ALLIANT ENERGY CORP, 10-K filed on 2/21/2025
Annual Report
v3.25.0.1
Document And Entity Information - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Jan. 31, 2025
Jun. 30, 2024
Entity Information [Line Items]      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Dec. 31, 2024    
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     $ 13,000.0
Entity Common Stock, Shares Outstanding   256,692,381  
Current Fiscal Year End Date --12-31    
Document Fiscal Year Focus 2024    
Document Fiscal Period Focus FY    
Amendment Flag false    
Documents Incorporated by Reference
Portions of the Proxy Statement relating to Alliant Energy Corporation’s 2025 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    
v3.25.0.1
Consolidated Statements Of Income - USD ($)
shares in Millions, $ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Revenues:      
Electric utility $ 3,372 $ 3,345 $ 3,421
Gas utility 465 540 642
Other utility 54 52 49
Non-utility 90 90 93
Total revenues 3,981 4,027 4,205
Operating expenses:      
Electric production fuel and purchased power 628 736 830
Electric transmission service 613 583 573
Cost of gas sold 224 299 389
Asset valuation charge for IPL's Lansing Generating Station 60 0 0
Other operation and maintenance 676 675 704
Depreciation and amortization 772 676 671
Taxes other than income taxes 122 115 110
Total operating expenses 3,095 3,084 3,277
Operating income (loss) 886 943 928
Other (income) and deductions:      
Interest expense 449 394 325
Equity income from unconsolidated investments, net (61) (61) (51)
Allowance for funds used during construction (75) (100) (60)
Other (3) 3 6
Total other (income) and deductions 310 236 220
Income before income taxes 576 707 708
Income tax expense (benefit) (114) 4 22
Net income attributable to common shareowners $ 690 $ 703 $ 686
Weighted average number of common shares outstanding:      
Basic (in shares) 256.5 253.0 250.9
Diluted (in shares) 256.8 253.3 251.2
Earnings per weighted average common share attributable to Alliant Energy common shareowners:      
Basic (in dollars per share) $ 2.69 $ 2.78 $ 2.73
Diluted (in dollars per share) $ 2.69 $ 2.78 $ 2.73
IPL [Member]      
Revenues:      
Electric utility $ 1,747 $ 1,761 $ 1,859
Gas utility 250 300 351
Other utility 49 49 46
Total revenues 2,046 2,110 2,256
Operating expenses:      
Electric production fuel and purchased power 269 282 383
Electric transmission service 417 420 407
Cost of gas sold 123 166 206
Asset valuation charge for IPL's Lansing Generating Station 60 0 0
Other operation and maintenance 358 353 369
Depreciation and amortization 404 388 381
Taxes other than income taxes 60 57 57
Total operating expenses 1,691 1,666 1,803
Operating income (loss) 355 444 453
Other (income) and deductions:      
Interest expense 177 155 148
Allowance for funds used during construction (43) (21) (11)
Other (12) 2 6
Total other (income) and deductions 122 136 143
Income before income taxes 233 308 310
Income tax expense (benefit) (129) (58) (50)
Net income attributable to common shareowners 362 366 360
WPL [Member]      
Revenues:      
Electric utility 1,625 1,584 1,562
Gas utility 215 240 291
Other utility 5 3 3
Total revenues 1,845 1,827 1,856
Operating expenses:      
Electric production fuel and purchased power 359 455 447
Electric transmission service 196 163 166
Cost of gas sold 101 134 183
Other operation and maintenance 279 271 278
Depreciation and amortization 357 280 283
Taxes other than income taxes 56 52 47
Total operating expenses 1,348 1,355 1,404
Operating income (loss) 497 472 452
Other (income) and deductions:      
Interest expense 165 149 121
Allowance for funds used during construction (32) (79) (49)
Other 8 (3) (1)
Total other (income) and deductions 141 67 71
Income before income taxes 356 405 381
Income tax expense (benefit) 11 60 66
Net income attributable to common shareowners $ 345 $ 345 $ 315
v3.25.0.1
Consolidated Balance Sheets - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Current assets:    
Cash and cash equivalents $ 81.0 $ 62.0
Accounts receivable, less allowance for expected credit losses 427.0 475.0
Production fuel, at weighted average cost 54.0 62.0
Gas stored underground, at weighted average cost 55.0 79.0
Materials and supplies, at weighted average cost 186.0 202.0
Regulatory assets 210.0 232.0
Other 171.0 160.0
Total current assets 1,184.0 1,272.0
Property, plant and equipment, net 18,701.0 17,157.0
Investments:    
ATC Holdings 415.0 386.0
Other 224.0 216.0
Total investments 639.0 602.0
Other assets:    
Regulatory assets 2,064.0 2,029.0
Deferred charges and other 126.0 177.0
Total other assets 2,190.0 2,206.0
Total assets 22,714.0 21,237.0
Current liabilities:    
Current maturities of long-term debt 1,171.0 809.0
Commercial paper 558.0 475.0
Accounts payable 532.0 611.0
Regulatory liabilities 69.0 107.0
Other 385.0 302.0
Total current liabilities 2,715.0 2,304.0
Long-term debt, net (excluding current portion) 8,677.0 8,225.0
Other liabilities:    
Deferred tax liabilities 2,188.0 2,042.0
Regulatory liabilities 959.0 1,023.0
Pension and other benefit obligations 224.0 249.0
Other 947.0 617.0
Total other liabilities 4,318.0 3,931.0
Commitments and contingencies (Note 16)
Common equity:    
Common stock 3.0 3.0
Additional paid-in capital 3,060.0 3,030.0
Retained earnings 3,954.0 3,756.0
Accumulated other comprehensive income 1.0 1.0
Shares in deferred compensation trust - 372,116 and 379,006 shares at a weighted average cost of $36.56 and $34.48 per share (14.0) (13.0)
Total common equity 7,004.0 6,777.0
Total liabilities and equity 22,714.0 21,237.0
IPL [Member]    
Current assets:    
Cash and cash equivalents 29.0 53.0
Accounts receivable, less allowance for expected credit losses 192.0 242.0
Production fuel, at weighted average cost 30.0 27.0
Gas stored underground, at weighted average cost 25.0 35.0
Materials and supplies, at weighted average cost 113.0 122.0
Regulatory assets 77.0 93.0
Other 43.0 51.0
Total current assets 509.0 623.0
Property, plant and equipment, net 9,336.0 8,298.0
Other assets:    
Regulatory assets 1,509.0 1,484.0
Deferred charges and other 53.0 84.0
Total other assets 1,562.0 1,568.0
Total assets 11,407.0 10,489.0
Current liabilities:    
Current maturities of long-term debt 300.0 500.0
Commercial paper 50.0 0.0
Accounts payable 263.0 262.0
Accounts payable to associated companies 47.0 51.0
Accrued taxes 77.0 50.0
Accrued interest 48.0 40.0
Regulatory liabilities 54.0 72.0
Other 89.0 50.0
Total current liabilities 928.0 1,025.0
Long-term debt, net (excluding current portion) 3,790.0 3,445.0
Other liabilities:    
Deferred tax liabilities 1,179.0 1,091.0
Regulatory liabilities 492.0 572.0
Pension and other benefit obligations 46.0 51.0
Other 511.0 331.0
Total other liabilities 2,228.0 2,045.0
Commitments and contingencies (Note 16)
Common equity:    
Common stock 33.0 33.0
Additional paid-in capital 3,212.0 2,887.0
Retained earnings 1,216.0 1,054.0
Total common equity 4,461.0 3,974.0
Total liabilities and equity 11,407.0 10,489.0
WPL [Member]    
Current assets:    
Cash and cash equivalents 51.0 7.0
Accounts receivable, less allowance for expected credit losses 220.0 219.0
Production fuel, at weighted average cost 24.0 35.0
Gas stored underground, at weighted average cost 30.0 44.0
Materials and supplies, at weighted average cost 69.0 77.0
Regulatory assets 133.0 139.0
Prepaid gross receipts tax 51.0 49.0
Other 57.0 43.0
Total current assets 635.0 613.0
Property, plant and equipment, net 8,861.0 8,415.0
Other assets:    
Regulatory assets 555.0 545.0
Deferred charges and other 55.0 61.0
Total other assets 610.0 606.0
Total assets 10,106.0 9,634.0
Current liabilities:    
Current maturities of long-term debt 0.0 0.0
Commercial paper 183.0 318.0
Accounts payable 209.0 293.0
Accrued interest 44.0 40.0
Regulatory liabilities 15.0 35.0
Other 94.0 89.0
Total current liabilities 545.0 775.0
Long-term debt, net (excluding current portion) 3,370.0 3,070.0
Other liabilities:    
Deferred tax liabilities 865.0 827.0
Regulatory liabilities 467.0 451.0
Pension and other benefit obligations 102.0 121.0
Other 656.0 493.0
Total other liabilities 2,090.0 1,892.0
Commitments and contingencies (Note 16)
Common equity:    
Common stock 66.0 66.0
Additional paid-in capital 2,533.0 2,478.0
Retained earnings 1,502.0 1,353.0
Total common equity 4,101.0 3,897.0
Total liabilities and equity $ 10,106.0 $ 9,634.0
v3.25.0.1
Consolidated Balance Sheets (Parenthetical) - $ / shares
Dec. 31, 2024
Dec. 31, 2023
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) 256,690,222 256,096,848
Shares in deferred compensation trust (in shares) 372,116 379,006
Shares in deferred compensation trust, weighted average cost per share (in dollars per share) $ 36.56 $ 34.48
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
v3.25.0.1
Consolidated Statements Of Cash Flows - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Cash flows from operating activities:      
Net income $ 690 $ 703 $ 686
Adjustments to reconcile net income to net cash flows from operating activities:      
Depreciation and amortization 772 676 671
Deferred tax expense (benefit) and tax credits (117) 14 13
Asset valuation charge for IPL's Lansing Generating Station 60 0 0
Other (22) (39) (17)
Other changes in assets and liabilities:      
Accounts receivable (547) (414) (672)
Regulatory assets 70 24 (108)
Derivative assets 13 149 (61)
Accounts payable 96 (122) 78
Regulatory liabilities (103) (149) 22
Deferred income taxes 259 84 4
Pension and other benefit obligations (25) (28) (97)
Other 21 (31) (33)
Net cash flows from operating activities 1,167 867 486
Cash flows from (used for) investing activities:      
Utility construction and acquisition expenditures (2,052) (1,731) (1,392)
Other construction and acquisition expenditures (197) (123) (92)
Cash receipts on sold receivables 593 453 598
Proceeds from sales of partial ownership interests in West Riverside 123 120 0
Other (14) (120) (47)
Net cash flows from (used for) investing activities (1,547) (1,401) (933)
Cash flows from (used for) financing activities:      
Common stock dividends (492) (456) (428)
Proceeds from issuance of common stock, net 23 246 25
Proceeds from issuance of long-term debt 1,613 1,455 1,338
Payments to retire long-term debt (809) (508) (633)
Net change in commercial paper 83 (167) 127
Other (20) 3 2
Net cash flows from (used for) financing activities 398 573 431
Net increase (decrease) in cash, cash equivalents and restricted cash 18 39 (16)
Cash, cash equivalents and restricted cash at beginning of period 63 24 40
Cash, cash equivalents and restricted cash at end of period 81 63 24
Supplemental cash flows information:      
Interest (434) (378) (311)
Income taxes, net 197 88 (6)
Significant non-cash investing and financing activities:      
Accrued capital expenditures 224 364 382
Beneficial interest obtained in exchange for securitized accounts receivable 163 216 185
Indemnification Agreement [Member] | Renewable Tax Credits Transferred [Member]      
Supplemental cash flows information:      
Proceeds from renewable tax credits transferred to other corporate taxpayers 216 98  
IPL [Member]      
Cash flows from operating activities:      
Net income 362 366 360
Adjustments to reconcile net income to net cash flows from operating activities:      
Depreciation and amortization 404 388 381
Deferred tax expense (benefit) and tax credits (91) 8 (13)
Asset valuation charge for IPL's Lansing Generating Station 60 0 0
Other (12) (10) (8)
Other changes in assets and liabilities:      
Accounts receivable (544) (437) (611)
Regulatory assets (2) 58 56
Derivative assets 6 84 (54)
Accounts payable 31 (68) 65
Regulatory liabilities (61) (92) 53
Deferred income taxes 178 36 (24)
Pension and other benefit obligations (5) (11) (65)
Other 31 (61) (57)
Net cash flows from operating activities 357 261 83
Cash flows from (used for) investing activities:      
Utility construction and acquisition expenditures (1,224) (712) (372)
Cash receipts on sold receivables 593 453 598
Other (53) (67) (11)
Net cash flows from (used for) investing activities (684) (326) 215
Cash flows from (used for) financing activities:      
Common stock dividends (200) (280) (321)
Capital contributions from parent 325 80 0
Proceeds from issuance of long-term debt 643 296 0
Payments to retire long-term debt (500) 0 0
Net change in commercial paper 50 0 0
Other (15) 7 4
Net cash flows from (used for) financing activities 303 103 (317)
Net increase (decrease) in cash, cash equivalents and restricted cash (24) 38 (19)
Cash, cash equivalents and restricted cash at beginning of period 53 15 34
Cash, cash equivalents and restricted cash at end of period 29 53 15
Supplemental cash flows information:      
Interest (169) (150) (148)
Income taxes, net 175 117 36
Significant non-cash investing and financing activities:      
Accrued capital expenditures 128 140 56
Beneficial interest obtained in exchange for securitized accounts receivable 163 216 185
IPL [Member] | Indemnification Agreement [Member] | Renewable Tax Credits Transferred [Member]      
Supplemental cash flows information:      
Proceeds from renewable tax credits transferred to other corporate taxpayers 117 76  
WPL [Member]      
Cash flows from operating activities:      
Net income 345 345 315
Adjustments to reconcile net income to net cash flows from operating activities:      
Depreciation and amortization 357 280 283
Equity component of allowance for funds used during construction (23) (59) (36)
Other (28) 12 25
Other changes in assets and liabilities:      
Regulatory assets 72 (34) (163)
Derivative assets 7 65 (7)
Accounts payable 50 (57) 22
Regulatory liabilities (41) (57) (31)
Deferred income taxes 84 50 32
Other (62) 33 (141)
Net cash flows from operating activities 761 578 299
Cash flows from (used for) investing activities:      
Utility construction and acquisition expenditures (828) (1,019) (1,020)
Proceeds from sales of partial ownership interests in West Riverside 123 120 0
Other (19) (47) (13)
Net cash flows from (used for) investing activities (724) (946) (1,033)
Cash flows from (used for) financing activities:      
Common stock dividends (196) (184) (176)
Capital contributions from parent 55 245 530
Proceeds from issuance of long-term debt 297 297 588
Payments to retire long-term debt 0 0 (250)
Net change in commercial paper (135) 28 54
Other (14) (16) (9)
Net cash flows from (used for) financing activities 7 370 737
Net increase (decrease) in cash, cash equivalents and restricted cash 44 2 3
Cash, cash equivalents and restricted cash at beginning of period 7 5 2
Cash, cash equivalents and restricted cash at end of period 51 7 5
Supplemental cash flows information:      
Interest (163) (146) (111)
Income taxes, net 14 (50) (56)
Significant non-cash investing and financing activities:      
Accrued capital expenditures 87 217 $ 319
WPL [Member] | Indemnification Agreement [Member] | Renewable Tax Credits Transferred [Member]      
Supplemental cash flows information:      
Proceeds from renewable tax credits transferred to other corporate taxpayers $ 99 $ 22  
v3.25.0.1
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, 2021       $ 3 $ 33 $ 66 $ 2,749 $ 2,807 $ 1,704 $ 3,250 $ 929 $ 1,053 $ 0 $ (12)
Beginning balance at Dec. 31, 2021 $ 5,990 $ 3,769 $ 2,823                      
Increase (Decrease) in Shareowners' Equity [Roll Forward]                            
Net income attributable to common shareowners 686 360 315             686 360 315    
Common stock dividends (428) (321) (176)             (428) (321) (176)    
At-the-market offering program, net and Shareowner Direct Plan issuances 25           25              
Capital contributions from parent   0 530           530          
Equity-based compensation plans and other 3   (1)       3   (1) 1       (1)
Ending balance at Dec. 31, 2022       3 33 66 2,777 2,807 2,233 3,509 968 1,192 0 (13)
Ending balance at Dec. 31, 2022 6,276 3,808 3,491                      
Increase (Decrease) in Shareowners' Equity [Roll Forward]                            
Net income attributable to common shareowners 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 6,777 3,974 3,897 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 attributable to common shareowners 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                      
v3.25.0.1
Consolidated Statements of Common Equity (Parenthetical) - $ / shares
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Statement of Stockholders' Equity [Abstract]      
Common stock dividends (in dollars per share) $ 1.92 $ 1.81 $ 1.71
v3.25.0.1
Summary Of Significant Accounting Policies
 12 Months Ended
Dec. 31, 2024
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 Minnesota, Illinois and Iowa, and is engaged in the generation and distribution of steam for two customers in Cedar Rapids, Iowa. In July 2025, IPL’s wholesale power agreement with Southern Minnesota Energy Cooperative will expire.

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; wind turbine blade recycling 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 various state regulatory commissions. 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).

The Inflation Reduction Act of 2022 provides the ability to transfer renewable tax credits to other corporate taxpayers. In 2023 and 2024, IPL and WPL 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. For renewable tax credits subject to future transfer, a valuation allowance is recorded for the difference between the tax value of the credits and the expected sales price. Renewable tax credits and any related valuation allowances 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 revenue deficiency in future years. At WPL, pursuant to escrow treatment approved by the PSCW, the difference between actual solar and energy storage 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 Notes 11 and 16(d) for further discussion of the transfer of renewable tax credits to other corporate taxpayers, including related valuation allowances and indemnification requirements, respectively.
(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, 2024, Alliant Energy’s, IPL’s and WPL’s cash and cash equivalents included $52 million, $9 million, and $43 million, respectively, of money market fund investments, with weighted average interest rates of 4%. At December 31, 2024 and 2023, 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
202420232022202420232022
Electric - generation3.3%3.3%3.4%3.4%3.0%3.4%
Electric - distribution2.8%2.8%2.8%2.7%2.7%2.5%
Electric - other5.2%5.6%5.7%6.1%6.3%6.8%
Gas3.3%3.3%3.3%2.5%2.5%2.4%
Other4.6%6.2%6.1%4.4%4.6%4.9%

In October 2024, the IUC issued an order approving the implementation of updated depreciation rates for IPL effective October 1, 2024. IPL estimates the new average rates of depreciation for its electric generation and electric distribution properties will be approximately 3.8% and 3.0%, respectively, during 2025.

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:
202420232022
IPL7.0%7.0%7.0%
WPL (retail jurisdiction)7.4%7.4%7.0%
WPL (wholesale jurisdiction)7.1%7.1%6.2%

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.

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, 2024, 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 primarily 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 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. 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.

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 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 related to leased land for solar generation are accounted for as operating leases for rate-making purposes. All other finance lease assets are depreciated on a straight-line basis over the shorter of the useful life of the underlying asset or the lease term.
IPL [Member]  
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 Minnesota, Illinois and Iowa, and is engaged in the generation and distribution of steam for two customers in Cedar Rapids, Iowa. In July 2025, IPL’s wholesale power agreement with Southern Minnesota Energy Cooperative will expire.

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; wind turbine blade recycling 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 various state regulatory commissions. 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).

The Inflation Reduction Act of 2022 provides the ability to transfer renewable tax credits to other corporate taxpayers. In 2023 and 2024, IPL and WPL 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. For renewable tax credits subject to future transfer, a valuation allowance is recorded for the difference between the tax value of the credits and the expected sales price. Renewable tax credits and any related valuation allowances 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 revenue deficiency in future years. At WPL, pursuant to escrow treatment approved by the PSCW, the difference between actual solar and energy storage 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 Notes 11 and 16(d) for further discussion of the transfer of renewable tax credits to other corporate taxpayers, including related valuation allowances and indemnification requirements, respectively.
(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, 2024, Alliant Energy’s, IPL’s and WPL’s cash and cash equivalents included $52 million, $9 million, and $43 million, respectively, of money market fund investments, with weighted average interest rates of 4%. At December 31, 2024 and 2023, 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
202420232022202420232022
Electric - generation3.3%3.3%3.4%3.4%3.0%3.4%
Electric - distribution2.8%2.8%2.8%2.7%2.7%2.5%
Electric - other5.2%5.6%5.7%6.1%6.3%6.8%
Gas3.3%3.3%3.3%2.5%2.5%2.4%
Other4.6%6.2%6.1%4.4%4.6%4.9%

In October 2024, the IUC issued an order approving the implementation of updated depreciation rates for IPL effective October 1, 2024. IPL estimates the new average rates of depreciation for its electric generation and electric distribution properties will be approximately 3.8% and 3.0%, respectively, during 2025.

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:
202420232022
IPL7.0%7.0%7.0%
WPL (retail jurisdiction)7.4%7.4%7.0%
WPL (wholesale jurisdiction)7.1%7.1%6.2%

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.

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, 2024, 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 primarily 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 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. 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.

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 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 related to leased land for solar generation are accounted for as operating leases for rate-making purposes. All other finance lease assets are depreciated on a straight-line basis over the shorter of the useful life of the underlying asset or the lease term.
WPL [Member]  
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 Minnesota, Illinois and Iowa, and is engaged in the generation and distribution of steam for two customers in Cedar Rapids, Iowa. In July 2025, IPL’s wholesale power agreement with Southern Minnesota Energy Cooperative will expire.

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; wind turbine blade recycling 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 various state regulatory commissions. 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).

The Inflation Reduction Act of 2022 provides the ability to transfer renewable tax credits to other corporate taxpayers. In 2023 and 2024, IPL and WPL 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. For renewable tax credits subject to future transfer, a valuation allowance is recorded for the difference between the tax value of the credits and the expected sales price. Renewable tax credits and any related valuation allowances 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 revenue deficiency in future years. At WPL, pursuant to escrow treatment approved by the PSCW, the difference between actual solar and energy storage 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 Notes 11 and 16(d) for further discussion of the transfer of renewable tax credits to other corporate taxpayers, including related valuation allowances and indemnification requirements, respectively.
(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, 2024, Alliant Energy’s, IPL’s and WPL’s cash and cash equivalents included $52 million, $9 million, and $43 million, respectively, of money market fund investments, with weighted average interest rates of 4%. At December 31, 2024 and 2023, 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
202420232022202420232022
Electric - generation3.3%3.3%3.4%3.4%3.0%3.4%
Electric - distribution2.8%2.8%2.8%2.7%2.7%2.5%
Electric - other5.2%5.6%5.7%6.1%6.3%6.8%
Gas3.3%3.3%3.3%2.5%2.5%2.4%
Other4.6%6.2%6.1%4.4%4.6%4.9%

In October 2024, the IUC issued an order approving the implementation of updated depreciation rates for IPL effective October 1, 2024. IPL estimates the new average rates of depreciation for its electric generation and electric distribution properties will be approximately 3.8% and 3.0%, respectively, during 2025.

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:
202420232022
IPL7.0%7.0%7.0%
WPL (retail jurisdiction)7.4%7.4%7.0%
WPL (wholesale jurisdiction)7.1%7.1%6.2%

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.

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, 2024, 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 primarily 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 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. 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.

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 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 related to leased land for solar generation are accounted for as operating leases for rate-making purposes. All other finance lease assets are depreciated on a straight-line basis over the shorter of the useful life of the underlying asset or the lease term.
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Regulatory Matters
 12 Months Ended
Dec. 31, 2024
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, 2024 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
202420232024202320242023
Tax-related$989 $934 $870 $831 $119 $103 
AROs401 194 281 160 120 34 
Pension and OPEB costs315 347 157 171 158 176 
Assets retired early180 273 168 259 12 14 
Commodity cost recovery68 120 2 12 66 108 
Derivatives60 102 15 34 45 68 
Non-service pension and OPEB costs51 46 19 18 32 28 
WPL’s Western Wisconsin gas distribution expansion investments42 44 — — 42 44 
IPL’s DAEC PPA amendment18 42 18 42 — — 
Other150 159 56 50 94 109 
$2,274 $2,261 $1,586 $1,577 $688 $684 

At December 31, 2024, IPL and WPL had $199 million and $23 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, emission allowances and costs for certain construction projects. WPL’s regulatory assets that were not earning a return consisted primarily of 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. Refer to Note 11 for discussion of Iowa Tax Reform, which resulted in a decrease in Alliant Energy’s and IPL’s tax-related regulatory assets in 2024.

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, 2024
RecoveryRegulatory Approval
IPLLansing2023$131Return of (IUC and FERC) and return on (FERC) remaining net book value through 2037 (a)IUC and FERC (b)
IPLAnalog electric meters201915Return of remaining net book value through 2028IUC and FERC
IPLSutherland Units 1 and 3201715Return of and return on remaining net book value through 2027 (a)IUC and FERC
IPLM.L. Kapp Unit 220187Return of and return on remaining net book value through 2029 (a)IUC and FERC
WPLEdgewater Unit 4201812Return 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 Generation 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.

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 is collecting from October 2023 through December 2025 from its retail electric customers, plus interest ($12 million and $50 million was collected in 2023 and 2024, 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.

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 2024, which resulted in comparable changes to regulatory assets/liabilities on the balance sheets.

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.

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.

IPL’s DAEC PPA Amendment - In 2020, IPL made a buyout payment of $110 million in exchange for shortening the term of its DAEC PPA by 5 years. The buyout payment, including a return on, is being recovered from IPL’s retail and wholesale customers from 2021 through 2025, and is currently being amortized to “Electric production fuel and purchased power” in Alliant Energy’s and IPL’s income statements.

Regulatory Liabilities - At December 31, regulatory liabilities were comprised of the following items (in millions):
Alliant EnergyIPLWPL
202420232024202320242023
Tax-related$582$566$286$299$296$267
Cost of removal obligations347366205242142124
Derivatives536529342431
Commodity cost recovery17481213535
Other298514561529
$1,028$1,130$546$644$482$486
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. The increase in Alliant Energy’s and WPL’s tax-related regulatory liabilities was primarily due to tax benefits resulting from WPL electing investment tax credit treatment for its Cassville solar facility in 2024. A majority of these benefits will be addressed in a future regulatory proceeding, with a portion of the benefits passed on to WPL’s electric customers in 2024 and 2025.

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 Fuel-related Rate Filing (2021 Forward-looking Test Period) - In 2023, WPL collected $37 million, plus interest, from its retail electric customers related to actual fuel-related costs for 2021 that were higher than fuel-related costs used to determine rates for such 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, 2024 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
202420232024202320242023
Tax-related$989 $934 $870 $831 $119 $103 
AROs401 194 281 160 120 34 
Pension and OPEB costs315 347 157 171 158 176 
Assets retired early180 273 168 259 12 14 
Commodity cost recovery68 120 2 12 66 108 
Derivatives60 102 15 34 45 68 
Non-service pension and OPEB costs51 46 19 18 32 28 
WPL’s Western Wisconsin gas distribution expansion investments42 44 — — 42 44 
IPL’s DAEC PPA amendment18 42 18 42 — — 
Other150 159 56 50 94 109 
$2,274 $2,261 $1,586 $1,577 $688 $684 

At December 31, 2024, IPL and WPL had $199 million and $23 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, emission allowances and costs for certain construction projects. WPL’s regulatory assets that were not earning a return consisted primarily of 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. Refer to Note 11 for discussion of Iowa Tax Reform, which resulted in a decrease in Alliant Energy’s and IPL’s tax-related regulatory assets in 2024.

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, 2024
RecoveryRegulatory Approval
IPLLansing2023$131Return of (IUC and FERC) and return on (FERC) remaining net book value through 2037 (a)IUC and FERC (b)
IPLAnalog electric meters201915Return of remaining net book value through 2028IUC and FERC
IPLSutherland Units 1 and 3201715Return of and return on remaining net book value through 2027 (a)IUC and FERC
IPLM.L. Kapp Unit 220187Return of and return on remaining net book value through 2029 (a)IUC and FERC
WPLEdgewater Unit 4201812Return 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 Generation 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.

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 is collecting from October 2023 through December 2025 from its retail electric customers, plus interest ($12 million and $50 million was collected in 2023 and 2024, 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.

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 2024, which resulted in comparable changes to regulatory assets/liabilities on the balance sheets.

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.

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.

IPL’s DAEC PPA Amendment - In 2020, IPL made a buyout payment of $110 million in exchange for shortening the term of its DAEC PPA by 5 years. The buyout payment, including a return on, is being recovered from IPL’s retail and wholesale customers from 2021 through 2025, and is currently being amortized to “Electric production fuel and purchased power” in Alliant Energy’s and IPL’s income statements.

Regulatory Liabilities - At December 31, regulatory liabilities were comprised of the following items (in millions):
Alliant EnergyIPLWPL
202420232024202320242023
Tax-related$582$566$286$299$296$267
Cost of removal obligations347366205242142124
Derivatives536529342431
Commodity cost recovery17481213535
Other298514561529
$1,028$1,130$546$644$482$486
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. The increase in Alliant Energy’s and WPL’s tax-related regulatory liabilities was primarily due to tax benefits resulting from WPL electing investment tax credit treatment for its Cassville solar facility in 2024. A majority of these benefits will be addressed in a future regulatory proceeding, with a portion of the benefits passed on to WPL’s electric customers in 2024 and 2025.

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 Fuel-related Rate Filing (2021 Forward-looking Test Period) - In 2023, WPL collected $37 million, plus interest, from its retail electric customers related to actual fuel-related costs for 2021 that were higher than fuel-related costs used to determine rates for such 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.
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, 2024 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
202420232024202320242023
Tax-related$989 $934 $870 $831 $119 $103 
AROs401 194 281 160 120 34 
Pension and OPEB costs315 347 157 171 158 176 
Assets retired early180 273 168 259 12 14 
Commodity cost recovery68 120 2 12 66 108 
Derivatives60 102 15 34 45 68 
Non-service pension and OPEB costs51 46 19 18 32 28 
WPL’s Western Wisconsin gas distribution expansion investments42 44 — — 42 44 
IPL’s DAEC PPA amendment18 42 18 42 — — 
Other150 159 56 50 94 109 
$2,274 $2,261 $1,586 $1,577 $688 $684 

At December 31, 2024, IPL and WPL had $199 million and $23 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, emission allowances and costs for certain construction projects. WPL’s regulatory assets that were not earning a return consisted primarily of 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. Refer to Note 11 for discussion of Iowa Tax Reform, which resulted in a decrease in Alliant Energy’s and IPL’s tax-related regulatory assets in 2024.

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, 2024
RecoveryRegulatory Approval
IPLLansing2023$131Return of (IUC and FERC) and return on (FERC) remaining net book value through 2037 (a)IUC and FERC (b)
IPLAnalog electric meters201915Return of remaining net book value through 2028IUC and FERC
IPLSutherland Units 1 and 3201715Return of and return on remaining net book value through 2027 (a)IUC and FERC
IPLM.L. Kapp Unit 220187Return of and return on remaining net book value through 2029 (a)IUC and FERC
WPLEdgewater Unit 4201812Return 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 Generation 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.

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 is collecting from October 2023 through December 2025 from its retail electric customers, plus interest ($12 million and $50 million was collected in 2023 and 2024, 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.

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 2024, which resulted in comparable changes to regulatory assets/liabilities on the balance sheets.

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.

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.

IPL’s DAEC PPA Amendment - In 2020, IPL made a buyout payment of $110 million in exchange for shortening the term of its DAEC PPA by 5 years. The buyout payment, including a return on, is being recovered from IPL’s retail and wholesale customers from 2021 through 2025, and is currently being amortized to “Electric production fuel and purchased power” in Alliant Energy’s and IPL’s income statements.

Regulatory Liabilities - At December 31, regulatory liabilities were comprised of the following items (in millions):
Alliant EnergyIPLWPL
202420232024202320242023
Tax-related$582$566$286$299$296$267
Cost of removal obligations347366205242142124
Derivatives536529342431
Commodity cost recovery17481213535
Other298514561529
$1,028$1,130$546$644$482$486
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. The increase in Alliant Energy’s and WPL’s tax-related regulatory liabilities was primarily due to tax benefits resulting from WPL electing investment tax credit treatment for its Cassville solar facility in 2024. A majority of these benefits will be addressed in a future regulatory proceeding, with a portion of the benefits passed on to WPL’s electric customers in 2024 and 2025.

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 Fuel-related Rate Filing (2021 Forward-looking Test Period) - In 2023, WPL collected $37 million, plus interest, from its retail electric customers related to actual fuel-related costs for 2021 that were higher than fuel-related costs used to determine rates for such period.
v3.25.0.1
Property, Plant and Equipment
 12 Months Ended
Dec. 31, 2024
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
202420232024202320242023
Utility:
Electric plant:
Generation in service (a)(b)$11,156 $9,180 $5,924 $5,025 $5,232 $4,155 
Distribution in service7,811 7,314 4,344 4,091 3,467 3,223 
Other in service595 567 385 356 210 211 
Anticipated to be retired early (c)784 1,629 — — 784 1,629 
Total electric plant20,346 18,690 10,653 9,472 9,693 9,218 
Gas plant in service1,863 1,791 981951 882 840 
Other plant in service (d)734 653 456411 278 242 
Accumulated depreciation (c)(6,229)(5,924)(3,360)(3,180)(2,869)(2,744)
Net plant16,714 15,210 8,730 7,654 7,984 7,556 
Leased Sheboygan Falls Energy Facility, net (e)— — — — 74 79 
Leased land for solar generation, net189 172 53 33 136 139 
Construction work in progress1,215 1,245 548605 667 640 
Other, net5 7 5 6 — 1 
Total utility18,123 16,634 9,336 8,298 8,861 8,415 
Non-utility and other:
Non-utility Generation, net (f)103 68 — — — — 
Corporate Services and other, net (g)475455 — — — — 
Total non-utility and other578 523 — — — — 
Total property, plant and equipment$18,701 $17,157 $9,336 $8,298 $8,861 $8,415 

(a)Alliant Energy and WPL currently expect construction costs associated with WPL’s approximately 1,100 MW of new solar generation will exceed 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. Alliant Energy and WPL concluded that there was not a probable disallowance of the higher rate base amounts as of December 31, 2024 given construction costs were reasonably and prudently incurred.
(b)In September 2024, the IUC approved IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period, which allows IPL to recover construction costs associated with its 400 MW of new solar generation, including AFUDC and transmission upgrade costs among other costs, above the original cost target of $1,650/kilowatt up to $1,837.5/kilowatt. The costs up to the original cost target of $1,650/kilowatt will earn a return on common equity of 10.25%. The costs between $1,650/kilowatt and $1,837.5/kilowatt will earn a return on common equity that is the same as other assets without advance rate-making principles, without having to establish that such costs were reasonably and prudently incurred. Alliant Energy and IPL currently do not expect these construction costs will exceed $1,837.5/kilowatt.
(c)WPL previously received approval from MISO to retire the coal-fired Columbia Units 1 and 2, and Edgewater Unit 5. WPL currently plans to cease coal operations at Columbia Units 1 and 2 by the end of 2029, as well as evaluate the conversion of Columbia Unit 1 and/or Unit 2 to natural gas. Alliant Energy and WPL concluded that Columbia Units 1 and 2 met the criteria to be considered probable of abandonment as of December 31, 2024. As of December 31, 2024 and 2023, the net book value of Columbia Units 1 and 2 in aggregate was $413 million and $428 million, respectively. As of December 31, 2023, WPL anticipated retiring Edgewater Unit 5 by June 1, 2025, and Alliant Energy and WPL concluded that Edgewater Unit 5 met the criteria to be considered probable of abandonment. In May 2024, WPL announced updated plans to convert Edgewater Unit 5 to natural gas by 2028, subject to regulatory approvals. As a result, as of December 31, 2024, Alliant Energy and WPL concluded that Edgewater Unit 5 no longer meets the criteria to be considered probable of abandonment. WPL is currently allowed a full recovery of and a full return on these EGUs from both its retail and wholesale customers, and as a result, as of December 31, 2024, Alliant Energy and WPL concluded that no disallowance was probable.
(d)Includes IPL’s steam service assets, which are fully depreciated as of December 31, 2024. IPL’s steam customers are each under contract through 2025 for taking minimum quantities of annual steam usage, with certain conditions.
(e)Less accumulated amortization of $116 million and $112 million for WPL as of December 31, 2024 and 2023, respectively. Refer to Note 9 for discussion of WPL’s renewal of this lease in 2024. 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.
(f)Less accumulated depreciation of $78 million and $75 million for Alliant Energy as of December 31, 2024 and 2023, respectively.
(g)Less accumulated depreciation of $289 million and $275 million for Alliant Energy as of December 31, 2024 and 2023, 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
202420232022202420232022202420232022
Equity$54$74$44$31$15$8$23$59$36
Debt212616126392013
$75$100$60$43$21$11$32$79$49

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 35-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; wind turbine blade recycling services; 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
202420232024202320242023
Utility:
Electric plant:
Generation in service (a)(b)$11,156 $9,180 $5,924 $5,025 $5,232 $4,155 
Distribution in service7,811 7,314 4,344 4,091 3,467 3,223 
Other in service595 567 385 356 210 211 
Anticipated to be retired early (c)784 1,629 — — 784 1,629 
Total electric plant20,346 18,690 10,653 9,472 9,693 9,218 
Gas plant in service1,863 1,791 981951 882 840 
Other plant in service (d)734 653 456411 278 242 
Accumulated depreciation (c)(6,229)(5,924)(3,360)(3,180)(2,869)(2,744)
Net plant16,714 15,210 8,730 7,654 7,984 7,556 
Leased Sheboygan Falls Energy Facility, net (e)— — — — 74 79 
Leased land for solar generation, net189 172 53 33 136 139 
Construction work in progress1,215 1,245 548605 667 640 
Other, net5 7 5 6 — 1 
Total utility18,123 16,634 9,336 8,298 8,861 8,415 
Non-utility and other:
Non-utility Generation, net (f)103 68 — — — — 
Corporate Services and other, net (g)475455 — — — — 
Total non-utility and other578 523 — — — — 
Total property, plant and equipment$18,701 $17,157 $9,336 $8,298 $8,861 $8,415 

(a)Alliant Energy and WPL currently expect construction costs associated with WPL’s approximately 1,100 MW of new solar generation will exceed 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. Alliant Energy and WPL concluded that there was not a probable disallowance of the higher rate base amounts as of December 31, 2024 given construction costs were reasonably and prudently incurred.
(b)In September 2024, the IUC approved IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period, which allows IPL to recover construction costs associated with its 400 MW of new solar generation, including AFUDC and transmission upgrade costs among other costs, above the original cost target of $1,650/kilowatt up to $1,837.5/kilowatt. The costs up to the original cost target of $1,650/kilowatt will earn a return on common equity of 10.25%. The costs between $1,650/kilowatt and $1,837.5/kilowatt will earn a return on common equity that is the same as other assets without advance rate-making principles, without having to establish that such costs were reasonably and prudently incurred. Alliant Energy and IPL currently do not expect these construction costs will exceed $1,837.5/kilowatt.
(c)WPL previously received approval from MISO to retire the coal-fired Columbia Units 1 and 2, and Edgewater Unit 5. WPL currently plans to cease coal operations at Columbia Units 1 and 2 by the end of 2029, as well as evaluate the conversion of Columbia Unit 1 and/or Unit 2 to natural gas. Alliant Energy and WPL concluded that Columbia Units 1 and 2 met the criteria to be considered probable of abandonment as of December 31, 2024. As of December 31, 2024 and 2023, the net book value of Columbia Units 1 and 2 in aggregate was $413 million and $428 million, respectively. As of December 31, 2023, WPL anticipated retiring Edgewater Unit 5 by June 1, 2025, and Alliant Energy and WPL concluded that Edgewater Unit 5 met the criteria to be considered probable of abandonment. In May 2024, WPL announced updated plans to convert Edgewater Unit 5 to natural gas by 2028, subject to regulatory approvals. As a result, as of December 31, 2024, Alliant Energy and WPL concluded that Edgewater Unit 5 no longer meets the criteria to be considered probable of abandonment. WPL is currently allowed a full recovery of and a full return on these EGUs from both its retail and wholesale customers, and as a result, as of December 31, 2024, Alliant Energy and WPL concluded that no disallowance was probable.
(d)Includes IPL’s steam service assets, which are fully depreciated as of December 31, 2024. IPL’s steam customers are each under contract through 2025 for taking minimum quantities of annual steam usage, with certain conditions.
(e)Less accumulated amortization of $116 million and $112 million for WPL as of December 31, 2024 and 2023, respectively. Refer to Note 9 for discussion of WPL’s renewal of this lease in 2024. 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.
(f)Less accumulated depreciation of $78 million and $75 million for Alliant Energy as of December 31, 2024 and 2023, respectively.
(g)Less accumulated depreciation of $289 million and $275 million for Alliant Energy as of December 31, 2024 and 2023, 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
202420232022202420232022202420232022
Equity$54$74$44$31$15$8$23$59$36
Debt212616126392013
$75$100$60$43$21$11$32$79$49
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
202420232024202320242023
Utility:
Electric plant:
Generation in service (a)(b)$11,156 $9,180 $5,924 $5,025 $5,232 $4,155 
Distribution in service7,811 7,314 4,344 4,091 3,467 3,223 
Other in service595 567 385 356 210 211 
Anticipated to be retired early (c)784 1,629 — — 784 1,629 
Total electric plant20,346 18,690 10,653 9,472 9,693 9,218 
Gas plant in service1,863 1,791 981951 882 840 
Other plant in service (d)734 653 456411 278 242 
Accumulated depreciation (c)(6,229)(5,924)(3,360)(3,180)(2,869)(2,744)
Net plant16,714 15,210 8,730 7,654 7,984 7,556 
Leased Sheboygan Falls Energy Facility, net (e)— — — — 74 79 
Leased land for solar generation, net189 172 53 33 136 139 
Construction work in progress1,215 1,245 548605 667 640 
Other, net5 7 5 6 — 1 
Total utility18,123 16,634 9,336 8,298 8,861 8,415 
Non-utility and other:
Non-utility Generation, net (f)103 68 — — — — 
Corporate Services and other, net (g)475455 — — — — 
Total non-utility and other578 523 — — — — 
Total property, plant and equipment$18,701 $17,157 $9,336 $8,298 $8,861 $8,415 

(a)Alliant Energy and WPL currently expect construction costs associated with WPL’s approximately 1,100 MW of new solar generation will exceed 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. Alliant Energy and WPL concluded that there was not a probable disallowance of the higher rate base amounts as of December 31, 2024 given construction costs were reasonably and prudently incurred.
(b)In September 2024, the IUC approved IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period, which allows IPL to recover construction costs associated with its 400 MW of new solar generation, including AFUDC and transmission upgrade costs among other costs, above the original cost target of $1,650/kilowatt up to $1,837.5/kilowatt. The costs up to the original cost target of $1,650/kilowatt will earn a return on common equity of 10.25%. The costs between $1,650/kilowatt and $1,837.5/kilowatt will earn a return on common equity that is the same as other assets without advance rate-making principles, without having to establish that such costs were reasonably and prudently incurred. Alliant Energy and IPL currently do not expect these construction costs will exceed $1,837.5/kilowatt.
(c)WPL previously received approval from MISO to retire the coal-fired Columbia Units 1 and 2, and Edgewater Unit 5. WPL currently plans to cease coal operations at Columbia Units 1 and 2 by the end of 2029, as well as evaluate the conversion of Columbia Unit 1 and/or Unit 2 to natural gas. Alliant Energy and WPL concluded that Columbia Units 1 and 2 met the criteria to be considered probable of abandonment as of December 31, 2024. As of December 31, 2024 and 2023, the net book value of Columbia Units 1 and 2 in aggregate was $413 million and $428 million, respectively. As of December 31, 2023, WPL anticipated retiring Edgewater Unit 5 by June 1, 2025, and Alliant Energy and WPL concluded that Edgewater Unit 5 met the criteria to be considered probable of abandonment. In May 2024, WPL announced updated plans to convert Edgewater Unit 5 to natural gas by 2028, subject to regulatory approvals. As a result, as of December 31, 2024, Alliant Energy and WPL concluded that Edgewater Unit 5 no longer meets the criteria to be considered probable of abandonment. WPL is currently allowed a full recovery of and a full return on these EGUs from both its retail and wholesale customers, and as a result, as of December 31, 2024, Alliant Energy and WPL concluded that no disallowance was probable.
(d)Includes IPL’s steam service assets, which are fully depreciated as of December 31, 2024. IPL’s steam customers are each under contract through 2025 for taking minimum quantities of annual steam usage, with certain conditions.
(e)Less accumulated amortization of $116 million and $112 million for WPL as of December 31, 2024 and 2023, respectively. Refer to Note 9 for discussion of WPL’s renewal of this lease in 2024. 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.
(f)Less accumulated depreciation of $78 million and $75 million for Alliant Energy as of December 31, 2024 and 2023, respectively.
(g)Less accumulated depreciation of $289 million and $275 million for Alliant Energy as of December 31, 2024 and 2023, 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
202420232022202420232022202420232022
Equity$54$74$44$31$15$8$23$59$36
Debt212616126392013
$75$100$60$43$21$11$32$79$49
v3.25.0.1
Jointly-Owned Electric Utility Plant
 12 Months Ended
Dec. 31, 2024
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, 2024 was as follows (dollars in millions):
OwnershipElectricAccumulated ProvisionConstruction
Interest %Plantfor DepreciationWork in Progress
IPL
Ottumwa Unit 148.0%$648$277$7
George Neal Unit 425.7%1971107
George Neal Unit 328.0%1818920
Louisa Unit 14.0%4323—
1,06949934
WPL
Columbia Units 1-2 and Energy Storage System53.5%8593786
West Riverside Energy Center and Solar Facility (a)56.6%449595
Forward Wind Energy Center42.6%11956—
1,42749311
Alliant Energy$2,496$992$45

(a)In 2023 and 2024, WEC Energy Group, Inc. and Madison Gas and Electric Company acquired partial ownership interests in West Riverside. The related proceeds are included in “Proceeds from sales of partial ownership interests in West Riverside” in investing activities in Alliant Energy’s and WPL’s cash flows statements in 2023 and 2024.
IPL [Member]  
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, 2024 was as follows (dollars in millions):
OwnershipElectricAccumulated ProvisionConstruction
Interest %Plantfor DepreciationWork in Progress
IPL
Ottumwa Unit 148.0%$648$277$7
George Neal Unit 425.7%1971107
George Neal Unit 328.0%1818920
Louisa Unit 14.0%4323—
1,06949934
WPL
Columbia Units 1-2 and Energy Storage System53.5%8593786
West Riverside Energy Center and Solar Facility (a)56.6%449595
Forward Wind Energy Center42.6%11956—
1,42749311
Alliant Energy$2,496$992$45

(a)In 2023 and 2024, WEC Energy Group, Inc. and Madison Gas and Electric Company acquired partial ownership interests in West Riverside. The related proceeds are included in “Proceeds from sales of partial ownership interests in West Riverside” in investing activities in Alliant Energy’s and WPL’s cash flows statements in 2023 and 2024.
WPL [Member]  
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, 2024 was as follows (dollars in millions):
OwnershipElectricAccumulated ProvisionConstruction
Interest %Plantfor DepreciationWork in Progress
IPL
Ottumwa Unit 148.0%$648$277$7
George Neal Unit 425.7%1971107
George Neal Unit 328.0%1818920
Louisa Unit 14.0%4323—
1,06949934
WPL
Columbia Units 1-2 and Energy Storage System53.5%8593786
West Riverside Energy Center and Solar Facility (a)56.6%449595
Forward Wind Energy Center42.6%11956—
1,42749311
Alliant Energy$2,496$992$45

(a)In 2023 and 2024, WEC Energy Group, Inc. and Madison Gas and Electric Company acquired partial ownership interests in West Riverside. The related proceeds are included in “Proceeds from sales of partial ownership interests in West Riverside” in investing activities in Alliant Energy’s and WPL’s cash flows statements in 2023 and 2024.
v3.25.0.1
Receivables
 12 Months Ended
Dec. 31, 2024
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
202420232024202320242023
Customer$113 $121 $— $— $98 $110 
Unbilled utility revenues101 93 — — 101 93 
Deferred proceeds163 216 163 216 — — 
Other58 53 29 26 29 24 
Allowance for expected credit losses(8)(8)— — (8)(8)
$427 $475 $192 $242 $220 $219 

In 2024, gross write-offs for accounts receivable were as follows (in millions):
Originated in 2023
Originated in 2024
Alliant Energy$12$14
IPL89
WPL45
(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, 2024, the limit on cash proceeds was $110 million and IPL had $40 million of 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
202420232022202420232022
Outstanding aggregate cash proceeds$110$110$80$31$51$14

As of December 31, the attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions):
20242023
Customer accounts receivable$137$130
Unbilled utility revenues10898
Other receivables—1
Receivables sold to third party245229
Less: cash proceeds701
Deferred proceeds175228
Less: allowance for expected credit losses1212
Fair value of deferred proceeds$163$216
Outstanding receivables past due$21$22

Additional attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions):
202420232022
Collections$2,090$2,233$2,302 
Write-offs, net of recoveries12129 
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
202420232024202320242023
Customer$113 $121 $— $— $98 $110 
Unbilled utility revenues101 93 — — 101 93 
Deferred proceeds163 216 163 216 — — 
Other58 53 29 26 29 24 
Allowance for expected credit losses(8)(8)— — (8)(8)
$427 $475 $192 $242 $220 $219 

In 2024, gross write-offs for accounts receivable were as follows (in millions):
Originated in 2023
Originated in 2024
Alliant Energy$12$14
IPL89
WPL45
(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, 2024, the limit on cash proceeds was $110 million and IPL had $40 million of 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
202420232022202420232022
Outstanding aggregate cash proceeds$110$110$80$31$51$14

As of December 31, the attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions):
20242023
Customer accounts receivable$137$130
Unbilled utility revenues10898
Other receivables—1
Receivables sold to third party245229
Less: cash proceeds701
Deferred proceeds175228
Less: allowance for expected credit losses1212
Fair value of deferred proceeds$163$216
Outstanding receivables past due$21$22

Additional attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions):
202420232022
Collections$2,090$2,233$2,302 
Write-offs, net of recoveries12129 
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
202420232024202320242023
Customer$113 $121 $— $— $98 $110 
Unbilled utility revenues101 93 — — 101 93 
Deferred proceeds163 216 163 216 — — 
Other58 53 29 26 29 24 
Allowance for expected credit losses(8)(8)— — (8)(8)
$427 $475 $192 $242 $220 $219 

In 2024, gross write-offs for accounts receivable were as follows (in millions):
Originated in 2023
Originated in 2024
Alliant Energy$12$14
IPL89
WPL45
v3.25.0.1
Investments
 12 Months Ended
Dec. 31, 2024
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, 202420242023202420232022
ATC Holdings
16%, 20%
$415$386($57)($49)($41)
Non-utility wind farm in Oklahoma50%107104(6)(7)(5)
Corporate venture investmentsVarious78743(2)(3)
OtherVarious2321(1)(3)(2)
$623$585($61)($61)($51)

Summary aggregate financial information from the financial statements of these holdings is as follows (in millions):
Alliant Energy
202420232022
Revenues$1,005$898$813
Operating income433384350
Net income434370675
As of December 31:
Current assets223221
Non-current assets9,9309,032
Current liabilities524528
Non-current liabilities3,9333,584
Noncontrolling interest221259

ATC Holdings - As of December 31, 2024, 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 Duke-American Transmission Company, LLC, a joint venture between Duke Energy Corporation and ATC, that owns electric transmission infrastructure in North America. Refer to Note 16(g) for discussion of a reduction in earnings recorded in 2022 related to a court decision, and subsequent FERC order, which reduced the base return on equity authorized for MISO transmission owners, including ATC.

