Interstate Power & Light (IPLDP) 10-K 16 Feb 24 2023 FY Annual report Financial data

Document And Entity Information

Document And Entity Information - USD ($) $ in Millions	12 Months Ended
	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
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
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
Entity Common Stock, Shares Outstanding		13,236,601
Auditor Name	DELOITTE & TOUCHE LLP
Auditor Location	Milwaukee, Wisconsin
Auditor Firm ID	34

Consolidated Statements Of Inco

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	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

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 (Pa

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

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 Comm

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 Co_2

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 Accounti

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. 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. 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. 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. 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. 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. 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. 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. 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. 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 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 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. 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. 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 payment
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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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 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 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. 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. 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 payment
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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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 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 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. 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. 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 payment

Regulatory Matters

Regulatory Matters	12 Months Ended
	Dec. 31, 2023
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, 2023 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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Tax-related $934 $929 $831 $848 $103 $81 Pension and OPEB costs 347 392 171 197 176 195 Assets retired early 273 70 259 53 14 17 AROs 194 151 160 110 34 41 Commodity cost recovery 120 160 12 1 108 159 Derivatives 102 84 34 48 68 36 WPL’s Western Wisconsin gas distribution expansion investments 44 48 — — 44 48 IPL’s DAEC PPA amendment 42 66 42 66 — — Other 205 146 68 63 137 83 $2,261 $2,046 $1,577 $1,386 $684 $660 At December 31, 2023, IPL and WPL had $74 million and $32 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 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. 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 12 for discussion of Iowa Tax Reform, which resulted in a decrease in Alliant Energy’s and IPL’s tax-related regulatory assets in 2023. Pension and other postretirement benefits costs - The IUB, 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): Entity Asset Retirement Date Regulatory Asset Balance as of Dec. 31, 2023 Recovery Regulatory Approval IPL Lansing 2023 $216 Return of and return on remaining net book value through 2037 FERC and pending with the IUB (a) IPL Analog electric meters 2019 20 Return of remaining net book value through 2028 IUB and FERC IPL Sutherland Units 1 and 3 2017 12 Return of and return on remaining net book value through 2027 IUB and FERC IPL M.L. Kapp Unit 2 2018 11 Return of and return on remaining net book value through 2029 IUB and FERC WPL Edgewater Unit 4 2018 14 Return of and return on remaining net book value through 2028 PSCW and FERC (a) IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period includes a request with the IUB for continued recovery of the remaining net book value of Lansing through 2037. 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. In 2023, in conjunction with IPL's retirement of the Lansing Generating Station, IPL reclassified the remaining net book value of the associated AROs from property, plant and equipment to a regulatory asset on Alliant Energy’s and IPL’s balance sheets. Commodity cost recovery - Refer to Note 1(g) for details of IPL’s and WPL’s commodity cost recovery mechanisms. The cost recovery mechanism for WPL’s retail electric customers is based on forecasts of certain fuel-related costs expected to be incurred during forward-looking test periods and fuel monitoring ranges determined by the PSCW during each retail electric rate proceeding or in a separate fuel cost plan approval proceeding. In 2021, WPL’s actual fuel-related costs fell outside these fuel monitoring ranges, resulting in a $37 million deferral as of December 31, 2022, which was collected in 2023 from its retail electric customers, plus interest. 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 was collected in 2023). In 2023, actual fuel-related costs fell outside these fuel monitoring ranges, resulting in a $34 million regulatory liability as of December 31, 2023, which is expected to be addressed in a future regulatory proceeding. 