in controlled subsidiaries on a consolidated basis and Alliant Energy’s, IPL’s and WPL’s proportionate shares of jointly-owned utility EGUs. Unconsolidated investments that Alliant Energy and WPL do not control are accounted for under the equity method of accounting. Under the equity method of accounting, Alliant Energy and WPL initially record the investment at cost, and adjust the carrying amount of the investment to recognize their respective share of the earnings or losses of the investee. Dividends received from an investee reduce the carrying amount of the equity investment. Investments that do not meet the criteria for consolidation or the equity method of accounting are accounted for under the cost method.All intercompany balances and transactions, other than certain transactions affecting the rate-making process at IPL and WPL, have been eliminated from the financial statements. Such transactions not eliminated include costs that are recoverable from customers through rate-making processes.
General, Basis of Accounting The financial statements are prepared in conformity with GAAP, which give recognition to the rate-making practices of FERC and state commissions having regulatory jurisdiction.
General, Reclassification
Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes.
General, Use of Estimates The preparation of the financial statements requires management to make estimates and assumptions that affect: (a) the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements; and (b) the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
Regulatory Assets and Regulatory Liabilities Alliant Energy, IPL and WPL are subject to regulation by FERC and state regulatory commissions in their service territories. As a result, Alliant Energy, IPL and WPL are subject to GAAP provisions for regulated operations, which provide that rate-regulated public utilities record certain costs and credits allowed in the rate-making process in different periods than for non-utility entities. Regulatory assets generally represent incurred costs that have been deferred as such costs are probable of recovery in future customer rates. Regulatory liabilities generally represent obligations to make refunds to customers or amounts collected in rates for which the related costs have not yet been incurred. Amounts recorded as regulatory assets or regulatory liabilities are generally recognized in the income statements at the time they are reflected in rates.
Income Taxes The liability method of accounting is followed for deferred taxes, which requires the establishment of deferred tax assets and liabilities, as appropriate, for temporary differences between the tax basis of assets and liabilities and the amounts reported in the financial statements. Deferred taxes are recorded using currently enacted tax rates and estimates of state apportionment. Changes in deferred tax assets and liabilities associated with certain property-related differences at IPL are accounted for differently than other subsidiaries of Alliant Energy due to rate-making practices in Iowa. Rate-making practices in Iowa do not allow the impact of certain deferred tax expenses (benefits) to be included in the determination of retail rates. Based on these rate-making practices, deferred tax expense (benefit) related to these property-related differences at IPL is not recorded in the income statement but instead recorded to regulatory assets or regulatory liabilities until these temporary differences reverse. In Wisconsin, the PSCW allows rate recovery of deferred tax expense on all temporary differences.
The flow-through method of accounting is used for investment tax credits. Certain federal investment tax credits related to utility property, plant and equipment are subject to statutory tax normalization rules limiting how they may be treated in rate-making. As appropriate to reflect the rate-making practices, investment tax credits are deferred and amortized over the book depreciable lives of the related property or other period prescribed by rate regulation.

Alliant Energy files a consolidated federal income tax return and a combined return in Wisconsin, which include Alliant Energy and its subsidiaries. Alliant Energy subsidiaries with a presence in Iowa file as part of a consolidated return in Iowa.

Alliant Energy allocates consolidated income tax expense to its subsidiaries that are members of the group that file a consolidated or combined income tax return. IPL and WPL use the separate return approach for calculating their income tax provisions and related deferred tax assets and liabilities. IPL and WPL are assumed to file separate tax returns with the federal and state taxing authorities, except that net operating losses (and other current or deferred tax attributes) are characterized as realized (or realizable) by IPL and WPL when those tax attributes are realized (or realizable) by the consolidated tax return group of Alliant Energy (even if IPL and WPL would not otherwise have realized the attributes on a stand-alone basis).
IPL and WPL have entered into agreements to transfer renewable tax credits from certain wind, solar and energy storage facilities to other corporate taxpayers in exchange for cash. Alliant Energy, IPL and WPL have elected to record transfers of renewable tax credits as part of income taxes, and cash received from the transfer of renewable tax credits is recorded in cash flows from operating activities. Renewable tax credits subject to future transfer are recorded at expected realizable value. Renewable tax credits are derecognized when control of the tax credits is transferred to other corporate taxpayers. Beginning October 1, 2024, IPL’s renewable energy rider was discontinued, and production tax credits, excluding production tax credits from the refurbishment of existing wind farms, are credited to IPL’s retail electric customers through its fuel-related cost recovery mechanism. Investment tax credits resulting from IPL’s renewable generation and energy storage projects that are not yet included in base rates may be utilized to offset any revenue deficiency on an annual basis up to IPL’s return on common equity threshold; any remaining investment tax credits, net of the cost of transferability, that are not used to offset any revenue deficiency, will be deferred by IPL and carried forward to offset any potential revenue deficiency in future years. At WPL, pursuant to escrow treatment approved by the PSCW, the difference between actual renewable tax credits and the amount of renewable tax credits collected from customers as electric revenues is recognized in “Income taxes” in Alliant Energy’s and WPL’s income statements. An offsetting amount is recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until reflected in future billings to customers.
Cash, Cash Equivalents and Restricted Cash Cash and cash equivalents include short-term liquid investments that have original maturities of less than 90 days. At December 31, 2025, Alliant Energy’s and WPL’s cash and cash equivalents included $411 million and $25 million, respectively, of money market fund investments, with weighted average interest rates of 4%. At December 31, 2025 and 2024, Alliant Energy’s restricted cash was not material.
Property, Plant and Equipment
Utility Plant -
General - Utility plant is recorded at the original cost of acquisition or construction, which includes material, labor, contractor services, AFUDC and allocable overheads, such as supervision, engineering, certain administrative costs directly related to construction, benefits, certain taxes and transportation. Repairs, replacements and renewals of items of property determined to be less than a unit of property or that do not increase the property’s life or functionality are charged to maintenance expense. Property, plant and equipment that is probable of being retired early is classified as plant anticipated to be retired early. Generally, ordinary retirements of utility plant and salvage value are netted and charged to accumulated depreciation upon removal from utility plant accounts and no gain or loss is recognized consistent with rate-making principles. However, if regulators have approved recovery of the remaining net book value of property, plant and equipment that is retired early, or such approval by regulators is probable, the remaining net book value is reclassified from property, plant and equipment to regulatory assets upon retirement.
Non-utility and Other Property -
General - Non-utility property is recorded at the original cost of acquisition or construction, which includes material, labor and contractor services. Repairs, replacements and renewals of items of property determined to be less than a unit of property or that do not increase the property’s life or functionality are charged to maintenance expense. Upon retirement or sale of non-utility property, the original cost and related accumulated depreciation are removed from the accounts and any gain or loss is included in the income statements.

Costs related to software developed or obtained for internal use are capitalized and amortized on a straight-line basis over the estimated useful life of the related software. If software is retired prior to being fully amortized, the remaining book value is recorded as a loss in the income statements.
Depreciation IPL and WPL use a combination of remaining life and straight-line depreciation methods as approved by their respective regulatory commissions. The composite or group method of depreciation is used, in which a single depreciation rate is applied to the gross investment in a particular class of property. This method pools similar assets and then depreciates each group as a whole. Periodic depreciation studies are performed to determine the appropriate group lives, net salvage, estimated cost of removal and group depreciation rates. These depreciation studies are subject to review and approval by IPL’s and WPL’s respective regulatory commissions. Depreciation expense is included within the recoverable cost of service component of rates collected from customers. The average rates of depreciation for electric, gas and other properties, consistent with current rate-making practices, were as follows:
IPLWPL
202520242023202520242023
Electric - generation3.5%3.3%3.3%3.4%3.4%3.0%
Electric - distribution2.9%2.8%2.8%2.7%2.7%2.7%
Electric - other3.6%5.2%5.6%4.2%6.1%6.3%
Gas3.3%3.3%3.3%2.4%2.5%2.5%
Other5.6%4.6%6.2%4.5%4.4%4.6%
AFUDC AFUDC represents costs to finance construction additions, including a return on equity component and cost of debt component as required by regulatory accounting. AFUDC for IPL’s construction projects is calculated in accordance with FERC guidelines. AFUDC for WPL’s retail and wholesale jurisdiction construction projects is calculated in accordance with PSCW and FERC guidelines, respectively. The AFUDC rates, computed in accordance with the prescribed regulatory formula, were as follows:
202520242023
IPL7.1%7.0%7.0%
WPL (retail jurisdiction)7.4%7.4%7.4%
WPL (wholesale jurisdiction)6.6%7.1%7.1%

In accordance with their respective regulatory commission decisions, IPL applies its AFUDC rates to 100% of applicable CWIP balances, and WPL generally applies its AFUDC rates to 50% of applicable CWIP balances and the remaining 50% of applicable CWIP balances earns a return on such balances as part of its rate base. WPL may be authorized to apply its AFUDC rates to 100% of the retail portion of the CWIP balances for construction projects requiring a CA or CPCN that were approved by the PSCW after its then most recent rate order. Beginning January 1, 2026, the PSCW also authorized an AFUDC applied to 100% of the retail portion of CWIP balances related to construction activity on capital projects requiring PSCW approval and are impacted by federal law changes.
Revenue Recognition
Utility - Revenues from Alliant Energy’s utility business are primarily from electric and gas sales to customers. Utility revenues are recognized over time as services are rendered or commodities are delivered to customers, and include billed and unbilled components. The billed component is based on the reading of customers’ meters, which occurs on a systematic basis throughout each reporting period and represents the fair value of the services provided or commodities delivered. The unbilled component is recorded at the end of each reporting period based on estimated amounts of energy delivered to customers but not yet billed.

IPL and WPL accrue revenues from their wholesale customers to the extent that the actual net revenue requirements calculated in accordance with FERC-approved formula rates for the reporting period are higher or lower than the amounts billed to wholesale customers during such period. Regulatory assets or regulatory liabilities are recorded as the offset for these accrued revenues under formulaic rate-making programs. As of December 31, 2025, the related amounts accrued for IPL and WPL were not material.
IPL and WPL participate in bid/offer-based wholesale energy and ancillary services markets operated by MISO. The MISO transactions are grouped together, resulting in a net supply to or net purchase from MISO for each hour of each day. The net supply to MISO is recorded as bulk power sales in “Electric utility revenues” and the net purchase from MISO is recorded in “Electric production fuel and purchased power” in the income statements.

Non-utility - Revenues from Alliant Energy’s non-utility businesses are primarily from its Travero business and are recognized over time as services are rendered to customers.

Taxes Collected from Customers - Sales or various other taxes collected by certain of Alliant Energy’s subsidiaries on behalf of other agencies are recorded on a net basis and are not included in revenues.

Other - Alliant Energy, IPL and WPL do not disclose the value of unsatisfied performance obligations for: (i) contracts with an original expected length of one year or less; and (ii) contracts for which revenue is recognized at the amount to which they have the right to invoice for services performed.
Utility Cost Recovery Mechanisms
Electric Production Fuel and Purchased Power (Fuel-related Costs) - Fuel-related costs are incurred to generate and purchase electricity to meet the demand of IPL’s and WPL’s electric customers. These fuel-related costs include the cost of fossil fuels (primarily natural gas and coal) used to produce electricity at their EGUs, and electricity purchased from MISO wholesale energy markets and under PPAs. These fuel-related costs are recorded in “Electric production fuel and purchased power” in the income statements.

IPL Retail - The cost recovery mechanisms for IPL’s retail electric customers provide for monthly adjustments to their electric rates for changes in fuel-related costs. Changes in the under-/over-collection of these costs are recognized in “Electric production fuel and purchased power” in Alliant Energy’s and IPL’s income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers.

WPL Retail - The cost recovery mechanism for WPL’s retail electric customers is based on forecasts of certain fuel-related costs expected to be incurred during forward-looking test periods and fuel monitoring ranges determined by the PSCW during each retail electric rate proceeding or in a separate fuel cost plan approval proceeding. If WPL’s actual fuel-related costs fall outside these fuel monitoring ranges, WPL is authorized to defer the incremental under-/over-collection of fuel-related costs that are outside the approved ranges. Deferral of under-collections are reduced to the extent actual return on common equity earned by WPL during the fuel cost plan year exceeds the most recently authorized return on common equity. Deferred amounts for fuel-related costs outside the approved fuel monitoring ranges are recognized in “Electric production fuel and purchased power” in Alliant Energy’s and WPL’s income statements. The cumulative effects of these deferred amounts are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until they are reflected in future billings to customers.

IPL and WPL Wholesale - The cost recovery mechanisms for IPL’s and WPL’s wholesale electric customers provide for subsequent adjustments to their electric rates for changes in fuel-related costs. Changes in the under-/over-collection of these costs are recognized in “Electric production fuel and purchased power” in the income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers.

Electric Capacity - PPAs help meet the electricity demand of IPL’s and WPL’s customers. Certain PPAs include minimum payments for IPL’s and WPL’s rights to electric generating capacity, which are charged each period to “Electric production fuel and purchased power” in the income statements. Purchased electric capacity expenses are recovered from IPL’s and WPL’s retail electric customers through changes in base rates determined during periodic rate proceedings. Purchased electric capacity expenses are recovered from IPL’s and WPL’s wholesale electric customers through annual changes in base rates determined by a formula rate structure. Electric capacity revenues are refunded to IPL's retail electric customers through changes in base rates determined during periodic rate proceedings, and to IPL and WPL's wholesale electric customers through annual changes in base rates determined by a formula rate structure. Electric capacity revenues are refunded to WPL's retail electric customers through its fuel cost recovery mechanism.

Electric Transmission Service - Costs incurred for the transmission of electricity to meet the demands of IPL’s and WPL’s customers are charged to “Electric transmission service” in the income statements.

IPL Retail - Electric transmission service expense is recovered from IPL’s retail electric customers through a transmission cost rider. This cost recovery mechanism provides for periodic adjustments to electric rates charged to retail electric customers for changes in electric transmission service expense. Changes in the under-/over-collection of these costs are recognized in “Electric transmission service” in Alliant Energy’s and IPL’s income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers.
WPL Retail - Electric transmission service expense is recovered from WPL’s retail electric customers through changes in base rates determined during periodic rate proceedings. Pursuant to escrow accounting treatment approved by the PSCW, the difference between actual electric transmission service expense incurred and the amount of electric transmission service costs collected from customers as electric revenues is recognized in “Electric transmission service” in Alliant Energy’s and WPL’s income statements. An offsetting amount is recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until reflected in future billings to customers.

IPL and WPL Wholesale - IPL and WPL arrange transmission service for the majority of their respective wholesale electric customers. Electric transmission service expense is allocated to and recovered from these customers based on a load ratio share computation.

Cost of Gas Sold - Costs are incurred for the purchase, transportation and storage of natural gas to serve IPL’s and WPL’s gas customers and the costs associated with the natural gas delivered to customers are charged to “Cost of gas sold” in the income statements. The tariffs for IPL’s and WPL’s retail gas customers provide for subsequent adjustments to their rates periodically for changes in the cost of gas sold. Changes in the under-/over-collection of these costs are also recognized in “Cost of gas sold” in the income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers.

Energy Efficiency Costs - Costs incurred to fund energy efficiency programs and initiatives that help customers reduce their energy usage are charged to “Other operation and maintenance” in the income statements. Energy efficiency costs incurred by IPL are recovered from its retail electric and gas customers through energy efficiency and demand response cost recovery factor tariffs, which are revised annually and include a reconciliation to eliminate any under-/over-collection of energy efficiency costs from prior periods. Pursuant to escrow accounting treatment approved by the PSCW, the difference between actual energy efficiency costs incurred by WPL and the amount collected from its retail electric and gas customers is recovered through changes in base rates determined during periodic rate proceedings, and reconciliations eliminate any under-/over-collection of energy efficiency costs from prior periods. Changes in the under-/over-collection of energy efficiency costs for IPL and WPL are recognized in “Other operation and maintenance” in the income statements. The cumulative effects of the under-/over-collection of these costs for IPL and WPL are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers.
Renewable Energy Rider - IPL utilized a renewable energy rider prior to its discontinuation on October 1, 2024, effective with the IUC’s order for IPL’s retail electric rate review for the October 2024 through September 2025 Test Period. Prior to October 1, 2024, IPL recovered a return of, as well as earned a return on, its wind generation placed in service in 2019 and 2020 from its retail electric customers through the renewable energy rider. Other applicable costs and tax benefits associated with this wind generation, excluding operation and maintenance expenses, were also included in the rider. This cost recovery mechanism provided for annual adjustments to electric rates charged to IPL’s retail electric customers for actual renewable energy costs and tax benefits. Changes in the under-/over-collection of these costs were recognized in “Electric utility revenue” in Alliant Energy’s and IPL’s income statements. The cumulative effects of the under-/over-collection of these costs for IPL is recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers.
Financial Instruments Financial instruments are periodically used for risk management purposes to mitigate exposures to fluctuations in certain commodity prices, transmission congestion costs and interest rates. The fair value of those financial instruments that are determined to be derivatives are recorded as assets or liabilities on the balance sheets. Certain commodity purchase and sales contracts qualified for and were designated under the normal purchase and sale exception, and were accounted for on the accrual basis of accounting. Alliant Energy, IPL and WPL have elected to not net the fair value amounts of derivatives subject to a master netting arrangement by counterparty. Alliant Energy, IPL and WPL do not offset fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) against fair value amounts recognized for derivative instruments that are executed with the same counterparty under the same master netting arrangement.
Asset Impairments
Property, Plant and Equipment of Regulated Operations - Property, plant and equipment of regulated operations are reviewed for possible impairment whenever events or changes in circumstances indicate all or a portion of the carrying value of the assets may be disallowed for rate-making purposes. If IPL or WPL are disallowed recovery of any portion of, or are only allowed a partial return on, the carrying value of their regulated property, plant and equipment that is under construction, has been recently completed or is probable of abandonment, or conclude it is probable recovery or a full return will be disallowed, then an impairment charge is recognized.
Property, Plant and Equipment of Non-utility Operations - Property, plant and equipment of non-utility operations are reviewed for possible impairment whenever events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Impairment is indicated if the carrying value of an asset exceeds its undiscounted future cash flows. If an impairment is indicated, a charge is recognized equal to the amount the carrying value exceeds the asset’s fair value. Refer to Note 17 for discussion of an asset valuation charge at Alliant Energy’s non-utility holdings in 2025.

Unconsolidated Equity Investments - If events or circumstances indicate the carrying value of investments accounted for under the equity method of accounting exceeds fair value and the decline in value is other than temporary, potential impairment is assessed. If an impairment is indicated, a charge is recognized equal to the amount the carrying value exceeds the investment’s fair value.
Asset Retirement Obligations The fair value of a legal obligation associated with the retirement of an asset is recorded as a liability when an asset is placed in service, when a legal obligation is subsequently identified or when sufficient information becomes available to determine a reasonable estimate of the fair value of future retirement costs. When an ARO is recorded as a liability, an equivalent amount is added to the asset cost. The fair value of AROs at inception is determined using discounted cash flows analyses. The liability is accreted to its present value and the capitalized cost is depreciated over the useful life of the related asset. Accretion and depreciation expenses related to AROs for IPL’s and WPL’s regulated operations are recorded to regulatory assets on the balance sheets. Revisions in estimated cash flows for IPL’s and WPL’s regulated operations are recorded as an increase or decrease to the ARO liability, with an offset to the asset cost, unless the asset is already retired and then the offset is recorded to regulatory assets or regulatory liabilities on the balance sheets. Upon regulatory approval to recover IPL’s AROs expenditures, its regulatory assets are amortized to depreciation and amortization expenses in Alliant Energy’s and IPL’s income statements over the same time period the ARO expenditures are recovered from IPL’s customers. WPL’s regulatory assets related to AROs are recovered as a component of depreciation rates pursuant to PSCW and FERC orders. Upon settlement of the ARO liability, an entity settles the obligation for its recorded amount or incurs a gain or loss. Any gains or losses related to AROs for IPL’s and WPL’s regulated operations are recorded to regulatory liabilities or regulatory assets on the balance sheets.
Debt Issuance and Retirement Costs Debt issuance costs and debt premiums or discounts are presented on the balance sheets as a direct adjustment to the carrying amount of the related debt liability, and are deferred and amortized over the expected life of each debt issue, considering maturity dates and, if applicable, redemption rights held by us or by others. Alliant Energy’s non-utility businesses and Corporate Services record to interest expense in the period of retirement any unamortized debt issuance costs and debt premiums or discounts on debt retired early.
Current Expected Credit Losses Estimates Current expected credit losses are estimated for trade and other receivables and credit exposures on guarantees of the performance by third parties. The current expected credit losses for short-term trade receivables are based on estimates of losses resulting from the inability of customers to make required payments. The methodology used to estimate losses is based on historical write-offs, regional economic conditions, significant events that could impact collectability, such as significant weather related matters and related regulatory actions, and actual and forecasted changes to the accounts receivable aging portfolio and write-offs. The current expected credit losses related to guarantees of the performance by third parties are estimated using both quantitative and qualitative information, which utilizes potential outcomes in a range of possible estimated amounts.
Variable Interest Entities An entity is considered a VIE if its equity investors do not have sufficient equity at risk for the entity to finance its activities without additional subordinated financial support from other parties, the entity is structured with disproportionate voting rights and substantially all of the entity’s activities are conducted on behalf of the investor with disproportionately fewer voting rights, or its equity investors lack any of the following characteristics: (1) power, through voting rights or similar rights, to direct the activities of the entity that most significantly impact the entity’s economic performance; (2) the obligation to absorb expected losses of the entity; or (3) the right to receive expected benefits of the entity. The primary beneficiary of a VIE is required to consolidate the VIE. The financial statements do not reflect any consolidation of VIEs.
Leases The determination of whether an arrangement qualifies as a lease occurs at the inception of the arrangement. Arrangements that qualify as leases are classified as either operating or finance. Operating and finance lease liabilities represent obligations to make payments arising from the lease. Operating and finance lease assets represent the right to use an underlying asset for the lease term and are recognized at the lease commencement date based on the present value of the lease payments over the lease term. Leases with initial terms less than 12 months are not recognized as leases. For operating leases, an incremental borrowing rate, as determined at the lease commencement date, is used to determine the present value of the lease payments. For finance leases, the rate implicit in the lease, if known, is used to determine the present value of the lease payments. If the rate implicit in the lease is not known, the incremental borrowing rate, as determined at the lease commencement date, is used to determine the present value of the lease payments. Lease terms include options to extend or terminate the lease when it is reasonably certain that the option will be exercised. Operating lease expense is recognized on a straight-line basis over the expected lease term. Finance lease expense is comprised of depreciation and amortization, and interest expenses. Finance lease assets are accounted for as operating leases for rate-making purposes.
WPL [Member]  
Property, Plant and Equipment [Line Items]  
General, Basis of Presentation The financial statements reflect investments in controlled subsidiaries on a consolidated basis and Alliant Energy’s, IPL’s and WPL’s proportionate shares of jointly-owned utility EGUs. Unconsolidated investments that Alliant Energy and WPL do not control are accounted for under the equity method of accounting. Under the equity method of accounting, Alliant Energy and WPL initially record the investment at cost, and adjust the carrying amount of the investment to recognize their respective share of the earnings or losses of the investee. Dividends received from an investee reduce the carrying amount of the equity investment. Investments that do not meet the criteria for consolidation or the equity method of accounting are accounted for under the cost method.All intercompany balances and transactions, other than certain transactions affecting the rate-making process at IPL and WPL, have been eliminated from the financial statements. Such transactions not eliminated include costs that are recoverable from customers through rate-making processes.
General, Basis of Accounting The financial statements are prepared in conformity with GAAP, which give recognition to the rate-making practices of FERC and state commissions having regulatory jurisdiction.
General, Reclassification
Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes.
General, Use of Estimates The preparation of the financial statements requires management to make estimates and assumptions that affect: (a) the reported amounts of assets and liabilities and the disclosure of contingent assets and liabilities at the date of the financial statements; and (b) the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.
Regulatory Assets and Regulatory Liabilities Alliant Energy, IPL and WPL are subject to regulation by FERC and state regulatory commissions in their service territories. As a result, Alliant Energy, IPL and WPL are subject to GAAP provisions for regulated operations, which provide that rate-regulated public utilities record certain costs and credits allowed in the rate-making process in different periods than for non-utility entities. Regulatory assets generally represent incurred costs that have been deferred as such costs are probable of recovery in future customer rates. Regulatory liabilities generally represent obligations to make refunds to customers or amounts collected in rates for which the related costs have not yet been incurred. Amounts recorded as regulatory assets or regulatory liabilities are generally recognized in the income statements at the time they are reflected in rates.
Income Taxes The liability method of accounting is followed for deferred taxes, which requires the establishment of deferred tax assets and liabilities, as appropriate, for temporary differences between the tax basis of assets and liabilities and the amounts reported in the financial statements. Deferred taxes are recorded using currently enacted tax rates and estimates of state apportionment. Changes in deferred tax assets and liabilities associated with certain property-related differences at IPL are accounted for differently than other subsidiaries of Alliant Energy due to rate-making practices in Iowa. Rate-making practices in Iowa do not allow the impact of certain deferred tax expenses (benefits) to be included in the determination of retail rates. Based on these rate-making practices, deferred tax expense (benefit) related to these property-related differences at IPL is not recorded in the income statement but instead recorded to regulatory assets or regulatory liabilities until these temporary differences reverse. In Wisconsin, the PSCW allows rate recovery of deferred tax expense on all temporary differences.
The flow-through method of accounting is used for investment tax credits. Certain federal investment tax credits related to utility property, plant and equipment are subject to statutory tax normalization rules limiting how they may be treated in rate-making. As appropriate to reflect the rate-making practices, investment tax credits are deferred and amortized over the book depreciable lives of the related property or other period prescribed by rate regulation.

Alliant Energy files a consolidated federal income tax return and a combined return in Wisconsin, which include Alliant Energy and its subsidiaries. Alliant Energy subsidiaries with a presence in Iowa file as part of a consolidated return in Iowa.

Alliant Energy allocates consolidated income tax expense to its subsidiaries that are members of the group that file a consolidated or combined income tax return. IPL and WPL use the separate return approach for calculating their income tax provisions and related deferred tax assets and liabilities. IPL and WPL are assumed to file separate tax returns with the federal and state taxing authorities, except that net operating losses (and other current or deferred tax attributes) are characterized as realized (or realizable) by IPL and WPL when those tax attributes are realized (or realizable) by the consolidated tax return group of Alliant Energy (even if IPL and WPL would not otherwise have realized the attributes on a stand-alone basis).
IPL and WPL have entered into agreements to transfer renewable tax credits from certain wind, solar and energy storage facilities to other corporate taxpayers in exchange for cash. Alliant Energy, IPL and WPL have elected to record transfers of renewable tax credits as part of income taxes, and cash received from the transfer of renewable tax credits is recorded in cash flows from operating activities. Renewable tax credits subject to future transfer are recorded at expected realizable value. Renewable tax credits are derecognized when control of the tax credits is transferred to other corporate taxpayers. Beginning October 1, 2024, IPL’s renewable energy rider was discontinued, and production tax credits, excluding production tax credits from the refurbishment of existing wind farms, are credited to IPL’s retail electric customers through its fuel-related cost recovery mechanism. Investment tax credits resulting from IPL’s renewable generation and energy storage projects that are not yet included in base rates may be utilized to offset any revenue deficiency on an annual basis up to IPL’s return on common equity threshold; any remaining investment tax credits, net of the cost of transferability, that are not used to offset any revenue deficiency, will be deferred by IPL and carried forward to offset any potential revenue deficiency in future years. At WPL, pursuant to escrow treatment approved by the PSCW, the difference between actual renewable tax credits and the amount of renewable tax credits collected from customers as electric revenues is recognized in “Income taxes” in Alliant Energy’s and WPL’s income statements. An offsetting amount is recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until reflected in future billings to customers.
Cash, Cash Equivalents and Restricted Cash Cash and cash equivalents include short-term liquid investments that have original maturities of less than 90 days. At December 31, 2025, Alliant Energy’s and WPL’s cash and cash equivalents included $411 million and $25 million, respectively, of money market fund investments, with weighted average interest rates of 4%. At December 31, 2025 and 2024, Alliant Energy’s restricted cash was not material.
Property, Plant and Equipment
Utility Plant -
General - Utility plant is recorded at the original cost of acquisition or construction, which includes material, labor, contractor services, AFUDC and allocable overheads, such as supervision, engineering, certain administrative costs directly related to construction, benefits, certain taxes and transportation. Repairs, replacements and renewals of items of property determined to be less than a unit of property or that do not increase the property’s life or functionality are charged to maintenance expense. Property, plant and equipment that is probable of being retired early is classified as plant anticipated to be retired early. Generally, ordinary retirements of utility plant and salvage value are netted and charged to accumulated depreciation upon removal from utility plant accounts and no gain or loss is recognized consistent with rate-making principles. However, if regulators have approved recovery of the remaining net book value of property, plant and equipment that is retired early, or such approval by regulators is probable, the remaining net book value is reclassified from property, plant and equipment to regulatory assets upon retirement.
Non-utility and Other Property -
General - Non-utility property is recorded at the original cost of acquisition or construction, which includes material, labor and contractor services. Repairs, replacements and renewals of items of property determined to be less than a unit of property or that do not increase the property’s life or functionality are charged to maintenance expense. Upon retirement or sale of non-utility property, the original cost and related accumulated depreciation are removed from the accounts and any gain or loss is included in the income statements.

Costs related to software developed or obtained for internal use are capitalized and amortized on a straight-line basis over the estimated useful life of the related software. If software is retired prior to being fully amortized, the remaining book value is recorded as a loss in the income statements.
Depreciation IPL and WPL use a combination of remaining life and straight-line depreciation methods as approved by their respective regulatory commissions. The composite or group method of depreciation is used, in which a single depreciation rate is applied to the gross investment in a particular class of property. This method pools similar assets and then depreciates each group as a whole. Periodic depreciation studies are performed to determine the appropriate group lives, net salvage, estimated cost of removal and group depreciation rates. These depreciation studies are subject to review and approval by IPL’s and WPL’s respective regulatory commissions. Depreciation expense is included within the recoverable cost of service component of rates collected from customers. The average rates of depreciation for electric, gas and other properties, consistent with current rate-making practices, were as follows:
IPLWPL
202520242023202520242023
Electric - generation3.5%3.3%3.3%3.4%3.4%3.0%
Electric - distribution2.9%2.8%2.8%2.7%2.7%2.7%
Electric - other3.6%5.2%5.6%4.2%6.1%6.3%
Gas3.3%3.3%3.3%2.4%2.5%2.5%
Other5.6%4.6%6.2%4.5%4.4%4.6%
AFUDC AFUDC represents costs to finance construction additions, including a return on equity component and cost of debt component as required by regulatory accounting. AFUDC for IPL’s construction projects is calculated in accordance with FERC guidelines. AFUDC for WPL’s retail and wholesale jurisdiction construction projects is calculated in accordance with PSCW and FERC guidelines, respectively. The AFUDC rates, computed in accordance with the prescribed regulatory formula, were as follows:
202520242023
IPL7.1%7.0%7.0%
WPL (retail jurisdiction)7.4%7.4%7.4%
WPL (wholesale jurisdiction)6.6%7.1%7.1%

In accordance with their respective regulatory commission decisions, IPL applies its AFUDC rates to 100% of applicable CWIP balances, and WPL generally applies its AFUDC rates to 50% of applicable CWIP balances and the remaining 50% of applicable CWIP balances earns a return on such balances as part of its rate base. WPL may be authorized to apply its AFUDC rates to 100% of the retail portion of the CWIP balances for construction projects requiring a CA or CPCN that were approved by the PSCW after its then most recent rate order. Beginning January 1, 2026, the PSCW also authorized an AFUDC applied to 100% of the retail portion of CWIP balances related to construction activity on capital projects requiring PSCW approval and are impacted by federal law changes.
Revenue Recognition
Utility - Revenues from Alliant Energy’s utility business are primarily from electric and gas sales to customers. Utility revenues are recognized over time as services are rendered or commodities are delivered to customers, and include billed and unbilled components. The billed component is based on the reading of customers’ meters, which occurs on a systematic basis throughout each reporting period and represents the fair value of the services provided or commodities delivered. The unbilled component is recorded at the end of each reporting period based on estimated amounts of energy delivered to customers but not yet billed.

IPL and WPL accrue revenues from their wholesale customers to the extent that the actual net revenue requirements calculated in accordance with FERC-approved formula rates for the reporting period are higher or lower than the amounts billed to wholesale customers during such period. Regulatory assets or regulatory liabilities are recorded as the offset for these accrued revenues under formulaic rate-making programs. As of December 31, 2025, the related amounts accrued for IPL and WPL were not material.
IPL and WPL participate in bid/offer-based wholesale energy and ancillary services markets operated by MISO. The MISO transactions are grouped together, resulting in a net supply to or net purchase from MISO for each hour of each day. The net supply to MISO is recorded as bulk power sales in “Electric utility revenues” and the net purchase from MISO is recorded in “Electric production fuel and purchased power” in the income statements.

Non-utility - Revenues from Alliant Energy’s non-utility businesses are primarily from its Travero business and are recognized over time as services are rendered to customers.

Taxes Collected from Customers - Sales or various other taxes collected by certain of Alliant Energy’s subsidiaries on behalf of other agencies are recorded on a net basis and are not included in revenues.

Other - Alliant Energy, IPL and WPL do not disclose the value of unsatisfied performance obligations for: (i) contracts with an original expected length of one year or less; and (ii) contracts for which revenue is recognized at the amount to which they have the right to invoice for services performed.
Utility Cost Recovery Mechanisms
Electric Production Fuel and Purchased Power (Fuel-related Costs) - Fuel-related costs are incurred to generate and purchase electricity to meet the demand of IPL’s and WPL’s electric customers. These fuel-related costs include the cost of fossil fuels (primarily natural gas and coal) used to produce electricity at their EGUs, and electricity purchased from MISO wholesale energy markets and under PPAs. These fuel-related costs are recorded in “Electric production fuel and purchased power” in the income statements.

IPL Retail - The cost recovery mechanisms for IPL’s retail electric customers provide for monthly adjustments to their electric rates for changes in fuel-related costs. Changes in the under-/over-collection of these costs are recognized in “Electric production fuel and purchased power” in Alliant Energy’s and IPL’s income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers.

WPL Retail - The cost recovery mechanism for WPL’s retail electric customers is based on forecasts of certain fuel-related costs expected to be incurred during forward-looking test periods and fuel monitoring ranges determined by the PSCW during each retail electric rate proceeding or in a separate fuel cost plan approval proceeding. If WPL’s actual fuel-related costs fall outside these fuel monitoring ranges, WPL is authorized to defer the incremental under-/over-collection of fuel-related costs that are outside the approved ranges. Deferral of under-collections are reduced to the extent actual return on common equity earned by WPL during the fuel cost plan year exceeds the most recently authorized return on common equity. Deferred amounts for fuel-related costs outside the approved fuel monitoring ranges are recognized in “Electric production fuel and purchased power” in Alliant Energy’s and WPL’s income statements. The cumulative effects of these deferred amounts are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until they are reflected in future billings to customers.

IPL and WPL Wholesale - The cost recovery mechanisms for IPL’s and WPL’s wholesale electric customers provide for subsequent adjustments to their electric rates for changes in fuel-related costs. Changes in the under-/over-collection of these costs are recognized in “Electric production fuel and purchased power” in the income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers.

Electric Capacity - PPAs help meet the electricity demand of IPL’s and WPL’s customers. Certain PPAs include minimum payments for IPL’s and WPL’s rights to electric generating capacity, which are charged each period to “Electric production fuel and purchased power” in the income statements. Purchased electric capacity expenses are recovered from IPL’s and WPL’s retail electric customers through changes in base rates determined during periodic rate proceedings. Purchased electric capacity expenses are recovered from IPL’s and WPL’s wholesale electric customers through annual changes in base rates determined by a formula rate structure. Electric capacity revenues are refunded to IPL's retail electric customers through changes in base rates determined during periodic rate proceedings, and to IPL and WPL's wholesale electric customers through annual changes in base rates determined by a formula rate structure. Electric capacity revenues are refunded to WPL's retail electric customers through its fuel cost recovery mechanism.

Electric Transmission Service - Costs incurred for the transmission of electricity to meet the demands of IPL’s and WPL’s customers are charged to “Electric transmission service” in the income statements.

IPL Retail - Electric transmission service expense is recovered from IPL’s retail electric customers through a transmission cost rider. This cost recovery mechanism provides for periodic adjustments to electric rates charged to retail electric customers for changes in electric transmission service expense. Changes in the under-/over-collection of these costs are recognized in “Electric transmission service” in Alliant Energy’s and IPL’s income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers.
WPL Retail - Electric transmission service expense is recovered from WPL’s retail electric customers through changes in base rates determined during periodic rate proceedings. Pursuant to escrow accounting treatment approved by the PSCW, the difference between actual electric transmission service expense incurred and the amount of electric transmission service costs collected from customers as electric revenues is recognized in “Electric transmission service” in Alliant Energy’s and WPL’s income statements. An offsetting amount is recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and WPL’s balance sheets until reflected in future billings to customers.

IPL and WPL Wholesale - IPL and WPL arrange transmission service for the majority of their respective wholesale electric customers. Electric transmission service expense is allocated to and recovered from these customers based on a load ratio share computation.

Cost of Gas Sold - Costs are incurred for the purchase, transportation and storage of natural gas to serve IPL’s and WPL’s gas customers and the costs associated with the natural gas delivered to customers are charged to “Cost of gas sold” in the income statements. The tariffs for IPL’s and WPL’s retail gas customers provide for subsequent adjustments to their rates periodically for changes in the cost of gas sold. Changes in the under-/over-collection of these costs are also recognized in “Cost of gas sold” in the income statements. The cumulative effects of the under-/over-collection of these costs are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers.

Energy Efficiency Costs - Costs incurred to fund energy efficiency programs and initiatives that help customers reduce their energy usage are charged to “Other operation and maintenance” in the income statements. Energy efficiency costs incurred by IPL are recovered from its retail electric and gas customers through energy efficiency and demand response cost recovery factor tariffs, which are revised annually and include a reconciliation to eliminate any under-/over-collection of energy efficiency costs from prior periods. Pursuant to escrow accounting treatment approved by the PSCW, the difference between actual energy efficiency costs incurred by WPL and the amount collected from its retail electric and gas customers is recovered through changes in base rates determined during periodic rate proceedings, and reconciliations eliminate any under-/over-collection of energy efficiency costs from prior periods. Changes in the under-/over-collection of energy efficiency costs for IPL and WPL are recognized in “Other operation and maintenance” in the income statements. The cumulative effects of the under-/over-collection of these costs for IPL and WPL are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers.
Renewable Energy Rider - IPL utilized a renewable energy rider prior to its discontinuation on October 1, 2024, effective with the IUC’s order for IPL’s retail electric rate review for the October 2024 through September 2025 Test Period. Prior to October 1, 2024, IPL recovered a return of, as well as earned a return on, its wind generation placed in service in 2019 and 2020 from its retail electric customers through the renewable energy rider. Other applicable costs and tax benefits associated with this wind generation, excluding operation and maintenance expenses, were also included in the rider. This cost recovery mechanism provided for annual adjustments to electric rates charged to IPL’s retail electric customers for actual renewable energy costs and tax benefits. Changes in the under-/over-collection of these costs were recognized in “Electric utility revenue” in Alliant Energy’s and IPL’s income statements. The cumulative effects of the under-/over-collection of these costs for IPL is recorded in regulatory assets or regulatory liabilities on Alliant Energy’s and IPL’s balance sheets until they are reflected in future billings to customers.
Financial Instruments Financial instruments are periodically used for risk management purposes to mitigate exposures to fluctuations in certain commodity prices, transmission congestion costs and interest rates. The fair value of those financial instruments that are determined to be derivatives are recorded as assets or liabilities on the balance sheets. Certain commodity purchase and sales contracts qualified for and were designated under the normal purchase and sale exception, and were accounted for on the accrual basis of accounting. Alliant Energy, IPL and WPL have elected to not net the fair value amounts of derivatives subject to a master netting arrangement by counterparty. Alliant Energy, IPL and WPL do not offset fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) against fair value amounts recognized for derivative instruments that are executed with the same counterparty under the same master netting arrangement.
Asset Impairments
Property, Plant and Equipment of Regulated Operations - Property, plant and equipment of regulated operations are reviewed for possible impairment whenever events or changes in circumstances indicate all or a portion of the carrying value of the assets may be disallowed for rate-making purposes. If IPL or WPL are disallowed recovery of any portion of, or are only allowed a partial return on, the carrying value of their regulated property, plant and equipment that is under construction, has been recently completed or is probable of abandonment, or conclude it is probable recovery or a full return will be disallowed, then an impairment charge is recognized.
Property, Plant and Equipment of Non-utility Operations - Property, plant and equipment of non-utility operations are reviewed for possible impairment whenever events or changes in circumstances indicate the carrying value of the assets may not be recoverable. Impairment is indicated if the carrying value of an asset exceeds its undiscounted future cash flows. If an impairment is indicated, a charge is recognized equal to the amount the carrying value exceeds the asset’s fair value. Refer to Note 17 for discussion of an asset valuation charge at Alliant Energy’s non-utility holdings in 2025.