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.
v3.25.0.1
Common Equity
 12 Months Ended
Dec. 31, 2024
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:
202420232022
Shares outstanding, January 1256,096,848 251,134,966 250,474,529 
At-the-market offering program— 4,372,561 — 
Shareowner Direct Plan439,107 454,987 437,669 
Equity-based compensation plans154,267 134,334 222,768 
Shares outstanding, December 31256,690,222 256,096,848 251,134,966 

At December 31, 2024, Alliant Energy had a total of 12 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.

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.
v3.25.0.1
Debt
 12 Months Ended
Dec. 31, 2024
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, 2024, the short-term borrowing capacity under a single credit facility agreement, which expires in December 2029, totaled $1.3 billion ($600 million for Alliant Energy at the parent company level, $300 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 classified as short-term debt was as follows (dollars in millions):
Alliant EnergyIPLWPL
December 31202420232024202320242023
Amount outstanding$558$475$50$—$183$318
Weighted average interest rates4.5%5.5%4.6%N/A4.5%5.4%
Available credit facility capacity$742$525$250$150$217$82
Alliant EnergyIPLWPL
For the year ended202420232024202320242023
Maximum amount outstanding (based on daily outstanding balances)$632$793$80$70$390$349
Average amount outstanding (based on daily outstanding balances)$327$386$1$2$70$157
Weighted average interest rates5.3%5.2%5.1%5.3%5.4%5.1%
(b) Long-Term Debt - Long-term debt, net as of December 31 was as follows (dollars in millions):
20242023
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Senior Debentures (a):
3.4%, due 2025
$250 $250 $— $250 $250 $— 
5.5%, due 2025
50 50 — 50 50 — 
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 (b)
350 350 — — — — 
6.3%, due 2034
125 125 — 125 125 — 
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 (b)
300 300 — — — — 
3.25% (Retired in 2024)
— — — 500 500 — 
4,125 4,125 — 3,975 3,975 — 
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 (c)
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 
3,400 — 3,400 3,100 — 3,100 
Other:
AEF term loan credit agreement through March 2025, 6% at December 31, 2024 (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)(f)
375 — — — — — 
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 — — 
AEF term loan credit agreement, 6% at December 31, 2023 (with Alliant Energy as guarantor) (Retired in 2024) (d)
— — — 300 — — 
Sheboygan Power, LLC 5.06% senior secured notes (secured by the Sheboygan Falls Energy Facility and related assets) (Retired in 2024)
— — — 9 — — 
2,400 — — 2,034 — — 
Subtotal9,925 4,125 3,400 9,109 3,975 3,100 
Current maturities(1,171)(300)— (809)(500)— 
Unamortized debt issuance costs(55)(25)(20)(54)(21)(19)
Unamortized debt (discount) and premium, net(22)(10)(10)(21)(9)(11)
Long-term debt, net (g)$8,677 $3,790 $3,370 $8,225 $3,445 $3,070 

(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 September 2024, IPL issued $350 million of 4.95% senior debentures due 2034 and $300 million of 5.45% senior debentures due 2054. A portion of the net proceeds was used for the retirement of IPL’s $500 million 3.25% senior debentures, and the remainder of the net proceeds was used for general corporate purposes.
(c)In March 2024, WPL issued $300 million of 5.375% debentures due 2034. The debentures were issued as green bonds, and an amount equal to or in excess of the net proceeds was disbursed for the development and acquisition of WPL’s solar EGUs.
(d)In March 2024, 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 2024, and retired the $300 million variable rate term loan set forth therein. 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.
(e)Refer to “Convertible Senior Notes” below for additional information.
(f)In June 2024, AEF issued $375 million of 5.4% senior notes due 2027. The net proceeds were used to reduce Alliant Energy’s outstanding commercial paper and for general corporate purposes.
(g)There were no significant sinking fund requirements related to the outstanding long-term debt.

Convertible Senior Notes - In March 2023, Alliant Energy issued $575 million of 3.875% convertible senior notes (the Notes), which are senior unsecured obligations, and used the net proceeds from the issuance for general corporate purposes. The Notes will mature on March 15, 2026 unless earlier converted or repurchased. Alliant Energy may not redeem the Notes prior to the maturity date. Holders may convert their 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 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 Notes at any time, regardless of the foregoing circumstances. Upon conversion of the Notes, Alliant Energy will pay cash up to the aggregate principal amount of the 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 Notes being converted.

The initial conversion rate is 15.5461 shares of common stock per $1,000 principal amount of 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 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 Notes may require Alliant Energy to repurchase for cash all or any portion of its Notes at a fundamental change repurchase price equal to 100% of the principal amount of the Notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date.

As of December 31, 2024, the conditions allowing holders of the Notes to convert their Notes were not met. As of December 31, 2024 and 2023, the Notes were classified on Alliant Energy’s balance sheets as “Current maturities of long-term debt” and “Long-term debt, net,” respectively. As of December 31, 2024 and 2023, the net carrying amount of the Notes was $571 million and $568 million, with unamortized debt issuance costs of $4 million and $7 million, and the estimated fair value (Level 2) of the Notes was $591 million and $572 million. As of December 31, 2024, there were no shares of Alliant Energy’s common stock related to the potential conversion of the Notes included in diluted EPS based on Alliant Energy’s average stock prices and the relevant terms of the Notes.
Five-Year Schedule of Long-term Debt Maturities - At December 31, 2024, long-term debt maturities for 2025 through 2029 were as follows (in millions):
20252026202720282029
IPL$300$—$—$500$300
WPL——300—350
AEF300200375300300
Alliant Energy parent company—575———
Alliant Energy$600$775$675$800$950

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, 2024, the short-term borrowing capacity under a single credit facility agreement, which expires in December 2029, totaled $1.3 billion ($600 million for Alliant Energy at the parent company level, $300 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 classified as short-term debt was as follows (dollars in millions):
Alliant EnergyIPLWPL
December 31202420232024202320242023
Amount outstanding$558$475$50$—$183$318
Weighted average interest rates4.5%5.5%4.6%N/A4.5%5.4%
Available credit facility capacity$742$525$250$150$217$82
Alliant EnergyIPLWPL
For the year ended202420232024202320242023
Maximum amount outstanding (based on daily outstanding balances)$632$793$80$70$390$349
Average amount outstanding (based on daily outstanding balances)$327$386$1$2$70$157
Weighted average interest rates5.3%5.2%5.1%5.3%5.4%5.1%
(b) Long-Term Debt - Long-term debt, net as of December 31 was as follows (dollars in millions):
20242023
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Senior Debentures (a):
3.4%, due 2025
$250 $250 $— $250 $250 $— 
5.5%, due 2025
50 50 — 50 50 — 
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 (b)
350 350 — — — — 
6.3%, due 2034
125 125 — 125 125 — 
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 (b)
300 300 — — — — 
3.25% (Retired in 2024)
— — — 500 500 — 
4,125 4,125 — 3,975 3,975 — 
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 (c)
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 
3,400 — 3,400 3,100 — 3,100 
Other:
AEF term loan credit agreement through March 2025, 6% at December 31, 2024 (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)(f)
375 — — — — — 
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 — — 
AEF term loan credit agreement, 6% at December 31, 2023 (with Alliant Energy as guarantor) (Retired in 2024) (d)
— — — 300 — — 
Sheboygan Power, LLC 5.06% senior secured notes (secured by the Sheboygan Falls Energy Facility and related assets) (Retired in 2024)
— — — 9 — — 
2,400 — — 2,034 — — 
Subtotal9,925 4,125 3,400 9,109 3,975 3,100 
Current maturities(1,171)(300)— (809)(500)— 
Unamortized debt issuance costs(55)(25)(20)(54)(21)(19)
Unamortized debt (discount) and premium, net(22)(10)(10)(21)(9)(11)
Long-term debt, net (g)$8,677 $3,790 $3,370 $8,225 $3,445 $3,070 

(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 September 2024, IPL issued $350 million of 4.95% senior debentures due 2034 and $300 million of 5.45% senior debentures due 2054. A portion of the net proceeds was used for the retirement of IPL’s $500 million 3.25% senior debentures, and the remainder of the net proceeds was used for general corporate purposes.
(c)In March 2024, WPL issued $300 million of 5.375% debentures due 2034. The debentures were issued as green bonds, and an amount equal to or in excess of the net proceeds was disbursed for the development and acquisition of WPL’s solar EGUs.
(d)In March 2024, 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 2024, and retired the $300 million variable rate term loan set forth therein. 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.
(e)Refer to “Convertible Senior Notes” below for additional information.
(f)In June 2024, AEF issued $375 million of 5.4% senior notes due 2027. The net proceeds were used to reduce Alliant Energy’s outstanding commercial paper and for general corporate purposes.
(g)There were no significant sinking fund requirements related to the outstanding long-term debt.

Convertible Senior Notes - In March 2023, Alliant Energy issued $575 million of 3.875% convertible senior notes (the Notes), which are senior unsecured obligations, and used the net proceeds from the issuance for general corporate purposes. The Notes will mature on March 15, 2026 unless earlier converted or repurchased. Alliant Energy may not redeem the Notes prior to the maturity date. Holders may convert their 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 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 Notes at any time, regardless of the foregoing circumstances. Upon conversion of the Notes, Alliant Energy will pay cash up to the aggregate principal amount of the 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 Notes being converted.

The initial conversion rate is 15.5461 shares of common stock per $1,000 principal amount of 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 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 Notes may require Alliant Energy to repurchase for cash all or any portion of its Notes at a fundamental change repurchase price equal to 100% of the principal amount of the Notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date.

As of December 31, 2024, the conditions allowing holders of the Notes to convert their Notes were not met. As of December 31, 2024 and 2023, the Notes were classified on Alliant Energy’s balance sheets as “Current maturities of long-term debt” and “Long-term debt, net,” respectively. As of December 31, 2024 and 2023, the net carrying amount of the Notes was $571 million and $568 million, with unamortized debt issuance costs of $4 million and $7 million, and the estimated fair value (Level 2) of the Notes was $591 million and $572 million. As of December 31, 2024, there were no shares of Alliant Energy’s common stock related to the potential conversion of the Notes included in diluted EPS based on Alliant Energy’s average stock prices and the relevant terms of the Notes.
Five-Year Schedule of Long-term Debt Maturities - At December 31, 2024, long-term debt maturities for 2025 through 2029 were as follows (in millions):
20252026202720282029
IPL$300$—$—$500$300
WPL——300—350
AEF300200375300300
Alliant Energy parent company—575———
Alliant Energy$600$775$675$800$950

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, 2024, the short-term borrowing capacity under a single credit facility agreement, which expires in December 2029, totaled $1.3 billion ($600 million for Alliant Energy at the parent company level, $300 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 classified as short-term debt was as follows (dollars in millions):
Alliant EnergyIPLWPL
December 31202420232024202320242023
Amount outstanding$558$475$50$—$183$318
Weighted average interest rates4.5%5.5%4.6%N/A4.5%5.4%
Available credit facility capacity$742$525$250$150$217$82
Alliant EnergyIPLWPL
For the year ended202420232024202320242023
Maximum amount outstanding (based on daily outstanding balances)$632$793$80$70$390$349
Average amount outstanding (based on daily outstanding balances)$327$386$1$2$70$157
Weighted average interest rates5.3%5.2%5.1%5.3%5.4%5.1%
(b) Long-Term Debt - Long-term debt, net as of December 31 was as follows (dollars in millions):
20242023
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Senior Debentures (a):
3.4%, due 2025
$250 $250 $— $250 $250 $— 
5.5%, due 2025
50 50 — 50 50 — 
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 (b)
350 350 — — — — 
6.3%, due 2034
125 125 — 125 125 — 
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 (b)
300 300 — — — — 
3.25% (Retired in 2024)
— — — 500 500 — 
4,125 4,125 — 3,975 3,975 — 
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 (c)
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 
3,400 — 3,400 3,100 — 3,100 
Other:
AEF term loan credit agreement through March 2025, 6% at December 31, 2024 (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)(f)
375 — — — — — 
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 — — 
AEF term loan credit agreement, 6% at December 31, 2023 (with Alliant Energy as guarantor) (Retired in 2024) (d)
— — — 300 — — 
Sheboygan Power, LLC 5.06% senior secured notes (secured by the Sheboygan Falls Energy Facility and related assets) (Retired in 2024)
— — — 9 — — 
2,400 — — 2,034 — — 
Subtotal9,925 4,125 3,400 9,109 3,975 3,100 
Current maturities(1,171)(300)— (809)(500)— 
Unamortized debt issuance costs(55)(25)(20)(54)(21)(19)
Unamortized debt (discount) and premium, net(22)(10)(10)(21)(9)(11)
Long-term debt, net (g)$8,677 $3,790 $3,370 $8,225 $3,445 $3,070 

(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 September 2024, IPL issued $350 million of 4.95% senior debentures due 2034 and $300 million of 5.45% senior debentures due 2054. A portion of the net proceeds was used for the retirement of IPL’s $500 million 3.25% senior debentures, and the remainder of the net proceeds was used for general corporate purposes.
(c)In March 2024, WPL issued $300 million of 5.375% debentures due 2034. The debentures were issued as green bonds, and an amount equal to or in excess of the net proceeds was disbursed for the development and acquisition of WPL’s solar EGUs.
(d)In March 2024, 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 2024, and retired the $300 million variable rate term loan set forth therein. 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.
(e)Refer to “Convertible Senior Notes” below for additional information.
(f)In June 2024, AEF issued $375 million of 5.4% senior notes due 2027. The net proceeds were used to reduce Alliant Energy’s outstanding commercial paper and for general corporate purposes.
(g)There were no significant sinking fund requirements related to the outstanding long-term debt.

Convertible Senior Notes - In March 2023, Alliant Energy issued $575 million of 3.875% convertible senior notes (the Notes), which are senior unsecured obligations, and used the net proceeds from the issuance for general corporate purposes. The Notes will mature on March 15, 2026 unless earlier converted or repurchased. Alliant Energy may not redeem the Notes prior to the maturity date. Holders may convert their 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 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 Notes at any time, regardless of the foregoing circumstances. Upon conversion of the Notes, Alliant Energy will pay cash up to the aggregate principal amount of the 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 Notes being converted.

The initial conversion rate is 15.5461 shares of common stock per $1,000 principal amount of 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 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 Notes may require Alliant Energy to repurchase for cash all or any portion of its Notes at a fundamental change repurchase price equal to 100% of the principal amount of the Notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date.

As of December 31, 2024, the conditions allowing holders of the Notes to convert their Notes were not met. As of December 31, 2024 and 2023, the Notes were classified on Alliant Energy’s balance sheets as “Current maturities of long-term debt” and “Long-term debt, net,” respectively. As of December 31, 2024 and 2023, the net carrying amount of the Notes was $571 million and $568 million, with unamortized debt issuance costs of $4 million and $7 million, and the estimated fair value (Level 2) of the Notes was $591 million and $572 million. As of December 31, 2024, there were no shares of Alliant Energy’s common stock related to the potential conversion of the Notes included in diluted EPS based on Alliant Energy’s average stock prices and the relevant terms of the Notes.
Five-Year Schedule of Long-term Debt Maturities - At December 31, 2024, long-term debt maturities for 2025 through 2029 were as follows (in millions):
20252026202720282029
IPL$300$—$—$500$300
WPL——300—350
AEF300200375300300
Alliant Energy parent company—575———
Alliant Energy$600$775$675$800$950

Fair Value of Long-term Debt - Refer to Note 15 for information on the fair value of long-term debt outstanding.
v3.25.0.1
Leases
 12 Months Ended
Dec. 31, 2024
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, 2024December 31, 2023
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net$22$12$9$23$13$9
Other current liabilities$2$1$1$2$1$1
Other liabilities2011821128
Total operating lease liabilities$22$12$9$23$13$9
Weighted average remaining lease term11 years11 years12 years12 years12 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. 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, 2024December 31, 2023
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net:
Sheboygan Falls Energy FacilityN/AN/A$74N/AN/A$79
Leased land for solar generation$189$53136$172$33139
$189$53$210$172$33$218
Other current liabilities:
Sheboygan Falls Energy FacilityN/AN/A$7N/AN/A$11
Leased land for solar generation$—$——$—$——
——7——11
Other liabilities:
Sheboygan Falls Energy FacilityN/AN/A71N/AN/A78
Leased land for solar generation1895313617233139
1895320717233217
Total finance lease liabilities$189$53$214$172$33$228
Weighted average remaining lease term31 years28 years28 years33 years29 years27 years
Weighted average discount rate5%5%5%5%5%5%
Alliant EnergyIPLWPL
202420232022202420232022202420232022
Depreciation and amortization expenses$— $1 $— $— $— $— $4 $6 $6 
Interest expense8 6 3 2 1 — 10 8 7 
Total finance lease expense$8 $7 $3 $2 $1 $— $14 $14 $13 
Finance lease liabilities arising from obtaining leased assets, which represent non-cash financing activities, were as follows (in millions):
Alliant EnergyIPLWPL
202420232024202320242023
Finance lease liabilities arising from obtaining leased assets
$20 $34 $20 $33 $— $71 

Expected Maturities - As of December 31, 2024, expected maturities of lease liabilities were as follows (in millions):
20252026202720282029ThereafterTotalLess: amount representing interestPresent value of minimum lease payments
Operating Leases:
Alliant Energy$3 $3 $3 $3 $2 $14$28$6$22
IPL2 2 1 1 1 815312
WPL1 1 1 1 1 71239
Finance Leases:
Alliant Energy9 9 9 10 10 337384195189
IPL3 3 3 3 3 921075453
WPL17 13 13 13 13 324393179214
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, 2024December 31, 2023
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net$22$12$9$23$13$9
Other current liabilities$2$1$1$2$1$1
Other liabilities2011821128
Total operating lease liabilities$22$12$9$23$13$9
Weighted average remaining lease term11 years11 years12 years12 years12 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. 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, 2024December 31, 2023
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net:
Sheboygan Falls Energy FacilityN/AN/A$74N/AN/A$79
Leased land for solar generation$189$53136$172$33139
$189$53$210$172$33$218
Other current liabilities:
Sheboygan Falls Energy FacilityN/AN/A$7N/AN/A$11
Leased land for solar generation$—$——$—$——
——7——11
Other liabilities:
Sheboygan Falls Energy FacilityN/AN/A71N/AN/A78
Leased land for solar generation1895313617233139
1895320717233217
Total finance lease liabilities$189$53$214$172$33$228
Weighted average remaining lease term31 years28 years28 years33 years29 years27 years
Weighted average discount rate5%5%5%5%5%5%
Alliant EnergyIPLWPL
202420232022202420232022202420232022
Depreciation and amortization expenses$— $1 $— $— $— $— $4 $6 $6 
Interest expense8 6 3 2 1 — 10 8 7 
Total finance lease expense$8 $7 $3 $2 $1 $— $14 $14 $13 
Finance lease liabilities arising from obtaining leased assets, which represent non-cash financing activities, were as follows (in millions):
Alliant EnergyIPLWPL
202420232024202320242023
Finance lease liabilities arising from obtaining leased assets
$20 $34 $20 $33 $— $71 

Expected Maturities - As of December 31, 2024, expected maturities of lease liabilities were as follows (in millions):
20252026202720282029ThereafterTotalLess: amount representing interestPresent value of minimum lease payments
Operating Leases:
Alliant Energy$3 $3 $3 $3 $2 $14$28$6$22
IPL2 2 1 1 1 815312
WPL1 1 1 1 1 71239
Finance Leases:
Alliant Energy9 9 9 10 10 337384195189
IPL3 3 3 3 3 921075453
WPL17 13 13 13 13 324393179214
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, 2024December 31, 2023
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net$22$12$9$23$13$9
Other current liabilities$2$1$1$2$1$1
Other liabilities2011821128
Total operating lease liabilities$22$12$9$23$13$9
Weighted average remaining lease term11 years11 years12 years12 years12 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. 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, 2024December 31, 2023
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net:
Sheboygan Falls Energy FacilityN/AN/A$74N/AN/A$79
Leased land for solar generation$189$53136$172$33139
$189$53$210$172$33$218
Other current liabilities:
Sheboygan Falls Energy FacilityN/AN/A$7N/AN/A$11
Leased land for solar generation$—$——$—$——
——7——11
Other liabilities:
Sheboygan Falls Energy FacilityN/AN/A71N/AN/A78
Leased land for solar generation1895313617233139
1895320717233217
Total finance lease liabilities$189$53$214$172$33$228
Weighted average remaining lease term31 years28 years28 years33 years29 years27 years
Weighted average discount rate5%5%5%5%5%5%
Alliant EnergyIPLWPL
202420232022202420232022202420232022
Depreciation and amortization expenses$— $1 $— $— $— $— $4 $6 $6 
Interest expense8 6 3 2 1 — 10 8 7 
Total finance lease expense$8 $7 $3 $2 $1 $— $14 $14 $13 
Finance lease liabilities arising from obtaining leased assets, which represent non-cash financing activities, were as follows (in millions):
Alliant EnergyIPLWPL
202420232024202320242023
Finance lease liabilities arising from obtaining leased assets
$20 $34 $20 $33 $— $71 

Expected Maturities - As of December 31, 2024, expected maturities of lease liabilities were as follows (in millions):
20252026202720282029ThereafterTotalLess: amount representing interestPresent value of minimum lease payments
Operating Leases:
Alliant Energy$3 $3 $3 $3 $2 $14$28$6$22
IPL2 2 1 1 1 815312
WPL1 1 1 1 1 71239
Finance Leases:
Alliant Energy9 9 9 10 10 337384195189
IPL3 3 3 3 3 921075453
WPL17 13 13 13 13 324393179214
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, 2024December 31, 2023
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net$22$12$9$23$13$9
Other current liabilities$2$1$1$2$1$1
Other liabilities2011821128
Total operating lease liabilities$22$12$9$23$13$9
Weighted average remaining lease term11 years11 years12 years12 years12 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. 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, 2024December 31, 2023
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net:
Sheboygan Falls Energy FacilityN/AN/A$74N/AN/A$79
Leased land for solar generation$189$53136$172$33139
$189$53$210$172$33$218
Other current liabilities:
Sheboygan Falls Energy FacilityN/AN/A$7N/AN/A$11
Leased land for solar generation$—$——$—$——
——7——11
Other liabilities:
Sheboygan Falls Energy FacilityN/AN/A71N/AN/A78
Leased land for solar generation1895313617233139
1895320717233217
Total finance lease liabilities$189$53$214$172$33$228
Weighted average remaining lease term31 years28 years28 years33 years29 years27 years
Weighted average discount rate5%5%5%5%5%5%
Alliant EnergyIPLWPL
202420232022202420232022202420232022
Depreciation and amortization expenses$— $1 $— $— $— $— $4 $6 $6 
Interest expense8 6 3 2 1 — 10 8 7 
Total finance lease expense$8 $7 $3 $2 $1 $— $14 $14 $13 
Finance lease liabilities arising from obtaining leased assets, which represent non-cash financing activities, were as follows (in millions):
Alliant EnergyIPLWPL
202420232024202320242023
Finance lease liabilities arising from obtaining leased assets
$20 $34 $20 $33 $— $71 

Expected Maturities - As of December 31, 2024, expected maturities of lease liabilities were as follows (in millions):
20252026202720282029ThereafterTotalLess: amount representing interestPresent value of minimum lease payments
Operating Leases:
Alliant Energy$3 $3 $3 $3 $2 $14$28$6$22
IPL2 2 1 1 1 815312
WPL1 1 1 1 1 71239
Finance Leases:
Alliant Energy9 9 9 10 10 337384195189
IPL3 3 3 3 3 921075453
WPL17 13 13 13 13 324393179214
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, 2024December 31, 2023
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net$22$12$9$23$13$9
Other current liabilities$2$1$1$2$1$1
Other liabilities2011821128
Total operating lease liabilities$22$12$9$23$13$9
Weighted average remaining lease term11 years11 years12 years12 years12 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. 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, 2024December 31, 2023
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net:
Sheboygan Falls Energy FacilityN/AN/A$74N/AN/A$79
Leased land for solar generation$189$53136$172$33139
$189$53$210$172$33$218
Other current liabilities:
Sheboygan Falls Energy FacilityN/AN/A$7N/AN/A$11
Leased land for solar generation$—$——$—$——
——7——11
Other liabilities:
Sheboygan Falls Energy FacilityN/AN/A71N/AN/A78
Leased land for solar generation1895313617233139
1895320717233217
Total finance lease liabilities$189$53$214$172$33$228
Weighted average remaining lease term31 years28 years28 years33 years29 years27 years
Weighted average discount rate5%5%5%5%5%5%
Alliant EnergyIPLWPL
202420232022202420232022202420232022
Depreciation and amortization expenses$— $1 $— $— $— $— $4 $6 $6 
Interest expense8 6 3 2 1 — 10 8 7 
Total finance lease expense$8 $7 $3 $2 $1 $— $14 $14 $13 
Finance lease liabilities arising from obtaining leased assets, which represent non-cash financing activities, were as follows (in millions):
Alliant EnergyIPLWPL
202420232024202320242023
Finance lease liabilities arising from obtaining leased assets
$20 $34 $20 $33 $— $71 

Expected Maturities - As of December 31, 2024, expected maturities of lease liabilities were as follows (in millions):
20252026202720282029ThereafterTotalLess: amount representing interestPresent value of minimum lease payments
Operating Leases:
Alliant Energy$3 $3 $3 $3 $2 $14$28$6$22
IPL2 2 1 1 1 815312
WPL1 1 1 1 1 71239
Finance Leases:
Alliant Energy9 9 9 10 10 337384195189
IPL3 3 3 3 3 921075453
WPL17 13 13 13 13 324393179214
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, 2024December 31, 2023
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net$22$12$9$23$13$9
Other current liabilities$2$1$1$2$1$1
Other liabilities2011821128
Total operating lease liabilities$22$12$9$23$13$9
Weighted average remaining lease term11 years11 years12 years12 years12 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. 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, 2024December 31, 2023
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net:
Sheboygan Falls Energy FacilityN/AN/A$74N/AN/A$79
Leased land for solar generation$189$53136$172$33139
$189$53$210$172$33$218
Other current liabilities:
Sheboygan Falls Energy FacilityN/AN/A$7N/AN/A$11
Leased land for solar generation$—$——$—$——
——7——11
Other liabilities:
Sheboygan Falls Energy FacilityN/AN/A71N/AN/A78
Leased land for solar generation1895313617233139
1895320717233217
Total finance lease liabilities$189$53$214$172$33$228
Weighted average remaining lease term31 years28 years28 years33 years29 years27 years
Weighted average discount rate5%5%5%5%5%5%
Alliant EnergyIPLWPL
202420232022202420232022202420232022
Depreciation and amortization expenses$— $1 $— $— $— $— $4 $6 $6 
Interest expense8 6 3 2 1 — 10 8 7 
Total finance lease expense$8 $7 $3 $2 $1 $— $14 $14 $13 
Finance lease liabilities arising from obtaining leased assets, which represent non-cash financing activities, were as follows (in millions):
Alliant EnergyIPLWPL
202420232024202320242023
Finance lease liabilities arising from obtaining leased assets
$20 $34 $20 $33 $— $71 

Expected Maturities - As of December 31, 2024, expected maturities of lease liabilities were as follows (in millions):
20252026202720282029ThereafterTotalLess: amount representing interestPresent value of minimum lease payments
Operating Leases:
Alliant Energy$3 $3 $3 $3 $2 $14$28$6$22
IPL2 2 1 1 1 815312
WPL1 1 1 1 1 71239
Finance Leases:
Alliant Energy9 9 9 10 10 337384195189
IPL3 3 3 3 3 921075453
WPL17 13 13 13 13 324393179214
v3.25.0.1
Revenues
 12 Months Ended
Dec. 31, 2024
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 Minnesota, Illinois and Iowa, as well as steam from its Prairie Creek Generating Station to high-pressure steam customers in Iowa.

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; wind turbine blade recycling 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
202420232022202420232022202420232022
Electric Utility:
Retail - residential$1,236 $1,220 $1,233 $640 $641 $673 $596 $579 $560 
Retail - commercial821 820 821 525 519 536 296 301 285 
Retail - industrial952 968 965 497 501 538 455 467 427 
Wholesale200 213 233 61 62 64 139 151 169 
Bulk power and other163 124 169 24 38 48 139 86 121 
Total Electric Utility3,372 3,345 3,421 1,747 1,761 1,859 1,625 1,584 1,562 
Gas Utility:
Retail - residential275 316 371 148 176 202 127 140 169 
Retail - commercial133 163 197 68 86 101 65 77 96 
Retail - industrial11 16 20 7 11 14 4 5 6 
Transportation/other46 45 54 27 27 34 19 18 20 
Total Gas Utility465 540 642 250 300 351 215 240 291 
Other Utility:
Steam40 45 39 40 45 39 — — — 
Other utility14 7 10 9 4 7 5 3 3 
Total Other Utility54 52 49 49 49 46 5 3 3 
Non-Utility and Other:
Travero and other90 90 93 — — — — — — 
Total Non-Utility and Other90 90 93 — — — — — — 
Total revenues$3,981 $4,027 $4,205 $2,046 $2,110 $2,256 $1,845 $1,827 $1,856 
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 Minnesota, Illinois and Iowa, as well as steam from its Prairie Creek Generating Station to high-pressure steam customers in Iowa.

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; wind turbine blade recycling 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
202420232022202420232022202420232022
Electric Utility:
Retail - residential$1,236 $1,220 $1,233 $640 $641 $673 $596 $579 $560 
Retail - commercial821 820 821 525 519 536 296 301 285 
Retail - industrial952 968 965 497 501 538 455 467 427 
Wholesale200 213 233 61 62 64 139 151 169 
Bulk power and other163 124 169 24 38 48 139 86 121 
Total Electric Utility3,372 3,345 3,421 1,747 1,761 1,859 1,625 1,584 1,562 
Gas Utility:
Retail - residential275 316 371 148 176 202 127 140 169 
Retail - commercial133 163 197 68 86 101 65 77 96 
Retail - industrial11 16 20 7 11 14 4 5 6 
Transportation/other46 45 54 27 27 34 19 18 20 
Total Gas Utility465 540 642 250 300 351 215 240 291 
Other Utility:
Steam40 45 39 40 45 39 — — — 
Other utility14 7 10 9 4 7 5 3 3 
Total Other Utility54 52 49 49 49 46 5 3 3 
Non-Utility and Other:
Travero and other90 90 93 — — — — — — 
Total Non-Utility and Other90 90 93 — — — — — — 
Total revenues$3,981 $4,027 $4,205 $2,046 $2,110 $2,256 $1,845 $1,827 $1,856 
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 Minnesota, Illinois and Iowa, as well as steam from its Prairie Creek Generating Station to high-pressure steam customers in Iowa.

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; wind turbine blade recycling 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
202420232022202420232022202420232022
Electric Utility:
Retail - residential$1,236 $1,220 $1,233 $640 $641 $673 $596 $579 $560 
Retail - commercial821 820 821 525 519 536 296 301 285 
Retail - industrial952 968 965 497 501 538 455 467 427 
Wholesale200 213 233 61 62 64 139 151 169 
Bulk power and other163 124 169 24 38 48 139 86 121 
Total Electric Utility3,372 3,345 3,421 1,747 1,761 1,859 1,625 1,584 1,562 
Gas Utility:
Retail - residential275 316 371 148 176 202 127 140 169 
Retail - commercial133 163 197 68 86 101 65 77 96 
Retail - industrial11 16 20 7 11 14 4 5 6 
Transportation/other46 45 54 27 27 34 19 18 20 
Total Gas Utility465 540 642 250 300 351 215 240 291 
Other Utility:
Steam40 45 39 40 45 39 — — — 
Other utility14 7 10 9 4 7 5 3 3 
Total Other Utility54 52 49 49 49 46 5 3 3 
Non-Utility and Other:
Travero and other90 90 93 — — — — — — 
Total Non-Utility and Other90 90 93 — — — — — — 
Total revenues$3,981 $4,027 $4,205 $2,046 $2,110 $2,256 $1,845 $1,827 $1,856 
v3.25.0.1
Income Taxes
 12 Months Ended
Dec. 31, 2024
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
202420232022202420232022202420232022
Current tax expense (benefit):
Federal$13($3)$7($19)($44)($29)$37$48$46
State(10)(6)2(19)(21)(8)232516
Deferred tax expense (benefit):
Federal60100109388791241010
State153628(17)1717312
Production tax credits(177)(121)(123)(108)(95)(105)(69)(26)(18)
Investment tax credits(15)(1)(1)(4)(1)—(11)——
Provision recorded as a change in accrued interest—(1)——(1)————
($114)$4$22($129)($58)($50)$11$60$66
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 Generation Station discussed in Note 2.
Alliant EnergyIPLWPL
202420232022202420232022202420232022
Statutory federal income tax rate21%21%21%21%21%21%21%21%21%
State income taxes, net of federal benefits(1)23(12)(2)(2)656
Production tax credits(31)(17)(18)(46)(31)(34)(20)(7)(5)
Investment tax credits(3)——(2)——(3)——
Amortization of excess deferred taxes (Refer to Note 2)
(2)(2)(2)(5)(2)(2)—(2)(3)
Effect of rate-making on property-related differences(5)(4)(1)(10)(5)(1)(1)(3)(2)
Other items, net11—(1)—2—1—
Overall income tax rate(20%)1%3%(55%)(19%)(16%)3%15%17%

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
202420232024202320242023
Deferred tax liabilities:
Property$2,596 $2,453 $1,521 $1,415 $999 $972 
ATC Holdings135 127 — — — — 
Other178 213 120 157 66 64 
Total deferred tax liabilities2,909 2,793 1,641 1,572 1,065 1,036 
Deferred tax assets:
Federal credit carryforwards605 649 426 449 166 191 
Net operating losses carryforwards - state20 26 1 1 — — 
Other98 79 37 32 34 19 
Subtotal deferred tax assets723 754 464 482 200 210 
Valuation allowances(2)(3)(2)(1)— (1)
Total deferred tax assets721 751 462 481 200 209 
Total deferred tax liabilities, net$2,188 $2,042 $1,179 $1,091 $865 $827 

Carryforwards - At December 31, 2024, carryforwards and expiration dates were estimated as follows (in millions):
Range of Expiration DatesAlliant EnergyIPLWPL
State net operating losses2025-2044$338$7$1
Federal tax credits2033-2044605426166

Valuation Allowances - Refer to Note 1(c) for discussion of valuation allowances related to the expected transfer of renewable tax credits to other corporate taxpayers.

Uncertain Tax Positions - At December 31, 2024, 2023 and 2022, there were no uncertain tax positions or penalties accrued related to uncertain tax positions. As of December 31, 2024, 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)2021-2023
Consolidated Iowa income tax returns (b)2021-2023
Wisconsin combined tax returns (c)2020-2023

(a)The 2021 and 2022 federal tax returns are 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 2022 and 2023, the Iowa Department of Revenue announced an Iowa corporate income tax rate of 8.4% effective January 1, 2023, and 7.1% effective January 1, 2024, respectively.

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 announcements of the new Iowa corporate income tax rates, Alliant Energy’s and IPL’s deferred tax liabilities were remeasured in 2022 and 2023 based upon the new rates effective January 1, 2023 and January 1, 2024, which resulted in a $77 million and $74 million reduction of Alliant Energy’s and IPL’s tax-related regulatory assets and a corresponding decrease in their deferred tax liabilities in 2022 and 2023, respectively. 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 rates effective January 1, 2023 and 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 $8 million, $10 million and $11 million recorded to income tax expense in Alliant Energy’s income statement and an increase in deferred income tax liabilities on Alliant Energy’s balance sheets in 2022, 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
202420232022202420232022202420232022
Current tax expense (benefit):
Federal$13($3)$7($19)($44)($29)$37$48$46
State(10)(6)2(19)(21)(8)232516
Deferred tax expense (benefit):
Federal60100109388791241010
State153628(17)1717312
Production tax credits(177)(121)(123)(108)(95)(105)(69)(26)(18)
Investment tax credits(15)(1)(1)(4)(1)—(11)——
Provision recorded as a change in accrued interest—(1)——(1)————
($114)$4$22($129)($58)($50)$11$60$66
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 Generation Station discussed in Note 2.
Alliant EnergyIPLWPL
202420232022202420232022202420232022
Statutory federal income tax rate21%21%21%21%21%21%21%21%21%
State income taxes, net of federal benefits(1)23(12)(2)(2)656
Production tax credits(31)(17)(18)(46)(31)(34)(20)(7)(5)
Investment tax credits(3)——(2)——(3)——
Amortization of excess deferred taxes (Refer to Note 2)
(2)(2)(2)(5)(2)(2)—(2)(3)
Effect of rate-making on property-related differences(5)(4)(1)(10)(5)(1)(1)(3)(2)
Other items, net11—(1)—2—1—
Overall income tax rate(20%)1%3%(55%)(19%)(16%)3%15%17%

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
202420232024202320242023
Deferred tax liabilities:
Property$2,596 $2,453 $1,521 $1,415 $999 $972 
ATC Holdings135 127 — — — — 
Other178 213 120 157 66 64 
Total deferred tax liabilities2,909 2,793 1,641 1,572 1,065 1,036 
Deferred tax assets:
Federal credit carryforwards605 649 426 449 166 191 
Net operating losses carryforwards - state20 26 1 1 — — 
Other98 79 37 32 34 19 
Subtotal deferred tax assets723 754 464 482 200 210 
Valuation allowances(2)(3)(2)(1)— (1)
Total deferred tax assets721 751 462 481 200 209 
Total deferred tax liabilities, net$2,188 $2,042 $1,179 $1,091 $865 $827 

Carryforwards - At December 31, 2024, carryforwards and expiration dates were estimated as follows (in millions):
Range of Expiration DatesAlliant EnergyIPLWPL
State net operating losses2025-2044$338$7$1
Federal tax credits2033-2044605426166

Valuation Allowances - Refer to Note 1(c) for discussion of valuation allowances related to the expected transfer of renewable tax credits to other corporate taxpayers.

Uncertain Tax Positions - At December 31, 2024, 2023 and 2022, there were no uncertain tax positions or penalties accrued related to uncertain tax positions. As of December 31, 2024, 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)2021-2023
Consolidated Iowa income tax returns (b)2021-2023
Wisconsin combined tax returns (c)2020-2023

(a)The 2021 and 2022 federal tax returns are 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 2022 and 2023, the Iowa Department of Revenue announced an Iowa corporate income tax rate of 8.4% effective January 1, 2023, and 7.1% effective January 1, 2024, respectively.

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 announcements of the new Iowa corporate income tax rates, Alliant Energy’s and IPL’s deferred tax liabilities were remeasured in 2022 and 2023 based upon the new rates effective January 1, 2023 and January 1, 2024, which resulted in a $77 million and $74 million reduction of Alliant Energy’s and IPL’s tax-related regulatory assets and a corresponding decrease in their deferred tax liabilities in 2022 and 2023, respectively. 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 rates effective January 1, 2023 and 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 $8 million, $10 million and $11 million recorded to income tax expense in Alliant Energy’s income statement and an increase in deferred income tax liabilities on Alliant Energy’s balance sheets in 2022, 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
202420232022202420232022202420232022
Current tax expense (benefit):
Federal$13($3)$7($19)($44)($29)$37$48$46
State(10)(6)2(19)(21)(8)232516
Deferred tax expense (benefit):
Federal60100109388791241010
State153628(17)1717312
Production tax credits(177)(121)(123)(108)(95)(105)(69)(26)(18)
Investment tax credits(15)(1)(1)(4)(1)—(11)——
Provision recorded as a change in accrued interest—(1)——(1)————
($114)$4$22($129)($58)($50)$11$60$66
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 Generation Station discussed in Note 2.
Alliant EnergyIPLWPL
202420232022202420232022202420232022
Statutory federal income tax rate21%21%21%21%21%21%21%21%21%
State income taxes, net of federal benefits(1)23(12)(2)(2)656
Production tax credits(31)(17)(18)(46)(31)(34)(20)(7)(5)
Investment tax credits(3)——(2)——(3)——
Amortization of excess deferred taxes (Refer to Note 2)
(2)(2)(2)(5)(2)(2)—(2)(3)
Effect of rate-making on property-related differences(5)(4)(1)(10)(5)(1)(1)(3)(2)
Other items, net11—(1)—2—1—
Overall income tax rate(20%)1%3%(55%)(19%)(16%)3%15%17%

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
202420232024202320242023
Deferred tax liabilities:
Property$2,596 $2,453 $1,521 $1,415 $999 $972 
ATC Holdings135 127 — — — — 
Other178 213 120 157 66 64 
Total deferred tax liabilities2,909 2,793 1,641 1,572 1,065 1,036 
Deferred tax assets:
Federal credit carryforwards605 649 426 449 166 191 
Net operating losses carryforwards - state20 26 1 1 — — 
Other98 79 37 32 34 19 
Subtotal deferred tax assets723 754 464 482 200 210 
Valuation allowances(2)(3)(2)(1)— (1)
Total deferred tax assets721 751 462 481 200 209 
Total deferred tax liabilities, net$2,188 $2,042 $1,179 $1,091 $865 $827 

Carryforwards - At December 31, 2024, carryforwards and expiration dates were estimated as follows (in millions):
Range of Expiration DatesAlliant EnergyIPLWPL
State net operating losses2025-2044$338$7$1
Federal tax credits2033-2044605426166

Valuation Allowances - Refer to Note 1(c) for discussion of valuation allowances related to the expected transfer of renewable tax credits to other corporate taxpayers.

Uncertain Tax Positions - At December 31, 2024, 2023 and 2022, there were no uncertain tax positions or penalties accrued related to uncertain tax positions. As of December 31, 2024, 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)2021-2023
Consolidated Iowa income tax returns (b)2021-2023
Wisconsin combined tax returns (c)2020-2023

(a)The 2021 and 2022 federal tax returns are 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 2022 and 2023, the Iowa Department of Revenue announced an Iowa corporate income tax rate of 8.4% effective January 1, 2023, and 7.1% effective January 1, 2024, respectively.

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 announcements of the new Iowa corporate income tax rates, Alliant Energy’s and IPL’s deferred tax liabilities were remeasured in 2022 and 2023 based upon the new rates effective January 1, 2023 and January 1, 2024, which resulted in a $77 million and $74 million reduction of Alliant Energy’s and IPL’s tax-related regulatory assets and a corresponding decrease in their deferred tax liabilities in 2022 and 2023, respectively. 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 rates effective January 1, 2023 and 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 $8 million, $10 million and $11 million recorded to income tax expense in Alliant Energy’s income statement and an increase in deferred income tax liabilities on Alliant Energy’s balance sheets in 2022, 2023 and 2024, respectively. Alliant Energy is currently unable to predict with certainty the timing or amount of any future rate reductions.
v3.25.0.1
Benefit Plans
 12 Months Ended
Dec. 31, 2024
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 Energy202420232022202420232022
Discount rate for benefit obligations5.65%5.36%5.54%5.62%5.40%5.53%
Discount rate for net periodic cost5.36%5.54%2.91%5.40%5.53%2.81%
Expected rate of return on plan assets7.73%7.80%7.80%6.22%6.50%6.40%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan6.24%10.75%9.22%N/AN/AN/A
Rate of compensation increase3.50%-4.50%3.30%-4.50%3.30%-4.50%N/AN/AN/A
Qualified Defined Benefit Pension PlanOPEB Plans
IPL202420232022202420232022
Discount rate for benefit obligations5.66%5.35%5.55%5.61%5.40%5.53%
Discount rate for net periodic cost5.35%5.55%2.94%5.40%5.53%2.80%
Expected rate of return on plan assets7.60%7.80%7.80%6.60%6.90%6.50%
Rate of compensation increase3.75%3.30%3.30%N/AN/AN/A
Qualified Defined Benefit Pension PlanOPEB Plans
WPL202420232022202420232022
Discount rate for benefit obligations5.66%5.35%5.54%5.61%5.40%5.53%
Discount rate for net periodic cost5.35%5.54%2.94%5.40%5.53%2.79%
Expected rate of return on plan assets7.80%7.80%7.80%5.61%5.65%5.49%
Rate of compensation increase3.50%3.30%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
202420232022202420232022
Service cost$5 $5 $9 $2 $2 $3 
Interest cost45 47 36 8 9 6 
Expected return on plan assets (a)(55)(53)(69)(5)(5)(5)
Amortization of prior service credit (b)(1)(1)(1)— — — 
Amortization of actuarial loss (c)24 28 32 — 1 2 
Settlement losses (d)— — 26 — — — 
$18 $26 $33 $5 $7 $6 
IPLDefined Benefit Pension PlansOPEB Plans
202420232022202420232022
Service cost$3 $3 $6 $1 $1 $1 
Interest cost20 21 16 3 3 2 
Expected return on plan assets (a)(26)(26)(31)(4)(3)(4)
Amortization of actuarial loss (c)9 11 13 — 1 1 
Settlement losses (d)— — 13 — — — 
$6 $9 $17 $— $2 $— 
WPLDefined Benefit Pension PlansOPEB Plans
202420232022202420232022
Service cost$2 $2 $3 $1 $1 $1 
Interest cost20 20 16 3 3 2 
Expected return on plan assets (a)(23)(22)(31)(1)(1)(1)
Amortization of actuarial loss (c)11 13 15 — 1 2 
Settlement losses (d)— — 13 — — — 
$10 $13 $16 $3 $4 $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.
(d)Settlement losses related to payments made to retired executives of Alliant Energy and lump sum payments related to IPL’s and WPL’s qualified defined benefit pension plans. In 2022, the majority of Alliant Energy’s, IPL’s, and WPL’s pension settlement losses were recognized as regulatory assets in accordance with regulatory treatment, and $7 million was included in “Other (income) and deductions” in Alliant Energy’s and IPL’s income statements related to IPL’s qualified defined benefit pension plan.