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 15 for discussion of changes in Alliant Energy’s, IPL’s and WPL’s derivative liabilities/assets during 2023, which resulted in comparable changes to regulatory assets/liabilities on the balance sheets. WPL’s Western Wisconsin gas distribution expansion investments - WPL made contributions in aid of construction to a third party for investments as part of its Western Wisconsin gas distribution expansion project. Pursuant to authorization by the PSCW, Alliant Energy and WPL have recorded a regulatory asset for these costs, and are authorized by the PSCW to recover these amounts from WPL’s retail gas customers in base rates from 2021 through the end of 2040. 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 the end of 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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Tax-related $566 $579 $299 $303 $267 $276 Cost of removal obligations 366 398 242 259 124 139 Derivatives 65 210 34 115 31 95 Commodity cost recovery 48 40 13 38 35 2 WPL’s West Riverside liquidated damages 1 32 — — 1 32 Other 84 65 56 39 28 26 $1,130 $1,324 $644 $754 $486 $570 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. 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. WPL’s West Riverside liquidated damages - Pursuant to terms included in the related West Riverside construction procurement contracts, WPL reached agreement with the contractor on liquidated damages in 2020. A significant portion of the liquidated damages was settled by WPL offsetting amounts owed to the contractor that were previously withheld for payment, which were non-cash investing activities. Pursuant to PSCW authorization, WPL’s amortization of liquidated damages related to West Riverside construction procurement contracts was used to offset increases in WPL’s retail electric 2022/2023 Test Period revenue requirement, resulting in decreases in regulatory liabilities on Alliant Energy’s and WPL’s balance sheets and decreases in depreciation and amortization expenses in Alliant Energy’s and WPL’s income statements in 2023. Rate Reviews - WPL’s Retail Electric and Gas Rate Reviews (2022/2023 Forward-looking Test Period) - In December 2021, the PSCW issued an order authorizing annual base rate increases of $114 million and $15 million for WPL’s retail electric and gas customers, respectively, covering the 2022/2023 forward-looking Test Period, which was based on a stipulated agreement between WPL and certain stakeholders. The key drivers for the annual base rate increases include higher retail fuel-related costs in 2022, lower excess deferred income tax benefits in 2022 and 2023 and revenue requirement impacts of increasing electric and gas rate base, including investments in solar generation. In addition, the PSCW authorized WPL to receive a recovery of and a return on the remaining net book value of Edgewater Unit 5 through 2023. WPL's settlement extended, with certain modifications, an earnings sharing mechanism through 2023. Retail electric rate changes were effective on January 1, 2022 and extended through the end of 2023. Retail gas rate changes were effective on January 1, 2022 and extended through the end of 2022. In December 2022, the PSCW issued an order authorizing an additional annual base rate increase of $9 million for WPL’s retail gas customers, covering the 2023 forward-looking Test Period, which reflects changes in weighted average cost of capital, updated depreciation rates and modifications to certain regulatory asset and regulatory liability amortizations. These retail gas rate changes were effective on January 1, 2023 and extended through the end of 2023. 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.
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, 2023 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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Tax-related $934 $929 $831 $848 $103 $81 Pension and OPEB costs 347 392 171 197 176 195 Assets retired early 273 70 259 53 14 17 AROs 194 151 160 110 34 41 Commodity cost recovery 120 160 12 1 108 159 Derivatives 102 84 34 48 68 36 WPL’s Western Wisconsin gas distribution expansion investments 44 48 — — 44 48 IPL’s DAEC PPA amendment 42 66 42 66 — — Other 205 146 68 63 137 83 $2,261 $2,046 $1,577 $1,386 $684 $660 At December 31, 2023, IPL and WPL had $74 million and $32 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 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. 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 12 for discussion of Iowa Tax Reform, which resulted in a decrease in Alliant Energy’s and IPL’s tax-related regulatory assets in 2023. Pension and other postretirement benefits costs - The IUB, 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): Entity Asset Retirement Date Regulatory Asset Balance as of Dec. 31, 2023 Recovery Regulatory Approval IPL Lansing 2023 $216 Return of and return on remaining net book value through 2037 FERC and pending with the IUB (a) IPL Analog electric meters 2019 20 Return of remaining net book value through 2028 IUB and FERC IPL Sutherland Units 1 and 3 2017 12 Return of and return on remaining net book value through 2027 IUB and FERC IPL M.L. Kapp Unit 2 2018 11 Return of and return on remaining net book value through 2029 IUB and FERC WPL Edgewater Unit 4 2018 14 Return of and return on remaining net book value through 2028 PSCW and FERC (a) IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period includes a request with the IUB for continued recovery of the remaining net book value of Lansing through 2037. 