Unconsolidated Equity Investments - If events or circumstances indicate the carrying value of investments accounted for under the equity method of accounting exceeds fair value and the decline in value is other than temporary, potential impairment is assessed. If an impairment is indicated, a charge is recognized equal to the amount the carrying value exceeds the investment’s fair value.
Asset Retirement Obligations The fair value of a legal obligation associated with the retirement of an asset is recorded as a liability when an asset is placed in service, when a legal obligation is subsequently identified or when sufficient information becomes available to determine a reasonable estimate of the fair value of future retirement costs. When an ARO is recorded as a liability, an equivalent amount is added to the asset cost. The fair value of AROs at inception is determined using discounted cash flows analyses. The liability is accreted to its present value and the capitalized cost is depreciated over the useful life of the related asset. Accretion and depreciation expenses related to AROs for IPL’s and WPL’s regulated operations are recorded to regulatory assets on the balance sheets. Revisions in estimated cash flows for IPL’s and WPL’s regulated operations are recorded as an increase or decrease to the ARO liability, with an offset to the asset cost, unless the asset is already retired and then the offset is recorded to regulatory assets or regulatory liabilities on the balance sheets. Upon regulatory approval to recover IPL’s AROs expenditures, its regulatory assets are amortized to depreciation and amortization expenses in Alliant Energy’s and IPL’s income statements over the same time period the ARO expenditures are recovered from IPL’s customers. WPL’s regulatory assets related to AROs are recovered as a component of depreciation rates pursuant to PSCW and FERC orders. Upon settlement of the ARO liability, an entity settles the obligation for its recorded amount or incurs a gain or loss. Any gains or losses related to AROs for IPL’s and WPL’s regulated operations are recorded to regulatory liabilities or regulatory assets on the balance sheets.
Debt Issuance and Retirement Costs Debt issuance costs and debt premiums or discounts are presented on the balance sheets as a direct adjustment to the carrying amount of the related debt liability, and are deferred and amortized over the expected life of each debt issue, considering maturity dates and, if applicable, redemption rights held by us or by others. Alliant Energy’s non-utility businesses and Corporate Services record to interest expense in the period of retirement any unamortized debt issuance costs and debt premiums or discounts on debt retired early.
Current Expected Credit Losses Estimates Current expected credit losses are estimated for trade and other receivables and credit exposures on guarantees of the performance by third parties. The current expected credit losses for short-term trade receivables are based on estimates of losses resulting from the inability of customers to make required payments. The methodology used to estimate losses is based on historical write-offs, regional economic conditions, significant events that could impact collectability, such as significant weather related matters and related regulatory actions, and actual and forecasted changes to the accounts receivable aging portfolio and write-offs. The current expected credit losses related to guarantees of the performance by third parties are estimated using both quantitative and qualitative information, which utilizes potential outcomes in a range of possible estimated amounts.
Variable Interest Entities An entity is considered a VIE if its equity investors do not have sufficient equity at risk for the entity to finance its activities without additional subordinated financial support from other parties, the entity is structured with disproportionate voting rights and substantially all of the entity’s activities are conducted on behalf of the investor with disproportionately fewer voting rights, or its equity investors lack any of the following characteristics: (1) power, through voting rights or similar rights, to direct the activities of the entity that most significantly impact the entity’s economic performance; (2) the obligation to absorb expected losses of the entity; or (3) the right to receive expected benefits of the entity. The primary beneficiary of a VIE is required to consolidate the VIE. The financial statements do not reflect any consolidation of VIEs.
Leases The determination of whether an arrangement qualifies as a lease occurs at the inception of the arrangement. Arrangements that qualify as leases are classified as either operating or finance. Operating and finance lease liabilities represent obligations to make payments arising from the lease. Operating and finance lease assets represent the right to use an underlying asset for the lease term and are recognized at the lease commencement date based on the present value of the lease payments over the lease term. Leases with initial terms less than 12 months are not recognized as leases. For operating leases, an incremental borrowing rate, as determined at the lease commencement date, is used to determine the present value of the lease payments. For finance leases, the rate implicit in the lease, if known, is used to determine the present value of the lease payments. If the rate implicit in the lease is not known, the incremental borrowing rate, as determined at the lease commencement date, is used to determine the present value of the lease payments. Lease terms include options to extend or terminate the lease when it is reasonably certain that the option will be exercised. Operating lease expense is recognized on a straight-line basis over the expected lease term. Finance lease expense is comprised of depreciation and amortization, and interest expenses. Finance lease assets are accounted for as operating leases for rate-making purposes.
v3.25.4
Summary Of Significant Accounting Policies (Tables)
 12 Months Ended
Dec. 31, 2025
Statement [Line Items]  
Schedule of Average Rates of Depreciation The average rates of depreciation for electric, gas and other properties, consistent with current rate-making practices, were as follows:
IPLWPL
202520242023202520242023
Electric - generation3.5%3.3%3.3%3.4%3.4%3.0%
Electric - distribution2.9%2.8%2.8%2.7%2.7%2.7%
Electric - other3.6%5.2%5.6%4.2%6.1%6.3%
Gas3.3%3.3%3.3%2.4%2.5%2.5%
Other5.6%4.6%6.2%4.5%4.4%4.6%
Schedule of Allowance for Funds Used During Construction Rate The AFUDC rates, computed in accordance with the prescribed regulatory formula, were as follows:
202520242023
IPL7.1%7.0%7.0%
WPL (retail jurisdiction)7.4%7.4%7.4%
WPL (wholesale jurisdiction)6.6%7.1%7.1%
IPL [Member]  
Statement [Line Items]  
Schedule of Average Rates of Depreciation The average rates of depreciation for electric, gas and other properties, consistent with current rate-making practices, were as follows:
IPLWPL
202520242023202520242023
Electric - generation3.5%3.3%3.3%3.4%3.4%3.0%
Electric - distribution2.9%2.8%2.8%2.7%2.7%2.7%
Electric - other3.6%5.2%5.6%4.2%6.1%6.3%
Gas3.3%3.3%3.3%2.4%2.5%2.5%
Other5.6%4.6%6.2%4.5%4.4%4.6%
Schedule of Allowance for Funds Used During Construction Rate The AFUDC rates, computed in accordance with the prescribed regulatory formula, were as follows:
202520242023
IPL7.1%7.0%7.0%
WPL (retail jurisdiction)7.4%7.4%7.4%
WPL (wholesale jurisdiction)6.6%7.1%7.1%
WPL [Member]  
Statement [Line Items]  
Schedule of Average Rates of Depreciation The average rates of depreciation for electric, gas and other properties, consistent with current rate-making practices, were as follows:
IPLWPL
202520242023202520242023
Electric - generation3.5%3.3%3.3%3.4%3.4%3.0%
Electric - distribution2.9%2.8%2.8%2.7%2.7%2.7%
Electric - other3.6%5.2%5.6%4.2%6.1%6.3%
Gas3.3%3.3%3.3%2.4%2.5%2.5%
Other5.6%4.6%6.2%4.5%4.4%4.6%
Schedule of Allowance for Funds Used During Construction Rate The AFUDC rates, computed in accordance with the prescribed regulatory formula, were as follows:
202520242023
IPL7.1%7.0%7.0%
WPL (retail jurisdiction)7.4%7.4%7.4%
WPL (wholesale jurisdiction)6.6%7.1%7.1%
v3.25.4
Regulatory Matters (Tables)
 12 Months Ended
Dec. 31, 2025
Regulatory Assets [Line Items]  
Schedule of Regulatory Assets At December 31, regulatory assets were comprised of the following items (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Tax-related$1,089 $989 $949 $870 $140 $119 
AROs455 401 312 281 143 120 
Pension and OPEB costs274 315 136 157 138 158 
Assets retired early158 180 149 168 9 12 
Non-service pension and OPEB costs57 51 21 19 36 32 
Derivatives52 60 12 15 40 45 
WPL’s Western Wisconsin gas distribution expansion investments39 42 — — 39 42 
Commodity cost recovery10 68 3 2 7 66 
Other140 168 34 74 106 94 
$2,274 $2,274 $1,616 $1,586 $658 $688 
Assets Retired Early Details regarding the recovery of the remaining net book value of these assets from IPL’s and WPL’s customers are as follows (dollars in millions):
EntityAssetRetirement Date
Regulatory Asset Balance as of Dec. 31, 2025
RecoveryRegulatory Approval
IPLLansing2023$123Return of (IUC and FERC) and return on (FERC) remaining net book value through 2037 (a)IUC and FERC (b)
IPLAnalog electric meters201910Return of remaining net book value through 2028IUC and FERC
IPLSutherland Units 1 and 3201711Return of and return on remaining net book value through 2027 (a)IUC and FERC
IPLM.L. Kapp Unit 220185Return of and return on remaining net book value through 2029 (a)IUC and FERC
WPLEdgewater Unit 420189Return of and return on remaining net book value through 2028PSCW and FERC

(a)The remaining regulatory asset balances include differences between expected and actual cost of removal obligations.
(b)IPL was previously allowed a full recovery of and a full return on the Lansing Generating Station from both its retail and wholesale customers. The IUC’s September 2024 order for IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period includes a return of the remaining net book value of Lansing, but does not include a return on the remaining net book value of Lansing, effective October 1, 2024. As a result, the return on the remaining net book value is no longer recoverable from IPL’s retail electric customers, and a pre-tax non-cash charge of $60 million was recorded to “Asset valuation charge for IPL’s Lansing Generating Station” in Alliant Energy’s and IPL’s income statements in 2024, with a corresponding decrease in Alliant Energy’s and IPL’s assets retired early regulatory assets.
Schedule of Regulatory Liabilities At December 31, regulatory liabilities were comprised of the following items (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Tax-related$690$582$304$286$386$296
Cost of removal obligations366347217205149142
Derivatives475326292124
Other984639265920
$1,201$1,028$586$546$615$482
IPL [Member]  
Regulatory Assets [Line Items]  
Schedule of Regulatory Assets At December 31, regulatory assets were comprised of the following items (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Tax-related$1,089 $989 $949 $870 $140 $119 
AROs455 401 312 281 143 120 
Pension and OPEB costs274 315 136 157 138 158 
Assets retired early158 180 149 168 9 12 
Non-service pension and OPEB costs57 51 21 19 36 32 
Derivatives52 60 12 15 40 45 
WPL’s Western Wisconsin gas distribution expansion investments39 42 — — 39 42 
Commodity cost recovery10 68 3 2 7 66 
Other140 168 34 74 106 94 
$2,274 $2,274 $1,616 $1,586 $658 $688 
Assets Retired Early Details regarding the recovery of the remaining net book value of these assets from IPL’s and WPL’s customers are as follows (dollars in millions):
EntityAssetRetirement Date
Regulatory Asset Balance as of Dec. 31, 2025
RecoveryRegulatory Approval
IPLLansing2023$123Return of (IUC and FERC) and return on (FERC) remaining net book value through 2037 (a)IUC and FERC (b)
IPLAnalog electric meters201910Return of remaining net book value through 2028IUC and FERC
IPLSutherland Units 1 and 3201711Return of and return on remaining net book value through 2027 (a)IUC and FERC
IPLM.L. Kapp Unit 220185Return of and return on remaining net book value through 2029 (a)IUC and FERC
WPLEdgewater Unit 420189Return of and return on remaining net book value through 2028PSCW and FERC

(a)The remaining regulatory asset balances include differences between expected and actual cost of removal obligations.
(b)IPL was previously allowed a full recovery of and a full return on the Lansing Generating Station from both its retail and wholesale customers. The IUC’s September 2024 order for IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period includes a return of the remaining net book value of Lansing, but does not include a return on the remaining net book value of Lansing, effective October 1, 2024. As a result, the return on the remaining net book value is no longer recoverable from IPL’s retail electric customers, and a pre-tax non-cash charge of $60 million was recorded to “Asset valuation charge for IPL’s Lansing Generating Station” in Alliant Energy’s and IPL’s income statements in 2024, with a corresponding decrease in Alliant Energy’s and IPL’s assets retired early regulatory assets.
Schedule of Regulatory Liabilities At December 31, regulatory liabilities were comprised of the following items (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Tax-related$690$582$304$286$386$296
Cost of removal obligations366347217205149142
Derivatives475326292124
Other984639265920
$1,201$1,028$586$546$615$482
WPL [Member]  
Regulatory Assets [Line Items]  
Schedule of Regulatory Assets At December 31, regulatory assets were comprised of the following items (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Tax-related$1,089 $989 $949 $870 $140 $119 
AROs455 401 312 281 143 120 
Pension and OPEB costs274 315 136 157 138 158 
Assets retired early158 180 149 168 9 12 
Non-service pension and OPEB costs57 51 21 19 36 32 
Derivatives52 60 12 15 40 45 
WPL’s Western Wisconsin gas distribution expansion investments39 42 — — 39 42 
Commodity cost recovery10 68 3 2 7 66 
Other140 168 34 74 106 94 
$2,274 $2,274 $1,616 $1,586 $658 $688 
Assets Retired Early Details regarding the recovery of the remaining net book value of these assets from IPL’s and WPL’s customers are as follows (dollars in millions):
EntityAssetRetirement Date
Regulatory Asset Balance as of Dec. 31, 2025
RecoveryRegulatory Approval
IPLLansing2023$123Return of (IUC and FERC) and return on (FERC) remaining net book value through 2037 (a)IUC and FERC (b)
IPLAnalog electric meters201910Return of remaining net book value through 2028IUC and FERC
IPLSutherland Units 1 and 3201711Return of and return on remaining net book value through 2027 (a)IUC and FERC
IPLM.L. Kapp Unit 220185Return of and return on remaining net book value through 2029 (a)IUC and FERC
WPLEdgewater Unit 420189Return of and return on remaining net book value through 2028PSCW and FERC

(a)The remaining regulatory asset balances include differences between expected and actual cost of removal obligations.
(b)IPL was previously allowed a full recovery of and a full return on the Lansing Generating Station from both its retail and wholesale customers. The IUC’s September 2024 order for IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period includes a return of the remaining net book value of Lansing, but does not include a return on the remaining net book value of Lansing, effective October 1, 2024. As a result, the return on the remaining net book value is no longer recoverable from IPL’s retail electric customers, and a pre-tax non-cash charge of $60 million was recorded to “Asset valuation charge for IPL’s Lansing Generating Station” in Alliant Energy’s and IPL’s income statements in 2024, with a corresponding decrease in Alliant Energy’s and IPL’s assets retired early regulatory assets.
Schedule of Regulatory Liabilities At December 31, regulatory liabilities were comprised of the following items (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Tax-related$690$582$304$286$386$296
Cost of removal obligations366347217205149142
Derivatives475326292124
Other984639265920
$1,201$1,028$586$546$615$482
v3.25.4
Property, Plant and Equipment (Tables)
 12 Months Ended
Dec. 31, 2025
Property, Plant and Equipment [Line Items]  
Property, Plant and Equipment
At December 31, details of property, plant and equipment on the balance sheets were as follows (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Utility:
Electric plant:
Generation and energy storage in service (a)(b)$12,757 $11,156 $6,251 $5,924 $6,506 $5,232 
Distribution in service8,418 7,811 4,691 4,344 3,727 3,467 
Other in service572 595 369 385 203 210 
Anticipated to be retired early (c)— 784 — — — 784 
Total electric plant21,747 20,346 11,311 10,653 10,436 9,693 
Gas plant in service1,938 1,863 1,020 981 918 882 
Other plant in service752 734 456456 296 278 
Accumulated depreciation (c)(6,690)(6,229)(3,574)(3,360)(3,116)(2,869)
Net plant17,747 16,714 9,213 8,730 8,534 7,984 
Leased Sheboygan Falls Energy Facility, net (d)— — — — 110 74 
Leased land for solar generation, net190 189 52 53 138 136 
Construction work in progress (e)1,742 1,215 1,166 548 576 667 
Other, net10 5 5 5 5 — 
Total utility19,689 18,123 10,436 9,336 9,363 8,861 
Non-utility and other:
Non-utility Generation, net (f)146 103 — — — — 
Corporate Services and other, net (g)509475 — — — — 
Total non-utility and other655 578 — — — — 
Total property, plant and equipment$20,344 $18,701 $10,436 $9,336 $9,363 $8,861 

(a)Construction costs associated with WPL’s approximately 1,100 MW of new solar generation exceeded the construction cost estimates previously approved by the PSCW by approximately $205 million. In 2024, the PSCW issued orders approving deferral of, and the deferral of a return on, the incremental solar generation construction costs in 2024 and 2025. In December 2025, the PSCW issued an order for the 2026/2027 forward-looking Test Period, which includes a full return of and on these solar generation construction costs from WPL’s retail electric customers. As a result, Alliant Energy and WPL concluded that there was not a probable disallowance of the higher rate base amounts as of December 31, 2025.
(b)WPL’s Grant County (100 MW) and Wood County (75 MW) energy storage facilities, and IPL’s Wever (99 MW) energy storage facility, were placed in service in 2025.
(c)WPL previously received approval from MISO to retire the coal-fired Columbia Units 1 and 2. As of December 31, 2024, WPL planned to cease coal operations at Columbia Units 1 and 2 by the end of 2029, and Alliant Energy and WPL concluded that Columbia Units 1 and 2 met the criteria to be considered probable of abandonment. WPL currently plans to continue coal operations at Columbia Units 1 and 2 at least through 2029 as well as evaluate the potential conversion of Columbia Unit 1 and/or Unit 2 to natural gas. As a result, as of December 31, 2025, Alliant Energy and WPL concluded that Columbia Units 1 and 2 no longer meet the criteria to be considered probable of abandonment.
(d)Less accumulated amortization of $120 million and $116 million for WPL as of December 31, 2025 and 2024, respectively. Refer to Note 9 for discussion of WPL’s remeasurement of this lease in 2025. For Alliant Energy, the leased Sheboygan Falls Energy Facility is eliminated upon consolidation and is included in the “Non-utility Generation, net” line within Alliant Energy’s consolidated property, plant and equipment.
(e)Alliant Energy’s and IPL’s CWIP balances were higher as of December 31, 2025, compared to December 31, 2024, primarily due to IPL’s energy storage and natural gas-fired generation projects.
(f)Less accumulated depreciation of $81 million and $78 million for Alliant Energy as of December 31, 2025 and 2024, respectively.
(g)Less accumulated depreciation of $305 million and $289 million for Alliant Energy as of December 31, 2025 and 2024, respectively.
Allowance For Funds Used During Construction The amount of AFUDC generated by equity and debt components was as follows (in millions):
Alliant EnergyIPLWPL
202520242023202520242023202520242023
Equity$63$54$74$39$31$15$24$23$59
Debt262126171269920
$89$75$100$56$43$21$33$32$79
IPL [Member]  
Property, Plant and Equipment [Line Items]  
Property, Plant and Equipment
At December 31, details of property, plant and equipment on the balance sheets were as follows (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Utility:
Electric plant:
Generation and energy storage in service (a)(b)$12,757 $11,156 $6,251 $5,924 $6,506 $5,232 
Distribution in service8,418 7,811 4,691 4,344 3,727 3,467 
Other in service572 595 369 385 203 210 
Anticipated to be retired early (c)— 784 — — — 784 
Total electric plant21,747 20,346 11,311 10,653 10,436 9,693 
Gas plant in service1,938 1,863 1,020 981 918 882 
Other plant in service752 734 456456 296 278 
Accumulated depreciation (c)(6,690)(6,229)(3,574)(3,360)(3,116)(2,869)
Net plant17,747 16,714 9,213 8,730 8,534 7,984 
Leased Sheboygan Falls Energy Facility, net (d)— — — — 110 74 
Leased land for solar generation, net190 189 52 53 138 136 
Construction work in progress (e)1,742 1,215 1,166 548 576 667 
Other, net10 5 5 5 5 — 
Total utility19,689 18,123 10,436 9,336 9,363 8,861 
Non-utility and other:
Non-utility Generation, net (f)146 103 — — — — 
Corporate Services and other, net (g)509475 — — — — 
Total non-utility and other655 578 — — — — 
Total property, plant and equipment$20,344 $18,701 $10,436 $9,336 $9,363 $8,861 

(a)Construction costs associated with WPL’s approximately 1,100 MW of new solar generation exceeded the construction cost estimates previously approved by the PSCW by approximately $205 million. In 2024, the PSCW issued orders approving deferral of, and the deferral of a return on, the incremental solar generation construction costs in 2024 and 2025. In December 2025, the PSCW issued an order for the 2026/2027 forward-looking Test Period, which includes a full return of and on these solar generation construction costs from WPL’s retail electric customers. As a result, Alliant Energy and WPL concluded that there was not a probable disallowance of the higher rate base amounts as of December 31, 2025.
(b)WPL’s Grant County (100 MW) and Wood County (75 MW) energy storage facilities, and IPL’s Wever (99 MW) energy storage facility, were placed in service in 2025.
(c)WPL previously received approval from MISO to retire the coal-fired Columbia Units 1 and 2. As of December 31, 2024, WPL planned to cease coal operations at Columbia Units 1 and 2 by the end of 2029, and Alliant Energy and WPL concluded that Columbia Units 1 and 2 met the criteria to be considered probable of abandonment. WPL currently plans to continue coal operations at Columbia Units 1 and 2 at least through 2029 as well as evaluate the potential conversion of Columbia Unit 1 and/or Unit 2 to natural gas. As a result, as of December 31, 2025, Alliant Energy and WPL concluded that Columbia Units 1 and 2 no longer meet the criteria to be considered probable of abandonment.
(d)Less accumulated amortization of $120 million and $116 million for WPL as of December 31, 2025 and 2024, respectively. Refer to Note 9 for discussion of WPL’s remeasurement of this lease in 2025. For Alliant Energy, the leased Sheboygan Falls Energy Facility is eliminated upon consolidation and is included in the “Non-utility Generation, net” line within Alliant Energy’s consolidated property, plant and equipment.
(e)Alliant Energy’s and IPL’s CWIP balances were higher as of December 31, 2025, compared to December 31, 2024, primarily due to IPL’s energy storage and natural gas-fired generation projects.
(f)Less accumulated depreciation of $81 million and $78 million for Alliant Energy as of December 31, 2025 and 2024, respectively.
(g)Less accumulated depreciation of $305 million and $289 million for Alliant Energy as of December 31, 2025 and 2024, respectively.
Allowance For Funds Used During Construction The amount of AFUDC generated by equity and debt components was as follows (in millions):
Alliant EnergyIPLWPL
202520242023202520242023202520242023
Equity$63$54$74$39$31$15$24$23$59
Debt262126171269920
$89$75$100$56$43$21$33$32$79
WPL [Member]  
Property, Plant and Equipment [Line Items]  
Property, Plant and Equipment
At December 31, details of property, plant and equipment on the balance sheets were as follows (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Utility:
Electric plant:
Generation and energy storage in service (a)(b)$12,757 $11,156 $6,251 $5,924 $6,506 $5,232 
Distribution in service8,418 7,811 4,691 4,344 3,727 3,467 
Other in service572 595 369 385 203 210 
Anticipated to be retired early (c)— 784 — — — 784 
Total electric plant21,747 20,346 11,311 10,653 10,436 9,693 
Gas plant in service1,938 1,863 1,020 981 918 882 
Other plant in service752 734 456456 296 278 
Accumulated depreciation (c)(6,690)(6,229)(3,574)(3,360)(3,116)(2,869)
Net plant17,747 16,714 9,213 8,730 8,534 7,984 
Leased Sheboygan Falls Energy Facility, net (d)— — — — 110 74 
Leased land for solar generation, net190 189 52 53 138 136 
Construction work in progress (e)1,742 1,215 1,166 548 576 667 
Other, net10 5 5 5 5 — 
Total utility19,689 18,123 10,436 9,336 9,363 8,861 
Non-utility and other:
Non-utility Generation, net (f)146 103 — — — — 
Corporate Services and other, net (g)509475 — — — — 
Total non-utility and other655 578 — — — — 
Total property, plant and equipment$20,344 $18,701 $10,436 $9,336 $9,363 $8,861 

(a)Construction costs associated with WPL’s approximately 1,100 MW of new solar generation exceeded the construction cost estimates previously approved by the PSCW by approximately $205 million. In 2024, the PSCW issued orders approving deferral of, and the deferral of a return on, the incremental solar generation construction costs in 2024 and 2025. In December 2025, the PSCW issued an order for the 2026/2027 forward-looking Test Period, which includes a full return of and on these solar generation construction costs from WPL’s retail electric customers. As a result, Alliant Energy and WPL concluded that there was not a probable disallowance of the higher rate base amounts as of December 31, 2025.
(b)WPL’s Grant County (100 MW) and Wood County (75 MW) energy storage facilities, and IPL’s Wever (99 MW) energy storage facility, were placed in service in 2025.
(c)WPL previously received approval from MISO to retire the coal-fired Columbia Units 1 and 2. As of December 31, 2024, WPL planned to cease coal operations at Columbia Units 1 and 2 by the end of 2029, and Alliant Energy and WPL concluded that Columbia Units 1 and 2 met the criteria to be considered probable of abandonment. WPL currently plans to continue coal operations at Columbia Units 1 and 2 at least through 2029 as well as evaluate the potential conversion of Columbia Unit 1 and/or Unit 2 to natural gas. As a result, as of December 31, 2025, Alliant Energy and WPL concluded that Columbia Units 1 and 2 no longer meet the criteria to be considered probable of abandonment.
(d)Less accumulated amortization of $120 million and $116 million for WPL as of December 31, 2025 and 2024, respectively. Refer to Note 9 for discussion of WPL’s remeasurement of this lease in 2025. For Alliant Energy, the leased Sheboygan Falls Energy Facility is eliminated upon consolidation and is included in the “Non-utility Generation, net” line within Alliant Energy’s consolidated property, plant and equipment.
(e)Alliant Energy’s and IPL’s CWIP balances were higher as of December 31, 2025, compared to December 31, 2024, primarily due to IPL’s energy storage and natural gas-fired generation projects.
(f)Less accumulated depreciation of $81 million and $78 million for Alliant Energy as of December 31, 2025 and 2024, respectively.
(g)Less accumulated depreciation of $305 million and $289 million for Alliant Energy as of December 31, 2025 and 2024, respectively.
Allowance For Funds Used During Construction The amount of AFUDC generated by equity and debt components was as follows (in millions):
Alliant EnergyIPLWPL
202520242023202520242023202520242023
Equity$63$54$74$39$31$15$24$23$59
Debt262126171269920
$89$75$100$56$43$21$33$32$79
v3.25.4
Jointly-Owned Electric Utility Plant (Tables)
 12 Months Ended
Dec. 31, 2025
Jointly Owned Electric Utility Plant [Line Items]  
Components of Jointly-Owned Electric Utility Plants Information relative to IPL’s and WPL’s ownership interest in these jointly-owned EGUs at December 31, 2025 was as follows (dollars in millions):
OwnershipElectricAccumulated ProvisionConstruction
Interest %Plantfor DepreciationWork in Progress
IPL
Ottumwa Unit 148.0%$662$302$7
George Neal Unit 425.7%2011134
George Neal Unit 328.0%192894
Louisa Unit 14.0%44241
1,09952816
WPL
Columbia Units 1-2 and Energy Storage System53.5%8684074
West Riverside Energy Center and Solar Facility56.6%456717
Forward Wind Energy Center42.6%11858—
1,44253611
Alliant Energy$2,541$1,064$27
IPL [Member]  
Jointly Owned Electric Utility Plant [Line Items]  
Components of Jointly-Owned Electric Utility Plants Information relative to IPL’s and WPL’s ownership interest in these jointly-owned EGUs at December 31, 2025 was as follows (dollars in millions):
OwnershipElectricAccumulated ProvisionConstruction
Interest %Plantfor DepreciationWork in Progress
IPL
Ottumwa Unit 148.0%$662$302$7
George Neal Unit 425.7%2011134
George Neal Unit 328.0%192894
Louisa Unit 14.0%44241
1,09952816
WPL
Columbia Units 1-2 and Energy Storage System53.5%8684074
West Riverside Energy Center and Solar Facility56.6%456717
Forward Wind Energy Center42.6%11858—
1,44253611
Alliant Energy$2,541$1,064$27
WPL [Member]  
Jointly Owned Electric Utility Plant [Line Items]  
Components of Jointly-Owned Electric Utility Plants Information relative to IPL’s and WPL’s ownership interest in these jointly-owned EGUs at December 31, 2025 was as follows (dollars in millions):
OwnershipElectricAccumulated ProvisionConstruction
Interest %Plantfor DepreciationWork in Progress
IPL
Ottumwa Unit 148.0%$662$302$7
George Neal Unit 425.7%2011134
George Neal Unit 328.0%192894
Louisa Unit 14.0%44241
1,09952816
WPL
Columbia Units 1-2 and Energy Storage System53.5%8684074
West Riverside Energy Center and Solar Facility56.6%456717
Forward Wind Energy Center42.6%11858—
1,44253611
Alliant Energy$2,541$1,064$27
v3.25.4
Receivables (Tables)
 12 Months Ended
Dec. 31, 2025
Receivables [Line Items]  
Accounts Receivable Details Details for accounts receivable included on the balance sheets as of December 31 were as follows (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Customer$139 $113 $— $— $126 $98 
Unbilled utility revenues117 101 — — 117 101 
Deferred proceeds126 163 126 163 — — 
Other104 58 59 29 39 29 
Allowance for expected credit losses(10)(8)— — (9)(8)
$476 $427 $185 $192 $273 $220 
Gross Write-offs for Accounts Receivable
In 2025, gross write-offs for accounts receivable were as follows (in millions):
Originated in 2023
Originated in 2024
Originated in 2025
Alliant Energy$1$12$16
IPL189
WPL—47
Maximum And Average Outstanding Cash Proceeds IPL’s maximum and average outstanding aggregate cash proceeds (based on daily outstanding balances) related to the sales of accounts receivable program were as follows (in millions):
MaximumAverage
202520242023202520242023
Outstanding aggregate cash proceeds$110$110$110$57$31$51
Receivables Sold Under the Agreement
As of December 31, the attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions):
20252024
Customer accounts receivable$147$137
Unbilled utility revenues104108
Receivables sold to third party251245
Less: cash proceeds11070
Deferred proceeds141175
Less: allowance for expected credit losses1512
Fair value of deferred proceeds$126$163
Outstanding receivables past due$21$21
Additional Attributes Of Receivables Sold Under The Agreement
Additional attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions):
202520242023
Collections$2,279$2,090$2,233 
Write-offs, net of recoveries121212 
IPL [Member]  
Receivables [Line Items]  
Accounts Receivable Details Details for accounts receivable included on the balance sheets as of December 31 were as follows (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Customer$139 $113 $— $— $126 $98 
Unbilled utility revenues117 101 — — 117 101 
Deferred proceeds126 163 126 163 — — 
Other104 58 59 29 39 29 
Allowance for expected credit losses(10)(8)— — (9)(8)
$476 $427 $185 $192 $273 $220 
Gross Write-offs for Accounts Receivable
In 2025, gross write-offs for accounts receivable were as follows (in millions):
Originated in 2023
Originated in 2024
Originated in 2025
Alliant Energy$1$12$16
IPL189
WPL—47
Maximum And Average Outstanding Cash Proceeds IPL’s maximum and average outstanding aggregate cash proceeds (based on daily outstanding balances) related to the sales of accounts receivable program were as follows (in millions):
MaximumAverage
202520242023202520242023
Outstanding aggregate cash proceeds$110$110$110$57$31$51
Receivables Sold Under the Agreement
As of December 31, the attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions):
20252024
Customer accounts receivable$147$137
Unbilled utility revenues104108
Receivables sold to third party251245
Less: cash proceeds11070
Deferred proceeds141175
Less: allowance for expected credit losses1512
Fair value of deferred proceeds$126$163
Outstanding receivables past due$21$21
Additional Attributes Of Receivables Sold Under The Agreement
Additional attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions):
202520242023
Collections$2,279$2,090$2,233 
Write-offs, net of recoveries121212 
WPL [Member]  
Receivables [Line Items]  
Accounts Receivable Details Details for accounts receivable included on the balance sheets as of December 31 were as follows (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Customer$139 $113 $— $— $126 $98 
Unbilled utility revenues117 101 — — 117 101 
Deferred proceeds126 163 126 163 — — 
Other104 58 59 29 39 29 
Allowance for expected credit losses(10)(8)— — (9)(8)
$476 $427 $185 $192 $273 $220 
Gross Write-offs for Accounts Receivable
In 2025, gross write-offs for accounts receivable were as follows (in millions):
Originated in 2023
Originated in 2024
Originated in 2025
Alliant Energy$1$12$16
IPL189
WPL—47
v3.25.4
Investments (Tables)
 12 Months Ended
Dec. 31, 2025
Schedule of Equity Method Investments [Line Items]  
Unconsolidated Equity Investments Alliant Energy’s unconsolidated investments accounted for under the equity method of accounting are as follows (in millions):
Ownership Interest atCarrying Value at December 31,Equity (Income) / Loss
December 31, 202520252024202520242023
ATC Holdings
16%, 20%
$463$415($59)($57)($49)
Non-utility wind farm in Oklahoma50%112107(9)(6)(7)
Corporate venture investmentsVarious7678103(2)
OtherVarious2323(2)(1)(3)
$674$623($60)($61)($61)
Summary Financial Information
Summary aggregate financial information from the financial statements of these holdings is as follows (in millions):
Alliant Energy
202520242023
Revenues$1,080$1,005$898
Operating income482433384
Net income91434370
As of December 31:
Current assets254223
Non-current assets10,8189,930
Current liabilities879524
Non-current liabilities4,2433,933
Noncontrolling interest184221
v3.25.4
Common Equity (Tables)
 12 Months Ended
Dec. 31, 2025
Schedule of Common Equity [Line Items]  
Common Stock Activity A summary of Alliant Energy’s common stock activity was as follows:
202520242023
Shares outstanding, January 1256,690,222 256,096,848 251,134,966 
At-the-market offering program— — 4,372,561 
Shareowner Direct Plan360,662 439,107 454,987 
Equity-based compensation plans86,377 154,267 134,334 
Shares outstanding, December 31257,137,261 256,690,222 256,096,848 
v3.25.4
Debt (Tables)
 12 Months Ended
Dec. 31, 2025
Debt Instrument [Line Items]  
Schedule of Other Short-term Borrowings Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper and borrowings under the single credit facility classified as short-term debt was as follows (dollars in millions):
Alliant EnergyIPLWPL
December 31202520242025202420252024
Amount outstanding$88$558$88$50$—$183
Weighted average interest rates3.8%4.5%3.8%4.6%N/A4.5%
Available credit facility capacity$1,212$742$262$250$400$217
Alliant EnergyIPLWPL
For the year ended202520242025202420252024
Maximum amount outstanding (based on daily outstanding balances)$741$632$141$80$297$390
Average amount outstanding (based on daily outstanding balances)$349$327$25$1$176$70
Weighted average interest rates4.5%5.3%4.6%5.1%4.5%5.4%
Schedule of Long-term Debt Long-Term Debt - Long-term debt, net as of December 31 was as follows (dollars in millions):
20252024
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Senior Debentures (a):
4.1%, due 2028
$500 $500 $— $500 $500 $— 
3.6%, due 2029
300 300 — 300 300 — 
2.3%, due 2030
400 400 — 400 400 — 
5.7%, due 2033
300 300 — 300 300 — 
6.45%, due 2033
100 100 — 100 100 — 
4.95%, due 2034
350 350 — 350 350 — 
6.3%, due 2034
125 125 — 125 125 — 
5.6%, due 2035 (b)
600 600 — — — — 
6.25%, due 2039
300 300 — 300 300 — 
4.7%, due 2043
250 250 — 250 250 — 
3.7%, due 2046
300 300 — 300 300 — 
3.5%, due 2049
300 300 — 300 300 — 
3.1%, due 2051
300 300 — 300 300 — 
5.45%, due 2054
300 300 — 300 300 — 
5.6%, due 2055 (b)
300 300 — — — — 
3.4%, (Retired in 2025)
— — — 250 250 — 
5.5%, (Retired in 2025)
— — — 50 50 — 
4,725 4,725 — 4,125 4,125 — 
Debentures (a):
3.05%, due 2027
300 — 300 300 — 300 
3%, due 2029
350 — 350 350 — 350 
1.95%, due 2031
300 — 300 300 — 300 
3.95%, due 2032
600 — 600 600 — 600 
4.95%, due 2033
300 — 300 300 — 300 
5.375%, due 2034
300 — 300 300 — 300 
6.25%, due 2034
100 — 100 100 — 100 
6.375%, due 2037
300 — 300 300 — 300 
7.6%, due 2038
250 — 250 250 — 250 
4.1%, due 2044
250 — 250 250 — 250 
3.65%, due 2050
350 — 350 350 — 350 
5.7%, due 2055 (c)
300 — 300 — — — 
3,700 — 3,700 3,400 — 3,400 
Other:
AEF term loan credit agreement through March 2026, 5% at December 31, 2025 (with Alliant Energy as guarantor) (d)
300 — — — — — 
AEF 1.4% senior notes, due 2026 (with Alliant Energy as guarantor) (a)
200 — — 200 — — 
Alliant Energy 3.875% convertible senior notes, due 2026 (e)
575 — — 575 — — 
AEF 5.4% senior notes, due 2027 (with Alliant Energy as guarantor) (a)
375 — — 375 — — 
Alliant Energy 3.25% convertible senior notes, due 2028 (e)
575 — — — — — 
AEF 4.25% senior notes, due 2028 (with Alliant Energy as guarantor) (a)
300 — — 300 — — 
AEF 5.95% senior notes, due 2029 (with Alliant Energy as guarantor) (a)
300 — — 300 — — 
AEF 3.6% senior notes, due 2032 (with Alliant Energy as guarantor) (a)
350 — — 350 — — 
Alliant Energy 5.75% junior subordinated notes, due 2056 (f)
725 — — — — — 
AEF term loan credit agreement, 6% at December 31, 2024 (with Alliant Energy as guarantor) (Retired in 2025) (d)
— — — 300 — — 
3,700 — — 2,400 — — 
Subtotal12,125 4,725 3,700 9,925 4,125 3,400 
Current maturities(1,074)— — (1,171)(300)— 
Unamortized debt issuance costs(70)(30)(21)(55)(25)(20)
Unamortized debt (discount) and premium, net(27)(15)(10)(22)(10)(10)
Long-term debt, net (g)$10,954 $4,680 $3,669 $8,677 $3,790 $3,370 
(a)Contains optional redemption provisions which, if elected by the issuer at its sole discretion, could require material redemption premium payments by the issuer. The redemption premium payments under these optional redemption provisions are variable and dependent on applicable U.S. Treasury rates at the time of redemption.
(b)In May 2025, IPL issued $600 million of 5.6% senior debentures due 2035. A portion of the net proceeds was used for the retirement of IPL’s $50 million 5.5% senior debentures and $250 million 3.4% senior debentures. The remainder of the proceeds were used to reduce cash amounts received from its sale of accounts receivable program and commercial paper classified as long-term debt, and for general corporate purposes. In September 2025, IPL issued $300 million of 5.6% senior debentures due 2055. The net proceeds were used to reduce cash amounts received from its sale of accounts receivable program, to reduce outstanding commercial paper, and for general corporate purposes.
(c)In December 2025, WPL issued $300 million of 5.7% debentures due 2055. The net proceeds were used to reduce outstanding commercial paper and for general corporate purposes.
(d)In March 2025, AEF entered into a $300 million variable rate term loan credit agreement, which amended and restated the term loan credit agreement that expired in March 2025, and retired the $300 million variable rate term loan set forth therein, which was classified as a non-cash financing activity. AEF’s restated agreement includes an option to increase the amount outstanding with one or more additional term loans in an aggregate amount not to exceed $100 million. Refer to Note 14 for information on AEF’s related interest rate swap. In January 2026, AEF retired its $300 million term loan.
(e)Refer to “Convertible Senior Notes” below for additional information.
(f)In September 2025, Alliant Energy issued $725 million of junior subordinated notes due 2056. The interest rate will reset every 5 years beginning April 1, 2031, to equal the then-current five-year U.S. Treasury rate plus a spread of 2.077%, provided the interest rate will not reset below 5.75%. The net proceeds were used to reduce outstanding commercial paper, retire long term debt and for general corporate purposes. Long term debt to be retired includes AEF’s $300 million variable rate term loan which was retired in January 2026, AEF’s $200 million of 1.4% senior notes and Alliant Energy’s $575 million of 3.875% convertible senior notes, each of which matures in March 2026 and is expected to be retired at or prior to maturity. Alliant Energy has the option to redeem the notes prior to maturity upon the occurrence of certain events and during specified periods, at redemption prices specified in the governing agreements.
(g)There were no significant sinking fund requirements related to the outstanding long-term debt.
Schedule of Maturities of Long-term Debt At December 31, 2025, long-term debt maturities for 2026 through 2030 were as follows (in millions):
20262027202820292030
IPL$—$—$500$300$400
WPL—300—350—
AEF500375300300—
Alliant Energy parent company575—575——
Alliant Energy$1,075$675$1,375$950$400
IPL [Member]  
Debt Instrument [Line Items]  
Schedule of Other Short-term Borrowings Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper and borrowings under the single credit facility classified as short-term debt was as follows (dollars in millions):
Alliant EnergyIPLWPL
December 31202520242025202420252024
Amount outstanding$88$558$88$50$—$183
Weighted average interest rates3.8%4.5%3.8%4.6%N/A4.5%
Available credit facility capacity$1,212$742$262$250$400$217
Alliant EnergyIPLWPL
For the year ended202520242025202420252024
Maximum amount outstanding (based on daily outstanding balances)$741$632$141$80$297$390
Average amount outstanding (based on daily outstanding balances)$349$327$25$1$176$70
Weighted average interest rates4.5%5.3%4.6%5.1%4.5%5.4%
Schedule of Long-term Debt Long-Term Debt - Long-term debt, net as of December 31 was as follows (dollars in millions):
20252024
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Senior Debentures (a):
4.1%, due 2028
$500 $500 $— $500 $500 $— 
3.6%, due 2029
300 300 — 300 300 — 
2.3%, due 2030
400 400 — 400 400 — 
5.7%, due 2033
300 300 — 300 300 — 
6.45%, due 2033
100 100 — 100 100 — 
4.95%, due 2034
350 350 — 350 350 — 
6.3%, due 2034
125 125 — 125 125 — 
5.6%, due 2035 (b)
600 600 — — — — 
6.25%, due 2039
300 300 — 300 300 — 
4.7%, due 2043
250 250 — 250 250 — 
3.7%, due 2046
300 300 — 300 300 — 
3.5%, due 2049
300 300 — 300 300 — 
3.1%, due 2051
300 300 — 300 300 — 
5.45%, due 2054
300 300 — 300 300 — 
5.6%, due 2055 (b)
300 300 — — — — 
3.4%, (Retired in 2025)
— — — 250 250 — 
5.5%, (Retired in 2025)
— — — 50 50 — 
4,725 4,725 — 4,125 4,125 — 
Debentures (a):
3.05%, due 2027
300 — 300 300 — 300 
3%, due 2029
350 — 350 350 — 350 
1.95%, due 2031
300 — 300 300 — 300 
3.95%, due 2032
600 — 600 600 — 600 
4.95%, due 2033
300 — 300 300 — 300 
5.375%, due 2034
300 — 300 300 — 300 
6.25%, due 2034
100 — 100 100 — 100 
6.375%, due 2037
300 — 300 300 — 300 
7.6%, due 2038
250 — 250 250 — 250 
4.1%, due 2044
250 — 250 250 — 250 
3.65%, due 2050
350 — 350 350 — 350 
5.7%, due 2055 (c)
300 — 300 — — — 
3,700 — 3,700 3,400 — 3,400 
Other:
AEF term loan credit agreement through March 2026, 5% at December 31, 2025 (with Alliant Energy as guarantor) (d)
300 — — — — — 
AEF 1.4% senior notes, due 2026 (with Alliant Energy as guarantor) (a)
200 — — 200 — — 
Alliant Energy 3.875% convertible senior notes, due 2026 (e)
575 — — 575 — — 
AEF 5.4% senior notes, due 2027 (with Alliant Energy as guarantor) (a)
375 — — 375 — — 
Alliant Energy 3.25% convertible senior notes, due 2028 (e)
575 — — — — — 
AEF 4.25% senior notes, due 2028 (with Alliant Energy as guarantor) (a)
300 — — 300 — — 
AEF 5.95% senior notes, due 2029 (with Alliant Energy as guarantor) (a)
300 — — 300 — — 
AEF 3.6% senior notes, due 2032 (with Alliant Energy as guarantor) (a)
350 — — 350 — — 
Alliant Energy 5.75% junior subordinated notes, due 2056 (f)
725 — — — — — 
AEF term loan credit agreement, 6% at December 31, 2024 (with Alliant Energy as guarantor) (Retired in 2025) (d)
— — — 300 — — 
3,700 — — 2,400 — — 
Subtotal12,125 4,725 3,700 9,925 4,125 3,400 
Current maturities(1,074)— — (1,171)(300)— 
Unamortized debt issuance costs(70)(30)(21)(55)(25)(20)
Unamortized debt (discount) and premium, net(27)(15)(10)(22)(10)(10)
Long-term debt, net (g)$10,954 $4,680 $3,669 $8,677 $3,790 $3,370 
(a)Contains optional redemption provisions which, if elected by the issuer at its sole discretion, could require material redemption premium payments by the issuer. The redemption premium payments under these optional redemption provisions are variable and dependent on applicable U.S. Treasury rates at the time of redemption.
(b)In May 2025, IPL issued $600 million of 5.6% senior debentures due 2035. A portion of the net proceeds was used for the retirement of IPL’s $50 million 5.5% senior debentures and $250 million 3.4% senior debentures. The remainder of the proceeds were used to reduce cash amounts received from its sale of accounts receivable program and commercial paper classified as long-term debt, and for general corporate purposes. In September 2025, IPL issued $300 million of 5.6% senior debentures due 2055. The net proceeds were used to reduce cash amounts received from its sale of accounts receivable program, to reduce outstanding commercial paper, and for general corporate purposes.
(c)In December 2025, WPL issued $300 million of 5.7% debentures due 2055. The net proceeds were used to reduce outstanding commercial paper and for general corporate purposes.
(d)In March 2025, AEF entered into a $300 million variable rate term loan credit agreement, which amended and restated the term loan credit agreement that expired in March 2025, and retired the $300 million variable rate term loan set forth therein, which was classified as a non-cash financing activity. AEF’s restated agreement includes an option to increase the amount outstanding with one or more additional term loans in an aggregate amount not to exceed $100 million. Refer to Note 14 for information on AEF’s related interest rate swap. In January 2026, AEF retired its $300 million term loan.
(e)Refer to “Convertible Senior Notes” below for additional information.
(f)In September 2025, Alliant Energy issued $725 million of junior subordinated notes due 2056. The interest rate will reset every 5 years beginning April 1, 2031, to equal the then-current five-year U.S. Treasury rate plus a spread of 2.077%, provided the interest rate will not reset below 5.75%. The net proceeds were used to reduce outstanding commercial paper, retire long term debt and for general corporate purposes. Long term debt to be retired includes AEF’s $300 million variable rate term loan which was retired in January 2026, AEF’s $200 million of 1.4% senior notes and Alliant Energy’s $575 million of 3.875% convertible senior notes, each of which matures in March 2026 and is expected to be retired at or prior to maturity. Alliant Energy has the option to redeem the notes prior to maturity upon the occurrence of certain events and during specified periods, at redemption prices specified in the governing agreements.
(g)There were no significant sinking fund requirements related to the outstanding long-term debt.
Schedule of Maturities of Long-term Debt At December 31, 2025, long-term debt maturities for 2026 through 2030 were as follows (in millions):
20262027202820292030
IPL$—$—$500$300$400
WPL—300—350—
AEF500375300300—
Alliant Energy parent company575—575——
Alliant Energy$1,075$675$1,375$950$400
WPL [Member]  
Debt Instrument [Line Items]  
Schedule of Other Short-term Borrowings Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper and borrowings under the single credit facility classified as short-term debt was as follows (dollars in millions):
Alliant EnergyIPLWPL
December 31202520242025202420252024
Amount outstanding$88$558$88$50$—$183
Weighted average interest rates3.8%4.5%3.8%4.6%N/A4.5%
Available credit facility capacity$1,212$742$262$250$400$217
Alliant EnergyIPLWPL
For the year ended202520242025202420252024
Maximum amount outstanding (based on daily outstanding balances)$741$632$141$80$297$390
Average amount outstanding (based on daily outstanding balances)$349$327$25$1$176$70
Weighted average interest rates4.5%5.3%4.6%5.1%4.5%5.4%
Schedule of Long-term Debt Long-Term Debt - Long-term debt, net as of December 31 was as follows (dollars in millions):
20252024
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Senior Debentures (a):
4.1%, due 2028
$500 $500 $— $500 $500 $— 
3.6%, due 2029
300 300 — 300 300 — 
2.3%, due 2030
400 400 — 400 400 — 
5.7%, due 2033
300 300 — 300 300 — 
6.45%, due 2033
100 100 — 100 100 — 
4.95%, due 2034
350 350 — 350 350 — 
6.3%, due 2034
125 125 — 125 125 — 
5.6%, due 2035 (b)
600 600 — — — — 
6.25%, due 2039
300 300 — 300 300 — 
4.7%, due 2043
250 250 — 250 250 — 
3.7%, due 2046
300 300 — 300 300 — 
3.5%, due 2049
300 300 — 300 300 — 
3.1%, due 2051
300 300 — 300 300 — 
5.45%, due 2054
300 300 — 300 300 — 
5.6%, due 2055 (b)
300 300 — — — — 
3.4%, (Retired in 2025)
— — — 250 250 — 
5.5%, (Retired in 2025)
— — — 50 50 — 
4,725 4,725 — 4,125 4,125 — 
Debentures (a):
3.05%, due 2027
300 — 300 300 — 300 
3%, due 2029
350 — 350 350 — 350 
1.95%, due 2031
300 — 300 300 — 300 
3.95%, due 2032
600 — 600 600 — 600 
4.95%, due 2033
300 — 300 300 — 300 
5.375%, due 2034
300 — 300 300 — 300 
6.25%, due 2034
100 — 100 100 — 100 
6.375%, due 2037
300 — 300 300 — 300 
7.6%, due 2038
250 — 250 250 — 250 
4.1%, due 2044
250 — 250 250 — 250 
3.65%, due 2050
350 — 350 350 — 350 
5.7%, due 2055 (c)
300 — 300 — — — 
3,700 — 3,700 3,400 — 3,400 
Other:
AEF term loan credit agreement through March 2026, 5% at December 31, 2025 (with Alliant Energy as guarantor) (d)
300 — — — — — 
AEF 1.4% senior notes, due 2026 (with Alliant Energy as guarantor) (a)
200 — — 200 — — 
Alliant Energy 3.875% convertible senior notes, due 2026 (e)
575 — — 575 — — 
AEF 5.4% senior notes, due 2027 (with Alliant Energy as guarantor) (a)
375 — — 375 — — 
Alliant Energy 3.25% convertible senior notes, due 2028 (e)
575 — — — — — 
AEF 4.25% senior notes, due 2028 (with Alliant Energy as guarantor) (a)
300 — — 300 — — 
AEF 5.95% senior notes, due 2029 (with Alliant Energy as guarantor) (a)
300 — — 300 — — 
AEF 3.6% senior notes, due 2032 (with Alliant Energy as guarantor) (a)
350 — — 350 — — 
Alliant Energy 5.75% junior subordinated notes, due 2056 (f)
725 — — — — — 
AEF term loan credit agreement, 6% at December 31, 2024 (with Alliant Energy as guarantor) (Retired in 2025) (d)
— — — 300 — — 
3,700 — — 2,400 — — 
Subtotal12,125 4,725 3,700 9,925 4,125 3,400 
Current maturities(1,074)— — (1,171)(300)— 
Unamortized debt issuance costs(70)(30)(21)(55)(25)(20)
Unamortized debt (discount) and premium, net(27)(15)(10)(22)(10)(10)
Long-term debt, net (g)$10,954 $4,680 $3,669 $8,677 $3,790 $3,370 
(a)Contains optional redemption provisions which, if elected by the issuer at its sole discretion, could require material redemption premium payments by the issuer. The redemption premium payments under these optional redemption provisions are variable and dependent on applicable U.S. Treasury rates at the time of redemption.
(b)In May 2025, IPL issued $600 million of 5.6% senior debentures due 2035. A portion of the net proceeds was used for the retirement of IPL’s $50 million 5.5% senior debentures and $250 million 3.4% senior debentures. The remainder of the proceeds were used to reduce cash amounts received from its sale of accounts receivable program and commercial paper classified as long-term debt, and for general corporate purposes. In September 2025, IPL issued $300 million of 5.6% senior debentures due 2055. The net proceeds were used to reduce cash amounts received from its sale of accounts receivable program, to reduce outstanding commercial paper, and for general corporate purposes.
(c)In December 2025, WPL issued $300 million of 5.7% debentures due 2055. The net proceeds were used to reduce outstanding commercial paper and for general corporate purposes.
(d)In March 2025, AEF entered into a $300 million variable rate term loan credit agreement, which amended and restated the term loan credit agreement that expired in March 2025, and retired the $300 million variable rate term loan set forth therein, which was classified as a non-cash financing activity. AEF’s restated agreement includes an option to increase the amount outstanding with one or more additional term loans in an aggregate amount not to exceed $100 million. Refer to Note 14 for information on AEF’s related interest rate swap. In January 2026, AEF retired its $300 million term loan.
(e)Refer to “Convertible Senior Notes” below for additional information.
(f)In September 2025, Alliant Energy issued $725 million of junior subordinated notes due 2056. The interest rate will reset every 5 years beginning April 1, 2031, to equal the then-current five-year U.S. Treasury rate plus a spread of 2.077%, provided the interest rate will not reset below 5.75%. The net proceeds were used to reduce outstanding commercial paper, retire long term debt and for general corporate purposes. Long term debt to be retired includes AEF’s $300 million variable rate term loan which was retired in January 2026, AEF’s $200 million of 1.4% senior notes and Alliant Energy’s $575 million of 3.875% convertible senior notes, each of which matures in March 2026 and is expected to be retired at or prior to maturity. Alliant Energy has the option to redeem the notes prior to maturity upon the occurrence of certain events and during specified periods, at redemption prices specified in the governing agreements.
(g)There were no significant sinking fund requirements related to the outstanding long-term debt.
Schedule of Maturities of Long-term Debt At December 31, 2025, long-term debt maturities for 2026 through 2030 were as follows (in millions):
20262027202820292030
IPL$—$—$500$300$400
WPL—300—350—
AEF500375300300—
Alliant Energy parent company575—575——
Alliant Energy$1,075$675$1,375$950$400
v3.25.4
Leases (Tables)
 12 Months Ended
Dec. 31, 2025
Leases [Line Items]  
Schedule of Lease Details Operating lease details are as follows (dollars in millions):
December 31, 2025December 31, 2024
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net$21$11$9$22$12$9
Other current liabilities$2$1$1$2$1$1
Other liabilities1910820118
Total operating lease liabilities$21$11$9$22$12$9
Weighted average remaining lease term10 years10 years11 years11 years11 years12 years
Weighted average discount rate4%4%4%4%4%4%
Finance lease details are as follows (dollars in millions):
December 31, 2025December 31, 2024
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net:
Sheboygan Falls Energy FacilityN/AN/A$110N/AN/A$74
Leased land for solar generation$190$52138$189$53136
$190$52$248$189$53$210
Other current liabilities:
Sheboygan Falls Energy FacilityN/AN/A$4N/AN/A$7
$—$—$4$—$—$7
Other liabilities:
Sheboygan Falls Energy FacilityN/AN/A$106N/AN/A$71
Leased land for solar generation1905213818953136
1905224418953207
Total finance lease liabilities$190$52$248$189$53$214
Weighted average remaining lease term30 years27 years26 years31 years28 years28 years
Weighted average discount rate5%5%6%5%5%5%
Alliant EnergyIPLWPL
202520242023202520242023202520242023
Depreciation and amortization expenses$— $— $1 $— $— $— $2 $4 $6 
Interest expense9 8 6 3 2 1 11 10 8 
Total finance lease expense$9 $8 $7 $3 $2 $1 $13 $14 $14 