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 Energy2024202320242023
Change in benefit obligation:
Net benefit obligation at January 1$876 $875 $160 $168 
Service cost5 5 2 2 
Interest cost45 47 8 9 
Plan participants’ contributions— — 3 4 
Actuarial (gain) loss(19)23 (7)(3)
Gross benefits paid(66)(74)(18)(20)
Net benefit obligation at December 31841 876 148 160 
Change in plan assets:
Fair value of plan assets at January 1732 706 83 83 
Actual return on plan assets38 86 5 8 
Employer contributions11 14 7 8 
Plan participants’ contributions— — 3 4 
Gross benefits paid(66)(74)(18)(20)
Fair value of plan assets at December 31715 732 80 83 
Under funded status at December 31($126)($144)($68)($77)
Defined Benefit Pension PlansOPEB Plans
Alliant Energy2024202320242023
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $17 $14 
Current liabilities(3)(2)(7)(8)
Pension and other benefit obligations(123)(142)(78)(83)
Net amounts recognized at December 31($126)($144)($68)($77)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$312 $337 $4 $11 
Prior service credit(2)(2)— — 
$310 $335 $4 $11 
Defined Benefit Pension PlansOPEB Plans
IPL2024202320242023
Change in benefit obligation:
Net benefit obligation at January 1$387 $389 $65 $68 
Service cost3 3 1 1 
Interest cost20 21 3 3 
Plan participants’ contributions— — 1 2 
Actuarial (gain) loss(8)9 (3)(1)
Gross benefits paid(30)(35)(8)(8)
Net benefit obligation at December 31372 387 59 65 
Change in plan assets:
Fair value of plan assets at January 1352 344 61 58 
Actual return on plan assets18 42 4 7 
Employer contributions— 1 1 2 
Plan participants’ contributions— — 1 2 
Gross benefits paid(30)(35)(8)(8)
Fair value of plan assets at December 31340 352 59 61 
Under funded status at December 31($32)($35)$— ($4)
Defined Benefit Pension PlansOPEB Plans
IPL2024202320242023
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $13 $10 
Current liabilities(1)— (1)(1)
Pension and other benefit obligations(31)(35)(12)(13)
Net amounts recognized at December 31($32)($35)$— ($4)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$126 $135 $7 $9 
Prior service credit(1)(1)— — 
$125 $134 $7 $9 
Defined Benefit Pension PlansOPEB Plans
WPL2024202320242023
Change in benefit obligation:
Net benefit obligation at January 1$381 $381 $61 $65 
Service cost2 2 1 1 
Interest cost20 20 3 3 
Plan participants’ contributions— — 1 2 
Actuarial (gain) loss (8)10 (3)(2)
Gross benefits paid(30)(32)(7)(8)
Net benefit obligation at December 31365 381 56 61 
Change in plan assets:
Fair value of plan assets at January 1306 291 14 14 
Actual return on plan assets17 35 — 1 
Employer contributions10 12 5 5 
Plan participants’ contributions— — 1 2 
Gross benefits paid(30)(32)(7)(8)
Fair value of plan assets at December 31303 306 13 14 
Under funded status at December 31($62)($75)($43)($47)
Defined Benefit Pension PlansOPEB Plans
WPL2024202320242023
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $4 $4 
Current liabilities— — (6)(6)
Pension and other benefit obligations(62)(75)(41)(45)
Net amounts recognized at December 31($62)($75)($43)($47)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$135 $148 $— $3 

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 Energy2024202320242023
Accumulated benefit obligations$824 $857 $148 $160 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations824 857 148 160 
Fair value of plan assets715 732 80 83 
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations841 876 N/AN/A
Fair value of plan assets715 732 N/AN/A
Defined Benefit Pension PlansOPEB Plans
IPL2024202320242023
Accumulated benefit obligations$362 $377 $59 $65 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations362 377 N/A65 
Fair value of plan assets340 352 N/A61 
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations372 387 N/AN/A
Fair value of plan assets340 352 N/AN/A
Defined Benefit Pension PlansOPEB Plans
WPL2024202320242023
Accumulated benefit obligations$358 $373 $56 $61 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations358 373 56 61 
Fair value of plan assets303 306 13 14 
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations365 381 N/AN/A
Fair value of plan assets303 306 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
2024202320242023
Regulatory assets$25$28$22$24

Estimated Future Employer Contributions and Benefit Payments - Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2025 is as follows (in millions):
Alliant EnergyIPLWPL
Defined benefit pension plans (a)$20$1$14
OPEB plans716

(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 Energy202520262027202820292030 - 2034
Defined benefit pension benefits$79 $75 $74 $74 $74 $329
OPEB16 16 15 15 14 62
$95 $91 $89 $89 $88 $391
IPL202520262027202820292030 - 2034
Defined benefit pension benefits$36 $34 $33 $33 $32 $148
OPEB7 6 6 6 6 24
$43 $40 $39 $39 $38 $172
WPL202520262027202820292030 - 2034
Defined benefit pension benefits$33 $31 $31 $31 $31 $144
OPEB7 6 6 5 5 23
$40 $37 $37 $36 $36 $167
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, 2024, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows:
Target RangeActual
AllocationAllocation
Public equity securities32%-49%44%
Liquid alternative securities0%-12%6%
Return-seeking fixed income securities4%-18%8%
Liability-hedging fixed income securities (including cash and equivalents)34%-53%42%

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, 2024, 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%1%
Public equity securities0%-40%27%
Fixed income securities40%-100%72%

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):
20242023
FairLevelLevelLevelFairLevelLevelLevel
Alliant EnergyValue123Value123
Cash and equivalents$49 $— $49 $— $19 $— $19 $— 
Equity securities— — — — 223 223 — — 
Global asset securities— — — — 39 39 — — 
Fixed income securities— — — — 143 31 112 — 
Total assets in fair value hierarchy49 $— $49 $— 424 $293 $131 $— 
Assets measured at net asset value667 306 
Accrued investment income— 2 
Due to brokers, net (pending trades with brokers)(1)— 
Total pension plan assets$715 $732 
20242023
FairLevelLevelLevelFairLevelLevelLevel
IPLValue123Value123
Cash and equivalents$21 $— $21 $— $9 $— $9 $— 
Equity securities— — — — 107 107 — — 
Global asset securities— — — — 19 19 — — 
Fixed income securities— — — — 69 15 54 — 
Total assets in fair value hierarchy21 $— $21 $— 204 $141 $63 $— 
Assets measured at net asset value319 147 
Accrued investment income— 1 
Total pension plan assets$340 $352 
20242023
FairLevelLevelLevelFairLevelLevelLevel
WPLValue123Value123
Cash and equivalents$22 $— $22 $— $8 $— $8 $— 
Equity securities— — — — 93 93 — — 
Global asset securities— — — — 16 16 — — 
Fixed income securities— — — — 60 13 47 — 
Total assets in fair value hierarchy22 $— $22 $— 177 $122 $55 $— 
Assets measured at net asset value281 128 
Accrued investment income— 1 
Total pension plan assets$303 $306 

At December 31, the fair values of OPEB plan assets were as follows (in millions):
20242023
FairLevelLevelLevelFairLevelLevelLevel
Alliant EnergyValue123Value123
Cash and equivalents$8 $— $8 $— $9 $— $9 $— 
Equity securities20 20 — — 8 8 — — 
Fixed income securities52 52 — — 47 47 — — 
Total assets in fair value hierarchy80 $72 $8 $— 64 $55 $9 $— 
Assets measured at net asset value— 19 
Total OPEB plan assets$80 $83 
20242023
FairLevelLevelLevelFairLevelLevelLevel
IPLValue123Value123
Cash and equivalents$1 $— $1 $— $1 $— $1 $— 
Equity securities18 18 — — 6 6 — — 
Fixed income securities40 40 — — 36 36 — — 
Total assets in fair value hierarchy59 $58 $1 $— 43 $42 $1 $— 
Assets measured at net asset value— 18 
Total OPEB plan assets$59 $61 
20242023
FairLevelLevelLevelFairLevelLevelLevel
WPLValue123Value123
Cash and equivalents$— $— $— $— $1 $— $1 $— 
Equity securities2 2 — — 2 2 — — 
Fixed income securities11 11 — — 11 11 — — 
Total OPEB plan assets$13 $13 $— $— $14 $13 $1 $— 

For the various defined benefit pension and OPEB plans, Alliant Energy common stock represented less than 1% of assets directly held in the plans at December 31, 2024 and 2023.

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% and 8% of total assets in the 401(k) savings plans at December 31, 2024 and 2023, respectively. 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
202420232022202420232022202420232022
401(k) costs$31 $30 $28 $14 $14 $13 $15 $14 $13 

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, 2024, 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
202420232022202420232022202420232022
Compensation expense$12$12$13$6$6$7$5$5$5
Income tax benefits333222111

As of December 31, 2024, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $10 million, $5 million and $5 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, 2024, 564,743 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:
202420232022
SharesWeighted
Average Grant
Date Fair Value		SharesWeighted
Average Grant
Date Fair Value		SharesWeighted
Average Grant
Date Fair Value
Nonvested awards, January 1233,954$52.60190,273$54.13196,429$51.59
Granted127,87446.04108,71255.6874,10654.45
Vested(47,497)46.19(53,431)64.04(71,101)47.48
Forfeited(24,932)46.16(11,600)53.88(9,161)53.99
Nonvested awards, December 31289,39951.31233,95452.60190,27354.13

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:
202420232022
UnitsWeighted
Average Grant
Date Fair Value		UnitsWeighted
Average Grant
Date Fair Value		UnitsWeighted
Average Grant
Date Fair Value
Nonvested awards, January 1234,259$52.58198,275$54.53217,819$50.54
Granted129,85448.69106,12452.7777,12256.88
Vested(71,441)48.65(55,345)59.40(82,770)46.08
Forfeited(3,524)48.40(14,795)54.53(13,896)55.53
Nonvested awards, December 31289,14851.85234,25952.58198,27554.53

Performance Shares (Net Income and Workforce Composition Metrics) (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 a workforce composition metric. 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:
202420232022
SharesWeighted Average Grant Date Fair ValueSharesWeighted Average Grant Date Fair ValueSharesWeighted Average Grant Date Fair Value
Nonvested awards, January 1257,639$52.76199,874$54.74196,429$50.74
Granted146,14348.55124,21752.7184,67057.01
Vested(67,852)48.66(53,431)59.36(71,101)46.24
Forfeited(5,230)48.40(13,021)55.47(10,124)55.92
Nonvested awards, December 31330,70051.81257,63952.76199,87454.74
(c) Deferred Compensation Plan - Alliant Energy maintains a DCP under which certain key employees may defer up to 100% 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):
20242023
Carrying value$14$13
Fair market value2219

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, 2024 and 2023, the carrying value of Alliant Energy’s deferred compensation obligations for participants’ interest, equity and mutual fund accounts, which approximates fair market value, was $23 million and $21 million, respectively.
IPL [Member]  
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 Energy202420232022202420232022
Discount rate for benefit obligations5.65%5.36%5.54%5.62%5.40%5.53%
Discount rate for net periodic cost5.36%5.54%2.91%5.40%5.53%2.81%
Expected rate of return on plan assets7.73%7.80%7.80%6.22%6.50%6.40%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan6.24%10.75%9.22%N/AN/AN/A
Rate of compensation increase3.50%-4.50%3.30%-4.50%3.30%-4.50%N/AN/AN/A
Qualified Defined Benefit Pension PlanOPEB Plans
IPL202420232022202420232022
Discount rate for benefit obligations5.66%5.35%5.55%5.61%5.40%5.53%
Discount rate for net periodic cost5.35%5.55%2.94%5.40%5.53%2.80%
Expected rate of return on plan assets7.60%7.80%7.80%6.60%6.90%6.50%
Rate of compensation increase3.75%3.30%3.30%N/AN/AN/A
Qualified Defined Benefit Pension PlanOPEB Plans
WPL202420232022202420232022
Discount rate for benefit obligations5.66%5.35%5.54%5.61%5.40%5.53%
Discount rate for net periodic cost5.35%5.54%2.94%5.40%5.53%2.79%
Expected rate of return on plan assets7.80%7.80%7.80%5.61%5.65%5.49%
Rate of compensation increase3.50%3.30%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
202420232022202420232022
Service cost$5 $5 $9 $2 $2 $3 
Interest cost45 47 36 8 9 6 
Expected return on plan assets (a)(55)(53)(69)(5)(5)(5)
Amortization of prior service credit (b)(1)(1)(1)— — — 
Amortization of actuarial loss (c)24 28 32 — 1 2 
Settlement losses (d)— — 26 — — — 
$18 $26 $33 $5 $7 $6 
IPLDefined Benefit Pension PlansOPEB Plans
202420232022202420232022
Service cost$3 $3 $6 $1 $1 $1 
Interest cost20 21 16 3 3 2 
Expected return on plan assets (a)(26)(26)(31)(4)(3)(4)
Amortization of actuarial loss (c)9 11 13 — 1 1 
Settlement losses (d)— — 13 — — — 
$6 $9 $17 $— $2 $— 
WPLDefined Benefit Pension PlansOPEB Plans
202420232022202420232022
Service cost$2 $2 $3 $1 $1 $1 
Interest cost20 20 16 3 3 2 
Expected return on plan assets (a)(23)(22)(31)(1)(1)(1)
Amortization of actuarial loss (c)11 13 15 — 1 2 
Settlement losses (d)— — 13 — — — 
$10 $13 $16 $3 $4 $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.
(d)Settlement losses related to payments made to retired executives of Alliant Energy and lump sum payments related to IPL’s and WPL’s qualified defined benefit pension plans. In 2022, the majority of Alliant Energy’s, IPL’s, and WPL’s pension settlement losses were recognized as regulatory assets in accordance with regulatory treatment, and $7 million was included in “Other (income) and deductions” in Alliant Energy’s and IPL’s income statements related to IPL’s qualified defined benefit pension plan.

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 Energy2024202320242023
Change in benefit obligation:
Net benefit obligation at January 1$876 $875 $160 $168 
Service cost5 5 2 2 
Interest cost45 47 8 9 
Plan participants’ contributions— — 3 4 
Actuarial (gain) loss(19)23 (7)(3)
Gross benefits paid(66)(74)(18)(20)
Net benefit obligation at December 31841 876 148 160 
Change in plan assets:
Fair value of plan assets at January 1732 706 83 83 
Actual return on plan assets38 86 5 8 
Employer contributions11 14 7 8 
Plan participants’ contributions— — 3 4 
Gross benefits paid(66)(74)(18)(20)
Fair value of plan assets at December 31715 732 80 83 
Under funded status at December 31($126)($144)($68)($77)
Defined Benefit Pension PlansOPEB Plans
Alliant Energy2024202320242023
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $17 $14 
Current liabilities(3)(2)(7)(8)
Pension and other benefit obligations(123)(142)(78)(83)
Net amounts recognized at December 31($126)($144)($68)($77)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$312 $337 $4 $11 
Prior service credit(2)(2)— — 
$310 $335 $4 $11 
Defined Benefit Pension PlansOPEB Plans
IPL2024202320242023
Change in benefit obligation:
Net benefit obligation at January 1$387 $389 $65 $68 
Service cost3 3 1 1 
Interest cost20 21 3 3 
Plan participants’ contributions— — 1 2 
Actuarial (gain) loss(8)9 (3)(1)
Gross benefits paid(30)(35)(8)(8)
Net benefit obligation at December 31372 387 59 65 
Change in plan assets:
Fair value of plan assets at January 1352 344 61 58 
Actual return on plan assets18 42 4 7 
Employer contributions— 1 1 2 
Plan participants’ contributions— — 1 2 
Gross benefits paid(30)(35)(8)(8)
Fair value of plan assets at December 31340 352 59 61 
Under funded status at December 31($32)($35)$— ($4)
Defined Benefit Pension PlansOPEB Plans
IPL2024202320242023
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $13 $10 
Current liabilities(1)— (1)(1)
Pension and other benefit obligations(31)(35)(12)(13)
Net amounts recognized at December 31($32)($35)$— ($4)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$126 $135 $7 $9 
Prior service credit(1)(1)— — 
$125 $134 $7 $9 
Defined Benefit Pension PlansOPEB Plans
WPL2024202320242023
Change in benefit obligation:
Net benefit obligation at January 1$381 $381 $61 $65 
Service cost2 2 1 1 
Interest cost20 20 3 3 
Plan participants’ contributions— — 1 2 
Actuarial (gain) loss (8)10 (3)(2)
Gross benefits paid(30)(32)(7)(8)
Net benefit obligation at December 31365 381 56 61 
Change in plan assets:
Fair value of plan assets at January 1306 291 14 14 
Actual return on plan assets17 35 — 1 
Employer contributions10 12 5 5 
Plan participants’ contributions— — 1 2 
Gross benefits paid(30)(32)(7)(8)
Fair value of plan assets at December 31303 306 13 14 
Under funded status at December 31($62)($75)($43)($47)
Defined Benefit Pension PlansOPEB Plans
WPL2024202320242023
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $4 $4 
Current liabilities— — (6)(6)
Pension and other benefit obligations(62)(75)(41)(45)
Net amounts recognized at December 31($62)($75)($43)($47)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$135 $148 $— $3 

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 Energy2024202320242023
Accumulated benefit obligations$824 $857 $148 $160 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations824 857 148 160 
Fair value of plan assets715 732 80 83 
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations841 876 N/AN/A
Fair value of plan assets715 732 N/AN/A
Defined Benefit Pension PlansOPEB Plans
IPL2024202320242023
Accumulated benefit obligations$362 $377 $59 $65 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations362 377 N/A65 
Fair value of plan assets340 352 N/A61 
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations372 387 N/AN/A
Fair value of plan assets340 352 N/AN/A
Defined Benefit Pension PlansOPEB Plans
WPL2024202320242023
Accumulated benefit obligations$358 $373 $56 $61 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations358 373 56 61 
Fair value of plan assets303 306 13 14 
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations365 381 N/AN/A
Fair value of plan assets303 306 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
2024202320242023
Regulatory assets$25$28$22$24

Estimated Future Employer Contributions and Benefit Payments - Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2025 is as follows (in millions):
Alliant EnergyIPLWPL
Defined benefit pension plans (a)$20$1$14
OPEB plans716

(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 Energy202520262027202820292030 - 2034
Defined benefit pension benefits$79 $75 $74 $74 $74 $329
OPEB16 16 15 15 14 62
$95 $91 $89 $89 $88 $391
IPL202520262027202820292030 - 2034
Defined benefit pension benefits$36 $34 $33 $33 $32 $148
OPEB7 6 6 6 6 24
$43 $40 $39 $39 $38 $172
WPL202520262027202820292030 - 2034
Defined benefit pension benefits$33 $31 $31 $31 $31 $144
OPEB7 6 6 5 5 23
$40 $37 $37 $36 $36 $167
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, 2024, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows:
Target RangeActual
AllocationAllocation
Public equity securities32%-49%44%
Liquid alternative securities0%-12%6%
Return-seeking fixed income securities4%-18%8%
Liability-hedging fixed income securities (including cash and equivalents)34%-53%42%

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, 2024, 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%1%
Public equity securities0%-40%27%
Fixed income securities40%-100%72%

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):
20242023
FairLevelLevelLevelFairLevelLevelLevel
Alliant EnergyValue123Value123
Cash and equivalents$49 $— $49 $— $19 $— $19 $— 
Equity securities— — — — 223 223 — — 
Global asset securities— — — — 39 39 — — 
Fixed income securities— — — — 143 31 112 — 
Total assets in fair value hierarchy49 $— $49 $— 424 $293 $131 $— 
Assets measured at net asset value667 306 
Accrued investment income— 2 
Due to brokers, net (pending trades with brokers)(1)— 
Total pension plan assets$715 $732 
20242023
FairLevelLevelLevelFairLevelLevelLevel
IPLValue123Value123
Cash and equivalents$21 $— $21 $— $9 $— $9 $— 
Equity securities— — — — 107 107 — — 
Global asset securities— — — — 19 19 — — 
Fixed income securities— — — — 69 15 54 — 
Total assets in fair value hierarchy21 $— $21 $— 204 $141 $63 $— 
Assets measured at net asset value319 147 
Accrued investment income— 1 
Total pension plan assets$340 $352 
20242023
FairLevelLevelLevelFairLevelLevelLevel
WPLValue123Value123
Cash and equivalents$22 $— $22 $— $8 $— $8 $— 
Equity securities— — — — 93 93 — — 
Global asset securities— — — — 16 16 — — 
Fixed income securities— — — — 60 13 47 — 
Total assets in fair value hierarchy22 $— $22 $— 177 $122 $55 $— 
Assets measured at net asset value281 128 
Accrued investment income— 1 
Total pension plan assets$303 $306 

At December 31, the fair values of OPEB plan assets were as follows (in millions):
20242023
FairLevelLevelLevelFairLevelLevelLevel
Alliant EnergyValue123Value123
Cash and equivalents$8 $— $8 $— $9 $— $9 $— 
Equity securities20 20 — — 8 8 — — 
Fixed income securities52 52 — — 47 47 — — 
Total assets in fair value hierarchy80 $72 $8 $— 64 $55 $9 $— 
Assets measured at net asset value— 19 
Total OPEB plan assets$80 $83 
20242023
FairLevelLevelLevelFairLevelLevelLevel
IPLValue123Value123
Cash and equivalents$1 $— $1 $— $1 $— $1 $— 
Equity securities18 18 — — 6 6 — — 
Fixed income securities40 40 — — 36 36 — — 
Total assets in fair value hierarchy59 $58 $1 $— 43 $42 $1 $— 
Assets measured at net asset value— 18 
Total OPEB plan assets$59 $61 
20242023
FairLevelLevelLevelFairLevelLevelLevel
WPLValue123Value123
Cash and equivalents$— $— $— $— $1 $— $1 $— 
Equity securities2 2 — — 2 2 — — 
Fixed income securities11 11 — — 11 11 — — 
Total OPEB plan assets$13 $13 $— $— $14 $13 $1 $— 

For the various defined benefit pension and OPEB plans, Alliant Energy common stock represented less than 1% of assets directly held in the plans at December 31, 2024 and 2023.

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% and 8% of total assets in the 401(k) savings plans at December 31, 2024 and 2023, respectively. 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
202420232022202420232022202420232022
401(k) costs$31 $30 $28 $14 $14 $13 $15 $14 $13 

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, 2024, 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
202420232022202420232022202420232022
Compensation expense$12$12$13$6$6$7$5$5$5
Income tax benefits333222111

As of December 31, 2024, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $10 million, $5 million and $5 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, 2024, 564,743 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:
202420232022
SharesWeighted
Average Grant
Date Fair Value		SharesWeighted
Average Grant
Date Fair Value		SharesWeighted
Average Grant
Date Fair Value
Nonvested awards, January 1233,954$52.60190,273$54.13196,429$51.59
Granted127,87446.04108,71255.6874,10654.45
Vested(47,497)46.19(53,431)64.04(71,101)47.48
Forfeited(24,932)46.16(11,600)53.88(9,161)53.99
Nonvested awards, December 31289,39951.31233,95452.60190,27354.13

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:
202420232022
UnitsWeighted
Average Grant
Date Fair Value		UnitsWeighted
Average Grant
Date Fair Value		UnitsWeighted
Average Grant
Date Fair Value
Nonvested awards, January 1234,259$52.58198,275$54.53217,819$50.54
Granted129,85448.69106,12452.7777,12256.88
Vested(71,441)48.65(55,345)59.40(82,770)46.08
Forfeited(3,524)48.40(14,795)54.53(13,896)55.53
Nonvested awards, December 31289,14851.85234,25952.58198,27554.53

Performance Shares (Net Income and Workforce Composition Metrics) (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 a workforce composition metric. 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:
202420232022
SharesWeighted Average Grant Date Fair ValueSharesWeighted Average Grant Date Fair ValueSharesWeighted Average Grant Date Fair Value
Nonvested awards, January 1257,639$52.76199,874$54.74196,429$50.74
Granted146,14348.55124,21752.7184,67057.01
Vested(67,852)48.66(53,431)59.36(71,101)46.24
Forfeited(5,230)48.40(13,021)55.47(10,124)55.92
Nonvested awards, December 31330,70051.81257,63952.76199,87454.74
WPL [Member]  
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 Energy202420232022202420232022
Discount rate for benefit obligations5.65%5.36%5.54%5.62%5.40%5.53%
Discount rate for net periodic cost5.36%5.54%2.91%5.40%5.53%2.81%
Expected rate of return on plan assets7.73%7.80%7.80%6.22%6.50%6.40%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan6.24%10.75%9.22%N/AN/AN/A
Rate of compensation increase3.50%-4.50%3.30%-4.50%3.30%-4.50%N/AN/AN/A
Qualified Defined Benefit Pension PlanOPEB Plans
IPL202420232022202420232022
Discount rate for benefit obligations5.66%5.35%5.55%5.61%5.40%5.53%
Discount rate for net periodic cost5.35%5.55%2.94%5.40%5.53%2.80%
Expected rate of return on plan assets7.60%7.80%7.80%6.60%6.90%6.50%
Rate of compensation increase3.75%3.30%3.30%N/AN/AN/A
Qualified Defined Benefit Pension PlanOPEB Plans
WPL202420232022202420232022
Discount rate for benefit obligations5.66%5.35%5.54%5.61%5.40%5.53%
Discount rate for net periodic cost5.35%5.54%2.94%5.40%5.53%2.79%
Expected rate of return on plan assets7.80%7.80%7.80%5.61%5.65%5.49%
Rate of compensation increase3.50%3.30%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
202420232022202420232022
Service cost$5 $5 $9 $2 $2 $3 
Interest cost45 47 36 8 9 6 
Expected return on plan assets (a)(55)(53)(69)(5)(5)(5)
Amortization of prior service credit (b)(1)(1)(1)— — — 
Amortization of actuarial loss (c)24 28 32 — 1 2 
Settlement losses (d)— — 26 — — — 
$18 $26 $33 $5 $7 $6 
IPLDefined Benefit Pension PlansOPEB Plans
202420232022202420232022
Service cost$3 $3 $6 $1 $1 $1 
Interest cost20 21 16 3 3 2 
Expected return on plan assets (a)(26)(26)(31)(4)(3)(4)
Amortization of actuarial loss (c)9 11 13 — 1 1 
Settlement losses (d)— — 13 — — — 
$6 $9 $17 $— $2 $— 
WPLDefined Benefit Pension PlansOPEB Plans
202420232022202420232022
Service cost$2 $2 $3 $1 $1 $1 
Interest cost20 20 16 3 3 2 
Expected return on plan assets (a)(23)(22)(31)(1)(1)(1)
Amortization of actuarial loss (c)11 13 15 — 1 2 
Settlement losses (d)— — 13 — — — 
$10 $13 $16 $3 $4 $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.
(d)Settlement losses related to payments made to retired executives of Alliant Energy and lump sum payments related to IPL’s and WPL’s qualified defined benefit pension plans. In 2022, the majority of Alliant Energy’s, IPL’s, and WPL’s pension settlement losses were recognized as regulatory assets in accordance with regulatory treatment, and $7 million was included in “Other (income) and deductions” in Alliant Energy’s and IPL’s income statements related to IPL’s qualified defined benefit pension plan.

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 Energy2024202320242023
Change in benefit obligation:
Net benefit obligation at January 1$876 $875 $160 $168 
Service cost5 5 2 2 
Interest cost45 47 8 9 
Plan participants’ contributions— — 3 4 
Actuarial (gain) loss(19)23 (7)(3)
Gross benefits paid(66)(74)(18)(20)
Net benefit obligation at December 31841 876 148 160 
Change in plan assets:
Fair value of plan assets at January 1732 706 83 83 
Actual return on plan assets38 86 5 8 
Employer contributions11 14 7 8 
Plan participants’ contributions— — 3 4 
Gross benefits paid(66)(74)(18)(20)
Fair value of plan assets at December 31715 732 80 83 
Under funded status at December 31($126)($144)($68)($77)
Defined Benefit Pension PlansOPEB Plans
Alliant Energy2024202320242023
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $17 $14 
Current liabilities(3)(2)(7)(8)
Pension and other benefit obligations(123)(142)(78)(83)
Net amounts recognized at December 31($126)($144)($68)($77)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$312 $337 $4 $11 
Prior service credit(2)(2)— — 
$310 $335 $4 $11 
Defined Benefit Pension PlansOPEB Plans
IPL2024202320242023
Change in benefit obligation:
Net benefit obligation at January 1$387 $389 $65 $68 
Service cost3 3 1 1 
Interest cost20 21 3 3 
Plan participants’ contributions— — 1 2 
Actuarial (gain) loss(8)9 (3)(1)
Gross benefits paid(30)(35)(8)(8)
Net benefit obligation at December 31372 387 59 65 
Change in plan assets:
Fair value of plan assets at January 1352 344 61 58 
Actual return on plan assets18 42 4 7 
Employer contributions— 1 1 2 
Plan participants’ contributions— — 1 2 
Gross benefits paid(30)(35)(8)(8)
Fair value of plan assets at December 31340 352 59 61 
Under funded status at December 31($32)($35)$— ($4)
Defined Benefit Pension PlansOPEB Plans
IPL2024202320242023
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $13 $10 
Current liabilities(1)— (1)(1)
Pension and other benefit obligations(31)(35)(12)(13)
Net amounts recognized at December 31($32)($35)$— ($4)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$126 $135 $7 $9 
Prior service credit(1)(1)— — 
$125 $134 $7 $9 
Defined Benefit Pension PlansOPEB Plans
WPL2024202320242023
Change in benefit obligation:
Net benefit obligation at January 1$381 $381 $61 $65 
Service cost2 2 1 1 
Interest cost20 20 3 3 
Plan participants’ contributions— — 1 2 
Actuarial (gain) loss (8)10 (3)(2)
Gross benefits paid(30)(32)(7)(8)
Net benefit obligation at December 31365 381 56 61 
Change in plan assets:
Fair value of plan assets at January 1306 291 14 14 
Actual return on plan assets17 35 — 1 
Employer contributions10 12 5 5 
Plan participants’ contributions— — 1 2 
Gross benefits paid(30)(32)(7)(8)
Fair value of plan assets at December 31303 306 13 14 
Under funded status at December 31($62)($75)($43)($47)
Defined Benefit Pension PlansOPEB Plans
WPL2024202320242023
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $4 $4 
Current liabilities— — (6)(6)
Pension and other benefit obligations(62)(75)(41)(45)
Net amounts recognized at December 31($62)($75)($43)($47)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$135 $148 $— $3 

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 Energy2024202320242023
Accumulated benefit obligations$824 $857 $148 $160 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations824 857 148 160 
Fair value of plan assets715 732 80 83 
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations841 876 N/AN/A
Fair value of plan assets715 732 N/AN/A
Defined Benefit Pension PlansOPEB Plans
IPL2024202320242023
Accumulated benefit obligations$362 $377 $59 $65 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations362 377 N/A65 
Fair value of plan assets340 352 N/A61 
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations372 387 N/AN/A
Fair value of plan assets340 352 N/AN/A
Defined Benefit Pension PlansOPEB Plans
WPL2024202320242023
Accumulated benefit obligations$358 $373 $56 $61 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations358 373 56 61 
Fair value of plan assets303 306 13 14 
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations365 381 N/AN/A
Fair value of plan assets303 306 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
2024202320242023
Regulatory assets$25$28$22$24

Estimated Future Employer Contributions and Benefit Payments - Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2025 is as follows (in millions):
Alliant EnergyIPLWPL
Defined benefit pension plans (a)$20$1$14
OPEB plans716

(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 Energy202520262027202820292030 - 2034
Defined benefit pension benefits$79 $75 $74 $74 $74 $329
OPEB16 16 15 15 14 62
$95 $91 $89 $89 $88 $391
IPL202520262027202820292030 - 2034
Defined benefit pension benefits$36 $34 $33 $33 $32 $148
OPEB7 6 6 6 6 24
$43 $40 $39 $39 $38 $172
WPL202520262027202820292030 - 2034
Defined benefit pension benefits$33 $31 $31 $31 $31 $144
OPEB7 6 6 5 5 23
$40 $37 $37 $36 $36 $167
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, 2024, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows:
Target RangeActual
AllocationAllocation
Public equity securities32%-49%44%
Liquid alternative securities0%-12%6%
Return-seeking fixed income securities4%-18%8%
Liability-hedging fixed income securities (including cash and equivalents)34%-53%42%

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, 2024, 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%1%
Public equity securities0%-40%27%
Fixed income securities40%-100%72%

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):
20242023
FairLevelLevelLevelFairLevelLevelLevel
Alliant EnergyValue123Value123
Cash and equivalents$49 $— $49 $— $19 $— $19 $— 
Equity securities— — — — 223 223 — — 
Global asset securities— — — — 39 39 — — 
Fixed income securities— — — — 143 31 112 — 
Total assets in fair value hierarchy49 $— $49 $— 424 $293 $131 $— 
Assets measured at net asset value667 306 
Accrued investment income— 2 
Due to brokers, net (pending trades with brokers)(1)— 
Total pension plan assets$715 $732 
20242023
FairLevelLevelLevelFairLevelLevelLevel
IPLValue123Value123
Cash and equivalents$21 $— $21 $— $9 $— $9 $— 
Equity securities— — — — 107 107 — — 
Global asset securities— — — — 19 19 — — 
Fixed income securities— — — — 69 15 54 — 
Total assets in fair value hierarchy21 $— $21 $— 204 $141 $63 $— 
Assets measured at net asset value319 147 
Accrued investment income— 1 
Total pension plan assets$340 $352 
20242023
FairLevelLevelLevelFairLevelLevelLevel
WPLValue123Value123
Cash and equivalents$22 $— $22 $— $8 $— $8 $— 
Equity securities— — — — 93 93 — — 
Global asset securities— — — — 16 16 — — 
Fixed income securities— — — — 60 13 47 — 
Total assets in fair value hierarchy22 $— $22 $— 177 $122 $55 $— 
Assets measured at net asset value281 128 
Accrued investment income— 1 
Total pension plan assets$303 $306 

At December 31, the fair values of OPEB plan assets were as follows (in millions):
20242023
FairLevelLevelLevelFairLevelLevelLevel
Alliant EnergyValue123Value123
Cash and equivalents$8 $— $8 $— $9 $— $9 $— 
Equity securities20 20 — — 8 8 — — 
Fixed income securities52 52 — — 47 47 — — 
Total assets in fair value hierarchy80 $72 $8 $— 64 $55 $9 $— 
Assets measured at net asset value— 19 
Total OPEB plan assets$80 $83 
20242023
FairLevelLevelLevelFairLevelLevelLevel
IPLValue123Value123
Cash and equivalents$1 $— $1 $— $1 $— $1 $— 
Equity securities18 18 — — 6 6 — — 
Fixed income securities40 40 — — 36 36 — — 
Total assets in fair value hierarchy59 $58 $1 $— 43 $42 $1 $— 
Assets measured at net asset value— 18 
Total OPEB plan assets$59 $61 
20242023
FairLevelLevelLevelFairLevelLevelLevel
WPLValue123Value123
Cash and equivalents$— $— $— $— $1 $— $1 $— 
Equity securities2 2 — — 2 2 — — 
Fixed income securities11 11 — — 11 11 — — 
Total OPEB plan assets$13 $13 $— $— $14 $13 $1 $— 

For the various defined benefit pension and OPEB plans, Alliant Energy common stock represented less than 1% of assets directly held in the plans at December 31, 2024 and 2023.

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% and 8% of total assets in the 401(k) savings plans at December 31, 2024 and 2023, respectively. 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
202420232022202420232022202420232022
401(k) costs$31 $30 $28 $14 $14 $13 $15 $14 $13 

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, 2024, 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
202420232022202420232022202420232022
Compensation expense$12$12$13$6$6$7$5$5$5
Income tax benefits333222111

As of December 31, 2024, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $10 million, $5 million and $5 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, 2024, 564,743 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:
202420232022
SharesWeighted
Average Grant
Date Fair Value		SharesWeighted
Average Grant
Date Fair Value		SharesWeighted
Average Grant
Date Fair Value
Nonvested awards, January 1233,954$52.60190,273$54.13196,429$51.59
Granted127,87446.04108,71255.6874,10654.45
Vested(47,497)46.19(53,431)64.04(71,101)47.48
Forfeited(24,932)46.16(11,600)53.88(9,161)53.99
Nonvested awards, December 31289,39951.31233,95452.60190,27354.13

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:
202420232022
UnitsWeighted
Average Grant
Date Fair Value		UnitsWeighted
Average Grant
Date Fair Value		UnitsWeighted
Average Grant
Date Fair Value
Nonvested awards, January 1234,259$52.58198,275$54.53217,819$50.54
Granted129,85448.69106,12452.7777,12256.88
Vested(71,441)48.65(55,345)59.40(82,770)46.08
Forfeited(3,524)48.40(14,795)54.53(13,896)55.53
Nonvested awards, December 31289,14851.85234,25952.58198,27554.53

Performance Shares (Net Income and Workforce Composition Metrics) (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 a workforce composition metric. 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:
202420232022
SharesWeighted Average Grant Date Fair ValueSharesWeighted Average Grant Date Fair ValueSharesWeighted Average Grant Date Fair Value
Nonvested awards, January 1257,639$52.76199,874$54.74196,429$50.74
Granted146,14348.55124,21752.7184,67057.01
Vested(67,852)48.66(53,431)59.36(71,101)46.24
Forfeited(5,230)48.40(13,021)55.47(10,124)55.92
Nonvested awards, December 31330,70051.81257,63952.76199,87454.74
v3.25.0.1
Asset Retirement Obligations
 12 Months Ended
Dec. 31, 2024
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 batteries. 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
202420232024202320242023
Balance, January 1$246 $279 $148 $195 $98 $84 
Revisions in estimated cash flows(3)(6)(1)(9)(2)3 
Liabilities settled(8)(51)(6)(44)(2)(7)
Liabilities incurred (a)409 16 201 1 208 15 
Accretion expense19 8 8 5 11 3 
Balance, December 31$663 $246 $350 $148 $313 $98 

(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 batteries. 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
202420232024202320242023
Balance, January 1$246 $279 $148 $195 $98 $84 
Revisions in estimated cash flows(3)(6)(1)(9)(2)3 
Liabilities settled(8)(51)(6)(44)(2)(7)
Liabilities incurred (a)409 16 201 1 208 15 
Accretion expense19 8 8 5 11 3 
Balance, December 31$663 $246 $350 $148 $313 $98 

(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 batteries. 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
202420232024202320242023
Balance, January 1$246 $279 $148 $195 $98 $84 
Revisions in estimated cash flows(3)(6)(1)(9)(2)3 
Liabilities settled(8)(51)(6)(44)(2)(7)
Liabilities incurred (a)409 16 201 1 208 15 
Accretion expense19 8 8 5 11 3 
Balance, December 31$663 $246 $350 $148 $313 $98 

(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.
v3.25.0.1
Derivative Instruments
 12 Months Ended
Dec. 31, 2024
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, 2024, 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
Alliant Energy1,422 2025-202610,232 2025147,894 2025-20322,520 2025
IPL383 2025-20263,551 202561,489 2025-2030— —
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, 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
202420232024202320242023
Current derivative assets$41$44$29$30$12$14
Non-current derivative assets344419241520
Current derivative liabilities265111221529
Non-current derivative liabilities3247283039

In 2024, Alliant Energy’s, IPL’s and WPL’s derivative liabilities decreased primarily due to settlements of natural gas contracts and higher natural gas prices. 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, 2024 and 2023, 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
2024
Derivative assets$75$64$48$43$27$21
Derivative liabilities58471384539
2023
Derivative assets884754323415
Derivative liabilities98573086849

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. The related interest rate derivative was valued based on quoted prices that utilize current market interest rate forecasts. As of both December 31, 2024 and 2023, $1 million of non-current interest rate derivative assets was recorded in “Deferred charges and other” on Alliant Energy’s balance sheets. This interest rate derivative was designated as a cash flow hedge, with changes in fair value recorded as other comprehensive income/loss. As of both December 31, 2024 and 2023, accumulated other comprehensive income included $1 million of income related to the interest rate swap. In 2024 and 2023, $4 million and $3 million, respectively, of reductions to interest expense were 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, 2024, 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
Alliant Energy1,422 2025-202610,232 2025147,894 2025-20322,520 2025
IPL383 2025-20263,551 202561,489 2025-2030— —
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, 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
202420232024202320242023
Current derivative assets$41$44$29$30$12$14
Non-current derivative assets344419241520
Current derivative liabilities265111221529
Non-current derivative liabilities3247283039

In 2024, Alliant Energy’s, IPL’s and WPL’s derivative liabilities decreased primarily due to settlements of natural gas contracts and higher natural gas prices. 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, 2024 and 2023, 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
2024
Derivative assets$75$64$48$43$27$21
Derivative liabilities58471384539
2023
Derivative assets884754323415
Derivative liabilities98573086849

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. The related interest rate derivative was valued based on quoted prices that utilize current market interest rate forecasts. As of both December 31, 2024 and 2023, $1 million of non-current interest rate derivative assets was recorded in “Deferred charges and other” on Alliant Energy’s balance sheets. This interest rate derivative was designated as a cash flow hedge, with changes in fair value recorded as other comprehensive income/loss. As of both December 31, 2024 and 2023, accumulated other comprehensive income included $1 million of income related to the interest rate swap. In 2024 and 2023, $4 million and $3 million, respectively, of reductions to interest expense were recorded in Alliant Energy’s income statement related to the interest rate swap.
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, 2024, 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
Alliant Energy1,422 2025-202610,232 2025147,894 2025-20322,520 2025
IPL383 2025-20263,551 202561,489 2025-2030— —
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, 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
202420232024202320242023
Current derivative assets$41$44$29$30$12$14
Non-current derivative assets344419241520
Current derivative liabilities265111221529
Non-current derivative liabilities3247283039

In 2024, Alliant Energy’s, IPL’s and WPL’s derivative liabilities decreased primarily due to settlements of natural gas contracts and higher natural gas prices. 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, 2024 and 2023, 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
2024
Derivative assets$75$64$48$43$27$21
Derivative liabilities58471384539
2023
Derivative assets884754323415
Derivative liabilities98573086849

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. The related interest rate derivative was valued based on quoted prices that utilize current market interest rate forecasts. As of both December 31, 2024 and 2023, $1 million of non-current interest rate derivative assets was recorded in “Deferred charges and other” on Alliant Energy’s balance sheets. This interest rate derivative was designated as a cash flow hedge, with changes in fair value recorded as other comprehensive income/loss. As of both December 31, 2024 and 2023, accumulated other comprehensive income included $1 million of income related to the interest rate swap. In 2024 and 2023, $4 million and $3 million, respectively, of reductions to interest expense were recorded in Alliant Energy’s income statement related to the interest rate swap.
v3.25.0.1
Fair Value Measurements
 12 Months Ended
Dec. 31, 2024
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 Energy20242023
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$52 $52 $— $— $52 $45 $45 $— $— $45 
Commodity derivatives75 — 48 27 75 88 — 59 29 88 
Interest rate derivatives1 — 1 — 1 1 — 1 — 1 
Deferred proceeds163 — — 163 163 216 — — 216 216 
Liabilities:
Commodity derivatives58 — 56 2 58 98 — 93 5 98 
Long-term debt (incl. current maturities)9,848 — 9,577 — 9,577 9,034 — 8,677 — 8,677 
IPL20242023
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$9 $9 $— $— $9 $45 $45 $— $— $45 
Commodity derivatives48 — 26 22 48 54 — 30 24 54 
Deferred proceeds163 — — 163 163 216 — — 216 216 
Liabilities:
Commodity derivatives13 — 11 2 13 30 — 25 5 30 
Long-term debt (incl. current maturities)4,090 — 3,736 — 3,736 3,945 — 3,664 — 3,664 
WPL20242023
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$43 $43 $— $— $43 $— $— $— $— $— 
Commodity derivatives27 — 22 5 27 34 — 29 5 34 
Liabilities:
Commodity derivatives45 — 45 — 45 68 — 68 — 68 
Long-term debt3,370 — 3,170 — 3,170 3,070 — 2,933 — 2,933 
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
2024202320242023
Beginning balance, January 1$24$19$216$185
Total net gains (losses) included in changes in net assets (realized/unrealized)(3)3——
Purchases5962——
Sales(3)(3)——
Settlements (a)(52)(57)(53)31
Ending balance, December 31$25$24$163$216
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($3)$3$—$—
IPLCommodity Contract Derivative
Assets and (Liabilities), netDeferred Proceeds
2024202320242023
Beginning balance, January 1$19$16$216$185
Total net losses included in changes in net assets (realized/unrealized)(4)(3)——
Purchases4551——
Sales(2)(3)——
Settlements (a)(38)(42)(53)31
Ending balance, December 31$20$19$163$216
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at December 31($4)($3)$—$—
WPLCommodity Contract Derivative
Assets and (Liabilities), net
20242023
Beginning balance, January 1$5$3
Total net gains included in changes in net assets (realized/unrealized)16
Purchases1411
Sales(1)—
Settlements(14)(15)
Ending balance, December 31$5$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$1$6

(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 FTR 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
2024$—$25$—$20$—$5
2023321316—5
IPL [Member]  
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 Energy20242023
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$52 $52 $— $— $52 $45 $45 $— $— $45 
Commodity derivatives75 — 48 27 75 88 — 59 29 88 
Interest rate derivatives1 — 1 — 1 1 — 1 — 1 
Deferred proceeds163 — — 163 163 216 — — 216 216 
Liabilities:
Commodity derivatives58 — 56 2 58 98 — 93 5 98 
Long-term debt (incl. current maturities)9,848 — 9,577 — 9,577 9,034 — 8,677 — 8,677 
IPL20242023
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$9 $9 $— $— $9 $45 $45 $— $— $45 
Commodity derivatives48 — 26 22 48 54 — 30 24 54 
Deferred proceeds163 — — 163 163 216 — — 216 216 
Liabilities:
Commodity derivatives13 — 11 2 13 30 — 25 5 30 
Long-term debt (incl. current maturities)4,090 — 3,736 — 3,736 3,945 — 3,664 — 3,664 
WPL20242023
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$43 $43 $— $— $43 $— $— $— $— $— 
Commodity derivatives27 — 22 5 27 34 — 29 5 34 
Liabilities:
Commodity derivatives45 — 45 — 45 68 — 68 — 68 
Long-term debt3,370 — 3,170 — 3,170 3,070 — 2,933 — 2,933 
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
2024202320242023
Beginning balance, January 1$24$19$216$185
Total net gains (losses) included in changes in net assets (realized/unrealized)(3)3——
Purchases5962——
Sales(3)(3)——
Settlements (a)(52)(57)(53)31
Ending balance, December 31$25$24$163$216
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($3)$3$—$—
IPLCommodity Contract Derivative
Assets and (Liabilities), netDeferred Proceeds
2024202320242023
Beginning balance, January 1$19$16$216$185
Total net losses included in changes in net assets (realized/unrealized)(4)(3)——
Purchases4551——
Sales(2)(3)——
Settlements (a)(38)(42)(53)31
Ending balance, December 31$20$19$163$216
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at December 31($4)($3)$—$—
WPLCommodity Contract Derivative
Assets and (Liabilities), net
20242023
Beginning balance, January 1$5$3
Total net gains included in changes in net assets (realized/unrealized)16
Purchases1411
Sales(1)—
Settlements(14)(15)
Ending balance, December 31$5$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$1$6

(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 FTR 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
2024$—$25$—$20$—$5
2023321316—5
WPL [Member]  
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 Energy20242023
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$52 $52 $— $— $52 $45 $45 $— $— $45 
Commodity derivatives75 — 48 27 75 88 — 59 29 88 
Interest rate derivatives1 — 1 — 1 1 — 1 — 1 
Deferred proceeds163 — — 163 163 216 — — 216 216 
Liabilities:
Commodity derivatives58 — 56 2 58 98 — 93 5 98 
Long-term debt (incl. current maturities)9,848 — 9,577 — 9,577 9,034 — 8,677 — 8,677 
IPL20242023
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$9 $9 $— $— $9 $45 $45 $— $— $45 
Commodity derivatives48 — 26 22 48 54 — 30 24 54 
Deferred proceeds163 — — 163 163 216 — — 216 216 
Liabilities:
Commodity derivatives13 — 11 2 13 30 — 25 5 30 
Long-term debt (incl. current maturities)4,090 — 3,736 — 3,736 3,945 — 3,664 — 3,664 
WPL20242023
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$43 $43 $— $— $43 $— $— $— $— $— 
Commodity derivatives27 — 22 5 27 34 — 29 5 34 
Liabilities:
Commodity derivatives45 — 45 — 45 68 — 68 — 68 
Long-term debt3,370 — 3,170 — 3,170 3,070 — 2,933 — 2,933 
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
2024202320242023
Beginning balance, January 1$24$19$216$185
Total net gains (losses) included in changes in net assets (realized/unrealized)(3)3——
Purchases5962——
Sales(3)(3)——
Settlements (a)(52)(57)(53)31
Ending balance, December 31$25$24$163$216
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($3)$3$—$—
IPLCommodity Contract Derivative
Assets and (Liabilities), netDeferred Proceeds
2024202320242023
Beginning balance, January 1$19$16$216$185
Total net losses included in changes in net assets (realized/unrealized)(4)(3)——
Purchases4551——
Sales(2)(3)——
Settlements (a)(38)(42)(53)31
Ending balance, December 31$20$19$163$216
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at December 31($4)($3)$—$—
WPLCommodity Contract Derivative
Assets and (Liabilities), net
20242023
Beginning balance, January 1$5$3
Total net gains included in changes in net assets (realized/unrealized)16
Purchases1411
Sales(1)—
Settlements(14)(15)
Ending balance, December 31$5$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$1$6

(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 FTR 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
2024$—$25$—$20$—$5
2023321316—5
v3.25.0.1
Commitments And Contingencies
 12 Months Ended
Dec. 31, 2024
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, and improvements at WPL’s natural gas-fired Neenah Energy Facility and Sheboygan Falls Energy Facility. At December 31, 2024, Alliant Energy’s, IPL’s, and WPL’s minimum future commitments in 2025 for these projects were $448 million, $294 million, and $153 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, 2024, the related minimum future commitments, excluding amounts for purchased power commitments that do not have minimum thresholds but will require payment when electricity is generated by the provider, were as follows (in millions):
Alliant Energy20252026202720282029ThereafterTotal
Natural gas$268$177$130$102$84$120$881
Coal7533225——135
Other (a)512077222109
$394$230$159$114$86$142$1,125
IPL20252026202720282029ThereafterTotal
Natural gas$160$104$85$64$49$20$482
Coal3419105——68
Other (a)1822222147
$212$125$97$71$51$41$597
WPL20252026202720282029ThereafterTotal
Natural gas$108$73$45$38$35$100$399
Coal411412———67
Other (a)221————23
$171$88$57$38$35$100$489

(a)Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2024.
(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, 2024, the currently known partnership obligations for the abandonment obligations are estimated at $54 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, 2024 and 2023.

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 $43 million as of December 31, 2024 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, 2024 and 2023.

