Document And Entity Information - USD ($) $ in Millions	12 Months Ended
Document And Entity Information - USD ($) $ in Millions	Dec. 31, 2023	Jan. 31, 2024	Jun. 30, 2023
Entity Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2023
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			$ 13,200.0
Entity Common Stock, Shares Outstanding		256,100,293
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2023
Document Fiscal Period Focus	FY
Amendment Flag	false
Documents Incorporated by Reference	Portions of the Proxy Statement relating to Alliant Energy Corporation’s 2024 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

Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Revenues:
Electric utility	$ 3,345	$ 3,421	$ 3,081
Gas utility	540	642	456
Other utility	52	49	49
Non-utility	90	93	83
Total revenues	4,027	4,205	3,669
Operating expenses:
Electric production fuel and purchased power	736	830	642
Electric transmission service	583	573	537
Cost of gas sold	299	389	258
Other operation and maintenance	675	704	676
Depreciation and amortization	676	671	657
Taxes other than income taxes	115	110	104
Total operating expenses	3,084	3,277	2,874
Operating income (loss)	943	928	795
Other (income) and deductions:
Interest expense	394	325	277
Equity income from unconsolidated investments, net	(61)	(51)	(62)
Allowance for funds used during construction	(100)	(60)	(25)
Other	3	6	5
Total other (income) and deductions	236	220	195
Income before income taxes	707	708	600
Income tax expense (benefit)	4	22	(74)
Net income	703	686	674
Preferred dividend requirements of Interstate Power and Light Company	0	0	15
Net income attributable to common shareowners	$ 703	$ 686	$ 659
Weighted average number of common shares outstanding:
Basic (in shares)	253.0	250.9	250.2
Diluted (in shares)	253.3	251.2	250.7
Earnings per weighted average common share attributable to Alliant Energy common shareowners:
Basic (in dollars per share)	$ 2.78	$ 2.73	$ 2.63
Diluted (in dollars per share)	$ 2.78	$ 2.73	$ 2.63
IPL [Member]
Revenues:
Electric utility	$ 1,761	$ 1,859	$ 1,752
Gas utility	300	351	265
Other utility	49	46	46
Total revenues	2,110	2,256	2,063
Operating expenses:
Electric production fuel and purchased power	282	383	295
Electric transmission service	420	407	367
Cost of gas sold	166	206	149
Other operation and maintenance	353	369	362
Depreciation and amortization	388	381	375
Taxes other than income taxes	57	57	55
Total operating expenses	1,666	1,803	1,603
Operating income (loss)	444	453	460
Other (income) and deductions:
Interest expense	155	148	139
Allowance for funds used during construction	(21)	(11)	(9)
Other	2	6	1
Total other (income) and deductions	136	143	131
Income before income taxes	308	310	329
Income tax expense (benefit)	(58)	(50)	(36)
Net income	366	360	365
Preferred dividend requirements of Interstate Power and Light Company	0	0	15
Net income attributable to common shareowners	366	360	350
WPL [Member]
Revenues:
Electric utility	1,584	1,562	1,329
Gas utility	240	291	191
Other utility	3	3	3
Total revenues	1,827	1,856	1,523
Operating expenses:
Electric production fuel and purchased power	455	447	347
Electric transmission service	163	166	170
Cost of gas sold	134	183	109
Other operation and maintenance	271	278	268
Depreciation and amortization	280	283	276
Taxes other than income taxes	52	47	45
Total operating expenses	1,355	1,404	1,215
Operating income (loss)	472	452	308
Other (income) and deductions:
Interest expense	149	121	105
Allowance for funds used during construction	(79)	(49)	(16)
Other	(3)	(1)	2
Total other (income) and deductions	67	71	91
Income before income taxes	405	381	217
Income tax expense (benefit)	60	66	(51)
Net income	$ 345	$ 315	$ 268