Finance lease liabilities arising from obtaining leased assets, which represent non-cash financing activities, were as follows (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Finance lease liabilities arising from obtaining leased assets
$1 $20 $— $20 $39 $— 
Schedule of Operating Lease Liability Maturities As of December 31, 2025, expected maturities of lease liabilities were as follows (in millions):
20262027202820292030ThereafterTotalLess: amount representing interestPresent value of minimum lease payments
Operating Leases:
Alliant Energy$3 $3 $3 $3 $2 $13$27$6$21
IPL2 1 1 1 1 814311
WPL1 1 1 1 1 71239
Finance Leases:
Alliant Energy9 10 10 10 10 328377187190
IPL3 3 3 3 3 871025052
WPL18 18 19 19 19 386479231248
Schedule of Finance Lease Liability Maturities As of December 31, 2025, expected maturities of lease liabilities were as follows (in millions):
20262027202820292030ThereafterTotalLess: amount representing interestPresent value of minimum lease payments
Operating Leases:
Alliant Energy$3 $3 $3 $3 $2 $13$27$6$21
IPL2 1 1 1 1 814311
WPL1 1 1 1 1 71239
Finance Leases:
Alliant Energy9 10 10 10 10 328377187190
IPL3 3 3 3 3 871025052
WPL18 18 19 19 19 386479231248
IPL [Member]  
Leases [Line Items]  
Schedule of Lease Details Operating lease details are as follows (dollars in millions):
December 31, 2025December 31, 2024
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net$21$11$9$22$12$9
Other current liabilities$2$1$1$2$1$1
Other liabilities1910820118
Total operating lease liabilities$21$11$9$22$12$9
Weighted average remaining lease term10 years10 years11 years11 years11 years12 years
Weighted average discount rate4%4%4%4%4%4%
Finance lease details are as follows (dollars in millions):
December 31, 2025December 31, 2024
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net:
Sheboygan Falls Energy FacilityN/AN/A$110N/AN/A$74
Leased land for solar generation$190$52138$189$53136
$190$52$248$189$53$210
Other current liabilities:
Sheboygan Falls Energy FacilityN/AN/A$4N/AN/A$7
$—$—$4$—$—$7
Other liabilities:
Sheboygan Falls Energy FacilityN/AN/A$106N/AN/A$71
Leased land for solar generation1905213818953136
1905224418953207
Total finance lease liabilities$190$52$248$189$53$214
Weighted average remaining lease term30 years27 years26 years31 years28 years28 years
Weighted average discount rate5%5%6%5%5%5%
Alliant EnergyIPLWPL
202520242023202520242023202520242023
Depreciation and amortization expenses$— $— $1 $— $— $— $2 $4 $6 
Interest expense9 8 6 3 2 1 11 10 8 
Total finance lease expense$9 $8 $7 $3 $2 $1 $13 $14 $14 

Finance lease liabilities arising from obtaining leased assets, which represent non-cash financing activities, were as follows (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Finance lease liabilities arising from obtaining leased assets
$1 $20 $— $20 $39 $— 
Schedule of Operating Lease Liability Maturities As of December 31, 2025, expected maturities of lease liabilities were as follows (in millions):
20262027202820292030ThereafterTotalLess: amount representing interestPresent value of minimum lease payments
Operating Leases:
Alliant Energy$3 $3 $3 $3 $2 $13$27$6$21
IPL2 1 1 1 1 814311
WPL1 1 1 1 1 71239
Finance Leases:
Alliant Energy9 10 10 10 10 328377187190
IPL3 3 3 3 3 871025052
WPL18 18 19 19 19 386479231248
Schedule of Finance Lease Liability Maturities As of December 31, 2025, expected maturities of lease liabilities were as follows (in millions):
20262027202820292030ThereafterTotalLess: amount representing interestPresent value of minimum lease payments
Operating Leases:
Alliant Energy$3 $3 $3 $3 $2 $13$27$6$21
IPL2 1 1 1 1 814311
WPL1 1 1 1 1 71239
Finance Leases:
Alliant Energy9 10 10 10 10 328377187190
IPL3 3 3 3 3 871025052
WPL18 18 19 19 19 386479231248
WPL [Member]  
Leases [Line Items]  
Schedule of Lease Details Operating lease details are as follows (dollars in millions):
December 31, 2025December 31, 2024
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net$21$11$9$22$12$9
Other current liabilities$2$1$1$2$1$1
Other liabilities1910820118
Total operating lease liabilities$21$11$9$22$12$9
Weighted average remaining lease term10 years10 years11 years11 years11 years12 years
Weighted average discount rate4%4%4%4%4%4%
Finance lease details are as follows (dollars in millions):
December 31, 2025December 31, 2024
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net:
Sheboygan Falls Energy FacilityN/AN/A$110N/AN/A$74
Leased land for solar generation$190$52138$189$53136
$190$52$248$189$53$210
Other current liabilities:
Sheboygan Falls Energy FacilityN/AN/A$4N/AN/A$7
$—$—$4$—$—$7
Other liabilities:
Sheboygan Falls Energy FacilityN/AN/A$106N/AN/A$71
Leased land for solar generation1905213818953136
1905224418953207
Total finance lease liabilities$190$52$248$189$53$214
Weighted average remaining lease term30 years27 years26 years31 years28 years28 years
Weighted average discount rate5%5%6%5%5%5%
Alliant EnergyIPLWPL
202520242023202520242023202520242023
Depreciation and amortization expenses$— $— $1 $— $— $— $2 $4 $6 
Interest expense9 8 6 3 2 1 11 10 8 
Total finance lease expense$9 $8 $7 $3 $2 $1 $13 $14 $14 

Finance lease liabilities arising from obtaining leased assets, which represent non-cash financing activities, were as follows (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Finance lease liabilities arising from obtaining leased assets
$1 $20 $— $20 $39 $— 
Schedule of Operating Lease Liability Maturities As of December 31, 2025, expected maturities of lease liabilities were as follows (in millions):
20262027202820292030ThereafterTotalLess: amount representing interestPresent value of minimum lease payments
Operating Leases:
Alliant Energy$3 $3 $3 $3 $2 $13$27$6$21
IPL2 1 1 1 1 814311
WPL1 1 1 1 1 71239
Finance Leases:
Alliant Energy9 10 10 10 10 328377187190
IPL3 3 3 3 3 871025052
WPL18 18 19 19 19 386479231248
Schedule of Finance Lease Liability Maturities As of December 31, 2025, expected maturities of lease liabilities were as follows (in millions):
20262027202820292030ThereafterTotalLess: amount representing interestPresent value of minimum lease payments
Operating Leases:
Alliant Energy$3 $3 $3 $3 $2 $13$27$6$21
IPL2 1 1 1 1 814311
WPL1 1 1 1 1 71239
Finance Leases:
Alliant Energy9 10 10 10 10 328377187190
IPL3 3 3 3 3 871025052
WPL18 18 19 19 19 386479231248
v3.25.4
Revenues (Tables)
 12 Months Ended
Dec. 31, 2025
Disaggregation of Revenue [Line Items]  
Disaggregation of Revenues
Disaggregation of revenues from contracts with customers is provided for each reportable segment (IPL and WPL), as well as by customer class within electric and gas sales, as follows (in millions):
Alliant EnergyIPLWPL
202520242023202520242023202520242023
Electric Utility:
Retail - residential$1,339 $1,236 $1,220 $661 $640 $641 $678 $596 $579 
Retail - commercial932 821 820 609 525 519 323 296 301 
Retail - industrial1,034 952 968 531 497 501 503 455 467 
Wholesale184 200 213 39 61 62 145 139 151 
Bulk power and other208 163 124 56 24 38 152 139 86 
Total Electric Utility3,697 3,372 3,345 1,896 1,747 1,761 1,801 1,625 1,584 
Gas Utility:
Retail - residential306 275 316 155 148 176 151 127 140 
Retail - commercial153 133 163 72 68 86 81 65 77 
Retail - industrial13 11 16 7 7 11 6 4 5 
Transportation/other53 46 45 31 27 27 22 19 18 
Total Gas Utility525 465 540 265 250 300 260 215 240 
Other Utility:
Steam37 40 45 37 40 45 — — — 
Other utility14 14 7 10 9 4 4 5 3 
Total Other Utility51 54 52 47 49 49 4 5 3 
Non-Utility and Other:
Travero and other89 90 90 — — — — — — 
Total Non-Utility and Other89 90 90 — — — — — — 
Total revenues$4,362 $3,981 $4,027 $2,208 $2,046 $2,110 $2,065 $1,845 $1,827 
IPL [Member]  
Disaggregation of Revenue [Line Items]  
Disaggregation of Revenues
Disaggregation of revenues from contracts with customers is provided for each reportable segment (IPL and WPL), as well as by customer class within electric and gas sales, as follows (in millions):
Alliant EnergyIPLWPL
202520242023202520242023202520242023
Electric Utility:
Retail - residential$1,339 $1,236 $1,220 $661 $640 $641 $678 $596 $579 
Retail - commercial932 821 820 609 525 519 323 296 301 
Retail - industrial1,034 952 968 531 497 501 503 455 467 
Wholesale184 200 213 39 61 62 145 139 151 
Bulk power and other208 163 124 56 24 38 152 139 86 
Total Electric Utility3,697 3,372 3,345 1,896 1,747 1,761 1,801 1,625 1,584 
Gas Utility:
Retail - residential306 275 316 155 148 176 151 127 140 
Retail - commercial153 133 163 72 68 86 81 65 77 
Retail - industrial13 11 16 7 7 11 6 4 5 
Transportation/other53 46 45 31 27 27 22 19 18 
Total Gas Utility525 465 540 265 250 300 260 215 240 
Other Utility:
Steam37 40 45 37 40 45 — — — 
Other utility14 14 7 10 9 4 4 5 3 
Total Other Utility51 54 52 47 49 49 4 5 3 
Non-Utility and Other:
Travero and other89 90 90 — — — — — — 
Total Non-Utility and Other89 90 90 — — — — — — 
Total revenues$4,362 $3,981 $4,027 $2,208 $2,046 $2,110 $2,065 $1,845 $1,827 
WPL [Member]  
Disaggregation of Revenue [Line Items]  
Disaggregation of Revenues
Disaggregation of revenues from contracts with customers is provided for each reportable segment (IPL and WPL), as well as by customer class within electric and gas sales, as follows (in millions):
Alliant EnergyIPLWPL
202520242023202520242023202520242023
Electric Utility:
Retail - residential$1,339 $1,236 $1,220 $661 $640 $641 $678 $596 $579 
Retail - commercial932 821 820 609 525 519 323 296 301 
Retail - industrial1,034 952 968 531 497 501 503 455 467 
Wholesale184 200 213 39 61 62 145 139 151 
Bulk power and other208 163 124 56 24 38 152 139 86 
Total Electric Utility3,697 3,372 3,345 1,896 1,747 1,761 1,801 1,625 1,584 
Gas Utility:
Retail - residential306 275 316 155 148 176 151 127 140 
Retail - commercial153 133 163 72 68 86 81 65 77 
Retail - industrial13 11 16 7 7 11 6 4 5 
Transportation/other53 46 45 31 27 27 22 19 18 
Total Gas Utility525 465 540 265 250 300 260 215 240 
Other Utility:
Steam37 40 45 37 40 45 — — — 
Other utility14 14 7 10 9 4 4 5 3 
Total Other Utility51 54 52 47 49 49 4 5 3 
Non-Utility and Other:
Travero and other89 90 90 — — — — — — 
Total Non-Utility and Other89 90 90 — — — — — — 
Total revenues$4,362 $3,981 $4,027 $2,208 $2,046 $2,110 $2,065 $1,845 $1,827 
v3.25.4
Income Taxes (Tables)
 12 Months Ended
Dec. 31, 2025
Income Tax [Line Items]  
Schedule of Components of Income Tax Expense (Benefit) The components of “Income tax expense (benefit)” in the income statements were as follows (in millions):
Alliant EnergyIPLWPL
202520242023202520242023202520242023
Current tax expense (benefit):
Federal$10$13($3)($21)($19)($44)$38$37$48
State(1)(10)(6)(10)(19)(21)182325
Deferred tax expense (benefit):
Federal5960100363887302410
State3315362(17)171673
Production tax credits(208)(177)(121)(133)(108)(95)(75)(69)(26)
Investment tax credits(42)(15)(1)(1)(4)(1)(41)(11)—
Provision recorded as a change in accrued interest——(1)——(1)———
($149)($114)$4($127)($129)($58)($14)$11$60
Schedule Of Effective Income Tax Rates The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income before income taxes. In 2024, Alliant Energy’s and IPL’s effective income tax rates were impacted by the pre-tax non-cash charge of $60 million for IPL’s Lansing Generating Station discussed in Note 2. In the fourth quarter of 2025, Alliant Energy, IPL and WPL retrospectively adopted the Financial Accounting Standards Board’s (FASB) accounting standard for improvements to income tax disclosures. Previously reported information for prior periods has been recast to conform with current period presentation.
Alliant Energy202520242023
AmountTax RateAmountTax RateAmountTax Rate
Statutory federal income tax rate$139 21%$121 21%$149 21%
State income taxes, net of federal benefits (primarily from state income taxes in Iowa and Wisconsin)22341213
Tax credits:
Production tax credits(206)(31)(171)(30)(121)(17)
Investment tax credits(156)(24)(42)(7)(3)—
Research and development credits(2)—(6)(1)——
Tax credit regulatory deferrals (Refer to Note 1(c) and Note 2)
112172032—
Other credits(1)—————
Nontaxable or nondeductible items412—(2)—
Other adjustments:
Effect of rate-making on property-related differences (Refer to Note 1(c) and Note 2)
(37)(6)(33)(6)(27)(4)
Amortization of excess deferred taxes (Refer to Note 2)
(24)(4)(13)(2)(13)(2)
Other ——41(2)—
Total income tax expense (benefit) and overall income tax rate($149)(23%)($114)(20%)$41%
IPL202520242023
AmountTax RateAmountTax RateAmountTax Rate
Statutory federal income tax rate$69 21%$49 21%$65 21%
State income taxes, net of federal benefits (primarily from state income taxes in Iowa)(10)(3)(27)(12)(5)(2)
Tax credits:
Production tax credits(133)(40)(108)(46)(95)(31)
Investment tax credits(43)(13)(8)(4)(2)(1)
Tax credit regulatory deferrals (Refer to Note 1(c) and Note 2)
4213411—
Other credits(1)—(1)———
Nontaxable or nondeductible items1—(1)—(1)—
Other adjustments:
Effect of rate-making on property-related differences (Refer to Note 1(c) and Note 2)
(30)(9)(24)(10)(16)(5)
Amortization of excess deferred taxes (Refer to Note 2)
(22)(7)(13)(5)(5)(1)
Total income tax expense (benefit) and overall income tax rate($127)(38%)($129)(55%)($58)(19%)
WPL202520242023
AmountTax RateAmountTax RateAmountTax Rate
Statutory federal income tax rate$81 21%$75 21%$85 21%
State income taxes, net of federal benefits (primarily from state income taxes in Wisconsin)277237225
Tax credits:
Production tax credits(73)(19)(63)(18)(26)(6)
Investment tax credits(114)(29)(34)(10)(1)—
Tax credit regulatory deferrals (Refer to Note 1(c) and Note 2)
70181741—
Other credits——(1)———
Nontaxable or nondeductible items1—(1)—(2)—
Other adjustments:
Effect of rate-making on property-related differences (Refer to Note 1(c) and Note 2)
(6)(2)(5)(1)(12)(4)
Amortization of excess deferred taxes (Refer to Note 2)
————(7)(1)
Total income tax expense (benefit) and overall income tax rate($14)(4%)$11 3%$60 15%
Schedule of Deferred Tax Assets and Liabilities The deferred tax assets and liabilities included on the balance sheets at December 31 arise from the following temporary differences (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Deferred tax liabilities:
Property$2,828 $2,596 $1,666 $1,521 $1,060 $999 
ATC Holdings139 135 — — — — 
Other167 178 112 120 62 66 
Total deferred tax liabilities3,134 2,909 1,778 1,641 1,122 1,065 
Deferred tax assets:
Federal credit carryforwards669 605 455 426 199 166 
Net operating losses carryforwards - state19 20 1 1 — — 
Other143 98 48 37 65 34 
Subtotal deferred tax assets831 723 504 464 264 200 
Valuation allowances(7)(2)(4)(2)(3)— 
Total deferred tax assets824 721 500 462 261 200 
Total deferred tax liabilities, net$2,310 $2,188 $1,278 $1,179 $861 $865 
Summary Of Tax Credit Carryforwards At December 31, 2025, carryforwards and expiration dates were estimated as follows (in millions):
Range of Expiration DatesAlliant EnergyIPLWPL
State net operating losses2025-2045$311$7$1
Federal tax credits2034-2045669455199
Schedule Of Open Tax Years Tax years that remain subject to the statute of limitations in the major jurisdictions for each of Alliant Energy, IPL and WPL are as follows:
Consolidated federal income tax returns (a)2022-2024
Consolidated Iowa income tax returns (b)2022-2024
Wisconsin combined tax returns (c)2021-2024

(a)The 2022 federal tax return is effectively settled as a result of participation in the IRS Compliance Assurance Program, which allows Alliant Energy and the IRS to work together to resolve issues related to Alliant Energy’s current tax year before filing its federal income tax return. The statute of limitations for these federal tax returns expires three years from each filing date.
(b)The statute of limitations for these Iowa tax returns expires three years from each filing date.
(c)The statute of limitations for these Wisconsin combined tax returns expires four years from each filing date.
IPL [Member]  
Income Tax [Line Items]  
Schedule of Components of Income Tax Expense (Benefit) The components of “Income tax expense (benefit)” in the income statements were as follows (in millions):
Alliant EnergyIPLWPL
202520242023202520242023202520242023
Current tax expense (benefit):
Federal$10$13($3)($21)($19)($44)$38$37$48
State(1)(10)(6)(10)(19)(21)182325
Deferred tax expense (benefit):
Federal5960100363887302410
State3315362(17)171673
Production tax credits(208)(177)(121)(133)(108)(95)(75)(69)(26)
Investment tax credits(42)(15)(1)(1)(4)(1)(41)(11)—
Provision recorded as a change in accrued interest——(1)——(1)———
($149)($114)$4($127)($129)($58)($14)$11$60
Schedule Of Effective Income Tax Rates The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income before income taxes. In 2024, Alliant Energy’s and IPL’s effective income tax rates were impacted by the pre-tax non-cash charge of $60 million for IPL’s Lansing Generating Station discussed in Note 2. In the fourth quarter of 2025, Alliant Energy, IPL and WPL retrospectively adopted the Financial Accounting Standards Board’s (FASB) accounting standard for improvements to income tax disclosures. Previously reported information for prior periods has been recast to conform with current period presentation.
Alliant Energy202520242023
AmountTax RateAmountTax RateAmountTax Rate
Statutory federal income tax rate$139 21%$121 21%$149 21%
State income taxes, net of federal benefits (primarily from state income taxes in Iowa and Wisconsin)22341213
Tax credits:
Production tax credits(206)(31)(171)(30)(121)(17)
Investment tax credits(156)(24)(42)(7)(3)—
Research and development credits(2)—(6)(1)——
Tax credit regulatory deferrals (Refer to Note 1(c) and Note 2)
112172032—
Other credits(1)—————
Nontaxable or nondeductible items412—(2)—
Other adjustments:
Effect of rate-making on property-related differences (Refer to Note 1(c) and Note 2)
(37)(6)(33)(6)(27)(4)
Amortization of excess deferred taxes (Refer to Note 2)
(24)(4)(13)(2)(13)(2)
Other ——41(2)—
Total income tax expense (benefit) and overall income tax rate($149)(23%)($114)(20%)$41%
IPL202520242023
AmountTax RateAmountTax RateAmountTax Rate
Statutory federal income tax rate$69 21%$49 21%$65 21%
State income taxes, net of federal benefits (primarily from state income taxes in Iowa)(10)(3)(27)(12)(5)(2)
Tax credits:
Production tax credits(133)(40)(108)(46)(95)(31)
Investment tax credits(43)(13)(8)(4)(2)(1)
Tax credit regulatory deferrals (Refer to Note 1(c) and Note 2)
4213411—
Other credits(1)—(1)———
Nontaxable or nondeductible items1—(1)—(1)—
Other adjustments:
Effect of rate-making on property-related differences (Refer to Note 1(c) and Note 2)
(30)(9)(24)(10)(16)(5)
Amortization of excess deferred taxes (Refer to Note 2)
(22)(7)(13)(5)(5)(1)
Total income tax expense (benefit) and overall income tax rate($127)(38%)($129)(55%)($58)(19%)
WPL202520242023
AmountTax RateAmountTax RateAmountTax Rate
Statutory federal income tax rate$81 21%$75 21%$85 21%
State income taxes, net of federal benefits (primarily from state income taxes in Wisconsin)277237225
Tax credits:
Production tax credits(73)(19)(63)(18)(26)(6)
Investment tax credits(114)(29)(34)(10)(1)—
Tax credit regulatory deferrals (Refer to Note 1(c) and Note 2)
70181741—
Other credits——(1)———
Nontaxable or nondeductible items1—(1)—(2)—
Other adjustments:
Effect of rate-making on property-related differences (Refer to Note 1(c) and Note 2)
(6)(2)(5)(1)(12)(4)
Amortization of excess deferred taxes (Refer to Note 2)
————(7)(1)
Total income tax expense (benefit) and overall income tax rate($14)(4%)$11 3%$60 15%
Schedule of Deferred Tax Assets and Liabilities The deferred tax assets and liabilities included on the balance sheets at December 31 arise from the following temporary differences (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Deferred tax liabilities:
Property$2,828 $2,596 $1,666 $1,521 $1,060 $999 
ATC Holdings139 135 — — — — 
Other167 178 112 120 62 66 
Total deferred tax liabilities3,134 2,909 1,778 1,641 1,122 1,065 
Deferred tax assets:
Federal credit carryforwards669 605 455 426 199 166 
Net operating losses carryforwards - state19 20 1 1 — — 
Other143 98 48 37 65 34 
Subtotal deferred tax assets831 723 504 464 264 200 
Valuation allowances(7)(2)(4)(2)(3)— 
Total deferred tax assets824 721 500 462 261 200 
Total deferred tax liabilities, net$2,310 $2,188 $1,278 $1,179 $861 $865 
Summary Of Tax Credit Carryforwards At December 31, 2025, carryforwards and expiration dates were estimated as follows (in millions):
Range of Expiration DatesAlliant EnergyIPLWPL
State net operating losses2025-2045$311$7$1
Federal tax credits2034-2045669455199
Schedule Of Open Tax Years Tax years that remain subject to the statute of limitations in the major jurisdictions for each of Alliant Energy, IPL and WPL are as follows:
Consolidated federal income tax returns (a)2022-2024
Consolidated Iowa income tax returns (b)2022-2024
Wisconsin combined tax returns (c)2021-2024

(a)The 2022 federal tax return is effectively settled as a result of participation in the IRS Compliance Assurance Program, which allows Alliant Energy and the IRS to work together to resolve issues related to Alliant Energy’s current tax year before filing its federal income tax return. The statute of limitations for these federal tax returns expires three years from each filing date.
(b)The statute of limitations for these Iowa tax returns expires three years from each filing date.
(c)The statute of limitations for these Wisconsin combined tax returns expires four years from each filing date.
WPL [Member]  
Income Tax [Line Items]  
Schedule of Components of Income Tax Expense (Benefit) The components of “Income tax expense (benefit)” in the income statements were as follows (in millions):
Alliant EnergyIPLWPL
202520242023202520242023202520242023
Current tax expense (benefit):
Federal$10$13($3)($21)($19)($44)$38$37$48
State(1)(10)(6)(10)(19)(21)182325
Deferred tax expense (benefit):
Federal5960100363887302410
State3315362(17)171673
Production tax credits(208)(177)(121)(133)(108)(95)(75)(69)(26)
Investment tax credits(42)(15)(1)(1)(4)(1)(41)(11)—
Provision recorded as a change in accrued interest——(1)——(1)———
($149)($114)$4($127)($129)($58)($14)$11$60
Schedule Of Effective Income Tax Rates The overall income tax rates shown in the following table were computed by dividing income tax expense (benefit) by income before income taxes. In 2024, Alliant Energy’s and IPL’s effective income tax rates were impacted by the pre-tax non-cash charge of $60 million for IPL’s Lansing Generating Station discussed in Note 2. In the fourth quarter of 2025, Alliant Energy, IPL and WPL retrospectively adopted the Financial Accounting Standards Board’s (FASB) accounting standard for improvements to income tax disclosures. Previously reported information for prior periods has been recast to conform with current period presentation.
Alliant Energy202520242023
AmountTax RateAmountTax RateAmountTax Rate
Statutory federal income tax rate$139 21%$121 21%$149 21%
State income taxes, net of federal benefits (primarily from state income taxes in Iowa and Wisconsin)22341213
Tax credits:
Production tax credits(206)(31)(171)(30)(121)(17)
Investment tax credits(156)(24)(42)(7)(3)—
Research and development credits(2)—(6)(1)——
Tax credit regulatory deferrals (Refer to Note 1(c) and Note 2)
112172032—
Other credits(1)—————
Nontaxable or nondeductible items412—(2)—
Other adjustments:
Effect of rate-making on property-related differences (Refer to Note 1(c) and Note 2)
(37)(6)(33)(6)(27)(4)
Amortization of excess deferred taxes (Refer to Note 2)
(24)(4)(13)(2)(13)(2)
Other ——41(2)—
Total income tax expense (benefit) and overall income tax rate($149)(23%)($114)(20%)$41%
IPL202520242023
AmountTax RateAmountTax RateAmountTax Rate
Statutory federal income tax rate$69 21%$49 21%$65 21%
State income taxes, net of federal benefits (primarily from state income taxes in Iowa)(10)(3)(27)(12)(5)(2)
Tax credits:
Production tax credits(133)(40)(108)(46)(95)(31)
Investment tax credits(43)(13)(8)(4)(2)(1)
Tax credit regulatory deferrals (Refer to Note 1(c) and Note 2)
4213411—
Other credits(1)—(1)———
Nontaxable or nondeductible items1—(1)—(1)—
Other adjustments:
Effect of rate-making on property-related differences (Refer to Note 1(c) and Note 2)
(30)(9)(24)(10)(16)(5)
Amortization of excess deferred taxes (Refer to Note 2)
(22)(7)(13)(5)(5)(1)
Total income tax expense (benefit) and overall income tax rate($127)(38%)($129)(55%)($58)(19%)
WPL202520242023
AmountTax RateAmountTax RateAmountTax Rate
Statutory federal income tax rate$81 21%$75 21%$85 21%
State income taxes, net of federal benefits (primarily from state income taxes in Wisconsin)277237225
Tax credits:
Production tax credits(73)(19)(63)(18)(26)(6)
Investment tax credits(114)(29)(34)(10)(1)—
Tax credit regulatory deferrals (Refer to Note 1(c) and Note 2)
70181741—
Other credits——(1)———
Nontaxable or nondeductible items1—(1)—(2)—
Other adjustments:
Effect of rate-making on property-related differences (Refer to Note 1(c) and Note 2)
(6)(2)(5)(1)(12)(4)
Amortization of excess deferred taxes (Refer to Note 2)
————(7)(1)
Total income tax expense (benefit) and overall income tax rate($14)(4%)$11 3%$60 15%
Schedule of Deferred Tax Assets and Liabilities The deferred tax assets and liabilities included on the balance sheets at December 31 arise from the following temporary differences (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Deferred tax liabilities:
Property$2,828 $2,596 $1,666 $1,521 $1,060 $999 
ATC Holdings139 135 — — — — 
Other167 178 112 120 62 66 
Total deferred tax liabilities3,134 2,909 1,778 1,641 1,122 1,065 
Deferred tax assets:
Federal credit carryforwards669 605 455 426 199 166 
Net operating losses carryforwards - state19 20 1 1 — — 
Other143 98 48 37 65 34 
Subtotal deferred tax assets831 723 504 464 264 200 
Valuation allowances(7)(2)(4)(2)(3)— 
Total deferred tax assets824 721 500 462 261 200 
Total deferred tax liabilities, net$2,310 $2,188 $1,278 $1,179 $861 $865 
Summary Of Tax Credit Carryforwards At December 31, 2025, carryforwards and expiration dates were estimated as follows (in millions):
Range of Expiration DatesAlliant EnergyIPLWPL
State net operating losses2025-2045$311$7$1
Federal tax credits2034-2045669455199
Schedule Of Open Tax Years Tax years that remain subject to the statute of limitations in the major jurisdictions for each of Alliant Energy, IPL and WPL are as follows:
Consolidated federal income tax returns (a)2022-2024
Consolidated Iowa income tax returns (b)2022-2024
Wisconsin combined tax returns (c)2021-2024

(a)The 2022 federal tax return is effectively settled as a result of participation in the IRS Compliance Assurance Program, which allows Alliant Energy and the IRS to work together to resolve issues related to Alliant Energy’s current tax year before filing its federal income tax return. The statute of limitations for these federal tax returns expires three years from each filing date.
(b)The statute of limitations for these Iowa tax returns expires three years from each filing date.
(c)The statute of limitations for these Wisconsin combined tax returns expires four years from each filing date.
v3.25.4
Benefit Plans (Tables)
 12 Months Ended
Dec. 31, 2025
Defined Benefit Plan Disclosure [Line Items]  
Assumptions Used To Measure Benefit Plans The weighted-average assumptions for defined benefit pension and OPEB plans at the measurement date of December 31 were as follows:
Defined Benefit Pension PlansOPEB Plans
Alliant Energy202520242023202520242023
Discount rate for benefit obligations5.52%5.65%5.36%5.40%5.62%5.40%
Discount rate for net periodic cost5.65%5.36%5.54%5.62%5.40%5.53%
Expected rate of return on plan assets7.60%7.73%7.80%6.37%6.22%6.50%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan5.60%6.24%10.75%N/AN/AN/A
Rate of compensation increase3.75%-4.50%3.50%-4.50%3.30%-4.50%N/AN/AN/A
Qualified Defined Benefit Pension PlanOPEB Plans
IPL202520242023202520242023
Discount rate for benefit obligations5.56%5.66%5.35%5.38%5.61%5.40%
Discount rate for net periodic cost5.66%5.35%5.55%5.61%5.40%5.53%
Expected rate of return on plan assets7.60%7.60%7.80%6.70%6.60%6.90%
Rate of compensation increase4.00%3.75%3.30%N/AN/AN/A
Qualified Defined Benefit Pension PlanOPEB Plans
WPL202520242023202520242023
Discount rate for benefit obligations5.56%5.66%5.35%5.38%5.61%5.40%
Discount rate for net periodic cost5.66%5.35%5.54%5.61%5.40%5.53%
Expected rate of return on plan assets7.60%7.80%7.80%5.75%5.61%5.65%
Rate of compensation increase3.75%3.50%3.30%N/AN/AN/A
Net Periodic Benefit Costs The service cost component of net periodic benefit costs is included in “Other operation and maintenance” expenses in the income statements and all other components of net periodic benefit costs are included in “Other (income) and deductions” in the income statements or regulatory assets on the balance sheets.
Alliant EnergyDefined Benefit Pension PlansOPEB Plans
202520242023202520242023
Service cost$4 $5 $5 $1 $2 $2 
Interest cost46 45 47 8 8 9 
Expected return on plan assets (a)(53)(55)(53)(4)(5)(5)
Amortization of prior service credit (b)— (1)(1)— — — 
Amortization of actuarial loss (c)22 24 28 — — 1 
$19 $18 $26 $5 $5 $7 
IPLDefined Benefit Pension PlansOPEB Plans
202520242023202520242023
Service cost$3 $3 $3 $1 $1 $1 
Interest cost20 20 21 3 3 3 
Expected return on plan assets (a)(25)(26)(26)(4)(4)(3)
Amortization of actuarial loss (c)9 9 11 — — 1 
$7 $6 $9 $— $— $2 
WPLDefined Benefit Pension PlansOPEB Plans
202520242023202520242023
Service cost$1 $2 $2 $1 $1 $1 
Interest cost20 20 20 3 3 3 
Expected return on plan assets (a)(23)(23)(22)(1)(1)(1)
Amortization of actuarial loss (c)11 11 13 — — 1 
$9 $10 $13 $3 $3 $4 