Transfers of Renewable Tax Credits - In 2023 and 2024, IPL and WPL 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, 2024, IPL and WPL provided indemnifications associated with $193 million and $121 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.
(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, 2024, 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 -$28$5 -$17$2 -$11
Current and non-current environmental liabilities$12$7$5

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 various requirements under the Consent Decree. IPL’s remaining requirements include fuel switching or retiring Prairie Creek Units 1 and 3 by December 31, 2025. 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 Minnesota, 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 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) MISO Transmission Owner Return on Equity Complaints - A group of stakeholders, including MISO cooperative and municipal utilities, previously filed complaints with FERC requesting a reduction to the base return on equity authorized for MISO transmission owners, including ITC and ATC. In 2019, FERC issued an order on the previously filed complaints and reduced the base return on equity authorized for the MISO transmission owners to 9.88% for November 12, 2013 through February 11, 2015, and subsequent to September 28, 2016. In 2020, FERC issued orders in response to various rehearing requests and increased the base return on equity authorized for the MISO transmission owners from 9.88% to 10.02% for November 12, 2013 through February 11, 2015, and subsequent to September 28, 2016. In 2022, the U.S. Court of Appeals for the District of Columbia vacated FERC’s prior orders that established the base return on equity authorized
for the MISO transmission owners and remanded the cases to FERC for further proceedings. As a result of the 2022 court decision, Alliant Energy recorded a $6 million reduction in “Equity income from unconsolidated investments” in its income statement in 2022 to reflect the then-anticipated reduction in the base return on equity authorized for the MISO transmission owners. In October 2024, FERC issued an order reducing the base return on equity authorized for MISO transmission owners to 9.98%, and as a result, the MISO transmission owners will provide refunds based on the 9.98% base return on equity, with interest, for November 12, 2013 through February 11, 2015, and subsequent to September 28, 2016, which did not result in any material impacts on Alliant Energy’s results of operations or financial condition in 2024. Any further changes in FERC’s decisions may have an impact on Alliant Energy’s share of ATC’s future earnings and customer costs; however, Alliant Energy is currently unable to predict with certainty the future outcome or impact of any further changes.
IPL [Member]  
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, and improvements at WPL’s natural gas-fired Neenah Energy Facility and Sheboygan Falls Energy Facility. At December 31, 2024, Alliant Energy’s, IPL’s, and WPL’s minimum future commitments in 2025 for these projects were $448 million, $294 million, and $153 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, 2024, the related minimum future commitments, excluding amounts for purchased power commitments that do not have minimum thresholds but will require payment when electricity is generated by the provider, were as follows (in millions):
Alliant Energy20252026202720282029ThereafterTotal
Natural gas$268$177$130$102$84$120$881
Coal7533225——135
Other (a)512077222109
$394$230$159$114$86$142$1,125
IPL20252026202720282029ThereafterTotal
Natural gas$160$104$85$64$49$20$482
Coal3419105——68
Other (a)1822222147
$212$125$97$71$51$41$597
WPL20252026202720282029ThereafterTotal
Natural gas$108$73$45$38$35$100$399
Coal411412———67
Other (a)221————23
$171$88$57$38$35$100$489

(a)Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2024.
(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, 2024, the currently known partnership obligations for the abandonment obligations are estimated at $54 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, 2024 and 2023.

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 $43 million as of December 31, 2024 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, 2024 and 2023.

Transfers of Renewable Tax Credits - In 2023 and 2024, IPL and WPL 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, 2024, IPL and WPL provided indemnifications associated with $193 million and $121 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.
(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, 2024, 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 -$28$5 -$17$2 -$11
Current and non-current environmental liabilities$12$7$5

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 various requirements under the Consent Decree. IPL’s remaining requirements include fuel switching or retiring Prairie Creek Units 1 and 3 by December 31, 2025. 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 Minnesota, 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 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) MISO Transmission Owner Return on Equity Complaints - A group of stakeholders, including MISO cooperative and municipal utilities, previously filed complaints with FERC requesting a reduction to the base return on equity authorized for MISO transmission owners, including ITC and ATC. In 2019, FERC issued an order on the previously filed complaints and reduced the base return on equity authorized for the MISO transmission owners to 9.88% for November 12, 2013 through February 11, 2015, and subsequent to September 28, 2016. In 2020, FERC issued orders in response to various rehearing requests and increased the base return on equity authorized for the MISO transmission owners from 9.88% to 10.02% for November 12, 2013 through February 11, 2015, and subsequent to September 28, 2016. In 2022, the U.S. Court of Appeals for the District of Columbia vacated FERC’s prior orders that established the base return on equity authorized
for the MISO transmission owners and remanded the cases to FERC for further proceedings. As a result of the 2022 court decision, Alliant Energy recorded a $6 million reduction in “Equity income from unconsolidated investments” in its income statement in 2022 to reflect the then-anticipated reduction in the base return on equity authorized for the MISO transmission owners. In October 2024, FERC issued an order reducing the base return on equity authorized for MISO transmission owners to 9.98%, and as a result, the MISO transmission owners will provide refunds based on the 9.98% base return on equity, with interest, for November 12, 2013 through February 11, 2015, and subsequent to September 28, 2016, which did not result in any material impacts on Alliant Energy’s results of operations or financial condition in 2024. Any further changes in FERC’s decisions may have an impact on Alliant Energy’s share of ATC’s future earnings and customer costs; however, Alliant Energy is currently unable to predict with certainty the future outcome or impact of any further changes.
WPL [Member]  
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, and improvements at WPL’s natural gas-fired Neenah Energy Facility and Sheboygan Falls Energy Facility. At December 31, 2024, Alliant Energy’s, IPL’s, and WPL’s minimum future commitments in 2025 for these projects were $448 million, $294 million, and $153 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, 2024, the related minimum future commitments, excluding amounts for purchased power commitments that do not have minimum thresholds but will require payment when electricity is generated by the provider, were as follows (in millions):
Alliant Energy20252026202720282029ThereafterTotal
Natural gas$268$177$130$102$84$120$881
Coal7533225——135
Other (a)512077222109
$394$230$159$114$86$142$1,125
IPL20252026202720282029ThereafterTotal
Natural gas$160$104$85$64$49$20$482
Coal3419105——68
Other (a)1822222147
$212$125$97$71$51$41$597
WPL20252026202720282029ThereafterTotal
Natural gas$108$73$45$38$35$100$399
Coal411412———67
Other (a)221————23
$171$88$57$38$35$100$489

(a)Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2024.
(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, 2024, the currently known partnership obligations for the abandonment obligations are estimated at $54 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, 2024 and 2023.

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 $43 million as of December 31, 2024 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, 2024 and 2023.

Transfers of Renewable Tax Credits - In 2023 and 2024, IPL and WPL 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, 2024, IPL and WPL provided indemnifications associated with $193 million and $121 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.
(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, 2024, 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 -$28$5 -$17$2 -$11
Current and non-current environmental liabilities$12$7$5

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 various requirements under the Consent Decree. IPL’s remaining requirements include fuel switching or retiring Prairie Creek Units 1 and 3 by December 31, 2025. 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 Minnesota, 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 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) MISO Transmission Owner Return on Equity Complaints - A group of stakeholders, including MISO cooperative and municipal utilities, previously filed complaints with FERC requesting a reduction to the base return on equity authorized for MISO transmission owners, including ITC and ATC. In 2019, FERC issued an order on the previously filed complaints and reduced the base return on equity authorized for the MISO transmission owners to 9.88% for November 12, 2013 through February 11, 2015, and subsequent to September 28, 2016. In 2020, FERC issued orders in response to various rehearing requests and increased the base return on equity authorized for the MISO transmission owners from 9.88% to 10.02% for November 12, 2013 through February 11, 2015, and subsequent to September 28, 2016. In 2022, the U.S. Court of Appeals for the District of Columbia vacated FERC’s prior orders that established the base return on equity authorized
for the MISO transmission owners and remanded the cases to FERC for further proceedings. As a result of the 2022 court decision, Alliant Energy recorded a $6 million reduction in “Equity income from unconsolidated investments” in its income statement in 2022 to reflect the then-anticipated reduction in the base return on equity authorized for the MISO transmission owners. In October 2024, FERC issued an order reducing the base return on equity authorized for MISO transmission owners to 9.98%, and as a result, the MISO transmission owners will provide refunds based on the 9.98% base return on equity, with interest, for November 12, 2013 through February 11, 2015, and subsequent to September 28, 2016, which did not result in any material impacts on Alliant Energy’s results of operations or financial condition in 2024. Any further changes in FERC’s decisions may have an impact on Alliant Energy’s share of ATC’s future earnings and customer costs; however, Alliant Energy is currently unable to predict with certainty the future outcome or impact of any further changes.
v3.25.0.1
Segments Of Business
 12 Months Ended
Dec. 31, 2024
Segment Reporting Information [Line Items]  
Segments Of Business SEGMENTS OF BUSINESS
Alliant Energy - Alliant Energy’s reportable segments as of December 31, 2024 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 Financial Accounting Standards Board’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
2024IPLWPLSegmentsOtherConsolidated
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 Generation Station60 — 60 N/A60
Other operation and maintenance expense358 279 637 39676
Other segment items:
Depreciation and amortization expense404 357 761 11772
Interest expense177165342107449
Equity income from unconsolidated investments, net— (2)(2)(59)(61)
Income tax expense (benefit)(129)11(118)4(114)
Other (a)5 3439 544
Net income (loss)362345707(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 (a)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
Utility
TotalAlliant
ReportableEnergy
2022IPLWPLSegmentsOtherConsolidated
Electric utility revenues$1,859 $1,562 $3,421 N/A$3,421
Gas utility revenues351 291 642 N/A642
Other revenues46 3 49 $93142
Total revenues2,256 1,856 4,112 934,205
Electric production fuel and purchased power expense383 447 830 N/A830
Electric transmission service expense407 166 573 N/A573
Cost of gas sold expense206 183 389 N/A389
Other operation and maintenance expense369 278 647 57704
Other segment items:
Depreciation and amortization expense381 283 664 7671
Interest expense148 121 269 56325
Equity income from unconsolidated investments, net— (1)(1)(50)(51)
Income tax expense (benefit)(50)66 16 622
Other (a)52 (2)50 656
Net income360 315 675 11686
Total assets10,075 8,987 19,062 1,10120,163
Investments in equity method subsidiaries5 15 20 522542
Construction and acquisition expenditures372 1,020 1,392 921,484

(a)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 reportable segments as of December 31, 2024 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 Financial Accounting Standards Board’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
2024IPLWPLSegmentsOtherConsolidated
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 Generation Station60 — 60 N/A60
Other operation and maintenance expense358 279 637 39676
Other segment items:
Depreciation and amortization expense404 357 761 11772
Interest expense177165342107449
Equity income from unconsolidated investments, net— (2)(2)(59)(61)
Income tax expense (benefit)(129)11(118)4(114)
Other (a)5 3439 544
Net income (loss)362345707(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 (a)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
Utility
TotalAlliant
ReportableEnergy
2022IPLWPLSegmentsOtherConsolidated
Electric utility revenues$1,859 $1,562 $3,421 N/A$3,421
Gas utility revenues351 291 642 N/A642
Other revenues46 3 49 $93142
Total revenues2,256 1,856 4,112 934,205
Electric production fuel and purchased power expense383 447 830 N/A830
Electric transmission service expense407 166 573 N/A573
Cost of gas sold expense206 183 389 N/A389
Other operation and maintenance expense369 278 647 57704
Other segment items:
Depreciation and amortization expense381 283 664 7671
Interest expense148 121 269 56325
Equity income from unconsolidated investments, net— (1)(1)(50)(51)
Income tax expense (benefit)(50)66 16 622
Other (a)52 (2)50 656
Net income360 315 675 11686
Total assets10,075 8,987 19,062 1,10120,163
Investments in equity method subsidiaries5 15 20 522542
Construction and acquisition expenditures372 1,020 1,392 921,484

(a)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 reportable segments as of December 31, 2024 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 Financial Accounting Standards Board’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
2024IPLWPLSegmentsOtherConsolidated
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 Generation Station60 — 60 N/A60
Other operation and maintenance expense358 279 637 39676
Other segment items:
Depreciation and amortization expense404 357 761 11772
Interest expense177165342107449
Equity income from unconsolidated investments, net— (2)(2)(59)(61)
Income tax expense (benefit)(129)11(118)4(114)
Other (a)5 3439 544
Net income (loss)362345707(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 (a)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
Utility
TotalAlliant
ReportableEnergy
2022IPLWPLSegmentsOtherConsolidated
Electric utility revenues$1,859 $1,562 $3,421 N/A$3,421
Gas utility revenues351 291 642 N/A642
Other revenues46 3 49 $93142
Total revenues2,256 1,856 4,112 934,205
Electric production fuel and purchased power expense383 447 830 N/A830
Electric transmission service expense407 166 573 N/A573
Cost of gas sold expense206 183 389 N/A389
Other operation and maintenance expense369 278 647 57704
Other segment items:
Depreciation and amortization expense381 283 664 7671
Interest expense148 121 269 56325
Equity income from unconsolidated investments, net— (1)(1)(50)(51)
Income tax expense (benefit)(50)66 16 622
Other (a)52 (2)50 656
Net income360 315 675 11686
Total assets10,075 8,987 19,062 1,10120,163
Investments in equity method subsidiaries5 15 20 522542
Construction and acquisition expenditures372 1,020 1,392 921,484

(a)Other segment items for each reportable segment include AFUDC, taxes other than income taxes, interest income, and other miscellaneous income and deductions.
v3.25.0.1
Related Parties
 12 Months Ended
Dec. 31, 2024
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
202420232022202420232022
Corporate Services billings$183$181$181$171$163$155
Sales credited—1119845574
Purchases billed4304314355435174

As of December 31, net intercompany payables to Corporate Services were as follows (in millions):
20242023
IPL$135$129
WPL6472

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):
202420232022
ATC billings to WPL$152$159$140
WPL billings to ATC162018

As of December 31, 2024 and 2023, 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
202420232022202420232022
Corporate Services billings$183$181$181$171$163$155
Sales credited—1119845574
Purchases billed4304314355435174

As of December 31, net intercompany payables to Corporate Services were as follows (in millions):
20242023
IPL$135$129
WPL6472
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
202420232022202420232022
Corporate Services billings$183$181$181$171$163$155
Sales credited—1119845574
Purchases billed4304314355435174

As of December 31, net intercompany payables to Corporate Services were as follows (in millions):
20242023
IPL$135$129
WPL6472

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):
202420232022
ATC billings to WPL$152$159$140
WPL billings to ATC162018

As of December 31, 2024 and 2023, 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.
v3.25.0.1
Condensed Parent Company Financial Statements
 12 Months Ended
Dec. 31, 2024
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 INCOME202420232022
(in millions)
Operating expenses$3 $3 $9 
Operating loss(3)(3)(9)
Other (income) and deductions:
Equity earnings from consolidated subsidiaries(734)(742)(707)
Interest expense40 34 6 
Other5 4 1 
Total other (income) and deductions(689)(704)(700)
Income before income taxes686 701 691 
Income tax expense (benefit)(3)(5)2 
Net income$689 $706 $689 
Refer to accompanying Notes to Condensed Financial Statements.

ALLIANT ENERGY CORPORATION (Parent Company Only)December 31,
CONDENSED BALANCE SHEETS20242023
(in millions)
ASSETS
Current assets:
Notes receivable from affiliated companies$103 $96 
Income tax refunds receivable12 — 
Other2 1 
Total current assets117 97 
Investments:
Investments in consolidated subsidiaries9,123 8,405 
Other1 2 
Total investments9,124 8,407 
Other assets84 90 
Total assets$9,325 $8,594 
LIABILITIES AND EQUITY
Current liabilities:
Current maturities of long-term debt$571 $— 
Commercial paper325 157 
Notes payable to affiliated companies1,401 1,068 
Other10 10 
Total current liabilities2,307 1,235 
Long-term debt, net (excluding current portion)— 568 
Other liabilities3 2 
Common equity:
Common stock and additional paid-in capital3,063 3,033 
Retained earnings3,965 3,768 
Accumulated other comprehensive income1 1 
Shares in deferred compensation trust(14)(13)
Total common equity7,015 6,789 
Total liabilities and equity$9,325 $8,594 
Refer to accompanying Notes to Condensed Financial Statements.
ALLIANT ENERGY CORPORATION (Parent Company Only)Year Ended December 31,
CONDENSED STATEMENTS OF CASH FLOWS202420232022
(in millions)
Net cash flows from operating activities$355 $445 $492 
Cash flows used for investing activities:
Capital contributions to consolidated subsidiaries(380)(325)(530)
Net change in notes receivable from and payable to affiliates326 (281)369 
Net cash flows used for investing activities(54)(606)(161)
Cash flows from (used for) financing activities:
Common stock dividends(492)(456)(428)
Proceeds from issuance of common stock, net23 246 25 
Proceeds from issuance of long-term debt— 565 — 
Net change in commercial paper168 (195)73 
Other— 1 (1)
Net cash flows from (used for) financing activities(301)161 (331)
Net increase (decrease) in cash, cash equivalents and restricted cash— — — 
Cash, cash equivalents and restricted cash at beginning of period— — — 
Cash, cash equivalents and restricted cash at end of period$— $— $— 
Supplemental cash flows information:
Cash (paid) received during the period for:
Interest($40)($27)($6)
Income taxes, net$8 $22 $15 
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 2024 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.
v3.25.0.1
Valuation and Qualifying Accounts And Reserves
 12 Months Ended
Dec. 31, 2024
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]  
Valuation and Qualifying Accounts And Reserves
SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES
Additions
Balance,(Charged toBalance,
DescriptionJanuary 1Expense)Deductions (a)December 31
(in millions)
Valuation and Qualifying Accounts Which are Deducted in the Balance Sheet from the Assets to Which They Apply:
Accumulated Provision for Uncollectible Accounts:
Alliant Energy (b)
Year ended December 31, 2024$8$24$24$8
Year ended December 31, 2023720198
Year ended December 31, 20221117217
IPL (b)
Year ended December 31, 2024$—$13$13$—
Year ended December 31, 2023—1111—
Year ended December 31, 2022178—
WPL
Year ended December 31, 2024$8$11$11$8
Year ended December 31, 20237988
Year ended December 31, 20221010137
Note: The above provisions relate to various customer, notes and other receivable balances included in various line items on the respective balance sheets.
(a)Deductions are of the nature for which the reserves were created. In the case of the accumulated provision for uncollectible accounts, deductions from this reserve are reduced by recoveries of amounts previously written off.
(b)Refer to Note 5(b) for discussion of IPL’s sales of accounts receivable program.
IPL [Member]  
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]  
Valuation and Qualifying Accounts And Reserves
SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES
Additions
Balance,(Charged toBalance,
DescriptionJanuary 1Expense)Deductions (a)December 31
(in millions)
Valuation and Qualifying Accounts Which are Deducted in the Balance Sheet from the Assets to Which They Apply:
Accumulated Provision for Uncollectible Accounts:
Alliant Energy (b)
Year ended December 31, 2024$8$24$24$8
Year ended December 31, 2023720198
Year ended December 31, 20221117217
IPL (b)
Year ended December 31, 2024$—$13$13$—
Year ended December 31, 2023—1111—
Year ended December 31, 2022178—
WPL
Year ended December 31, 2024$8$11$11$8
Year ended December 31, 20237988
Year ended December 31, 20221010137
Note: The above provisions relate to various customer, notes and other receivable balances included in various line items on the respective balance sheets.
(a)Deductions are of the nature for which the reserves were created. In the case of the accumulated provision for uncollectible accounts, deductions from this reserve are reduced by recoveries of amounts previously written off.
(b)Refer to Note 5(b) for discussion of IPL’s sales of accounts receivable program.
WPL [Member]  
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]  
Valuation and Qualifying Accounts And Reserves
SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES
Additions
Balance,(Charged toBalance,
DescriptionJanuary 1Expense)Deductions (a)December 31
(in millions)
Valuation and Qualifying Accounts Which are Deducted in the Balance Sheet from the Assets to Which They Apply:
Accumulated Provision for Uncollectible Accounts:
Alliant Energy (b)
Year ended December 31, 2024$8$24$24$8
Year ended December 31, 2023720198
Year ended December 31, 20221117217
IPL (b)
Year ended December 31, 2024$—$13$13$—
Year ended December 31, 2023—1111—
Year ended December 31, 2022178—
WPL
Year ended December 31, 2024$8$11$11$8
Year ended December 31, 20237988
Year ended December 31, 20221010137
Note: The above provisions relate to various customer, notes and other receivable balances included in various line items on the respective balance sheets.
(a)Deductions are of the nature for which the reserves were created. In the case of the accumulated provision for uncollectible accounts, deductions from this reserve are reduced by recoveries of amounts previously written off.
(b)Refer to Note 5(b) for discussion of IPL’s sales of accounts receivable program.
v3.25.0.1
Pay vs Performance Disclosure - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Pay vs Performance Disclosure      
Net income $ 690 $ 703 $ 686
v3.25.0.1
Insider Trading Arrangements
 3 Months Ended
Dec. 31, 2024
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
v3.25.0.1
Cybersecurity Risk Management and Strategy Disclosure
 12 Months Ended
Dec. 31, 2024
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 certain Center for Internet Security critical security controls. 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.
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 CFO. 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
v3.25.0.1
Summary Of Significant Accounting Policies (Policy)
 12 Months Ended
Dec. 31, 2024
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 various state regulatory commissions. 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).
The Inflation Reduction Act of 2022 provides the ability to transfer renewable tax credits to other corporate taxpayers. In 2023 and 2024, IPL and WPL 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. For renewable tax credits subject to future transfer, a valuation allowance is recorded for the difference between the tax value of the credits and the expected sales price. Renewable tax credits and any related valuation allowances 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 revenue deficiency in future years. At WPL, pursuant to escrow treatment approved by the PSCW, the difference between actual solar and energy storage 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, 2024, Alliant Energy’s, IPL’s and WPL’s cash and cash equivalents included $52 million, $9 million, and $43 million, respectively, of money market fund investments, with weighted average interest rates of 4%. At December 31, 2024 and 2023, 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
202420232022202420232022
Electric - generation3.3%3.3%3.4%3.4%3.0%3.4%
Electric - distribution2.8%2.8%2.8%2.7%2.7%2.5%
Electric - other5.2%5.6%5.7%6.1%6.3%6.8%
Gas3.3%3.3%3.3%2.5%2.5%2.4%
Other4.6%6.2%6.1%4.4%4.6%4.9%

In October 2024, the IUC issued an order approving the implementation of updated depreciation rates for IPL effective October 1, 2024. IPL estimates the new average rates of depreciation for its electric generation and electric distribution properties will be approximately 3.8% and 3.0%, respectively, during 2025.
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:
202420232022
IPL7.0%7.0%7.0%
WPL (retail jurisdiction)7.4%7.4%7.0%
WPL (wholesale jurisdiction)7.1%7.1%6.2%

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.
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, 2024, 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 primarily 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 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.
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.

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 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 related to leased land for solar generation are accounted for as operating leases for rate-making purposes. All other finance lease assets are depreciated on a straight-line basis over the shorter of the useful life of the underlying asset or the lease term.
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 various state regulatory commissions. 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).
The Inflation Reduction Act of 2022 provides the ability to transfer renewable tax credits to other corporate taxpayers. In 2023 and 2024, IPL and WPL 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. For renewable tax credits subject to future transfer, a valuation allowance is recorded for the difference between the tax value of the credits and the expected sales price. Renewable tax credits and any related valuation allowances 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 revenue deficiency in future years. At WPL, pursuant to escrow treatment approved by the PSCW, the difference between actual solar and energy storage 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, 2024, Alliant Energy’s, IPL’s and WPL’s cash and cash equivalents included $52 million, $9 million, and $43 million, respectively, of money market fund investments, with weighted average interest rates of 4%. At December 31, 2024 and 2023, 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
202420232022202420232022
Electric - generation3.3%3.3%3.4%3.4%3.0%3.4%
Electric - distribution2.8%2.8%2.8%2.7%2.7%2.5%
Electric - other5.2%5.6%5.7%6.1%6.3%6.8%
Gas3.3%3.3%3.3%2.5%2.5%2.4%
Other4.6%6.2%6.1%4.4%4.6%4.9%

In October 2024, the IUC issued an order approving the implementation of updated depreciation rates for IPL effective October 1, 2024. IPL estimates the new average rates of depreciation for its electric generation and electric distribution properties will be approximately 3.8% and 3.0%, respectively, during 2025.
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:
202420232022
IPL7.0%7.0%7.0%
WPL (retail jurisdiction)7.4%7.4%7.0%
WPL (wholesale jurisdiction)7.1%7.1%6.2%

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.
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, 2024, 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 primarily 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 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.
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.

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 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 related to leased land for solar generation are accounted for as operating leases for rate-making purposes. All other finance lease assets are depreciated on a straight-line basis over the shorter of the useful life of the underlying asset or the lease term.
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 various state regulatory commissions. 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).
The Inflation Reduction Act of 2022 provides the ability to transfer renewable tax credits to other corporate taxpayers. In 2023 and 2024, IPL and WPL 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. For renewable tax credits subject to future transfer, a valuation allowance is recorded for the difference between the tax value of the credits and the expected sales price. Renewable tax credits and any related valuation allowances 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 revenue deficiency in future years. At WPL, pursuant to escrow treatment approved by the PSCW, the difference between actual solar and energy storage 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, 2024, Alliant Energy’s, IPL’s and WPL’s cash and cash equivalents included $52 million, $9 million, and $43 million, respectively, of money market fund investments, with weighted average interest rates of 4%. At December 31, 2024 and 2023, 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
202420232022202420232022
Electric - generation3.3%3.3%3.4%3.4%3.0%3.4%
Electric - distribution2.8%2.8%2.8%2.7%2.7%2.5%
Electric - other5.2%5.6%5.7%6.1%6.3%6.8%
Gas3.3%3.3%3.3%2.5%2.5%2.4%
Other4.6%6.2%6.1%4.4%4.6%4.9%

In October 2024, the IUC issued an order approving the implementation of updated depreciation rates for IPL effective October 1, 2024. IPL estimates the new average rates of depreciation for its electric generation and electric distribution properties will be approximately 3.8% and 3.0%, respectively, during 2025.
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:
202420232022
IPL7.0%7.0%7.0%
WPL (retail jurisdiction)7.4%7.4%7.0%
WPL (wholesale jurisdiction)7.1%7.1%6.2%

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.
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, 2024, 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 primarily 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 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.
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.

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 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 related to leased land for solar generation are accounted for as operating leases for rate-making purposes. All other finance lease assets are depreciated on a straight-line basis over the shorter of the useful life of the underlying asset or the lease term.
v3.25.0.1
Summary Of Significant Accounting Policies (Tables)
 12 Months Ended
Dec. 31, 2024
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
202420232022202420232022
Electric - generation3.3%3.3%3.4%3.4%3.0%3.4%
Electric - distribution2.8%2.8%2.8%2.7%2.7%2.5%
Electric - other5.2%5.6%5.7%6.1%6.3%6.8%
Gas3.3%3.3%3.3%2.5%2.5%2.4%
Other4.6%6.2%6.1%4.4%4.6%4.9%
Schedule of Allowance for Funds Used During Construction Rate The AFUDC rates, computed in accordance with the prescribed regulatory formula, were as follows:
202420232022
IPL7.0%7.0%7.0%
WPL (retail jurisdiction)7.4%7.4%7.0%
WPL (wholesale jurisdiction)7.1%7.1%6.2%
IPL [Member]  
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
202420232022202420232022
Electric - generation3.3%3.3%3.4%3.4%3.0%3.4%
Electric - distribution2.8%2.8%2.8%2.7%2.7%2.5%
Electric - other5.2%5.6%5.7%6.1%6.3%6.8%
Gas3.3%3.3%3.3%2.5%2.5%2.4%
Other4.6%6.2%6.1%4.4%4.6%4.9%
Schedule of Allowance for Funds Used During Construction Rate The AFUDC rates, computed in accordance with the prescribed regulatory formula, were as follows:
202420232022
IPL7.0%7.0%7.0%
WPL (retail jurisdiction)7.4%7.4%7.0%
WPL (wholesale jurisdiction)7.1%7.1%6.2%
WPL [Member]  
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
202420232022202420232022
Electric - generation3.3%3.3%3.4%3.4%3.0%3.4%
Electric - distribution2.8%2.8%2.8%2.7%2.7%2.5%
Electric - other5.2%5.6%5.7%6.1%6.3%6.8%
Gas3.3%3.3%3.3%2.5%2.5%2.4%
Other4.6%6.2%6.1%4.4%4.6%4.9%
Schedule of Allowance for Funds Used During Construction Rate The AFUDC rates, computed in accordance with the prescribed regulatory formula, were as follows:
202420232022
IPL7.0%7.0%7.0%
WPL (retail jurisdiction)7.4%7.4%7.0%
WPL (wholesale jurisdiction)7.1%7.1%6.2%
v3.25.0.1
Regulatory Matters (Tables)
 12 Months Ended
Dec. 31, 2024
Regulatory Assets [Line Items]  
Schedule of Regulatory Assets At December 31, regulatory assets were comprised of the following items (in millions):
Alliant EnergyIPLWPL
202420232024202320242023
Tax-related$989 $934 $870 $831 $119 $103 
AROs401 194 281 160 120 34 
Pension and OPEB costs315 347 157 171 158 176 
Assets retired early180 273 168 259 12 14 
Commodity cost recovery68 120 2 12 66 108 
Derivatives60 102 15 34 45 68 
Non-service pension and OPEB costs51 46 19 18 32 28 
WPL’s Western Wisconsin gas distribution expansion investments42 44 — — 42 44 
IPL’s DAEC PPA amendment18 42 18 42 — — 
Other150 159 56 50 94 109 
$2,274 $2,261 $1,586 $1,577 $688 $684 
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, 2024
RecoveryRegulatory Approval
IPLLansing2023$131Return of (IUC and FERC) and return on (FERC) remaining net book value through 2037 (a)IUC and FERC (b)
IPLAnalog electric meters201915Return of remaining net book value through 2028IUC and FERC
IPLSutherland Units 1 and 3201715Return of and return on remaining net book value through 2027 (a)IUC and FERC
IPLM.L. Kapp Unit 220187Return of and return on remaining net book value through 2029 (a)IUC and FERC
WPLEdgewater Unit 4201812Return 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 Generation 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
202420232024202320242023
Tax-related$582$566$286$299$296$267
Cost of removal obligations347366205242142124
Derivatives536529342431
Commodity cost recovery17481213535
Other298514561529
$1,028$1,130$546$644$482$486
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
202420232024202320242023
Tax-related$989 $934 $870 $831 $119 $103 
AROs401 194 281 160 120 34 
Pension and OPEB costs315 347 157 171 158 176 
Assets retired early180 273 168 259 12 14 
Commodity cost recovery68 120 2 12 66 108 
Derivatives60 102 15 34 45 68 
Non-service pension and OPEB costs51 46 19 18 32 28 
WPL’s Western Wisconsin gas distribution expansion investments42 44 — — 42 44 
IPL’s DAEC PPA amendment18 42 18 42 — — 
Other150 159 56 50 94 109 
$2,274 $2,261 $1,586 $1,577 $688 $684 
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, 2024
RecoveryRegulatory Approval
IPLLansing2023$131Return of (IUC and FERC) and return on (FERC) remaining net book value through 2037 (a)IUC and FERC (b)
IPLAnalog electric meters201915Return of remaining net book value through 2028IUC and FERC
IPLSutherland Units 1 and 3201715Return of and return on remaining net book value through 2027 (a)IUC and FERC
IPLM.L. Kapp Unit 220187Return of and return on remaining net book value through 2029 (a)IUC and FERC
WPLEdgewater Unit 4201812Return 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 Generation 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
202420232024202320242023
Tax-related$582$566$286$299$296$267
Cost of removal obligations347366205242142124
Derivatives536529342431
Commodity cost recovery17481213535
Other298514561529
$1,028$1,130$546$644$482$486
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
202420232024202320242023
Tax-related$989 $934 $870 $831 $119 $103 
AROs401 194 281 160 120 34 
Pension and OPEB costs315 347 157 171 158 176 
Assets retired early180 273 168 259 12 14 
Commodity cost recovery68 120 2 12 66 108 
Derivatives60 102 15 34 45 68 
Non-service pension and OPEB costs51 46 19 18 32 28 
WPL’s Western Wisconsin gas distribution expansion investments42 44 — — 42 44 
IPL’s DAEC PPA amendment18 42 18 42 — — 
Other150 159 56 50 94 109 
$2,274 $2,261 $1,586 $1,577 $688 $684 
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, 2024
RecoveryRegulatory Approval
IPLLansing2023$131Return of (IUC and FERC) and return on (FERC) remaining net book value through 2037 (a)IUC and FERC (b)
IPLAnalog electric meters201915Return of remaining net book value through 2028IUC and FERC
IPLSutherland Units 1 and 3201715Return of and return on remaining net book value through 2027 (a)IUC and FERC
IPLM.L. Kapp Unit 220187Return of and return on remaining net book value through 2029 (a)IUC and FERC
WPLEdgewater Unit 4201812Return 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 Generation 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
202420232024202320242023
Tax-related$582$566$286$299$296$267
Cost of removal obligations347366205242142124
Derivatives536529342431
Commodity cost recovery17481213535
Other298514561529
$1,028$1,130$546$644$482$486
v3.25.0.1
Property, Plant and Equipment (Tables)
 12 Months Ended
Dec. 31, 2024
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
202420232024202320242023
Utility:
Electric plant:
Generation in service (a)(b)$11,156 $9,180 $5,924 $5,025 $5,232 $4,155 
Distribution in service7,811 7,314 4,344 4,091 3,467 3,223 
Other in service595 567 385 356 210 211 
Anticipated to be retired early (c)784 1,629 — — 784 1,629 
Total electric plant20,346 18,690 10,653 9,472 9,693 9,218 
Gas plant in service1,863 1,791 981951 882 840 
Other plant in service (d)734 653 456411 278 242 
Accumulated depreciation (c)(6,229)(5,924)(3,360)(3,180)(2,869)(2,744)
Net plant16,714 15,210 8,730 7,654 7,984 7,556 
Leased Sheboygan Falls Energy Facility, net (e)— — — — 74 79 
Leased land for solar generation, net189 172 53 33 136 139 
Construction work in progress1,215 1,245 548605 667 640 
Other, net5 7 5 6 — 1 
Total utility18,123 16,634 9,336 8,298 8,861 8,415 
Non-utility and other:
Non-utility Generation, net (f)103 68 — — — — 
Corporate Services and other, net (g)475455 — — — — 
Total non-utility and other578 523 — — — — 
Total property, plant and equipment$18,701 $17,157 $9,336 $8,298 $8,861 $8,415 

(a)Alliant Energy and WPL currently expect construction costs associated with WPL’s approximately 1,100 MW of new solar generation will exceed 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. Alliant Energy and WPL concluded that there was not a probable disallowance of the higher rate base amounts as of December 31, 2024 given construction costs were reasonably and prudently incurred.
(b)In September 2024, the IUC approved IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period, which allows IPL to recover construction costs associated with its 400 MW of new solar generation, including AFUDC and transmission upgrade costs among other costs, above the original cost target of $1,650/kilowatt up to $1,837.5/kilowatt. The costs up to the original cost target of $1,650/kilowatt will earn a return on common equity of 10.25%. The costs between $1,650/kilowatt and $1,837.5/kilowatt will earn a return on common equity that is the same as other assets without advance rate-making principles, without having to establish that such costs were reasonably and prudently incurred. Alliant Energy and IPL currently do not expect these construction costs will exceed $1,837.5/kilowatt.
(c)WPL previously received approval from MISO to retire the coal-fired Columbia Units 1 and 2, and Edgewater Unit 5. WPL currently plans to cease coal operations at Columbia Units 1 and 2 by the end of 2029, as well as evaluate the conversion of Columbia Unit 1 and/or Unit 2 to natural gas. Alliant Energy and WPL concluded that Columbia Units 1 and 2 met the criteria to be considered probable of abandonment as of December 31, 2024. As of December 31, 2024 and 2023, the net book value of Columbia Units 1 and 2 in aggregate was $413 million and $428 million, respectively. As of December 31, 2023, WPL anticipated retiring Edgewater Unit 5 by June 1, 2025, and Alliant Energy and WPL concluded that Edgewater Unit 5 met the criteria to be considered probable of abandonment. In May 2024, WPL announced updated plans to convert Edgewater Unit 5 to natural gas by 2028, subject to regulatory approvals. As a result, as of December 31, 2024, Alliant Energy and WPL concluded that Edgewater Unit 5 no longer meets the criteria to be considered probable of abandonment. WPL is currently allowed a full recovery of and a full return on these EGUs from both its retail and wholesale customers, and as a result, as of December 31, 2024, Alliant Energy and WPL concluded that no disallowance was probable.
(d)Includes IPL’s steam service assets, which are fully depreciated as of December 31, 2024. IPL’s steam customers are each under contract through 2025 for taking minimum quantities of annual steam usage, with certain conditions.
(e)Less accumulated amortization of $116 million and $112 million for WPL as of December 31, 2024 and 2023, respectively. Refer to Note 9 for discussion of WPL’s renewal of this lease in 2024. 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.
(f)Less accumulated depreciation of $78 million and $75 million for Alliant Energy as of December 31, 2024 and 2023, respectively.
(g)Less accumulated depreciation of $289 million and $275 million for Alliant Energy as of December 31, 2024 and 2023, respectively.
Allowance For Funds Used During Construction The amount of AFUDC generated by equity and debt components was as follows (in millions):
Alliant EnergyIPLWPL
202420232022202420232022202420232022
Equity$54$74$44$31$15$8$23$59$36
Debt212616126392013
$75$100$60$43$21$11$32$79$49
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
202420232024202320242023
Utility:
Electric plant:
Generation in service (a)(b)$11,156 $9,180 $5,924 $5,025 $5,232 $4,155 
Distribution in service7,811 7,314 4,344 4,091 3,467 3,223 
Other in service595 567 385 356 210 211 
Anticipated to be retired early (c)784 1,629 — — 784 1,629 
Total electric plant20,346 18,690 10,653 9,472 9,693 9,218 
Gas plant in service1,863 1,791 981951 882 840 
Other plant in service (d)734 653 456411 278 242 
Accumulated depreciation (c)(6,229)(5,924)(3,360)(3,180)(2,869)(2,744)
Net plant16,714 15,210 8,730 7,654 7,984 7,556 
Leased Sheboygan Falls Energy Facility, net (e)— — — — 74 79 
Leased land for solar generation, net189 172 53 33 136 139 
Construction work in progress1,215 1,245 548605 667 640 
Other, net5 7 5 6 — 1 
Total utility18,123 16,634 9,336 8,298 8,861 8,415 
Non-utility and other:
Non-utility Generation, net (f)103 68 — — — — 
Corporate Services and other, net (g)475455 — — — — 
Total non-utility and other578 523 — — — — 
Total property, plant and equipment$18,701 $17,157 $9,336 $8,298 $8,861 $8,415 

(a)Alliant Energy and WPL currently expect construction costs associated with WPL’s approximately 1,100 MW of new solar generation will exceed 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. Alliant Energy and WPL concluded that there was not a probable disallowance of the higher rate base amounts as of December 31, 2024 given construction costs were reasonably and prudently incurred.
(b)In September 2024, the IUC approved IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period, which allows IPL to recover construction costs associated with its 400 MW of new solar generation, including AFUDC and transmission upgrade costs among other costs, above the original cost target of $1,650/kilowatt up to $1,837.5/kilowatt. The costs up to the original cost target of $1,650/kilowatt will earn a return on common equity of 10.25%. The costs between $1,650/kilowatt and $1,837.5/kilowatt will earn a return on common equity that is the same as other assets without advance rate-making principles, without having to establish that such costs were reasonably and prudently incurred. Alliant Energy and IPL currently do not expect these construction costs will exceed $1,837.5/kilowatt.
(c)WPL previously received approval from MISO to retire the coal-fired Columbia Units 1 and 2, and Edgewater Unit 5. WPL currently plans to cease coal operations at Columbia Units 1 and 2 by the end of 2029, as well as evaluate the conversion of Columbia Unit 1 and/or Unit 2 to natural gas. Alliant Energy and WPL concluded that Columbia Units 1 and 2 met the criteria to be considered probable of abandonment as of December 31, 2024. As of December 31, 2024 and 2023, the net book value of Columbia Units 1 and 2 in aggregate was $413 million and $428 million, respectively. As of December 31, 2023, WPL anticipated retiring Edgewater Unit 5 by June 1, 2025, and Alliant Energy and WPL concluded that Edgewater Unit 5 met the criteria to be considered probable of abandonment. In May 2024, WPL announced updated plans to convert Edgewater Unit 5 to natural gas by 2028, subject to regulatory approvals. As a result, as of December 31, 2024, Alliant Energy and WPL concluded that Edgewater Unit 5 no longer meets the criteria to be considered probable of abandonment. WPL is currently allowed a full recovery of and a full return on these EGUs from both its retail and wholesale customers, and as a result, as of December 31, 2024, Alliant Energy and WPL concluded that no disallowance was probable.
(d)Includes IPL’s steam service assets, which are fully depreciated as of December 31, 2024. IPL’s steam customers are each under contract through 2025 for taking minimum quantities of annual steam usage, with certain conditions.
(e)Less accumulated amortization of $116 million and $112 million for WPL as of December 31, 2024 and 2023, respectively. Refer to Note 9 for discussion of WPL’s renewal of this lease in 2024. 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.
(f)Less accumulated depreciation of $78 million and $75 million for Alliant Energy as of December 31, 2024 and 2023, respectively.
(g)Less accumulated depreciation of $289 million and $275 million for Alliant Energy as of December 31, 2024 and 2023, respectively.
Allowance For Funds Used During Construction The amount of AFUDC generated by equity and debt components was as follows (in millions):
Alliant EnergyIPLWPL
202420232022202420232022202420232022
Equity$54$74$44$31$15$8$23$59$36
Debt212616126392013
$75$100$60$43$21$11$32$79$49
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
202420232024202320242023
Utility:
Electric plant:
Generation in service (a)(b)$11,156 $9,180 $5,924 $5,025 $5,232 $4,155 
Distribution in service7,811 7,314 4,344 4,091 3,467 3,223 
Other in service595 567 385 356 210 211 
Anticipated to be retired early (c)784 1,629 — — 784 1,629 
Total electric plant20,346 18,690 10,653 9,472 9,693 9,218 
Gas plant in service1,863 1,791 981951 882 840 
Other plant in service (d)734 653 456411 278 242 
Accumulated depreciation (c)(6,229)(5,924)(3,360)(3,180)(2,869)(2,744)
Net plant16,714 15,210 8,730 7,654 7,984 7,556 
Leased Sheboygan Falls Energy Facility, net (e)— — — — 74 79 
Leased land for solar generation, net189 172 53 33 136 139 
Construction work in progress1,215 1,245 548605 667 640 
Other, net5 7 5 6 — 1 
Total utility18,123 16,634 9,336 8,298 8,861 8,415 
Non-utility and other:
Non-utility Generation, net (f)103 68 — — — — 
Corporate Services and other, net (g)475455 — — — — 
Total non-utility and other578 523 — — — — 
Total property, plant and equipment$18,701 $17,157 $9,336 $8,298 $8,861 $8,415 

(a)Alliant Energy and WPL currently expect construction costs associated with WPL’s approximately 1,100 MW of new solar generation will exceed 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. Alliant Energy and WPL concluded that there was not a probable disallowance of the higher rate base amounts as of December 31, 2024 given construction costs were reasonably and prudently incurred.
(b)In September 2024, the IUC approved IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period, which allows IPL to recover construction costs associated with its 400 MW of new solar generation, including AFUDC and transmission upgrade costs among other costs, above the original cost target of $1,650/kilowatt up to $1,837.5/kilowatt. The costs up to the original cost target of $1,650/kilowatt will earn a return on common equity of 10.25%. The costs between $1,650/kilowatt and $1,837.5/kilowatt will earn a return on common equity that is the same as other assets without advance rate-making principles, without having to establish that such costs were reasonably and prudently incurred. Alliant Energy and IPL currently do not expect these construction costs will exceed $1,837.5/kilowatt.
(c)WPL previously received approval from MISO to retire the coal-fired Columbia Units 1 and 2, and Edgewater Unit 5. WPL currently plans to cease coal operations at Columbia Units 1 and 2 by the end of 2029, as well as evaluate the conversion of Columbia Unit 1 and/or Unit 2 to natural gas. Alliant Energy and WPL concluded that Columbia Units 1 and 2 met the criteria to be considered probable of abandonment as of December 31, 2024. As of December 31, 2024 and 2023, the net book value of Columbia Units 1 and 2 in aggregate was $413 million and $428 million, respectively. As of December 31, 2023, WPL anticipated retiring Edgewater Unit 5 by June 1, 2025, and Alliant Energy and WPL concluded that Edgewater Unit 5 met the criteria to be considered probable of abandonment. In May 2024, WPL announced updated plans to convert Edgewater Unit 5 to natural gas by 2028, subject to regulatory approvals. As a result, as of December 31, 2024, Alliant Energy and WPL concluded that Edgewater Unit 5 no longer meets the criteria to be considered probable of abandonment. WPL is currently allowed a full recovery of and a full return on these EGUs from both its retail and wholesale customers, and as a result, as of December 31, 2024, Alliant Energy and WPL concluded that no disallowance was probable.
(d)Includes IPL’s steam service assets, which are fully depreciated as of December 31, 2024. IPL’s steam customers are each under contract through 2025 for taking minimum quantities of annual steam usage, with certain conditions.
(e)Less accumulated amortization of $116 million and $112 million for WPL as of December 31, 2024 and 2023, respectively. Refer to Note 9 for discussion of WPL’s renewal of this lease in 2024. 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.
(f)Less accumulated depreciation of $78 million and $75 million for Alliant Energy as of December 31, 2024 and 2023, respectively.
(g)Less accumulated depreciation of $289 million and $275 million for Alliant Energy as of December 31, 2024 and 2023, respectively.
Allowance For Funds Used During Construction The amount of AFUDC generated by equity and debt components was as follows (in millions):
Alliant EnergyIPLWPL
202420232022202420232022202420232022
Equity$54$74$44$31$15$8$23$59$36
Debt212616126392013
$75$100$60$43$21$11$32$79$49
v3.25.0.1
Jointly-Owned Electric Utility Plant (Tables)
 12 Months Ended
Dec. 31, 2024
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, 2024 was as follows (dollars in millions):
OwnershipElectricAccumulated ProvisionConstruction
Interest %Plantfor DepreciationWork in Progress
IPL
Ottumwa Unit 148.0%$648$277$7
George Neal Unit 425.7%1971107
George Neal Unit 328.0%1818920
Louisa Unit 14.0%4323—
1,06949934
WPL
Columbia Units 1-2 and Energy Storage System53.5%8593786
West Riverside Energy Center and Solar Facility (a)56.6%449595
Forward Wind Energy Center42.6%11956—
1,42749311
Alliant Energy$2,496$992$45

(a)In 2023 and 2024, WEC Energy Group, Inc. and Madison Gas and Electric Company acquired partial ownership interests in West Riverside. The related proceeds are included in “Proceeds from sales of partial ownership interests in West Riverside” in investing activities in Alliant Energy’s and WPL’s cash flows statements in 2023 and 2024.
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, 2024 was as follows (dollars in millions):
OwnershipElectricAccumulated ProvisionConstruction
Interest %Plantfor DepreciationWork in Progress
IPL
Ottumwa Unit 148.0%$648$277$7
George Neal Unit 425.7%1971107
George Neal Unit 328.0%1818920
Louisa Unit 14.0%4323—
1,06949934
WPL
Columbia Units 1-2 and Energy Storage System53.5%8593786
West Riverside Energy Center and Solar Facility (a)56.6%449595
Forward Wind Energy Center42.6%11956—
1,42749311
Alliant Energy$2,496$992$45

(a)In 2023 and 2024, WEC Energy Group, Inc. and Madison Gas and Electric Company acquired partial ownership interests in West Riverside. The related proceeds are included in “Proceeds from sales of partial ownership interests in West Riverside” in investing activities in Alliant Energy’s and WPL’s cash flows statements in 2023 and 2024.
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, 2024 was as follows (dollars in millions):
OwnershipElectricAccumulated ProvisionConstruction
Interest %Plantfor DepreciationWork in Progress
IPL
Ottumwa Unit 148.0%$648$277$7
George Neal Unit 425.7%1971107
George Neal Unit 328.0%1818920
Louisa Unit 14.0%4323—
1,06949934
WPL
Columbia Units 1-2 and Energy Storage System53.5%8593786
West Riverside Energy Center and Solar Facility (a)56.6%449595
Forward Wind Energy Center42.6%11956—
1,42749311
Alliant Energy$2,496$992$45