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. In 2023, in conjunction with IPL's retirement of the Lansing Generating Station, IPL reclassified the remaining net book value of the associated AROs from property, plant and equipment to a regulatory asset on Alliant Energy’s and IPL’s balance sheets. Commodity cost recovery - Refer to Note 1(g) for details of IPL’s and WPL’s commodity cost recovery mechanisms. The cost recovery mechanism for WPL’s retail electric customers is based on forecasts of certain fuel-related costs expected to be incurred during forward-looking test periods and fuel monitoring ranges determined by the PSCW during each retail electric rate proceeding or in a separate fuel cost plan approval proceeding. In 2021, WPL’s actual fuel-related costs fell outside these fuel monitoring ranges, resulting in a $37 million deferral as of December 31, 2022, which was collected in 2023 from its retail electric customers, plus interest. 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 was collected in 2023). In 2023, actual fuel-related costs fell outside these fuel monitoring ranges, resulting in a $34 million regulatory liability as of December 31, 2023, which is expected to be addressed in a future regulatory proceeding. 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 15 for discussion of changes in Alliant Energy’s, IPL’s and WPL’s derivative liabilities/assets during 2023, which resulted in comparable changes to regulatory assets/liabilities on the balance sheets. WPL’s Western Wisconsin gas distribution expansion investments - WPL made contributions in aid of construction to a third party for investments as part of its Western Wisconsin gas distribution expansion project. Pursuant to authorization by the PSCW, Alliant Energy and WPL have recorded a regulatory asset for these costs, and are authorized by the PSCW to recover these amounts from WPL’s retail gas customers in base rates from 2021 through the end of 2040. 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 the end of 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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Tax-related $566 $579 $299 $303 $267 $276 Cost of removal obligations 366 398 242 259 124 139 Derivatives 65 210 34 115 31 95 Commodity cost recovery 48 40 13 38 35 2 WPL’s West Riverside liquidated damages 1 32 — — 1 32 Other 84 65 56 39 28 26 $1,130 $1,324 $644 $754 $486 $570 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. 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. WPL’s West Riverside liquidated damages - Pursuant to terms included in the related West Riverside construction procurement contracts, WPL reached agreement with the contractor on liquidated damages in 2020. A significant portion of the liquidated damages was settled by WPL offsetting amounts owed to the contractor that were previously withheld for payment, which were non-cash investing activities. Pursuant to PSCW authorization, WPL’s amortization of liquidated damages related to West Riverside construction procurement contracts was used to offset increases in WPL’s retail electric 2022/2023 Test Period revenue requirement, resulting in decreases in regulatory liabilities on Alliant Energy’s and WPL’s balance sheets and decreases in depreciation and amortization expenses in Alliant Energy’s and WPL’s income statements in 2023. Rate Reviews - WPL’s Retail Electric and Gas Rate Reviews (2022/2023 Forward-looking Test Period) - In December 2021, the PSCW issued an order authorizing annual base rate increases of $114 million and $15 million for WPL’s retail electric and gas customers, respectively, covering the 2022/2023 forward-looking Test Period, which was based on a stipulated agreement between WPL and certain stakeholders. The key drivers for the annual base rate increases include higher retail fuel-related costs in 2022, lower excess deferred income tax benefits in 2022 and 2023 and revenue requirement impacts of increasing electric and gas rate base, including investments in solar generation. In addition, the PSCW authorized WPL to receive a recovery of and a return on the remaining net book value of Edgewater Unit 5 through 2023. WPL's settlement extended, with certain modifications, an earnings sharing mechanism through 2023. Retail electric rate changes were effective on January 1, 2022 and extended through the end of 2023. Retail gas rate changes were effective on January 1, 2022 and extended through the end of 2022. In December 2022, the PSCW issued an order authorizing an additional annual base rate increase of $9 million for WPL’s retail gas customers, covering the 2023 forward-looking Test Period, which reflects changes in weighted average cost of capital, updated depreciation rates and modifications to certain regulatory asset and regulatory liability amortizations. These retail gas rate changes were effective on January 1, 2023 and extended through the end of 2023. 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.
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, 2023 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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Tax-related $934 $929 $831 $848 $103 $81 Pension and OPEB costs 347 392 171 197 176 195 Assets retired early 273 70 259 53 14 17 AROs 194 151 160 110 34 41 Commodity cost recovery 120 160 12 1 108 159 Derivatives 102 84 34 48 68 36 WPL’s Western Wisconsin gas distribution expansion investments 44 48 — — 44 48 IPL’s DAEC PPA amendment 42 66 42 66 — — Other 205 146 68 63 137 83 $2,261 $2,046 $1,577 $1,386 $684 $660 At December 31, 2023, IPL and WPL had $74 million and $32 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 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. 