(a)The expected return on plan assets is based on the expected rate of return on plan assets and the fair value approach to the market-related value of plan assets.
(b)Unrecognized prior service credits for the OPEB plans are amortized over the average future service period to full eligibility of the participants of each plan.
(c)Unrecognized net actuarial gains or losses in excess of 10% of the greater of the plans’ benefit obligations or assets are amortized over the average future service lives of plan participants, except for the Alliant Energy Cash Balance Pension Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits.
Funded Status Of Benefit Plans A reconciliation of the funded status of qualified and non-qualified defined benefit pension and OPEB plans to the amounts recognized on the balance sheets at December 31 was as follows (in millions):
Defined Benefit Pension PlansOPEB Plans
Alliant Energy2025202420252024
Change in benefit obligation:
Net benefit obligation at January 1$841 $876 $148 $160 
Service cost4 5 1 2 
Interest cost46 45 8 8 
Plan participants’ contributions— — 4 3 
Actuarial (gain) loss17 (19)6 (7)
Gross benefits paid(84)(66)(21)(18)
Net benefit obligation at December 31824 841 146 148 
Change in plan assets:
Fair value of plan assets at January 1715 732 80 83 
Actual return on plan assets93 38 7 5 
Employer contributions23 11 8 7 
Plan participants’ contributions— — 4 3 
Gross benefits paid(84)(66)(21)(18)
Fair value of plan assets at December 31747 715 78 80 
Under funded status at December 31($77)($126)($68)($68)
Defined Benefit Pension PlansOPEB Plans
Alliant Energy2025202420252024
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $18 $17 
Current liabilities(5)(3)(6)(7)
Pension and other benefit obligations(72)(123)(80)(78)
Net amounts recognized at December 31($77)($126)($68)($68)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$267 $312 $7 $4 
Prior service credit(1)(2)— — 
$266 $310 $7 $4 
Defined Benefit Pension PlansOPEB Plans
IPL2025202420252024
Change in benefit obligation:
Net benefit obligation at January 1$372 $387 $59 $65 
Service cost3 3 1 1 
Interest cost20 20 3 3 
Plan participants’ contributions— — 2 1 
Actuarial (gain) loss6 (8)3 (3)
Gross benefits paid(38)(30)(9)(8)
Net benefit obligation at December 31363 372 59 59 
Change in plan assets:
Fair value of plan assets at January 1340 352 59 61 
Actual return on plan assets43 18 6 4 
Employer contributions1 — 2 1 
Plan participants’ contributions— — 2 1 
Gross benefits paid(38)(30)(9)(8)
Fair value of plan assets at December 31346 340 60 59 
(Under) Over funded status at December 31($17)($32)$1 $— 
Defined Benefit Pension PlansOPEB Plans
IPL2025202420252024
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $14 $13 
Current liabilities— (1)(1)(1)
Pension and other benefit obligations(17)(31)(12)(12)
Net amounts recognized at December 31($17)($32)$1 $— 
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$105 $126 $7 $7 
Prior service credit— (1)— — 
$105 $125 $7 $7 
Defined Benefit Pension PlansOPEB Plans
WPL2025202420252024
Change in benefit obligation:
Net benefit obligation at January 1$365 $381 $56 $61 
Service cost1 2 1 1 
Interest cost20 20 3 3 
Plan participants’ contributions— — 1 1 
Actuarial (gain) loss 9 (8)2 (3)
Gross benefits paid(33)(30)(8)(7)
Net benefit obligation at December 31362 365 55 56 
Change in plan assets:
Fair value of plan assets at January 1303 306 13 14 
Actual return on plan assets41 17 2 — 
Employer contributions16 10 6 5 
Plan participants’ contributions— — 1 1 
Gross benefits paid(33)(30)(8)(7)
Fair value of plan assets at December 31327 303 14 13 
Under funded status at December 31($35)($62)($41)($43)
Defined Benefit Pension PlansOPEB Plans
WPL2025202420252024
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $4 $4 
Current liabilities— — (5)(6)
Pension and other benefit obligations(35)(62)(40)(41)
Net amounts recognized at December 31($35)($62)($41)($43)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$115 $135 $1 $— 
Accumulated Benefit Obligations
Accumulated benefit obligations, aggregate amounts applicable to defined benefit pension and OPEB plans with accumulated benefit obligations in excess of plan assets, as well as defined benefit pension plans with projected benefit obligations in excess of plan assets as of the December 31 measurement date are as follows (in millions):
Defined Benefit Pension PlansOPEB Plans
Alliant Energy2025202420252024
Accumulated benefit obligations$805 $824 $146 $148 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations805 824 146 148 
Fair value of plan assets747 715 78 80 
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations824 841 N/AN/A
Fair value of plan assets747 715 N/AN/A
Defined Benefit Pension PlansOPEB Plans
IPL2025202420252024
Accumulated benefit obligations$353 $362 $59 $59 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations353 362 N/AN/A
Fair value of plan assets346 340 N/AN/A
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations363 372 N/AN/A
Fair value of plan assets346 340 N/AN/A
Defined Benefit Pension PlansOPEB Plans
WPL2025202420252024
Accumulated benefit obligations$354 $358 $55 $56 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations354 358 55 56 
Fair value of plan assets327 303 14 13 
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations362 365 N/AN/A
Fair value of plan assets327 303 N/AN/A
Regulatory Assets
In addition to the amounts recognized in regulatory assets in the above tables for IPL and WPL, regulatory assets were recognized for amounts associated with Corporate Services employees participating in other Alliant Energy sponsored benefit plans that were allocated to IPL and WPL at December 31 as follows (in millions):
IPLWPL
2025202420252024
Regulatory assets$23$25$21$22
Estimated Future Employer Contributions Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2026 is as follows (in millions):
Alliant EnergyIPLWPL
Defined benefit pension plans (a)$23$3$13
OPEB plans715

(a)Alliant Energy sponsors several non-qualified defined benefit pension plans that cover certain current and former key employees of IPL and WPL. Alliant Energy allocates pension costs to IPL and WPL for these plans. In addition, IPL and WPL amounts reflect funding for their non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans.
Expected Benefit Payments
Expected benefit payments for the qualified and non-qualified defined benefit plans, which reflect expected future service, as appropriate, are as follows (in millions):
Alliant Energy202620272028202920302031 - 2035
Defined benefit pension benefits$75 $75 $75 $74 $69 $320
OPEB16 15 15 14 14 61
$91 $90 $90 $88 $83 $381
IPL202620272028202920302031 - 2035
Defined benefit pension benefits$34 $33 $33 $32 $32 $143
OPEB6 6 6 6 6 24
$40 $39 $39 $38 $38 $167
WPL202620272028202920302031 - 2035
Defined benefit pension benefits$32 $31 $31 $31 $30 $142
OPEB6 6 5 5 5 23
$38 $37 $36 $36 $35 $165
Recognized Compensation Expense And Income Tax Benefits A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards was as follows (in millions):
Alliant EnergyIPLWPL
202520242023202520242023202520242023
Compensation expense$22$12$12$11$6$6$10$5$5
Income tax benefits333222111
Schedule of Carrying Value and Fair Market Value of the Deferred Compensation Obligation At December 31, the carrying value of the deferred compensation obligation for the company stock account and the shares in the deferred compensation trust based on the historical value of the shares of Alliant Energy common stock contributed to the rabbi trust, and the fair market value of the shares held in the rabbi trust, were as follows (in millions):
20252024
Carrying value$14$14
Fair market value2422
IPL [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Assumptions Used To Measure Benefit Plans The weighted-average assumptions for defined benefit pension and OPEB plans at the measurement date of December 31 were as follows:
Defined Benefit Pension PlansOPEB Plans
Alliant Energy202520242023202520242023
Discount rate for benefit obligations5.52%5.65%5.36%5.40%5.62%5.40%
Discount rate for net periodic cost5.65%5.36%5.54%5.62%5.40%5.53%
Expected rate of return on plan assets7.60%7.73%7.80%6.37%6.22%6.50%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan5.60%6.24%10.75%N/AN/AN/A
Rate of compensation increase3.75%-4.50%3.50%-4.50%3.30%-4.50%N/AN/AN/A
Qualified Defined Benefit Pension PlanOPEB Plans
IPL202520242023202520242023
Discount rate for benefit obligations5.56%5.66%5.35%5.38%5.61%5.40%
Discount rate for net periodic cost5.66%5.35%5.55%5.61%5.40%5.53%
Expected rate of return on plan assets7.60%7.60%7.80%6.70%6.60%6.90%
Rate of compensation increase4.00%3.75%3.30%N/AN/AN/A
Qualified Defined Benefit Pension PlanOPEB Plans
WPL202520242023202520242023
Discount rate for benefit obligations5.56%5.66%5.35%5.38%5.61%5.40%
Discount rate for net periodic cost5.66%5.35%5.54%5.61%5.40%5.53%
Expected rate of return on plan assets7.60%7.80%7.80%5.75%5.61%5.65%
Rate of compensation increase3.75%3.50%3.30%N/AN/AN/A
Net Periodic Benefit Costs The service cost component of net periodic benefit costs is included in “Other operation and maintenance” expenses in the income statements and all other components of net periodic benefit costs are included in “Other (income) and deductions” in the income statements or regulatory assets on the balance sheets.
Alliant EnergyDefined Benefit Pension PlansOPEB Plans
202520242023202520242023
Service cost$4 $5 $5 $1 $2 $2 
Interest cost46 45 47 8 8 9 
Expected return on plan assets (a)(53)(55)(53)(4)(5)(5)
Amortization of prior service credit (b)— (1)(1)— — — 
Amortization of actuarial loss (c)22 24 28 — — 1 
$19 $18 $26 $5 $5 $7 
IPLDefined Benefit Pension PlansOPEB Plans
202520242023202520242023
Service cost$3 $3 $3 $1 $1 $1 
Interest cost20 20 21 3 3 3 
Expected return on plan assets (a)(25)(26)(26)(4)(4)(3)
Amortization of actuarial loss (c)9 9 11 — — 1 
$7 $6 $9 $— $— $2 
WPLDefined Benefit Pension PlansOPEB Plans
202520242023202520242023
Service cost$1 $2 $2 $1 $1 $1 
Interest cost20 20 20 3 3 3 
Expected return on plan assets (a)(23)(23)(22)(1)(1)(1)
Amortization of actuarial loss (c)11 11 13 — — 1 
$9 $10 $13 $3 $3 $4 

(a)The expected return on plan assets is based on the expected rate of return on plan assets and the fair value approach to the market-related value of plan assets.
(b)Unrecognized prior service credits for the OPEB plans are amortized over the average future service period to full eligibility of the participants of each plan.
(c)Unrecognized net actuarial gains or losses in excess of 10% of the greater of the plans’ benefit obligations or assets are amortized over the average future service lives of plan participants, except for the Alliant Energy Cash Balance Pension Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits.
Funded Status Of Benefit Plans A reconciliation of the funded status of qualified and non-qualified defined benefit pension and OPEB plans to the amounts recognized on the balance sheets at December 31 was as follows (in millions):
Defined Benefit Pension PlansOPEB Plans
Alliant Energy2025202420252024
Change in benefit obligation:
Net benefit obligation at January 1$841 $876 $148 $160 
Service cost4 5 1 2 
Interest cost46 45 8 8 
Plan participants’ contributions— — 4 3 
Actuarial (gain) loss17 (19)6 (7)
Gross benefits paid(84)(66)(21)(18)
Net benefit obligation at December 31824 841 146 148 
Change in plan assets:
Fair value of plan assets at January 1715 732 80 83 
Actual return on plan assets93 38 7 5 
Employer contributions23 11 8 7 
Plan participants’ contributions— — 4 3 
Gross benefits paid(84)(66)(21)(18)
Fair value of plan assets at December 31747 715 78 80 
Under funded status at December 31($77)($126)($68)($68)
Defined Benefit Pension PlansOPEB Plans
Alliant Energy2025202420252024
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $18 $17 
Current liabilities(5)(3)(6)(7)
Pension and other benefit obligations(72)(123)(80)(78)
Net amounts recognized at December 31($77)($126)($68)($68)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$267 $312 $7 $4 
Prior service credit(1)(2)— — 
$266 $310 $7 $4 
Defined Benefit Pension PlansOPEB Plans
IPL2025202420252024
Change in benefit obligation:
Net benefit obligation at January 1$372 $387 $59 $65 
Service cost3 3 1 1 
Interest cost20 20 3 3 
Plan participants’ contributions— — 2 1 
Actuarial (gain) loss6 (8)3 (3)
Gross benefits paid(38)(30)(9)(8)
Net benefit obligation at December 31363 372 59 59 
Change in plan assets:
Fair value of plan assets at January 1340 352 59 61 
Actual return on plan assets43 18 6 4 
Employer contributions1 — 2 1 
Plan participants’ contributions— — 2 1 
Gross benefits paid(38)(30)(9)(8)
Fair value of plan assets at December 31346 340 60 59 
(Under) Over funded status at December 31($17)($32)$1 $— 
Defined Benefit Pension PlansOPEB Plans
IPL2025202420252024
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $14 $13 
Current liabilities— (1)(1)(1)
Pension and other benefit obligations(17)(31)(12)(12)
Net amounts recognized at December 31($17)($32)$1 $— 
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$105 $126 $7 $7 
Prior service credit— (1)— — 
$105 $125 $7 $7 
Defined Benefit Pension PlansOPEB Plans
WPL2025202420252024
Change in benefit obligation:
Net benefit obligation at January 1$365 $381 $56 $61 
Service cost1 2 1 1 
Interest cost20 20 3 3 
Plan participants’ contributions— — 1 1 
Actuarial (gain) loss 9 (8)2 (3)
Gross benefits paid(33)(30)(8)(7)
Net benefit obligation at December 31362 365 55 56 
Change in plan assets:
Fair value of plan assets at January 1303 306 13 14 
Actual return on plan assets41 17 2 — 
Employer contributions16 10 6 5 
Plan participants’ contributions— — 1 1 
Gross benefits paid(33)(30)(8)(7)
Fair value of plan assets at December 31327 303 14 13 
Under funded status at December 31($35)($62)($41)($43)
Defined Benefit Pension PlansOPEB Plans
WPL2025202420252024
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $4 $4 
Current liabilities— — (5)(6)
Pension and other benefit obligations(35)(62)(40)(41)
Net amounts recognized at December 31($35)($62)($41)($43)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$115 $135 $1 $— 
Accumulated Benefit Obligations
Accumulated benefit obligations, aggregate amounts applicable to defined benefit pension and OPEB plans with accumulated benefit obligations in excess of plan assets, as well as defined benefit pension plans with projected benefit obligations in excess of plan assets as of the December 31 measurement date are as follows (in millions):
Defined Benefit Pension PlansOPEB Plans
Alliant Energy2025202420252024
Accumulated benefit obligations$805 $824 $146 $148 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations805 824 146 148 
Fair value of plan assets747 715 78 80 
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations824 841 N/AN/A
Fair value of plan assets747 715 N/AN/A
Defined Benefit Pension PlansOPEB Plans
IPL2025202420252024
Accumulated benefit obligations$353 $362 $59 $59 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations353 362 N/AN/A
Fair value of plan assets346 340 N/AN/A
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations363 372 N/AN/A
Fair value of plan assets346 340 N/AN/A
Defined Benefit Pension PlansOPEB Plans
WPL2025202420252024
Accumulated benefit obligations$354 $358 $55 $56 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations354 358 55 56 
Fair value of plan assets327 303 14 13 
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations362 365 N/AN/A
Fair value of plan assets327 303 N/AN/A
Regulatory Assets
In addition to the amounts recognized in regulatory assets in the above tables for IPL and WPL, regulatory assets were recognized for amounts associated with Corporate Services employees participating in other Alliant Energy sponsored benefit plans that were allocated to IPL and WPL at December 31 as follows (in millions):
IPLWPL
2025202420252024
Regulatory assets$23$25$21$22
Estimated Future Employer Contributions Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2026 is as follows (in millions):
Alliant EnergyIPLWPL
Defined benefit pension plans (a)$23$3$13
OPEB plans715

(a)Alliant Energy sponsors several non-qualified defined benefit pension plans that cover certain current and former key employees of IPL and WPL. Alliant Energy allocates pension costs to IPL and WPL for these plans. In addition, IPL and WPL amounts reflect funding for their non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans.
Expected Benefit Payments
Expected benefit payments for the qualified and non-qualified defined benefit plans, which reflect expected future service, as appropriate, are as follows (in millions):
Alliant Energy202620272028202920302031 - 2035
Defined benefit pension benefits$75 $75 $75 $74 $69 $320
OPEB16 15 15 14 14 61
$91 $90 $90 $88 $83 $381
IPL202620272028202920302031 - 2035
Defined benefit pension benefits$34 $33 $33 $32 $32 $143
OPEB6 6 6 6 6 24
$40 $39 $39 $38 $38 $167
WPL202620272028202920302031 - 2035
Defined benefit pension benefits$32 $31 $31 $31 $30 $142
OPEB6 6 5 5 5 23
$38 $37 $36 $36 $35 $165
Recognized Compensation Expense And Income Tax Benefits A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards was as follows (in millions):
Alliant EnergyIPLWPL
202520242023202520242023202520242023
Compensation expense$22$12$12$11$6$6$10$5$5
Income tax benefits333222111
WPL [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Assumptions Used To Measure Benefit Plans The weighted-average assumptions for defined benefit pension and OPEB plans at the measurement date of December 31 were as follows:
Defined Benefit Pension PlansOPEB Plans
Alliant Energy202520242023202520242023
Discount rate for benefit obligations5.52%5.65%5.36%5.40%5.62%5.40%
Discount rate for net periodic cost5.65%5.36%5.54%5.62%5.40%5.53%
Expected rate of return on plan assets7.60%7.73%7.80%6.37%6.22%6.50%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan5.60%6.24%10.75%N/AN/AN/A
Rate of compensation increase3.75%-4.50%3.50%-4.50%3.30%-4.50%N/AN/AN/A
Qualified Defined Benefit Pension PlanOPEB Plans
IPL202520242023202520242023
Discount rate for benefit obligations5.56%5.66%5.35%5.38%5.61%5.40%
Discount rate for net periodic cost5.66%5.35%5.55%5.61%5.40%5.53%
Expected rate of return on plan assets7.60%7.60%7.80%6.70%6.60%6.90%
Rate of compensation increase4.00%3.75%3.30%N/AN/AN/A
Qualified Defined Benefit Pension PlanOPEB Plans
WPL202520242023202520242023
Discount rate for benefit obligations5.56%5.66%5.35%5.38%5.61%5.40%
Discount rate for net periodic cost5.66%5.35%5.54%5.61%5.40%5.53%
Expected rate of return on plan assets7.60%7.80%7.80%5.75%5.61%5.65%
Rate of compensation increase3.75%3.50%3.30%N/AN/AN/A
Net Periodic Benefit Costs The service cost component of net periodic benefit costs is included in “Other operation and maintenance” expenses in the income statements and all other components of net periodic benefit costs are included in “Other (income) and deductions” in the income statements or regulatory assets on the balance sheets.
Alliant EnergyDefined Benefit Pension PlansOPEB Plans
202520242023202520242023
Service cost$4 $5 $5 $1 $2 $2 
Interest cost46 45 47 8 8 9 
Expected return on plan assets (a)(53)(55)(53)(4)(5)(5)
Amortization of prior service credit (b)— (1)(1)— — — 
Amortization of actuarial loss (c)22 24 28 — — 1 
$19 $18 $26 $5 $5 $7 
IPLDefined Benefit Pension PlansOPEB Plans
202520242023202520242023
Service cost$3 $3 $3 $1 $1 $1 
Interest cost20 20 21 3 3 3 
Expected return on plan assets (a)(25)(26)(26)(4)(4)(3)
Amortization of actuarial loss (c)9 9 11 — — 1 
$7 $6 $9 $— $— $2 
WPLDefined Benefit Pension PlansOPEB Plans
202520242023202520242023
Service cost$1 $2 $2 $1 $1 $1 
Interest cost20 20 20 3 3 3 
Expected return on plan assets (a)(23)(23)(22)(1)(1)(1)
Amortization of actuarial loss (c)11 11 13 — — 1 
$9 $10 $13 $3 $3 $4 

(a)The expected return on plan assets is based on the expected rate of return on plan assets and the fair value approach to the market-related value of plan assets.
(b)Unrecognized prior service credits for the OPEB plans are amortized over the average future service period to full eligibility of the participants of each plan.
(c)Unrecognized net actuarial gains or losses in excess of 10% of the greater of the plans’ benefit obligations or assets are amortized over the average future service lives of plan participants, except for the Alliant Energy Cash Balance Pension Plan where gains or losses outside the 10% threshold are amortized over the time period the participants are expected to receive benefits.
Funded Status Of Benefit Plans A reconciliation of the funded status of qualified and non-qualified defined benefit pension and OPEB plans to the amounts recognized on the balance sheets at December 31 was as follows (in millions):
Defined Benefit Pension PlansOPEB Plans
Alliant Energy2025202420252024
Change in benefit obligation:
Net benefit obligation at January 1$841 $876 $148 $160 
Service cost4 5 1 2 
Interest cost46 45 8 8 
Plan participants’ contributions— — 4 3 
Actuarial (gain) loss17 (19)6 (7)
Gross benefits paid(84)(66)(21)(18)
Net benefit obligation at December 31824 841 146 148 
Change in plan assets:
Fair value of plan assets at January 1715 732 80 83 
Actual return on plan assets93 38 7 5 
Employer contributions23 11 8 7 
Plan participants’ contributions— — 4 3 
Gross benefits paid(84)(66)(21)(18)
Fair value of plan assets at December 31747 715 78 80 
Under funded status at December 31($77)($126)($68)($68)
Defined Benefit Pension PlansOPEB Plans
Alliant Energy2025202420252024
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $18 $17 
Current liabilities(5)(3)(6)(7)
Pension and other benefit obligations(72)(123)(80)(78)
Net amounts recognized at December 31($77)($126)($68)($68)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$267 $312 $7 $4 
Prior service credit(1)(2)— — 
$266 $310 $7 $4 
Defined Benefit Pension PlansOPEB Plans
IPL2025202420252024
Change in benefit obligation:
Net benefit obligation at January 1$372 $387 $59 $65 
Service cost3 3 1 1 
Interest cost20 20 3 3 
Plan participants’ contributions— — 2 1 
Actuarial (gain) loss6 (8)3 (3)
Gross benefits paid(38)(30)(9)(8)
Net benefit obligation at December 31363 372 59 59 
Change in plan assets:
Fair value of plan assets at January 1340 352 59 61 
Actual return on plan assets43 18 6 4 
Employer contributions1 — 2 1 
Plan participants’ contributions— — 2 1 
Gross benefits paid(38)(30)(9)(8)
Fair value of plan assets at December 31346 340 60 59 
(Under) Over funded status at December 31($17)($32)$1 $— 
Defined Benefit Pension PlansOPEB Plans
IPL2025202420252024
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $14 $13 
Current liabilities— (1)(1)(1)
Pension and other benefit obligations(17)(31)(12)(12)
Net amounts recognized at December 31($17)($32)$1 $— 
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$105 $126 $7 $7 
Prior service credit— (1)— — 
$105 $125 $7 $7 
Defined Benefit Pension PlansOPEB Plans
WPL2025202420252024
Change in benefit obligation:
Net benefit obligation at January 1$365 $381 $56 $61 
Service cost1 2 1 1 
Interest cost20 20 3 3 
Plan participants’ contributions— — 1 1 
Actuarial (gain) loss 9 (8)2 (3)
Gross benefits paid(33)(30)(8)(7)
Net benefit obligation at December 31362 365 55 56 
Change in plan assets:
Fair value of plan assets at January 1303 306 13 14 
Actual return on plan assets41 17 2 — 
Employer contributions16 10 6 5 
Plan participants’ contributions— — 1 1 
Gross benefits paid(33)(30)(8)(7)
Fair value of plan assets at December 31327 303 14 13 
Under funded status at December 31($35)($62)($41)($43)
Defined Benefit Pension PlansOPEB Plans
WPL2025202420252024
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $4 $4 
Current liabilities— — (5)(6)
Pension and other benefit obligations(35)(62)(40)(41)
Net amounts recognized at December 31($35)($62)($41)($43)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$115 $135 $1 $— 
Accumulated Benefit Obligations
Accumulated benefit obligations, aggregate amounts applicable to defined benefit pension and OPEB plans with accumulated benefit obligations in excess of plan assets, as well as defined benefit pension plans with projected benefit obligations in excess of plan assets as of the December 31 measurement date are as follows (in millions):
Defined Benefit Pension PlansOPEB Plans
Alliant Energy2025202420252024
Accumulated benefit obligations$805 $824 $146 $148 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations805 824 146 148 
Fair value of plan assets747 715 78 80 
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations824 841 N/AN/A
Fair value of plan assets747 715 N/AN/A
Defined Benefit Pension PlansOPEB Plans
IPL2025202420252024
Accumulated benefit obligations$353 $362 $59 $59 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations353 362 N/AN/A
Fair value of plan assets346 340 N/AN/A
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations363 372 N/AN/A
Fair value of plan assets346 340 N/AN/A
Defined Benefit Pension PlansOPEB Plans
WPL2025202420252024
Accumulated benefit obligations$354 $358 $55 $56 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations354 358 55 56 
Fair value of plan assets327 303 14 13 
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations362 365 N/AN/A
Fair value of plan assets327 303 N/AN/A
Regulatory Assets
In addition to the amounts recognized in regulatory assets in the above tables for IPL and WPL, regulatory assets were recognized for amounts associated with Corporate Services employees participating in other Alliant Energy sponsored benefit plans that were allocated to IPL and WPL at December 31 as follows (in millions):
IPLWPL
2025202420252024
Regulatory assets$23$25$21$22
Estimated Future Employer Contributions Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2026 is as follows (in millions):
Alliant EnergyIPLWPL
Defined benefit pension plans (a)$23$3$13
OPEB plans715

(a)Alliant Energy sponsors several non-qualified defined benefit pension plans that cover certain current and former key employees of IPL and WPL. Alliant Energy allocates pension costs to IPL and WPL for these plans. In addition, IPL and WPL amounts reflect funding for their non-bargaining employees who are participants in the Alliant Energy and Corporate Services sponsored qualified and non-qualified defined benefit pension plans.
Expected Benefit Payments
Expected benefit payments for the qualified and non-qualified defined benefit plans, which reflect expected future service, as appropriate, are as follows (in millions):
Alliant Energy202620272028202920302031 - 2035
Defined benefit pension benefits$75 $75 $75 $74 $69 $320
OPEB16 15 15 14 14 61
$91 $90 $90 $88 $83 $381
IPL202620272028202920302031 - 2035
Defined benefit pension benefits$34 $33 $33 $32 $32 $143
OPEB6 6 6 6 6 24
$40 $39 $39 $38 $38 $167
WPL202620272028202920302031 - 2035
Defined benefit pension benefits$32 $31 $31 $31 $30 $142
OPEB6 6 5 5 5 23
$38 $37 $36 $36 $35 $165
Recognized Compensation Expense And Income Tax Benefits A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards was as follows (in millions):
Alliant EnergyIPLWPL
202520242023202520242023202520242023
Compensation expense$22$12$12$11$6$6$10$5$5
Income tax benefits333222111
Pension Plans, Defined Benefit [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations At December 31, 2025, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows:
Target RangeActual
AllocationAllocation
Public equity securities32%-44%40%
Liquid alternative securities0%-11%5%
Return-seeking fixed income securities4%-16%7%
Liability-hedging fixed income securities (including cash and equivalents)41%-54%48%
At December 31, the fair values of qualified and non-qualified defined benefit pension plan assets were as follows (in millions):
20252024
FairLevelLevelLevelFairLevelLevelLevel
Alliant EnergyValue123Value123
Cash and equivalents$71 $— $71 $— $49 $— $49 $— 
Assets measured at net asset value676 667 
Due to brokers, net (pending trades with brokers)— (1)
Total pension plan assets$747 $715 
20252024
FairLevelLevelLevelFairLevelLevelLevel
IPLValue123Value123
Cash and equivalents$31 $— $31 $— $21 $— $21 $— 
Assets measured at net asset value315 319 
Total pension plan assets$346 $340 
20252024
FairLevelLevelLevelFairLevelLevelLevel
WPLValue123Value123
Cash and equivalents$32 $— $32 $— $22 $— $22 $— 
Assets measured at net asset value295 281 
Total pension plan assets$327 $303 
Pension Plans, Defined Benefit [Member] | IPL [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations At December 31, 2025, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows:
Target RangeActual
AllocationAllocation
Public equity securities32%-44%40%
Liquid alternative securities0%-11%5%
Return-seeking fixed income securities4%-16%7%
Liability-hedging fixed income securities (including cash and equivalents)41%-54%48%
At December 31, the fair values of qualified and non-qualified defined benefit pension plan assets were as follows (in millions):
20252024
FairLevelLevelLevelFairLevelLevelLevel
Alliant EnergyValue123Value123
Cash and equivalents$71 $— $71 $— $49 $— $49 $— 
Assets measured at net asset value676 667 
Due to brokers, net (pending trades with brokers)— (1)
Total pension plan assets$747 $715 
20252024
FairLevelLevelLevelFairLevelLevelLevel
IPLValue123Value123
Cash and equivalents$31 $— $31 $— $21 $— $21 $— 
Assets measured at net asset value315 319 
Total pension plan assets$346 $340 
20252024
FairLevelLevelLevelFairLevelLevelLevel
WPLValue123Value123
Cash and equivalents$32 $— $32 $— $22 $— $22 $— 
Assets measured at net asset value295 281 
Total pension plan assets$327 $303 
Pension Plans, Defined Benefit [Member] | WPL [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations At December 31, 2025, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows:
Target RangeActual
AllocationAllocation
Public equity securities32%-44%40%
Liquid alternative securities0%-11%5%
Return-seeking fixed income securities4%-16%7%
Liability-hedging fixed income securities (including cash and equivalents)41%-54%48%
At December 31, the fair values of qualified and non-qualified defined benefit pension plan assets were as follows (in millions):
20252024
FairLevelLevelLevelFairLevelLevelLevel
Alliant EnergyValue123Value123
Cash and equivalents$71 $— $71 $— $49 $— $49 $— 
Assets measured at net asset value676 667 
Due to brokers, net (pending trades with brokers)— (1)
Total pension plan assets$747 $715 
20252024
FairLevelLevelLevelFairLevelLevelLevel
IPLValue123Value123
Cash and equivalents$31 $— $31 $— $21 $— $21 $— 
Assets measured at net asset value315 319 
Total pension plan assets$346 $340 
20252024
FairLevelLevelLevelFairLevelLevelLevel
WPLValue123Value123
Cash and equivalents$32 $— $32 $— $22 $— $22 $— 
Assets measured at net asset value295 281 
Total pension plan assets$327 $303 
Other Postretirement Benefits Plans [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations At December 31, 2025, the current target ranges and actual allocations for assets with a long-term investment horizon were as follows:
Target RangeActual
AllocationAllocation
Cash and equivalents0%-5%3%
Public equity securities0%-40%26%
Fixed income securities34%-100%71%
At December 31, the fair values of OPEB plan assets were as follows (in millions):
20252024
FairLevelLevelLevelFairLevelLevelLevel
Alliant EnergyValue123Value123
Cash and equivalents$7 $— $7 $— $8 $— $8 $— 
Equity securities19 19 — — 20 20 — — 
Fixed income securities52 52 — — 52 52 — — 
Total OPEB plan assets$78 $71 $7 $— $80 $72 $8 $— 
20252024
FairLevelLevelLevelFairLevelLevelLevel
IPLValue123Value123
Cash and equivalents$3 $— $3 $— $1 $— $1 $— 
Equity securities17 17 — — 18 18 — — 
Fixed income securities40 40 — — 40 40 — — 
Total OPEB plan assets$60 $57 $3 $— $59 $58 $1 $— 
20252024
FairLevelLevelLevelFairLevelLevelLevel
WPLValue123Value123
Equity securities$2 $2 — — $2 $2 — — 
Fixed income securities12 12 — — 11 11 — — 
Total OPEB plan assets$14 $14 $— $— $13 $13 $— $— 
Other Postretirement Benefits Plans [Member] | IPL [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations At December 31, 2025, the current target ranges and actual allocations for assets with a long-term investment horizon were as follows:
Target RangeActual
AllocationAllocation
Cash and equivalents0%-5%3%
Public equity securities0%-40%26%
Fixed income securities34%-100%71%
At December 31, the fair values of OPEB plan assets were as follows (in millions):
20252024
FairLevelLevelLevelFairLevelLevelLevel
Alliant EnergyValue123Value123
Cash and equivalents$7 $— $7 $— $8 $— $8 $— 
Equity securities19 19 — — 20 20 — — 
Fixed income securities52 52 — — 52 52 — — 
Total OPEB plan assets$78 $71 $7 $— $80 $72 $8 $— 
20252024
FairLevelLevelLevelFairLevelLevelLevel
IPLValue123Value123
Cash and equivalents$3 $— $3 $— $1 $— $1 $— 
Equity securities17 17 — — 18 18 — — 
Fixed income securities40 40 — — 40 40 — — 
Total OPEB plan assets$60 $57 $3 $— $59 $58 $1 $— 
20252024
FairLevelLevelLevelFairLevelLevelLevel
WPLValue123Value123
Equity securities$2 $2 — — $2 $2 — — 
Fixed income securities12 12 — — 11 11 — — 
Total OPEB plan assets$14 $14 $— $— $13 $13 $— $— 
Other Postretirement Benefits Plans [Member] | WPL [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Fair Value Of Plan Assets By Asset Category, Fair Value Hierarchy Level and Allocations At December 31, 2025, the current target ranges and actual allocations for assets with a long-term investment horizon were as follows:
Target RangeActual
AllocationAllocation
Cash and equivalents0%-5%3%
Public equity securities0%-40%26%
Fixed income securities34%-100%71%
At December 31, the fair values of OPEB plan assets were as follows (in millions):
20252024
FairLevelLevelLevelFairLevelLevelLevel
Alliant EnergyValue123Value123
Cash and equivalents$7 $— $7 $— $8 $— $8 $— 
Equity securities19 19 — — 20 20 — — 
Fixed income securities52 52 — — 52 52 — — 
Total OPEB plan assets$78 $71 $7 $— $80 $72 $8 $— 
20252024
FairLevelLevelLevelFairLevelLevelLevel
IPLValue123Value123
Cash and equivalents$3 $— $3 $— $1 $— $1 $— 
Equity securities17 17 — — 18 18 — — 
Fixed income securities40 40 — — 40 40 — — 
Total OPEB plan assets$60 $57 $3 $— $59 $58 $1 $— 
20252024
FairLevelLevelLevelFairLevelLevelLevel
WPLValue123Value123
Equity securities$2 $2 — — $2 $2 — — 
Fixed income securities12 12 — — 11 11 — — 
Total OPEB plan assets$14 $14 $— $— $13 $13 $— $— 
401(k) Savings Plan [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Employees Participate In Defined Contribution Retirement Plans Costs related to the 401(k) savings plans, which are partially based on the participants’ contributions and include allocated costs associated with Corporate Services employees for IPL and WPL, were as follows (in millions):
Alliant EnergyIPLWPL
202520242023202520242023202520242023
401(k) costs$30 $31 $30 $14 $14 $14 $14 $15 $14 
401(k) Savings Plan [Member] | IPL [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Employees Participate In Defined Contribution Retirement Plans Costs related to the 401(k) savings plans, which are partially based on the participants’ contributions and include allocated costs associated with Corporate Services employees for IPL and WPL, were as follows (in millions):
Alliant EnergyIPLWPL
202520242023202520242023202520242023
401(k) costs$30 $31 $30 $14 $14 $14 $14 $15 $14 
401(k) Savings Plan [Member] | WPL [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Employees Participate In Defined Contribution Retirement Plans Costs related to the 401(k) savings plans, which are partially based on the participants’ contributions and include allocated costs associated with Corporate Services employees for IPL and WPL, were as follows (in millions):
Alliant EnergyIPLWPL
202520242023202520242023202520242023
401(k) costs$30 $31 $30 $14 $14 $14 $14 $15 $14 
Performance Shares (TSR Metric) [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Schedule Of Equity-based Compensation Plans Activity A summary of the performance shares activity, with amounts representing the target number of awards, was as follows:
202520242023
SharesWeighted
Average Grant
Date Fair Value		SharesWeighted
Average Grant
Date Fair Value		SharesWeighted
Average Grant
Date Fair Value
Nonvested awards, January 1289,399$51.31233,954$52.60190,273$54.13
Granted105,89666.52127,87446.04108,71255.68
Vested——(47,497)46.19(53,431)64.04
Forfeited(73,918)54.14(24,932)46.16(11,600)53.88
Nonvested awards, December 31321,37755.67289,39951.31233,95452.60
Restricted Stock Units [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Schedule Of Equity-based Compensation Plans Activity A summary of the restricted stock units activity was as follows:
202520242023
UnitsWeighted
Average Grant
Date Fair Value		UnitsWeighted
Average Grant
Date Fair Value		UnitsWeighted
Average Grant
Date Fair Value
Nonvested awards, January 1289,148$51.85234,259$52.58198,275$54.53
Granted102,24061.73129,85448.69106,12452.77
Vested(63,789)56.70(71,441)48.65(55,345)59.40
Forfeited(14,215)51.13(3,524)48.40(14,795)54.53
Nonvested awards, December 31313,38454.06289,14851.85234,25952.58
Performance Shares (Net Income and Workforce Composition Metrics) [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Schedule Of Equity-based Compensation Plans Activity A summary of the performance shares activity, with amounts representing the target number of awards, was as follows:
202520242023
SharesWeighted Average Grant Date Fair ValueSharesWeighted Average Grant Date Fair ValueSharesWeighted Average Grant Date Fair Value
Nonvested awards, January 1330,700$51.81257,639$52.76199,874$54.74
Granted118,88361.63146,14348.55124,21752.71
Vested(68,233)56.74(67,852)48.66(53,431)59.36
Forfeited(16,225)53.05(5,230)48.40(13,021)55.47
Nonvested awards, December 31365,12554.03330,70051.81257,63952.76
v3.25.4
Asset Retirement Obligations (Tables)
 12 Months Ended
Dec. 31, 2025
Schedule of Asset Retirement Obligations [Line Items]  
Reconciliation Of Changes In Asset Retirement Obligations (AROs) A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Balance, January 1$663 $246 $350 $148 $313 $98 
Revisions in estimated cash flows(1)(3)— (1)(1)(2)
Liabilities settled(5)(8)(2)(6)(3)(2)
Liabilities incurred (a)16 409 3 201 13 208 
Accretion expense31 19 16 8 15 11 
Balance, December 31$704 $663 $367 $350 $337 $313 

(a)In 2024, substantially due to the enactment of the revised CCR Rule, which significantly expands the scope of regulation to include coal ash ponds at sites that no longer produce electricity and inactive landfills, including some IPL and WPL facilities, Alliant Energy, IPL and WPL initially recorded additional AROs, additional ARO regulatory assets for EGUs no longer in operation, additional property, plant and equipment for EGUs still in operation, and a pre-tax non-cash charge of $20 million recorded to “Other operation and maintenance” in Alliant Energy’s and IPL’s income statements for the portion allocated to IPL’s steam business for IPL’s Prairie Creek Generating Station and the retired Sixth Street Generating Station as established in prior rate reviews. The amounts initially recorded in 2024 are expected to be adjusted in the future as additional information is obtained for the specific site closure plans, including the determination of whether or not individual sites are considered legal obligations and the acceptance and approval of compliance approaches, which could change management assumptions and result in a material change to the recorded amounts.
IPL [Member]  
Schedule of Asset Retirement Obligations [Line Items]  
Reconciliation Of Changes In Asset Retirement Obligations (AROs) A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Balance, January 1$663 $246 $350 $148 $313 $98 
Revisions in estimated cash flows(1)(3)— (1)(1)(2)
Liabilities settled(5)(8)(2)(6)(3)(2)
Liabilities incurred (a)16 409 3 201 13 208 
Accretion expense31 19 16 8 15 11 
Balance, December 31$704 $663 $367 $350 $337 $313 

(a)In 2024, substantially due to the enactment of the revised CCR Rule, which significantly expands the scope of regulation to include coal ash ponds at sites that no longer produce electricity and inactive landfills, including some IPL and WPL facilities, Alliant Energy, IPL and WPL initially recorded additional AROs, additional ARO regulatory assets for EGUs no longer in operation, additional property, plant and equipment for EGUs still in operation, and a pre-tax non-cash charge of $20 million recorded to “Other operation and maintenance” in Alliant Energy’s and IPL’s income statements for the portion allocated to IPL’s steam business for IPL’s Prairie Creek Generating Station and the retired Sixth Street Generating Station as established in prior rate reviews. The amounts initially recorded in 2024 are expected to be adjusted in the future as additional information is obtained for the specific site closure plans, including the determination of whether or not individual sites are considered legal obligations and the acceptance and approval of compliance approaches, which could change management assumptions and result in a material change to the recorded amounts.
WPL [Member]  
Schedule of Asset Retirement Obligations [Line Items]  
Reconciliation Of Changes In Asset Retirement Obligations (AROs) A reconciliation of the changes in AROs associated with long-lived assets is as follows (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Balance, January 1$663 $246 $350 $148 $313 $98 
Revisions in estimated cash flows(1)(3)— (1)(1)(2)
Liabilities settled(5)(8)(2)(6)(3)(2)
Liabilities incurred (a)16 409 3 201 13 208 
Accretion expense31 19 16 8 15 11 
Balance, December 31$704 $663 $367 $350 $337 $313 