(a)In 2023 and 2024, WEC Energy Group, Inc. and Madison Gas and Electric Company acquired partial ownership interests in West Riverside. The related proceeds are included in “Proceeds from sales of partial ownership interests in West Riverside” in investing activities in Alliant Energy’s and WPL’s cash flows statements in 2023 and 2024.
v3.25.0.1
Receivables (Tables)
 12 Months Ended
Dec. 31, 2024
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
202420232024202320242023
Customer$113 $121 $— $— $98 $110 
Unbilled utility revenues101 93 — — 101 93 
Deferred proceeds163 216 163 216 — — 
Other58 53 29 26 29 24 
Allowance for expected credit losses(8)(8)— — (8)(8)
$427 $475 $192 $242 $220 $219 
Gross Write-offs for Accounts Receivable
In 2024, gross write-offs for accounts receivable were as follows (in millions):
Originated in 2023
Originated in 2024
Alliant Energy$12$14
IPL89
WPL45
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
202420232022202420232022
Outstanding aggregate cash proceeds$110$110$80$31$51$14
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):
20242023
Customer accounts receivable$137$130
Unbilled utility revenues10898
Other receivables—1
Receivables sold to third party245229
Less: cash proceeds701
Deferred proceeds175228
Less: allowance for expected credit losses1212
Fair value of deferred proceeds$163$216
Outstanding receivables past due$21$22
Additional Attributes Of Receivables Sold Under The Agreement
Additional attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions):
202420232022
Collections$2,090$2,233$2,302 
Write-offs, net of recoveries12129 
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
202420232024202320242023
Customer$113 $121 $— $— $98 $110 
Unbilled utility revenues101 93 — — 101 93 
Deferred proceeds163 216 163 216 — — 
Other58 53 29 26 29 24 
Allowance for expected credit losses(8)(8)— — (8)(8)
$427 $475 $192 $242 $220 $219 
Gross Write-offs for Accounts Receivable
In 2024, gross write-offs for accounts receivable were as follows (in millions):
Originated in 2023
Originated in 2024
Alliant Energy$12$14
IPL89
WPL45
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
202420232022202420232022
Outstanding aggregate cash proceeds$110$110$80$31$51$14
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):
20242023
Customer accounts receivable$137$130
Unbilled utility revenues10898
Other receivables—1
Receivables sold to third party245229
Less: cash proceeds701
Deferred proceeds175228
Less: allowance for expected credit losses1212
Fair value of deferred proceeds$163$216
Outstanding receivables past due$21$22
Additional Attributes Of Receivables Sold Under The Agreement
Additional attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions):
202420232022
Collections$2,090$2,233$2,302 
Write-offs, net of recoveries12129 
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
202420232024202320242023
Customer$113 $121 $— $— $98 $110 
Unbilled utility revenues101 93 — — 101 93 
Deferred proceeds163 216 163 216 — — 
Other58 53 29 26 29 24 
Allowance for expected credit losses(8)(8)— — (8)(8)
$427 $475 $192 $242 $220 $219 
Gross Write-offs for Accounts Receivable
In 2024, gross write-offs for accounts receivable were as follows (in millions):
Originated in 2023
Originated in 2024
Alliant Energy$12$14
IPL89
WPL45
v3.25.0.1
Investments (Tables)
 12 Months Ended
Dec. 31, 2024
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, 202420242023202420232022
ATC Holdings
16%, 20%
$415$386($57)($49)($41)
Non-utility wind farm in Oklahoma50%107104(6)(7)(5)
Corporate venture investmentsVarious78743(2)(3)
OtherVarious2321(1)(3)(2)
$623$585($61)($61)($51)
Summary Financial Information
Summary aggregate financial information from the financial statements of these holdings is as follows (in millions):
Alliant Energy
202420232022
Revenues$1,005$898$813
Operating income433384350
Net income434370675
As of December 31:
Current assets223221
Non-current assets9,9309,032
Current liabilities524528
Non-current liabilities3,9333,584
Noncontrolling interest221259
v3.25.0.1
Common Equity (Tables)
 12 Months Ended
Dec. 31, 2024
Schedule of Common Equity [Line Items]  
Common Stock Activity A summary of Alliant Energy’s common stock activity was as follows:
202420232022
Shares outstanding, January 1256,096,848 251,134,966 250,474,529 
At-the-market offering program— 4,372,561 — 
Shareowner Direct Plan439,107 454,987 437,669 
Equity-based compensation plans154,267 134,334 222,768 
Shares outstanding, December 31256,690,222 256,096,848 251,134,966 
v3.25.0.1
Debt (Tables)
 12 Months Ended
Dec. 31, 2024
Debt Instrument [Line Items]  
Schedule of Other Short-term Borrowings Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper classified as short-term debt was as follows (dollars in millions):
Alliant EnergyIPLWPL
December 31202420232024202320242023
Amount outstanding$558$475$50$—$183$318
Weighted average interest rates4.5%5.5%4.6%N/A4.5%5.4%
Available credit facility capacity$742$525$250$150$217$82
Alliant EnergyIPLWPL
For the year ended202420232024202320242023
Maximum amount outstanding (based on daily outstanding balances)$632$793$80$70$390$349
Average amount outstanding (based on daily outstanding balances)$327$386$1$2$70$157
Weighted average interest rates5.3%5.2%5.1%5.3%5.4%5.1%
Schedule of Long-term Debt Long-term debt, net as of December 31 was as follows (dollars in millions):
20242023
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Senior Debentures (a):
3.4%, due 2025
$250 $250 $— $250 $250 $— 
5.5%, due 2025
50 50 — 50 50 — 
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 (b)
350 350 — — — — 
6.3%, due 2034
125 125 — 125 125 — 
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 (b)
300 300 — — — — 
3.25% (Retired in 2024)
— — — 500 500 — 
4,125 4,125 — 3,975 3,975 — 
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 (c)
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 
3,400 — 3,400 3,100 — 3,100 
Other:
AEF term loan credit agreement through March 2025, 6% at December 31, 2024 (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)(f)
375 — — — — — 
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 — — 
AEF term loan credit agreement, 6% at December 31, 2023 (with Alliant Energy as guarantor) (Retired in 2024) (d)
— — — 300 — — 
Sheboygan Power, LLC 5.06% senior secured notes (secured by the Sheboygan Falls Energy Facility and related assets) (Retired in 2024)
— — — 9 — — 
2,400 — — 2,034 — — 
Subtotal9,925 4,125 3,400 9,109 3,975 3,100 
Current maturities(1,171)(300)— (809)(500)— 
Unamortized debt issuance costs(55)(25)(20)(54)(21)(19)
Unamortized debt (discount) and premium, net(22)(10)(10)(21)(9)(11)
Long-term debt, net (g)$8,677 $3,790 $3,370 $8,225 $3,445 $3,070 

(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 September 2024, IPL issued $350 million of 4.95% senior debentures due 2034 and $300 million of 5.45% senior debentures due 2054. A portion of the net proceeds was used for the retirement of IPL’s $500 million 3.25% senior debentures, and the remainder of the net proceeds was used for general corporate purposes.
(c)In March 2024, WPL issued $300 million of 5.375% debentures due 2034. The debentures were issued as green bonds, and an amount equal to or in excess of the net proceeds was disbursed for the development and acquisition of WPL’s solar EGUs.
(d)In March 2024, 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 2024, and retired the $300 million variable rate term loan set forth therein. 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.
(e)Refer to “Convertible Senior Notes” below for additional information.
(f)In June 2024, AEF issued $375 million of 5.4% senior notes due 2027. The net proceeds were used to reduce Alliant Energy’s outstanding commercial paper and for general corporate purposes.
(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, 2024, long-term debt maturities for 2025 through 2029 were as follows (in millions):
20252026202720282029
IPL$300$—$—$500$300
WPL——300—350
AEF300200375300300
Alliant Energy parent company—575———
Alliant Energy$600$775$675$800$950
IPL [Member]  
Debt Instrument [Line Items]  
Schedule of Other Short-term Borrowings Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper classified as short-term debt was as follows (dollars in millions):
Alliant EnergyIPLWPL
December 31202420232024202320242023
Amount outstanding$558$475$50$—$183$318
Weighted average interest rates4.5%5.5%4.6%N/A4.5%5.4%
Available credit facility capacity$742$525$250$150$217$82
Alliant EnergyIPLWPL
For the year ended202420232024202320242023
Maximum amount outstanding (based on daily outstanding balances)$632$793$80$70$390$349
Average amount outstanding (based on daily outstanding balances)$327$386$1$2$70$157
Weighted average interest rates5.3%5.2%5.1%5.3%5.4%5.1%
Schedule of Long-term Debt Long-term debt, net as of December 31 was as follows (dollars in millions):
20242023
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Senior Debentures (a):
3.4%, due 2025
$250 $250 $— $250 $250 $— 
5.5%, due 2025
50 50 — 50 50 — 
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 (b)
350 350 — — — — 
6.3%, due 2034
125 125 — 125 125 — 
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 (b)
300 300 — — — — 
3.25% (Retired in 2024)
— — — 500 500 — 
4,125 4,125 — 3,975 3,975 — 
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 (c)
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 
3,400 — 3,400 3,100 — 3,100 
Other:
AEF term loan credit agreement through March 2025, 6% at December 31, 2024 (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)(f)
375 — — — — — 
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 — — 
AEF term loan credit agreement, 6% at December 31, 2023 (with Alliant Energy as guarantor) (Retired in 2024) (d)
— — — 300 — — 
Sheboygan Power, LLC 5.06% senior secured notes (secured by the Sheboygan Falls Energy Facility and related assets) (Retired in 2024)
— — — 9 — — 
2,400 — — 2,034 — — 
Subtotal9,925 4,125 3,400 9,109 3,975 3,100 
Current maturities(1,171)(300)— (809)(500)— 
Unamortized debt issuance costs(55)(25)(20)(54)(21)(19)
Unamortized debt (discount) and premium, net(22)(10)(10)(21)(9)(11)
Long-term debt, net (g)$8,677 $3,790 $3,370 $8,225 $3,445 $3,070 

(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 September 2024, IPL issued $350 million of 4.95% senior debentures due 2034 and $300 million of 5.45% senior debentures due 2054. A portion of the net proceeds was used for the retirement of IPL’s $500 million 3.25% senior debentures, and the remainder of the net proceeds was used for general corporate purposes.
(c)In March 2024, WPL issued $300 million of 5.375% debentures due 2034. The debentures were issued as green bonds, and an amount equal to or in excess of the net proceeds was disbursed for the development and acquisition of WPL’s solar EGUs.
(d)In March 2024, 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 2024, and retired the $300 million variable rate term loan set forth therein. 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.
(e)Refer to “Convertible Senior Notes” below for additional information.
(f)In June 2024, AEF issued $375 million of 5.4% senior notes due 2027. The net proceeds were used to reduce Alliant Energy’s outstanding commercial paper and for general corporate purposes.
(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, 2024, long-term debt maturities for 2025 through 2029 were as follows (in millions):
20252026202720282029
IPL$300$—$—$500$300
WPL——300—350
AEF300200375300300
Alliant Energy parent company—575———
Alliant Energy$600$775$675$800$950
WPL [Member]  
Debt Instrument [Line Items]  
Schedule of Other Short-term Borrowings Information regarding Alliant Energy’s, IPL’s and WPL’s commercial paper classified as short-term debt was as follows (dollars in millions):
Alliant EnergyIPLWPL
December 31202420232024202320242023
Amount outstanding$558$475$50$—$183$318
Weighted average interest rates4.5%5.5%4.6%N/A4.5%5.4%
Available credit facility capacity$742$525$250$150$217$82
Alliant EnergyIPLWPL
For the year ended202420232024202320242023
Maximum amount outstanding (based on daily outstanding balances)$632$793$80$70$390$349
Average amount outstanding (based on daily outstanding balances)$327$386$1$2$70$157
Weighted average interest rates5.3%5.2%5.1%5.3%5.4%5.1%
Schedule of Long-term Debt Long-term debt, net as of December 31 was as follows (dollars in millions):
20242023
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Senior Debentures (a):
3.4%, due 2025
$250 $250 $— $250 $250 $— 
5.5%, due 2025
50 50 — 50 50 — 
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 (b)
350 350 — — — — 
6.3%, due 2034
125 125 — 125 125 — 
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 (b)
300 300 — — — — 
3.25% (Retired in 2024)
— — — 500 500 — 
4,125 4,125 — 3,975 3,975 — 
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 (c)
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 
3,400 — 3,400 3,100 — 3,100 
Other:
AEF term loan credit agreement through March 2025, 6% at December 31, 2024 (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)(f)
375 — — — — — 
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 — — 
AEF term loan credit agreement, 6% at December 31, 2023 (with Alliant Energy as guarantor) (Retired in 2024) (d)
— — — 300 — — 
Sheboygan Power, LLC 5.06% senior secured notes (secured by the Sheboygan Falls Energy Facility and related assets) (Retired in 2024)
— — — 9 — — 
2,400 — — 2,034 — — 
Subtotal9,925 4,125 3,400 9,109 3,975 3,100 
Current maturities(1,171)(300)— (809)(500)— 
Unamortized debt issuance costs(55)(25)(20)(54)(21)(19)
Unamortized debt (discount) and premium, net(22)(10)(10)(21)(9)(11)
Long-term debt, net (g)$8,677 $3,790 $3,370 $8,225 $3,445 $3,070 

(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 September 2024, IPL issued $350 million of 4.95% senior debentures due 2034 and $300 million of 5.45% senior debentures due 2054. A portion of the net proceeds was used for the retirement of IPL’s $500 million 3.25% senior debentures, and the remainder of the net proceeds was used for general corporate purposes.
(c)In March 2024, WPL issued $300 million of 5.375% debentures due 2034. The debentures were issued as green bonds, and an amount equal to or in excess of the net proceeds was disbursed for the development and acquisition of WPL’s solar EGUs.
(d)In March 2024, 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 2024, and retired the $300 million variable rate term loan set forth therein. 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.
(e)Refer to “Convertible Senior Notes” below for additional information.
(f)In June 2024, AEF issued $375 million of 5.4% senior notes due 2027. The net proceeds were used to reduce Alliant Energy’s outstanding commercial paper and for general corporate purposes.
(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, 2024, long-term debt maturities for 2025 through 2029 were as follows (in millions):
20252026202720282029
IPL$300$—$—$500$300
WPL——300—350
AEF300200375300300
Alliant Energy parent company—575———
Alliant Energy$600$775$675$800$950
v3.25.0.1
Leases (Tables)
 12 Months Ended
Dec. 31, 2024
Leases [Line Items]  
Schedule of Lease Details Operating lease details are as follows (dollars in millions):
December 31, 2024December 31, 2023
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net$22$12$9$23$13$9
Other current liabilities$2$1$1$2$1$1
Other liabilities2011821128
Total operating lease liabilities$22$12$9$23$13$9
Weighted average remaining lease term11 years11 years12 years12 years12 years12 years
Weighted average discount rate4%4%4%4%4%4%
Finance lease details are as follows (dollars in millions):
December 31, 2024December 31, 2023
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net:
Sheboygan Falls Energy FacilityN/AN/A$74N/AN/A$79
Leased land for solar generation$189$53136$172$33139
$189$53$210$172$33$218
Other current liabilities:
Sheboygan Falls Energy FacilityN/AN/A$7N/AN/A$11
Leased land for solar generation$—$——$—$——
——7——11
Other liabilities:
Sheboygan Falls Energy FacilityN/AN/A71N/AN/A78
Leased land for solar generation1895313617233139
1895320717233217
Total finance lease liabilities$189$53$214$172$33$228
Weighted average remaining lease term31 years28 years28 years33 years29 years27 years
Weighted average discount rate5%5%5%5%5%5%
Alliant EnergyIPLWPL
202420232022202420232022202420232022
Depreciation and amortization expenses$— $1 $— $— $— $— $4 $6 $6 
Interest expense8 6 3 2 1 — 10 8 7 
Total finance lease expense$8 $7 $3 $2 $1 $— $14 $14 $13 
Finance lease liabilities arising from obtaining leased assets, which represent non-cash financing activities, were as follows (in millions):
Alliant EnergyIPLWPL
202420232024202320242023
Finance lease liabilities arising from obtaining leased assets
$20 $34 $20 $33 $— $71 
Schedule of Operating Lease Liability Maturities As of December 31, 2024, expected maturities of lease liabilities were as follows (in millions):
20252026202720282029ThereafterTotalLess: amount representing interestPresent value of minimum lease payments
Operating Leases:
Alliant Energy$3 $3 $3 $3 $2 $14$28$6$22
IPL2 2 1 1 1 815312
WPL1 1 1 1 1 71239
Finance Leases:
Alliant Energy9 9 9 10 10 337384195189
IPL3 3 3 3 3 921075453
WPL17 13 13 13 13 324393179214
Schedule of Finance Lease Liability Maturities As of December 31, 2024, expected maturities of lease liabilities were as follows (in millions):
20252026202720282029ThereafterTotalLess: amount representing interestPresent value of minimum lease payments
Operating Leases:
Alliant Energy$3 $3 $3 $3 $2 $14$28$6$22
IPL2 2 1 1 1 815312
WPL1 1 1 1 1 71239
Finance Leases:
Alliant Energy9 9 9 10 10 337384195189
IPL3 3 3 3 3 921075453
WPL17 13 13 13 13 324393179214
IPL [Member]  
Leases [Line Items]  
Schedule of Lease Details Operating lease details are as follows (dollars in millions):
December 31, 2024December 31, 2023
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net$22$12$9$23$13$9
Other current liabilities$2$1$1$2$1$1
Other liabilities2011821128
Total operating lease liabilities$22$12$9$23$13$9
Weighted average remaining lease term11 years11 years12 years12 years12 years12 years
Weighted average discount rate4%4%4%4%4%4%
Finance lease details are as follows (dollars in millions):
December 31, 2024December 31, 2023
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net:
Sheboygan Falls Energy FacilityN/AN/A$74N/AN/A$79
Leased land for solar generation$189$53136$172$33139
$189$53$210$172$33$218
Other current liabilities:
Sheboygan Falls Energy FacilityN/AN/A$7N/AN/A$11
Leased land for solar generation$—$——$—$——
——7——11
Other liabilities:
Sheboygan Falls Energy FacilityN/AN/A71N/AN/A78
Leased land for solar generation1895313617233139
1895320717233217
Total finance lease liabilities$189$53$214$172$33$228
Weighted average remaining lease term31 years28 years28 years33 years29 years27 years
Weighted average discount rate5%5%5%5%5%5%
Alliant EnergyIPLWPL
202420232022202420232022202420232022
Depreciation and amortization expenses$— $1 $— $— $— $— $4 $6 $6 
Interest expense8 6 3 2 1 — 10 8 7 
Total finance lease expense$8 $7 $3 $2 $1 $— $14 $14 $13 
Finance lease liabilities arising from obtaining leased assets, which represent non-cash financing activities, were as follows (in millions):
Alliant EnergyIPLWPL
202420232024202320242023
Finance lease liabilities arising from obtaining leased assets
$20 $34 $20 $33 $— $71 
Schedule of Operating Lease Liability Maturities As of December 31, 2024, expected maturities of lease liabilities were as follows (in millions):
20252026202720282029ThereafterTotalLess: amount representing interestPresent value of minimum lease payments
Operating Leases:
Alliant Energy$3 $3 $3 $3 $2 $14$28$6$22
IPL2 2 1 1 1 815312
WPL1 1 1 1 1 71239
Finance Leases:
Alliant Energy9 9 9 10 10 337384195189
IPL3 3 3 3 3 921075453
WPL17 13 13 13 13 324393179214
Schedule of Finance Lease Liability Maturities As of December 31, 2024, expected maturities of lease liabilities were as follows (in millions):
20252026202720282029ThereafterTotalLess: amount representing interestPresent value of minimum lease payments
Operating Leases:
Alliant Energy$3 $3 $3 $3 $2 $14$28$6$22
IPL2 2 1 1 1 815312
WPL1 1 1 1 1 71239
Finance Leases:
Alliant Energy9 9 9 10 10 337384195189
IPL3 3 3 3 3 921075453
WPL17 13 13 13 13 324393179214
WPL [Member]  
Leases [Line Items]  
Schedule of Lease Details Operating lease details are as follows (dollars in millions):
December 31, 2024December 31, 2023
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net$22$12$9$23$13$9
Other current liabilities$2$1$1$2$1$1
Other liabilities2011821128
Total operating lease liabilities$22$12$9$23$13$9
Weighted average remaining lease term11 years11 years12 years12 years12 years12 years
Weighted average discount rate4%4%4%4%4%4%
Finance lease details are as follows (dollars in millions):
December 31, 2024December 31, 2023
Alliant EnergyIPLWPLAlliant EnergyIPLWPL
Property, plant and equipment, net:
Sheboygan Falls Energy FacilityN/AN/A$74N/AN/A$79
Leased land for solar generation$189$53136$172$33139
$189$53$210$172$33$218
Other current liabilities:
Sheboygan Falls Energy FacilityN/AN/A$7N/AN/A$11
Leased land for solar generation$—$——$—$——
——7——11
Other liabilities:
Sheboygan Falls Energy FacilityN/AN/A71N/AN/A78
Leased land for solar generation1895313617233139
1895320717233217
Total finance lease liabilities$189$53$214$172$33$228
Weighted average remaining lease term31 years28 years28 years33 years29 years27 years
Weighted average discount rate5%5%5%5%5%5%
Alliant EnergyIPLWPL
202420232022202420232022202420232022
Depreciation and amortization expenses$— $1 $— $— $— $— $4 $6 $6 
Interest expense8 6 3 2 1 — 10 8 7 
Total finance lease expense$8 $7 $3 $2 $1 $— $14 $14 $13 
Finance lease liabilities arising from obtaining leased assets, which represent non-cash financing activities, were as follows (in millions):
Alliant EnergyIPLWPL
202420232024202320242023
Finance lease liabilities arising from obtaining leased assets
$20 $34 $20 $33 $— $71 
Schedule of Operating Lease Liability Maturities As of December 31, 2024, expected maturities of lease liabilities were as follows (in millions):
20252026202720282029ThereafterTotalLess: amount representing interestPresent value of minimum lease payments
Operating Leases:
Alliant Energy$3 $3 $3 $3 $2 $14$28$6$22
IPL2 2 1 1 1 815312
WPL1 1 1 1 1 71239
Finance Leases:
Alliant Energy9 9 9 10 10 337384195189
IPL3 3 3 3 3 921075453
WPL17 13 13 13 13 324393179214
Schedule of Finance Lease Liability Maturities As of December 31, 2024, expected maturities of lease liabilities were as follows (in millions):
20252026202720282029ThereafterTotalLess: amount representing interestPresent value of minimum lease payments
Operating Leases:
Alliant Energy$3 $3 $3 $3 $2 $14$28$6$22
IPL2 2 1 1 1 815312
WPL1 1 1 1 1 71239
Finance Leases:
Alliant Energy9 9 9 10 10 337384195189
IPL3 3 3 3 3 921075453
WPL17 13 13 13 13 324393179214
v3.25.0.1
Revenues (Tables)
 12 Months Ended
Dec. 31, 2024
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
202420232022202420232022202420232022
Electric Utility:
Retail - residential$1,236 $1,220 $1,233 $640 $641 $673 $596 $579 $560 
Retail - commercial821 820 821 525 519 536 296 301 285 
Retail - industrial952 968 965 497 501 538 455 467 427 
Wholesale200 213 233 61 62 64 139 151 169 
Bulk power and other163 124 169 24 38 48 139 86 121 
Total Electric Utility3,372 3,345 3,421 1,747 1,761 1,859 1,625 1,584 1,562 
Gas Utility:
Retail - residential275 316 371 148 176 202 127 140 169 
Retail - commercial133 163 197 68 86 101 65 77 96 
Retail - industrial11 16 20 7 11 14 4 5 6 
Transportation/other46 45 54 27 27 34 19 18 20 
Total Gas Utility465 540 642 250 300 351 215 240 291 
Other Utility:
Steam40 45 39 40 45 39 — — — 
Other utility14 7 10 9 4 7 5 3 3 
Total Other Utility54 52 49 49 49 46 5 3 3 
Non-Utility and Other:
Travero and other90 90 93 — — — — — — 
Total Non-Utility and Other90 90 93 — — — — — — 
Total revenues$3,981 $4,027 $4,205 $2,046 $2,110 $2,256 $1,845 $1,827 $1,856 
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
202420232022202420232022202420232022
Electric Utility:
Retail - residential$1,236 $1,220 $1,233 $640 $641 $673 $596 $579 $560 
Retail - commercial821 820 821 525 519 536 296 301 285 
Retail - industrial952 968 965 497 501 538 455 467 427 
Wholesale200 213 233 61 62 64 139 151 169 
Bulk power and other163 124 169 24 38 48 139 86 121 
Total Electric Utility3,372 3,345 3,421 1,747 1,761 1,859 1,625 1,584 1,562 
Gas Utility:
Retail - residential275 316 371 148 176 202 127 140 169 
Retail - commercial133 163 197 68 86 101 65 77 96 
Retail - industrial11 16 20 7 11 14 4 5 6 
Transportation/other46 45 54 27 27 34 19 18 20 
Total Gas Utility465 540 642 250 300 351 215 240 291 
Other Utility:
Steam40 45 39 40 45 39 — — — 
Other utility14 7 10 9 4 7 5 3 3 
Total Other Utility54 52 49 49 49 46 5 3 3 
Non-Utility and Other:
Travero and other90 90 93 — — — — — — 
Total Non-Utility and Other90 90 93 — — — — — — 
Total revenues$3,981 $4,027 $4,205 $2,046 $2,110 $2,256 $1,845 $1,827 $1,856 
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
202420232022202420232022202420232022
Electric Utility:
Retail - residential$1,236 $1,220 $1,233 $640 $641 $673 $596 $579 $560 
Retail - commercial821 820 821 525 519 536 296 301 285 
Retail - industrial952 968 965 497 501 538 455 467 427 
Wholesale200 213 233 61 62 64 139 151 169 
Bulk power and other163 124 169 24 38 48 139 86 121 
Total Electric Utility3,372 3,345 3,421 1,747 1,761 1,859 1,625 1,584 1,562 
Gas Utility:
Retail - residential275 316 371 148 176 202 127 140 169 
Retail - commercial133 163 197 68 86 101 65 77 96 
Retail - industrial11 16 20 7 11 14 4 5 6 
Transportation/other46 45 54 27 27 34 19 18 20 
Total Gas Utility465 540 642 250 300 351 215 240 291 
Other Utility:
Steam40 45 39 40 45 39 — — — 
Other utility14 7 10 9 4 7 5 3 3 
Total Other Utility54 52 49 49 49 46 5 3 3 
Non-Utility and Other:
Travero and other90 90 93 — — — — — — 
Total Non-Utility and Other90 90 93 — — — — — — 
Total revenues$3,981 $4,027 $4,205 $2,046 $2,110 $2,256 $1,845 $1,827 $1,856 
v3.25.0.1
Income Taxes (Tables)
 12 Months Ended
Dec. 31, 2024
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
202420232022202420232022202420232022
Current tax expense (benefit):
Federal$13($3)$7($19)($44)($29)$37$48$46
State(10)(6)2(19)(21)(8)232516
Deferred tax expense (benefit):
Federal60100109388791241010
State153628(17)1717312
Production tax credits(177)(121)(123)(108)(95)(105)(69)(26)(18)
Investment tax credits(15)(1)(1)(4)(1)—(11)——
Provision recorded as a change in accrued interest—(1)——(1)————
($114)$4$22($129)($58)($50)$11$60$66
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 Generation Station discussed in Note 2.
Alliant EnergyIPLWPL
202420232022202420232022202420232022
Statutory federal income tax rate21%21%21%21%21%21%21%21%21%
State income taxes, net of federal benefits(1)23(12)(2)(2)656
Production tax credits(31)(17)(18)(46)(31)(34)(20)(7)(5)
Investment tax credits(3)——(2)——(3)——
Amortization of excess deferred taxes (Refer to Note 2)
(2)(2)(2)(5)(2)(2)—(2)(3)
Effect of rate-making on property-related differences(5)(4)(1)(10)(5)(1)(1)(3)(2)
Other items, net11—(1)—2—1—
Overall income tax rate(20%)1%3%(55%)(19%)(16%)3%15%17%
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
202420232024202320242023
Deferred tax liabilities:
Property$2,596 $2,453 $1,521 $1,415 $999 $972 
ATC Holdings135 127 — — — — 
Other178 213 120 157 66 64 
Total deferred tax liabilities2,909 2,793 1,641 1,572 1,065 1,036 
Deferred tax assets:
Federal credit carryforwards605 649 426 449 166 191 
Net operating losses carryforwards - state20 26 1 1 — — 
Other98 79 37 32 34 19 
Subtotal deferred tax assets723 754 464 482 200 210 
Valuation allowances(2)(3)(2)(1)— (1)
Total deferred tax assets721 751 462 481 200 209 
Total deferred tax liabilities, net$2,188 $2,042 $1,179 $1,091 $865 $827 
Summary Of Tax Credit Carryforwards At December 31, 2024, carryforwards and expiration dates were estimated as follows (in millions):
Range of Expiration DatesAlliant EnergyIPLWPL
State net operating losses2025-2044$338$7$1
Federal tax credits2033-2044605426166
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)2021-2023
Consolidated Iowa income tax returns (b)2021-2023
Wisconsin combined tax returns (c)2020-2023

(a)The 2021 and 2022 federal tax returns are 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
202420232022202420232022202420232022
Current tax expense (benefit):
Federal$13($3)$7($19)($44)($29)$37$48$46
State(10)(6)2(19)(21)(8)232516
Deferred tax expense (benefit):
Federal60100109388791241010
State153628(17)1717312
Production tax credits(177)(121)(123)(108)(95)(105)(69)(26)(18)
Investment tax credits(15)(1)(1)(4)(1)—(11)——
Provision recorded as a change in accrued interest—(1)——(1)————
($114)$4$22($129)($58)($50)$11$60$66
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 Generation Station discussed in Note 2.
Alliant EnergyIPLWPL
202420232022202420232022202420232022
Statutory federal income tax rate21%21%21%21%21%21%21%21%21%
State income taxes, net of federal benefits(1)23(12)(2)(2)656
Production tax credits(31)(17)(18)(46)(31)(34)(20)(7)(5)
Investment tax credits(3)——(2)——(3)——
Amortization of excess deferred taxes (Refer to Note 2)
(2)(2)(2)(5)(2)(2)—(2)(3)
Effect of rate-making on property-related differences(5)(4)(1)(10)(5)(1)(1)(3)(2)
Other items, net11—(1)—2—1—
Overall income tax rate(20%)1%3%(55%)(19%)(16%)3%15%17%
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
202420232024202320242023
Deferred tax liabilities:
Property$2,596 $2,453 $1,521 $1,415 $999 $972 
ATC Holdings135 127 — — — — 
Other178 213 120 157 66 64 
Total deferred tax liabilities2,909 2,793 1,641 1,572 1,065 1,036 
Deferred tax assets:
Federal credit carryforwards605 649 426 449 166 191 
Net operating losses carryforwards - state20 26 1 1 — — 
Other98 79 37 32 34 19 
Subtotal deferred tax assets723 754 464 482 200 210 
Valuation allowances(2)(3)(2)(1)— (1)
Total deferred tax assets721 751 462 481 200 209 
Total deferred tax liabilities, net$2,188 $2,042 $1,179 $1,091 $865 $827 
Summary Of Tax Credit Carryforwards At December 31, 2024, carryforwards and expiration dates were estimated as follows (in millions):
Range of Expiration DatesAlliant EnergyIPLWPL
State net operating losses2025-2044$338$7$1
Federal tax credits2033-2044605426166
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)2021-2023
Consolidated Iowa income tax returns (b)2021-2023
Wisconsin combined tax returns (c)2020-2023

(a)The 2021 and 2022 federal tax returns are 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
202420232022202420232022202420232022
Current tax expense (benefit):
Federal$13($3)$7($19)($44)($29)$37$48$46
State(10)(6)2(19)(21)(8)232516
Deferred tax expense (benefit):
Federal60100109388791241010
State153628(17)1717312
Production tax credits(177)(121)(123)(108)(95)(105)(69)(26)(18)
Investment tax credits(15)(1)(1)(4)(1)—(11)——
Provision recorded as a change in accrued interest—(1)——(1)————
($114)$4$22($129)($58)($50)$11$60$66
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 Generation Station discussed in Note 2.
Alliant EnergyIPLWPL
202420232022202420232022202420232022
Statutory federal income tax rate21%21%21%21%21%21%21%21%21%
State income taxes, net of federal benefits(1)23(12)(2)(2)656
Production tax credits(31)(17)(18)(46)(31)(34)(20)(7)(5)
Investment tax credits(3)——(2)——(3)——
Amortization of excess deferred taxes (Refer to Note 2)
(2)(2)(2)(5)(2)(2)—(2)(3)
Effect of rate-making on property-related differences(5)(4)(1)(10)(5)(1)(1)(3)(2)
Other items, net11—(1)—2—1—
Overall income tax rate(20%)1%3%(55%)(19%)(16%)3%15%17%
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
202420232024202320242023
Deferred tax liabilities:
Property$2,596 $2,453 $1,521 $1,415 $999 $972 
ATC Holdings135 127 — — — — 
Other178 213 120 157 66 64 
Total deferred tax liabilities2,909 2,793 1,641 1,572 1,065 1,036 
Deferred tax assets:
Federal credit carryforwards605 649 426 449 166 191 
Net operating losses carryforwards - state20 26 1 1 — — 
Other98 79 37 32 34 19 
Subtotal deferred tax assets723 754 464 482 200 210 
Valuation allowances(2)(3)(2)(1)— (1)
Total deferred tax assets721 751 462 481 200 209 
Total deferred tax liabilities, net$2,188 $2,042 $1,179 $1,091 $865 $827 
Summary Of Tax Credit Carryforwards At December 31, 2024, carryforwards and expiration dates were estimated as follows (in millions):
Range of Expiration DatesAlliant EnergyIPLWPL
State net operating losses2025-2044$338$7$1
Federal tax credits2033-2044605426166
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)2021-2023
Consolidated Iowa income tax returns (b)2021-2023
Wisconsin combined tax returns (c)2020-2023

(a)The 2021 and 2022 federal tax returns are 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.
v3.25.0.1
Benefit Plans (Tables)
 12 Months Ended
Dec. 31, 2024
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 Energy202420232022202420232022
Discount rate for benefit obligations5.65%5.36%5.54%5.62%5.40%5.53%
Discount rate for net periodic cost5.36%5.54%2.91%5.40%5.53%2.81%
Expected rate of return on plan assets7.73%7.80%7.80%6.22%6.50%6.40%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan6.24%10.75%9.22%N/AN/AN/A
Rate of compensation increase3.50%-4.50%3.30%-4.50%3.30%-4.50%N/AN/AN/A
Qualified Defined Benefit Pension PlanOPEB Plans
IPL202420232022202420232022
Discount rate for benefit obligations5.66%5.35%5.55%5.61%5.40%5.53%
Discount rate for net periodic cost5.35%5.55%2.94%5.40%5.53%2.80%
Expected rate of return on plan assets7.60%7.80%7.80%6.60%6.90%6.50%
Rate of compensation increase3.75%3.30%3.30%N/AN/AN/A
Qualified Defined Benefit Pension PlanOPEB Plans
WPL202420232022202420232022
Discount rate for benefit obligations5.66%5.35%5.54%5.61%5.40%5.53%
Discount rate for net periodic cost5.35%5.54%2.94%5.40%5.53%2.79%
Expected rate of return on plan assets7.80%7.80%7.80%5.61%5.65%5.49%
Rate of compensation increase3.50%3.30%3.30%N/AN/AN/A
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
202420232022202420232022
Service cost$5 $5 $9 $2 $2 $3 
Interest cost45 47 36 8 9 6 
Expected return on plan assets (a)(55)(53)(69)(5)(5)(5)
Amortization of prior service credit (b)(1)(1)(1)— — — 
Amortization of actuarial loss (c)24 28 32 — 1 2 
Settlement losses (d)— — 26 — — — 
$18 $26 $33 $5 $7 $6 
IPLDefined Benefit Pension PlansOPEB Plans
202420232022202420232022
Service cost$3 $3 $6 $1 $1 $1 
Interest cost20 21 16 3 3 2 
Expected return on plan assets (a)(26)(26)(31)(4)(3)(4)
Amortization of actuarial loss (c)9 11 13 — 1 1 
Settlement losses (d)— — 13 — — — 
$6 $9 $17 $— $2 $— 
WPLDefined Benefit Pension PlansOPEB Plans
202420232022202420232022
Service cost$2 $2 $3 $1 $1 $1 
Interest cost20 20 16 3 3 2 
Expected return on plan assets (a)(23)(22)(31)(1)(1)(1)
Amortization of actuarial loss (c)11 13 15 — 1 2 
Settlement losses (d)— — 13 — — — 
$10 $13 $16 $3 $4 $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.
(d)Settlement losses related to payments made to retired executives of Alliant Energy and lump sum payments related to IPL’s and WPL’s qualified defined benefit pension plans. In 2022, the majority of Alliant Energy’s, IPL’s, and WPL’s pension settlement losses were recognized as regulatory assets in accordance with regulatory treatment, and $7 million was included in “Other (income) and deductions” in Alliant Energy’s and IPL’s income statements related to IPL’s qualified defined benefit pension plan.
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 Energy2024202320242023
Change in benefit obligation:
Net benefit obligation at January 1$876 $875 $160 $168 
Service cost5 5 2 2 
Interest cost45 47 8 9 
Plan participants’ contributions— — 3 4 
Actuarial (gain) loss(19)23 (7)(3)
Gross benefits paid(66)(74)(18)(20)
Net benefit obligation at December 31841 876 148 160 
Change in plan assets:
Fair value of plan assets at January 1732 706 83 83 
Actual return on plan assets38 86 5 8 
Employer contributions11 14 7 8 
Plan participants’ contributions— — 3 4 
Gross benefits paid(66)(74)(18)(20)
Fair value of plan assets at December 31715 732 80 83 
Under funded status at December 31($126)($144)($68)($77)
Defined Benefit Pension PlansOPEB Plans
Alliant Energy2024202320242023
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $17 $14 
Current liabilities(3)(2)(7)(8)
Pension and other benefit obligations(123)(142)(78)(83)
Net amounts recognized at December 31($126)($144)($68)($77)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$312 $337 $4 $11 
Prior service credit(2)(2)— — 
$310 $335 $4 $11 
Defined Benefit Pension PlansOPEB Plans
IPL2024202320242023
Change in benefit obligation:
Net benefit obligation at January 1$387 $389 $65 $68 
Service cost3 3 1 1 
Interest cost20 21 3 3 
Plan participants’ contributions— — 1 2 
Actuarial (gain) loss(8)9 (3)(1)
Gross benefits paid(30)(35)(8)(8)
Net benefit obligation at December 31372 387 59 65 
Change in plan assets:
Fair value of plan assets at January 1352 344 61 58 
Actual return on plan assets18 42 4 7 
Employer contributions— 1 1 2 
Plan participants’ contributions— — 1 2 
Gross benefits paid(30)(35)(8)(8)
Fair value of plan assets at December 31340 352 59 61 
Under funded status at December 31($32)($35)$— ($4)
Defined Benefit Pension PlansOPEB Plans
IPL2024202320242023
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $13 $10 
Current liabilities(1)— (1)(1)
Pension and other benefit obligations(31)(35)(12)(13)
Net amounts recognized at December 31($32)($35)$— ($4)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$126 $135 $7 $9 
Prior service credit(1)(1)— — 
$125 $134 $7 $9 
Defined Benefit Pension PlansOPEB Plans
WPL2024202320242023
Change in benefit obligation:
Net benefit obligation at January 1$381 $381 $61 $65 
Service cost2 2 1 1 
Interest cost20 20 3 3 
Plan participants’ contributions— — 1 2 
Actuarial (gain) loss (8)10 (3)(2)
Gross benefits paid(30)(32)(7)(8)
Net benefit obligation at December 31365 381 56 61 
Change in plan assets:
Fair value of plan assets at January 1306 291 14 14 
Actual return on plan assets17 35 — 1 
Employer contributions10 12 5 5 
Plan participants’ contributions— — 1 2 
Gross benefits paid(30)(32)(7)(8)
Fair value of plan assets at December 31303 306 13 14 
Under funded status at December 31($62)($75)($43)($47)
Defined Benefit Pension PlansOPEB Plans
WPL2024202320242023
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $4 $4 
Current liabilities— — (6)(6)
Pension and other benefit obligations(62)(75)(41)(45)
Net amounts recognized at December 31($62)($75)($43)($47)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$135 $148 $— $3 
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 Energy2024202320242023
Accumulated benefit obligations$824 $857 $148 $160 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations824 857 148 160 
Fair value of plan assets715 732 80 83 
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations841 876 N/AN/A
Fair value of plan assets715 732 N/AN/A
Defined Benefit Pension PlansOPEB Plans
IPL2024202320242023
Accumulated benefit obligations$362 $377 $59 $65 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations362 377 N/A65 
Fair value of plan assets340 352 N/A61 
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations372 387 N/AN/A
Fair value of plan assets340 352 N/AN/A
Defined Benefit Pension PlansOPEB Plans
WPL2024202320242023
Accumulated benefit obligations$358 $373 $56 $61 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations358 373 56 61 
Fair value of plan assets303 306 13 14 
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations365 381 N/AN/A
Fair value of plan assets303 306 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
2024202320242023
Regulatory assets$25$28$22$24
Estimated Future Employer Contributions Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2025 is as follows (in millions):
Alliant EnergyIPLWPL
Defined benefit pension plans (a)$20$1$14
OPEB plans716

(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 Energy202520262027202820292030 - 2034
Defined benefit pension benefits$79 $75 $74 $74 $74 $329
OPEB16 16 15 15 14 62
$95 $91 $89 $89 $88 $391
IPL202520262027202820292030 - 2034
Defined benefit pension benefits$36 $34 $33 $33 $32 $148
OPEB7 6 6 6 6 24
$43 $40 $39 $39 $38 $172
WPL202520262027202820292030 - 2034
Defined benefit pension benefits$33 $31 $31 $31 $31 $144
OPEB7 6 6 5 5 23
$40 $37 $37 $36 $36 $167
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
202420232022202420232022202420232022
Compensation expense$12$12$13$6$6$7$5$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):
20242023
Carrying value$14$13
Fair market value2219
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 Energy202420232022202420232022
Discount rate for benefit obligations5.65%5.36%5.54%5.62%5.40%5.53%
Discount rate for net periodic cost5.36%5.54%2.91%5.40%5.53%2.81%
Expected rate of return on plan assets7.73%7.80%7.80%6.22%6.50%6.40%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan6.24%10.75%9.22%N/AN/AN/A
Rate of compensation increase3.50%-4.50%3.30%-4.50%3.30%-4.50%N/AN/AN/A
Qualified Defined Benefit Pension PlanOPEB Plans
IPL202420232022202420232022
Discount rate for benefit obligations5.66%5.35%5.55%5.61%5.40%5.53%
Discount rate for net periodic cost5.35%5.55%2.94%5.40%5.53%2.80%
Expected rate of return on plan assets7.60%7.80%7.80%6.60%6.90%6.50%
Rate of compensation increase3.75%3.30%3.30%N/AN/AN/A
Qualified Defined Benefit Pension PlanOPEB Plans
WPL202420232022202420232022
Discount rate for benefit obligations5.66%5.35%5.54%5.61%5.40%5.53%
Discount rate for net periodic cost5.35%5.54%2.94%5.40%5.53%2.79%
Expected rate of return on plan assets7.80%7.80%7.80%5.61%5.65%5.49%
Rate of compensation increase3.50%3.30%3.30%N/AN/AN/A
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
202420232022202420232022
Service cost$5 $5 $9 $2 $2 $3 
Interest cost45 47 36 8 9 6 
Expected return on plan assets (a)(55)(53)(69)(5)(5)(5)
Amortization of prior service credit (b)(1)(1)(1)— — — 
Amortization of actuarial loss (c)24 28 32 — 1 2 
Settlement losses (d)— — 26 — — — 
$18 $26 $33 $5 $7 $6 
IPLDefined Benefit Pension PlansOPEB Plans
202420232022202420232022
Service cost$3 $3 $6 $1 $1 $1 
Interest cost20 21 16 3 3 2 
Expected return on plan assets (a)(26)(26)(31)(4)(3)(4)
Amortization of actuarial loss (c)9 11 13 — 1 1 
Settlement losses (d)— — 13 — — — 
$6 $9 $17 $— $2 $— 
WPLDefined Benefit Pension PlansOPEB Plans
202420232022202420232022
Service cost$2 $2 $3 $1 $1 $1 
Interest cost20 20 16 3 3 2 
Expected return on plan assets (a)(23)(22)(31)(1)(1)(1)
Amortization of actuarial loss (c)11 13 15 — 1 2 
Settlement losses (d)— — 13 — — — 
$10 $13 $16 $3 $4 $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.
(d)Settlement losses related to payments made to retired executives of Alliant Energy and lump sum payments related to IPL’s and WPL’s qualified defined benefit pension plans. In 2022, the majority of Alliant Energy’s, IPL’s, and WPL’s pension settlement losses were recognized as regulatory assets in accordance with regulatory treatment, and $7 million was included in “Other (income) and deductions” in Alliant Energy’s and IPL’s income statements related to IPL’s qualified defined benefit pension plan.
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 Energy2024202320242023
Change in benefit obligation:
Net benefit obligation at January 1$876 $875 $160 $168 
Service cost5 5 2 2 
Interest cost45 47 8 9 
Plan participants’ contributions— — 3 4 
Actuarial (gain) loss(19)23 (7)(3)
Gross benefits paid(66)(74)(18)(20)
Net benefit obligation at December 31841 876 148 160 
Change in plan assets:
Fair value of plan assets at January 1732 706 83 83 
Actual return on plan assets38 86 5 8 
Employer contributions11 14 7 8 
Plan participants’ contributions— — 3 4 
Gross benefits paid(66)(74)(18)(20)
Fair value of plan assets at December 31715 732 80 83 
Under funded status at December 31($126)($144)($68)($77)
Defined Benefit Pension PlansOPEB Plans
Alliant Energy2024202320242023
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $17 $14 
Current liabilities(3)(2)(7)(8)
Pension and other benefit obligations(123)(142)(78)(83)
Net amounts recognized at December 31($126)($144)($68)($77)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$312 $337 $4 $11 
Prior service credit(2)(2)— — 
$310 $335 $4 $11 
Defined Benefit Pension PlansOPEB Plans
IPL2024202320242023
Change in benefit obligation:
Net benefit obligation at January 1$387 $389 $65 $68 
Service cost3 3 1 1 
Interest cost20 21 3 3 
Plan participants’ contributions— — 1 2 
Actuarial (gain) loss(8)9 (3)(1)
Gross benefits paid(30)(35)(8)(8)
Net benefit obligation at December 31372 387 59 65 
Change in plan assets:
Fair value of plan assets at January 1352 344 61 58 
Actual return on plan assets18 42 4 7 
Employer contributions— 1 1 2 
Plan participants’ contributions— — 1 2 
Gross benefits paid(30)(35)(8)(8)
Fair value of plan assets at December 31340 352 59 61 
Under funded status at December 31($32)($35)$— ($4)
Defined Benefit Pension PlansOPEB Plans
IPL2024202320242023
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $13 $10 
Current liabilities(1)— (1)(1)
Pension and other benefit obligations(31)(35)(12)(13)
Net amounts recognized at December 31($32)($35)$— ($4)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$126 $135 $7 $9 
Prior service credit(1)(1)— — 
$125 $134 $7 $9 
Defined Benefit Pension PlansOPEB Plans
WPL2024202320242023
Change in benefit obligation:
Net benefit obligation at January 1$381 $381 $61 $65 
Service cost2 2 1 1 
Interest cost20 20 3 3 
Plan participants’ contributions— — 1 2 
Actuarial (gain) loss (8)10 (3)(2)
Gross benefits paid(30)(32)(7)(8)
Net benefit obligation at December 31365 381 56 61 
Change in plan assets:
Fair value of plan assets at January 1306 291 14 14 
Actual return on plan assets17 35 — 1 
Employer contributions10 12 5 5 
Plan participants’ contributions— — 1 2 
Gross benefits paid(30)(32)(7)(8)
Fair value of plan assets at December 31303 306 13 14 
Under funded status at December 31($62)($75)($43)($47)
Defined Benefit Pension PlansOPEB Plans
WPL2024202320242023
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $4 $4 
Current liabilities— — (6)(6)
Pension and other benefit obligations(62)(75)(41)(45)
Net amounts recognized at December 31($62)($75)($43)($47)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$135 $148 $— $3 
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 Energy2024202320242023
Accumulated benefit obligations$824 $857 $148 $160 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations824 857 148 160 
Fair value of plan assets715 732 80 83 
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations841 876 N/AN/A
Fair value of plan assets715 732 N/AN/A
Defined Benefit Pension PlansOPEB Plans
IPL2024202320242023
Accumulated benefit obligations$362 $377 $59 $65 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations362 377 N/A65 
Fair value of plan assets340 352 N/A61 
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations372 387 N/AN/A
Fair value of plan assets340 352 N/AN/A
Defined Benefit Pension PlansOPEB Plans
WPL2024202320242023
Accumulated benefit obligations$358 $373 $56 $61 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations358 373 56 61 
Fair value of plan assets303 306 13 14 
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations365 381 N/AN/A
Fair value of plan assets303 306 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
2024202320242023
Regulatory assets$25$28$22$24
Estimated Future Employer Contributions Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2025 is as follows (in millions):
Alliant EnergyIPLWPL
Defined benefit pension plans (a)$20$1$14
OPEB plans716