Consolidated Balance Sheets - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Current assets:
Cash and cash equivalents	$ 62	$ 20
Accounts receivable, less allowance for expected credit losses	475	516
Production fuel, at weighted average cost	62	53
Gas stored underground, at weighted average cost	79	132
Materials and supplies, at weighted average cost	202	140
Regulatory assets	232	166
Other	160	223
Total current assets	1,272	1,250
Property, plant and equipment, net	17,157	16,247
Investments:
ATC Holdings	386	358
Other	216	201
Total investments	602	559
Other assets:
Regulatory assets	2,029	1,880
Deferred charges and other	177	227
Total other assets	2,206	2,107
Total assets	21,237	20,163
Current liabilities:
Current maturities of long-term debt	809	408
Commercial paper	475	642
Accounts payable	611	756
Regulatory liabilities	107	206
Other	302	351
Total current liabilities	2,304	2,363
Long-term debt, net (excluding current portion)	8,225	7,668
Other liabilities:
Deferred tax liabilities	2,042	1,943
Regulatory liabilities	1,023	1,118
Pension and other benefit obligations	249	277
Other	617	518
Total other liabilities	3,931	3,856
Commitments and contingencies (Note 17)
Common equity:
Common stock	3	3
Additional paid-in capital	3,030	2,777
Retained earnings	3,756	3,509
Accumulated other comprehensive income	1	0
Shares in deferred compensation trust - 379,006 and 402,134 shares at a weighted average cost of $34.48 and $32.63 per share	(13)	(13)
Total common equity	6,777	6,276
Total liabilities and equity	21,237	20,163
IPL [Member]
Current assets:
Cash and cash equivalents	53	15
Accounts receivable, less allowance for expected credit losses	242	259
Production fuel, at weighted average cost	27	23
Gas stored underground, at weighted average cost	35	60
Materials and supplies, at weighted average cost	122	83
Regulatory assets	93	85
Other	51	93
Total current assets	623	618
Property, plant and equipment, net	8,298	8,046
Other assets:
Regulatory assets	1,484	1,301
Deferred charges and other	84	110
Total other assets	1,568	1,411
Total assets	10,489	10,075
Current liabilities:
Current maturities of long-term debt	500	0
Commercial paper	0	0
Accounts payable	262	239
Accrued taxes	50	52
Accrued interest	40	35
Regulatory liabilities	72	114
Other	101	141
Total current liabilities	1,025	581
Long-term debt, net (excluding current portion)	3,445	3,646
Other liabilities:
Deferred tax liabilities	1,091	1,047
Regulatory liabilities	572	640
Pension and other benefit obligations	51	62
Other	331	291
Total other liabilities	2,045	2,040
Commitments and contingencies (Note 17)
Common equity:
Common stock	33	33
Additional paid-in capital	2,887	2,807
Retained earnings	1,054	968
Total common equity	3,974	3,808
Total liabilities and equity	10,489	10,075
WPL [Member]
Current assets:
Cash and cash equivalents	7	5
Accounts receivable, less allowance for expected credit losses	219	244
Production fuel, at weighted average cost	35	29
Gas stored underground, at weighted average cost	44	73
Materials and supplies, at weighted average cost	77	54
Regulatory assets	139	81
Prepaid gross receipts tax	49	42
Other	43	60
Total current assets	613	588
Property, plant and equipment, net	8,415	7,722
Other assets:
Regulatory assets	545	579
Deferred charges and other	61	98
Total other assets	606	677
Total assets	9,634	8,987
Current liabilities:
Current maturities of long-term debt	0	0
Commercial paper	318	290
Accounts payable	293	456
Accrued interest	40	38
Regulatory liabilities	35	92
Other	89	73
Total current liabilities	775	949
Long-term debt, net (excluding current portion)	3,070	2,770
Other liabilities:
Deferred tax liabilities	827	789
Regulatory liabilities	451	478
Pension and other benefit obligations	121	140
Other	493	370
Total other liabilities	1,892	1,777
Commitments and contingencies (Note 17)
Common equity:
Common stock	66	66
Additional paid-in capital	2,478	2,233
Retained earnings	1,353	1,192
Total common equity	3,897	3,491
Total liabilities and equity	$ 9,634	$ 8,987

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2023	Dec. 31, 2022
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)	256,096,848	251,134,966
Shares in deferred compensation trust (in shares)	379,006	402,134
Shares in deferred compensation trust, weighted average cost per share (in dollars per share)	$ 34.48	$ 32.63
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