(a)In 2024, substantially due to the enactment of the revised CCR Rule, which significantly expands the scope of regulation to include coal ash ponds at sites that no longer produce electricity and inactive landfills, including some IPL and WPL facilities, Alliant Energy, IPL and WPL initially recorded additional AROs, additional ARO regulatory assets for EGUs no longer in operation, additional property, plant and equipment for EGUs still in operation, and a pre-tax non-cash charge of $20 million recorded to “Other operation and maintenance” in Alliant Energy’s and IPL’s income statements for the portion allocated to IPL’s steam business for IPL’s Prairie Creek Generating Station and the retired Sixth Street Generating Station as established in prior rate reviews. The amounts initially recorded in 2024 are expected to be adjusted in the future as additional information is obtained for the specific site closure plans, including the determination of whether or not individual sites are considered legal obligations and the acceptance and approval of compliance approaches, which could change management assumptions and result in a material change to the recorded amounts.
v3.25.4
Derivative Instruments (Tables)
 12 Months Ended
Dec. 31, 2025
Derivative [Line Items]  
Notional Amounts of Derivative Instruments As of December 31, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands):
ElectricityFTRsNatural GasDiesel Fuel
MWhsYearsMWhsYearsDthsYearsGallonsYears
2025
Alliant Energy1,682 202611,332 2026140,731 2026-2032— N/A
IPL634 20264,482 202660,773 2026-2030— N/A
WPL1,048 20266,850 202679,958 2026-2032— N/A
2024
Alliant Energy1,422 2025-202610,232 2025147,894 2025-20322,520 2025
IPL383 2025-20263,551 202561,489 2025-2030— N/A
WPL1,039 2025-20266,681 202586,405 2025-20322,520 2025
Fair Value of Financial Instruments At December 31, based on the maturities of the underlying contracts, the fair values of current derivative assets are included in “Other current assets,” non-current derivative assets are included in “Deferred charges and other,” current derivative liabilities are included in “Other current liabilities” and non-current derivative liabilities are included in “Other liabilities” on the balance sheets as follows (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Current derivative assets$49$41$33$29$16$12
Non-current derivative assets20341119915
Current derivative liabilities25269111615
Non-current derivative liabilities2632222430
Balance Sheet Offsetting However, if the fair value amounts of derivative instruments by counterparty were netted, derivative assets and derivative liabilities related to commodity contracts would have been presented on the balance sheets at December 31 as follows:
Alliant EnergyIPLWPL
GrossGrossGross
(as reported)Net(as reported)Net(as reported)Net
2025
Derivative assets$69$59$44$40$25$19
Derivative liabilities51411174034
2024
Derivative assets756448432721
Derivative liabilities58471384539
IPL [Member]  
Derivative [Line Items]  
Notional Amounts of Derivative Instruments As of December 31, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands):
ElectricityFTRsNatural GasDiesel Fuel
MWhsYearsMWhsYearsDthsYearsGallonsYears
2025
Alliant Energy1,682 202611,332 2026140,731 2026-2032— N/A
IPL634 20264,482 202660,773 2026-2030— N/A
WPL1,048 20266,850 202679,958 2026-2032— N/A
2024
Alliant Energy1,422 2025-202610,232 2025147,894 2025-20322,520 2025
IPL383 2025-20263,551 202561,489 2025-2030— N/A
WPL1,039 2025-20266,681 202586,405 2025-20322,520 2025
Fair Value of Financial Instruments At December 31, based on the maturities of the underlying contracts, the fair values of current derivative assets are included in “Other current assets,” non-current derivative assets are included in “Deferred charges and other,” current derivative liabilities are included in “Other current liabilities” and non-current derivative liabilities are included in “Other liabilities” on the balance sheets as follows (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Current derivative assets$49$41$33$29$16$12
Non-current derivative assets20341119915
Current derivative liabilities25269111615
Non-current derivative liabilities2632222430
Balance Sheet Offsetting However, if the fair value amounts of derivative instruments by counterparty were netted, derivative assets and derivative liabilities related to commodity contracts would have been presented on the balance sheets at December 31 as follows:
Alliant EnergyIPLWPL
GrossGrossGross
(as reported)Net(as reported)Net(as reported)Net
2025
Derivative assets$69$59$44$40$25$19
Derivative liabilities51411174034
2024
Derivative assets756448432721
Derivative liabilities58471384539
WPL [Member]  
Derivative [Line Items]  
Notional Amounts of Derivative Instruments As of December 31, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands):
ElectricityFTRsNatural GasDiesel Fuel
MWhsYearsMWhsYearsDthsYearsGallonsYears
2025
Alliant Energy1,682 202611,332 2026140,731 2026-2032— N/A
IPL634 20264,482 202660,773 2026-2030— N/A
WPL1,048 20266,850 202679,958 2026-2032— N/A
2024
Alliant Energy1,422 2025-202610,232 2025147,894 2025-20322,520 2025
IPL383 2025-20263,551 202561,489 2025-2030— N/A
WPL1,039 2025-20266,681 202586,405 2025-20322,520 2025
Fair Value of Financial Instruments At December 31, based on the maturities of the underlying contracts, the fair values of current derivative assets are included in “Other current assets,” non-current derivative assets are included in “Deferred charges and other,” current derivative liabilities are included in “Other current liabilities” and non-current derivative liabilities are included in “Other liabilities” on the balance sheets as follows (in millions):
Alliant EnergyIPLWPL
202520242025202420252024
Current derivative assets$49$41$33$29$16$12
Non-current derivative assets20341119915
Current derivative liabilities25269111615
Non-current derivative liabilities2632222430
Balance Sheet Offsetting However, if the fair value amounts of derivative instruments by counterparty were netted, derivative assets and derivative liabilities related to commodity contracts would have been presented on the balance sheets at December 31 as follows:
Alliant EnergyIPLWPL
GrossGrossGross
(as reported)Net(as reported)Net(as reported)Net
2025
Derivative assets$69$59$44$40$25$19
Derivative liabilities51411174034
2024
Derivative assets756448432721
Derivative liabilities58471384539
v3.25.4
Fair Value Measurements (Tables)
 12 Months Ended
Dec. 31, 2025
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Recurring Fair Value Measurements Carrying amounts and related estimated fair values of other financial instruments at December 31 were as follows (in millions):
Alliant Energy20252024
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$411 $411 $— $— $411 $52 $52 $— $— $52 
Commodity derivatives69 — 36 33 69 75 — 48 27 75 
Interest rate derivatives1 — 1 — 1 1 — 1 — 1 
Deferred proceeds126 — — 126 126 163 — — 163 163 
Liabilities:
Commodity derivatives51 — 50 1 51 58 — 56 2 58 
Long-term debt (incl. current maturities)12,028 — 11,748 — 11,748 9,848 — 9,577 — 9,577 
IPL20252024
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$— $— $— $— $— $9 $9 $— $— $9 
Commodity derivatives44 — 18 26 44 48 — 26 22 48 
Deferred proceeds126 — — 126 126 163 — — 163 163 
Liabilities:
Commodity derivatives11 — 10 1 11 13 — 11 2 13 
Long-term debt (incl. current maturities)4,680 — 4,445 — 4,445 4,090 — 3,736 — 3,736 
WPL20252024
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$25 $25 $— $— $25 $43 $43 $— $— $43 
Commodity derivatives25 — 18 7 25 27 — 22 5 27 
Liabilities:
Commodity derivatives40 — 40 — 40 45 — 45 — 45 
Long-term debt3,669 — 3,575 — 3,575 3,370 — 3,170 — 3,170 
Fair Value Measurements Using Significant Unobservable Inputs
Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions):
Alliant EnergyCommodity Contract Derivative
Assets and (Liabilities), netDeferred Proceeds
2025202420252024
Beginning balance, January 1$25$24$163$216
Total net gains (losses) included in changes in net assets (realized/unrealized)11(3)——
Purchases5059——
Sales(3)(3)——
Settlements (a)(51)(52)(37)(53)
Ending balance, December 31$32$25$126$163
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31$11($3)$—$—
IPLCommodity Contract Derivative
Assets and (Liabilities), netDeferred Proceeds
2025202420252024
Beginning balance, January 1$20$19$163$216
Total net gains (losses) included in changes in net assets (realized/unrealized)5(4)——
Purchases4045——
Sales(2)(2)——
Settlements (a)(38)(38)(37)(53)
Ending balance, December 31$25$20$126$163
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31$5($4)$—$—
WPLCommodity Contract Derivative
Assets and (Liabilities), net
20252024
Beginning balance, January 1$5$5
Total net gains included in changes in net assets (realized/unrealized)61
Purchases1014
Sales(1)(1)
Settlements(13)(14)
Ending balance, December 31$7$5
The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at December 31$6$1

(a)Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for expected credit losses associated with the receivables sold and cash amounts received from the receivables sold.
Fair Value Of Net Derivative Assets (Liabilities) The fair value of FTRs and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets at December 31 as follows (in millions):
Alliant EnergyIPLWPL
Excluding FTRsFTRsExcluding FTRsFTRsExcluding FTRsFTRs
2025$3$29$3$22$—$7
2024—25—20—5
IPL [Member]  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Recurring Fair Value Measurements Carrying amounts and related estimated fair values of other financial instruments at December 31 were as follows (in millions):
Alliant Energy20252024
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$411 $411 $— $— $411 $52 $52 $— $— $52 
Commodity derivatives69 — 36 33 69 75 — 48 27 75 
Interest rate derivatives1 — 1 — 1 1 — 1 — 1 
Deferred proceeds126 — — 126 126 163 — — 163 163 
Liabilities:
Commodity derivatives51 — 50 1 51 58 — 56 2 58 
Long-term debt (incl. current maturities)12,028 — 11,748 — 11,748 9,848 — 9,577 — 9,577 
IPL20252024
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$— $— $— $— $— $9 $9 $— $— $9 
Commodity derivatives44 — 18 26 44 48 — 26 22 48 
Deferred proceeds126 — — 126 126 163 — — 163 163 
Liabilities:
Commodity derivatives11 — 10 1 11 13 — 11 2 13 
Long-term debt (incl. current maturities)4,680 — 4,445 — 4,445 4,090 — 3,736 — 3,736 
WPL20252024
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$25 $25 $— $— $25 $43 $43 $— $— $43 
Commodity derivatives25 — 18 7 25 27 — 22 5 27 
Liabilities:
Commodity derivatives40 — 40 — 40 45 — 45 — 45 
Long-term debt3,669 — 3,575 — 3,575 3,370 — 3,170 — 3,170 
Fair Value Measurements Using Significant Unobservable Inputs
Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions):
Alliant EnergyCommodity Contract Derivative
Assets and (Liabilities), netDeferred Proceeds
2025202420252024
Beginning balance, January 1$25$24$163$216
Total net gains (losses) included in changes in net assets (realized/unrealized)11(3)——
Purchases5059——
Sales(3)(3)——
Settlements (a)(51)(52)(37)(53)
Ending balance, December 31$32$25$126$163
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31$11($3)$—$—
IPLCommodity Contract Derivative
Assets and (Liabilities), netDeferred Proceeds
2025202420252024
Beginning balance, January 1$20$19$163$216
Total net gains (losses) included in changes in net assets (realized/unrealized)5(4)——
Purchases4045——
Sales(2)(2)——
Settlements (a)(38)(38)(37)(53)
Ending balance, December 31$25$20$126$163
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31$5($4)$—$—
WPLCommodity Contract Derivative
Assets and (Liabilities), net
20252024
Beginning balance, January 1$5$5
Total net gains included in changes in net assets (realized/unrealized)61
Purchases1014
Sales(1)(1)
Settlements(13)(14)
Ending balance, December 31$7$5
The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at December 31$6$1

(a)Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for expected credit losses associated with the receivables sold and cash amounts received from the receivables sold.
Fair Value Of Net Derivative Assets (Liabilities) The fair value of FTRs and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets at December 31 as follows (in millions):
Alliant EnergyIPLWPL
Excluding FTRsFTRsExcluding FTRsFTRsExcluding FTRsFTRs
2025$3$29$3$22$—$7
2024—25—20—5
WPL [Member]  
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]  
Recurring Fair Value Measurements Carrying amounts and related estimated fair values of other financial instruments at December 31 were as follows (in millions):
Alliant Energy20252024
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$411 $411 $— $— $411 $52 $52 $— $— $52 
Commodity derivatives69 — 36 33 69 75 — 48 27 75 
Interest rate derivatives1 — 1 — 1 1 — 1 — 1 
Deferred proceeds126 — — 126 126 163 — — 163 163 
Liabilities:
Commodity derivatives51 — 50 1 51 58 — 56 2 58 
Long-term debt (incl. current maturities)12,028 — 11,748 — 11,748 9,848 — 9,577 — 9,577 
IPL20252024
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$— $— $— $— $— $9 $9 $— $— $9 
Commodity derivatives44 — 18 26 44 48 — 26 22 48 
Deferred proceeds126 — — 126 126 163 — — 163 163 
Liabilities:
Commodity derivatives11 — 10 1 11 13 — 11 2 13 
Long-term debt (incl. current maturities)4,680 — 4,445 — 4,445 4,090 — 3,736 — 3,736 
WPL20252024
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$25 $25 $— $— $25 $43 $43 $— $— $43 
Commodity derivatives25 — 18 7 25 27 — 22 5 27 
Liabilities:
Commodity derivatives40 — 40 — 40 45 — 45 — 45 
Long-term debt3,669 — 3,575 — 3,575 3,370 — 3,170 — 3,170 
Fair Value Measurements Using Significant Unobservable Inputs
Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions):
Alliant EnergyCommodity Contract Derivative
Assets and (Liabilities), netDeferred Proceeds
2025202420252024
Beginning balance, January 1$25$24$163$216
Total net gains (losses) included in changes in net assets (realized/unrealized)11(3)——
Purchases5059——
Sales(3)(3)——
Settlements (a)(51)(52)(37)(53)
Ending balance, December 31$32$25$126$163
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31$11($3)$—$—
IPLCommodity Contract Derivative
Assets and (Liabilities), netDeferred Proceeds
2025202420252024
Beginning balance, January 1$20$19$163$216
Total net gains (losses) included in changes in net assets (realized/unrealized)5(4)——
Purchases4045——
Sales(2)(2)——
Settlements (a)(38)(38)(37)(53)
Ending balance, December 31$25$20$126$163
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31$5($4)$—$—
WPLCommodity Contract Derivative
Assets and (Liabilities), net
20252024
Beginning balance, January 1$5$5
Total net gains included in changes in net assets (realized/unrealized)61
Purchases1014
Sales(1)(1)
Settlements(13)(14)
Ending balance, December 31$7$5
The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at December 31$6$1

(a)Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for expected credit losses associated with the receivables sold and cash amounts received from the receivables sold.
Fair Value Of Net Derivative Assets (Liabilities) The fair value of FTRs and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets at December 31 as follows (in millions):
Alliant EnergyIPLWPL
Excluding FTRsFTRsExcluding FTRsFTRsExcluding FTRsFTRs
2025$3$29$3$22$—$7
2024—25—20—5
v3.25.4
Commitments And Contingencies (Tables)
 12 Months Ended
Dec. 31, 2025
Long-term Purchase Commitment [Line Items]  
Other Purchase Commitments At December 31, 2025, the related minimum future commitments, excluding amounts for purchased power commitments that do not have minimum thresholds but require payment when electricity is generated by the provider and amounts for future commitments to deliver power to electric customers that do not have current minimum thresholds but will be billed for requirements when power is provided, were as follows (in millions):
Alliant Energy20262027202820292030ThereafterTotal
Natural gas$271$191$163$145$103$245$1,118
Coal764228———146
Other (a)571684317105
$404$249$199$149$106$262$1,369
IPL20262027202820292030ThereafterTotal
Natural gas$149$105$85$70$31$52$492
Coal341410———58
Other (a)2422221648
$207$121$97$72$33$68$598
WPL20262027202820292030ThereafterTotal
Natural gas$122$86$78$75$72$193$626
Coal422818———88
Other (a)251————26
$189$115$96$75$72$193$740

(a)Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2025.
Schedule of Environmental Liabilities At December 31, 2025, estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, which are not discounted, were as follows (in millions):
Alliant EnergyIPLWPL
Range of estimated future costs$7 -$29$5 -$18$2 -$11
Current and non-current environmental liabilities$12$8$4
IPL [Member]  
Long-term Purchase Commitment [Line Items]  
Other Purchase Commitments At December 31, 2025, the related minimum future commitments, excluding amounts for purchased power commitments that do not have minimum thresholds but require payment when electricity is generated by the provider and amounts for future commitments to deliver power to electric customers that do not have current minimum thresholds but will be billed for requirements when power is provided, were as follows (in millions):
Alliant Energy20262027202820292030ThereafterTotal
Natural gas$271$191$163$145$103$245$1,118
Coal764228———146
Other (a)571684317105
$404$249$199$149$106$262$1,369
IPL20262027202820292030ThereafterTotal
Natural gas$149$105$85$70$31$52$492
Coal341410———58
Other (a)2422221648
$207$121$97$72$33$68$598
WPL20262027202820292030ThereafterTotal
Natural gas$122$86$78$75$72$193$626
Coal422818———88
Other (a)251————26
$189$115$96$75$72$193$740

(a)Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2025.
Schedule of Environmental Liabilities At December 31, 2025, estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, which are not discounted, were as follows (in millions):
Alliant EnergyIPLWPL
Range of estimated future costs$7 -$29$5 -$18$2 -$11
Current and non-current environmental liabilities$12$8$4
WPL [Member]  
Long-term Purchase Commitment [Line Items]  
Other Purchase Commitments At December 31, 2025, the related minimum future commitments, excluding amounts for purchased power commitments that do not have minimum thresholds but require payment when electricity is generated by the provider and amounts for future commitments to deliver power to electric customers that do not have current minimum thresholds but will be billed for requirements when power is provided, were as follows (in millions):
Alliant Energy20262027202820292030ThereafterTotal
Natural gas$271$191$163$145$103$245$1,118
Coal764228———146
Other (a)571684317105
$404$249$199$149$106$262$1,369
IPL20262027202820292030ThereafterTotal
Natural gas$149$105$85$70$31$52$492
Coal341410———58
Other (a)2422221648
$207$121$97$72$33$68$598
WPL20262027202820292030ThereafterTotal
Natural gas$122$86$78$75$72$193$626
Coal422818———88
Other (a)251————26
$189$115$96$75$72$193$740

(a)Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2025.
Schedule of Environmental Liabilities At December 31, 2025, estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, which are not discounted, were as follows (in millions):
Alliant EnergyIPLWPL
Range of estimated future costs$7 -$29$5 -$18$2 -$11
Current and non-current environmental liabilities$12$8$4
v3.25.4
Segments Of Business (Tables)
 12 Months Ended
Dec. 31, 2025
Segment Reporting Information [Line Items]  
Schedule of Segments of Business Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s reportable segments, which represents the services provided to their customers, and reconciliation to consolidated amounts, was as follows (in millions):
Utility
TotalAlliant
ReportableEnergy
2025IPLWPLSegmentsOtherConsolidated
Electric utility revenues$1,896 $1,801 $3,697 N/A$3,697
Gas utility revenues265 260 525 N/A525
Other revenues47 4 51 $89140
Total revenues2,208 2,065 4,273 894,362
Electric production fuel and purchased power expense283 459 742 N/A742
Electric transmission service expense422 203 625 N/A625
Cost of gas sold expense130 133 263 N/A263
Other operation and maintenance expense (a)373 306 679 61740
Other segment items:
Depreciation and amortization expense463 370 833 13846
Interest expense211173384128512
Equity income from unconsolidated investments, net— (2)(2)(58)(60)
Income tax benefit(127)(14)(141)(8)(149)
Other (b)(4)3632 133
Net income (loss)457401858(48)810
Total assets12,495 10,655 23,150 1,84124,991
Investments in equity method subsidiaries5 19 24 650674
Construction and acquisition expenditures1,473 804 2,277 2062,483
Utility
TotalAlliant
ReportableEnergy
2024
IPLWPLSegmentsOtherConsolidated
Electric utility revenues$1,747 $1,625 $3,372 N/A$3,372
Gas utility revenues250 215 465 N/A465
Other revenues49 5 54 $90144
Total revenues2,046 1,845 3,891 903,981
Electric production fuel and purchased power expense269 359 628 N/A628
Electric transmission service expense417 196 613 N/A613
Cost of gas sold expense123 101 224 N/A224
Asset valuation charge for IPL’s Lansing Generating Station60 — 60 N/A60
Other operation and maintenance expense358 279 637 39676
Other segment items:
Depreciation and amortization expense404 357 761 11772
Interest expense177 165 342 107449
Equity income from unconsolidated investments, net— (2)(2)(59)(61)
Income tax expense (benefit)(129)11 (118)4(114)
Other (b)5 34 39 544
Net income (loss)362 345 707 (17)690
Total assets11,407 10,106 21,513 1,20122,714
Investments in equity method subsidiaries5 17 22 601623
Construction and acquisition expenditures1,224 828 2,052 1972,249
Utility
TotalAlliant
ReportableEnergy
2023 (amounts may not foot due to rounding)
IPLWPLSegmentsOtherConsolidated
Electric utility revenues$1,761 $1,584 $3,345 N/A$3,345
Gas utility revenues300 240 540 N/A540
Other revenues49 3 52 $90142
Total revenues2,110 1,827 3,937 904,027
Electric production fuel and purchased power expense282 455 737 N/A736
Electric transmission service expense420 163 583 N/A583
Cost of gas sold expense166 134 300 N/A299
Other operation and maintenance expense353 271 624 51675
Other segment items:
Depreciation and amortization expense388 280 668 8676
Interest expense155 149 304 90394
Equity income from unconsolidated investments, net— (3)(3)(58)(61)
Income tax expense (benefit)(58)60 2 24
Other (b)38 (27)11 518
Net income (loss)366 345 711 (8)703
Total assets10,489 9,634 20,123 1,11421,237
Investments in equity method subsidiaries5 16 21 564585
Construction and acquisition expenditures712 1,019 1,731 1231,854

(a)Alliant Energy’s non-utility holdings include Travero’s wind turbine blade recycling services, which commenced commercial operations in 2024, and whose assets are primarily included in “Property, plant and equipment, net” on Alliant Energy’s balance sheets. Alliant Energy suspended production of Travero’s wind turbine blade recycling services in November 2025 based on a review of strategic options, and as a result, a pre-tax non-cash asset valuation charge of $16 million was recorded to “Other operation and maintenance” in Alliant Energy’s income statement in 2025.
(b)Other segment items for each reportable segment include AFUDC, taxes other than income taxes, interest income, and other miscellaneous income and deductions.
IPL [Member]  
Segment Reporting Information [Line Items]  
Schedule of Segments of Business Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s reportable segments, which represents the services provided to their customers, and reconciliation to consolidated amounts, was as follows (in millions):
Utility
TotalAlliant
ReportableEnergy
2025IPLWPLSegmentsOtherConsolidated
Electric utility revenues$1,896 $1,801 $3,697 N/A$3,697
Gas utility revenues265 260 525 N/A525
Other revenues47 4 51 $89140
Total revenues2,208 2,065 4,273 894,362
Electric production fuel and purchased power expense283 459 742 N/A742
Electric transmission service expense422 203 625 N/A625
Cost of gas sold expense130 133 263 N/A263
Other operation and maintenance expense (a)373 306 679 61740
Other segment items:
Depreciation and amortization expense463 370 833 13846
Interest expense211173384128512
Equity income from unconsolidated investments, net— (2)(2)(58)(60)
Income tax benefit(127)(14)(141)(8)(149)
Other (b)(4)3632 133
Net income (loss)457401858(48)810
Total assets12,495 10,655 23,150 1,84124,991
Investments in equity method subsidiaries5 19 24 650674
Construction and acquisition expenditures1,473 804 2,277 2062,483
Utility
TotalAlliant
ReportableEnergy
2024
IPLWPLSegmentsOtherConsolidated
Electric utility revenues$1,747 $1,625 $3,372 N/A$3,372
Gas utility revenues250 215 465 N/A465
Other revenues49 5 54 $90144
Total revenues2,046 1,845 3,891 903,981
Electric production fuel and purchased power expense269 359 628 N/A628
Electric transmission service expense417 196 613 N/A613
Cost of gas sold expense123 101 224 N/A224
Asset valuation charge for IPL’s Lansing Generating Station60 — 60 N/A60
Other operation and maintenance expense358 279 637 39676
Other segment items:
Depreciation and amortization expense404 357 761 11772
Interest expense177 165 342 107449
Equity income from unconsolidated investments, net— (2)(2)(59)(61)
Income tax expense (benefit)(129)11 (118)4(114)
Other (b)5 34 39 544
Net income (loss)362 345 707 (17)690
Total assets11,407 10,106 21,513 1,20122,714
Investments in equity method subsidiaries5 17 22 601623
Construction and acquisition expenditures1,224 828 2,052 1972,249
Utility
TotalAlliant
ReportableEnergy
2023 (amounts may not foot due to rounding)
IPLWPLSegmentsOtherConsolidated
Electric utility revenues$1,761 $1,584 $3,345 N/A$3,345
Gas utility revenues300 240 540 N/A540
Other revenues49 3 52 $90142
Total revenues2,110 1,827 3,937 904,027
Electric production fuel and purchased power expense282 455 737 N/A736
Electric transmission service expense420 163 583 N/A583
Cost of gas sold expense166 134 300 N/A299
Other operation and maintenance expense353 271 624 51675
Other segment items:
Depreciation and amortization expense388 280 668 8676
Interest expense155 149 304 90394
Equity income from unconsolidated investments, net— (3)(3)(58)(61)
Income tax expense (benefit)(58)60 2 24
Other (b)38 (27)11 518
Net income (loss)366 345 711 (8)703
Total assets10,489 9,634 20,123 1,11421,237
Investments in equity method subsidiaries5 16 21 564585
Construction and acquisition expenditures712 1,019 1,731 1231,854

(a)Alliant Energy’s non-utility holdings include Travero’s wind turbine blade recycling services, which commenced commercial operations in 2024, and whose assets are primarily included in “Property, plant and equipment, net” on Alliant Energy’s balance sheets. Alliant Energy suspended production of Travero’s wind turbine blade recycling services in November 2025 based on a review of strategic options, and as a result, a pre-tax non-cash asset valuation charge of $16 million was recorded to “Other operation and maintenance” in Alliant Energy’s income statement in 2025.
(b)Other segment items for each reportable segment include AFUDC, taxes other than income taxes, interest income, and other miscellaneous income and deductions.
WPL [Member]  
Segment Reporting Information [Line Items]  
Schedule of Segments of Business Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s reportable segments, which represents the services provided to their customers, and reconciliation to consolidated amounts, was as follows (in millions):
Utility
TotalAlliant
ReportableEnergy
2025IPLWPLSegmentsOtherConsolidated
Electric utility revenues$1,896 $1,801 $3,697 N/A$3,697
Gas utility revenues265 260 525 N/A525
Other revenues47 4 51 $89140
Total revenues2,208 2,065 4,273 894,362
Electric production fuel and purchased power expense283 459 742 N/A742
Electric transmission service expense422 203 625 N/A625
Cost of gas sold expense130 133 263 N/A263
Other operation and maintenance expense (a)373 306 679 61740
Other segment items:
Depreciation and amortization expense463 370 833 13846
Interest expense211173384128512
Equity income from unconsolidated investments, net— (2)(2)(58)(60)
Income tax benefit(127)(14)(141)(8)(149)
Other (b)(4)3632 133
Net income (loss)457401858(48)810
Total assets12,495 10,655 23,150 1,84124,991
Investments in equity method subsidiaries5 19 24 650674
Construction and acquisition expenditures1,473 804 2,277 2062,483
Utility
TotalAlliant
ReportableEnergy
2024
IPLWPLSegmentsOtherConsolidated
Electric utility revenues$1,747 $1,625 $3,372 N/A$3,372
Gas utility revenues250 215 465 N/A465
Other revenues49 5 54 $90144
Total revenues2,046 1,845 3,891 903,981
Electric production fuel and purchased power expense269 359 628 N/A628
Electric transmission service expense417 196 613 N/A613
Cost of gas sold expense123 101 224 N/A224
Asset valuation charge for IPL’s Lansing Generating Station60 — 60 N/A60
Other operation and maintenance expense358 279 637 39676
Other segment items:
Depreciation and amortization expense404 357 761 11772
Interest expense177 165 342 107449
Equity income from unconsolidated investments, net— (2)(2)(59)(61)
Income tax expense (benefit)(129)11 (118)4(114)
Other (b)5 34 39 544
Net income (loss)362 345 707 (17)690
Total assets11,407 10,106 21,513 1,20122,714
Investments in equity method subsidiaries5 17 22 601623
Construction and acquisition expenditures1,224 828 2,052 1972,249
Utility
TotalAlliant
ReportableEnergy
2023 (amounts may not foot due to rounding)
IPLWPLSegmentsOtherConsolidated
Electric utility revenues$1,761 $1,584 $3,345 N/A$3,345
Gas utility revenues300 240 540 N/A540
Other revenues49 3 52 $90142
Total revenues2,110 1,827 3,937 904,027
Electric production fuel and purchased power expense282 455 737 N/A736
Electric transmission service expense420 163 583 N/A583
Cost of gas sold expense166 134 300 N/A299
Other operation and maintenance expense353 271 624 51675
Other segment items:
Depreciation and amortization expense388 280 668 8676
Interest expense155 149 304 90394
Equity income from unconsolidated investments, net— (3)(3)(58)(61)
Income tax expense (benefit)(58)60 2 24
Other (b)38 (27)11 518
Net income (loss)366 345 711 (8)703
Total assets10,489 9,634 20,123 1,11421,237
Investments in equity method subsidiaries5 16 21 564585
Construction and acquisition expenditures712 1,019 1,731 1231,854