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 12 for discussion of Iowa Tax Reform, which resulted in a decrease in Alliant Energy’s and IPL’s tax-related regulatory assets in 2023. Pension and other postretirement benefits costs - The IUB, 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): Entity Asset Retirement Date Regulatory Asset Balance as of Dec. 31, 2023 Recovery Regulatory Approval IPL Lansing 2023 $216 Return of and return on remaining net book value through 2037 FERC and pending with the IUB (a) IPL Analog electric meters 2019 20 Return of remaining net book value through 2028 IUB and FERC IPL Sutherland Units 1 and 3 2017 12 Return of and return on remaining net book value through 2027 IUB and FERC IPL M.L. Kapp Unit 2 2018 11 Return of and return on remaining net book value through 2029 IUB and FERC WPL Edgewater Unit 4 2018 14 Return of and return on remaining net book value through 2028 PSCW and FERC (a) IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period includes a request with the IUB for continued recovery of the remaining net book value of Lansing through 2037. 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. In 2023, in conjunction with IPL's retirement of the Lansing Generating Station, IPL reclassified the remaining net book value of the associated AROs from property, plant and equipment to a regulatory asset on Alliant Energy’s and IPL’s balance sheets. Commodity cost recovery - Refer to Note 1(g) for details of IPL’s and WPL’s commodity cost recovery mechanisms. The cost recovery mechanism for WPL’s retail electric customers is based on forecasts of certain fuel-related costs expected to be incurred during forward-looking test periods and fuel monitoring ranges determined by the PSCW during each retail electric rate proceeding or in a separate fuel cost plan approval proceeding. In 2021, WPL’s actual fuel-related costs fell outside these fuel monitoring ranges, resulting in a $37 million deferral as of December 31, 2022, which was collected in 2023 from its retail electric customers, plus interest. 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 was collected in 2023). In 2023, actual fuel-related costs fell outside these fuel monitoring ranges, resulting in a $34 million regulatory liability as of December 31, 2023, which is expected to be addressed in a future regulatory proceeding. 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 15 for discussion of changes in Alliant Energy’s, IPL’s and WPL’s derivative liabilities/assets during 2023, which resulted in comparable changes to regulatory assets/liabilities on the balance sheets. WPL’s Western Wisconsin gas distribution expansion investments - WPL made contributions in aid of construction to a third party for investments as part of its Western Wisconsin gas distribution expansion project. Pursuant to authorization by the PSCW, Alliant Energy and WPL have recorded a regulatory asset for these costs, and are authorized by the PSCW to recover these amounts from WPL’s retail gas customers in base rates from 2021 through the end of 2040. 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 the end of 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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Tax-related $566 $579 $299 $303 $267 $276 Cost of removal obligations 366 398 242 259 124 139 Derivatives 65 210 34 115 31 95 Commodity cost recovery 48 40 13 38 35 2 WPL’s West Riverside liquidated damages 1 32 — — 1 32 Other 84 65 56 39 28 26 $1,130 $1,324 $644 $754 $486 $570 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. 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. WPL’s West Riverside liquidated damages - Pursuant to terms included in the related West Riverside construction procurement contracts, WPL reached agreement with the contractor on liquidated damages in 2020. A significant portion of the liquidated damages was settled by WPL offsetting amounts owed to the contractor that were previously withheld for payment, which were non-cash investing activities. Pursuant to PSCW authorization, WPL’s amortization of liquidated damages related to West Riverside construction procurement contracts was used to offset increases in WPL’s retail electric 2022/2023 Test Period revenue requirement, resulting in decreases in regulatory liabilities on Alliant Energy’s and WPL’s balance sheets and decreases in depreciation and amortization expenses in Alliant Energy’s and WPL’s income statements in 2023. Rate Reviews - WPL’s Retail Electric and Gas Rate Reviews (2022/2023 Forward-looking Test Period) - In December 2021, the PSCW issued an order authorizing annual base rate increases of $114 million and $15 million for WPL’s retail electric and gas customers, respectively, covering the 2022/2023 forward-looking Test Period, which was based on a stipulated agreement between WPL and certain stakeholders. The key drivers for the annual base rate increases include higher retail fuel-related costs in 2022, lower excess deferred income tax benefits in 2022 and 2023 and revenue requirement impacts of increasing electric and gas rate base, including investments in solar generation. In addition, the PSCW authorized WPL to receive a recovery of and a return on the remaining net book value of Edgewater Unit 5 through 2023. WPL's settlement extended, with certain modifications, an earnings sharing mechanism through 2023. Retail electric rate changes were effective on January 1, 2022 and extended through the end of 2023. Retail gas rate changes were effective on January 1, 2022 and extended through the end of 2022. In December 2022, the PSCW issued an order authorizing an additional annual base rate increase of $9 million for WPL’s retail gas customers, covering the 2023 forward-looking Test Period, which reflects changes in weighted average cost of capital, updated depreciation rates and modifications to certain regulatory asset and regulatory liability amortizations. These retail gas rate changes were effective on January 1, 2023 and extended through the end of 2023. 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.