Consolidated Statements Of Cash Flows - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Cash flows from operating activities:
Net income	$ 703	$ 686	$ 674
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	676	671	657
Deferred tax expense (benefit) and tax credits	14	13	(78)
Equity component of allowance for funds used during construction	(74)	(44)	(18)
Other	35	27	35
Other changes in assets and liabilities:
Accounts receivable	(414)	(672)	(530)
Materials and supplies	(62)	(27)	(13)
Regulatory assets	24	(108)	51
Derivative assets	149	(61)	(142)
Accounts payable	(122)	78	37
Regulatory liabilities	(149)	22	(66)
Derivative liabilities	19	70	(17)
Deferred income taxes	84	4	193
Pension and other benefit obligations	(28)	(97)	(137)
Other	12	(76)	(64)
Net cash flows from operating activities	867	486	582
Cash flows from (used for) investing activities:
Utility construction and acquisition expenditures	(1,731)	(1,392)	(1,070)
Other construction and acquisition expenditures	(123)	(92)	(99)
Cash receipts on sold receivables	453	598	502
Proceeds from sales of partial ownership interests in West Riverside	120	0	0
Other	(120)	(47)	(61)
Net cash flows from (used for) investing activities	(1,401)	(933)	(728)
Cash flows from (used for) financing activities:
Common stock dividends	(456)	(428)	(403)
Proceeds from issuance of common stock, net	246	25	28
Redemption of cumulative preferred stock of IPL	0	0	(200)
Proceeds from issuance of long-term debt	1,455	1,338	600
Payments to retire long-term debt	(508)	(633)	(8)
Net change in commercial paper	(167)	127	126
Other	3	2	(13)
Net cash flows from (used for) financing activities	573	431	130
Net increase (decrease) in cash, cash equivalents and restricted cash	39	(16)	(16)
Cash, cash equivalents and restricted cash at beginning of period	24	40	56
Cash, cash equivalents and restricted cash at end of period	63	24	40
Supplemental cash flows information:
Interest	(378)	(311)	(272)
Income taxes, net	88	(6)	(3)
Significant non-cash investing and financing activities:
Accrued capital expenditures	364	382	141
Beneficial interest obtained in exchange for securitized accounts receivable	216	185	214
Indemnification Agreement [Member] \| Renewable Tax Credits Transferred [Member]
Supplemental cash flows information:
Proceeds from renewable tax credits transferred to other corporate taxpayers	98
IPL [Member]
Cash flows from operating activities:
Net income	366	360	365
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	388	381	375
Other	(2)	(21)	(10)
Other changes in assets and liabilities:
Accounts receivable	(437)	(611)	(539)
Materials and supplies	(39)	(13)	(7)
Regulatory assets	58	56	30
Derivative assets	84	(54)	(55)
Accounts payable	(68)	65	15
Regulatory liabilities	(92)	53	1
Derivative liabilities	(16)	42	(8)
Deferred income taxes	36	(24)	62
Pension and other benefit obligations	(11)	(65)	(59)
Other	(6)	(86)	(17)
Net cash flows from operating activities	261	83	153
Cash flows from (used for) investing activities:
Utility construction and acquisition expenditures	(712)	(372)	(384)
Cash receipts on sold receivables	453	598	502
Other	(67)	(11)	(27)
Net cash flows from (used for) investing activities	(326)	215	91
Cash flows from (used for) financing activities:
Common stock dividends	(280)	(321)	(400)
Capital contributions from parent	80	0	50
Redemption of cumulative preferred stock of IPL	0	0	(200)
Proceeds from issuance of long-term debt	296	0	300
Other	7	4	(10)
Net cash flows from (used for) financing activities	103	(317)	(260)
Net increase (decrease) in cash, cash equivalents and restricted cash	38	(19)	(16)
Cash, cash equivalents and restricted cash at beginning of period	15	34	50
Cash, cash equivalents and restricted cash at end of period	53	15	34
Supplemental cash flows information:
Interest	(150)	(148)	(138)
Income taxes, net	117	36	47
Significant non-cash investing and financing activities:
Accrued capital expenditures	140	56	57
Beneficial interest obtained in exchange for securitized accounts receivable	216	185	214
IPL [Member] \| Indemnification Agreement [Member] \| Renewable Tax Credits Transferred [Member]
Supplemental cash flows information:
Proceeds from renewable tax credits transferred to other corporate taxpayers	76
WPL [Member]
Cash flows from operating activities:
Net income	345	315	268
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	280	283	276
Deferred tax expense (benefit) and tax credits	(13)	4	(79)
Equity component of allowance for funds used during construction	(59)	(36)	(11)
Other	25	21	22
Other changes in assets and liabilities:
Accounts receivable	23	(53)	3
Regulatory assets	(34)	(163)	21
Derivative assets	65	(7)	(87)
Accounts payable	(57)	22	4
Regulatory liabilities	(57)	(31)	(67)
Deferred income taxes	50	32	132
Pension and other benefit obligations	(19)	(19)	(63)
Other	29	(69)	(48)
Net cash flows from operating activities	578	299	371
Cash flows from (used for) investing activities:
Utility construction and acquisition expenditures	(1,019)	(1,020)	(686)
Proceeds from sales of partial ownership interests in West Riverside	120	0	0
Other	(47)	(13)	(30)
Net cash flows from (used for) investing activities	(946)	(1,033)	(716)
Cash flows from (used for) financing activities:
Common stock dividends	(184)	(176)	(168)
Capital contributions from parent	245	530	245
Proceeds from issuance of long-term debt	297	588	300
Payments to retire long-term debt	0	(250)	0
Net change in commercial paper	28	54	(21)
Other	(16)	(9)	(12)
Net cash flows from (used for) financing activities	370	737	344
Net increase (decrease) in cash, cash equivalents and restricted cash	2	3	(1)
Cash, cash equivalents and restricted cash at beginning of period	5	2	3
Cash, cash equivalents and restricted cash at end of period	7	5	2
Supplemental cash flows information:
Interest	(146)	(111)	(101)
Income taxes, net	(50)	(56)	(38)
Significant non-cash investing and financing activities:
Accrued capital expenditures	217	$ 319	$ 81
WPL [Member] \| Indemnification Agreement [Member] \| Renewable Tax Credits Transferred [Member]
Supplemental cash flows information:
Proceeds from renewable tax credits transferred to other corporate taxpayers	$ 22