(a)Alliant Energy’s non-utility holdings include Travero’s wind turbine blade recycling services, which commenced commercial operations in 2024, and whose assets are primarily included in “Property, plant and equipment, net” on Alliant Energy’s balance sheets. Alliant Energy suspended production of Travero’s wind turbine blade recycling services in November 2025 based on a review of strategic options, and as a result, a pre-tax non-cash asset valuation charge of $16 million was recorded to “Other operation and maintenance” in Alliant Energy’s income statement in 2025.
(b)Other segment items for each reportable segment include AFUDC, taxes other than income taxes, interest income, and other miscellaneous income and deductions.
v3.25.4
Related Parties (Tables)
 12 Months Ended
Dec. 31, 2025
Related Party Transaction [Line Items]  
Services Provided, Sales Credited And Purchases Billed The amounts billed for services provided, sales credited and purchases were as follows (in millions):
IPLWPL
202520242023202520242023
Corporate Services billings$194$183$181$189$171$163
Sales credited27—111318455
Purchases billed416430431755435
Net Intercompany Payables
As of December 31, net intercompany payables to Corporate Services were as follows (in millions):
20252024
IPL$135$135
WPL8464
Related Amounts Billed Between Parties The related amounts billed between the parties were as follows (in millions):
202520242023
ATC billings to WPL$162$152$159
WPL billings to ATC271620
IPL [Member]  
Related Party Transaction [Line Items]  
Services Provided, Sales Credited And Purchases Billed The amounts billed for services provided, sales credited and purchases were as follows (in millions):
IPLWPL
202520242023202520242023
Corporate Services billings$194$183$181$189$171$163
Sales credited27—111318455
Purchases billed416430431755435
Net Intercompany Payables
As of December 31, net intercompany payables to Corporate Services were as follows (in millions):
20252024
IPL$135$135
WPL8464
WPL [Member]  
Related Party Transaction [Line Items]  
Services Provided, Sales Credited And Purchases Billed The amounts billed for services provided, sales credited and purchases were as follows (in millions):
IPLWPL
202520242023202520242023
Corporate Services billings$194$183$181$189$171$163
Sales credited27—111318455
Purchases billed416430431755435
Net Intercompany Payables
As of December 31, net intercompany payables to Corporate Services were as follows (in millions):
20252024
IPL$135$135
WPL8464
Related Amounts Billed Between Parties The related amounts billed between the parties were as follows (in millions):
202520242023
ATC billings to WPL$162$152$159
WPL billings to ATC271620
v3.25.4
Condensed Parent Company Financial Statements (Tables)
 12 Months Ended
Dec. 31, 2025
Condensed Financial Information Disclosure [Abstract]  
Condensed Statements of Income
ALLIANT ENERGY CORPORATION (Parent Company Only)Year Ended December 31,
CONDENSED STATEMENTS OF INCOME202520242023
(in millions)
Operating expenses$4 $3 $3 
Operating loss(4)(3)(3)
Other (income) and deductions:
Equity earnings from consolidated subsidiaries(863)(734)(742)
Interest expense57 40 34 
Other(3)5 4 
Total other (income) and deductions(809)(689)(704)
Income before income taxes805 686 701 
Income tax benefit(6)(3)(5)
Net income$811 $689 $706 
Refer to accompanying Notes to Condensed Financial Statements.
Condensed Balance Sheets
ALLIANT ENERGY CORPORATION (Parent Company Only)December 31,
CONDENSED BALANCE SHEETS20252024
(in millions)
ASSETS
Current assets:
Cash and cash equivalents$512 $— 
Notes receivable from affiliated companies114 103 
Income tax refunds receivable12 12 
Other6 2 
Total current assets644 117 
Investments:
Investments in consolidated subsidiaries9,784 9,123 
Other1 1 
Total investments9,785 9,124 
Other assets102 84 
Total assets$10,531 $9,325 
LIABILITIES AND EQUITY
Current liabilities:
Current maturities of long-term debt$574 $571 
Commercial paper— 325 
Notes payable to affiliated companies1,300 1,401 
Other21 10 
Total current liabilities1,895 2,307 
Long-term debt, net (excluding current portion)1,286 — 
Other liabilities4 3 
Common equity:
Common stock and additional paid-in capital3,104 3,063 
Retained earnings4,255 3,965 
Accumulated other comprehensive income1 1 
Shares in deferred compensation trust(14)(14)
Total common equity7,346 7,015 
Total liabilities and equity$10,531 $9,325 
Refer to accompanying Notes to Condensed Financial Statements.
Condensed Statements of Cash Flows
ALLIANT ENERGY CORPORATION (Parent Company Only)Year Ended December 31,
CONDENSED STATEMENTS OF CASH FLOWS202520242023
(in millions)
Net cash flows from operating activities$529 $355 $445 
Cash flows used for investing activities:
Capital contributions to consolidated subsidiaries(365)(380)(325)
Net change in notes receivable from and payable to affiliates(113)326 (281)
Net cash flows used for investing activities(478)(54)(606)
Cash flows from (used for) financing activities:
Common stock dividends(521)(492)(456)
Proceeds from issuance of common stock, net23 23 246 
Proceeds from issuance of long-term debt1,286 — 565 
Net change in commercial paper(325)168 (195)
Other(2)— 1 
Net cash flows from (used for) financing activities461 (301)161 
Net increase (decrease) in cash, cash equivalents and restricted cash512 — — 
Cash, cash equivalents and restricted cash at beginning of period— — — 
Cash, cash equivalents and restricted cash at end of period$512 $— $— 
Supplemental cash flows information:
Cash (paid) received during the period for:
Interest($45)($40)($27)
Income taxes, net:
Federal$4 $11 $8 
State - Iowa— (15)(13)
State - Wisconsin— 12 27 
Total income taxes, net$4 $8 $22 
Refer to accompanying Notes to Condensed Financial Statements.
v3.25.4
Summary Of Significant Accounting Policies (Narrative) (Details)
$ in Millions
 12 Months Ended
Dec. 31, 2025
USD ($)
MW
Dec. 31, 2024
USD ($)
Dec. 31, 2023
Cash, Cash Equivalents and Restricted Cash:      
Money market fund investments $ 411 $ 52  
Money market fund investments interest rate, percentage 4.00%    
Non-utility wind farm in Oklahoma [Member]      
General:      
Ownership interest 50.00%    
IPL [Member]      
Cash, Cash Equivalents and Restricted Cash:      
Money market fund investments $ 0 9  
Money market fund investments interest rate, percentage 4.00%    
Property, Plant and Equipment:      
AFUDC accrual recorded, percentage of estimated CWIP 100.00%    
WPL [Member]      
Cash, Cash Equivalents and Restricted Cash:      
Money market fund investments $ 25 $ 43  
Money market fund investments interest rate, percentage 4.00%    
Property, Plant and Equipment:      
AFUDC accrual recorded, percentage of estimated CWIP 50.00%    
AFUDC accrual recorded, percentage earning a return as part of rate base 50.00%    
AFUDC rates, projects with approval, percent 100.00%    
Alliant Energy Finance, LLC [Member] | Non-utility wind farm in Oklahoma [Member]      
General:      
Ownership interest 50.00%    
Electric capacity of wind farm (in megawatts) | MW 225    
Sheboygan Falls Energy Facility [Member]      
General:      
Fossil-fueled EGU capacity (in megawatts) | MW 347    
Electric - generation [Member] | IPL [Member]      
Property, Plant and Equipment:      
Average rate of depreciation, percent 3.50% 3.30% 3.30%
Electric - generation [Member] | WPL [Member]      
Property, Plant and Equipment:      
Average rate of depreciation, percent 3.40% 3.40% 3.00%
Electric - distribution [Member] | IPL [Member]      
Property, Plant and Equipment:      
Average rate of depreciation, percent 2.90% 2.80% 2.80%
Electric - distribution [Member] | WPL [Member]      
Property, Plant and Equipment:      
Average rate of depreciation, percent 2.70% 2.70% 2.70%
v3.25.4
Summary Of Significant Accounting Policies (Schedule Of Average Rates Of Depreciation) (Details)
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Electric - generation [Member] | IPL [Member]      
Public Utility, Property, Plant and Equipment [Line Items]      
Average rate of depreciation, percent 3.50% 3.30% 3.30%
Electric - generation [Member] | WPL [Member]      
Public Utility, Property, Plant and Equipment [Line Items]      
Average rate of depreciation, percent 3.40% 3.40% 3.00%
Electric - distribution [Member] | IPL [Member]      
Public Utility, Property, Plant and Equipment [Line Items]      
Average rate of depreciation, percent 2.90% 2.80% 2.80%
Electric - distribution [Member] | WPL [Member]      
Public Utility, Property, Plant and Equipment [Line Items]      
Average rate of depreciation, percent 2.70% 2.70% 2.70%
Electric - other [Member] | IPL [Member]      
Public Utility, Property, Plant and Equipment [Line Items]      
Average rate of depreciation, percent 3.60% 5.20% 5.60%
Electric - other [Member] | WPL [Member]      
Public Utility, Property, Plant and Equipment [Line Items]      
Average rate of depreciation, percent 4.20% 6.10% 6.30%
Gas [Member] | IPL [Member]      
Public Utility, Property, Plant and Equipment [Line Items]      
Average rate of depreciation, percent 3.30% 3.30% 3.30%
Gas [Member] | WPL [Member]      
Public Utility, Property, Plant and Equipment [Line Items]      
Average rate of depreciation, percent 2.40% 2.50% 2.50%
Other [Member] | IPL [Member]      
Public Utility, Property, Plant and Equipment [Line Items]      
Average rate of depreciation, percent 5.60% 4.60% 6.20%
Other [Member] | WPL [Member]      
Public Utility, Property, Plant and Equipment [Line Items]      
Average rate of depreciation, percent 4.50% 4.40% 4.60%
v3.25.4
Summary Of Significant Accounting Policies (Schedule Of Allowance For Funds Used During Construction Recovery Rate) (Details)
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
IPL [Member]      
Public Utility, Property, Plant and Equipment [Line Items]      
Recovery rates, percent 7.10% 7.00% 7.00%
WPL [Member] | WPL (retail jurisdiction) [Member]      
Public Utility, Property, Plant and Equipment [Line Items]      
Recovery rates, percent 7.40% 7.40% 7.40%
WPL [Member] | WPL (wholesale jurisdiction) [Member]      
Public Utility, Property, Plant and Equipment [Line Items]      
Recovery rates, percent 6.60% 7.10% 7.10%
v3.25.4
Regulatory Matters (Narrative) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Regulatory Matters [Line Items]        
Regulatory assets $ 2,274 $ 2,274    
Collected from retail electric customers 3,697 3,372 $ 3,345  
Regulatory liabilities 1,201 1,028    
IPL [Member]        
Regulatory Matters [Line Items]        
Regulatory assets not earning a return 165      
Regulatory assets 1,616 1,586    
Collected from retail electric customers 1,896 1,747 1,761  
Regulatory liabilities 586 546    
WPL [Member]        
Regulatory Matters [Line Items]        
Regulatory assets not earning a return 28      
Regulatory assets 658 688    
Collected from retail electric customers 1,801 1,625 1,584  
Regulatory liabilities 615 482    
2022 Test Period Fuel-related Costs [Member] | WPL [Member]        
Regulatory Matters [Line Items]        
Regulatory assets       $ 117
Collected from retail electric customers 52 50 12  
2023 Test Period Fuel-related Costs | WPL [Member]        
Regulatory Matters [Line Items]        
Regulatory liabilities     $ 34  
2024 Test Period Retail Electric [Member] | WPL [Member]        
Regulatory Matters [Line Items]        
Authorized increase (decrease) in final rates, amount   49    
2024 Test Period Retail Gas [Member] | WPL [Member]        
Regulatory Matters [Line Items]        
Authorized increase (decrease) in final rates, amount   13    
2025 Test Period Retail Electric [Member] | WPL [Member]        
Regulatory Matters [Line Items]        
Authorized increase (decrease) in final rates, amount 60      
October 2024 Through September 2025 Test Period Retail Electric [Member] | IPL [Member]        
Regulatory Matters [Line Items]        
Authorized increase (decrease) in final rates, amount   185    
October 2024 Through September 2025 Test Period Retail Gas [Member] | IPL [Member]        
Regulatory Matters [Line Items]        
Authorized increase (decrease) in final rates, amount   $ 10    
Two Thousand Twenty six Test Period Retail Electric | WPL [Member]        
Regulatory Matters [Line Items]        
Authorized increase (decrease) in final rates, amount 69      
Two Thousand Twenty six Test Period Retail Gas | WPL [Member]        
Regulatory Matters [Line Items]        
Authorized increase (decrease) in final rates, amount 7      
Two Thousand Twenty seven Test Period Retail Electric | WPL [Member]        
Regulatory Matters [Line Items]        
Authorized increase (decrease) in final rates, amount 75      
Two Thousand Twenty SevenTest Period Retail Gas | WPL [Member]        
Regulatory Matters [Line Items]        
Authorized increase (decrease) in final rates, amount $ 5      
v3.25.4
Regulatory Matters (Regulatory Assets) (Details) - USD ($)
$ in Millions
Dec. 31, 2025
Dec. 31, 2024
Regulatory Assets [Line Items]    
Regulatory assets $ 2,274 $ 2,274
Tax-related [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 1,089 989
AROs [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 455 401
Pension and OPEB costs [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 274 315
Assets retired early [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 158 180
Commodity cost recovery [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 10 68
Derivatives [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 52 60
Non-service pension and OPEB costs [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 57 51
WPL's Western Wisconsin gas distribution expansion investments [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 39 42
Other [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 140 168
IPL [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 1,616 1,586
IPL [Member] | Tax-related [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 949 870
IPL [Member] | AROs [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 312 281
IPL [Member] | Pension and OPEB costs [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 136 157
IPL [Member] | Assets retired early [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 149 168
IPL [Member] | Commodity cost recovery [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 3 2
IPL [Member] | Derivatives [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 12 15
IPL [Member] | Non-service pension and OPEB costs [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 21 19
IPL [Member] | Other [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 34 74
WPL [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 658 688
WPL [Member] | Tax-related [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 140 119
WPL [Member] | AROs [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 143 120
WPL [Member] | Pension and OPEB costs [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 138 158
WPL [Member] | Assets retired early [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 9 12
WPL [Member] | Commodity cost recovery [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 7 66
WPL [Member] | Derivatives [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 40 45
WPL [Member] | Non-service pension and OPEB costs [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 36 32
WPL [Member] | WPL's Western Wisconsin gas distribution expansion investments [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 39 42
WPL [Member] | Other [Member]    
Regulatory Assets [Line Items]    
Regulatory assets $ 106 $ 94
v3.25.4
Regulatory Matters (Assets Retired Early) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Regulatory Assets [Line Items]      
Regulatory assets $ 2,274 $ 2,274  
Asset valuation charge for IPL's Lansing Generating Station 0 60 $ 0
Assets retired early [Member]      
Regulatory Assets [Line Items]      
Regulatory assets 158 180  
IPL [Member]      
Regulatory Assets [Line Items]      
Regulatory assets 1,616 1,586  
Asset valuation charge for IPL's Lansing Generating Station 0 60 $ 0
IPL [Member] | Assets retired early [Member]      
Regulatory Assets [Line Items]      
Regulatory assets 149 168  
IPL [Member] | Assets retired early [Member] | Lansing [Member]      
Regulatory Assets [Line Items]      
Regulatory assets 123    
IPL [Member] | Assets retired early [Member] | Analog Electric Meters [Member]      
Regulatory Assets [Line Items]      
Regulatory assets 10    
IPL [Member] | Assets retired early [Member] | Sutherland Units 1 and 3 [Member]      
Regulatory Assets [Line Items]      
Regulatory assets 11    
IPL [Member] | Assets retired early [Member] | M.L. Kapp Unit 2 [Member]      
Regulatory Assets [Line Items]      
Regulatory assets 5    
WPL [Member]      
Regulatory Assets [Line Items]      
Regulatory assets 658 688  
WPL [Member] | Assets retired early [Member]      
Regulatory Assets [Line Items]      
Regulatory assets 9 $ 12  
WPL [Member] | Assets retired early [Member] | Edgewater Unit 4 [Member]      
Regulatory Assets [Line Items]      
Regulatory assets $ 9    
v3.25.4
Regulatory Matters (Regulatory Liabilities) (Details) - USD ($)
$ in Millions
Dec. 31, 2025
Dec. 31, 2024
Regulatory Liabilities [Line Items]    
Regulatory liabilities $ 1,201 $ 1,028
Tax-related [Member]    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 690 582
Cost of removal obligations [Member]    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 366 347
Derivatives [Member]    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 47 53
Other [Member]    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 98 46
IPL [Member]    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 586 546
IPL [Member] | Tax-related [Member]    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 304 286
IPL [Member] | Cost of removal obligations [Member]    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 217 205
IPL [Member] | Derivatives [Member]    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 26 29
IPL [Member] | Other [Member]    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 39 26
WPL [Member]    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 615 482
WPL [Member] | Tax-related [Member]    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 386 296
WPL [Member] | Cost of removal obligations [Member]    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 149 142
WPL [Member] | Derivatives [Member]    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 21 24
WPL [Member] | Other [Member]    
Regulatory Liabilities [Line Items]    
Regulatory liabilities $ 59 $ 20
v3.25.4
Property, Plant and Equipment (Narrative) (Details)
Dec. 31, 2025
Corporate Services [Member] | Minimum [Member]  
Property, Plant and Equipment [Line Items]  
Property, plant and equipment, useful life 5 years
Corporate Services [Member] | Maximum [Member]  
Property, Plant and Equipment [Line Items]  
Property, plant and equipment, useful life 30 years
Sheboygan Falls Energy Facility [Member]  
Property, Plant and Equipment [Line Items]  
Property, plant and equipment, useful life 45 years
Software [Member]  
Property, Plant and Equipment [Line Items]  
Property, plant and equipment, useful life 5 years
v3.25.4
Property, Plant and Equipment (Property, Plant and Equipment) (Details)
$ in Millions
Dec. 31, 2025
USD ($)
MW
Dec. 31, 2024
USD ($)
Property, Plant and Equipment [Line Items]    
Electric plant anticipated to be retired early $ 0 $ 784
Total electric plant 21,747 20,346
Gas plant in service 1,938 1,863
Other plant in service 752 734
Accumulated depreciation (6,690) (6,229)
Net plant 17,747 16,714
Leased land for solar generation, net 190 189
Construction work in progress 1,742 1,215
Other, net 10 5
Total utility 19,689 18,123
Non-utility Generation, net 146 103
Corporate Services and other, net 509 475
Total non-utility and other 655 578
Total property, plant and equipment 20,344 18,701
Non-utility Generation, accumulated depreciation 81 78
Corporate Services and other, accumulated depreciation 305 289
Generation [Member]    
Property, Plant and Equipment [Line Items]    
Electric plant in service 12,757 11,156
Distribution [Member]    
Property, Plant and Equipment [Line Items]    
Electric plant in service 8,418 7,811
Other [Member]    
Property, Plant and Equipment [Line Items]    
Electric plant in service 572 595
IPL [Member]    
Property, Plant and Equipment [Line Items]    
Electric plant anticipated to be retired early 0 0
Total electric plant 11,311 10,653
Gas plant in service 1,020 981
Other plant in service 456 456
Accumulated depreciation (3,574) (3,360)
Net plant 9,213 8,730
Leased land for solar generation, net 52 53
Construction work in progress 1,166 548
Other, net 5 5
Total utility 10,436 9,336
Total property, plant and equipment $ 10,436 9,336
IPL [Member] | Wever    
Property, Plant and Equipment [Line Items]    
Battery Electric Capacity | MW 99  
IPL [Member] | Generation [Member]    
Property, Plant and Equipment [Line Items]    
Electric plant in service $ 6,251 5,924
IPL [Member] | Distribution [Member]    
Property, Plant and Equipment [Line Items]    
Electric plant in service 4,691 4,344
IPL [Member] | Other [Member]    
Property, Plant and Equipment [Line Items]    
Electric plant in service 369 385
WPL [Member]    
Property, Plant and Equipment [Line Items]    
Electric plant anticipated to be retired early 0 784
Total electric plant 10,436 9,693
Gas plant in service 918 882
Other plant in service 296 278
Accumulated depreciation (3,116) (2,869)
Net plant 8,534 7,984
Leased Sheboygan Falls Energy Facility, net 110 74
Leased land for solar generation, net 138 136
Construction work in progress 576 667
Other, net 5 0
Total utility 9,363 8,861
Total property, plant and equipment 9,363 8,861
Construction project cost target exceedance   205
Leased Sheboygan Falls Energy Facility, accumulated depreciation $ 120 116
Electric capacity of solar project | MW 1,100  
WPL [Member] | Grant County    
Property, Plant and Equipment [Line Items]    
Battery Electric Capacity | MW 100  
WPL [Member] | Wood County    
Property, Plant and Equipment [Line Items]    
Battery Electric Capacity | MW 75  
WPL [Member] | Generation [Member]    
Property, Plant and Equipment [Line Items]    
Electric plant in service $ 6,506 5,232
WPL [Member] | Distribution [Member]    
Property, Plant and Equipment [Line Items]    
Electric plant in service 3,727 3,467
WPL [Member] | Other [Member]    
Property, Plant and Equipment [Line Items]    
Electric plant in service $ 203 $ 210
v3.25.4
Property, Plant and Equipment (Equity and Debt AFUDC) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Property, Plant and Equipment [Line Items]      
Allowance for funds used during construction $ 89 $ 75 $ 100
Equity [Member]      
Property, Plant and Equipment [Line Items]      
Allowance for funds used during construction 63 54 74
Debt [Member]      
Property, Plant and Equipment [Line Items]      
Allowance for funds used during construction 26 21 26
IPL [Member]      
Property, Plant and Equipment [Line Items]      
Allowance for funds used during construction 56 43 21
IPL [Member] | Equity [Member]      
Property, Plant and Equipment [Line Items]      
Allowance for funds used during construction 39 31 15
IPL [Member] | Debt [Member]      
Property, Plant and Equipment [Line Items]      
Allowance for funds used during construction 17 12 6
WPL [Member]      
Property, Plant and Equipment [Line Items]      
Allowance for funds used during construction 33 32 79
WPL [Member] | Equity [Member]      
Property, Plant and Equipment [Line Items]      
Allowance for funds used during construction 24 23 59
WPL [Member] | Debt [Member]      
Property, Plant and Equipment [Line Items]      
Allowance for funds used during construction $ 9 $ 9 $ 20
v3.25.4
Jointly-Owned Electric Utility Plant (Details)
$ in Millions
Dec. 31, 2025
USD ($)
Jointly Owned Electric Utility Plant [Line Items]  
Electric Plant $ 2,541
Accumulated Provision for Depreciation 1,064
Construction Work in Progress 27
IPL [Member]  
Jointly Owned Electric Utility Plant [Line Items]  
Electric Plant 1,099
Accumulated Provision for Depreciation 528
Construction Work in Progress 16
WPL [Member]  
Jointly Owned Electric Utility Plant [Line Items]  
Electric Plant 1,442
Accumulated Provision for Depreciation 536
Construction Work in Progress $ 11
Ottumwa Unit 1 [Member] | IPL [Member]  
Jointly Owned Electric Utility Plant [Line Items]  
Ownership Interest % 48.00%
Electric Plant $ 662
Accumulated Provision for Depreciation 302
Construction Work in Progress $ 7
George Neal Unit 4 [Member] | IPL [Member]  
Jointly Owned Electric Utility Plant [Line Items]  
Ownership Interest % 25.70%
Electric Plant $ 201
Accumulated Provision for Depreciation 113
Construction Work in Progress $ 4
George Neal Unit 3 [Member] | IPL [Member]  
Jointly Owned Electric Utility Plant [Line Items]  
Ownership Interest % 28.00%
Electric Plant $ 192
Accumulated Provision for Depreciation 89
Construction Work in Progress $ 4
Louisa Unit 1 [Member] | IPL [Member]  
Jointly Owned Electric Utility Plant [Line Items]  
Ownership Interest % 4.00%
Electric Plant $ 44
Accumulated Provision for Depreciation 24
Construction Work in Progress $ 1
Columbia Units 1-2 and Energy Storage System [Member] | WPL [Member]  
Jointly Owned Electric Utility Plant [Line Items]  
Ownership Interest % 53.50%
Electric Plant $ 868
Accumulated Provision for Depreciation 407
Construction Work in Progress $ 4
West Riverside Energy Center and Solar Facility [Member] | WPL [Member]  
Jointly Owned Electric Utility Plant [Line Items]  
Ownership Interest % 56.60%
Electric Plant $ 456
Accumulated Provision for Depreciation 71
Construction Work in Progress $ 7
Forward Wind Energy Center [Member] | WPL [Member]  
Jointly Owned Electric Utility Plant [Line Items]  
Ownership Interest % 42.60%
Electric Plant $ 118
Accumulated Provision for Depreciation 58
Construction Work in Progress $ 0
v3.25.4
Receivables (Narrative) (Details)
$ in Millions
Dec. 31, 2025
USD ($)
Minimum [Member]  
Receivables [Line Items]  
Limit on cash proceeds to be received from third-party $ 5
Maximum [Member]  
Receivables [Line Items]  
Limit on cash proceeds to be received from third-party 110
Receivables Sold [Member] | IPL [Member]  
Receivables [Line Items]  
Available capacity $ 0
v3.25.4
Receivables (Details of Accounts Receivable) (Details) - USD ($)
$ in Millions
Dec. 31, 2025
Dec. 31, 2024
Receivables [Line Items]    
Customer $ 139 $ 113
Unbilled utility revenues 117 101
Deferred proceeds 126 163
Other 104 58
Allowance for expected credit losses (10) (8)
Accounts receivable, less allowance for expected credit losses 476 427
IPL [Member]    
Receivables [Line Items]    
Customer 0 0
Unbilled utility revenues 0 0
Deferred proceeds 126 163
Other 59 29
Allowance for expected credit losses 0 0
Accounts receivable, less allowance for expected credit losses 185 192
WPL [Member]    
Receivables [Line Items]    
Customer 126 98
Unbilled utility revenues 117 101
Other 39 29
Allowance for expected credit losses (9) (8)
Accounts receivable, less allowance for expected credit losses $ 273 $ 220
v3.25.4
Receivables (Gross Write-offs for Accounts Receivable (Details)
$ in Millions
 12 Months Ended
Dec. 31, 2025
USD ($)
Financing Receivable, Credit Quality Indicator [Line Items]  
Gross write-offs for accounts receivable, originated in 2023 $ 1
Gross write-offs for accounts receivable, originated in 2024 12
Gross write-offs for accounts receivable, originated in 2025 16
IPL [Member]  
Financing Receivable, Credit Quality Indicator [Line Items]  
Gross write-offs for accounts receivable, originated in 2023 1
Gross write-offs for accounts receivable, originated in 2024 8
Gross write-offs for accounts receivable, originated in 2025 9
WPL [Member]  
Financing Receivable, Credit Quality Indicator [Line Items]  
Gross write-offs for accounts receivable, originated in 2024 4
Gross write-offs for accounts receivable, originated in 2025 $ 7
v3.25.4
Receivables (Maximum And Average Outstanding Cash Proceeds) (Details) - IPL [Member] - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Maximum [Member]      
Receivables [Line Items]      
Outstanding aggregate cash proceeds (based on daily outstanding balances) $ 110 $ 110 $ 110
Average [Member]      
Receivables [Line Items]      
Outstanding aggregate cash proceeds (based on daily outstanding balances) $ 57 $ 31 $ 51
v3.25.4
Receivables (Receivables Sold Under The Agreement) (Details) - USD ($)
$ in Millions
Dec. 31, 2025
Dec. 31, 2024
Receivables [Line Items]    
Fair value of deferred proceeds $ 126 $ 163
IPL [Member]    
Receivables [Line Items]    
Fair value of deferred proceeds 126 163
Receivables Sold [Member] | IPL [Member]    
Receivables [Line Items]    
Customer accounts receivable 147 137
Unbilled utility revenues 104 108
Receivables sold to third party 251 245
Less: cash proceeds 110 70
Deferred proceeds 141 175
Less: allowance for expected credit losses 15 12
Fair value of deferred proceeds 126 163
Outstanding receivables past due $ 21 $ 21
v3.25.4
Receivables (Additional Attributes Of Receivables Sold Under The Agreement) (Details) - IPL [Member] - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Receivables [Line Items]      
Collections $ 2,279 $ 2,090 $ 2,233
Write-offs, net of recoveries $ 12 $ 12 $ 12
v3.25.4
Investments (Narrative) (Details)
Dec. 31, 2025
ATC LLC [Member]  
Schedule of Equity Method Investments [Line Items]  
Ownership interest 16.00%
ATC Holdco LLC [Member]  
Schedule of Equity Method Investments [Line Items]  
Ownership interest 20.00%
v3.25.4
Investments (Unconsolidated Equity Investments) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Schedule of Equity Method Investments [Line Items]      
Carrying value $ 674 $ 623 $ 585
Equity (income) / loss (60) (61) (61)
ATC Holdings [Member]      
Schedule of Equity Method Investments [Line Items]      
Carrying value 463 415  
Equity (income) / loss $ (59) (57) (49)
ATC LLC [Member]      
Schedule of Equity Method Investments [Line Items]      
Ownership interest 16.00%    
ATC Holdco LLC [Member]      
Schedule of Equity Method Investments [Line Items]      
Ownership interest 20.00%    
Non-utility wind farm in Oklahoma [Member]      
Schedule of Equity Method Investments [Line Items]      
Ownership interest 50.00%    
Carrying value $ 112 107  
Equity (income) / loss (9) (6) (7)
Corporate venture investments [Member]      
Schedule of Equity Method Investments [Line Items]      
Carrying value 76 78  
Equity (income) / loss 10 3 (2)
Other [Member]      
Schedule of Equity Method Investments [Line Items]      
Carrying value 23 23  
Equity (income) / loss (2) (1) (3)
Total [Member]      
Schedule of Equity Method Investments [Line Items]      
Carrying value 674 623  
Equity (income) / loss $ (60) $ (61) $ (61)
v3.25.4
Investments (Summary Financial Information) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Schedule of Equity Method Investments [Line Items]      
Revenues $ 4,362 $ 3,981 $ 4,027
Current assets 1,697 1,184  
Current liabilities 2,123 2,715  
Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]      
Schedule of Equity Method Investments [Line Items]      
Revenues 1,080 1,005 898
Operating income 482 433 384
Net income 91 434 $ 370
Current assets 254 223  
Non-current assets 10,818 9,930  
Current liabilities 879 524  
Non-current liabilities 4,243 3,933  
Noncontrolling interest $ 184 $ 221  
v3.25.4
Common Equity (Narrative) (Details) - USD ($)
$ / shares in Units, $ in Millions
 3 Months Ended 8 Months Ended 12 Months Ended 44 Months Ended
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2028
Schedule of Common Equity [Line Items]            
Shares available for issuance under the 2020 OIP, Shareowner Direct Plan and 401(k) Savings Plan (in shares) 11,000,000 11,000,000 11,000,000      
Proceeds from issuance of common stock, net     $ 23 $ 23 $ 246  
2023 At The Market Offering Program            
Schedule of Common Equity [Line Items]            
Proceeds from issuance of common stock, net         $ 223  
Common stock issued during the period, At-the-market offering program (in shares)         4,372,561  
Fees and commissions from issuance of common stock         $ 2  
2023 At The Market Offering Program | Maximum [Member]            
Schedule of Common Equity [Line Items]            
Proceeds from issuance of common stock, net         $ 225  
2025 At The Market Offering Program            
Schedule of Common Equity [Line Items]            
Common stock issued during the period, At-the-market offering program (in shares)     0 0    
Fees and commissions from issuance of common stock $ 2   $ 7      
Forward Contract Indexed to Issuer's Equity, Shares 3,831,429   14,595,532      
Aggregate Gross Sales Price Of Common Stock $ 258   $ 944      
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share   $ 64.44        
Forward Contract Indexed to Equity, Settlement, Number of Shares 14,595,532 14,595,532 14,595,532      
Forward Contract Indexed to Equity, Settlement, Cash, Amount $ 941 $ 941 $ 941      
Incremental Common Shares Attributable to Dilutive Effect of Equity Forward Agreements     569,944      
Forecast [Member] | 2025 At The Market Offering Program            
Schedule of Common Equity [Line Items]            
Proceeds from issuance of common stock, net           $ 1,300
v3.25.4
Common Equity (Common Share Activity) (Details) - shares
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Common Stock Oustanding [Roll Forward]      
Shares outstanding, January 1 (in shares) 256,690,222 256,096,848 251,134,966
Common stock issued during the period, Shareowner Direct Plan (in shares) 360,662 439,107 454,987
Common stock issued during the period, Equity-based compensation plans (in shares) 86,377 154,267 134,334
Shares outstanding, December 31 (in shares) 257,137,261 256,690,222 256,096,848
2023 At The Market Offering Program      
Schedule of Common Equity [Line Items]      
Common stock issued during the period, At-the-market offering program (in shares)     4,372,561
Common Stock Oustanding [Roll Forward]      
Common stock issued during the period, At-the-market offering program (in shares)     4,372,561
v3.25.4
Debt (Narrative) (Details)
 12 Months Ended
Dec. 31, 2025
USD ($)
Days
$ / shares
shares
Dec. 31, 2026
USD ($)
Dec. 31, 2024
USD ($)
Debt Instrument [Line Items]      
Line of credit facility, current borrowing capacity $ 1,300,000,000    
Long-term debt 12,125,000,000   $ 9,925,000,000
Current maturities of long-term debt 1,074,000,000   1,171,000,000
Long-term debt, fair value $ 11,748,000,000   9,577,000,000
Convertible Debt [Member]      
Debt Instrument [Line Items]      
Trading days | Days 20    
Trading days consecutive | Days 30    
3.875% senior notes, due 2026 [Member] | Convertible Debt [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 575,000,000    
Interest rate, percent 3.875%    
Trading days | Days 20    
Trading days consecutive | Days 10    
Principal amount of Notes conversion rate applied to $ 1,000    
Initial conversion ratio (in shares) 15.5461    
Initial conversion price | $ / shares $ 64.32    
Fundamental change repurchase conversion price, percent 100.00%    
Current maturities of long-term debt $ 574,000,000    
Long-term debt, carrying value     571,000,000
Unamortized debt issuance costs 1,000,000   4,000,000
Long-term debt, fair value $ 599,000,000   591,000,000
Shares included in diluted earnings per share (in shares) | shares 407,821    
Debt Instrument Convertible Threshold Business Days | Days 5    
3.875% senior notes, due 2026 [Member] | Convertible Debt [Member] | Maximum [Member]      
Debt Instrument [Line Items]      
Conversion price, percent 130.00%    
Threshold, product of last report sale price of common stock and conversion rate 98.00%    
3.875% senior notes, due 2026 [Member] | Senior Notes [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 575,000,000   $ 575,000,000
Interest rate, percent 3.875%   3.875%
Trading days consecutive | Days 30    
Three Point Two Five Percent Senior Notes Due Two Thousand Twenty Eight | Convertible Debt [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 575,000,000    
Interest rate, percent 3.25%    
Trading days | Days 5    
Trading days consecutive | Days 10    
Principal amount of Notes conversion rate applied to $ 1,000    
Initial conversion ratio (in shares) 13.1773    
Initial conversion price | $ / shares $ 75.89    
Fundamental change repurchase conversion price, percent 100.00%    
Long-term debt, carrying value $ 569,000,000    
Unamortized debt issuance costs 6,000,000    
Long-term debt, fair value $ 587,000,000    
Three Point Two Five Percent Senior Notes Due Two Thousand Twenty Eight | Convertible Debt [Member] | Maximum [Member]      
Debt Instrument [Line Items]      
Conversion price, percent 130.00%    
Threshold, product of last report sale price of common stock and conversion rate 98.00%    
Three Point Two Five Percent Senior Notes Due Two Thousand Twenty Eight | Senior Notes [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 575,000,000   $ 0
Interest rate, percent 3.25%    
Parent Company [Member]      
Debt Instrument [Line Items]      
Line of credit facility, current borrowing capacity $ 550,000,000    
Current maturities of long-term debt 574,000,000   571,000,000
IPL [Member]      
Debt Instrument [Line Items]      
Line of credit facility, current borrowing capacity 350,000,000    
Long-term debt 4,725,000,000   4,125,000,000
Current maturities of long-term debt 0   300,000,000
Long-term debt, fair value 4,445,000,000   3,736,000,000
WPL [Member]      
Debt Instrument [Line Items]      
Line of credit facility, current borrowing capacity 400,000,000    
Long-term debt 3,700,000,000   3,400,000,000
Current maturities of long-term debt 0   0
Long-term debt, fair value $ 3,575,000,000   $ 3,170,000,000
Forecast [Member] | Parent Company [Member]      
Debt Instrument [Line Items]      
Line of credit facility, maximum borrowing capacity   $ 1,000,000,000  
Forecast [Member] | IPL [Member]      
Debt Instrument [Line Items]      
Line of credit facility, maximum borrowing capacity   400,000,000  
Forecast [Member] | WPL [Member]      
Debt Instrument [Line Items]      
Line of credit facility, maximum borrowing capacity   $ 500,000,000  
v3.25.4
Debt (Credit Facilities) (Details) - USD ($)
$ in Millions
Dec. 31, 2025
Dec. 31, 2024
Commercial paper and borrowings under the single credit facility:    
Amount outstanding $ 88 $ 558
Weighted average interest rates 3.80% 4.50%
Available credit facility capacity $ 1,212 $ 742
IPL [Member]    
Commercial paper and borrowings under the single credit facility:    
Amount outstanding $ 88 $ 50
Weighted average interest rates 3.80% 4.60%
Available credit facility capacity $ 262 $ 250
WPL [Member]    
Commercial paper and borrowings under the single credit facility:    
Amount outstanding 0 $ 183
Weighted average interest rates   4.50%
Available credit facility capacity $ 400 $ 217
v3.25.4
Debt (Other Short-Term Borrowings) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Debt Instrument [Line Items]    
Maximum amount outstanding (based on daily outstanding balances) $ 741 $ 632
Average amount outstanding (based on daily outstanding balances) $ 349 $ 327
Weighted average interest rates 4.50% 5.30%
IPL [Member]    
Debt Instrument [Line Items]    
Maximum amount outstanding (based on daily outstanding balances) $ 141 $ 80
Average amount outstanding (based on daily outstanding balances) $ 25 $ 1
Weighted average interest rates 4.60% 5.10%
WPL [Member]    
Debt Instrument [Line Items]    
Maximum amount outstanding (based on daily outstanding balances) $ 297 $ 390
Average amount outstanding (based on daily outstanding balances) $ 176 $ 70
Weighted average interest rates 4.50% 5.40%
v3.25.4
Debt (Long-term Debt) (Details)
 12 Months Ended
Dec. 31, 2025
USD ($)
Days
Integer
$ / shares
Dec. 31, 2026
USD ($)
Dec. 31, 2024
USD ($)
Debt Instrument [Line Items]      
Long-term debt $ 12,125,000,000   $ 9,925,000,000
Current maturities (1,074,000,000)   (1,171,000,000)
Unamortized debt issuance costs (70,000,000)   (55,000,000)
Unamortized debt (discount) and premium, net (27,000,000)   (22,000,000)
Long-term debt, net 10,954,000,000   8,677,000,000
Long-term debt, fair value 11,748,000,000   9,577,000,000
Senior Debentures [Member]      
Debt Instrument [Line Items]      
Long-term debt 4,725,000,000   4,125,000,000
Senior Debentures [Member] | 4.1% senior debenture, due 2028 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 500,000,000   $ 500,000,000
Interest rate, percent 4.10%   4.10%
Senior Debentures [Member] | 3.6% senior debenture, due 2029 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 300,000,000   $ 300,000,000
Interest rate, percent 3.60%   3.60%
Senior Debentures [Member] | 2.3% senior debenture, due 2030 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 400,000,000   $ 400,000,000
Interest rate, percent 2.30%   2.30%
Senior Debentures [Member] | 5.7%, senior debentures, due 2033 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 300,000,000   $ 300,000,000
Interest rate, percent 5.70%   5.70%
Senior Debentures [Member] | 6.45% senior debenture, due 2033 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 100,000,000   $ 100,000,000
Interest rate, percent 6.45%   6.45%
Senior Debentures [Member] | 4.95% senior debenture, due 2034 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 350,000,000   $ 350,000,000
Interest rate, percent 4.95%   4.95%
Senior Debentures [Member] | 6.3% senior debenture, due 2034 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 125,000,000   $ 125,000,000
Interest rate, percent 6.30%   6.30%
Senior Debentures [Member] | Five Point Six Percent Senior Debentures Due Two Thousand Thirty Five      
Debt Instrument [Line Items]      
Long-term debt $ 600,000,000   $ 0
Interest rate, percent 5.60%    
Senior Debentures [Member] | 6.25% senior debenture, due 2039 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 300,000,000   $ 300,000,000
Interest rate, percent 6.25%   6.25%
Senior Debentures [Member] | 4.7% senior debenture, due 2043 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 250,000,000   $ 250,000,000
Interest rate, percent 4.70%   4.70%
Senior Debentures [Member] | 3.7% senior debenture, due 2046 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 300,000,000   $ 300,000,000
Interest rate, percent 3.70%   3.70%
Senior Debentures [Member] | 3.5% senior debenture, due 2049 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 300,000,000   $ 300,000,000
Interest rate, percent 3.50%   3.50%
Senior Debentures [Member] | 3.1% senior debenture, due 2051 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 300,000,000   $ 300,000,000
Interest rate, percent 3.10%   3.10%
Senior Debentures [Member] | 5.45% senior debenture, due 2054 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 300,000,000   $ 300,000,000
Interest rate, percent 5.45%   5.45%
Senior Debentures [Member] | Five Point Six Percent Senior Debenture Due Two Thousand Fifty Five      
Debt Instrument [Line Items]      
Long-term debt $ 300,000,000   $ 0
Interest rate, percent 5.60%    
Senior Debentures [Member] | 3.4% senior debenture, due 2025 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 0   $ 250,000,000
Interest rate, percent 3.40%   3.40%
Senior Debentures [Member] | 5.5% senior debenture, due 2025 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 0   $ 50,000,000
Interest rate, percent 5.50%   5.50%
Debentures [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 3,700,000,000   $ 3,400,000,000
Debentures [Member] | 3.05% debenture, due 2027 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 300,000,000   $ 300,000,000
Interest rate, percent 3.05%   3.05%
Debentures [Member] | 3% debenture, due 2029 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 350,000,000   $ 350,000,000
Interest rate, percent 3.00%   3.00%
Debentures [Member] | 1.95% debenture, due 2031 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 300,000,000   $ 300,000,000
Interest rate, percent 1.95%   1.95%
Debentures [Member] | 3.95% debenture, due 2032 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 600,000,000   $ 600,000,000
Interest rate, percent 3.95%   3.95%
Debentures [Member] | 4.95% debenture, due 2033 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 300,000,000   $ 300,000,000
Interest rate, percent 4.95%   4.95%
Debentures [Member] | 5.375% debenture, due 2034 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 300,000,000   $ 300,000,000
Interest rate, percent 5.375%   5.375%
Debentures [Member] | 6.25% debenture, due 2034 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 100,000,000   $ 100,000,000
Interest rate, percent 6.25%   6.25%
Debentures [Member] | 6.375% debenture, due 2037 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 300,000,000   $ 300,000,000
Interest rate, percent 6.375%   6.375%
Debentures [Member] | 7.6% debenture, due 2038 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 250,000,000   $ 250,000,000
Interest rate, percent 7.60%   7.60%
Debentures [Member] | 4.1% debenture, due 2044 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 250,000,000   $ 250,000,000
Interest rate, percent 4.10%   4.10%
Debentures [Member] | 3.65% debenture, due 2050 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 350,000,000   $ 350,000,000
Interest rate, percent 3.65%   3.65%
Debentures [Member] | five Point seven Percent Debentures Due Two Thousand Fifty five      
Debt Instrument [Line Items]      
Long-term debt $ 300,000,000    
Interest rate, percent 5.70%    
Senior Notes [Member] | 3.875% senior notes, due 2026 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 575,000,000   $ 575,000,000
Interest rate, percent 3.875%   3.875%
Trading days consecutive | Days 30    
Senior Notes [Member] | Three Point Two Five Percent Senior Notes Due Two Thousand Twenty Eight      
Debt Instrument [Line Items]      
Long-term debt $ 575,000,000   $ 0
Interest rate, percent 3.25%    
Other Long Term Debt [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 3,700,000,000   2,400,000,000
Junior Notes | Five Point Seven Five Percent Junior Subordinated Notes Due Two Thousand Fifty Six      
Debt Instrument [Line Items]      
Long-term debt $ 725,000,000    
Interest rate, percent 5.75%    
Convertible Debt [Member]      
Debt Instrument [Line Items]      
Trading days consecutive | Days 30    
Trading days | Days 20    
Convertible Debt [Member] | 3.875% senior notes, due 2026 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 575,000,000    
Current maturities $ (574,000,000)    
Interest rate, percent 3.875%    
Trading days consecutive | Days 10    
Trading days | Days 20    
Principal amount of Notes conversion rate applied to $ 1,000    
Initial conversion ratio (in shares) 15.5461    
Initial conversion price | $ / shares $ 64.32    
Fundamental change repurchase conversion price, percent 100.00%    
Unamortized debt issuance costs $ 1,000,000   4,000,000
Long-term debt, fair value $ 599,000,000   591,000,000
Convertible Debt [Member] | 3.875% senior notes, due 2026 [Member] | Maximum [Member]      
Debt Instrument [Line Items]      
Conversion price, percent 130.00%    
Threshold, product of last report sale price of common stock and conversion rate 98.00%    
Convertible Debt [Member] | Three Point Two Five Percent Senior Notes Due Two Thousand Twenty Eight      
Debt Instrument [Line Items]      
Long-term debt $ 575,000,000    
Interest rate, percent 3.25%    
Trading days consecutive | Days 10    
Trading days | Days 5    
Principal amount of Notes conversion rate applied to $ 1,000    
Initial conversion ratio (in shares) 13.1773    
Initial conversion price | $ / shares $ 75.89    
Fundamental change repurchase conversion price, percent 100.00%    
Unamortized debt issuance costs $ 6,000,000    
Long-term debt, fair value $ 587,000,000    
Convertible Debt [Member] | Three Point Two Five Percent Senior Notes Due Two Thousand Twenty Eight | Maximum [Member]      
Debt Instrument [Line Items]      
Conversion price, percent 130.00%    
Threshold, product of last report sale price of common stock and conversion rate 98.00%    
Junior Subordinated Debt      
Debt Instrument [Line Items]      
Debt Instrument Interest Reset Period | Integer 5    
Junior Subordinated Debt | Two Point Zero Seven Seven Percent Spread Junior Subordinated Notes      
Debt Instrument [Line Items]      
Debt Instrument, Basis Spread on Variable Rate 2.077%    
IPL [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 4,725,000,000   4,125,000,000
Current maturities 0   (300,000,000)
Unamortized debt issuance costs (30,000,000)   (25,000,000)
Unamortized debt (discount) and premium, net (15,000,000)   (10,000,000)
Long-term debt, net 4,680,000,000   3,790,000,000
Long-term debt, fair value 4,445,000,000   3,736,000,000
IPL [Member] | Senior Debentures [Member]      
Debt Instrument [Line Items]      
Long-term debt 4,725,000,000   4,125,000,000
IPL [Member] | Senior Debentures [Member] | 4.1% senior debenture, due 2028 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 500,000,000   $ 500,000,000
Interest rate, percent 4.10%   4.10%
IPL [Member] | Senior Debentures [Member] | 3.6% senior debenture, due 2029 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 300,000,000   $ 300,000,000
Interest rate, percent 3.60%   3.60%
IPL [Member] | Senior Debentures [Member] | 2.3% senior debenture, due 2030 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 400,000,000   $ 400,000,000
Interest rate, percent 2.30%   2.30%
IPL [Member] | Senior Debentures [Member] | 5.7%, senior debentures, due 2033 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 300,000,000   $ 300,000,000
Interest rate, percent 5.70%   5.70%
IPL [Member] | Senior Debentures [Member] | 6.45% senior debenture, due 2033 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 100,000,000   $ 100,000,000
Interest rate, percent 6.45%   6.45%
IPL [Member] | Senior Debentures [Member] | 4.95% senior debenture, due 2034 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 350,000,000   $ 350,000,000
Interest rate, percent 4.95%   4.95%
IPL [Member] | Senior Debentures [Member] | 6.3% senior debenture, due 2034 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 125,000,000   $ 125,000,000
Interest rate, percent 6.30%   6.30%
IPL [Member] | Senior Debentures [Member] | Five Point Six Percent Senior Debentures Due Two Thousand Thirty Five      
Debt Instrument [Line Items]      
Long-term debt $ 600,000,000   $ 0
Interest rate, percent 5.60%    