(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 Energy202520262027202820292030 - 2034
Defined benefit pension benefits$79 $75 $74 $74 $74 $329
OPEB16 16 15 15 14 62
$95 $91 $89 $89 $88 $391
IPL202520262027202820292030 - 2034
Defined benefit pension benefits$36 $34 $33 $33 $32 $148
OPEB7 6 6 6 6 24
$43 $40 $39 $39 $38 $172
WPL202520262027202820292030 - 2034
Defined benefit pension benefits$33 $31 $31 $31 $31 $144
OPEB7 6 6 5 5 23
$40 $37 $37 $36 $36 $167
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
202420232022202420232022202420232022
Compensation expense$12$12$13$6$6$7$5$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 Energy202420232022202420232022
Discount rate for benefit obligations5.65%5.36%5.54%5.62%5.40%5.53%
Discount rate for net periodic cost5.36%5.54%2.91%5.40%5.53%2.81%
Expected rate of return on plan assets7.73%7.80%7.80%6.22%6.50%6.40%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan6.24%10.75%9.22%N/AN/AN/A
Rate of compensation increase3.50%-4.50%3.30%-4.50%3.30%-4.50%N/AN/AN/A
Qualified Defined Benefit Pension PlanOPEB Plans
IPL202420232022202420232022
Discount rate for benefit obligations5.66%5.35%5.55%5.61%5.40%5.53%
Discount rate for net periodic cost5.35%5.55%2.94%5.40%5.53%2.80%
Expected rate of return on plan assets7.60%7.80%7.80%6.60%6.90%6.50%
Rate of compensation increase3.75%3.30%3.30%N/AN/AN/A
Qualified Defined Benefit Pension PlanOPEB Plans
WPL202420232022202420232022
Discount rate for benefit obligations5.66%5.35%5.54%5.61%5.40%5.53%
Discount rate for net periodic cost5.35%5.54%2.94%5.40%5.53%2.79%
Expected rate of return on plan assets7.80%7.80%7.80%5.61%5.65%5.49%
Rate of compensation increase3.50%3.30%3.30%N/AN/AN/A
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
202420232022202420232022
Service cost$5 $5 $9 $2 $2 $3 
Interest cost45 47 36 8 9 6 
Expected return on plan assets (a)(55)(53)(69)(5)(5)(5)
Amortization of prior service credit (b)(1)(1)(1)— — — 
Amortization of actuarial loss (c)24 28 32 — 1 2 
Settlement losses (d)— — 26 — — — 
$18 $26 $33 $5 $7 $6 
IPLDefined Benefit Pension PlansOPEB Plans
202420232022202420232022
Service cost$3 $3 $6 $1 $1 $1 
Interest cost20 21 16 3 3 2 
Expected return on plan assets (a)(26)(26)(31)(4)(3)(4)
Amortization of actuarial loss (c)9 11 13 — 1 1 
Settlement losses (d)— — 13 — — — 
$6 $9 $17 $— $2 $— 
WPLDefined Benefit Pension PlansOPEB Plans
202420232022202420232022
Service cost$2 $2 $3 $1 $1 $1 
Interest cost20 20 16 3 3 2 
Expected return on plan assets (a)(23)(22)(31)(1)(1)(1)
Amortization of actuarial loss (c)11 13 15 — 1 2 
Settlement losses (d)— — 13 — — — 
$10 $13 $16 $3 $4 $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.
(d)Settlement losses related to payments made to retired executives of Alliant Energy and lump sum payments related to IPL’s and WPL’s qualified defined benefit pension plans. In 2022, the majority of Alliant Energy’s, IPL’s, and WPL’s pension settlement losses were recognized as regulatory assets in accordance with regulatory treatment, and $7 million was included in “Other (income) and deductions” in Alliant Energy’s and IPL’s income statements related to IPL’s qualified defined benefit pension plan.
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 Energy2024202320242023
Change in benefit obligation:
Net benefit obligation at January 1$876 $875 $160 $168 
Service cost5 5 2 2 
Interest cost45 47 8 9 
Plan participants’ contributions— — 3 4 
Actuarial (gain) loss(19)23 (7)(3)
Gross benefits paid(66)(74)(18)(20)
Net benefit obligation at December 31841 876 148 160 
Change in plan assets:
Fair value of plan assets at January 1732 706 83 83 
Actual return on plan assets38 86 5 8 
Employer contributions11 14 7 8 
Plan participants’ contributions— — 3 4 
Gross benefits paid(66)(74)(18)(20)
Fair value of plan assets at December 31715 732 80 83 
Under funded status at December 31($126)($144)($68)($77)
Defined Benefit Pension PlansOPEB Plans
Alliant Energy2024202320242023
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $17 $14 
Current liabilities(3)(2)(7)(8)
Pension and other benefit obligations(123)(142)(78)(83)
Net amounts recognized at December 31($126)($144)($68)($77)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$312 $337 $4 $11 
Prior service credit(2)(2)— — 
$310 $335 $4 $11 
Defined Benefit Pension PlansOPEB Plans
IPL2024202320242023
Change in benefit obligation:
Net benefit obligation at January 1$387 $389 $65 $68 
Service cost3 3 1 1 
Interest cost20 21 3 3 
Plan participants’ contributions— — 1 2 
Actuarial (gain) loss(8)9 (3)(1)
Gross benefits paid(30)(35)(8)(8)
Net benefit obligation at December 31372 387 59 65 
Change in plan assets:
Fair value of plan assets at January 1352 344 61 58 
Actual return on plan assets18 42 4 7 
Employer contributions— 1 1 2 
Plan participants’ contributions— — 1 2 
Gross benefits paid(30)(35)(8)(8)
Fair value of plan assets at December 31340 352 59 61 
Under funded status at December 31($32)($35)$— ($4)
Defined Benefit Pension PlansOPEB Plans
IPL2024202320242023
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $13 $10 
Current liabilities(1)— (1)(1)
Pension and other benefit obligations(31)(35)(12)(13)
Net amounts recognized at December 31($32)($35)$— ($4)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$126 $135 $7 $9 
Prior service credit(1)(1)— — 
$125 $134 $7 $9 
Defined Benefit Pension PlansOPEB Plans
WPL2024202320242023
Change in benefit obligation:
Net benefit obligation at January 1$381 $381 $61 $65 
Service cost2 2 1 1 
Interest cost20 20 3 3 
Plan participants’ contributions— — 1 2 
Actuarial (gain) loss (8)10 (3)(2)
Gross benefits paid(30)(32)(7)(8)
Net benefit obligation at December 31365 381 56 61 
Change in plan assets:
Fair value of plan assets at January 1306 291 14 14 
Actual return on plan assets17 35 — 1 
Employer contributions10 12 5 5 
Plan participants’ contributions— — 1 2 
Gross benefits paid(30)(32)(7)(8)
Fair value of plan assets at December 31303 306 13 14 
Under funded status at December 31($62)($75)($43)($47)
Defined Benefit Pension PlansOPEB Plans
WPL2024202320242023
Amounts recognized on the balance sheets consist of:
Non-current assets$— $— $4 $4 
Current liabilities— — (6)(6)
Pension and other benefit obligations(62)(75)(41)(45)
Net amounts recognized at December 31($62)($75)($43)($47)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss$135 $148 $— $3 
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 Energy2024202320242023
Accumulated benefit obligations$824 $857 $148 $160 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations824 857 148 160 
Fair value of plan assets715 732 80 83 
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations841 876 N/AN/A
Fair value of plan assets715 732 N/AN/A
Defined Benefit Pension PlansOPEB Plans
IPL2024202320242023
Accumulated benefit obligations$362 $377 $59 $65 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations362 377 N/A65 
Fair value of plan assets340 352 N/A61 
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations372 387 N/AN/A
Fair value of plan assets340 352 N/AN/A
Defined Benefit Pension PlansOPEB Plans
WPL2024202320242023
Accumulated benefit obligations$358 $373 $56 $61 
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations358 373 56 61 
Fair value of plan assets303 306 13 14 
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations365 381 N/AN/A
Fair value of plan assets303 306 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
2024202320242023
Regulatory assets$25$28$22$24
Estimated Future Employer Contributions Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2025 is as follows (in millions):
Alliant EnergyIPLWPL
Defined benefit pension plans (a)$20$1$14
OPEB plans716

(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 Energy202520262027202820292030 - 2034
Defined benefit pension benefits$79 $75 $74 $74 $74 $329
OPEB16 16 15 15 14 62
$95 $91 $89 $89 $88 $391
IPL202520262027202820292030 - 2034
Defined benefit pension benefits$36 $34 $33 $33 $32 $148
OPEB7 6 6 6 6 24
$43 $40 $39 $39 $38 $172
WPL202520262027202820292030 - 2034
Defined benefit pension benefits$33 $31 $31 $31 $31 $144
OPEB7 6 6 5 5 23
$40 $37 $37 $36 $36 $167
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
202420232022202420232022202420232022
Compensation expense$12$12$13$6$6$7$5$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, 2024, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows:
Target RangeActual
AllocationAllocation
Public equity securities32%-49%44%
Liquid alternative securities0%-12%6%
Return-seeking fixed income securities4%-18%8%
Liability-hedging fixed income securities (including cash and equivalents)34%-53%42%
At December 31, the fair values of qualified and non-qualified defined benefit pension plan assets were as follows (in millions):
20242023
FairLevelLevelLevelFairLevelLevelLevel
Alliant EnergyValue123Value123
Cash and equivalents$49 $— $49 $— $19 $— $19 $— 
Equity securities— — — — 223 223 — — 
Global asset securities— — — — 39 39 — — 
Fixed income securities— — — — 143 31 112 — 
Total assets in fair value hierarchy49 $— $49 $— 424 $293 $131 $— 
Assets measured at net asset value667 306 
Accrued investment income— 2 
Due to brokers, net (pending trades with brokers)(1)— 
Total pension plan assets$715 $732 
20242023
FairLevelLevelLevelFairLevelLevelLevel
IPLValue123Value123
Cash and equivalents$21 $— $21 $— $9 $— $9 $— 
Equity securities— — — — 107 107 — — 
Global asset securities— — — — 19 19 — — 
Fixed income securities— — — — 69 15 54 — 
Total assets in fair value hierarchy21 $— $21 $— 204 $141 $63 $— 
Assets measured at net asset value319 147 
Accrued investment income— 1 
Total pension plan assets$340 $352 
20242023
FairLevelLevelLevelFairLevelLevelLevel
WPLValue123Value123
Cash and equivalents$22 $— $22 $— $8 $— $8 $— 
Equity securities— — — — 93 93 — — 
Global asset securities— — — — 16 16 — — 
Fixed income securities— — — — 60 13 47 — 
Total assets in fair value hierarchy22 $— $22 $— 177 $122 $55 $— 
Assets measured at net asset value281 128 
Accrued investment income— 1 
Total pension plan assets$303 $306 
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, 2024, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows:
Target RangeActual
AllocationAllocation
Public equity securities32%-49%44%
Liquid alternative securities0%-12%6%
Return-seeking fixed income securities4%-18%8%
Liability-hedging fixed income securities (including cash and equivalents)34%-53%42%
At December 31, the fair values of qualified and non-qualified defined benefit pension plan assets were as follows (in millions):
20242023
FairLevelLevelLevelFairLevelLevelLevel
Alliant EnergyValue123Value123
Cash and equivalents$49 $— $49 $— $19 $— $19 $— 
Equity securities— — — — 223 223 — — 
Global asset securities— — — — 39 39 — — 
Fixed income securities— — — — 143 31 112 — 
Total assets in fair value hierarchy49 $— $49 $— 424 $293 $131 $— 
Assets measured at net asset value667 306 
Accrued investment income— 2 
Due to brokers, net (pending trades with brokers)(1)— 
Total pension plan assets$715 $732 
20242023
FairLevelLevelLevelFairLevelLevelLevel
IPLValue123Value123
Cash and equivalents$21 $— $21 $— $9 $— $9 $— 
Equity securities— — — — 107 107 — — 
Global asset securities— — — — 19 19 — — 
Fixed income securities— — — — 69 15 54 — 
Total assets in fair value hierarchy21 $— $21 $— 204 $141 $63 $— 
Assets measured at net asset value319 147 
Accrued investment income— 1 
Total pension plan assets$340 $352 
20242023
FairLevelLevelLevelFairLevelLevelLevel
WPLValue123Value123
Cash and equivalents$22 $— $22 $— $8 $— $8 $— 
Equity securities— — — — 93 93 — — 
Global asset securities— — — — 16 16 — — 
Fixed income securities— — — — 60 13 47 — 
Total assets in fair value hierarchy22 $— $22 $— 177 $122 $55 $— 
Assets measured at net asset value281 128 
Accrued investment income— 1 
Total pension plan assets$303 $306 
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, 2024, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows:
Target RangeActual
AllocationAllocation
Public equity securities32%-49%44%
Liquid alternative securities0%-12%6%
Return-seeking fixed income securities4%-18%8%
Liability-hedging fixed income securities (including cash and equivalents)34%-53%42%
At December 31, the fair values of qualified and non-qualified defined benefit pension plan assets were as follows (in millions):
20242023
FairLevelLevelLevelFairLevelLevelLevel
Alliant EnergyValue123Value123
Cash and equivalents$49 $— $49 $— $19 $— $19 $— 
Equity securities— — — — 223 223 — — 
Global asset securities— — — — 39 39 — — 
Fixed income securities— — — — 143 31 112 — 
Total assets in fair value hierarchy49 $— $49 $— 424 $293 $131 $— 
Assets measured at net asset value667 306 
Accrued investment income— 2 
Due to brokers, net (pending trades with brokers)(1)— 
Total pension plan assets$715 $732 
20242023
FairLevelLevelLevelFairLevelLevelLevel
IPLValue123Value123
Cash and equivalents$21 $— $21 $— $9 $— $9 $— 
Equity securities— — — — 107 107 — — 
Global asset securities— — — — 19 19 — — 
Fixed income securities— — — — 69 15 54 — 
Total assets in fair value hierarchy21 $— $21 $— 204 $141 $63 $— 
Assets measured at net asset value319 147 
Accrued investment income— 1 
Total pension plan assets$340 $352 
20242023
FairLevelLevelLevelFairLevelLevelLevel
WPLValue123Value123
Cash and equivalents$22 $— $22 $— $8 $— $8 $— 
Equity securities— — — — 93 93 — — 
Global asset securities— — — — 16 16 — — 
Fixed income securities— — — — 60 13 47 — 
Total assets in fair value hierarchy22 $— $22 $— 177 $122 $55 $— 
Assets measured at net asset value281 128 
Accrued investment income— 1 
Total pension plan assets$303 $306 
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, 2024, 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%1%
Public equity securities0%-40%27%
Fixed income securities40%-100%72%
At December 31, the fair values of OPEB plan assets were as follows (in millions):
20242023
FairLevelLevelLevelFairLevelLevelLevel
Alliant EnergyValue123Value123
Cash and equivalents$8 $— $8 $— $9 $— $9 $— 
Equity securities20 20 — — 8 8 — — 
Fixed income securities52 52 — — 47 47 — — 
Total assets in fair value hierarchy80 $72 $8 $— 64 $55 $9 $— 
Assets measured at net asset value— 19 
Total OPEB plan assets$80 $83 
20242023
FairLevelLevelLevelFairLevelLevelLevel
IPLValue123Value123
Cash and equivalents$1 $— $1 $— $1 $— $1 $— 
Equity securities18 18 — — 6 6 — — 
Fixed income securities40 40 — — 36 36 — — 
Total assets in fair value hierarchy59 $58 $1 $— 43 $42 $1 $— 
Assets measured at net asset value— 18 
Total OPEB plan assets$59 $61 
20242023
FairLevelLevelLevelFairLevelLevelLevel
WPLValue123Value123
Cash and equivalents$— $— $— $— $1 $— $1 $— 
Equity securities2 2 — — 2 2 — — 
Fixed income securities11 11 — — 11 11 — — 
Total OPEB plan assets$13 $13 $— $— $14 $13 $1 $— 
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, 2024, 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%1%
Public equity securities0%-40%27%
Fixed income securities40%-100%72%
At December 31, the fair values of OPEB plan assets were as follows (in millions):
20242023
FairLevelLevelLevelFairLevelLevelLevel
Alliant EnergyValue123Value123
Cash and equivalents$8 $— $8 $— $9 $— $9 $— 
Equity securities20 20 — — 8 8 — — 
Fixed income securities52 52 — — 47 47 — — 
Total assets in fair value hierarchy80 $72 $8 $— 64 $55 $9 $— 
Assets measured at net asset value— 19 
Total OPEB plan assets$80 $83 
20242023
FairLevelLevelLevelFairLevelLevelLevel
IPLValue123Value123
Cash and equivalents$1 $— $1 $— $1 $— $1 $— 
Equity securities18 18 — — 6 6 — — 
Fixed income securities40 40 — — 36 36 — — 
Total assets in fair value hierarchy59 $58 $1 $— 43 $42 $1 $— 
Assets measured at net asset value— 18 
Total OPEB plan assets$59 $61 
20242023
FairLevelLevelLevelFairLevelLevelLevel
WPLValue123Value123
Cash and equivalents$— $— $— $— $1 $— $1 $— 
Equity securities2 2 — — 2 2 — — 
Fixed income securities11 11 — — 11 11 — — 
Total OPEB plan assets$13 $13 $— $— $14 $13 $1 $— 
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, 2024, 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%1%
Public equity securities0%-40%27%
Fixed income securities40%-100%72%
At December 31, the fair values of OPEB plan assets were as follows (in millions):
20242023
FairLevelLevelLevelFairLevelLevelLevel
Alliant EnergyValue123Value123
Cash and equivalents$8 $— $8 $— $9 $— $9 $— 
Equity securities20 20 — — 8 8 — — 
Fixed income securities52 52 — — 47 47 — — 
Total assets in fair value hierarchy80 $72 $8 $— 64 $55 $9 $— 
Assets measured at net asset value— 19 
Total OPEB plan assets$80 $83 
20242023
FairLevelLevelLevelFairLevelLevelLevel
IPLValue123Value123
Cash and equivalents$1 $— $1 $— $1 $— $1 $— 
Equity securities18 18 — — 6 6 — — 
Fixed income securities40 40 — — 36 36 — — 
Total assets in fair value hierarchy59 $58 $1 $— 43 $42 $1 $— 
Assets measured at net asset value— 18 
Total OPEB plan assets$59 $61 
20242023
FairLevelLevelLevelFairLevelLevelLevel
WPLValue123Value123
Cash and equivalents$— $— $— $— $1 $— $1 $— 
Equity securities2 2 — — 2 2 — — 
Fixed income securities11 11 — — 11 11 — — 
Total OPEB plan assets$13 $13 $— $— $14 $13 $1 $— 
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
202420232022202420232022202420232022
401(k) costs$31 $30 $28 $14 $14 $13 $15 $14 $13 
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
202420232022202420232022202420232022
401(k) costs$31 $30 $28 $14 $14 $13 $15 $14 $13 
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
202420232022202420232022202420232022
401(k) costs$31 $30 $28 $14 $14 $13 $15 $14 $13 
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:
202420232022
SharesWeighted
Average Grant
Date Fair Value		SharesWeighted
Average Grant
Date Fair Value		SharesWeighted
Average Grant
Date Fair Value
Nonvested awards, January 1233,954$52.60190,273$54.13196,429$51.59
Granted127,87446.04108,71255.6874,10654.45
Vested(47,497)46.19(53,431)64.04(71,101)47.48
Forfeited(24,932)46.16(11,600)53.88(9,161)53.99
Nonvested awards, December 31289,39951.31233,95452.60190,27354.13
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:
202420232022
UnitsWeighted
Average Grant
Date Fair Value		UnitsWeighted
Average Grant
Date Fair Value		UnitsWeighted
Average Grant
Date Fair Value
Nonvested awards, January 1234,259$52.58198,275$54.53217,819$50.54
Granted129,85448.69106,12452.7777,12256.88
Vested(71,441)48.65(55,345)59.40(82,770)46.08
Forfeited(3,524)48.40(14,795)54.53(13,896)55.53
Nonvested awards, December 31289,14851.85234,25952.58198,27554.53
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:
202420232022
SharesWeighted Average Grant Date Fair ValueSharesWeighted Average Grant Date Fair ValueSharesWeighted Average Grant Date Fair Value
Nonvested awards, January 1257,639$52.76199,874$54.74196,429$50.74
Granted146,14348.55124,21752.7184,67057.01
Vested(67,852)48.66(53,431)59.36(71,101)46.24
Forfeited(5,230)48.40(13,021)55.47(10,124)55.92
Nonvested awards, December 31330,70051.81257,63952.76199,87454.74
v3.25.0.1
Asset Retirement Obligations (Tables)
 12 Months Ended
Dec. 31, 2024
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
202420232024202320242023
Balance, January 1$246 $279 $148 $195 $98 $84 
Revisions in estimated cash flows(3)(6)(1)(9)(2)3 
Liabilities settled(8)(51)(6)(44)(2)(7)
Liabilities incurred (a)409 16 201 1 208 15 
Accretion expense19 8 8 5 11 3 
Balance, December 31$663 $246 $350 $148 $313 $98 

(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
202420232024202320242023
Balance, January 1$246 $279 $148 $195 $98 $84 
Revisions in estimated cash flows(3)(6)(1)(9)(2)3 
Liabilities settled(8)(51)(6)(44)(2)(7)
Liabilities incurred (a)409 16 201 1 208 15 
Accretion expense19 8 8 5 11 3 
Balance, December 31$663 $246 $350 $148 $313 $98 

(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
202420232024202320242023
Balance, January 1$246 $279 $148 $195 $98 $84 
Revisions in estimated cash flows(3)(6)(1)(9)(2)3 
Liabilities settled(8)(51)(6)(44)(2)(7)
Liabilities incurred (a)409 16 201 1 208 15 
Accretion expense19 8 8 5 11 3 
Balance, December 31$663 $246 $350 $148 $313 $98 

(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.
v3.25.0.1
Derivative Instruments (Tables)
 12 Months Ended
Dec. 31, 2024
Derivative [Line Items]  
Notional Amounts of Derivative Instruments As of December 31, 2024, 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
Alliant Energy1,422 2025-202610,232 2025147,894 2025-20322,520 2025
IPL383 2025-20263,551 202561,489 2025-2030— —
WPL1,039 2025-20266,681 202586,405 2025-20322,520 2025
Fair Value of Financial Instruments At December 31, 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
202420232024202320242023
Current derivative assets$41$44$29$30$12$14
Non-current derivative assets344419241520
Current derivative liabilities265111221529
Non-current derivative liabilities3247283039
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
2024
Derivative assets$75$64$48$43$27$21
Derivative liabilities58471384539
2023
Derivative assets884754323415
Derivative liabilities98573086849
IPL [Member]  
Derivative [Line Items]  
Notional Amounts of Derivative Instruments As of December 31, 2024, 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
Alliant Energy1,422 2025-202610,232 2025147,894 2025-20322,520 2025
IPL383 2025-20263,551 202561,489 2025-2030— —
WPL1,039 2025-20266,681 202586,405 2025-20322,520 2025
Fair Value of Financial Instruments At December 31, 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
202420232024202320242023
Current derivative assets$41$44$29$30$12$14
Non-current derivative assets344419241520
Current derivative liabilities265111221529
Non-current derivative liabilities3247283039
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
2024
Derivative assets$75$64$48$43$27$21
Derivative liabilities58471384539
2023
Derivative assets884754323415
Derivative liabilities98573086849
WPL [Member]  
Derivative [Line Items]  
Notional Amounts of Derivative Instruments As of December 31, 2024, 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
Alliant Energy1,422 2025-202610,232 2025147,894 2025-20322,520 2025
IPL383 2025-20263,551 202561,489 2025-2030— —
WPL1,039 2025-20266,681 202586,405 2025-20322,520 2025
Fair Value of Financial Instruments At December 31, 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
202420232024202320242023
Current derivative assets$41$44$29$30$12$14
Non-current derivative assets344419241520
Current derivative liabilities265111221529
Non-current derivative liabilities3247283039
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
2024
Derivative assets$75$64$48$43$27$21
Derivative liabilities58471384539
2023
Derivative assets884754323415
Derivative liabilities98573086849
v3.25.0.1
Fair Value Measurements (Tables)
 12 Months Ended
Dec. 31, 2024
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 Energy20242023
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$52 $52 $— $— $52 $45 $45 $— $— $45 
Commodity derivatives75 — 48 27 75 88 — 59 29 88 
Interest rate derivatives1 — 1 — 1 1 — 1 — 1 
Deferred proceeds163 — — 163 163 216 — — 216 216 
Liabilities:
Commodity derivatives58 — 56 2 58 98 — 93 5 98 
Long-term debt (incl. current maturities)9,848 — 9,577 — 9,577 9,034 — 8,677 — 8,677 
IPL20242023
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$9 $9 $— $— $9 $45 $45 $— $— $45 
Commodity derivatives48 — 26 22 48 54 — 30 24 54 
Deferred proceeds163 — — 163 163 216 — — 216 216 
Liabilities:
Commodity derivatives13 — 11 2 13 30 — 25 5 30 
Long-term debt (incl. current maturities)4,090 — 3,736 — 3,736 3,945 — 3,664 — 3,664 
WPL20242023
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$43 $43 $— $— $43 $— $— $— $— $— 
Commodity derivatives27 — 22 5 27 34 — 29 5 34 
Liabilities:
Commodity derivatives45 — 45 — 45 68 — 68 — 68 
Long-term debt3,370 — 3,170 — 3,170 3,070 — 2,933 — 2,933 
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
2024202320242023
Beginning balance, January 1$24$19$216$185
Total net gains (losses) included in changes in net assets (realized/unrealized)(3)3——
Purchases5962——
Sales(3)(3)——
Settlements (a)(52)(57)(53)31
Ending balance, December 31$25$24$163$216
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($3)$3$—$—
IPLCommodity Contract Derivative
Assets and (Liabilities), netDeferred Proceeds
2024202320242023
Beginning balance, January 1$19$16$216$185
Total net losses included in changes in net assets (realized/unrealized)(4)(3)——
Purchases4551——
Sales(2)(3)——
Settlements (a)(38)(42)(53)31
Ending balance, December 31$20$19$163$216
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at December 31($4)($3)$—$—
WPLCommodity Contract Derivative
Assets and (Liabilities), net
20242023
Beginning balance, January 1$5$3
Total net gains included in changes in net assets (realized/unrealized)16
Purchases1411
Sales(1)—
Settlements(14)(15)
Ending balance, December 31$5$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$1$6

(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 FTR 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
2024$—$25$—$20$—$5
2023321316—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 Energy20242023
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$52 $52 $— $— $52 $45 $45 $— $— $45 
Commodity derivatives75 — 48 27 75 88 — 59 29 88 
Interest rate derivatives1 — 1 — 1 1 — 1 — 1 
Deferred proceeds163 — — 163 163 216 — — 216 216 
Liabilities:
Commodity derivatives58 — 56 2 58 98 — 93 5 98 
Long-term debt (incl. current maturities)9,848 — 9,577 — 9,577 9,034 — 8,677 — 8,677 
IPL20242023
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$9 $9 $— $— $9 $45 $45 $— $— $45 
Commodity derivatives48 — 26 22 48 54 — 30 24 54 
Deferred proceeds163 — — 163 163 216 — — 216 216 
Liabilities:
Commodity derivatives13 — 11 2 13 30 — 25 5 30 
Long-term debt (incl. current maturities)4,090 — 3,736 — 3,736 3,945 — 3,664 — 3,664 
WPL20242023
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$43 $43 $— $— $43 $— $— $— $— $— 
Commodity derivatives27 — 22 5 27 34 — 29 5 34 
Liabilities:
Commodity derivatives45 — 45 — 45 68 — 68 — 68 
Long-term debt3,370 — 3,170 — 3,170 3,070 — 2,933 — 2,933 
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
2024202320242023
Beginning balance, January 1$24$19$216$185
Total net gains (losses) included in changes in net assets (realized/unrealized)(3)3——
Purchases5962——
Sales(3)(3)——
Settlements (a)(52)(57)(53)31
Ending balance, December 31$25$24$163$216
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($3)$3$—$—
IPLCommodity Contract Derivative
Assets and (Liabilities), netDeferred Proceeds
2024202320242023
Beginning balance, January 1$19$16$216$185
Total net losses included in changes in net assets (realized/unrealized)(4)(3)——
Purchases4551——
Sales(2)(3)——
Settlements (a)(38)(42)(53)31
Ending balance, December 31$20$19$163$216
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at December 31($4)($3)$—$—
WPLCommodity Contract Derivative
Assets and (Liabilities), net
20242023
Beginning balance, January 1$5$3
Total net gains included in changes in net assets (realized/unrealized)16
Purchases1411
Sales(1)—
Settlements(14)(15)
Ending balance, December 31$5$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$1$6

(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 FTR 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
2024$—$25$—$20$—$5
2023321316—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 Energy20242023
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$52 $52 $— $— $52 $45 $45 $— $— $45 
Commodity derivatives75 — 48 27 75 88 — 59 29 88 
Interest rate derivatives1 — 1 — 1 1 — 1 — 1 
Deferred proceeds163 — — 163 163 216 — — 216 216 
Liabilities:
Commodity derivatives58 — 56 2 58 98 — 93 5 98 
Long-term debt (incl. current maturities)9,848 — 9,577 — 9,577 9,034 — 8,677 — 8,677 
IPL20242023
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$9 $9 $— $— $9 $45 $45 $— $— $45 
Commodity derivatives48 — 26 22 48 54 — 30 24 54 
Deferred proceeds163 — — 163 163 216 — — 216 216 
Liabilities:
Commodity derivatives13 — 11 2 13 30 — 25 5 30 
Long-term debt (incl. current maturities)4,090 — 3,736 — 3,736 3,945 — 3,664 — 3,664 
WPL20242023
Fair ValueFair Value
CarryingLevelLevelLevelCarryingLevelLevelLevel
Amount123TotalAmount123Total
Assets:
Money market fund investments$43 $43 $— $— $43 $— $— $— $— $— 
Commodity derivatives27 — 22 5 27 34 — 29 5 34 
Liabilities:
Commodity derivatives45 — 45 — 45 68 — 68 — 68 
Long-term debt3,370 — 3,170 — 3,170 3,070 — 2,933 — 2,933 
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
2024202320242023
Beginning balance, January 1$24$19$216$185
Total net gains (losses) included in changes in net assets (realized/unrealized)(3)3——
Purchases5962——
Sales(3)(3)——
Settlements (a)(52)(57)(53)31
Ending balance, December 31$25$24$163$216
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($3)$3$—$—
IPLCommodity Contract Derivative
Assets and (Liabilities), netDeferred Proceeds
2024202320242023
Beginning balance, January 1$19$16$216$185
Total net losses included in changes in net assets (realized/unrealized)(4)(3)——
Purchases4551——
Sales(2)(3)——
Settlements (a)(38)(42)(53)31
Ending balance, December 31$20$19$163$216
The amount of total net losses for the period included in changes in net assets attributable to the change in unrealized losses relating to assets and liabilities held at December 31($4)($3)$—$—
WPLCommodity Contract Derivative
Assets and (Liabilities), net
20242023
Beginning balance, January 1$5$3
Total net gains included in changes in net assets (realized/unrealized)16
Purchases1411
Sales(1)—
Settlements(14)(15)
Ending balance, December 31$5$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$1$6

(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 FTR 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
2024$—$25$—$20$—$5
2023321316—5
v3.25.0.1
Commitments And Contingencies (Tables)
 12 Months Ended
Dec. 31, 2024
Long-term Purchase Commitment [Line Items]  
Other Purchase Commitments At December 31, 2024, the related minimum future commitments, excluding amounts for purchased power commitments that do not have minimum thresholds but will require payment when electricity is generated by the provider, were as follows (in millions):
Alliant Energy20252026202720282029ThereafterTotal
Natural gas$268$177$130$102$84$120$881
Coal7533225——135
Other (a)512077222109
$394$230$159$114$86$142$1,125
IPL20252026202720282029ThereafterTotal
Natural gas$160$104$85$64$49$20$482
Coal3419105——68
Other (a)1822222147
$212$125$97$71$51$41$597
WPL20252026202720282029ThereafterTotal
Natural gas$108$73$45$38$35$100$399
Coal411412———67
Other (a)221————23
$171$88$57$38$35$100$489

(a)Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2024.
Schedule of Environmental Liabilities At December 31, 2024, 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 -$28$5 -$17$2 -$11
Current and non-current environmental liabilities$12$7$5
IPL [Member]  
Long-term Purchase Commitment [Line Items]  
Other Purchase Commitments At December 31, 2024, the related minimum future commitments, excluding amounts for purchased power commitments that do not have minimum thresholds but will require payment when electricity is generated by the provider, were as follows (in millions):
Alliant Energy20252026202720282029ThereafterTotal
Natural gas$268$177$130$102$84$120$881
Coal7533225——135
Other (a)512077222109
$394$230$159$114$86$142$1,125
IPL20252026202720282029ThereafterTotal
Natural gas$160$104$85$64$49$20$482
Coal3419105——68
Other (a)1822222147
$212$125$97$71$51$41$597
WPL20252026202720282029ThereafterTotal
Natural gas$108$73$45$38$35$100$399
Coal411412———67
Other (a)221————23
$171$88$57$38$35$100$489

(a)Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2024.
Schedule of Environmental Liabilities At December 31, 2024, 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 -$28$5 -$17$2 -$11
Current and non-current environmental liabilities$12$7$5
WPL [Member]  
Long-term Purchase Commitment [Line Items]  
Other Purchase Commitments At December 31, 2024, the related minimum future commitments, excluding amounts for purchased power commitments that do not have minimum thresholds but will require payment when electricity is generated by the provider, were as follows (in millions):
Alliant Energy20252026202720282029ThereafterTotal
Natural gas$268$177$130$102$84$120$881
Coal7533225——135
Other (a)512077222109
$394$230$159$114$86$142$1,125
IPL20252026202720282029ThereafterTotal
Natural gas$160$104$85$64$49$20$482
Coal3419105——68
Other (a)1822222147
$212$125$97$71$51$41$597
WPL20252026202720282029ThereafterTotal
Natural gas$108$73$45$38$35$100$399
Coal411412———67
Other (a)221————23
$171$88$57$38$35$100$489

(a)Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2024.
Schedule of Environmental Liabilities At December 31, 2024, 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 -$28$5 -$17$2 -$11
Current and non-current environmental liabilities$12$7$5
v3.25.0.1
Segments Of Business (Tables)
 12 Months Ended
Dec. 31, 2024
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
2024IPLWPLSegmentsOtherConsolidated
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 Generation Station60 — 60 N/A60
Other operation and maintenance expense358 279 637 39676
Other segment items:
Depreciation and amortization expense404 357 761 11772
Interest expense177165342107449
Equity income from unconsolidated investments, net— (2)(2)(59)(61)
Income tax expense (benefit)(129)11(118)4(114)
Other (a)5 3439 544
Net income (loss)362345707(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 (a)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
Utility
TotalAlliant
ReportableEnergy
2022IPLWPLSegmentsOtherConsolidated
Electric utility revenues$1,859 $1,562 $3,421 N/A$3,421
Gas utility revenues351 291 642 N/A642
Other revenues46 3 49 $93142
Total revenues2,256 1,856 4,112 934,205
Electric production fuel and purchased power expense383 447 830 N/A830
Electric transmission service expense407 166 573 N/A573
Cost of gas sold expense206 183 389 N/A389
Other operation and maintenance expense369 278 647 57704
Other segment items:
Depreciation and amortization expense381 283 664 7671
Interest expense148 121 269 56325
Equity income from unconsolidated investments, net— (1)(1)(50)(51)
Income tax expense (benefit)(50)66 16 622
Other (a)52 (2)50 656
Net income360 315 675 11686
Total assets10,075 8,987 19,062 1,10120,163
Investments in equity method subsidiaries5 15 20 522542
Construction and acquisition expenditures372 1,020 1,392 921,484

(a)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
2024IPLWPLSegmentsOtherConsolidated
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 Generation Station60 — 60 N/A60
Other operation and maintenance expense358 279 637 39676
Other segment items:
Depreciation and amortization expense404 357 761 11772
Interest expense177165342107449
Equity income from unconsolidated investments, net— (2)(2)(59)(61)
Income tax expense (benefit)(129)11(118)4(114)
Other (a)5 3439 544
Net income (loss)362345707(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 (a)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
Utility
TotalAlliant
ReportableEnergy
2022IPLWPLSegmentsOtherConsolidated
Electric utility revenues$1,859 $1,562 $3,421 N/A$3,421
Gas utility revenues351 291 642 N/A642
Other revenues46 3 49 $93142
Total revenues2,256 1,856 4,112 934,205
Electric production fuel and purchased power expense383 447 830 N/A830
Electric transmission service expense407 166 573 N/A573
Cost of gas sold expense206 183 389 N/A389
Other operation and maintenance expense369 278 647 57704
Other segment items:
Depreciation and amortization expense381 283 664 7671
Interest expense148 121 269 56325
Equity income from unconsolidated investments, net— (1)(1)(50)(51)
Income tax expense (benefit)(50)66 16 622
Other (a)52 (2)50 656
Net income360 315 675 11686
Total assets10,075 8,987 19,062 1,10120,163
Investments in equity method subsidiaries5 15 20 522542
Construction and acquisition expenditures372 1,020 1,392 921,484

(a)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
2024IPLWPLSegmentsOtherConsolidated
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 Generation Station60 — 60 N/A60
Other operation and maintenance expense358 279 637 39676
Other segment items:
Depreciation and amortization expense404 357 761 11772
Interest expense177165342107449
Equity income from unconsolidated investments, net— (2)(2)(59)(61)
Income tax expense (benefit)(129)11(118)4(114)
Other (a)5 3439 544
Net income (loss)362345707(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 (a)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
Utility
TotalAlliant
ReportableEnergy
2022IPLWPLSegmentsOtherConsolidated
Electric utility revenues$1,859 $1,562 $3,421 N/A$3,421
Gas utility revenues351 291 642 N/A642
Other revenues46 3 49 $93142
Total revenues2,256 1,856 4,112 934,205
Electric production fuel and purchased power expense383 447 830 N/A830
Electric transmission service expense407 166 573 N/A573
Cost of gas sold expense206 183 389 N/A389
Other operation and maintenance expense369 278 647 57704
Other segment items:
Depreciation and amortization expense381 283 664 7671
Interest expense148 121 269 56325
Equity income from unconsolidated investments, net— (1)(1)(50)(51)
Income tax expense (benefit)(50)66 16 622
Other (a)52 (2)50 656
Net income360 315 675 11686
Total assets10,075 8,987 19,062 1,10120,163
Investments in equity method subsidiaries5 15 20 522542
Construction and acquisition expenditures372 1,020 1,392 921,484