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]	Cumulative Preferred Stock [Member]	Cumulative Preferred Stock [Member] IPL [Member]
Beginning balance at Dec. 31, 2020				$ 2	$ 33	$ 66	$ 2,704	$ 2,752	$ 1,459	$ 2,994	$ 979	$ 953	$ (1)	$ (11)	$ 200	$ 200
Beginning balance at Dec. 31, 2020	$ 5,888	$ 3,964	$ 2,478
Increase (Decrease) in Shareowners' Equity [Roll Forward]
Net income attributable to common shareowners	659	350								659	350
Net income	674	365	268									268
Common stock dividends	(403)	(400)	(168)							(403)	(400)	(168)
At-the-market offering program, net and Shareowner Direct Plan issuances	28			1			27
Capital contributions from parent		50	245					50	245
Equity-based compensation plans and other	17	5					18	5						(1)
Redemption of cumulative preferred stock of IPL	(200)	(200)													(200)	(200)
Other comprehensive income (loss), net of tax	1												1
Ending balance at Dec. 31, 2021				3	33	66	2,749	2,807	1,704	3,250	929	1,053	0	(12)	0	0
Ending 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								686	360
Net income	686	360	315									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)
Redemption of cumulative preferred stock of IPL	0	0
Ending balance at Dec. 31, 2022	6,276	3,808	3,491	3	33	66	2,777	2,807	2,233	3,509	968	1,192	0	(13)	0	0
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								703	366
Net income	703	366	345									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
Redemption of cumulative preferred stock of IPL	0	0
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)	$ 0	$ 0
Ending balance at Dec. 31, 2023	$ 6,777	$ 3,974	$ 3,897

Consolidated Statements of Common Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Statement of Stockholders' Equity [Abstract]
Common stock dividends (in dollars per share)	$ 1.81	$ 1.71	$ 1.61

Summary Of Significant Accounting Policies

12 Months Ended

Dec. 31, 2023

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.

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 advance the transition towards a cleaner, more sustainable, and inclusive energy future, by identifying and researching 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 2039.

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, IPL and WPL entered into agreements to transfer renewable tax credits from certain wind, solar and battery 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. 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. A majority of the differences between actual renewable tax credits and renewable tax credits used to determine rates are recorded in regulatory assets or regulatory liabilities on the balance sheets until they are reflected in future billings to customers. The cash received from the transfer of renewable tax credits is recorded in cash flows from operating activities. Refer to Notes 12 and 17(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, 2023, Alliant Energy’s and IPL’s cash and cash equivalents included $45 million of money market fund investments, with a weighted average interest rate of 5%. At December 31, 2023 and 2022, Alliant Energy’s restricted cash related to requirements in Sheboygan Power, LLC’s debt agreement.(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:


	IPL			WPL
	2023	2022	2021	2023	2022	2021
Electric - generation	3.3%	3.4%	3.4%	3.0%	3.4%	3.5%
Electric - distribution	2.8%	2.8%	2.9%	2.7%	2.5%	2.6%
Electric - other	5.6%	5.7%	5.7%	6.3%	6.8%	7.4%
Gas	3.3%	3.3%	3.3%	2.5%	2.4%	2.4%
Other	6.2%	6.1%	6.1%	4.6%	4.9%	5.4%

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:


	2023	2022	2021
IPL (Wind generation CWIP)	6.9%	6.9%	7.0%
IPL (other CWIP)	7.0%	7.0%	7.2%
WPL (retail jurisdiction)	7.4%	7.0%	7.0%
WPL (wholesale jurisdiction)	7.1%	6.2%	5.6%

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 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, including the first and second solar generation CAs.

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, 2023, 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 recovers a return of, as well as earns a return on, its wind generation placed in service in 2019 and 2020 from its retail electric customers through a renewable energy rider. Other applicable costs and tax benefits associated with this wind generation, excluding operation and maintenance expenses, are also included in the rider. This cost recovery mechanism provides 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 are 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.

(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 15, 16 and 17(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.

(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 amortized on a straight-line basis over the lease term, and 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]