IPL [Member] | Senior Debentures [Member] | 6.25% senior debenture, due 2039 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 300,000,000   $ 300,000,000
Interest rate, percent 6.25%   6.25%
IPL [Member] | Senior Debentures [Member] | 4.7% senior debenture, due 2043 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 250,000,000   $ 250,000,000
Interest rate, percent 4.70%   4.70%
IPL [Member] | Senior Debentures [Member] | 3.7% senior debenture, due 2046 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 300,000,000   $ 300,000,000
Interest rate, percent 3.70%   3.70%
IPL [Member] | Senior Debentures [Member] | 3.5% senior debenture, due 2049 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 300,000,000   $ 300,000,000
Interest rate, percent 3.50%   3.50%
IPL [Member] | Senior Debentures [Member] | 3.1% senior debenture, due 2051 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 300,000,000   $ 300,000,000
Interest rate, percent 3.10%   3.10%
IPL [Member] | Senior Debentures [Member] | 5.45% senior debenture, due 2054 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 300,000,000   $ 300,000,000
Interest rate, percent 5.45%   5.45%
IPL [Member] | Senior Debentures [Member] | Five Point Six Percent Senior Debenture Due Two Thousand Fifty Five      
Debt Instrument [Line Items]      
Long-term debt $ 300,000,000   $ 0
Interest rate, percent 5.60%    
IPL [Member] | Senior Debentures [Member] | 3.4% senior debenture, due 2025 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 0   $ 250,000,000
Interest rate, percent 3.40%   3.40%
IPL [Member] | Senior Debentures [Member] | 5.5% senior debenture, due 2025 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 0   $ 50,000,000
Interest rate, percent 5.50%   5.50%
WPL [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 3,700,000,000   $ 3,400,000,000
Current maturities 0   0
Unamortized debt issuance costs (21,000,000)   (20,000,000)
Unamortized debt (discount) and premium, net (10,000,000)   (10,000,000)
Long-term debt, net 3,669,000,000   3,370,000,000
Long-term debt, fair value 3,575,000,000   3,170,000,000
WPL [Member] | Debentures [Member]      
Debt Instrument [Line Items]      
Long-term debt 3,700,000,000   3,400,000,000
WPL [Member] | Debentures [Member] | 3.05% debenture, due 2027 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 300,000,000   $ 300,000,000
Interest rate, percent 3.05%   3.05%
WPL [Member] | Debentures [Member] | 3% debenture, due 2029 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 350,000,000   $ 350,000,000
Interest rate, percent 3.00%   3.00%
WPL [Member] | Debentures [Member] | 1.95% debenture, due 2031 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 300,000,000   $ 300,000,000
Interest rate, percent 1.95%   1.95%
WPL [Member] | Debentures [Member] | 3.95% debenture, due 2032 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 600,000,000   $ 600,000,000
Interest rate, percent 3.95%   3.95%
WPL [Member] | Debentures [Member] | 4.95% debenture, due 2033 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 300,000,000   $ 300,000,000
Interest rate, percent 4.95%   4.95%
WPL [Member] | Debentures [Member] | 5.375% debenture, due 2034 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 300,000,000   $ 300,000,000
Interest rate, percent 5.375%   5.375%
WPL [Member] | Debentures [Member] | 6.25% debenture, due 2034 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 100,000,000   $ 100,000,000
Interest rate, percent 6.25%   6.25%
WPL [Member] | Debentures [Member] | 6.375% debenture, due 2037 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 300,000,000   $ 300,000,000
Interest rate, percent 6.375%   6.375%
WPL [Member] | Debentures [Member] | 7.6% debenture, due 2038 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 250,000,000   $ 250,000,000
Interest rate, percent 7.60%   7.60%
WPL [Member] | Debentures [Member] | 4.1% debenture, due 2044 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 250,000,000   $ 250,000,000
Interest rate, percent 4.10%   4.10%
WPL [Member] | Debentures [Member] | 3.65% debenture, due 2050 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 350,000,000   $ 350,000,000
Interest rate, percent 3.65%   3.65%
WPL [Member] | Debentures [Member] | five Point seven Percent Debentures Due Two Thousand Fifty five      
Debt Instrument [Line Items]      
Long-term debt $ 300,000,000    
Interest rate, percent 5.70%    
Alliant Energy Finance, LLC [Member] | Term Loan Credit Agreement [Member] | Term Loan Credit Agreement Through March Two Thousand Twenty Six      
Debt Instrument [Line Items]      
Long-term debt $ 300,000,000    
Interest rate, percent 5.00%    
Alliant Energy Finance, LLC [Member] | Term Loan Credit Agreement [Member] | Term Loan Credit Agreement Through March Two Thousand Twenty Six | Forecast [Member]      
Debt Instrument [Line Items]      
Long-term debt   $ 100,000,000  
Alliant Energy Finance, LLC [Member] | Term Loan Credit Agreement [Member] | Term loan credit agreement through March 2025, Variable Rate [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 0   $ 300,000,000
Interest rate, percent     6.00%
Alliant Energy Finance, LLC [Member] | Senior Notes [Member] | 1.4% senior notes, due 2026 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 200,000,000   $ 200,000,000
Interest rate, percent 1.40%   1.40%
Alliant Energy Finance, LLC [Member] | Senior Notes [Member] | 5.4% senior notes, due 2027 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 375,000,000   $ 375,000,000
Interest rate, percent 5.40%   5.40%
Alliant Energy Finance, LLC [Member] | Senior Notes [Member] | 4.25% senior notes, due 2028 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 300,000,000   $ 300,000,000
Interest rate, percent 4.25%   4.25%
Alliant Energy Finance, LLC [Member] | Senior Notes [Member] | 5.95% senior notes, due 2029 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 300,000,000   $ 300,000,000
Interest rate, percent 5.95%   5.95%
Alliant Energy Finance, LLC [Member] | Senior Notes [Member] | 3.6% senior notes, due 2032 [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 350,000,000   $ 350,000,000
Interest rate, percent 3.60%   3.60%
v3.25.4
Debt (Schedule Of Debt Maturities) (Details)
$ in Millions
Dec. 31, 2025
USD ($)
Debt Instrument [Line Items]  
2026 $ 1,075
2027 675
2028 1,375
2029 950
2030 400
Parent Company [Member]  
Debt Instrument [Line Items]  
2026 575
2027 0
2028 575
2029 0
2030 0
IPL [Member]  
Debt Instrument [Line Items]  
2026 0
2027 0
2028 500
2029 300
2030 400
WPL [Member]  
Debt Instrument [Line Items]  
2026 0
2027 300
2028 0
2029 350
2030 0
Alliant Energy Finance, LLC [Member]  
Debt Instrument [Line Items]  
2026 500
2027 375
2028 300
2029 300
2030 $ 0
v3.25.4
Leases (Narrative) (Details)
 12 Months Ended
Dec. 31, 2025
lease_renewal_period_option
Sheboygan Falls Energy Facility [Member] | WPL [Member]  
Leases [Line Items]  
Finance lease, renewal options (in number of renewal periods) 0
v3.25.4
Leases (Operating Leases) (Details) - USD ($)
$ in Millions
Dec. 31, 2025
Dec. 31, 2024
Leases [Line Items]    
Operating leases assets, Property, plant and equipment, net $ 21 $ 22
Operating leases liabilities, Other current liabilities 2 2
Operating leases liabilities, Other liabilities 19 20
Operating leases liabilities, Total $ 21 $ 22
Operating leases, Weighted average remaining lease term 10 years 11 years
Operating leases, Weighted average discount rate, percent 4.00% 4.00%
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration] Property, plant and equipment, net Property, plant and equipment, net
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List] Other Other
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List] Other Other
IPL [Member]    
Leases [Line Items]    
Operating leases assets, Property, plant and equipment, net $ 11 $ 12
Operating leases liabilities, Other current liabilities 1 1
Operating leases liabilities, Other liabilities 10 11
Operating leases liabilities, Total $ 11 $ 12
Operating leases, Weighted average remaining lease term 10 years 11 years
Operating leases, Weighted average discount rate, percent 4.00% 4.00%
WPL [Member]    
Leases [Line Items]    
Operating leases assets, Property, plant and equipment, net $ 9 $ 9
Operating leases liabilities, Other current liabilities 1 1
Operating leases liabilities, Other liabilities 8 8
Operating leases liabilities, Total $ 9 $ 9
Operating leases, Weighted average remaining lease term 11 years 12 years
Operating leases, Weighted average discount rate, percent 4.00% 4.00%
v3.25.4
Leases (Finance Lease) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Leases [Line Items]      
Finance lease assets, Property, plant and equipment, net $ 190 $ 189  
Finance lease liabilities, Other current liabilities 0 0  
Finance lease liabilities, Other liabilities 190 189  
Finance lease liabilities, Total $ 190 $ 189  
Finance lease, Remaining lease term 30 years 31 years  
Finance lease, Discount rate, percent 5.00% 5.00%  
Finance lease, Depreciation expense $ 0 $ 0 $ 1
Finance lease, Interest expense 9 8 6
Finance lease, Total expense $ 9 $ 8 7
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration] Property, plant and equipment, net Property, plant and equipment, net  
Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] Other Other  
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration] Other Other  
Leased land for solar generation [Member]      
Leases [Line Items]      
Finance lease assets, Property, plant and equipment, net $ 190 $ 189  
Finance lease liabilities, Other liabilities $ 190 $ 189  
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration] Property, plant and equipment, net Property, plant and equipment, net  
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration] Other Other  
IPL [Member]      
Leases [Line Items]      
Finance lease assets, Property, plant and equipment, net $ 52 $ 53  
Finance lease liabilities, Other current liabilities 0 0  
Finance lease liabilities, Other liabilities 52 53  
Finance lease liabilities, Total $ 52 $ 53  
Finance lease, Remaining lease term 27 years 28 years  
Finance lease, Discount rate, percent 5.00% 5.00%  
Finance lease, Depreciation expense $ 0 $ 0 0
Finance lease, Interest expense 3 2 1
Finance lease, Total expense 3 2 1
IPL [Member] | Leased land for solar generation [Member]      
Leases [Line Items]      
Finance lease assets, Property, plant and equipment, net 52 53  
Finance lease liabilities, Other liabilities 52 53  
WPL [Member]      
Leases [Line Items]      
Finance lease assets, Property, plant and equipment, net 248 210  
Finance lease liabilities, Other current liabilities 4 7  
Finance lease liabilities, Other liabilities 244 207  
Finance lease liabilities, Total $ 248 $ 214  
Finance lease, Remaining lease term 26 years 28 years  
Finance lease, Discount rate, percent 6.00% 5.00%  
Finance lease, Depreciation expense $ 2 $ 4 6
Finance lease, Interest expense 11 10 8
Finance lease, Total expense 13 14 $ 14
WPL [Member] | Sheboygan Falls Energy Facility [Member]      
Leases [Line Items]      
Finance lease assets, Property, plant and equipment, net 110 74  
Finance lease liabilities, Other current liabilities 4 7  
Finance lease liabilities, Other liabilities $ 106 $ 71  
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration] Property, plant and equipment, net Property, plant and equipment, net  
Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration] Other Other  
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration] Other Other  
WPL [Member] | Leased land for solar generation [Member]      
Leases [Line Items]      
Finance lease assets, Property, plant and equipment, net $ 138 $ 136  
Finance lease liabilities, Other liabilities $ 138 $ 136  
v3.25.4
Leases (Liabilities Arising from Obtaining Leased Assets (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Leases [Line Items]    
Finance lease liabilities arising from obtaining leased assets $ 1 $ 20
IPL [Member]    
Leases [Line Items]    
Finance lease liabilities arising from obtaining leased assets 0 20
WPL [Member]    
Leases [Line Items]    
Finance lease liabilities arising from obtaining leased assets $ 39 $ 0
v3.25.4
Leases (Expected Maturities of Operating and Finance Lease Liabilities (Details) - USD ($)
$ in Millions
Dec. 31, 2025
Dec. 31, 2024
Leases [Line Items]    
Operating Leases Liability, 2026 $ 3  
Operating Leases Liability, 2027 3  
Operating Leases Liability, 2028 3  
Operating Leases Liability, 2029 3  
Operating Leases Liability, 2030 2  
Operating Leases Liability, Thereafter 13  
Operating Leases Liability, Total 27  
Operating Leases Liability, Less: amount representing interest 6  
Operating Leases Liability, Present value of minimum lease payments 21 $ 22
Finance Lease Liability, 2026 9  
Finance Lease Liability, 2027 10  
Finance Lease Liability, 2028 10  
Finance Lease Liability, 2029 10  
Finance Lease Liability, 2030 10  
Finance Lease Liability, Thereafter 328  
Finance Lease Liability, Total 377  
Finance Lease Liability, Less: amount representing interest 187  
Finance Lease Liability, Present value of minimum lease payments 190 189
IPL [Member]    
Leases [Line Items]    
Operating Leases Liability, 2026 2  
Operating Leases Liability, 2027 1  
Operating Leases Liability, 2028 1  
Operating Leases Liability, 2029 1  
Operating Leases Liability, 2030 1  
Operating Leases Liability, Thereafter 8  
Operating Leases Liability, Total 14  
Operating Leases Liability, Less: amount representing interest 3  
Operating Leases Liability, Present value of minimum lease payments 11 12
Finance Lease Liability, 2026 3  
Finance Lease Liability, 2027 3  
Finance Lease Liability, 2028 3  
Finance Lease Liability, 2029 3  
Finance Lease Liability, 2030 3  
Finance Lease Liability, Thereafter 87  
Finance Lease Liability, Total 102  
Finance Lease Liability, Less: amount representing interest 50  
Finance Lease Liability, Present value of minimum lease payments 52 53
WPL [Member]    
Leases [Line Items]    
Operating Leases Liability, 2026 1  
Operating Leases Liability, 2027 1  
Operating Leases Liability, 2028 1  
Operating Leases Liability, 2029 1  
Operating Leases Liability, 2030 1  
Operating Leases Liability, Thereafter 7  
Operating Leases Liability, Total 12  
Operating Leases Liability, Less: amount representing interest 3  
Operating Leases Liability, Present value of minimum lease payments 9 9
Finance Lease Liability, 2026 18  
Finance Lease Liability, 2027 18  
Finance Lease Liability, 2028 19  
Finance Lease Liability, 2029 19  
Finance Lease Liability, 2030 19  
Finance Lease Liability, Thereafter 386  
Finance Lease Liability, Total 479  
Finance Lease Liability, Less: amount representing interest 231  
Finance Lease Liability, Present value of minimum lease payments $ 248 $ 214
v3.25.4
Disaggregation of Revenues (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Disaggregation of Revenue [Line Items]      
Revenues $ 4,362 $ 3,981 $ 4,027
IPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 2,208 2,046 2,110
WPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 2,065 1,845 1,827
Electric [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 3,697 3,372 3,345
Electric [Member] | IPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 1,896 1,747 1,761
Electric [Member] | WPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 1,801 1,625 1,584
Electric [Member] | Retail - Residential [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 1,339 1,236 1,220
Electric [Member] | Retail - Residential [Member] | IPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 661 640 641
Electric [Member] | Retail - Residential [Member] | WPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 678 596 579
Electric [Member] | Retail - Commercial [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 932 821 820
Electric [Member] | Retail - Commercial [Member] | IPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 609 525 519
Electric [Member] | Retail - Commercial [Member] | WPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 323 296 301
Electric [Member] | Retail - Industrial [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 1,034 952 968
Electric [Member] | Retail - Industrial [Member] | IPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 531 497 501
Electric [Member] | Retail - Industrial [Member] | WPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 503 455 467
Electric [Member] | Wholesale [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 184 200 213
Electric [Member] | Wholesale [Member] | IPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 39 61 62
Electric [Member] | Wholesale [Member] | WPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 145 139 151
Electric [Member] | Other [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 208 163 124
Electric [Member] | Other [Member] | IPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 56 24 38
Electric [Member] | Other [Member] | WPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 152 139 86
Gas [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 525 465 540
Gas [Member] | IPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 265 250 300
Gas [Member] | WPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 260 215 240
Gas [Member] | Retail - Residential [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 306 275 316
Gas [Member] | Retail - Residential [Member] | IPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 155 148 176
Gas [Member] | Retail - Residential [Member] | WPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 151 127 140
Gas [Member] | Retail - Commercial [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 153 133 163
Gas [Member] | Retail - Commercial [Member] | IPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 72 68 86
Gas [Member] | Retail - Commercial [Member] | WPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 81 65 77
Gas [Member] | Retail - Industrial [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 13 11 16
Gas [Member] | Retail - Industrial [Member] | IPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 7 7 11
Gas [Member] | Retail - Industrial [Member] | WPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 6 4 5
Gas [Member] | Other [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 53 46 45
Gas [Member] | Other [Member] | IPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 31 27 27
Gas [Member] | Other [Member] | WPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 22 19 18
Other Utility [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 51 54 52
Other Utility [Member] | IPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 47 49 49
Other Utility [Member] | WPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 4 5 3
Other Utility [Member] | Other [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 14 14 7
Other Utility [Member] | Other [Member] | IPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 10 9 4
Other Utility [Member] | Other [Member] | WPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 4 5 3
Other Utility [Member] | Steam [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 37 40 45
Other Utility [Member] | Steam [Member] | IPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 37 40 45
Non-Utility and Other [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 89 90 90
Non-Utility and Other [Member] | Other [Member]      
Disaggregation of Revenue [Line Items]      
Revenues $ 89 $ 90 $ 90
v3.25.4
Income Taxes (Narrative) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2027
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Income Tax [Line Items]          
Asset valuation charge for IPL's Lansing Generating Station   $ 0 $ 60 $ 0  
State income tax rate, percent   3.00% 1.00% 3.00%  
Income tax expense (benefit)   $ (149) $ (114) $ 4  
Income Tax Expense (Benefit), Continuing Operations, Adjustment of Deferred Tax (Asset) Liability   8      
State   33 15 36  
Tax-related [Member]          
Income Tax [Line Items]          
Reduction of tax-related regulatory assets     26 74  
Income tax expense (benefit)     11 10  
IPL [Member]          
Income Tax [Line Items]          
Asset valuation charge for IPL's Lansing Generating Station   $ 0 $ 60 $ 0  
State income tax rate, percent   (3.00%) (12.00%) (2.00%)  
Reduction of tax-related regulatory assets   $ (72) $ (2) $ 58  
Income tax expense (benefit)   (127) (129) (58)  
State   $ 2 (17) 17  
IPL [Member] | Tax-related [Member]          
Income Tax [Line Items]          
Reduction of tax-related regulatory assets     $ 26 $ 74  
WPL [Member]          
Income Tax [Line Items]          
State income tax rate, percent   7.00% 7.00% 5.00%  
Reduction of tax-related regulatory assets   $ 43 $ 72 $ (34)  
Income tax expense (benefit)   (14) 11 60  
State   $ 16 $ 7 $ 3  
Iowa State [Member]          
Income Tax [Line Items]          
State income tax rate, percent     7.10%   9.80%
Iowa State [Member] | Forecast [Member]          
Income Tax [Line Items]          
State income tax rate, percent 5.50%        
v3.25.4
Income Taxes (Schedule Of Components Of Income Tax) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Current tax expense (benefit):      
Federal $ 10 $ 13 $ (3)
State (1) (10) (6)
Deferred tax expense (benefit):      
Federal 59 60 100
State 33 15 36
Production tax credits (208) (177) (121)
Investment tax credits (42) (15) (1)
Provision recorded as a change in accrued interest 0 0 (1)
Income tax expense (benefit) (149) (114) 4
IPL [Member]      
Current tax expense (benefit):      
Federal (21) (19) (44)
State (10) (19) (21)
Deferred tax expense (benefit):      
Federal 36 38 87
State 2 (17) 17
Production tax credits (133) (108) (95)
Investment tax credits (1) (4) (1)
Provision recorded as a change in accrued interest 0 0 (1)
Income tax expense (benefit) (127) (129) (58)
WPL [Member]      
Current tax expense (benefit):      
Federal 38 37 48
State 18 23 25
Deferred tax expense (benefit):      
Federal 30 24 10
State 16 7 3
Production tax credits (75) (69) (26)
Investment tax credits (41) (11) 0
Provision recorded as a change in accrued interest 0 0 0
Income tax expense (benefit) $ (14) $ 11 $ 60
v3.25.4
Income Taxes (Schedule Of Effective Income Tax Rates) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Effective Tax Rate [Line Items]      
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount $ 139 $ 121 $ 149
Statutory federal income tax rate 21.00% 21.00% 21.00%
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount $ 22 $ 4 $ 21
State income taxes, net of federal benefits 3.00% 1.00% 3.00%
Effective Income Tax Rate Reconciliation, Tax Credit, Energy-Related, Amount $ (206) $ (171) $ (121)
Effective Income Tax Rate Reconciliation, Tax Credit, Energy-Related, Percent (31.00%) (30.00%) (17.00%)
Effective Income Tax Rate Reconciliation, Tax Credit, Investment, Amount $ (156) $ (42) $ (3)
Investment tax credits (24.00%) (7.00%) 0.00%
Effective Income Tax Rate Reconciliation, Tax Credit, Research, Amount $ (2) $ (6) $ 0
Effective Income Tax Rate Reconciliation, Tax Credit, Research, Percent 0.00% (1.00%) 0.00%
Effective Income Tax Rate Reconciliation, Tax credit regulatory deferrals Amount $ 112 $ 20 $ 2
Effective Income Tax Rate Reconciliation, Tax credit regulatory deferrals percent 17.00% 3.00% 0.00%
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Amount $ (1) $ 0 $ 0
Other credits 0.00% 0.00% 0.00%
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Amount $ 4 $ 2 $ (2)
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Percent 1.00% 0.00% 0.00%
Effective Income Tax Rate Reconciliation Effect Of Rate Making On Property Related Difference Amount $ (37) $ (33) $ (27)
Effective Income Tax Rate Reconciliation Effect Of Rate Making On Property Related Differences Percent (6.00%) (6.00%) (4.00%)
Effective Income Tax Rate Reconciliation Amortization Of Excess Deferred TaxesAmount $ (24) $ (13) $ (13)
Effective Income Tax Rate Reconciliation Amortization Of Excess Deferred Taxes Percent (4.00%) (2.00%) (2.00%)
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount $ 0 $ 4 $ (2)
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent 0.00% 1.00% 0.00%
Overall income tax rate (23.00%) (20.00%) 1.00%
Income tax benefit $ (149) $ (114) $ 4
IPL [Member]      
Effective Tax Rate [Line Items]      
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount $ 69 $ 49 $ 65
Statutory federal income tax rate 21.00% 21.00% 21.00%
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount $ (10) $ (27) $ (5)
State income taxes, net of federal benefits (3.00%) (12.00%) (2.00%)
Effective Income Tax Rate Reconciliation, Tax Credit, Energy-Related, Amount $ (133) $ (108) $ (95)
Effective Income Tax Rate Reconciliation, Tax Credit, Energy-Related, Percent (40.00%) (46.00%) (31.00%)
Effective Income Tax Rate Reconciliation, Tax Credit, Investment, Amount $ (43) $ (8) $ (2)
Investment tax credits (13.00%) (4.00%) (1.00%)
Effective Income Tax Rate Reconciliation, Tax credit regulatory deferrals Amount $ 42 $ 4 $ 1
Effective Income Tax Rate Reconciliation, Tax credit regulatory deferrals percent 13.00% 1.00% 0.00%
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Amount $ (1) $ (1) $ 0
Other credits 0.00% 0.00% 0.00%
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Amount $ 1 $ (1) $ (1)
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Percent 0.00% 0.00% 0.00%
Effective Income Tax Rate Reconciliation Effect Of Rate Making On Property Related Difference Amount $ (30) $ (24) $ (16)
Effective Income Tax Rate Reconciliation Effect Of Rate Making On Property Related Differences Percent (9.00%) (10.00%) (5.00%)
Effective Income Tax Rate Reconciliation Amortization Of Excess Deferred TaxesAmount $ (22) $ (13) $ (5)
Effective Income Tax Rate Reconciliation Amortization Of Excess Deferred Taxes Percent (7.00%) (5.00%) (1.00%)
Overall income tax rate (38.00%) (55.00%) (19.00%)
Income tax benefit $ (127) $ (129) $ (58)
WPL [Member]      
Effective Tax Rate [Line Items]      
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount $ 81 $ 75 $ 85
Statutory federal income tax rate 21.00% 21.00% 21.00%
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount $ 27 $ 23 $ 22
State income taxes, net of federal benefits 7.00% 7.00% 5.00%
Effective Income Tax Rate Reconciliation, Tax Credit, Energy-Related, Amount $ (73) $ (63) $ (26)
Effective Income Tax Rate Reconciliation, Tax Credit, Energy-Related, Percent (19.00%) (18.00%) (6.00%)
Effective Income Tax Rate Reconciliation, Tax Credit, Investment, Amount $ (114) $ (34) $ (1)
Investment tax credits (29.00%) (10.00%) 0.00%
Effective Income Tax Rate Reconciliation, Tax credit regulatory deferrals Amount $ 70 $ 17 $ 1
Effective Income Tax Rate Reconciliation, Tax credit regulatory deferrals percent 18.00% 4.00% 0.00%
Effective Income Tax Rate Reconciliation, Tax Credit, Other, Amount $ 0 $ (1) $ 0
Other credits 0.00% 0.00% 0.00%
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Amount $ 1 $ (1) $ (2)
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Percent 0.00% 0.00% 0.00%
Effective Income Tax Rate Reconciliation Effect Of Rate Making On Property Related Difference Amount $ (6) $ (5) $ (12)
Effective Income Tax Rate Reconciliation Effect Of Rate Making On Property Related Differences Percent (2.00%) (1.00%) (4.00%)
Effective Income Tax Rate Reconciliation Amortization Of Excess Deferred TaxesAmount $ 0 $ 0 $ (7)
Effective Income Tax Rate Reconciliation Amortization Of Excess Deferred Taxes Percent 0.00% 0.00% (1.00%)
Overall income tax rate (4.00%) 3.00% 15.00%
Income tax benefit $ (14) $ 11 $ 60
v3.25.4
Income Taxes (Schedule Of Deferred Tax Assets And Liabilities) (Details) - USD ($)
$ in Millions
Dec. 31, 2025
Dec. 31, 2024
Income Tax [Line Items]    
Deferred tax liabilities, property $ 2,828 $ 2,596
Deferred tax liabilities, other 167 178
Total deferred tax liabilities 3,134 2,909
Deferred tax assets, federal credit carryforwards 669 605
Deferred tax assets, net operating losses carryforwards - state 19 20
Deferred tax assets, other 143 98
Subtotal deferred tax assets 831 723
Deferred tax assets, valuation allowances (7) (2)
Total deferred tax assets 824 721
Total deferred tax liabilities, net 2,310 2,188
IPL [Member]    
Income Tax [Line Items]    
Deferred tax liabilities, property 1,666 1,521
Deferred tax liabilities, other 112 120
Total deferred tax liabilities 1,778 1,641
Deferred tax assets, federal credit carryforwards 455 426
Deferred tax assets, net operating losses carryforwards - state 1 1
Deferred tax assets, other 48 37
Subtotal deferred tax assets 504 464
Deferred tax assets, valuation allowances (4) (2)
Total deferred tax assets 500 462
Total deferred tax liabilities, net 1,278 1,179
WPL [Member]    
Income Tax [Line Items]    
Deferred tax liabilities, property 1,060 999
Deferred tax liabilities, other 62 66
Total deferred tax liabilities 1,122 1,065
Deferred tax assets, federal credit carryforwards 199 166
Deferred tax assets, net operating losses carryforwards - state 0 0
Deferred tax assets, other 65 34
Subtotal deferred tax assets 264 200
Deferred tax assets, valuation allowances (3) 0
Total deferred tax assets 261 200
Total deferred tax liabilities, net 861 865
ATC Holdings [Member]    
Income Tax [Line Items]    
Deferred tax liabilities, ATC Holdings 139 135
ATC Holdings [Member] | IPL [Member]    
Income Tax [Line Items]    
Deferred tax liabilities, ATC Holdings 0 0
ATC Holdings [Member] | WPL [Member]    
Income Tax [Line Items]    
Deferred tax liabilities, ATC Holdings $ 0 $ 0
v3.25.4
Income Taxes (Summary Of Tax Credit Carryforwards) (Details)
$ in Millions
Dec. 31, 2025
USD ($)
Iowa State [Member]  
Income Tax [Line Items]  
Tax carryforwards, net operating losses $ 311
Iowa State [Member] | IPL [Member]  
Income Tax [Line Items]  
Tax carryforwards, net operating losses 7
Iowa State [Member] | WPL [Member]  
Income Tax [Line Items]  
Tax carryforwards, net operating losses 1
Federal [Member]  
Income Tax [Line Items]  
Tax carryforwards, tax credits 669
Federal [Member] | IPL [Member]  
Income Tax [Line Items]  
Tax carryforwards, tax credits 455
Federal [Member] | WPL [Member]  
Income Tax [Line Items]  
Tax carryforwards, tax credits $ 199
v3.25.4
Income Taxes (Schedule Of Uncertain Tax Positions) (Details)
 12 Months Ended
Dec. 31, 2025
Income Tax [Line Items]  
Statute of limitations, expiration period from extended due date of federal tax return 3 years
Statute of limitations, expiration period from extended due date of Iowa tax return 3 years
Statute of limitations, expiration period from extended due date of Wisconsin tax return 4 years
v3.25.4
Benefit Plans (Narrative) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Benefit Plans [Line Items]      
Total plan assets (less than 1%), percentage of common stock 1.00% 1.00%  
Common stock percentage in assets held in 401(k) saving plans 7.00% 7.00%  
Unrecognized compensation cost $ 14    
Percentage of base salary and short-term cash incentive compensation 80.00%    
Carrying value of deferred compensation obligations $ 22 $ 23  
Restructuring and voluntary employee separation package pre-tax charge $ 740 $ 676 $ 675
Employee Severance [Member]      
Benefit Plans [Line Items]      
Employees accepting voluntary separation package, percent   5.00%  
Restructuring and voluntary employee separation package pre-tax charge   $ 29  
Performance Shares (TSR Metric) [Member]      
Benefit Plans [Line Items]      
Performance period 3 years    
Restricted Stock Units [Member]      
Benefit Plans [Line Items]      
Performance period 3 years    
Instrument valuation based on shares of common stock, number of shares 1    
Performance Shares (Net Income and Workforce Composition Metrics) [Member]      
Benefit Plans [Line Items]      
Performance period 3 years    
Instrument valuation based on shares of common stock, number of shares 1    
Minimum [Member]      
Benefit Plans [Line Items]      
Unrecognized compensation cost recognized over a weighted average period 1 year    
Minimum [Member] | Performance Shares (TSR Metric) [Member]      
Benefit Plans [Line Items]      
Actual number of shares paid out upon vesting, percentage of target shares 0.00%    
Minimum [Member] | Performance Shares (Net Income and Workforce Composition Metrics) [Member]      
Benefit Plans [Line Items]      
Actual number of shares paid out upon vesting, percentage of target shares 0.00%    
Maximum [Member]      
Benefit Plans [Line Items]      
Unrecognized compensation cost recognized over a weighted average period 2 years    
Maximum [Member] | Performance Shares (TSR Metric) [Member]      
Benefit Plans [Line Items]      
Actual number of shares paid out upon vesting, percentage of target shares 200.00%    
Maximum [Member] | Performance Shares (Net Income and Workforce Composition Metrics) [Member]      
Benefit Plans [Line Items]      
Actual number of shares paid out upon vesting, percentage of target shares 200.00%    
IPL [Member]      
Benefit Plans [Line Items]      
Unrecognized compensation cost $ 7    
IPL [Member] | Employee Severance [Member]      
Benefit Plans [Line Items]      
Restructuring and voluntary employee separation package pre-tax charge   14  
WPL [Member]      
Benefit Plans [Line Items]      
Unrecognized compensation cost $ 6    
WPL [Member] | Employee Severance [Member]      
Benefit Plans [Line Items]      
Restructuring and voluntary employee separation package pre-tax charge   $ 13  
Omnibus Incentive Plan [Member]      
Benefit Plans [Line Items]      
Shares available for issuance under the Amended and Restated OIP (in shares) 7,000,000    
Shares included in diluted earnings per share (in shares) 725,647    
v3.25.4
Benefit Plans (Assumptions Used To Measure Benefit Plans) (Details)
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Pension Plans, Defined Benefit [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate for benefit obligations 5.52% 5.65% 5.36%
Discount rate for net periodic cost 5.65% 5.36% 5.54%
Expected rate of return on plan assets 7.60% 7.73% 7.80%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan 5.60% 6.24% 10.75%
Pension Plans, Defined Benefit [Member] | IPL [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate for benefit obligations 5.56% 5.66% 5.35%
Discount rate for net periodic cost 5.66% 5.35% 5.55%
Expected rate of return on plan assets 7.60% 7.60% 7.80%
Rate of compensation increase 4.00% 3.75% 3.30%
Pension Plans, Defined Benefit [Member] | WPL [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate for benefit obligations 5.56% 5.66% 5.35%
Discount rate for net periodic cost 5.66% 5.35% 5.54%
Expected rate of return on plan assets 7.60% 7.80% 7.80%
Rate of compensation increase 3.75% 3.50% 3.30%
Other Postretirement Benefits Plans [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate for benefit obligations 5.40% 5.62% 5.40%
Discount rate for net periodic cost 5.62% 5.40% 5.53%
Expected rate of return on plan assets 6.37% 6.22% 6.50%
Other Postretirement Benefits Plans [Member] | IPL [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate for benefit obligations 5.38% 5.61% 5.40%
Discount rate for net periodic cost 5.61% 5.40% 5.53%
Expected rate of return on plan assets 6.70% 6.60% 6.90%
Other Postretirement Benefits Plans [Member] | WPL [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate for benefit obligations 5.38% 5.61% 5.40%
Discount rate for net periodic cost 5.61% 5.40% 5.53%
Expected rate of return on plan assets 5.75% 5.61% 5.65%
Minimum [Member] | Pension Plans, Defined Benefit [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Rate of compensation increase 3.75% 3.50% 3.30%
Maximum [Member] | Pension Plans, Defined Benefit [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Rate of compensation increase 4.50% 4.50% 4.50%
v3.25.4
Benefit Plans (Net Periodic Benefit Costs) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Defined Benefit Plan Disclosure [Line Items]      
Pension settlement losses $ (1) $ 3 $ (3)
Defined Benefit Pension Plans [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Service cost 4 5 5
Interest cost 46 45 47
Expected return on plan assets (53) (55) (53)
Amortization of prior service cost (credit) 0 (1) (1)
Amortization of actuarial loss 22 24 28
Total 19 18 26
Other Postretirement Benefits Plans [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Service cost 1 2 2
Interest cost 8 8 9
Expected return on plan assets (4) (5) (5)
Amortization of prior service cost (credit) 0 0 0
Amortization of actuarial loss 0 0 1
Total 5 5 7
IPL [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Pension settlement losses 7 12 (2)
IPL [Member] | Defined Benefit Pension Plans [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Service cost 3 3 3
Interest cost 20 20 21
Expected return on plan assets (25) (26) (26)
Amortization of actuarial loss 9 9 11
Total 7 6 9
IPL [Member] | Other Postretirement Benefits Plans [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Service cost 1 1 1
Interest cost 3 3 3
Expected return on plan assets (4) (4) (3)
Amortization of actuarial loss 0 0 1
Total 0 0 2
WPL [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Pension settlement losses (12) (8) 3
WPL [Member] | Defined Benefit Pension Plans [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Service cost 1 2 2
Interest cost 20 20 20
Expected return on plan assets (23) (23) (22)
Amortization of actuarial loss 11 11 13
Total 9 10 13
WPL [Member] | Other Postretirement Benefits Plans [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Service cost 1 1 1
Interest cost 3 3 3
Expected return on plan assets (1) (1) (1)
Amortization of actuarial loss 0 0 1
Total $ 3 $ 3 $ 4
v3.25.4
Benefit Plans (Funded Status of Benefits Plans) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Pension Plans, Defined Benefit [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Projected benefit obligations $ 824 $ 841  
Change in benefit obligation:      
Net benefit obligation at January 1 841 876  
Service cost 4 5 $ 5
Interest cost 46 45 47
Plan participants' contributions 0 0  
Actuarial (gain) loss 17 (19)  
Gross benefits paid (84) (66)  
Net benefit obligation at December 31 824 841 876
Change in plan assets:      
Fair value of plan assets at January 1 715 732  
Actual return on plan assets 93 38  
Employer contributions 23 11  
Plan participants' contributions 0 0  
Gross benefits paid (84) (66)  
Fair value of plan assets at December 31 747 715 732
Under funded status at December 31 (77) (126)  
Fair value of plan assets 747 715  
Pension Plans, Defined Benefit [Member] | IPL [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Projected benefit obligations 363 372  
Change in benefit obligation:      
Net benefit obligation at January 1 372 387  
Service cost 3 3 3
Interest cost 20 20 21
Plan participants' contributions 0 0  
Actuarial (gain) loss 6 (8)  
Gross benefits paid (38) (30)  
Net benefit obligation at December 31 363 372 387
Change in plan assets:      
Fair value of plan assets at January 1 340 352  
Actual return on plan assets 43 18  
Employer contributions 1 0  
Plan participants' contributions 0 0  
Gross benefits paid (38) (30)  
Fair value of plan assets at December 31 346 340 352
Under funded status at December 31 (17) (32)  
Fair value of plan assets 346 340  
Pension Plans, Defined Benefit [Member] | WPL [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Projected benefit obligations 362 365  
Change in benefit obligation:      
Net benefit obligation at January 1 365 381  
Service cost 1 2 2
Interest cost 20 20 20
Plan participants' contributions 0 0  
Actuarial (gain) loss 9 (8)  
Gross benefits paid (33) (30)  
Net benefit obligation at December 31 362 365 381
Change in plan assets:      
Fair value of plan assets at January 1 303 306  
Actual return on plan assets 41 17  
Employer contributions 16 10  
Plan participants' contributions 0 0  
Gross benefits paid (33) (30)  
Fair value of plan assets at December 31 327 303 306
Under funded status at December 31 (35) (62)  
Fair value of plan assets 327 303  
Other Postretirement Benefits Plans [Member]      
Change in benefit obligation:      
Net benefit obligation at January 1 148 160  
Service cost 1 2 2
Interest cost 8 8 9
Plan participants' contributions 4 3  
Actuarial (gain) loss 6 (7)  
Gross benefits paid (21) (18)  
Net benefit obligation at December 31 146 148 160
Change in plan assets:      
Fair value of plan assets at January 1 80 83  
Actual return on plan assets 7 5  
Employer contributions 8 7  
Plan participants' contributions 4 3  
Gross benefits paid (21) (18)  
Fair value of plan assets at December 31 78 80 83
Under funded status at December 31 (68) (68)  
Other Postretirement Benefits Plans [Member] | IPL [Member]      
Change in benefit obligation:      
Net benefit obligation at January 1 59 65  
Service cost 1 1 1
Interest cost 3 3 3
Plan participants' contributions 2 1  
Actuarial (gain) loss 3 (3)  
Gross benefits paid (9) (8)  
Net benefit obligation at December 31 59 59 65
Change in plan assets:      
Fair value of plan assets at January 1 59 61  
Actual return on plan assets 6 4  
Employer contributions 2 1  
Plan participants' contributions 2 1  
Gross benefits paid (9) (8)  
Fair value of plan assets at December 31 60 59 61
Under funded status at December 31 1 0  
Other Postretirement Benefits Plans [Member] | WPL [Member]      
Change in benefit obligation:      
Net benefit obligation at January 1 56 61  
Service cost 1 1 1
Interest cost 3 3 3
Plan participants' contributions 1 1  
Actuarial (gain) loss 2 (3)  
Gross benefits paid (8) (7)  
Net benefit obligation at December 31 55 56 61
Change in plan assets:      
Fair value of plan assets at January 1 13 14  
Actual return on plan assets 2 0  
Employer contributions 6 5  
Plan participants' contributions 1 1  
Gross benefits paid (8) (7)  
Fair value of plan assets at December 31 14 13 $ 14
Under funded status at December 31 $ (41) $ (43)  
v3.25.4
Benefit Plans (Amounts Recognized On The Consolidated Balance Sheets) (Details) - USD ($)
$ in Millions
Dec. 31, 2025
Dec. 31, 2024
Amounts recognized on the balance sheets consist of:    
Pension and other benefit obligations $ (173) $ (224)
Pension Plans, Defined Benefit [Member]    
Amounts recognized on the balance sheets consist of:    
Non-current assets 0 0
Current liabilities (5) (3)
Pension and other benefit obligations (72) (123)
Net amounts recognized at December 31 (77) (126)
Amounts recognized in Regulatory Assets consist of:    
Net actuarial loss 267 312
Prior service credit (1) (2)
Net amount recognized at December 31 266 310
Other Postretirement Benefits Plans [Member]    
Amounts recognized on the balance sheets consist of:    
Non-current assets 18 17
Current liabilities (6) (7)
Pension and other benefit obligations (80) (78)
Net amounts recognized at December 31 (68) (68)
Amounts recognized in Regulatory Assets consist of:    
Net actuarial loss 7 4
Prior service credit 0 0
Net amount recognized at December 31 7 4
IPL [Member]    
Amounts recognized on the balance sheets consist of:    
Pension and other benefit obligations (30) (46)
IPL [Member] | Pension Plans, Defined Benefit [Member]    
Amounts recognized on the balance sheets consist of:    
Non-current assets 0 0
Current liabilities 0 (1)
Pension and other benefit obligations (17) (31)
Net amounts recognized at December 31 (17) (32)
Amounts recognized in Regulatory Assets consist of:    
Net actuarial loss 105 126
Prior service credit 0 (1)
Net amount recognized at December 31 105 125
IPL [Member] | Other Postretirement Benefits Plans [Member]    
Amounts recognized on the balance sheets consist of:    
Non-current assets 14 13
Current liabilities (1) (1)
Pension and other benefit obligations (12) (12)
Net amounts recognized at December 31 1 0
Amounts recognized in Regulatory Assets consist of:    
Net actuarial loss 7 7
Prior service credit 0 0
Net amount recognized at December 31 7 7
WPL [Member]    
Amounts recognized on the balance sheets consist of:    
Pension and other benefit obligations (75) (102)
WPL [Member] | Pension Plans, Defined Benefit [Member]    
Amounts recognized on the balance sheets consist of:    
Non-current assets 0 0
Current liabilities 0 0
Pension and other benefit obligations (35) (62)
Net amounts recognized at December 31 (35) (62)
Amounts recognized in Regulatory Assets consist of:    
Net actuarial loss 115 135
WPL [Member] | Other Postretirement Benefits Plans [Member]    
Amounts recognized on the balance sheets consist of:    
Non-current assets 4 4
Current liabilities (5) (6)
Pension and other benefit obligations (40) (41)
Net amounts recognized at December 31 (41) (43)
Amounts recognized in Regulatory Assets consist of:    
Net actuarial loss $ 1 $ 0
v3.25.4
Benefit Plans (Accumulated Benefit Obligations) (Details) - USD ($)
$ in Millions
Dec. 31, 2025
Dec. 31, 2024
Pension Plans, Defined Benefit [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Accumulated benefit obligations $ 805 $ 824
Plans with accumulated benefit obligations in excess of plan assets:    
Accumulated benefit obligations 805 824
Fair value of plan assets 747 715
Plans with projected benefit obligations in excess of plan assets:    
Projected benefit obligations 824 841
Fair value of plan assets 747 715
Other Postretirement Benefits Plans [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Accumulated benefit obligations 146 148
Plans with accumulated benefit obligations in excess of plan assets:    
Accumulated benefit obligations 146 148
Fair value of plan assets 78 80
IPL [Member] | Pension Plans, Defined Benefit [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Accumulated benefit obligations 353 362
Plans with accumulated benefit obligations in excess of plan assets:    
Accumulated benefit obligations 353 362
Fair value of plan assets 346 340
Plans with projected benefit obligations in excess of plan assets:    
Projected benefit obligations 363 372
Fair value of plan assets 346 340
IPL [Member] | Other Postretirement Benefits Plans [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Accumulated benefit obligations 59 59
WPL [Member] | Pension Plans, Defined Benefit [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Accumulated benefit obligations 354 358
Plans with accumulated benefit obligations in excess of plan assets:    
Accumulated benefit obligations 354 358
Fair value of plan assets 327 303
Plans with projected benefit obligations in excess of plan assets:    
Projected benefit obligations 362 365
Fair value of plan assets 327 303
WPL [Member] | Other Postretirement Benefits Plans [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Accumulated benefit obligations 55 56
Plans with accumulated benefit obligations in excess of plan assets:    
Accumulated benefit obligations 55 56
Fair value of plan assets $ 14 $ 13
v3.25.4
Benefit Plans (Regulatory Assets) (Details) - USD ($)
$ in Millions
Dec. 31, 2025
Dec. 31, 2024
IPL [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Regulatory assets $ 23 $ 25
WPL [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Regulatory assets $ 21 $ 22
v3.25.4
Benefit Plans (Estimated Future Funding) (Details) - Forecast [Member]
$ in Millions
Dec. 31, 2026
USD ($)
Defined Benefit Pension Plans [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Estimated funding for calendar year 2025 $ 23
Defined Benefit Pension Plans [Member] | IPL [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Estimated funding for calendar year 2025 3
Defined Benefit Pension Plans [Member] | WPL [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Estimated funding for calendar year 2025 13
Other Postretirement Benefits Plans [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Estimated funding for calendar year 2025 7
Other Postretirement Benefits Plans [Member] | IPL [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Estimated funding for calendar year 2025 1
Other Postretirement Benefits Plans [Member] | WPL [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Estimated funding for calendar year 2025 $ 5
v3.25.4
Benefit Plans (Expected Benefit Payments) (Details)
$ in Millions
Dec. 31, 2025
USD ($)
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2026 $ 91
Expected benefit payments, 2027 90
Expected benefit payments, 2028 90
Expected benefit payments, 2029 88
Expected benefit payments, 2030 83
Expected benefit payments, 2031 - 2035 381
Defined Benefit Pension Plans [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2026 75
Expected benefit payments, 2027 75
Expected benefit payments, 2028 75
Expected benefit payments, 2029 74
Expected benefit payments, 2030 69
Expected benefit payments, 2031 - 2035 320
Other Postretirement Benefits Plans [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2026 16
Expected benefit payments, 2027 15
Expected benefit payments, 2028 15
Expected benefit payments, 2029 14
Expected benefit payments, 2030 14
Expected benefit payments, 2031 - 2035 61
IPL [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2026 40
Expected benefit payments, 2027 39
Expected benefit payments, 2028 39
Expected benefit payments, 2029 38
Expected benefit payments, 2030 38
Expected benefit payments, 2031 - 2035 167
IPL [Member] | Defined Benefit Pension Plans [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2026 34
Expected benefit payments, 2027 33
Expected benefit payments, 2028 33
Expected benefit payments, 2029 32
Expected benefit payments, 2030 32
Expected benefit payments, 2031 - 2035 143
IPL [Member] | Other Postretirement Benefits Plans [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2026 6
Expected benefit payments, 2027 6
Expected benefit payments, 2028 6
Expected benefit payments, 2029 6
Expected benefit payments, 2030 6
Expected benefit payments, 2031 - 2035 24
WPL [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2026 38
Expected benefit payments, 2027 37
Expected benefit payments, 2028 36
Expected benefit payments, 2029 36
Expected benefit payments, 2030 35
Expected benefit payments, 2031 - 2035 165
WPL [Member] | Defined Benefit Pension Plans [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2026 32
Expected benefit payments, 2027 31
Expected benefit payments, 2028 31
Expected benefit payments, 2029 31
Expected benefit payments, 2030 30
Expected benefit payments, 2031 - 2035 142
WPL [Member] | Other Postretirement Benefits Plans [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2026 6
Expected benefit payments, 2027 6
Expected benefit payments, 2028 5
Expected benefit payments, 2029 5
Expected benefit payments, 2030 5