(a)Other segment items for each reportable segment include AFUDC, taxes other than income taxes, interest income, and other miscellaneous income and deductions.
v3.25.0.1
Related Parties (Tables)
 12 Months Ended
Dec. 31, 2024
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
202420232022202420232022
Corporate Services billings$183$181$181$171$163$155
Sales credited—1119845574
Purchases billed4304314355435174
Net Intercompany Payables
As of December 31, net intercompany payables to Corporate Services were as follows (in millions):
20242023
IPL$135$129
WPL6472
Related Amounts Billed Between Parties The related amounts billed between the parties were as follows (in millions):
202420232022
ATC billings to WPL$152$159$140
WPL billings to ATC162018
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
202420232022202420232022
Corporate Services billings$183$181$181$171$163$155
Sales credited—1119845574
Purchases billed4304314355435174
Net Intercompany Payables
As of December 31, net intercompany payables to Corporate Services were as follows (in millions):
20242023
IPL$135$129
WPL6472
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
202420232022202420232022
Corporate Services billings$183$181$181$171$163$155
Sales credited—1119845574
Purchases billed4304314355435174
Net Intercompany Payables
As of December 31, net intercompany payables to Corporate Services were as follows (in millions):
20242023
IPL$135$129
WPL6472
Related Amounts Billed Between Parties The related amounts billed between the parties were as follows (in millions):
202420232022
ATC billings to WPL$152$159$140
WPL billings to ATC162018
v3.25.0.1
Condensed Parent Company Financial Statements (Tables)
 12 Months Ended
Dec. 31, 2024
Condensed Financial Information Disclosure [Abstract]  
Condensed Statements of Income
ALLIANT ENERGY CORPORATION (Parent Company Only)Year Ended December 31,
CONDENSED STATEMENTS OF INCOME202420232022
(in millions)
Operating expenses$3 $3 $9 
Operating loss(3)(3)(9)
Other (income) and deductions:
Equity earnings from consolidated subsidiaries(734)(742)(707)
Interest expense40 34 6 
Other5 4 1 
Total other (income) and deductions(689)(704)(700)
Income before income taxes686 701 691 
Income tax expense (benefit)(3)(5)2 
Net income$689 $706 $689 
Refer to accompanying Notes to Condensed Financial Statements.
Condensed Balance Sheets
ALLIANT ENERGY CORPORATION (Parent Company Only)December 31,
CONDENSED BALANCE SHEETS20242023
(in millions)
ASSETS
Current assets:
Notes receivable from affiliated companies$103 $96 
Income tax refunds receivable12 — 
Other2 1 
Total current assets117 97 
Investments:
Investments in consolidated subsidiaries9,123 8,405 
Other1 2 
Total investments9,124 8,407 
Other assets84 90 
Total assets$9,325 $8,594 
LIABILITIES AND EQUITY
Current liabilities:
Current maturities of long-term debt$571 $— 
Commercial paper325 157 
Notes payable to affiliated companies1,401 1,068 
Other10 10 
Total current liabilities2,307 1,235 
Long-term debt, net (excluding current portion)— 568 
Other liabilities3 2 
Common equity:
Common stock and additional paid-in capital3,063 3,033 
Retained earnings3,965 3,768 
Accumulated other comprehensive income1 1 
Shares in deferred compensation trust(14)(13)
Total common equity7,015 6,789 
Total liabilities and equity$9,325 $8,594 
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 FLOWS202420232022
(in millions)
Net cash flows from operating activities$355 $445 $492 
Cash flows used for investing activities:
Capital contributions to consolidated subsidiaries(380)(325)(530)
Net change in notes receivable from and payable to affiliates326 (281)369 
Net cash flows used for investing activities(54)(606)(161)
Cash flows from (used for) financing activities:
Common stock dividends(492)(456)(428)
Proceeds from issuance of common stock, net23 246 25 
Proceeds from issuance of long-term debt— 565 — 
Net change in commercial paper168 (195)73 
Other— 1 (1)
Net cash flows from (used for) financing activities(301)161 (331)
Net increase (decrease) in cash, cash equivalents and restricted cash— — — 
Cash, cash equivalents and restricted cash at beginning of period— — — 
Cash, cash equivalents and restricted cash at end of period$— $— $— 
Supplemental cash flows information:
Cash (paid) received during the period for:
Interest($40)($27)($6)
Income taxes, net$8 $22 $15 
Refer to accompanying Notes to Condensed Financial Statements.
v3.25.0.1
Summary Of Significant Accounting Policies (Narrative) (Details)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
USD ($)
customer
MW
Dec. 31, 2023
USD ($)
Dec. 31, 2022
Cash, Cash Equivalents and Restricted Cash:        
Money market fund investments   $ 52 $ 45  
Money market fund investments interest rate, percentage   4.00%    
Non-utility wind farm in Oklahoma [Member]        
General:        
Ownership interest   50.00%    
IPL [Member]        
General:        
Generation and distribution of steam, number of customers served (in customers) | customer   2    
Cash, Cash Equivalents and Restricted Cash:        
Money market fund investments   $ 9 45  
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   $ 43 $ 0  
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   3.30% 3.30% 3.40%
Electric - generation [Member] | WPL [Member]        
Property, Plant and Equipment:        
Average rate of depreciation, percent   3.40% 3.00% 3.40%
Electric - distribution [Member] | IPL [Member]        
Property, Plant and Equipment:        
Average rate of depreciation, percent   2.80% 2.80% 2.80%
Electric - distribution [Member] | WPL [Member]        
Property, Plant and Equipment:        
Average rate of depreciation, percent   2.70% 2.70% 2.50%
Forecast [Member] | Electric - generation [Member] | IPL [Member]        
Property, Plant and Equipment:        
Average rate of depreciation, percent 3.80%      
Forecast [Member] | Electric - distribution [Member] | IPL [Member]        
Property, Plant and Equipment:        
Average rate of depreciation, percent 3.00%      
v3.25.0.1
Summary Of Significant Accounting Policies (Schedule Of Average Rates Of Depreciation) (Details)
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Electric - generation [Member] | IPL [Member]        
Public Utility, Property, Plant and Equipment [Line Items]        
Average rate of depreciation, percent   3.30% 3.30% 3.40%
Electric - generation [Member] | IPL [Member] | Forecast [Member]        
Public Utility, Property, Plant and Equipment [Line Items]        
Average rate of depreciation, percent 3.80%      
Electric - generation [Member] | WPL [Member]        
Public Utility, Property, Plant and Equipment [Line Items]        
Average rate of depreciation, percent   3.40% 3.00% 3.40%
Electric - distribution [Member] | IPL [Member]        
Public Utility, Property, Plant and Equipment [Line Items]        
Average rate of depreciation, percent   2.80% 2.80% 2.80%
Electric - distribution [Member] | IPL [Member] | Forecast [Member]        
Public Utility, Property, Plant and Equipment [Line Items]        
Average rate of depreciation, percent 3.00%      
Electric - distribution [Member] | WPL [Member]        
Public Utility, Property, Plant and Equipment [Line Items]        
Average rate of depreciation, percent   2.70% 2.70% 2.50%
Electric - other [Member] | IPL [Member]        
Public Utility, Property, Plant and Equipment [Line Items]        
Average rate of depreciation, percent   5.20% 5.60% 5.70%
Electric - other [Member] | WPL [Member]        
Public Utility, Property, Plant and Equipment [Line Items]        
Average rate of depreciation, percent   6.10% 6.30% 6.80%
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   2.50% 2.50% 2.40%
Other [Member] | IPL [Member]        
Public Utility, Property, Plant and Equipment [Line Items]        
Average rate of depreciation, percent   4.60% 6.20% 6.10%
Other [Member] | WPL [Member]        
Public Utility, Property, Plant and Equipment [Line Items]        
Average rate of depreciation, percent   4.40% 4.60% 4.90%
v3.25.0.1
Summary Of Significant Accounting Policies (Schedule Of Allowance For Funds Used During Construction Recovery Rate) (Details)
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
IPL [Member]      
Public Utility, Property, Plant and Equipment [Line Items]      
Recovery rates, percent 7.00% 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% 7.00%
WPL [Member] | WPL (wholesale jurisdiction) [Member]      
Public Utility, Property, Plant and Equipment [Line Items]      
Recovery rates, percent 7.10% 7.10% 6.20%
v3.25.0.1
Regulatory Matters (Narrative) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2020
Regulatory Matters [Line Items]          
Regulatory assets   $ 2,274 $ 2,261    
Collected from retail electric customers   3,372 3,345 $ 3,421  
Regulatory liabilities   1,028 1,130    
IPL [Member]          
Regulatory Matters [Line Items]          
Regulatory assets not earning a return   199      
Regulatory assets   1,586 1,577    
Collected from retail electric customers   1,747 1,761 1,859  
Regulatory liabilities   546 644    
WPL [Member]          
Regulatory Matters [Line Items]          
Regulatory assets not earning a return   23      
Regulatory assets   688 684    
Collected from retail electric customers   1,625 1,584 1,562  
Regulatory liabilities   482 486    
2022 Test Period Fuel-related Costs [Member] | WPL [Member]          
Regulatory Matters [Line Items]          
Regulatory assets       $ 117  
Collected from retail electric customers   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      
2021 Test Period Fuel-related Costs [Member] | WPL [Member]          
Regulatory Matters [Line Items]          
Collected from retail electric customers     $ 37    
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      
DAEC PPA [Member]          
Regulatory Matters [Line Items]          
Buyout payment         $ 110
PPA term amendment         5 years
Forecast [Member] | 2025 Test Period Retail Electric [Member] | WPL [Member]          
Regulatory Matters [Line Items]          
Authorized increase (decrease) in final rates, amount $ 60        
v3.25.0.1
Regulatory Matters (Regulatory Assets) (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Regulatory Assets [Line Items]    
Regulatory assets $ 2,274.0 $ 2,261.0
Tax-related [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 989.0 934.0
AROs [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 401.0 194.0
Pension and OPEB costs [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 315.0 347.0
Assets retired early [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 180.0 273.0
Commodity cost recovery [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 68.0 120.0
Derivatives [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 60.0 102.0
Non-service pension and OPEB costs [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 51.0 46.0
WPL's Western Wisconsin gas distribution expansion investments [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 42.0 44.0
IPL's DAEC PPA amendment [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 18.0 42.0
Other [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 150.0 159.0
IPL [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 1,586.0 1,577.0
IPL [Member] | Tax-related [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 870.0 831.0
IPL [Member] | AROs [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 281.0 160.0
IPL [Member] | Pension and OPEB costs [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 157.0 171.0
IPL [Member] | Assets retired early [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 168.0 259.0
IPL [Member] | Commodity cost recovery [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 2.0 12.0
IPL [Member] | Derivatives [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 15.0 34.0
IPL [Member] | Non-service pension and OPEB costs [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 19.0 18.0
IPL [Member] | IPL's DAEC PPA amendment [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 18.0 42.0
IPL [Member] | Other [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 56.0 50.0
WPL [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 688.0 684.0
WPL [Member] | Tax-related [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 119.0 103.0
WPL [Member] | AROs [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 120.0 34.0
WPL [Member] | Pension and OPEB costs [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 158.0 176.0
WPL [Member] | Assets retired early [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 12.0 14.0
WPL [Member] | Commodity cost recovery [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 66.0 108.0
WPL [Member] | Derivatives [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 45.0 68.0
WPL [Member] | Non-service pension and OPEB costs [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 32.0 28.0
WPL [Member] | WPL's Western Wisconsin gas distribution expansion investments [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 42.0 44.0
WPL [Member] | Other [Member]    
Regulatory Assets [Line Items]    
Regulatory assets $ 94.0 $ 109.0
v3.25.0.1
Regulatory Matters (Assets Retired Early) (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Regulatory Assets [Line Items]    
Regulatory assets $ 2,274 $ 2,261
Assets retired early [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 180 273
IPL [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 1,586 1,577
IPL [Member] | Assets retired early [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 168 259
IPL [Member] | Assets retired early [Member] | Lansing [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 131  
IPL [Member] | Assets retired early [Member] | Analog Electric Meters [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 15  
IPL [Member] | Assets retired early [Member] | Sutherland Units 1 and 3 [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 15  
IPL [Member] | Assets retired early [Member] | M.L. Kapp Unit 2 [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 7  
WPL [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 688 684
WPL [Member] | Assets retired early [Member]    
Regulatory Assets [Line Items]    
Regulatory assets 12 $ 14
WPL [Member] | Assets retired early [Member] | Edgewater Unit 4 [Member]    
Regulatory Assets [Line Items]    
Regulatory assets $ 12  
v3.25.0.1
Regulatory Matters (Regulatory Liabilities) (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Regulatory Liabilities [Line Items]    
Regulatory liabilities $ 1,028.0 $ 1,130.0
Tax-related [Member]    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 582.0 566.0
Cost of removal obligations [Member]    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 347.0 366.0
Derivatives [Member]    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 53.0 65.0
Commodity cost recovery [Member]    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 17.0 48.0
Other [Member]    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 29.0 85.0
IPL [Member]    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 546.0 644.0
IPL [Member] | Tax-related [Member]    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 286.0 299.0
IPL [Member] | Cost of removal obligations [Member]    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 205.0 242.0
IPL [Member] | Derivatives [Member]    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 29.0 34.0
IPL [Member] | Commodity cost recovery [Member]    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 12.0 13.0
IPL [Member] | Other [Member]    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 14.0 56.0
WPL [Member]    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 482.0 486.0
WPL [Member] | Tax-related [Member]    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 296.0 267.0
WPL [Member] | Cost of removal obligations [Member]    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 142.0 124.0
WPL [Member] | Derivatives [Member]    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 24.0 31.0
WPL [Member] | Commodity cost recovery [Member]    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 5.0 35.0
WPL [Member] | Other [Member]    
Regulatory Liabilities [Line Items]    
Regulatory liabilities $ 15.0 $ 29.0
v3.25.0.1
Property, Plant and Equipment (Narrative) (Details)
Dec. 31, 2024
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 35 years
Software [Member]  
Property, Plant and Equipment [Line Items]  
Property, plant and equipment, useful life 5 years
v3.25.0.1
Property, Plant and Equipment (Property, Plant and Equipment) (Details)
 12 Months Ended
Dec. 31, 2024
USD ($)
MW
Dec. 31, 2023
USD ($)
Property, Plant and Equipment [Line Items]    
Electric plant anticipated to be retired early $ 784,000,000 $ 1,629,000,000
Total electric plant 20,346,000,000 18,690,000,000
Gas plant in service 1,863,000,000 1,791,000,000
Other plant in service 734,000,000 653,000,000
Accumulated depreciation (6,229,000,000) (5,924,000,000)
Net plant 16,714,000,000 15,210,000,000
Leased land for solar generation, net 189,000,000 172,000,000
Construction work in progress 1,215,000,000 1,245,000,000
Other, net 5,000,000 7,000,000
Total utility 18,123,000,000 16,634,000,000
Non-utility Generation, net 103,000,000 68,000,000
Corporate Services and other, net 475,000,000 455,000,000
Total non-utility and other 578,000,000 523,000,000
Total property, plant and equipment 18,701,000,000 17,157,000,000
Non-utility Generation, accumulated depreciation 78,000,000 75,000,000
Corporate Services and other, accumulated depreciation 289,000,000 275,000,000
Generation [Member]    
Property, Plant and Equipment [Line Items]    
Electric plant in service 11,156,000,000 9,180,000,000
Distribution [Member]    
Property, Plant and Equipment [Line Items]    
Electric plant in service 7,811,000,000 7,314,000,000
Other [Member]    
Property, Plant and Equipment [Line Items]    
Electric plant in service 595,000,000 567,000,000
IPL [Member]    
Property, Plant and Equipment [Line Items]    
Electric plant anticipated to be retired early 0 0
Total electric plant 10,653,000,000 9,472,000,000
Gas plant in service 981,000,000 951,000,000
Other plant in service 456,000,000 411,000,000
Accumulated depreciation (3,360,000,000) (3,180,000,000)
Net plant 8,730,000,000 7,654,000,000
Leased land for solar generation, net 53,000,000 33,000,000
Construction work in progress 548,000,000 605,000,000
Other, net 5,000,000 6,000,000
Total utility 9,336,000,000 8,298,000,000
Total property, plant and equipment $ 9,336,000,000 8,298,000,000
Electric capacity of solar project | MW 400  
Construction project cost target exceedance $ 1,837.5  
Construction project cost target $ 1,650  
Base return on equity, percentage 10.25%  
IPL [Member] | Generation [Member]    
Property, Plant and Equipment [Line Items]    
Electric plant in service $ 5,924,000,000 5,025,000,000
IPL [Member] | Distribution [Member]    
Property, Plant and Equipment [Line Items]    
Electric plant in service 4,344,000,000 4,091,000,000
IPL [Member] | Other [Member]    
Property, Plant and Equipment [Line Items]    
Electric plant in service 385,000,000 356,000,000
WPL [Member]    
Property, Plant and Equipment [Line Items]    
Electric plant anticipated to be retired early 784,000,000 1,629,000,000
Total electric plant 9,693,000,000 9,218,000,000
Gas plant in service 882,000,000 840,000,000
Other plant in service 278,000,000 242,000,000
Accumulated depreciation (2,869,000,000) (2,744,000,000)
Net plant 7,984,000,000 7,556,000,000
Leased Sheboygan Falls Energy Facility, net 74,000,000 79,000,000
Leased land for solar generation, net 136,000,000 139,000,000
Construction work in progress 667,000,000 640,000,000
Other, net 0 1,000,000
Total utility 8,861,000,000 8,415,000,000
Total property, plant and equipment $ 8,861,000,000 8,415,000,000
Electric capacity of solar project | MW 1,100  
Construction project cost target exceedance $ 205,000,000  
Leased Sheboygan Falls Energy Facility, accumulated depreciation 116,000,000 112,000,000
WPL [Member] | Columbia Units 1-2 [Member]    
Property, Plant and Equipment [Line Items]    
Electric plant anticipated to be retired early 413,000,000 428,000,000
WPL [Member] | Generation [Member]    
Property, Plant and Equipment [Line Items]    
Electric plant in service 5,232,000,000 4,155,000,000
WPL [Member] | Distribution [Member]    
Property, Plant and Equipment [Line Items]    
Electric plant in service 3,467,000,000 3,223,000,000
WPL [Member] | Other [Member]    
Property, Plant and Equipment [Line Items]    
Electric plant in service $ 210,000,000 $ 211,000,000
v3.25.0.1
Property, Plant and Equipment (Equity and Debt AFUDC) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Property, Plant and Equipment [Line Items]      
Allowance for funds used during construction $ 75 $ 100 $ 60
Equity [Member]      
Property, Plant and Equipment [Line Items]      
Allowance for funds used during construction 54 74 44
Debt [Member]      
Property, Plant and Equipment [Line Items]      
Allowance for funds used during construction 21 26 16
IPL [Member]      
Property, Plant and Equipment [Line Items]      
Allowance for funds used during construction 43 21 11
IPL [Member] | Equity [Member]      
Property, Plant and Equipment [Line Items]      
Allowance for funds used during construction 31 15 8
IPL [Member] | Debt [Member]      
Property, Plant and Equipment [Line Items]      
Allowance for funds used during construction 12 6 3
WPL [Member]      
Property, Plant and Equipment [Line Items]      
Allowance for funds used during construction 32 79 49
WPL [Member] | Equity [Member]      
Property, Plant and Equipment [Line Items]      
Allowance for funds used during construction 23 59 36
WPL [Member] | Debt [Member]      
Property, Plant and Equipment [Line Items]      
Allowance for funds used during construction $ 9 $ 20 $ 13
v3.25.0.1
Jointly-Owned Electric Utility Plant (Details)
$ in Millions
Dec. 31, 2024
USD ($)
Jointly Owned Electric Utility Plant [Line Items]  
Electric Plant $ 2,496
Accumulated Provision for Depreciation 992
Construction Work in Progress 45
IPL [Member]  
Jointly Owned Electric Utility Plant [Line Items]  
Electric Plant 1,069
Accumulated Provision for Depreciation 499
Construction Work in Progress 34
WPL [Member]  
Jointly Owned Electric Utility Plant [Line Items]  
Electric Plant 1,427
Accumulated Provision for Depreciation 493
Construction Work in Progress $ 11
Ottumwa Unit 1 [Member] | IPL [Member]  
Jointly Owned Electric Utility Plant [Line Items]  
Ownership Interest % 48.00%
Electric Plant $ 648
Accumulated Provision for Depreciation 277
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 $ 197
Accumulated Provision for Depreciation 110
Construction Work in Progress $ 7
George Neal Unit 3 [Member] | IPL [Member]  
Jointly Owned Electric Utility Plant [Line Items]  
Ownership Interest % 28.00%
Electric Plant $ 181
Accumulated Provision for Depreciation 89
Construction Work in Progress $ 20
Louisa Unit 1 [Member] | IPL [Member]  
Jointly Owned Electric Utility Plant [Line Items]  
Ownership Interest % 4.00%
Electric Plant $ 43
Accumulated Provision for Depreciation 23
Construction Work in Progress $ 0
Columbia Units 1-2 and Energy Storage System [Member] | WPL [Member]  
Jointly Owned Electric Utility Plant [Line Items]  
Ownership Interest % 53.50%
Electric Plant $ 859
Accumulated Provision for Depreciation 378
Construction Work in Progress $ 6
West Riverside Energy Center and Solar Facility [Member] | WPL [Member]  
Jointly Owned Electric Utility Plant [Line Items]  
Ownership Interest % 56.60%
Electric Plant $ 449
Accumulated Provision for Depreciation 59
Construction Work in Progress $ 5
Forward Wind Energy Center [Member] | WPL [Member]  
Jointly Owned Electric Utility Plant [Line Items]  
Ownership Interest % 42.60%
Electric Plant $ 119
Accumulated Provision for Depreciation 56
Construction Work in Progress $ 0
v3.25.0.1
Receivables (Narrative) (Details)
$ in Millions
Dec. 31, 2024
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 $ 40
v3.25.0.1
Receivables (Details of Accounts Receivable) (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Receivables [Line Items]    
Customer $ 113 $ 121
Unbilled utility revenues 101 93
Deferred proceeds 163 216
Other 58 53
Allowance for expected credit losses (8) (8)
Accounts receivable, less allowance for expected credit losses 427 475
IPL [Member]    
Receivables [Line Items]    
Customer 0 0
Unbilled utility revenues 0 0
Deferred proceeds 163 216
Other 29 26
Allowance for expected credit losses 0 0
Accounts receivable, less allowance for expected credit losses 192 242
WPL [Member]    
Receivables [Line Items]    
Customer 98 110
Unbilled utility revenues 101 93
Other 29 24
Allowance for expected credit losses (8) (8)
Accounts receivable, less allowance for expected credit losses $ 220 $ 219
v3.25.0.1
Receivables (Gross Write-offs for Accounts Receivable (Details)
$ in Millions
 12 Months Ended
Dec. 31, 2024
USD ($)
Financing Receivable, Credit Quality Indicator [Line Items]  
Gross write-offs for accounts receivable, originated in 2023 $ 12
Gross write-offs for accounts receivable, originated in 2024 14
IPL [Member]  
Financing Receivable, Credit Quality Indicator [Line Items]  
Gross write-offs for accounts receivable, originated in 2023 8
Gross write-offs for accounts receivable, originated in 2024 9
WPL [Member]  
Financing Receivable, Credit Quality Indicator [Line Items]  
Gross write-offs for accounts receivable, originated in 2023 4
Gross write-offs for accounts receivable, originated in 2024 $ 5
v3.25.0.1
Receivables (Maximum And Average Outstanding Cash Proceeds) (Details) - IPL [Member] - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Maximum [Member]      
Receivables [Line Items]      
Outstanding aggregate cash proceeds (based on daily outstanding balances) $ 110 $ 110 $ 80
Average [Member]      
Receivables [Line Items]      
Outstanding aggregate cash proceeds (based on daily outstanding balances) $ 31 $ 51 $ 14
v3.25.0.1
Receivables (Receivables Sold Under The Agreement) (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Receivables [Line Items]    
Fair value of deferred proceeds $ 163 $ 216
IPL [Member]    
Receivables [Line Items]    
Fair value of deferred proceeds 163 216
Receivables Sold [Member] | IPL [Member]    
Receivables [Line Items]    
Customer accounts receivable 137 130
Unbilled utility revenues 108 98
Other receivables 0 1
Receivables sold to third party 245 229
Less: cash proceeds 70 1
Deferred proceeds 175 228
Less: allowance for expected credit losses 12 12
Fair value of deferred proceeds 163 216
Outstanding receivables past due $ 21 $ 22
v3.25.0.1
Receivables (Additional Attributes Of Receivables Sold Under The Agreement) (Details) - IPL [Member] - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Receivables [Line Items]      
Collections $ 2,090 $ 2,233 $ 2,302
Write-offs, net of recoveries $ 12 $ 12 $ 9
v3.25.0.1
Investments (Narrative) (Details)
Dec. 31, 2024
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%
v3.25.0.1
Investments (Unconsolidated Equity Investments) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Schedule of Equity Method Investments [Line Items]      
Carrying value $ 623 $ 585 $ 542
Equity (income) / loss (61) (61) (51)
ATC Holdings [Member]      
Schedule of Equity Method Investments [Line Items]      
Carrying value 415 386  
Equity (income) / loss $ (57) (49) (41)
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 $ 107 104  
Equity (income) / loss (6) (7) (5)
Corporate venture investments [Member]      
Schedule of Equity Method Investments [Line Items]      
Carrying value 78 74  
Equity (income) / loss 3 (2) (3)
Other [Member]      
Schedule of Equity Method Investments [Line Items]      
Carrying value 23 21  
Equity (income) / loss (1) (3) (2)
Total [Member]      
Schedule of Equity Method Investments [Line Items]      
Carrying value 623 585  
Equity (income) / loss $ (61) $ (61) $ (51)
v3.25.0.1
Investments (Summary Financial Information) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Revenues $ 3,981 $ 4,027 $ 4,205
Current assets 1,184 1,272  
Current liabilities 2,715 2,304  
Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]      
Revenues 1,005 898 813
Operating income 433 384 350
Net income 434 370 $ 675
Current assets 223 221  
Non-current assets 9,930 9,032  
Current liabilities 524 528  
Non-current liabilities 3,933 3,584  
Noncontrolling interest $ 221 $ 259  
v3.25.0.1
Common Equity (Narrative) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Schedule of Common Equity [Line Items]      
Shares available for issuance under the 2020 OIP, Shareowner Direct Plan and 401(k) Savings Plan (in shares) 12,000,000    
Proceeds from issuance of common stock, net $ 23 $ 246 $ 25
At-the-market Offering Program [Member]      
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) 0 4,372,561 0
Fees and commissions from issuance of common stock   $ 2  
At-the-market Offering Program [Member] | Maximum [Member]      
Schedule of Common Equity [Line Items]      
Proceeds from issuance of common stock, net   $ 225  
v3.25.0.1
Common Equity (Common Share Activity) (Details) - shares
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Common Stock Oustanding [Roll Forward]      
Shares outstanding, January 1 (in shares) 256,096,848 251,134,966 250,474,529
Common stock issued during the period, Shareowner Direct Plan (in shares) 439,107 454,987 437,669
Common stock issued during the period, Equity-based compensation plans (in shares) 154,267 134,334 222,768
Shares outstanding, December 31 (in shares) 256,690,222 256,096,848 251,134,966
At-the-market Offering Program [Member]      
Common Stock Oustanding [Roll Forward]      
Common stock issued during the period, At-the-market offering program (in shares) 0 4,372,561 0
v3.25.0.1
Debt (Narrative) (Details)
 12 Months Ended
Dec. 31, 2024
USD ($)
Integer
$ / shares
shares
Dec. 31, 2025
USD ($)
Dec. 31, 2023
USD ($)
Debt Instrument [Line Items]      
Line of credit facility, current borrowing capacity $ 1,300,000,000    
Long-term debt 9,925,000,000   $ 9,109,000,000
Current maturities of long-term debt 1,171,000,000   809,000,000
Long-term debt, fair value $ 9,577,000,000   8,677,000,000
Convertible Debt [Member]      
Debt Instrument [Line Items]      
Trading days | Integer 20    
Trading days consecutive | Integer 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 | Integer 5    
Trading days consecutive | Integer 10    
Principal amount of Notes conversion rate applied to $ 1,000    
Initial conversion ratio 15.5461    
Initial conversion price | $ / shares $ 64.32    
Fundamental change repurchase conversion price, percent 100.00%    
Current maturities of long-term debt $ 571,000,000    
Long-term debt, carrying value     568,000,000
Unamortized debt issuance costs 4,000,000   7,000,000
Long-term debt, fair value $ 591,000,000   572,000,000
Shares included in diluted earnings per share (in shares) | shares 0    
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%    
Parent Company [Member]      
Debt Instrument [Line Items]      
Line of credit facility, current borrowing capacity $ 600,000,000    
Current maturities of long-term debt 571,000,000   0
IPL [Member]      
Debt Instrument [Line Items]      
Line of credit facility, current borrowing capacity 300,000,000    
Long-term debt 4,125,000,000   3,975,000,000
Current maturities of long-term debt 300,000,000   500,000,000
Long-term debt, fair value 3,736,000,000   3,664,000,000
WPL [Member]      
Debt Instrument [Line Items]      
Line of credit facility, current borrowing capacity 400,000,000    
Long-term debt 3,400,000,000   3,100,000,000
Current maturities of long-term debt 0   0
Long-term debt, fair value $ 3,170,000,000   $ 2,933,000,000
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  
v3.25.0.1
Debt (Credit Facilities) (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Commercial paper and borrowings under the single credit facility:    
Amount outstanding $ 558.0 $ 475.0
Weighted average interest rates 4.50% 5.50%
Available credit facility capacity $ 742.0 $ 525.0
IPL [Member]    
Commercial paper and borrowings under the single credit facility:    
Amount outstanding $ 50.0 0.0
Weighted average interest rates 4.60%  
Available credit facility capacity $ 250.0 150.0
WPL [Member]    
Commercial paper and borrowings under the single credit facility:    
Amount outstanding $ 183.0 $ 318.0
Weighted average interest rates 4.50% 5.40%
Available credit facility capacity $ 217.0 $ 82.0
v3.25.0.1
Debt (Other Short-Term Borrowings) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Debt Instrument [Line Items]    
Maximum amount outstanding (based on daily outstanding balances) $ 632 $ 793
Average amount outstanding (based on daily outstanding balances) $ 327 $ 386
Weighted average interest rates 5.30% 5.20%
IPL [Member]    
Debt Instrument [Line Items]    
Maximum amount outstanding (based on daily outstanding balances) $ 80 $ 70
Average amount outstanding (based on daily outstanding balances) $ 1 $ 2
Weighted average interest rates 5.10% 5.30%
WPL [Member]    
Debt Instrument [Line Items]    
Maximum amount outstanding (based on daily outstanding balances) $ 390 $ 349
Average amount outstanding (based on daily outstanding balances) $ 70 $ 157
Weighted average interest rates 5.40% 5.10%
v3.25.0.1
Debt (Long-term Debt) (Details) - USD ($)
$ in Millions
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Debt Instrument [Line Items]      
Long-term debt   $ 9,925 $ 9,109
Current maturities   (1,171) (809)
Unamortized debt issuance costs   (55) (54)
Unamortized debt (discount) and premium, net   (22) (21)
Long-term debt, net   8,677 8,225
Senior Debentures [Member]      
Debt Instrument [Line Items]      
Long-term debt   4,125 3,975
Senior Debentures [Member] | 3.4% senior debenture, due 2025 [Member]      
Debt Instrument [Line Items]      
Long-term debt   $ 250 $ 250
Interest rate, percent   3.40% 3.40%
Senior Debentures [Member] | 5.5% senior debenture, due 2025 [Member]      
Debt Instrument [Line Items]      
Long-term debt   $ 50 $ 50
Interest rate, percent   5.50% 5.50%
Senior Debentures [Member] | 4.1% senior debenture, due 2028 [Member]      
Debt Instrument [Line Items]      
Long-term debt   $ 500 $ 500
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 $ 300
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 $ 400
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 $ 300
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 $ 100
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  
Interest rate, percent   4.95%  
Senior Debentures [Member] | 6.3% senior debenture, due 2034 [Member]      
Debt Instrument [Line Items]      
Long-term debt   $ 125 $ 125
Interest rate, percent   6.30% 6.30%
Senior Debentures [Member] | 6.25% senior debenture, due 2039 [Member]      
Debt Instrument [Line Items]      
Long-term debt   $ 300 $ 300
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 $ 250
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 $ 300
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 $ 300
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 $ 300
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  
Interest rate, percent   5.45%  
Senior Debentures [Member] | 3.25% senior debenture, retired in 2024      
Debt Instrument [Line Items]      
Long-term debt     $ 500
Interest rate, percent     3.25%
Debentures [Member]      
Debt Instrument [Line Items]      
Long-term debt   $ 3,400 $ 3,100
Debentures [Member] | 3.05% debenture, due 2027 [Member]      
Debt Instrument [Line Items]      
Long-term debt   $ 300 $ 300
Interest rate, percent   3.05% 3.05%
Debentures [Member] | 3% debenture, due 2029 [Member]      
Debt Instrument [Line Items]      
Long-term debt   $ 350 $ 350
Interest rate, percent   3.00% 3.00%
Debentures [Member] | 1.95% debenture, due 2031 [Member]      
Debt Instrument [Line Items]      
Long-term debt   $ 300 $ 300
Interest rate, percent   1.95% 1.95%
Debentures [Member] | 3.95% debenture, due 2032 [Member]      
Debt Instrument [Line Items]      
Long-term debt   $ 600 $ 600
Interest rate, percent   3.95% 3.95%
Debentures [Member] | 4.95% debenture, due 2033 [Member]      
Debt Instrument [Line Items]      
Long-term debt   $ 300 $ 300
Interest rate, percent   4.95% 4.95%
Debentures [Member] | 5.375% debenture, due 2034 [Member]      
Debt Instrument [Line Items]      
Long-term debt   $ 300  
Interest rate, percent   5.375%  
Debentures [Member] | 6.25% debenture, due 2034 [Member]      
Debt Instrument [Line Items]      
Long-term debt   $ 100 $ 100
Interest rate, percent   6.25% 6.25%
Debentures [Member] | 6.375% debenture, due 2037 [Member]      
Debt Instrument [Line Items]      
Long-term debt   $ 300 $ 300
Interest rate, percent   6.375% 6.375%
Debentures [Member] | 7.6% debenture, due 2038 [Member]      
Debt Instrument [Line Items]      
Long-term debt   $ 250 $ 250
Interest rate, percent   7.60% 7.60%
Debentures [Member] | 4.1% debenture, due 2044 [Member]      
Debt Instrument [Line Items]      
Long-term debt   $ 250 $ 250
Interest rate, percent   4.10% 4.10%
Debentures [Member] | 3.65% debenture, due 2050 [Member]      
Debt Instrument [Line Items]      
Long-term debt   $ 350 $ 350
Interest rate, percent   3.65% 3.65%
Senior Notes [Member] | 3.875% senior notes, due 2026 [Member]      
Debt Instrument [Line Items]      
Long-term debt   $ 575 $ 575
Interest rate, percent   3.875% 3.875%
Other Long Term Debt [Member]      
Debt Instrument [Line Items]      
Long-term debt   $ 2,400 $ 2,034
IPL [Member]      
Debt Instrument [Line Items]      
Long-term debt   4,125 3,975
Current maturities   (300) (500)
Unamortized debt issuance costs   (25) (21)
Unamortized debt (discount) and premium, net   (10) (9)
Long-term debt, net   3,790 3,445
IPL [Member] | Senior Debentures [Member]      
Debt Instrument [Line Items]      
Long-term debt   4,125 3,975
IPL [Member] | Senior Debentures [Member] | 3.4% senior debenture, due 2025 [Member]      
Debt Instrument [Line Items]      
Long-term debt   $ 250 $ 250
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   $ 50 $ 50
Interest rate, percent   5.50% 5.50%
IPL [Member] | Senior Debentures [Member] | 4.1% senior debenture, due 2028 [Member]      
Debt Instrument [Line Items]      
Long-term debt   $ 500 $ 500
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 $ 300
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 $ 400
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 $ 300
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 $ 100
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  
Interest rate, percent   4.95%  
IPL [Member] | Senior Debentures [Member] | 6.3% senior debenture, due 2034 [Member]      
Debt Instrument [Line Items]      
Long-term debt   $ 125 $ 125
Interest rate, percent   6.30% 6.30%
IPL [Member] | Senior Debentures [Member] | 6.25% senior debenture, due 2039 [Member]      
Debt Instrument [Line Items]      
Long-term debt   $ 300 $ 300
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 $ 250
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 $ 300
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 $ 300
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 $ 300
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  
Interest rate, percent   5.45%  
IPL [Member] | Senior Debentures [Member] | 3.25% senior debenture, retired in 2024      
Debt Instrument [Line Items]      
Long-term debt     $ 500
Interest rate, percent     3.25%
WPL [Member]      
Debt Instrument [Line Items]      
Long-term debt   $ 3,400 $ 3,100
Current maturities   0 0
Unamortized debt issuance costs   (20) (19)
Unamortized debt (discount) and premium, net   (10) (11)
Long-term debt, net   3,370 3,070
WPL [Member] | Debentures [Member]      
Debt Instrument [Line Items]      
Long-term debt   3,400 3,100
WPL [Member] | Debentures [Member] | 3.05% debenture, due 2027 [Member]      
Debt Instrument [Line Items]      
Long-term debt   $ 300 $ 300
Interest rate, percent   3.05% 3.05%
WPL [Member] | Debentures [Member] | 3% debenture, due 2029 [Member]      
Debt Instrument [Line Items]      
Long-term debt   $ 350 $ 350
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 $ 300
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 $ 600
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 $ 300
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  
Interest rate, percent   5.375%  
WPL [Member] | Debentures [Member] | 6.25% debenture, due 2034 [Member]      
Debt Instrument [Line Items]      
Long-term debt   $ 100 $ 100
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 $ 300
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 $ 250
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 $ 250
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 $ 350
Interest rate, percent   3.65% 3.65%
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   $ 300  
Interest rate, percent   6.00%  
Alliant Energy Finance, LLC [Member] | Term Loan Credit Agreement [Member] | Term loan credit agreement through March 2025, Variable Rate [Member] | Forecast [Member]      
Debt Instrument [Line Items]      
Long-term debt $ 100    
Alliant Energy Finance, LLC [Member] | Term Loan Credit Agreement [Member] | Term loan credit agreement, retired in 2024, Variable Rate [Member]      
Debt Instrument [Line Items]      
Long-term debt     $ 300
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 $ 200
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  
Interest rate, percent   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 $ 300
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 $ 300
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 $ 350
Interest rate, percent   3.60% 3.60%
Sheboygan Power, LLC [Member] | Senior Secured Notes [Member] | 5.06% senior secured notes, retired in 2024 [Member]      
Debt Instrument [Line Items]      
Long-term debt     $ 9
Interest rate, percent     5.06%
v3.25.0.1
Debt (Schedule Of Debt Maturities) (Details)
$ in Millions
Dec. 31, 2024
USD ($)
2025 $ 600
2026 775
2027 675
2028 800
2029 950
Parent Company [Member]  
2025 0
2026 575
2027 0
2028 0
2029 0
IPL [Member]  
2025 300
2026 0
2027 0
2028 500
2029 300
WPL [Member]  
2025 0
2026 0
2027 300
2028 0
2029 350
Alliant Energy Finance, LLC [Member]  
2025 300
2026 200
2027 375
2028 300
2029 $ 300
v3.25.0.1
Leases (Narrative) (Details)
 12 Months Ended
Dec. 31, 2024
lease_renewal_period_option
Sheboygan Falls Energy Facility [Member] | WPL [Member]  
Leases [Line Items]  
Finance lease, renewal options (in number of renewal periods) 0
v3.25.0.1
Leases (Operating Leases) (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Leases [Line Items]    
Operating leases assets, Property, plant and equipment, net $ 22 $ 23
Operating leases liabilities, Other current liabilities 2 2
Operating leases liabilities, Other liabilities 20 21
Operating leases liabilities, Total $ 22 $ 23
Operating leases, Weighted average remaining lease term 11 years 12 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 $ 12 $ 13
Operating leases liabilities, Other current liabilities 1 1
Operating leases liabilities, Other liabilities 11 12
Operating leases liabilities, Total $ 12 $ 13
Operating leases, Weighted average remaining lease term 11 years 12 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 12 years 12 years
Operating leases, Weighted average discount rate, percent 4.00% 4.00%
v3.25.0.1
Leases (Finance Lease) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Leases [Line Items]      
Finance lease assets, Property, plant and equipment, net $ 189 $ 172  
Finance lease liabilities, Other current liabilities 0 0  
Finance lease liabilities, Other liabilities 189 172  
Finance lease liabilities, Total $ 189 $ 172  
Finance lease, Remaining lease term 31 years 33 years  
Finance lease, Discount rate, percent 5.00% 5.00%  
Finance lease, Depreciation expense $ 0 $ 1 $ 0
Finance lease, Interest expense 8 6 3
Finance lease, Total expense $ 8 $ 7 3
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  
Sheboygan Falls Energy Facility [Member]      
Leases [Line Items]      
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 $ 189 $ 172  
Finance lease liabilities, Other current liabilities 0 0  
Finance lease liabilities, Other liabilities $ 189 $ 172  
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  
IPL [Member]      
Leases [Line Items]      
Finance lease assets, Property, plant and equipment, net $ 53 $ 33  
Finance lease liabilities, Other current liabilities 0 0  
Finance lease liabilities, Other liabilities 53 33  
Finance lease liabilities, Total $ 53 $ 33  
Finance lease, Remaining lease term 28 years 29 years  
Finance lease, Discount rate, percent 5.00% 5.00%  
Finance lease, Depreciation expense $ 0 $ 0 0
Finance lease, Interest expense 2 1 0
Finance lease, Total expense 2 1 0
IPL [Member] | Leased land for solar generation [Member]      
Leases [Line Items]      
Finance lease assets, Property, plant and equipment, net 53 33  
Finance lease liabilities, Other current liabilities 0 0  
Finance lease liabilities, Other liabilities 53 33  
WPL [Member]      
Leases [Line Items]      
Finance lease assets, Property, plant and equipment, net 210 218  
Finance lease liabilities, Other current liabilities 7 11  
Finance lease liabilities, Other liabilities 207 217  
Finance lease liabilities, Total $ 214 $ 228  
Finance lease, Remaining lease term 28 years 27 years  
Finance lease, Discount rate, percent 5.00% 5.00%  
Finance lease, Depreciation expense $ 4 $ 6 6
Finance lease, Interest expense 10 8 7
Finance lease, Total expense 14 14 $ 13
WPL [Member] | Sheboygan Falls Energy Facility [Member]      
Leases [Line Items]      
Finance lease assets, Property, plant and equipment, net 74 79  
Finance lease liabilities, Other current liabilities 7 11  
Finance lease liabilities, Other liabilities 71 78  
WPL [Member] | Leased land for solar generation [Member]      
Leases [Line Items]      
Finance lease assets, Property, plant and equipment, net 136 139  
Finance lease liabilities, Other current liabilities 0 0  
Finance lease liabilities, Other liabilities $ 136 $ 139  
v3.25.0.1
Leases (Liabilities Arising from Obtaining Leased Assets (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Leases [Line Items]    
Finance lease liabilities arising from obtaining leased assets $ 20 $ 34
IPL [Member]    
Leases [Line Items]    
Finance lease liabilities arising from obtaining leased assets 20 33
WPL [Member]    
Leases [Line Items]    
Finance lease liabilities arising from obtaining leased assets $ 0 $ 71
v3.25.0.1
Leases (Expected Maturities of Operating and Finance Lease Liabilities (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Leases [Line Items]    
Operating Leases Liability, 2025 $ 3  
Operating Leases Liability, 2026 3  
Operating Leases Liability, 2027 3  
Operating Leases Liability, 2028 3  
Operating Leases Liability, 2029 2  
Operating Leases Liability, Thereafter 14  
Operating Leases Liability, Total 28  
Operating Leases Liability, Less: amount representing interest 6  
Operating Leases Liability, Present value of minimum lease payments 22 $ 23
Finance Lease Liability, 2025 9  
Finance Lease Liability, 2026 9  
Finance Lease Liability, 2027 9  
Finance Lease Liability, 2028 10  
Finance Lease Liability, 2029 10  
Finance Lease Liability, Thereafter 337  
Finance Lease Liability, Total 384  
Finance Lease Liability, Less: amount representing interest 195  
Finance Lease Liability, Present value of minimum lease payments 189 172
IPL [Member]    
Leases [Line Items]    
Operating Leases Liability, 2025 2  
Operating Leases Liability, 2026 2  
Operating Leases Liability, 2027 1  
Operating Leases Liability, 2028 1  
Operating Leases Liability, 2029 1  
Operating Leases Liability, Thereafter 8  
Operating Leases Liability, Total 15  
Operating Leases Liability, Less: amount representing interest 3  
Operating Leases Liability, Present value of minimum lease payments 12 13
Finance Lease Liability, 2025 3  
Finance Lease Liability, 2026 3  
Finance Lease Liability, 2027 3  
Finance Lease Liability, 2028 3  
Finance Lease Liability, 2029 3  
Finance Lease Liability, Thereafter 92  
Finance Lease Liability, Total 107  
Finance Lease Liability, Less: amount representing interest 54  
Finance Lease Liability, Present value of minimum lease payments 53 33
WPL [Member]    
Leases [Line Items]    
Operating Leases Liability, 2025 1  
Operating Leases Liability, 2026 1  
Operating Leases Liability, 2027 1  
Operating Leases Liability, 2028 1  
Operating Leases Liability, 2029 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, 2025 17  
Finance Lease Liability, 2026 13  
Finance Lease Liability, 2027 13  
Finance Lease Liability, 2028 13  
Finance Lease Liability, 2029 13  
Finance Lease Liability, Thereafter 324  
Finance Lease Liability, Total 393  
Finance Lease Liability, Less: amount representing interest 179  
Finance Lease Liability, Present value of minimum lease payments $ 214 $ 228
v3.25.0.1
Disaggregation of Revenues (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Disaggregation of Revenue [Line Items]      
Revenues $ 3,981 $ 4,027 $ 4,205
IPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 2,046 2,110 2,256
WPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 1,845 1,827 1,856
Electric [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 3,372 3,345 3,421
Electric [Member] | IPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 1,747 1,761 1,859
Electric [Member] | WPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 1,625 1,584 1,562
Electric [Member] | Retail - Residential [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 1,236 1,220 1,233
Electric [Member] | Retail - Residential [Member] | IPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 640 641 673
Electric [Member] | Retail - Residential [Member] | WPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 596 579 560
Electric [Member] | Retail - Commercial [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 821 820 821
Electric [Member] | Retail - Commercial [Member] | IPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 525 519 536
Electric [Member] | Retail - Commercial [Member] | WPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 296 301 285
Electric [Member] | Retail - Industrial [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 952 968 965
Electric [Member] | Retail - Industrial [Member] | IPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 497 501 538
Electric [Member] | Retail - Industrial [Member] | WPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 455 467 427
Electric [Member] | Wholesale [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 200 213 233
Electric [Member] | Wholesale [Member] | IPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 61 62 64
Electric [Member] | Wholesale [Member] | WPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 139 151 169
Electric [Member] | Other [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 163 124 169
Electric [Member] | Other [Member] | IPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 24 38 48
Electric [Member] | Other [Member] | WPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 139 86 121
Gas [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 465 540 642
Gas [Member] | IPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 250 300 351
Gas [Member] | WPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 215 240 291
Gas [Member] | Retail - Residential [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 275 316 371
Gas [Member] | Retail - Residential [Member] | IPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 148 176 202
Gas [Member] | Retail - Residential [Member] | WPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 127 140 169
Gas [Member] | Retail - Commercial [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 133 163 197
Gas [Member] | Retail - Commercial [Member] | IPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 68 86 101
Gas [Member] | Retail - Commercial [Member] | WPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 65 77 96
Gas [Member] | Retail - Industrial [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 11 16 20
Gas [Member] | Retail - Industrial [Member] | IPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 7 11 14
Gas [Member] | Retail - Industrial [Member] | WPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 4 5 6
Gas [Member] | Other [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 46 45 54
Gas [Member] | Other [Member] | IPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 27 27 34
Gas [Member] | Other [Member] | WPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 19 18 20
Other Utility [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 54 52 49
Other Utility [Member] | IPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 49 49 46
Other Utility [Member] | WPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 5 3 3
Other Utility [Member] | Other [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 14 7 10
Other Utility [Member] | Other [Member] | IPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 9 4 7
Other Utility [Member] | Other [Member] | WPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 5 3 3
Other Utility [Member] | Steam [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 40 45 39
Other Utility [Member] | Steam [Member] | IPL [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 40 45 39
Non-Utility and Other [Member]      
Disaggregation of Revenue [Line Items]      
Revenues 90 90 93
Non-Utility and Other [Member] | Other [Member]      
Disaggregation of Revenue [Line Items]      
Revenues $ 90 $ 90 $ 93
v3.25.0.1
Income Taxes (Narrative) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2026
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Income Tax [Line Items]        
Asset valuation charge for IPL's Lansing Generating Station   $ 60 $ 0 $ 0
State income tax rate, percent   (1.00%) 2.00% 3.00%
Reduction of tax-related regulatory assets   $ 70 $ 24 $ (108)
Income tax expense (benefit)   (114) 4 22
Tax-related [Member]        
Income Tax [Line Items]        
Reduction of tax-related regulatory assets   26 74 77
Income tax expense (benefit)   11 10 8
IPL [Member]        
Income Tax [Line Items]        
Asset valuation charge for IPL's Lansing Generating Station   $ 60 $ 0 $ 0
State income tax rate, percent   (12.00%) (2.00%) (2.00%)
Reduction of tax-related regulatory assets   $ (2) $ 58 $ 56
Income tax expense (benefit)   (129) (58) (50)
IPL [Member] | Tax-related [Member]        
Income Tax [Line Items]        
Reduction of tax-related regulatory assets   $ 26 $ 74 $ 77
WPL [Member]        
Income Tax [Line Items]        
State income tax rate, percent   6.00% 5.00% 6.00%
Reduction of tax-related regulatory assets   $ 72 $ (34) $ (163)
Income tax expense (benefit)   $ 11 $ 60 $ 66
State [Member]        
Income Tax [Line Items]        
State income tax rate, percent   7.10% 8.40% 9.80%
State [Member] | Forecast [Member]        
Income Tax [Line Items]        
State income tax rate, percent 5.50%      
v3.25.0.1
Income Taxes (Schedule Of Components Of Income Tax) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Current tax expense (benefit):      
Federal $ 13 $ (3) $ 7
State (10) (6) 2
Deferred tax expense (benefit):      
Federal 60 100 109
State 15 36 28
Production tax credits (177) (121) (123)
Investment tax credits (15) (1) (1)
Provision recorded as a change in accrued interest 0 (1) 0
Income tax expense (benefit) (114) 4 22
IPL [Member]      
Current tax expense (benefit):      
Federal (19) (44) (29)
State (19) (21) (8)
Deferred tax expense (benefit):      
Federal 38 87 91
State (17) 17 1
Production tax credits (108) (95) (105)
Investment tax credits (4) (1) 0
Provision recorded as a change in accrued interest 0 (1) 0
Income tax expense (benefit) (129) (58) (50)
WPL [Member]      
Current tax expense (benefit):      
Federal 37 48 46
State 23 25 16
Deferred tax expense (benefit):      
Federal 24 10 10
State 7 3 12
Production tax credits (69) (26) (18)
Investment tax credits (11) 0 0
Provision recorded as a change in accrued interest 0 0 0
Income tax expense (benefit) $ 11 $ 60 $ 66
v3.25.0.1
Income Taxes (Schedule Of Effective Income Tax Rates) (Details)
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Effective Tax Rate [Line Items]      
Statutory federal income tax rate 21.00% 21.00% 21.00%
State income taxes, net of federal benefits (1.00%) 2.00% 3.00%
Production tax credits (31.00%) (17.00%) (18.00%)
Investment tax credits (3.00%) 0.00% 0.00%
Amortization of excess deferred taxes (2.00%) (2.00%) (2.00%)
Effect of rate-making on property-related differences (5.00%) (4.00%) (1.00%)
Other items, net 1.00% 1.00% 0.00%
Overall income tax rate (20.00%) 1.00% 3.00%
IPL [Member]      
Effective Tax Rate [Line Items]      
Statutory federal income tax rate 21.00% 21.00% 21.00%
State income taxes, net of federal benefits (12.00%) (2.00%) (2.00%)
Production tax credits (46.00%) (31.00%) (34.00%)
Investment tax credits (2.00%) 0.00% 0.00%
Amortization of excess deferred taxes (5.00%) (2.00%) (2.00%)
Effect of rate-making on property-related differences (10.00%) (5.00%) (1.00%)
Other items, net (1.00%) 0.00% 2.00%
Overall income tax rate (55.00%) (19.00%) (16.00%)
WPL [Member]      
Effective Tax Rate [Line Items]      
Statutory federal income tax rate 21.00% 21.00% 21.00%
State income taxes, net of federal benefits 6.00% 5.00% 6.00%
Production tax credits (20.00%) (7.00%) (5.00%)
Investment tax credits (3.00%) 0.00% 0.00%
Amortization of excess deferred taxes 0.00% (2.00%) (3.00%)
Effect of rate-making on property-related differences (1.00%) (3.00%) (2.00%)
Other items, net 0.00% 1.00% 0.00%
Overall income tax rate 3.00% 15.00% 17.00%
v3.25.0.1
Income Taxes (Schedule Of Deferred Tax Assets And Liabilities) (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Deferred tax liabilities, property $ 2,596 $ 2,453
Deferred tax liabilities, other 178 213
Total deferred tax liabilities 2,909 2,793
Deferred tax assets, federal credit carryforwards 605 649
Deferred tax assets, net operating losses carryforwards - state 20 26
Deferred tax assets, other 98 79
Subtotal deferred tax assets 723 754
Deferred tax assets, valuation allowances (2) (3)
Total deferred tax assets 721 751
Total deferred tax liabilities, net 2,188 2,042
IPL [Member]    
Deferred tax liabilities, property 1,521 1,415
Deferred tax liabilities, other 120 157
Total deferred tax liabilities 1,641 1,572
Deferred tax assets, federal credit carryforwards 426 449
Deferred tax assets, net operating losses carryforwards - state 1 1
Deferred tax assets, other 37 32
Subtotal deferred tax assets 464 482
Deferred tax assets, valuation allowances (2) (1)
Total deferred tax assets 462 481
Total deferred tax liabilities, net 1,179 1,091
WPL [Member]    
Deferred tax liabilities, property 999 972
Deferred tax liabilities, other 66 64
Total deferred tax liabilities 1,065 1,036
Deferred tax assets, federal credit carryforwards 166 191
Deferred tax assets, net operating losses carryforwards - state 0 0
Deferred tax assets, other 34 19
Subtotal deferred tax assets 200 210
Deferred tax assets, valuation allowances 0 (1)
Total deferred tax assets 200 209
Total deferred tax liabilities, net 865 827
ATC Holdings [Member]    
Deferred tax liabilities, ATC Holdings 135 127
ATC Holdings [Member] | IPL [Member]    
Deferred tax liabilities, ATC Holdings 0 0
ATC Holdings [Member] | WPL [Member]    
Deferred tax liabilities, ATC Holdings $ 0 $ 0
v3.25.0.1
Income Taxes (Summary Of Tax Credit Carryforwards) (Details)
$ in Millions
Dec. 31, 2024
USD ($)
State [Member]  
Tax carryforwards, net operating losses $ 338
State [Member] | IPL [Member]  
Tax carryforwards, net operating losses 7
State [Member] | WPL [Member]  
Tax carryforwards, net operating losses 1
Federal [Member]  
Tax carryforwards, tax credits 605
Federal [Member] | IPL [Member]  
Tax carryforwards, tax credits 426
Federal [Member] | WPL [Member]  
Tax carryforwards, tax credits $ 166
v3.25.0.1
Income Taxes (Schedule Of Uncertain Tax Positions) (Details)
 12 Months Ended
Dec. 31, 2024
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
v3.25.0.1
Benefit Plans (Narrative) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
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% 8.00%  
Unrecognized compensation cost $ 10    
Percentage of base salary and short-term cash incentive compensation 100.00%    
Carrying value of deferred compensation obligations $ 23 $ 21  
Restructuring and voluntary employee separation package pre-tax charge $ 676 $ 675 $ 704
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 $ 5    
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 5    
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) 564,743    
v3.25.0.1
Benefit Plans (Assumptions Used To Measure Benefit Plans) (Details)
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Pension Plans, Defined Benefit [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate for benefit obligations 5.65% 5.36% 5.54%
Discount rate for net periodic cost 5.36% 5.54% 2.91%
Expected rate of return on plan assets 7.73% 7.80% 7.80%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan 6.24% 10.75% 9.22%
Pension Plans, Defined Benefit [Member] | IPL [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate for benefit obligations 5.66% 5.35% 5.55%
Discount rate for net periodic cost 5.35% 5.55% 2.94%
Expected rate of return on plan assets 7.60% 7.80% 7.80%
Rate of compensation increase 3.75% 3.30% 3.30%
Pension Plans, Defined Benefit [Member] | WPL [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate for benefit obligations 5.66% 5.35% 5.54%
Discount rate for net periodic cost 5.35% 5.54% 2.94%
Expected rate of return on plan assets 7.80% 7.80% 7.80%
Rate of compensation increase 3.50% 3.30% 3.30%
Other Postretirement Benefits Plans [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate for benefit obligations 5.62% 5.40% 5.53%