Property, Plant and Equipment

Property, Plant and Equipment	12 Months Ended
	Dec. 31, 2023
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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Utility: Electric plant: Generation in service (a) $9,180 $8,060 $5,025 $4,962 $4,155 $3,098 Distribution in service 7,314 6,912 4,091 3,876 3,223 3,036 Other in service 567 543 356 354 211 189 Anticipated to be retired early (b) 1,629 2,103 — 491 1,629 1,612 Total electric plant 18,690 17,618 9,472 9,683 9,218 7,935 Gas plant in service 1,791 1,705 951 910 840 795 Other plant in service 653 624 411 402 242 222 Accumulated depreciation (b) (5,924) (5,690) (3,180) (3,149) (2,744) (2,541) Net plant 15,210 14,257 7,654 7,846 7,556 6,411 Leased Sheboygan Falls Energy Facility, net (c) — — — — 79 15 Leased land for solar generation, net 172 133 33 — 139 133 Construction work in progress 1,245 1,357 605 194 640 1,163 Other, net 7 6 6 6 1 — Total utility 16,634 15,753 8,298 8,046 8,415 7,722 Non-utility and other: Non-utility Generation, net (d) 68 71 — — — — Corporate Services and other, net (e) 455 423 — — — — Total non-utility and other 523 494 — — — — Total property, plant and equipment $17,157 $16,247 $8,298 $8,046 $8,415 $7,722 (a) Alliant Energy and WPL currently expect estimated construction costs associated with WPL’s approximately 1,100 MW of new solar generation will exceed amounts previously approved by the PSCW by approximately $180 million. In February 2024, the PSCW issued an oral decision approving WPL’s deferral request to seek recovery of these costs in a future regulatory proceeding. Alliant Energy and IPL currently expect the estimated construction costs associated with IPL’s 400 MW of new solar generation will exceed the cost target of $1,650/kilowatt, including AFUDC and transmission upgrade costs among other costs, approved in the IUB’s advance rate-making principles by approximately 10%. Alliant Energy, IPL and WPL concluded that there was not a probable disallowance of anticipated higher rate base amounts as of December 31, 2023 given construction costs were reasonably and prudently incurred. (b) In 2023, IPL retired Lansing and reclassified the remaining net book value of this EGU from property, plant and equipment to a regulatory asset on Alliant Energy’s and IPL’s balance sheets. In 2020 and 2021, WPL received approval from MISO to retire Edgewater Unit 5, and Columbia Units 1 and 2, respectively. WPL currently anticipates retiring Edgewater Unit 5 by June 1, 2025, and Columbia Units 1 and 2 by June 1, 2026. Alliant Energy and WPL concluded that Edgewater Unit 5 and Columbia Units 1 and 2 met the criteria to be considered probable of abandonment as of December 31, 2023. 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, Alliant Energy and WPL concluded that no disallowance was required as of December 31, 2023. As of December 31, 2023, net book values were $504 million for Edgewater Unit 5, and $428 million for Columbia Units 1 and 2 in aggregate. (c) Less accumulated amortization of $112 million and $106 million for WPL as of December 31, 2023 and 2022, respectively. Refer to Note 10 for discussion of WPL’s renewal of this lease in 2023. 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. (d) Less accumulated depreciation of $75 million and $71 million for Alliant Energy as of December 31, 2023 and 2022, respectively. (e) Less accumulated depreciation of $275 million and $269 million for Alliant Energy as of December 31, 2023 and 2022, 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 Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Equity $74 $44 $18 $15 $8 $7 $59 $36 $11 Debt 26 16 7 6 3 2 20 13 5 $100 $60 $25 $21 $11 $9 $79 $49 $16 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 a customer billing and information system for IPL and WPL and other computer software, and the corporate headquarters building located in Madison, Wisconsin. The customer billing and information system is amortized using the straight-line method over a 12-year period. The majority of the remaining 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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Utility: Electric plant: Generation in service (a) $9,180 $8,060 $5,025 $4,962 $4,155 $3,098 Distribution in service 7,314 6,912 4,091 3,876 3,223 3,036 Other in service 567 543 356 354 211 189 Anticipated to be retired early (b) 1,629 2,103 — 491 1,629 1,612 Total electric plant 18,690 17,618 9,472 9,683 9,218 7,935 Gas plant in service 1,791 1,705 951 910 840 795 Other plant in service 653 624 411 402 242 222 Accumulated depreciation (b) (5,924) (5,690) (3,180) (3,149) (2,744) (2,541) Net plant 15,210 14,257 7,654 7,846 7,556 6,411 Leased Sheboygan Falls Energy Facility, net (c) — — — — 79 15 Leased land for solar generation, net 172 133 33 — 139 133 Construction work in progress 1,245 1,357 605 194 640 1,163 Other, net 7 6 6 6 1 — Total utility 16,634 15,753 8,298 8,046 8,415 7,722 Non-utility and other: Non-utility Generation, net (d) 68 71 — — — — Corporate Services and other, net (e) 455 423 — — — — Total non-utility and other 523 494 — — — — Total property, plant and equipment $17,157 $16,247 $8,298 $8,046 $8,415 $7,722 (a) Alliant Energy and WPL currently expect estimated construction costs associated with WPL’s approximately 1,100 MW of new solar generation will exceed amounts previously approved by the PSCW by approximately $180 million. In February 2024, the PSCW issued an oral decision approving WPL’s deferral request to seek recovery of these costs in a future regulatory proceeding. Alliant Energy and IPL currently expect the estimated construction costs