Expected benefit payments, 2031 - 2035 $ 23
v3.25.4
Benefit Plans (Allocation Of Plan Assets) (Details)
Dec. 31, 2025
Pension Plans, Defined Benefit [Member] | Public equity securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Actual allocation, percentage 40.00%
Pension Plans, Defined Benefit [Member] | Liquid alternative securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Actual allocation, percentage 5.00%
Pension Plans, Defined Benefit [Member] | Return-seeking fixed income securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Actual allocation, percentage 7.00%
Pension Plans, Defined Benefit [Member] | Liability hedging fixed income securities (including cash and equivalents) [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Actual allocation, percentage 48.00%
Other Postretirement Benefits Plans [Member] | Cash and equivalents [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Actual allocation, percentage 3.00%
Other Postretirement Benefits Plans [Member] | Public equity securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Actual allocation, percentage 26.00%
Other Postretirement Benefits Plans [Member] | Fixed income securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Actual allocation, percentage 71.00%
Minimum [Member] | Pension Plans, Defined Benefit [Member] | Public equity securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Target range allocation, percentage 32.00%
Minimum [Member] | Pension Plans, Defined Benefit [Member] | Liquid alternative securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Target range allocation, percentage 0.00%
Minimum [Member] | Pension Plans, Defined Benefit [Member] | Return-seeking fixed income securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Target range allocation, percentage 4.00%
Minimum [Member] | Pension Plans, Defined Benefit [Member] | Liability hedging fixed income securities (including cash and equivalents) [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Target range allocation, percentage 41.00%
Minimum [Member] | Other Postretirement Benefits Plans [Member] | Cash and equivalents [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Target range allocation, percentage 0.00%
Minimum [Member] | Other Postretirement Benefits Plans [Member] | Public equity securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Target range allocation, percentage 0.00%
Minimum [Member] | Other Postretirement Benefits Plans [Member] | Fixed income securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Target range allocation, percentage 34.00%
Maximum [Member] | Pension Plans, Defined Benefit [Member] | Public equity securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Target range allocation, percentage 44.00%
Maximum [Member] | Pension Plans, Defined Benefit [Member] | Liquid alternative securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Target range allocation, percentage 11.00%
Maximum [Member] | Pension Plans, Defined Benefit [Member] | Return-seeking fixed income securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Target range allocation, percentage 16.00%
Maximum [Member] | Pension Plans, Defined Benefit [Member] | Liability hedging fixed income securities (including cash and equivalents) [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Target range allocation, percentage 54.00%
Maximum [Member] | Other Postretirement Benefits Plans [Member] | Cash and equivalents [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Target range allocation, percentage 5.00%
Maximum [Member] | Other Postretirement Benefits Plans [Member] | Public equity securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Target range allocation, percentage 40.00%
Maximum [Member] | Other Postretirement Benefits Plans [Member] | Fixed income securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Target range allocation, percentage 100.00%
v3.25.4
Benefit Plans (Fair Value Of Plan Assets By Asset Category And Fair Value Hierarchy Level) (Details) - USD ($)
$ in Millions
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Pension Plans, Defined Benefit [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets $ 747 $ 715 $ 732
Pension Plans, Defined Benefit [Member] | Assets Measured at Net Asset Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 676 667  
Pension Plans, Defined Benefit [Member] | Cash and equivalents [Member] | Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 71 49  
Pension Plans, Defined Benefit [Member] | Cash and equivalents [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0 0  
Pension Plans, Defined Benefit [Member] | Cash and equivalents [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 71 49  
Pension Plans, Defined Benefit [Member] | Cash and equivalents [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0 0  
Pension Plans, Defined Benefit [Member] | Due to brokers, net (pending trades with brokers) [Member] | Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0 (1)  
Pension Plans, Defined Benefit [Member] | IPL [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 346 340 352
Pension Plans, Defined Benefit [Member] | IPL [Member] | Assets Measured at Net Asset Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 315 319  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Cash and equivalents [Member] | Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 31 21  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Cash and equivalents [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0 0  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Cash and equivalents [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 31 21  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Cash and equivalents [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0 0  
Pension Plans, Defined Benefit [Member] | WPL [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 327 303 306
Pension Plans, Defined Benefit [Member] | WPL [Member] | Assets Measured at Net Asset Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 295 281  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Cash and equivalents [Member] | Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 32 22  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Cash and equivalents [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0 0  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Cash and equivalents [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 32 22  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Cash and equivalents [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0 0  
Other Postretirement Benefit Plans, Defined Benefit [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 78 80 83
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 78 80  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 71 72  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 7 8  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0 0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Cash and equivalents [Member] | Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 7 8  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Cash and equivalents [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0 0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Cash and equivalents [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 7 8  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Cash and equivalents [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0 0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity securities [Member] | Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 19 20  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity securities [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 19 20  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity securities [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0 0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity securities [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0 0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fixed income securities [Member] | Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 52 52  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fixed income securities [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 52 52  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fixed income securities [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0 0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fixed income securities [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0 0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 60 59 61
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 60 59  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 57 58  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 3 1  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0 0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Cash and equivalents [Member] | Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 3 1  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Cash and equivalents [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0 0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Cash and equivalents [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 3 1  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Cash and equivalents [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0 0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Equity securities [Member] | Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 17 18  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Equity securities [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 17 18  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Equity securities [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0 0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Equity securities [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0 0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Fixed income securities [Member] | Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 40 40  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Fixed income securities [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 40 40  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Fixed income securities [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0 0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Fixed income securities [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0 0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 14 13 $ 14
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 14 13  
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0 0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0 0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Equity securities [Member] | Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 2 2  
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Equity securities [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 2 2  
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Equity securities [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0 0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Equity securities [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0 0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Fixed income securities [Member] | Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 12 11  
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Fixed income securities [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 12 11  
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Fixed income securities [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0 0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Fixed income securities [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets $ 0 $ 0  
v3.25.4
Benefit Plans (Employees Participate In Defined Contribution Retirement Plans) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Statement [Line Items]      
401(k) costs $ 30 $ 31 $ 30
IPL [Member]      
Statement [Line Items]      
401(k) costs 14 14 14
WPL [Member]      
Statement [Line Items]      
401(k) costs $ 14 $ 15 $ 14
v3.25.4
Benefit Plans (Recognized Compensation Expense And Income Tax Benefits) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Statement [Line Items]      
Compensation expense $ 22 $ 12 $ 12
Income tax benefits 3 3 3
IPL [Member]      
Statement [Line Items]      
Compensation expense 11 6 6
Income tax benefits 2 2 2
WPL [Member]      
Statement [Line Items]      
Compensation expense 10 5 5
Income tax benefits $ 1 $ 1 $ 1
v3.25.4
Benefit Plans (Summary Of Performance Shares (TSR Metric)) (Details) - Performance Shares (TSR Metric) [Member] - $ / shares
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]      
Nonvested, January 1 (in shares/awards) 289,399 233,954 190,273
Nonvested, January 1, weighted average grant date fair value (in dollars per share) $ 51.31 $ 52.60 $ 54.13
Granted (in shares/awards) 105,896 127,874 108,712
Granted, weighted average grant date fair value (in dollars per share) $ 66.52 $ 46.04 $ 55.68
Vested (in shares/awards) 0 (47,497) (53,431)
Vested, weighted average grant date fair value (in dollars per share) $ 0 $ 46.19 $ 64.04
Forfeited (in shares/awards) (73,918) (24,932) (11,600)
Forfeited, weighted average grant date fair value (in dollars per share) $ 54.14 $ 46.16 $ 53.88
Nonvested, December 31 (in shares/awards) 321,377 289,399 233,954
Nonvested, December 31, weighted average grant date fair value (in dollars per share) $ 55.67 $ 51.31 $ 52.60
v3.25.4
Benefit Plans (Summary of Restricted Stock Units) (Details) - Restricted Stock Units [Member] - $ / shares
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]      
Nonvested, January 1 (in shares/awards) 289,148 234,259 198,275
Nonvested, January 1, weighted average grant date fair value (in dollars per share) $ 51.85 $ 52.58 $ 54.53
Granted (in shares/awards) 102,240 129,854 106,124
Granted, weighted average grant date fair value (in dollars per share) $ 61.73 $ 48.69 $ 52.77
Vested (in shares/awards) (63,789) (71,441) (55,345)
Vested, weighted average grant date fair value (in dollars per share) $ 56.70 $ 48.65 $ 59.40
Forfeited (in shares/awards) (14,215) (3,524) (14,795)
Forfeited, weighted average grant date fair value (in dollars per share) $ 51.13 $ 48.40 $ 54.53
Nonvested, December 31 (in shares/awards) 313,384 289,148 234,259
Nonvested, December 31, weighted average grant date fair value (in dollars per share) $ 54.06 $ 51.85 $ 52.58
v3.25.4
Benefit Plans (Summary of Performance Shares (Net Income and Workforce Representation Metrics)) (Details) - Performance Shares (Net Income and Workforce Composition Metrics) [Member] - $ / shares
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]      
Nonvested, January 1 (in shares/awards) 330,700 257,639 199,874
Nonvested, January 1, weighted average grant date fair value (in dollars per share) $ 51.81 $ 52.76 $ 54.74
Granted (in shares/awards) 118,883 146,143 124,217
Granted, weighted average grant date fair value (in dollars per share) $ 61.63 $ 48.55 $ 52.71
Vested (in shares/awards) (68,233) (67,852) (53,431)
Vested, weighted average grant date fair value (in dollars per share) $ 56.74 $ 48.66 $ 59.36
Forfeited (in shares/awards) (16,225) (5,230) (13,021)
Forfeited, weighted average grant date fair value (in dollars per share) $ 53.05 $ 48.40 $ 55.47
Nonvested, December 31 (in shares/awards) 365,125 330,700 257,639
Nonvested, December 31, weighted average grant date fair value (in dollars per share) $ 54.03 $ 51.81 $ 52.76
v3.25.4
Benefit Plans (Carrying Value And Fair Market Value Of The Deferred Compensation Obligation for Company Stock Account) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Defined Benefit Plan Disclosure [Line Items]    
Carrying value of deferred compensation obligation $ 14 $ 14
Fair market value of deferred compensation obligation $ 24 $ 22
v3.25.4
Asset Retirement Obligations (Reconciliation Of Changes In Asset Retirement Obligations) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]      
Balance, January 1 $ 663 $ 246  
Revisions in estimated cash flows (1) (3)  
Liabilities settled (5) (8)  
Liabilities incurred 16 409  
Accretion expense 31 19  
Balance, December 31 704 663 $ 246
Steam [Member]      
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]      
Asset retirement obligation charge for IPL's steam assets   20  
IPL [Member]      
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]      
Balance, January 1 350 148  
Revisions in estimated cash flows 0 (1)  
Liabilities settled (2) (6)  
Liabilities incurred 3 201  
Accretion expense 16 8  
Balance, December 31 367 350 148
Asset retirement obligation charge for IPL's steam assets 373 358 353
IPL [Member] | Steam [Member]      
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]      
Asset retirement obligation charge for IPL's steam assets   20  
WPL [Member]      
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]      
Balance, January 1 313 98  
Revisions in estimated cash flows (1) (2)  
Liabilities settled (3) (2)  
Liabilities incurred 13 208  
Accretion expense 15 11  
Balance, December 31 337 313 98
Asset retirement obligation charge for IPL's steam assets $ 306 $ 279 $ 271
v3.25.4
Derivative Instruments (Narrative) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Derivative [Line Items]      
Interest rate swap $ 12,125 $ 9,925  
Non-current interest rate swap assets 137 126  
Accumulated other comprehensive income 1 1  
Interest expense, interest rate swap 512 449 $ 394
Interest Rate Swap [Member] | Term Loan Credit Agreement [Member]      
Derivative [Line Items]      
Interest rate swap $ 300    
Interest rate swap, fixed interest rate percentage 3.10%    
Interest Rate Swap [Member] | Term Loan Credit Agreement [Member] | Other Noncurrent Liabilities      
Derivative [Line Items]      
Non-current interest rate swap assets $ 1    
Interest Rate Swap [Member] | Term Loan Credit Agreement [Member] | AOCI Including Portion Attributable to Noncontrolling Interest      
Derivative [Line Items]      
Accumulated other comprehensive income 1    
IPL [Member]      
Derivative [Line Items]      
Interest rate swap 4,725 4,125  
Non-current interest rate swap assets 40 53  
WPL [Member]      
Derivative [Line Items]      
Interest rate swap 3,700 3,400  
Non-current interest rate swap assets 79 55  
Alliant Energy Finance, LLC [Member] | Interest Rate Swap [Member] | Term Loan Credit Agreement [Member]      
Derivative [Line Items]      
Interest rate swap $ 300    
Interest rate swap, fixed interest rate percentage 3.93%    
Interest expense, interest rate swap $ 1 $ 4 $ 3
v3.25.4
Derivative Instruments (Notional Amounts Of Derivative Instruments) (Details) - Commodity [Member]
gal in Thousands
 12 Months Ended
Dec. 31, 2025
Dekatherms
MWh
gal
Dec. 31, 2024
Dekatherms
MWh
gal
Electricity (MWhs) [Member]    
Notional Amount of Derivatives [Line Items]    
Notional unit amount of derivatives (in MWhs) 1,682 1,422
Electricity (MWhs) [Member] | IPL [Member]    
Notional Amount of Derivatives [Line Items]    
Notional unit amount of derivatives (in MWhs) 634 383
Electricity (MWhs) [Member] | WPL [Member]    
Notional Amount of Derivatives [Line Items]    
Notional unit amount of derivatives (in MWhs) 1,048 1,039
FTRs (MWhs) [Member]    
Notional Amount of Derivatives [Line Items]    
Notional unit amount of derivatives (in MWhs) 11,332 10,232
FTRs (MWhs) [Member] | IPL [Member]    
Notional Amount of Derivatives [Line Items]    
Notional unit amount of derivatives (in MWhs) 4,482 3,551
FTRs (MWhs) [Member] | WPL [Member]    
Notional Amount of Derivatives [Line Items]    
Notional unit amount of derivatives (in MWhs) 6,850 6,681
Gas (Dths) [Member]    
Notional Amount of Derivatives [Line Items]    
Notional unit amount of derivatives (in Dths) | Dekatherms 140,731 147,894
Gas (Dths) [Member] | IPL [Member]    
Notional Amount of Derivatives [Line Items]    
Notional unit amount of derivatives (in Dths) | Dekatherms 60,773 61,489
Gas (Dths) [Member] | WPL [Member]    
Notional Amount of Derivatives [Line Items]    
Notional unit amount of derivatives (in Dths) | Dekatherms 79,958 86,405
Diesel Fuel (gallons) [Member]    
Notional Amount of Derivatives [Line Items]    
Notional unit amount of derivatives (in Gallons) | gal 0 2,520
Diesel Fuel (gallons) [Member] | IPL [Member]    
Notional Amount of Derivatives [Line Items]    
Notional unit amount of derivatives (in Gallons) | gal 0 0
Diesel Fuel (gallons) [Member] | WPL [Member]    
Notional Amount of Derivatives [Line Items]    
Notional unit amount of derivatives (in Gallons) | gal 0 2,520
v3.25.4
Derivative Instruments (Fair Value Of Financial Instruments) (Details) - Commodity Contracts [Member] - USD ($)
$ in Millions
Dec. 31, 2025
Dec. 31, 2024
Derivatives, Fair Value [Line Items]    
Current derivative assets $ 49 $ 41
Non-current derivative assets 20 34
Current derivative liabilities 25 26
Non-current derivative liabilities 26 32
IPL [Member]    
Derivatives, Fair Value [Line Items]    
Current derivative assets 33 29
Non-current derivative assets 11 19
Current derivative liabilities 9 11
Non-current derivative liabilities 2 2
WPL [Member]    
Derivatives, Fair Value [Line Items]    
Current derivative assets 16 12
Non-current derivative assets 9 15
Current derivative liabilities 16 15
Non-current derivative liabilities $ 24 $ 30
v3.25.4
Derivative Instruments (Balance Sheet Offsetting) (Details) - Commodity Contracts [Member] - USD ($)
$ in Millions
Dec. 31, 2025
Dec. 31, 2024
Derivative [Line Items]    
Derivative assets, Gross (as reported) $ 69 $ 75
Derivative assets, net 59 64
Derivative liabilities, gross (as reported) 51 58
Derivative liabilities, net 41 47
IPL [Member]    
Derivative [Line Items]    
Derivative assets, Gross (as reported) 44 48
Derivative assets, net 40 43
Derivative liabilities, gross (as reported) 11 13
Derivative liabilities, net 7 8
WPL [Member]    
Derivative [Line Items]    
Derivative assets, Gross (as reported) 25 27
Derivative assets, net 19 21
Derivative liabilities, gross (as reported) 40 45
Derivative liabilities, net $ 34 $ 39
v3.25.4
Fair Value Measurements (Recurring Fair Value Measurements) (Details) - USD ($)
$ in Millions
Dec. 31, 2025
Dec. 31, 2024
Carrying Amount [Member]    
Assets:    
Money market fund investments $ 411 $ 52
Deferred proceeds 126 163
Liabilities and equity:    
Long-term debt (including current maturities) 12,028 9,848
Carrying Amount [Member] | Commodity Contracts [Member]    
Assets:    
Derivatives 69 75
Liabilities and equity:    
Derivatives 51 58
Carrying Amount [Member] | Interest Rate Swap [Member]    
Assets:    
Derivatives 1 1
Money market fund investments 411 52
Deferred proceeds 126 163
Liabilities and equity:    
Long-Term Debt, Fair Value 11,748 9,577
Commodity Contracts [Member]    
Assets:    
Derivatives 69 75
Liabilities and equity:    
Derivatives 51 58
Interest Rate Swap [Member]    
Assets:    
Derivatives 1 1
Level 1 [Member]    
Assets:    
Money market fund investments 411 52
Deferred proceeds 0 0
Liabilities and equity:    
Long-Term Debt, Fair Value 0 0
Level 1 [Member] | Commodity Contracts [Member]    
Assets:    
Derivatives 0 0
Liabilities and equity:    
Derivatives 0 0
Level 1 [Member] | Interest Rate Swap [Member]    
Assets:    
Derivatives 0 0
Level 2 [Member]    
Assets:    
Money market fund investments 0 0
Deferred proceeds 0 0
Liabilities and equity:    
Long-Term Debt, Fair Value 11,748 9,577
Level 2 [Member] | Commodity Contracts [Member]    
Assets:    
Derivatives 36 48
Liabilities and equity:    
Derivatives 50 56
Level 2 [Member] | Interest Rate Swap [Member]    
Assets:    
Derivatives 1 1
Level 3 [Member]    
Assets:    
Money market fund investments 0 0
Deferred proceeds 126 163
Liabilities and equity:    
Long-Term Debt, Fair Value 0 0
Level 3 [Member] | Commodity Contracts [Member]    
Assets:    
Derivatives 33 27
Liabilities and equity:    
Derivatives 1 2
Level 3 [Member] | Interest Rate Swap [Member]    
Assets:    
Derivatives 0 0
IPL [Member] | Carrying Amount [Member]    
Assets:    
Money market fund investments 0 9
Deferred proceeds 126 163
Liabilities and equity:    
Long-term debt (including current maturities) 4,680 4,090
IPL [Member] | Carrying Amount [Member] | Commodity Contracts [Member]    
Assets:    
Derivatives 44 48
Liabilities and equity:    
Derivatives 11 13
IPL [Member]    
Assets:    
Money market fund investments 0 9
Deferred proceeds 126 163
Liabilities and equity:    
Long-Term Debt, Fair Value 4,445 3,736
IPL [Member] | Commodity Contracts [Member]    
Assets:    
Derivatives 44 48
Liabilities and equity:    
Derivatives 11 13
IPL [Member] | Level 1 [Member]    
Assets:    
Money market fund investments 0 9
Deferred proceeds 0 0
Liabilities and equity:    
Long-Term Debt, Fair Value 0 0
IPL [Member] | Level 1 [Member] | Commodity Contracts [Member]    
Assets:    
Derivatives 0 0
Liabilities and equity:    
Derivatives 0 0
IPL [Member] | Level 2 [Member]    
Assets:    
Money market fund investments 0 0
Deferred proceeds 0 0
Liabilities and equity:    
Long-Term Debt, Fair Value 4,445 3,736
IPL [Member] | Level 2 [Member] | Commodity Contracts [Member]    
Assets:    
Derivatives 18 26
Liabilities and equity:    
Derivatives 10 11
IPL [Member] | Level 3 [Member]    
Assets:    
Money market fund investments 0 0
Deferred proceeds 126 163
Liabilities and equity:    
Long-Term Debt, Fair Value 0 0
IPL [Member] | Level 3 [Member] | Commodity Contracts [Member]    
Assets:    
Derivatives 26 22
Liabilities and equity:    
Derivatives 1 2
WPL [Member] | Carrying Amount [Member]    
Assets:    
Money market fund investments 25 43
Liabilities and equity:    
Long-term debt (including current maturities) 3,669 3,370
WPL [Member] | Carrying Amount [Member] | Commodity Contracts [Member]    
Assets:    
Derivatives 25 27
Liabilities and equity:    
Derivatives 40 45
WPL [Member]    
Assets:    
Money market fund investments 25 43
Liabilities and equity:    
Long-Term Debt, Fair Value 3,575 3,170
WPL [Member] | Commodity Contracts [Member]    
Assets:    
Derivatives 25 27
Liabilities and equity:    
Derivatives 40 45
WPL [Member] | Level 1 [Member]    
Assets:    
Money market fund investments 25 43
Liabilities and equity:    
Long-Term Debt, Fair Value 0 0
WPL [Member] | Level 1 [Member] | Commodity Contracts [Member]    
Assets:    
Derivatives 0 0
Liabilities and equity:    
Derivatives 0 0
WPL [Member] | Level 2 [Member]    
Assets:    
Money market fund investments 0 0
Liabilities and equity:    
Long-Term Debt, Fair Value 3,575 3,170
WPL [Member] | Level 2 [Member] | Commodity Contracts [Member]    
Assets:    
Derivatives 18 22
Liabilities and equity:    
Derivatives 40 45
WPL [Member] | Level 3 [Member]    
Assets:    
Money market fund investments 0 0
Liabilities and equity:    
Long-Term Debt, Fair Value 0 0
WPL [Member] | Level 3 [Member] | Commodity Contracts [Member]    
Assets:    
Derivatives 7 5
Liabilities and equity:    
Derivatives $ 0 $ 0
v3.25.4
Fair Value Measurements (Fair Value Measurements Using Significant Unobservable Inputs) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Commodity Contracts Derivative Assets and (Liabilities), net [Member]    
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance, January 1 $ 25 $ 24
Total net gains (losses) included in changes in net assets (realized/unrealized) 11 (3)
Purchases 50 59
Sales (3) (3)
Settlements (51) (52)
Ending balance, December 31 32 25
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31 11 (3)
Commodity Contracts Derivative Assets and (Liabilities), net [Member] | IPL [Member]    
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance, January 1 20 19
Total net gains (losses) included in changes in net assets (realized/unrealized) 5 (4)
Purchases 40 45
Sales (2) (2)
Settlements (38) (38)
Ending balance, December 31 25 20
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31 5 (4)
Commodity Contracts Derivative Assets and (Liabilities), net [Member] | WPL [Member]    
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance, January 1 5 5
Total net gains (losses) included in changes in net assets (realized/unrealized) 6 1
Purchases 10 14
Sales (1) (1)
Settlements (13) (14)
Ending balance, December 31 7 5
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31 6 1
Deferred Proceeds [Member]    
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance, January 1 163 216
Total net gains (losses) included in changes in net assets (realized/unrealized) 0 0
Purchases 0 0
Sales 0 0
Settlements (37) (53)
Ending balance, December 31 126 163
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31 0 0
Deferred Proceeds [Member] | IPL [Member]    
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance, January 1 163 216
Total net gains (losses) included in changes in net assets (realized/unrealized) 0 0
Purchases 0 0
Sales 0 0
Settlements (37) (53)
Ending balance, December 31 126 163
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31 $ 0 $ 0
v3.25.4
Fair Value Measurements (Fair Value Of Net Derivative Assets (Liabilities)) (Details) - Commodity Contracts [Member] - USD ($)
$ in Millions
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Fair value, net derivative assets $ 32 $ 25 $ 24
Excluding FTRs [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Fair value, net derivative assets 3 0  
FTRs [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Fair value, net derivative assets 29 25  
IPL [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Fair value, net derivative assets 25 20 19
IPL [Member] | Excluding FTRs [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Fair value, net derivative assets 3 0  
IPL [Member] | FTRs [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Fair value, net derivative assets 22 20  
WPL [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Fair value, net derivative assets 7 5 $ 5
WPL [Member] | Excluding FTRs [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Fair value, net derivative assets 0 0  
WPL [Member] | FTRs [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Fair value, net derivative assets $ 7 $ 5  
v3.25.4
Commitments And Contingencies (Narrative) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Long-term Purchase Commitment [Line Items]      
Equity income from unconsolidated investments, net $ (60) $ (61) $ (61)
Workforce Subject to Collective Bargaining Arrangements [Member] | Unionized Employees Concentration Risk      
Long-term Purchase Commitment [Line Items]      
Employees covered by collective bargaining agreement 58.00%    
Collective-Bargaining Arrangement, Other | Workforce Subject to Collective Bargaining Arrangements [Member] | Unionized Employees Concentration Risk      
Long-term Purchase Commitment [Line Items]      
Employees covered by collective bargaining agreement 29.00%    
Whiting Petroleum Corporation      
Long-term Purchase Commitment [Line Items]      
Partnership share, percent 6.00%    
Obligations, maximum $ 92    
Capital Purchase Commitment [Member]      
Long-term Purchase Commitment [Line Items]      
Minimum future commitments $ 459    
IPL [Member] | Workforce Subject to Collective Bargaining Arrangements [Member] | Unionized Employees Concentration Risk      
Long-term Purchase Commitment [Line Items]      
Employees covered by collective bargaining agreement 74.00%    
IPL [Member] | Capital Purchase Commitment [Member]      
Long-term Purchase Commitment [Line Items]      
Minimum future commitments $ 302    
WPL [Member] | Workforce Subject to Collective Bargaining Arrangements [Member] | Unionized Employees Concentration Risk      
Long-term Purchase Commitment [Line Items]      
Employees covered by collective bargaining agreement 86.00%    
WPL [Member] | Collective-Bargaining Arrangement, Other | Workforce Subject to Collective Bargaining Arrangements [Member] | Unionized Employees Concentration Risk      
Long-term Purchase Commitment [Line Items]      
Employees covered by collective bargaining agreement 86.00%    
WPL [Member] | Capital Purchase Commitment [Member]      
Long-term Purchase Commitment [Line Items]      
Minimum future commitments $ 155    
Indemnification Agreement [Member]      
Long-term Purchase Commitment [Line Items]      
Obligations, maximum 35    
Indemnification Agreement [Member] | Purchased Power [Member]      
Long-term Purchase Commitment [Line Items]      
Obligations, maximum 17    
Indemnification Agreement [Member] | IPL [Member] | Renewable Tax Credits Transferred [Member]      
Long-term Purchase Commitment [Line Items]      
Obligations, maximum 333    
Indemnification Agreement [Member] | IPL [Member] | Reimbursement of Transmission Construction Costs      
Long-term Purchase Commitment [Line Items]      
Obligations, maximum 130    
Indemnification Agreement [Member] | WPL [Member] | Renewable Tax Credits Transferred [Member]      
Long-term Purchase Commitment [Line Items]      
Obligations, maximum 266    
Indemnification Agreement [Member] | WPL [Member] | Reimbursement of Transmission Construction Costs      
Long-term Purchase Commitment [Line Items]      
Obligations, maximum $ 55    
v3.25.4
Commitments And Contingencies (Other Purchase Commitments) (Details)
$ in Millions
Dec. 31, 2025
USD ($)
Long-term Purchase Commitment [Line Items]  
Minimum future commitments, 2026 $ 404
Minimum future commitments, 2027 249
Minimum future commitments, 2028 199
Minimum future commitments, 2029 149
Minimum future commitments, 2030 106
Minimum future commitments, Thereafter 262
Minimum future commitments, Total 1,369
Individual commitments incurred 1
Natural Gas [Member]  
Long-term Purchase Commitment [Line Items]  
Minimum future commitments, 2026 271
Minimum future commitments, 2027 191
Minimum future commitments, 2028 163
Minimum future commitments, 2029 145
Minimum future commitments, 2030 103
Minimum future commitments, Thereafter 245
Minimum future commitments, Total 1,118
Coal [Member]  
Long-term Purchase Commitment [Line Items]  
Minimum future commitments, 2026 76
Minimum future commitments, 2027 42
Minimum future commitments, 2028 28
Minimum future commitments, 2029 0
Minimum future commitments, 2030 0
Minimum future commitments, Thereafter 0
Minimum future commitments, Total 146
Other [Member]  
Long-term Purchase Commitment [Line Items]  
Minimum future commitments, 2026 57
Minimum future commitments, 2027 16
Minimum future commitments, 2028 8
Minimum future commitments, 2029 4
Minimum future commitments, 2030 3
Minimum future commitments, Thereafter 17
Minimum future commitments, Total 105
IPL [Member]  
Long-term Purchase Commitment [Line Items]  
Minimum future commitments, 2026 207
Minimum future commitments, 2027 121
Minimum future commitments, 2028 97
Minimum future commitments, 2029 72
Minimum future commitments, 2030 33
Minimum future commitments, Thereafter 68
Minimum future commitments, Total 598
Individual commitments incurred 1
IPL [Member] | Natural Gas [Member]  
Long-term Purchase Commitment [Line Items]  
Minimum future commitments, 2026 149
Minimum future commitments, 2027 105
Minimum future commitments, 2028 85
Minimum future commitments, 2029 70
Minimum future commitments, 2030 31
Minimum future commitments, Thereafter 52
Minimum future commitments, Total 492
IPL [Member] | Coal [Member]  
Long-term Purchase Commitment [Line Items]  
Minimum future commitments, 2026 34
Minimum future commitments, 2027 14
Minimum future commitments, 2028 10
Minimum future commitments, 2029 0
Minimum future commitments, 2030 0
Minimum future commitments, Thereafter 0
Minimum future commitments, Total 58
IPL [Member] | Other [Member]  
Long-term Purchase Commitment [Line Items]  
Minimum future commitments, 2026 24
Minimum future commitments, 2027 2
Minimum future commitments, 2028 2
Minimum future commitments, 2029 2
Minimum future commitments, 2030 2
Minimum future commitments, Thereafter 16
Minimum future commitments, Total 48
WPL [Member]  
Long-term Purchase Commitment [Line Items]  
Minimum future commitments, 2026 189
Minimum future commitments, 2027 115
Minimum future commitments, 2028 96
Minimum future commitments, 2029 75
Minimum future commitments, 2030 72
Minimum future commitments, Thereafter 193
Minimum future commitments, Total 740
Individual commitments incurred 1
WPL [Member] | Natural Gas [Member]  
Long-term Purchase Commitment [Line Items]  
Minimum future commitments, 2026 122
Minimum future commitments, 2027 86
Minimum future commitments, 2028 78
Minimum future commitments, 2029 75
Minimum future commitments, 2030 72
Minimum future commitments, Thereafter 193
Minimum future commitments, Total 626
WPL [Member] | Coal [Member]  
Long-term Purchase Commitment [Line Items]  
Minimum future commitments, 2026 42
Minimum future commitments, 2027 28
Minimum future commitments, 2028 18
Minimum future commitments, 2029 0
Minimum future commitments, 2030 0
Minimum future commitments, Thereafter 0
Minimum future commitments, Total 88
WPL [Member] | Other [Member]  
Long-term Purchase Commitment [Line Items]  
Minimum future commitments, 2026 25
Minimum future commitments, 2027 1
Minimum future commitments, 2028 0
Minimum future commitments, 2029 0
Minimum future commitments, 2030 0
Minimum future commitments, Thereafter 0
Minimum future commitments, Total $ 26
v3.25.4
Commitments And Contingencies (Schedule Of Environmental Liabilities) (Details) - Natural Gas Processing Plant [Member]
$ in Millions
 12 Months Ended
Dec. 31, 2025
USD ($)
Statement [Line Items]  
Current and non-current environmental liabilities $ 12
IPL [Member]  
Statement [Line Items]  
Current and non-current environmental liabilities 8
WPL [Member]  
Statement [Line Items]  
Current and non-current environmental liabilities 4
Minimum [Member]  
Statement [Line Items]  
Range of estimated future costs 7
Minimum [Member] | IPL [Member]  
Statement [Line Items]  
Range of estimated future costs 5
Minimum [Member] | WPL [Member]  
Statement [Line Items]  
Range of estimated future costs 2
Maximum [Member]  
Statement [Line Items]  
Range of estimated future costs 29
Maximum [Member] | IPL [Member]  
Statement [Line Items]  
Range of estimated future costs 18
Maximum [Member] | WPL [Member]  
Statement [Line Items]  
Range of estimated future costs $ 11
v3.25.4
Segments Of Business (Narrative) (Details)
 12 Months Ended
Dec. 31, 2025
segement
Segment Reporting Information [Line Items]  
Number of reportable segments (in segments) 2
v3.25.4
Segments Of Business (Schedule Of Segment Of Business) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Segment Reporting Information [Line Items]      
Electric utility $ 3,697 $ 3,372 $ 3,345
Gas utility 525 465 540
Other 140 144 142
Total revenues 4,362 3,981 4,027
Electric production fuel and purchased power 742 628 736
Electric transmission service 625 613 583
Cost of gas sold 263 224 299
Asset valuation charge for IPL's Lansing Generating Station 0 60 0
Other operation and maintenance 740 676 675
Depreciation and amortization 846 772 676
Interest expense 512 449 394
Equity income from unconsolidated investments, net (60) (61) (61)
Income tax expense (benefit) (149) (114) 4
Other 33 44 18
Net income (loss) 810 690 703
Total assets 24,991 22,714 21,237
Investments in equity method subsidiaries 674 623 585
Construction and acquisition expenditures 2,483 2,249 1,854
IPL [Member]      
Segment Reporting Information [Line Items]      
Electric utility 1,896 1,747 1,761
Gas utility 265 250 300
Total revenues 2,208 2,046 2,110
Electric production fuel and purchased power 283 269 282
Electric transmission service 422 417 420
Cost of gas sold 130 123 166
Asset valuation charge for IPL's Lansing Generating Station 0 60 0
Depreciation and amortization 463 404 388
Income tax expense (benefit) (127) (129) (58)
Net income (loss) 457 362 366
Total assets 12,495 11,407  
Other operation and maintenance 373 358 353
WPL [Member]      
Segment Reporting Information [Line Items]      
Electric utility 1,801 1,625 1,584
Gas utility 260 215 240
Total revenues 2,065 1,845 1,827
Electric production fuel and purchased power 459 359 455
Electric transmission service 203 196 163
Cost of gas sold 133 101 134
Depreciation and amortization 370 357 280
Income tax expense (benefit) (14) 11 60
Net income (loss) 401 345 345
Total assets 10,655 10,106  
Other operation and maintenance 306 279 271
Total Reportable Segments [Member]      
Segment Reporting Information [Line Items]      
Electric utility 3,697 3,372 3,345
Gas utility 525 465 540
Other 51 54 52
Total revenues 4,273 3,891 3,937
Electric production fuel and purchased power 742 628 737
Electric transmission service 625 613 583
Cost of gas sold 263 224 300
Asset valuation charge for IPL's Lansing Generating Station   60  
Other operation and maintenance 679 637 624
Depreciation and amortization 833 761 668
Interest expense 384 342 304
Equity income from unconsolidated investments, net (2) (2) (3)
Income tax expense (benefit) (141) (118) 2
Other 32 39 11
Net income (loss) 858 707 711
Total assets 23,150 21,513 20,123
Investments in equity method subsidiaries 24 22 21
Construction and acquisition expenditures 2,277 2,052 1,731
IPL [Member]      
Segment Reporting Information [Line Items]      
Electric utility 1,896 1,747 1,761
Gas utility 265 250 300
Other 47 49 49
Total revenues 2,208 2,046 2,110
Electric production fuel and purchased power 283 269 282
Electric transmission service 422 417 420
Cost of gas sold 130 123 166
Asset valuation charge for IPL's Lansing Generating Station   60  
Other operation and maintenance 373 358 353
Depreciation and amortization 463 404 388
Interest expense 211 177 155
Equity income from unconsolidated investments, net 0 0 0
Income tax expense (benefit) (127) (129) (58)
Other (4) 5 38
Net income (loss) 457 362 366
Total assets 12,495 11,407 10,489
Investments in equity method subsidiaries 5 5 5
Construction and acquisition expenditures 1,473 1,224 712
WPL [Member]      
Segment Reporting Information [Line Items]      
Electric utility 1,801 1,625 1,584
Gas utility 260 215 240
Other 4 5 3
Total revenues 2,065 1,845 1,827
Electric production fuel and purchased power 459 359 455
Electric transmission service 203 196 163
Cost of gas sold 133 101 134
Other operation and maintenance 306 279 271
Depreciation and amortization 370 357 280
Interest expense 173 165 149
Equity income from unconsolidated investments, net (2) (2) (3)
Income tax expense (benefit) (14) 11 60
Other 36 34 (27)
Net income (loss) 401 345 345
Total assets 10,655 10,106 9,634
Investments in equity method subsidiaries 19 17 16
Construction and acquisition expenditures 804 828 1,019
Other [Member]      
Segment Reporting Information [Line Items]      
Other 89 90 90
Total revenues 89 90 90
Other operation and maintenance 61 39 51
Depreciation and amortization 13 11 8
Interest expense 128 107 90
Equity income from unconsolidated investments, net (58) (59) (58)
Income tax expense (benefit) (8) 4 2
Other 1 5 5
Net income (loss) (48) (17) (8)
Total assets 1,841 1,201 1,114
Investments in equity method subsidiaries 650 601 564
Construction and acquisition expenditures 206 $ 197 $ 123
Other Noncash Expense $ 16    
v3.25.4
Related Parties (Narrative) (Details) - USD ($)
$ in Millions
Dec. 31, 2025
Dec. 31, 2024
WPL [Member] | Related Party [Member] | WPL Owed ATC LLC [Member] | ATC LLC [Member]    
Related Party Transaction [Line Items]    
Net amounts owed $ 10 $ 10
v3.25.4
Related Parties (Service Agreements) (Details) - Corporate Services [Member] - Subsidiary of Common Parent [Member] - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Administrative and General Services Billings [Member] | IPL [Member]      
Related Party Transaction [Line Items]      
Amounts billed between related parties $ 194 $ 183 $ 181
Administrative and General Services Billings [Member] | WPL [Member]      
Related Party Transaction [Line Items]      
Amounts billed between related parties 189 171 163
Transmission Sales Credited [Member] | IPL [Member]      
Related Party Transaction [Line Items]      
Amounts billed between related parties 27 0 11
Transmission Sales Credited [Member] | WPL [Member]      
Related Party Transaction [Line Items]      
Amounts billed between related parties 131 84 55
Transmission Purchases Billed [Member] | IPL [Member]      
Related Party Transaction [Line Items]      
Amounts billed between related parties 416 430 431
Transmission Purchases Billed [Member] | WPL [Member]      
Related Party Transaction [Line Items]      
Amounts billed between related parties $ 75 $ 54 $ 35
v3.25.4
Related Parties (Net Intercompany Payables) (Details) - Corporate Services [Member] - Related Party [Member] - USD ($)
$ in Millions
Dec. 31, 2025
Dec. 31, 2024
IPL [Member]    
Related Party Transaction [Line Items]    
Net amounts owed $ 135 $ 135
WPL [Member]    
Related Party Transaction [Line Items]    
Net amounts owed $ 84 $ 64
v3.25.4
Related Parties (Related Amounts Billed Between Parties) (Details) - WPL [Member] - ATC LLC [Member] - Equity Method Investment [Member] - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
ATC Billings To WPL [Member]      
Related Party Transaction [Line Items]      
Amounts billed between related parties $ 162 $ 152 $ 159
WPL Billings To ATC [Member]      
Related Party Transaction [Line Items]      
Amounts billed between related parties $ 27 $ 16 $ 20
v3.25.4
Condensed Parent Company Financial Statements (Condensed Statements Of Income) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Statement [Line Items]      
Operating expenses $ 3,337 $ 3,095 $ 3,084
Operating income (loss) 1,025 886 943
Other (income) and deductions:      
Equity earnings from consolidated subsidiaries (60) (61) (61)
Interest expense 512 449 394
Other 1 (3) 3
Total other (income) and deductions 364 310 236
Income before income taxes 661 576 707
Income tax expense (benefit) (149) (114) 4
Net income 810 690 703
Parent Company [Member]      
Statement [Line Items]      
Operating expenses 4 3 3
Operating income (loss) (4) (3) (3)
Other (income) and deductions:      
Equity earnings from consolidated subsidiaries (863) (734) (742)
Interest expense 57 40 34
Other (3) 5 4
Total other (income) and deductions (809) (689) (704)
Income before income taxes 805 686 701
Income tax expense (benefit) (6) (3) (5)
Net income $ 811 $ 689 $ 706
v3.25.4
Condensed Parent Company Financial Statements (Condensed Balance Sheets) (Details) - USD ($)
$ in Millions
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Current assets:      
Cash and cash equivalents $ 556 $ 81  
Other 222 171  
Current assets 1,697 1,184  
Investments:      
Other 231 224  
Total investments 694 639  
Other assets 2,256 2,190  
Total assets 24,991 22,714 $ 21,237
Current liabilities:      
Current maturities of long-term debt 1,074 1,171  
Commercial paper 88 558  
Other 251 273  
Current liabilities 2,123 2,715  
Long-term debt, net 10,954 8,677  
Other liabilities 984 947  
Common Equity:      
Retained earnings 4,243 3,954  
Accumulated other comprehensive income 1 1  
Shares in deferred compensation trust (14) (14)  
Total common equity 7,334 7,004  
Total liabilities and equity 24,991 22,714  
Parent Company [Member]      
Current assets:      
Cash and cash equivalents 512 0  
Notes receivable from affiliated companies 114 103  
Income taxes refunds receivable 12 12  
Other 6 2  
Current assets 644 117  
Investments:      
Investments in consolidated subsidiaries 9,784 9,123  
Other 1 1  
Total investments 9,785 9,124  
Other assets 102 84  
Total assets 10,531 9,325  
Current liabilities:      
Current maturities of long-term debt 574 571  
Commercial paper 0 325  
Notes payable to affiliated companies 1,300 1,401  
Other 21 10  
Current liabilities 1,895 2,307  
Long-term debt, net 1,286 0  
Other liabilities 4 3  
Common Equity:      
Common stock and additional paid-in capital 3,104 3,063  
Retained earnings 4,255 3,965  
Accumulated other comprehensive income 1 1  
Shares in deferred compensation trust (14) (14)  
Total common equity 7,346 7,015  
Total liabilities and equity $ 10,531 $ 9,325  
v3.25.4
Condensed Parent Company Financial Statements (Condensed Statements of Cash Flows) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Statement [Line Items]      
Net cash flows from operating activities $ 1,169 $ 1,167 $ 867
Cash flows from (used for) investing activities:      
Net cash flows from (used for) investing activities (1,896) (1,547) (1,401)
Cash flows used for financing activities:      
Common stock dividends (521) (492) (456)
Proceeds from issuance of common stock, net 23 23 246
Proceeds from issuance of long-term debt 2,470 1,613 1,455
Net change in commercial paper (470) 83 (167)
Other 0 (20) 3
Net cash flows from (used for) financing activities 1,202 398 573
Net increase (decrease) in cash, cash equivalents and restricted cash 475 18 39
Cash, cash equivalents and restricted cash at beginning of period 81 63 24
Cash, cash equivalents and restricted cash at end of period 556 81 63
Supplemental cash flows information:      
Interest (500) (434) (378)
Income taxes, net 266 197 88
Federal [Member]      
Supplemental cash flows information:      
Income taxes, net 271 202 82
Iowa State [Member]      
Supplemental cash flows information:      
Income taxes, net (5) (5) 6
Parent Company [Member]      
Statement [Line Items]      
Net cash flows from operating activities 529 355 445
Cash flows from (used for) investing activities:      
Capital contributions to consolidated subsidiaries (365) (380) (325)
Net change in notes receivable from and payable to affiliates (113) 326 (281)
Net cash flows from (used for) investing activities (478) (54) (606)
Cash flows used for financing activities:      
Common stock dividends (521) (492) (456)
Proceeds from issuance of common stock, net 23 23 246
Proceeds from issuance of long-term debt 1,286 0 565
Net change in commercial paper (325) 168 (195)
Other (2) 0 1
Net cash flows from (used for) financing activities 461 (301) 161
Net increase (decrease) in cash, cash equivalents and restricted cash 512 0 0
Cash, cash equivalents and restricted cash at beginning of period 0 0 0
Cash, cash equivalents and restricted cash at end of period 512 0 0
Supplemental cash flows information:      
Interest (45) (40) (27)
Income taxes, net 4 8 22
Parent Company [Member] | Federal [Member]      
Supplemental cash flows information:      
Income taxes, net 4 11 8
Parent Company [Member] | Iowa State [Member]      
Supplemental cash flows information:      
Income taxes, net 0 (15) (13)
Parent Company [Member] | State Taxes - Wisconsin [Member]      
Supplemental cash flows information:      
Income taxes, net $ 0 $ 12 $ 27