Discount rate for net periodic cost 5.40% 5.53% 2.81%
Expected rate of return on plan assets 6.22% 6.50% 6.40%
Other Postretirement Benefits Plans [Member] | IPL [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate for benefit obligations 5.61% 5.40% 5.53%
Discount rate for net periodic cost 5.40% 5.53% 2.80%
Expected rate of return on plan assets 6.60% 6.90% 6.50%
Other Postretirement Benefits Plans [Member] | WPL [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate for benefit obligations 5.61% 5.40% 5.53%
Discount rate for net periodic cost 5.40% 5.53% 2.79%
Expected rate of return on plan assets 5.61% 5.65% 5.49%
Minimum [Member] | Pension Plans, Defined Benefit [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Rate of compensation increase 3.50% 3.30% 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%
v3.25.0.1
Benefit Plans (Net Periodic Benefit Costs) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]      
Pension settlement losses $ 3 $ (3) $ (6)
Defined Benefit Pension Plans [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Service cost 5 5 9
Interest cost 45 47 36
Expected return on plan assets (55) (53) (69)
Amortization of prior service cost (credit) (1) (1) (1)
Amortization of actuarial loss 24 28 32
Settlement losses 0 0 26
Total 18 26 33
Pension settlement losses     7
Other Postretirement Benefits Plans [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Service cost 2 2 3
Interest cost 8 9 6
Expected return on plan assets (5) (5) (5)
Amortization of prior service cost (credit) 0 0 0
Amortization of actuarial loss 0 1 2
Settlement losses 0 0 0
Total 5 7 6
IPL [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Pension settlement losses 12 (2) (6)
IPL [Member] | Defined Benefit Pension Plans [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Service cost 3 3 6
Interest cost 20 21 16
Expected return on plan assets (26) (26) (31)
Amortization of actuarial loss 9 11 13
Settlement losses 0 0 13
Total 6 9 17
Pension settlement losses     7
IPL [Member] | Other Postretirement Benefits Plans [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Service cost 1 1 1
Interest cost 3 3 2
Expected return on plan assets (4) (3) (4)
Amortization of actuarial loss 0 1 1
Settlement losses 0 0 0
Total 0 2 0
WPL [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Pension settlement losses (8) 3 1
WPL [Member] | Defined Benefit Pension Plans [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Service cost 2 2 3
Interest cost 20 20 16
Expected return on plan assets (23) (22) (31)
Amortization of actuarial loss 11 13 15
Settlement losses 0 0 13
Total 10 13 16
WPL [Member] | Other Postretirement Benefits Plans [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Service cost 1 1 1
Interest cost 3 3 2
Expected return on plan assets (1) (1) (1)
Amortization of actuarial loss 0 1 2
Settlement losses 0 0 0
Total $ 3 $ 4 $ 4
v3.25.0.1
Benefit Plans (Funded Status of Benefits Plans) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Pension Plans, Defined Benefit [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Projected benefit obligations $ 841 $ 876  
Change in benefit obligation:      
Net benefit obligation at January 1 876 875  
Service cost 5 5 $ 9
Interest cost 45 47 36
Plan participants' contributions 0 0  
Actuarial (gain) loss (19) 23  
Gross benefits paid (66) (74)  
Net benefit obligation at December 31 841 876 875
Change in plan assets:      
Fair value of plan assets at January 1 732 706  
Actual return on plan assets 38 86  
Employer contributions 11 14  
Plan participants' contributions 0 0  
Gross benefits paid (66) (74)  
Fair value of plan assets at December 31 715 732 706
Under funded status at December 31 (126) (144)  
Fair value of plan assets 715 732  
Pension Plans, Defined Benefit [Member] | IPL [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Projected benefit obligations 372 387  
Change in benefit obligation:      
Net benefit obligation at January 1 387 389  
Service cost 3 3 6
Interest cost 20 21 16
Plan participants' contributions 0 0  
Actuarial (gain) loss (8) 9  
Gross benefits paid (30) (35)  
Net benefit obligation at December 31 372 387 389
Change in plan assets:      
Fair value of plan assets at January 1 352 344  
Actual return on plan assets 18 42  
Employer contributions 0 1  
Plan participants' contributions 0 0  
Gross benefits paid (30) (35)  
Fair value of plan assets at December 31 340 352 344
Under funded status at December 31 (32) (35)  
Fair value of plan assets 340 352  
Pension Plans, Defined Benefit [Member] | WPL [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Projected benefit obligations 365 381  
Change in benefit obligation:      
Net benefit obligation at January 1 381 381  
Service cost 2 2 3
Interest cost 20 20 16
Plan participants' contributions 0 0  
Actuarial (gain) loss (8) 10  
Gross benefits paid (30) (32)  
Net benefit obligation at December 31 365 381 381
Change in plan assets:      
Fair value of plan assets at January 1 306 291  
Actual return on plan assets 17 35  
Employer contributions 10 12  
Plan participants' contributions 0 0  
Gross benefits paid (30) (32)  
Fair value of plan assets at December 31 303 306 291
Under funded status at December 31 (62) (75)  
Fair value of plan assets 303 306  
Other Postretirement Benefits Plans [Member]      
Change in benefit obligation:      
Net benefit obligation at January 1 160 168  
Service cost 2 2 3
Interest cost 8 9 6
Plan participants' contributions 3 4  
Actuarial (gain) loss (7) (3)  
Gross benefits paid (18) (20)  
Net benefit obligation at December 31 148 160 168
Change in plan assets:      
Fair value of plan assets at January 1 83 83  
Actual return on plan assets 5 8  
Employer contributions 7 8  
Plan participants' contributions 3 4  
Gross benefits paid (18) (20)  
Fair value of plan assets at December 31 80 83 83
Under funded status at December 31 (68) (77)  
Other Postretirement Benefits Plans [Member] | IPL [Member]      
Change in benefit obligation:      
Net benefit obligation at January 1 65 68  
Service cost 1 1 1
Interest cost 3 3 2
Plan participants' contributions 1 2  
Actuarial (gain) loss (3) (1)  
Gross benefits paid (8) (8)  
Net benefit obligation at December 31 59 65 68
Change in plan assets:      
Fair value of plan assets at January 1 61 58  
Actual return on plan assets 4 7  
Employer contributions 1 2  
Plan participants' contributions 1 2  
Gross benefits paid (8) (8)  
Fair value of plan assets at December 31 59 61 58
Under funded status at December 31 0 (4)  
Other Postretirement Benefits Plans [Member] | WPL [Member]      
Change in benefit obligation:      
Net benefit obligation at January 1 61 65  
Service cost 1 1 1
Interest cost 3 3 2
Plan participants' contributions 1 2  
Actuarial (gain) loss (3) (2)  
Gross benefits paid (7) (8)  
Net benefit obligation at December 31 56 61 65
Change in plan assets:      
Fair value of plan assets at January 1 14 14  
Actual return on plan assets 0 1  
Employer contributions 5 5  
Plan participants' contributions 1 2  
Gross benefits paid (7) (8)  
Fair value of plan assets at December 31 13 14 $ 14
Under funded status at December 31 $ (43) $ (47)  
v3.25.0.1
Benefit Plans (Amounts Recognized On The Consolidated Balance Sheets) (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Amounts recognized on the balance sheets consist of:    
Pension and other benefit obligations $ (224) $ (249)
Pension Plans, Defined Benefit [Member]    
Amounts recognized on the balance sheets consist of:    
Non-current assets 0 0
Current liabilities (3) (2)
Pension and other benefit obligations (123) (142)
Net amounts recognized at December 31 (126) (144)
Amounts recognized in Regulatory Assets consist of:    
Net actuarial loss 312 337
Prior service credit (2) (2)
Net amount recognized at December 31 310 335
Other Postretirement Benefits Plans [Member]    
Amounts recognized on the balance sheets consist of:    
Non-current assets 17 14
Current liabilities (7) (8)
Pension and other benefit obligations (78) (83)
Net amounts recognized at December 31 (68) (77)
Amounts recognized in Regulatory Assets consist of:    
Net actuarial loss 4 11
Prior service credit 0 0
Net amount recognized at December 31 4 11
IPL [Member]    
Amounts recognized on the balance sheets consist of:    
Pension and other benefit obligations (46) (51)
IPL [Member] | Pension Plans, Defined Benefit [Member]    
Amounts recognized on the balance sheets consist of:    
Non-current assets 0 0
Current liabilities (1) 0
Pension and other benefit obligations (31) (35)
Net amounts recognized at December 31 (32) (35)
Amounts recognized in Regulatory Assets consist of:    
Net actuarial loss 126 135
Prior service credit (1) (1)
Net amount recognized at December 31 125 134
IPL [Member] | Other Postretirement Benefits Plans [Member]    
Amounts recognized on the balance sheets consist of:    
Non-current assets 13 10
Current liabilities (1) (1)
Pension and other benefit obligations (12) (13)
Net amounts recognized at December 31 0 (4)
Amounts recognized in Regulatory Assets consist of:    
Net actuarial loss 7 9
Prior service credit 0 0
Net amount recognized at December 31 7 9
WPL [Member]    
Amounts recognized on the balance sheets consist of:    
Pension and other benefit obligations (102) (121)
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 (62) (75)
Net amounts recognized at December 31 (62) (75)
Amounts recognized in Regulatory Assets consist of:    
Net actuarial loss 135 148
WPL [Member] | Other Postretirement Benefits Plans [Member]    
Amounts recognized on the balance sheets consist of:    
Non-current assets 4 4
Current liabilities (6) (6)
Pension and other benefit obligations (41) (45)
Net amounts recognized at December 31 (43) (47)
Amounts recognized in Regulatory Assets consist of:    
Net actuarial loss $ 0 $ 3
v3.25.0.1
Benefit Plans (Accumulated Benefit Obligations) (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Pension Plans, Defined Benefit [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Accumulated benefit obligations $ 824 $ 857
Plans with accumulated benefit obligations in excess of plan assets:    
Accumulated benefit obligations 824 857
Fair value of plan assets 715 732
Plans with projected benefit obligations in excess of plan assets:    
Projected benefit obligations 841 876
Fair value of plan assets 715 732
Other Postretirement Benefits Plans [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Accumulated benefit obligations 148 160
Plans with accumulated benefit obligations in excess of plan assets:    
Accumulated benefit obligations 148 160
Fair value of plan assets 80 83
IPL [Member] | Pension Plans, Defined Benefit [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Accumulated benefit obligations 362 377
Plans with accumulated benefit obligations in excess of plan assets:    
Accumulated benefit obligations 362 377
Fair value of plan assets 340 352
Plans with projected benefit obligations in excess of plan assets:    
Projected benefit obligations 372 387
Fair value of plan assets 340 352
IPL [Member] | Other Postretirement Benefits Plans [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Accumulated benefit obligations 59 65
Plans with accumulated benefit obligations in excess of plan assets:    
Accumulated benefit obligations   65
Fair value of plan assets   61
WPL [Member] | Pension Plans, Defined Benefit [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Accumulated benefit obligations 358 373
Plans with accumulated benefit obligations in excess of plan assets:    
Accumulated benefit obligations 358 373
Fair value of plan assets 303 306
Plans with projected benefit obligations in excess of plan assets:    
Projected benefit obligations 365 381
Fair value of plan assets 303 306
WPL [Member] | Other Postretirement Benefits Plans [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Accumulated benefit obligations 56 61
Plans with accumulated benefit obligations in excess of plan assets:    
Accumulated benefit obligations 56 61
Fair value of plan assets $ 13 $ 14
v3.25.0.1
Benefit Plans (Regulatory Assets) (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
IPL [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Regulatory assets $ 25 $ 28
WPL [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Regulatory assets $ 22 $ 24
v3.25.0.1
Benefit Plans (Estimated Future Funding) (Details) - Forecast [Member]
$ in Millions
Dec. 31, 2025
USD ($)
Defined Benefit Pension Plans [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Estimated funding for calendar year 2025 $ 20
Defined Benefit Pension Plans [Member] | IPL [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Estimated funding for calendar year 2025 1
Defined Benefit Pension Plans [Member] | WPL [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Estimated funding for calendar year 2025 14
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 $ 6
v3.25.0.1
Benefit Plans (Expected Benefit Payments) (Details)
$ in Millions
Dec. 31, 2024
USD ($)
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2025 $ 95
Expected benefit payments, 2026 91
Expected benefit payments, 2027 89
Expected benefit payments, 2028 89
Expected benefit payments, 2029 88
Expected benefit payments, 2030 - 2034 391
Defined Benefit Pension Plans [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2025 79
Expected benefit payments, 2026 75
Expected benefit payments, 2027 74
Expected benefit payments, 2028 74
Expected benefit payments, 2029 74
Expected benefit payments, 2030 - 2034 329
Other Postretirement Benefits Plans [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2025 16
Expected benefit payments, 2026 16
Expected benefit payments, 2027 15
Expected benefit payments, 2028 15
Expected benefit payments, 2029 14
Expected benefit payments, 2030 - 2034 62
IPL [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2025 43
Expected benefit payments, 2026 40
Expected benefit payments, 2027 39
Expected benefit payments, 2028 39
Expected benefit payments, 2029 38
Expected benefit payments, 2030 - 2034 172
IPL [Member] | Defined Benefit Pension Plans [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2025 36
Expected benefit payments, 2026 34
Expected benefit payments, 2027 33
Expected benefit payments, 2028 33
Expected benefit payments, 2029 32
Expected benefit payments, 2030 - 2034 148
IPL [Member] | Other Postretirement Benefits Plans [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2025 7
Expected benefit payments, 2026 6
Expected benefit payments, 2027 6
Expected benefit payments, 2028 6
Expected benefit payments, 2029 6
Expected benefit payments, 2030 - 2034 24
WPL [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2025 40
Expected benefit payments, 2026 37
Expected benefit payments, 2027 37
Expected benefit payments, 2028 36
Expected benefit payments, 2029 36
Expected benefit payments, 2030 - 2034 167
WPL [Member] | Defined Benefit Pension Plans [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2025 33
Expected benefit payments, 2026 31
Expected benefit payments, 2027 31
Expected benefit payments, 2028 31
Expected benefit payments, 2029 31
Expected benefit payments, 2030 - 2034 144
WPL [Member] | Other Postretirement Benefits Plans [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Expected benefit payments, 2025 7
Expected benefit payments, 2026 6
Expected benefit payments, 2027 6
Expected benefit payments, 2028 5
Expected benefit payments, 2029 5
Expected benefit payments, 2030 - 2034 $ 23
v3.25.0.1
Benefit Plans (Allocation Of Plan Assets) (Details)
Dec. 31, 2024
Pension Plans, Defined Benefit [Member] | Public equity securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Actual allocation, percentage 44.00%
Pension Plans, Defined Benefit [Member] | Liquid alternative securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Actual allocation, percentage 6.00%
Pension Plans, Defined Benefit [Member] | Return-seeking fixed income securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Actual allocation, percentage 8.00%
Pension Plans, Defined Benefit [Member] | Liability hedging fixed income securities (including cash and equivalents) [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Actual allocation, percentage 42.00%
Other Postretirement Benefits Plans [Member] | Cash and equivalents [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Actual allocation, percentage 1.00%
Other Postretirement Benefits Plans [Member] | Public equity securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Actual allocation, percentage 27.00%
Other Postretirement Benefits Plans [Member] | Fixed income securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Actual allocation, percentage 72.00%
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 34.00%
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 40.00%
Maximum [Member] | Pension Plans, Defined Benefit [Member] | Public equity securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Target range allocation, percentage 49.00%
Maximum [Member] | Pension Plans, Defined Benefit [Member] | Liquid alternative securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Target range allocation, percentage 12.00%
Maximum [Member] | Pension Plans, Defined Benefit [Member] | Return-seeking fixed income securities [Member]  
Defined Benefit Plan Disclosure [Line Items]  
Target range allocation, percentage 18.00%
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 53.00%
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%
v3.25.0.1
Benefit Plans (Fair Value Of Plan Assets By Asset Category And Fair Value Hierarchy Level) (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Pension Plans, Defined Benefit [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets $ 715.0 $ 732.0 $ 706.0
Pension Plans, Defined Benefit [Member] | Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 49.0 424.0  
Pension Plans, Defined Benefit [Member] | Assets Measured at Net Asset Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 667.0 306.0  
Pension Plans, Defined Benefit [Member] | Cash and equivalents [Member] | Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 49.0 19.0  
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 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 49.0 19.0  
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 0.0  
Pension Plans, Defined Benefit [Member] | Equity securities [Member] | Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 223.0  
Pension Plans, Defined Benefit [Member] | Equity securities [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 223.0  
Pension Plans, Defined Benefit [Member] | Equity securities [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | Equity securities [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | Global asset securities [Member] | Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 39.0  
Pension Plans, Defined Benefit [Member] | Global asset securities [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 39.0  
Pension Plans, Defined Benefit [Member] | Global asset securities [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | Global asset securities [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | Fixed income securities [Member] | Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 143.0  
Pension Plans, Defined Benefit [Member] | Fixed income securities [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 31.0  
Pension Plans, Defined Benefit [Member] | Fixed income securities [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 112.0  
Pension Plans, Defined Benefit [Member] | Fixed income securities [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | Subtotal [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 293.0  
Pension Plans, Defined Benefit [Member] | Subtotal [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 49.0 131.0  
Pension Plans, Defined Benefit [Member] | Subtotal [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | Accrued investment income [Member] | Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 2.0  
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 (1.0) 0.0  
Pension Plans, Defined Benefit [Member] | IPL [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 340.0 352.0 344.0
Pension Plans, Defined Benefit [Member] | IPL [Member] | Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 21.0 204.0  
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 319.0 147.0  
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 21.0 9.0  
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 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 21.0 9.0  
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 0.0  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Equity securities [Member] | Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 107.0  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Equity securities [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 107.0  
Pension 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 0.0  
Pension 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 0.0  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Global asset securities [Member] | Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 19.0  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Global asset securities [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 19.0  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Global asset securities [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Global asset securities [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Fixed income securities [Member] | Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 69.0  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Fixed income securities [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 15.0  
Pension 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 54.0  
Pension 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 0.0  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Subtotal [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 141.0  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Subtotal [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 21.0 63.0  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Subtotal [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | IPL [Member] | Accrued investment income [Member] | Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 1.0  
Pension Plans, Defined Benefit [Member] | WPL [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 303.0 306.0 291.0
Pension Plans, Defined Benefit [Member] | WPL [Member] | Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 22.0 177.0  
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 281.0 128.0  
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 22.0 8.0  
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 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 22.0 8.0  
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 0.0  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Equity securities [Member] | Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 93.0  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Equity securities [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 93.0  
Pension 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 0.0  
Pension 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 0.0  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Global asset securities [Member] | Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 16.0  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Global asset securities [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 16.0  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Global asset securities [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Global asset securities [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Fixed income securities [Member] | Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 60.0  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Fixed income securities [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 13.0  
Pension 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 47.0  
Pension 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 0.0  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Subtotal [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 122.0  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Subtotal [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 22.0 55.0  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Subtotal [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Pension Plans, Defined Benefit [Member] | WPL [Member] | Accrued investment income [Member] | Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 1.0  
Other Postretirement Benefit Plans, Defined Benefit [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 80.0 83.0 83.0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 80.0 64.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 72.0 55.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 8.0 9.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Assets Measured at Net Asset Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 19.0  
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 8.0 9.0  
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 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 8.0 9.0  
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 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 20.0 8.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity securities [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 20.0 8.0  
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 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 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 52.0 47.0  
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 52.0 47.0  
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 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 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 59.0 61.0 58.0
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 59.0 43.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 58.0 42.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 1.0 1.0  
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 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Assets Measured at Net Asset Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 18.0  
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 1.0 1.0  
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 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 1.0 1.0  
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 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 18.0 6.0  
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 18.0 6.0  
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 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 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 40.0 36.0  
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 40.0 36.0  
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 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 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 13.0 14.0 $ 14.0
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 13.0 13.0  
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 1.0  
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 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Cash and equivalents [Member] | Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 1.0  
Other Postretirement Benefit 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 0.0  
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Cash and equivalents [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Fair value of plan assets 0.0 1.0  
Other Postretirement Benefit 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 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 2.0 2.0  
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 2.0 2.0  
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 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 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 11.0 11.0  
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 11.0 11.0  
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 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 $ 0.0  
v3.25.0.1
Benefit Plans (Employees Participate In Defined Contribution Retirement Plans) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
401(k) costs $ 31 $ 30 $ 28
IPL [Member]      
401(k) costs 14 14 13
WPL [Member]      
401(k) costs $ 15 $ 14 $ 13
v3.25.0.1
Benefit Plans (Recognized Compensation Expense And Income Tax Benefits) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Compensation expense $ 12 $ 12 $ 13
Income tax benefits 3 3 3
IPL [Member]      
Compensation expense 6 6 7
Income tax benefits 2 2 2
WPL [Member]      
Compensation expense 5 5 5
Income tax benefits $ 1 $ 1 $ 1
v3.25.0.1
Benefit Plans (Summary Of Performance Shares (TSR Metric)) (Details) - Performance Shares (TSR Metric) [Member] - $ / shares
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]      
Nonvested, January 1 (in shares/awards) 233,954 190,273 196,429
Nonvested, January 1, weighted average grant date fair value (in dollars per share) $ 52.60 $ 54.13 $ 51.59
Granted (in shares/awards) 127,874 108,712 74,106
Granted, weighted average grant date fair value (in dollars per share) $ 46.04 $ 55.68 $ 54.45
Vested (in shares/awards) (47,497) (53,431) (71,101)
Vested, weighted average grant date fair value (in dollars per share) $ 46.19 $ 64.04 $ 47.48
Forfeited (in shares/awards) (24,932) (11,600) (9,161)
Forfeited, weighted average grant date fair value (in dollars per share) $ 46.16 $ 53.88 $ 53.99
Nonvested, December 31 (in shares/awards) 289,399 233,954 190,273
Nonvested, December 31, weighted average grant date fair value (in dollars per share) $ 51.31 $ 52.60 $ 54.13
v3.25.0.1
Benefit Plans (Summary of Restricted Stock Units) (Details) - Restricted Stock Units [Member] - $ / shares
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]      
Nonvested, January 1 (in shares/awards) 234,259 198,275 217,819
Nonvested, January 1, weighted average grant date fair value (in dollars per share) $ 52.58 $ 54.53 $ 50.54
Granted (in shares/awards) 129,854 106,124 77,122
Granted, weighted average grant date fair value (in dollars per share) $ 48.69 $ 52.77 $ 56.88
Vested (in shares/awards) (71,441) (55,345) (82,770)
Vested, weighted average grant date fair value (in dollars per share) $ 48.65 $ 59.40 $ 46.08
Forfeited (in shares/awards) (3,524) (14,795) (13,896)
Forfeited, weighted average grant date fair value (in dollars per share) $ 48.40 $ 54.53 $ 55.53
Nonvested, December 31 (in shares/awards) 289,148 234,259 198,275
Nonvested, December 31, weighted average grant date fair value (in dollars per share) $ 51.85 $ 52.58 $ 54.53
v3.25.0.1
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, 2024
Dec. 31, 2023
Dec. 31, 2022
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]      
Nonvested, January 1 (in shares/awards) 257,639 199,874 196,429
Nonvested, January 1, weighted average grant date fair value (in dollars per share) $ 52.76 $ 54.74 $ 50.74
Granted (in shares/awards) 146,143 124,217 84,670
Granted, weighted average grant date fair value (in dollars per share) $ 48.55 $ 52.71 $ 57.01
Vested (in shares/awards) (67,852) (53,431) (71,101)
Vested, weighted average grant date fair value (in dollars per share) $ 48.66 $ 59.36 $ 46.24
Forfeited (in shares/awards) (5,230) (13,021) (10,124)
Forfeited, weighted average grant date fair value (in dollars per share) $ 48.40 $ 55.47 $ 55.92
Nonvested, December 31 (in shares/awards) 330,700 257,639 199,874
Nonvested, December 31, weighted average grant date fair value (in dollars per share) $ 51.81 $ 52.76 $ 54.74
v3.25.0.1
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, 2024
Dec. 31, 2023
Defined Benefit Plan Disclosure [Line Items]    
Carrying value of deferred compensation obligation $ 14 $ 13
Fair market value of deferred compensation obligation $ 22 $ 19
v3.25.0.1
Asset Retirement Obligations (Reconciliation Of Changes In Asset Retirement Obligations) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]      
Balance, January 1 $ 246 $ 279  
Revisions in estimated cash flows (3) (6)  
Liabilities settled (8) (51)  
Liabilities incurred 409 16  
Accretion expense 19 8  
Balance, December 31 663 246 $ 279
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 1 148 195  
Revisions in estimated cash flows (1) (9)  
Liabilities settled (6) (44)  
Liabilities incurred 201 1  
Accretion expense 8 5  
Balance, December 31 350 148 195
Asset retirement obligation charge for IPL's steam assets 358 353 369
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 98 84  
Revisions in estimated cash flows (2) 3  
Liabilities settled (2) (7)  
Liabilities incurred 208 15  
Accretion expense 11 3  
Balance, December 31 313 98 84
Asset retirement obligation charge for IPL's steam assets $ 279 $ 271 $ 278
v3.25.0.1
Derivative Instruments (Narrative) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Derivative [Line Items]      
Interest rate swap $ 9,925 $ 9,109  
Non-current interest rate swap assets 126 177  
Accumulated other comprehensive income 1 1  
Interest expense, interest rate swap 449 394 $ 325
IPL [Member]      
Derivative [Line Items]      
Interest rate swap 4,125 3,975  
Non-current interest rate swap assets 53 84  
WPL [Member]      
Derivative [Line Items]      
Interest rate swap 3,400 3,100  
Non-current interest rate swap assets 55 61  
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%    
Non-current interest rate swap assets $ 1 1  
Accumulated other comprehensive income 1 1  
Interest expense, interest rate swap $ 4 $ 3  
v3.25.0.1
Derivative Instruments (Notional Amounts Of Derivative Instruments) (Details) - Commodity [Member]
gal in Thousands
 12 Months Ended
Dec. 31, 2024
Dekatherms
MWh
gal
Electricity (MWhs) [Member]  
Notional Amount of Derivatives [Line Items]  
Notional unit amount of derivatives (in MWhs) 1,422
Electricity (MWhs) [Member] | IPL [Member]  
Notional Amount of Derivatives [Line Items]  
Notional unit amount of derivatives (in MWhs) 383
Electricity (MWhs) [Member] | WPL [Member]  
Notional Amount of Derivatives [Line Items]  
Notional unit amount of derivatives (in MWhs) 1,039
FTRs (MWhs) [Member]  
Notional Amount of Derivatives [Line Items]  
Notional unit amount of derivatives (in MWhs) 10,232
FTRs (MWhs) [Member] | IPL [Member]  
Notional Amount of Derivatives [Line Items]  
Notional unit amount of derivatives (in MWhs) 3,551
FTRs (MWhs) [Member] | WPL [Member]  
Notional Amount of Derivatives [Line Items]  
Notional unit amount of derivatives (in MWhs) 6,681
Gas (Dths) [Member]  
Notional Amount of Derivatives [Line Items]  
Notional unit amount of derivatives (in Dths) | Dekatherms 147,894
Gas (Dths) [Member] | IPL [Member]  
Notional Amount of Derivatives [Line Items]  
Notional unit amount of derivatives (in Dths) | Dekatherms 61,489
Gas (Dths) [Member] | WPL [Member]  
Notional Amount of Derivatives [Line Items]  
Notional unit amount of derivatives (in Dths) | Dekatherms 86,405
Diesel Fuel (gallons) [Member]  
Notional Amount of Derivatives [Line Items]  
Notional unit amount of derivatives (in Gallons) | gal 2,520
Diesel Fuel (gallons) [Member] | IPL [Member]  
Notional Amount of Derivatives [Line Items]  
Notional unit amount of derivatives (in Gallons) | gal 0
Diesel Fuel (gallons) [Member] | WPL [Member]  
Notional Amount of Derivatives [Line Items]  
Notional unit amount of derivatives (in Gallons) | gal 2,520
v3.25.0.1
Derivative Instruments (Fair Value Of Financial Instruments) (Details) - Commodity Contracts [Member] - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Derivatives, Fair Value [Line Items]    
Current derivative assets $ 41 $ 44
Non-current derivative assets 34 44
Current derivative liabilities 26 51
Non-current derivative liabilities 32 47
IPL [Member]    
Derivatives, Fair Value [Line Items]    
Current derivative assets 29 30
Non-current derivative assets 19 24
Current derivative liabilities 11 22
Non-current derivative liabilities 2 8
WPL [Member]    
Derivatives, Fair Value [Line Items]    
Current derivative assets 12 14
Non-current derivative assets 15 20
Current derivative liabilities 15 29
Non-current derivative liabilities $ 30 $ 39
v3.25.0.1
Derivative Instruments (Balance Sheet Offsetting) (Details) - Commodity Contracts [Member] - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Derivative [Line Items]    
Derivative assets, Gross (as reported) $ 75 $ 88
Derivative assets, net 64 47
Derivative liabilities, gross (as reported) 58 98
Derivative liabilities, net 47 57
IPL [Member]    
Derivative [Line Items]    
Derivative assets, Gross (as reported) 48 54
Derivative assets, net 43 32
Derivative liabilities, gross (as reported) 13 30
Derivative liabilities, net 8 8
WPL [Member]    
Derivative [Line Items]    
Derivative assets, Gross (as reported) 27 34
Derivative assets, net 21 15
Derivative liabilities, gross (as reported) 45 68
Derivative liabilities, net $ 39 $ 49
v3.25.0.1
Fair Value Measurements (Recurring Fair Value Measurements) (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Carrying Amount [Member]    
Assets:    
Money market fund investments $ 52 $ 45
Deferred proceeds 163 216
Liabilities and equity:    
Long-term debt (including current maturities) 9,848 9,034
Carrying Amount [Member] | Commodity Contracts [Member]    
Assets:    
Derivatives 75 88
Liabilities and equity:    
Derivatives 58 98
Carrying Amount [Member] | Interest Rate Swap [Member]    
Assets:    
Derivatives 1 1
Money market fund investments 52 45
Deferred proceeds 163 216
Liabilities and equity:    
Long-Term Debt, Fair Value 9,577 8,677
Commodity Contracts [Member]    
Assets:    
Derivatives 75 88
Liabilities and equity:    
Derivatives 58 98
Interest Rate Swap [Member]    
Assets:    
Derivatives 1 1
Level 1 [Member]    
Assets:    
Money market fund investments 52 45
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 9,577 8,677
Level 2 [Member] | Commodity Contracts [Member]    
Assets:    
Derivatives 48 59
Liabilities and equity:    
Derivatives 56 93
Level 2 [Member] | Interest Rate Swap [Member]    
Assets:    
Derivatives 1 1
Level 3 [Member]    
Assets:    
Money market fund investments 0 0
Deferred proceeds 163 216
Liabilities and equity:    
Long-Term Debt, Fair Value 0 0
Level 3 [Member] | Commodity Contracts [Member]    
Assets:    
Derivatives 27 29
Liabilities and equity:    
Derivatives 2 5
Level 3 [Member] | Interest Rate Swap [Member]    
Assets:    
Derivatives 0 0
IPL [Member] | Carrying Amount [Member]    
Assets:    
Money market fund investments 9 45
Deferred proceeds 163 216
Liabilities and equity:    
Long-term debt (including current maturities) 4,090 3,945
IPL [Member] | Carrying Amount [Member] | Commodity Contracts [Member]    
Assets:    
Derivatives 48 54
Liabilities and equity:    
Derivatives 13 30
IPL [Member]    
Assets:    
Money market fund investments 9 45
Deferred proceeds 163 216
Liabilities and equity:    
Long-Term Debt, Fair Value 3,736 3,664
IPL [Member] | Commodity Contracts [Member]    
Assets:    
Derivatives 48 54
Liabilities and equity:    
Derivatives 13 30
IPL [Member] | Level 1 [Member]    
Assets:    
Money market fund investments 9 45
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 3,736 3,664
IPL [Member] | Level 2 [Member] | Commodity Contracts [Member]    
Assets:    
Derivatives 26 30
Liabilities and equity:    
Derivatives 11 25
IPL [Member] | Level 3 [Member]    
Assets:    
Money market fund investments 0 0
Deferred proceeds 163 216
Liabilities and equity:    
Long-Term Debt, Fair Value 0 0
IPL [Member] | Level 3 [Member] | Commodity Contracts [Member]    
Assets:    
Derivatives 22 24
Liabilities and equity:    
Derivatives 2 5
WPL [Member] | Carrying Amount [Member]    
Assets:    
Money market fund investments 43 0
Liabilities and equity:    
Long-term debt (including current maturities) 3,370 3,070
WPL [Member] | Carrying Amount [Member] | Commodity Contracts [Member]    
Assets:    
Derivatives 27 34
Liabilities and equity:    
Derivatives 45 68
WPL [Member]    
Assets:    
Money market fund investments 43 0
Liabilities and equity:    
Long-Term Debt, Fair Value 3,170 2,933
WPL [Member] | Commodity Contracts [Member]    
Assets:    
Derivatives 27 34
Liabilities and equity:    
Derivatives 45 68
WPL [Member] | Level 1 [Member]    
Assets:    
Money market fund investments 43 0
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 3,170 2,933
WPL [Member] | Level 2 [Member] | Commodity Contracts [Member]    
Assets:    
Derivatives 22 29
Liabilities and equity:    
Derivatives 45 68
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 5 5
Liabilities and equity:    
Derivatives $ 0 $ 0
v3.25.0.1
Fair Value Measurements (Fair Value Measurements Using Significant Unobservable Inputs) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
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 $ 24 $ 19
Total net gains (losses) included in changes in net assets (realized/unrealized) (3) 3
Purchases 59 62
Sales (3) (3)
Settlements (52) (57)
Ending balance, December 31 25 24
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 (3) 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 19 16
Total net gains (losses) included in changes in net assets (realized/unrealized) (4) (3)
Purchases 45 51
Sales (2) (3)
Settlements (38) (42)
Ending balance, December 31 20 19
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 (4) (3)
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 3
Total net gains (losses) included in changes in net assets (realized/unrealized) 1 6
Purchases 14 11
Sales (1) 0
Settlements (14) (15)
Ending balance, December 31 5 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 1 6
Deferred Proceeds [Member]    
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]    
Beginning balance, January 1 216 185
Total net gains (losses) included in changes in net assets (realized/unrealized) 0 0
Purchases 0 0
Sales 0 0
Settlements (53) 31
Ending balance, December 31 163 216
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 1 216 185
Total net gains (losses) included in changes in net assets (realized/unrealized) 0 0
Purchases 0 0
Sales 0 0
Settlements (53) 31
Ending balance, December 31 163 216
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
v3.25.0.1
Fair Value Measurements (Fair Value Of Net Derivative Assets (Liabilities)) (Details) - Commodity Contracts [Member] - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Fair value, net derivative assets $ 25 $ 24 $ 19
Excluding FTRs [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Fair value, net derivative assets 0 3  
FTRs [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Fair value, net derivative assets 25 21  
IPL [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Fair value, net derivative assets 20 19 16
IPL [Member] | Excluding FTRs [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Fair value, net derivative assets 0 3  
IPL [Member] | FTRs [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Fair value, net derivative assets 20 16  
WPL [Member]      
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]      
Fair value, net derivative assets 5 5 $ 3
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 $ 5 $ 5  
v3.25.0.1
Commitments And Contingencies (Narrative) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2020
Dec. 31, 2019
Long-term Purchase Commitment [Line Items]          
Equity income from unconsolidated investments, net $ (61) $ (61) $ (51)    
Whiting Petroleum Corporation          
Long-term Purchase Commitment [Line Items]          
Partnership share, percent 6.00%        
Obligations, maximum $ 54        
Capital Purchase Commitment [Member]          
Long-term Purchase Commitment [Line Items]          
Minimum future commitments $ 448        
IPL [Member]          
Long-term Purchase Commitment [Line Items]          
Base return on equity, percentage 10.25%        
IPL [Member] | Capital Purchase Commitment [Member]          
Long-term Purchase Commitment [Line Items]          
Minimum future commitments $ 294        
WPL [Member] | Capital Purchase Commitment [Member]          
Long-term Purchase Commitment [Line Items]          
Minimum future commitments 153        
Indemnification Agreement [Member]          
Long-term Purchase Commitment [Line Items]          
Obligations, maximum 43        
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 193        
Indemnification Agreement [Member] | WPL [Member] | Renewable Tax Credits Transferred [Member]          
Long-term Purchase Commitment [Line Items]          
Obligations, maximum $ 121        
FERC [Member]          
Long-term Purchase Commitment [Line Items]          
Base return on equity, percentage 9.98%     10.02% 9.88%
Equity income from unconsolidated investments, net     $ 6    
v3.25.0.1
Commitments And Contingencies (Other Purchase Commitments) (Details)
$ in Millions
Dec. 31, 2024
USD ($)
Long-term Purchase Commitment [Line Items]  
Minimum future commitments, 2025 $ 394
Minimum future commitments, 2026 230
Minimum future commitments, 2027 159
Minimum future commitments, 2028 114
Minimum future commitments, 2029 86
Minimum future commitments, Thereafter 142
Minimum future commitments, Total 1,125
Individual commitments incurred 1
Natural Gas [Member]  
Long-term Purchase Commitment [Line Items]  
Minimum future commitments, 2025 268
Minimum future commitments, 2026 177
Minimum future commitments, 2027 130
Minimum future commitments, 2028 102
Minimum future commitments, 2029 84
Minimum future commitments, Thereafter 120
Minimum future commitments, Total 881
Coal [Member]  
Long-term Purchase Commitment [Line Items]  
Minimum future commitments, 2025 75
Minimum future commitments, 2026 33
Minimum future commitments, 2027 22
Minimum future commitments, 2028 5
Minimum future commitments, 2029 0
Minimum future commitments, Thereafter 0
Minimum future commitments, Total 135
Other [Member]  
Long-term Purchase Commitment [Line Items]  
Minimum future commitments, 2025 51
Minimum future commitments, 2026 20
Minimum future commitments, 2027 7
Minimum future commitments, 2028 7
Minimum future commitments, 2029 2
Minimum future commitments, Thereafter 22
Minimum future commitments, Total 109
IPL [Member]  
Long-term Purchase Commitment [Line Items]  
Minimum future commitments, 2025 212
Minimum future commitments, 2026 125
Minimum future commitments, 2027 97
Minimum future commitments, 2028 71
Minimum future commitments, 2029 51
Minimum future commitments, Thereafter 41
Minimum future commitments, Total 597
Individual commitments incurred 1
IPL [Member] | Natural Gas [Member]  
Long-term Purchase Commitment [Line Items]  
Minimum future commitments, 2025 160
Minimum future commitments, 2026 104
Minimum future commitments, 2027 85
Minimum future commitments, 2028 64
Minimum future commitments, 2029 49
Minimum future commitments, Thereafter 20
Minimum future commitments, Total 482
IPL [Member] | Coal [Member]  
Long-term Purchase Commitment [Line Items]  
Minimum future commitments, 2025 34
Minimum future commitments, 2026 19
Minimum future commitments, 2027 10
Minimum future commitments, 2028 5
Minimum future commitments, 2029 0
Minimum future commitments, Thereafter 0
Minimum future commitments, Total 68
IPL [Member] | Other [Member]  
Long-term Purchase Commitment [Line Items]  
Minimum future commitments, 2025 18
Minimum future commitments, 2026 2
Minimum future commitments, 2027 2
Minimum future commitments, 2028 2
Minimum future commitments, 2029 2
Minimum future commitments, Thereafter 21
Minimum future commitments, Total 47
WPL [Member]  
Long-term Purchase Commitment [Line Items]  
Minimum future commitments, 2025 171
Minimum future commitments, 2026 88
Minimum future commitments, 2027 57
Minimum future commitments, 2028 38
Minimum future commitments, 2029 35
Minimum future commitments, Thereafter 100
Minimum future commitments, Total 489
Individual commitments incurred 1
WPL [Member] | Natural Gas [Member]  
Long-term Purchase Commitment [Line Items]  
Minimum future commitments, 2025 108
Minimum future commitments, 2026 73
Minimum future commitments, 2027 45
Minimum future commitments, 2028 38
Minimum future commitments, 2029 35
Minimum future commitments, Thereafter 100
Minimum future commitments, Total 399
WPL [Member] | Coal [Member]  
Long-term Purchase Commitment [Line Items]  
Minimum future commitments, 2025 41
Minimum future commitments, 2026 14
Minimum future commitments, 2027 12
Minimum future commitments, 2028 0
Minimum future commitments, 2029 0
Minimum future commitments, Thereafter 0
Minimum future commitments, Total 67
WPL [Member] | Other [Member]  
Long-term Purchase Commitment [Line Items]  
Minimum future commitments, 2025 22
Minimum future commitments, 2026 1
Minimum future commitments, 2027 0
Minimum future commitments, 2028 0
Minimum future commitments, 2029 0
Minimum future commitments, Thereafter 0
Minimum future commitments, Total $ 23
v3.25.0.1
Commitments And Contingencies (Schedule Of Environmental Liabilities) (Details) - Natural Gas Processing Plant [Member]
$ in Millions
 12 Months Ended
Dec. 31, 2024
USD ($)
Current and non-current environmental liabilities $ 12
IPL [Member]  
Current and non-current environmental liabilities 7
WPL [Member]  
Current and non-current environmental liabilities 5
Minimum [Member]  
Range of estimated future costs 7
Minimum [Member] | IPL [Member]  
Range of estimated future costs 5
Minimum [Member] | WPL [Member]  
Range of estimated future costs 2
Maximum [Member]  
Range of estimated future costs 28
Maximum [Member] | IPL [Member]  
Range of estimated future costs 17
Maximum [Member] | WPL [Member]  
Range of estimated future costs $ 11
v3.25.0.1
Segments Of Business (Schedule Of Segment Of Business) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Segment Reporting Information [Line Items]      
Electric utility $ 3,372 $ 3,345 $ 3,421
Gas utility 465 540 642
Other 144 142 142
Total revenues 3,981 4,027 4,205
Electric production fuel and purchased power 628 736 830
Electric transmission service 613 583 573
Cost of gas sold 224 299 389
Asset valuation charge for IPL's Lansing Generating Station 60 0 0
Other operation and maintenance 676 675 704
Depreciation and amortization 772 676 671
Interest expense 449 394 325
Equity income from unconsolidated investments, net (61) (61) (51)
Income tax expense (benefit) (114) 4 22
Other 44 18 56
Net income (loss) 690 703 686
Total assets 22,714 21,237 20,163
Investments in equity method subsidiaries 623 585 542
Construction and acquisition expenditures 2,249 1,854 1,484
IPL [Member]      
Segment Reporting Information [Line Items]      
Electric utility 1,747 1,761 1,859
Gas utility 250 300 351
Total revenues 2,046 2,110 2,256
Electric production fuel and purchased power 269 282 383
Electric transmission service 417 420 407
Cost of gas sold 123 166 206
Asset valuation charge for IPL's Lansing Generating Station 60 0 0
Depreciation and amortization 404 388 381
Income tax expense (benefit) (129) (58) (50)
Net income (loss) 362 366 360
Total assets 11,407 10,489  
WPL [Member]      
Segment Reporting Information [Line Items]      
Electric utility 1,625 1,584 1,562
Gas utility 215 240 291
Total revenues 1,845 1,827 1,856
Electric production fuel and purchased power 359 455 447
Electric transmission service 196 163 166
Cost of gas sold 101 134 183
Depreciation and amortization 357 280 283
Income tax expense (benefit) 11 60 66
Net income (loss) 345 345 315
Total assets 10,106 9,634  
Total Reportable Segments [Member]      
Segment Reporting Information [Line Items]      
Electric utility 3,372 3,345 3,421
Gas utility 465 540 642
Other 54 52 49
Total revenues 3,891 3,937 4,112
Electric production fuel and purchased power 628 737 830
Electric transmission service 613 583 573
Cost of gas sold 224 300 389
Asset valuation charge for IPL's Lansing Generating Station 60    
Other operation and maintenance 637 624 647
Depreciation and amortization 761 668 664
Interest expense 342 304 269
Equity income from unconsolidated investments, net (2) (3) (1)
Income tax expense (benefit) (118) 2 16
Other 39 11 50
Net income (loss) 707 711 675
Total assets 21,513 20,123 19,062
Investments in equity method subsidiaries 22 21 20
Construction and acquisition expenditures 2,052 1,731 1,392
IPL [Member]      
Segment Reporting Information [Line Items]      
Electric utility 1,747 1,761 1,859
Gas utility 250 300 351
Other 49 49 46
Total revenues 2,046 2,110 2,256
Electric production fuel and purchased power 269 282 383
Electric transmission service 417 420 407
Cost of gas sold 123 166 206
Asset valuation charge for IPL's Lansing Generating Station 60    
Other operation and maintenance 358 353 369
Depreciation and amortization 404 388 381
Interest expense 177 155 148
Equity income from unconsolidated investments, net 0 0 0
Income tax expense (benefit) (129) (58) (50)
Other 5 38 52
Net income (loss) 362 366 360
Total assets 11,407 10,489 10,075
Investments in equity method subsidiaries 5 5 5
Construction and acquisition expenditures 1,224 712 372
WPL [Member]      
Segment Reporting Information [Line Items]      
Electric utility 1,625 1,584 1,562
Gas utility 215 240 291
Other 5 3 3
Total revenues 1,845 1,827 1,856
Electric production fuel and purchased power 359 455 447
Electric transmission service 196 163 166
Cost of gas sold 101 134 183
Asset valuation charge for IPL's Lansing Generating Station 0    
Other operation and maintenance 279 271 278
Depreciation and amortization 357 280 283
Interest expense 165 149 121
Equity income from unconsolidated investments, net (2) (3) (1)
Income tax expense (benefit) 11 60 66
Other 34 (27) (2)
Net income (loss) 345 345 315
Total assets 10,106 9,634 8,987
Investments in equity method subsidiaries 17 16 15
Construction and acquisition expenditures 828 1,019 1,020
Other [Member]      
Segment Reporting Information [Line Items]      
Other 90 90 93
Total revenues 90 90 93
Other operation and maintenance 39 51 57
Depreciation and amortization 11 8 7
Interest expense 107 90 56
Equity income from unconsolidated investments, net (59) (58) (50)
Income tax expense (benefit) 4 2 6
Other 5 5 6
Net income (loss) (17) (8) 11
Total assets 1,201 1,114 1,101
Investments in equity method subsidiaries 601 564 522
Construction and acquisition expenditures $ 197 $ 123 $ 92
v3.25.0.1
Related Parties (Narrative) (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
WPL [Member] | Related Party [Member] | WPL Owed ATC LLC [Member] | ATC LLC [Member]    
Related Party Transaction [Line Items]    
Net amounts owed $ 10 $ 10
v3.25.0.1
Related Parties (Service Agreements) (Details) - Corporate Services [Member] - Subsidiary of Common Parent [Member] - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Administrative and General Services Billings [Member] | IPL [Member]      
Related Party Transaction [Line Items]      
Amounts billed between related parties $ 183 $ 181 $ 181
Administrative and General Services Billings [Member] | WPL [Member]      
Related Party Transaction [Line Items]      
Amounts billed between related parties 171 163 155
Transmission Sales Credited [Member] | IPL [Member]      
Related Party Transaction [Line Items]      
Amounts billed between related parties 0 11 19
Transmission Sales Credited [Member] | WPL [Member]      
Related Party Transaction [Line Items]      
Amounts billed between related parties 84 55 74
Transmission Purchases Billed [Member] | IPL [Member]      
Related Party Transaction [Line Items]      
Amounts billed between related parties 430 431 435
Transmission Purchases Billed [Member] | WPL [Member]      
Related Party Transaction [Line Items]      
Amounts billed between related parties $ 54 $ 35 $ 174
v3.25.0.1
Related Parties (Net Intercompany Payables) (Details) - Corporate Services [Member] - Related Party [Member] - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
IPL [Member]    
Related Party Transaction [Line Items]    
Net amounts owed $ 135 $ 129
WPL [Member]    
Related Party Transaction [Line Items]    
Net amounts owed $ 64 $ 72
v3.25.0.1
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, 2024
Dec. 31, 2023
Dec. 31, 2022
ATC Billings To WPL [Member]      
Related Party Transaction [Line Items]      
Amounts billed between related parties $ 152 $ 159 $ 140
WPL Billings To ATC [Member]      
Related Party Transaction [Line Items]      
Amounts billed between related parties $ 16 $ 20 $ 18
v3.25.0.1
Condensed Parent Company Financial Statements (Condensed Statements Of Income) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Operating expenses $ 3,095 $ 3,084 $ 3,277
Operating income (loss) 886 943 928
Other (income) and deductions:      
Equity earnings from consolidated subsidiaries (61) (61) (51)
Interest expense 449 394 325
Other (3) 3 6
Total other (income) and deductions 310 236 220
Income before income taxes 576 707 708
Income tax expense (benefit) (114) 4 22
Net income 690 703 686
Parent Company [Member]      
Operating expenses 3 3 9
Operating income (loss) (3) (3) (9)
Other (income) and deductions:      
Equity earnings from consolidated subsidiaries (734) (742) (707)
Interest expense 40 34 6
Other 5 4 1
Total other (income) and deductions (689) (704) (700)
Income before income taxes 686 701 691
Income tax expense (benefit) (3) (5) 2
Net income $ 689 $ 706 $ 689
v3.25.0.1
Condensed Parent Company Financial Statements (Condensed Balance Sheets) (Details) - USD ($)
$ in Millions
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Current assets:      
Other $ 171 $ 160  
Current assets 1,184 1,272  
Investments:      
Other 224 216  
Total investments 639 602  
Other assets 2,190 2,206  
Total assets 22,714 21,237 $ 20,163
Current liabilities:      
Current maturities of long-term debt 1,171 809  
Commercial paper 558 475  
Other 385 302  
Current liabilities 2,715 2,304  
Long-term debt, net 8,677 8,225  
Other liabilities 947 617  
Common Equity:      
Retained earnings 3,954 3,756  
Accumulated other comprehensive income 1 1  
Shares in deferred compensation trust (14) (13)  
Total common equity 7,004 6,777  
Total liabilities and equity 22,714 21,237  
Parent Company [Member]      
Current assets:      
Notes receivable from affiliated companies 103 96  
Income taxes refunds receivable 12 0  
Other 2 1  
Current assets 117 97  
Investments:      
Investments in consolidated subsidiaries 9,123 8,405  
Other 1 2  
Total investments 9,124 8,407  
Other assets 84 90  
Total assets 9,325 8,594  
Current liabilities:      
Current maturities of long-term debt 571 0  
Commercial paper 325 157  
Notes payable to affiliated companies 1,401 1,068  
Other 10 10  
Current liabilities 2,307 1,235  
Long-term debt, net 0 568  
Other liabilities 3 2  
Common Equity:      
Common stock and additional paid-in capital 3,063 3,033  
Retained earnings 3,965 3,768  
Accumulated other comprehensive income 1 1  
Shares in deferred compensation trust (14) (13)  
Total common equity 7,015 6,789  
Total liabilities and equity $ 9,325 $ 8,594  
v3.25.0.1
Condensed Parent Company Financial Statements (Condensed Statements of Cash Flows) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
Net cash flows from operating activities $ 1,167.0 $ 867.0 $ 486.0
Cash flows from (used for) investing activities:      
Net cash flows from (used for) investing activities (1,547.0) (1,401.0) (933.0)
Cash flows used for financing activities:      
Common stock dividends (492.0) (456.0) (428.0)
Proceeds from issuance of common stock, net 23.0 246.0 25.0
Proceeds from issuance of long-term debt 1,613.0 1,455.0 1,338.0
Net change in commercial paper 83.0 (167.0) 127.0
Other (20.0) 3.0 2.0
Net cash flows from (used for) financing activities 398.0 573.0 431.0
Net increase (decrease) in cash, cash equivalents and restricted cash 18.0 39.0 (16.0)
Cash, cash equivalents and restricted cash at beginning of period 63.0 24.0 40.0
Cash, cash equivalents and restricted cash at end of period 81.0 63.0 24.0
Supplemental cash flows information:      
Interest (434.0) (378.0) (311.0)
Income taxes, net 197.0 88.0 (6.0)
Parent Company [Member]      
Net cash flows from operating activities 355.0 445.0 492.0
Cash flows from (used for) investing activities:      
Capital contributions to consolidated subsidiaries (380.0) (325.0) (530.0)
Net change in notes receivable from and payable to affiliates 326.0 (281.0) 369.0
Net cash flows from (used for) investing activities (54.0) (606.0) (161.0)
Cash flows used for financing activities:      
Common stock dividends (492.0) (456.0) (428.0)
Proceeds from issuance of common stock, net 23.0 246.0 25.0
Proceeds from issuance of long-term debt 0.0 565.0 0.0
Net change in commercial paper 168.0 (195.0) 73.0
Other 0.0 1.0 (1.0)
Net cash flows from (used for) financing activities (301.0) 161.0 (331.0)
Net increase (decrease) in cash, cash equivalents and restricted cash 0.0 0.0 0.0
Cash, cash equivalents and restricted cash at beginning of period 0.0 0.0 0.0
Cash, cash equivalents and restricted cash at end of period 0.0 0.0 0.0
Supplemental cash flows information:      
Interest (40.0) (27.0) (6.0)
Income taxes, net $ 8.0 $ 22.0 $ 15.0
v3.25.0.1
Valuation And Qualifying Accounts and Reserves (Details) - Accumulated Provision for Uncollectible Accounts [Member] - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2024
Dec. 31, 2023
Dec. 31, 2022
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]      
Beginning Balance $ 8.0 $ 7.0 $ 11.0
Additions (Charged to Expense) 24.0 20.0 17.0
Deductions 24.0 19.0 21.0
Ending Balance 8.0 8.0 7.0
IPL [Member]      
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]      
Beginning Balance 0.0 0.0 1.0
Additions (Charged to Expense) 13.0 11.0 7.0
Deductions 13.0 11.0 8.0
Ending Balance 0.0 0.0 0.0
WPL [Member]      
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]      
Beginning Balance 8.0 7.0 10.0
Additions (Charged to Expense) 11.0 9.0 10.0
Deductions 11.0 8.0 13.0
Ending Balance $ 8.0 $ 8.0 $ 7.0