associated with IPL’s 400 MW of new solar generation will exceed the cost target of $1,650/kilowatt, including AFUDC and transmission upgrade costs among other costs, approved in the IUB’s advance rate-making principles by approximately 10%. Alliant Energy, IPL and WPL concluded that there was not a probable disallowance of anticipated higher rate base amounts as of December 31, 2023 given construction costs were reasonably and prudently incurred. (b) In 2023, IPL retired Lansing and reclassified the remaining net book value of this EGU from property, plant and equipment to a regulatory asset on Alliant Energy’s and IPL’s balance sheets. In 2020 and 2021, WPL received approval from MISO to retire Edgewater Unit 5, and Columbia Units 1 and 2, respectively. WPL currently anticipates retiring Edgewater Unit 5 by June 1, 2025, and Columbia Units 1 and 2 by June 1, 2026. Alliant Energy and WPL concluded that Edgewater Unit 5 and Columbia Units 1 and 2 met the criteria to be considered probable of abandonment as of December 31, 2023. 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, Alliant Energy and WPL concluded that no disallowance was required as of December 31, 2023. As of December 31, 2023, net book values were $504 million for Edgewater Unit 5, and $428 million for Columbia Units 1 and 2 in aggregate. (c) Less accumulated amortization of $112 million and $106 million for WPL as of December 31, 2023 and 2022, respectively. Refer to Note 10 for discussion of WPL’s renewal of this lease in 2023. 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. (d) Less accumulated depreciation of $75 million and $71 million for Alliant Energy as of December 31, 2023 and 2022, respectively. (e) Less accumulated depreciation of $275 million and $269 million for Alliant Energy as of December 31, 2023 and 2022, 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 Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Equity $74 $44 $18 $15 $8 $7 $59 $36 $11 Debt 26 16 7 6 3 2 20 13 5 $100 $60 $25 $21 $11 $9 $79 $49 $16
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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Utility: Electric plant: Generation in service (a) $9,180 $8,060 $5,025 $4,962 $4,155 $3,098 Distribution in service 7,314 6,912 4,091 3,876 3,223 3,036 Other in service 567 543 356 354 211 189 Anticipated to be retired early (b) 1,629 2,103 — 491 1,629 1,612 Total electric plant 18,690 17,618 9,472 9,683 9,218 7,935 Gas plant in service 1,791 1,705 951 910 840 795 Other plant in service 653 624 411 402 242 222 Accumulated depreciation (b) (5,924) (5,690) (3,180) (3,149) (2,744) (2,541) Net plant 15,210 14,257 7,654 7,846 7,556 6,411 Leased Sheboygan Falls Energy Facility, net (c) — — — — 79 15 Leased land for solar generation, net 172 133 33 — 139 133 Construction work in progress 1,245 1,357 605 194 640 1,163 Other, net 7 6 6 6 1 — Total utility 16,634 15,753 8,298 8,046 8,415 7,722 Non-utility and other: Non-utility Generation, net (d) 68 71 — — — — Corporate Services and other, net (e) 455 423 — — — — Total non-utility and other 523 494 — — — — Total property, plant and equipment $17,157 $16,247 $8,298 $8,046 $8,415 $7,722 (a) Alliant Energy and WPL currently expect estimated construction costs associated with WPL’s approximately 1,100 MW of new solar generation will exceed amounts previously approved by the PSCW by approximately $180 million. In February 2024, the PSCW issued an oral decision approving WPL’s deferral request to seek recovery of these costs in a future regulatory proceeding. Alliant Energy and IPL currently expect the estimated construction costs associated with IPL’s 400 MW of new solar generation will exceed the cost target of $1,650/kilowatt, including AFUDC and transmission upgrade costs among other costs, approved in the IUB’s advance rate-making principles by approximately 10%. Alliant Energy, IPL and WPL concluded that there was not a probable disallowance of anticipated higher rate base amounts as of December 31, 2023 given construction costs were reasonably and prudently incurred. (b) In 2023, IPL retired Lansing and reclassified the remaining net book value of this EGU from property, plant and equipment to a regulatory asset on Alliant Energy’s and IPL’s balance sheets. In 2020 and 2021, WPL received approval from MISO to retire Edgewater Unit 5, and Columbia Units 1 and 2, respectively. WPL currently anticipates retiring Edgewater Unit 5 by June 1, 2025, and Columbia Units 1 and 2 by June 1, 2026. Alliant Energy and WPL concluded that Edgewater Unit 5 and Columbia Units 1 and 2 met the criteria to be considered probable of abandonment as of December 31, 2023. 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, Alliant Energy and WPL concluded that no disallowance was required as of December 31, 2023. As of December 31, 2023, net book values were $504 million for Edgewater Unit 5, and $428 million for Columbia Units 1 and 2 in aggregate. (c) Less accumulated amortization of $112 million and $106 million for WPL as of December 31, 2023 and 2022, respectively. Refer to Note 10 for discussion of WPL’s renewal of this lease in 2023. 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. (d) Less accumulated depreciation of $75 million and $71 million for Alliant Energy as of December 31, 2023 and 2022, respectively. (e) Less accumulated depreciation of $275 million and $269 million for Alliant Energy as of December 31, 2023 and 2022, 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 Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Equity $74 $44 $18 $15 $8 $7 $59 $36 $11 Debt 26 16 7 6 3 2 20 13 5 $100 $60 $25 $21 $11 $9 $79 $49 $16

Jointly-Owned Electric Utility

Jointly-Owned Electric Utility Plant	12 Months Ended
	Dec. 31, 2023
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, 2023 was as follows (dollars in millions): Ownership Electric Accumulated Provision Construction Interest % Plant for Depreciation Work in Progress IPL Ottumwa Unit 1 48.0% $632 $264 $7 George Neal Unit 4 25.7% 196 107 6 George Neal Unit 3 28.0% 181 85 8 Louisa Unit 1 4.0% 44 22 — 1,053 478 21 WPL Columbia Units 1-2 53.5% 818 361 6 West Riverside Energy Center and Solar Facility (a) 73.8% 581 60 6 Forward Wind Energy Center 42.6% 118 53 — 1,517 474 12 Alliant Energy $2,570 $952 $33 (a) In 2023, Madison Gas and Electric Company and WEC Energy Group, Inc. 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.
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, 2023 was as follows (dollars in millions): Ownership Electric Accumulated Provision Construction Interest % Plant for Depreciation Work in Progress IPL Ottumwa Unit 1 48.0% $632 $264 $7 George Neal Unit 4 25.7% 196 107 6 George Neal Unit 3 28.0% 181 85 8 Louisa Unit 1 4.0% 44 22 — 1,053 478 21 WPL Columbia Units 1-2 53.5% 818 361 6 West Riverside Energy Center and Solar Facility (a) 73.8% 581 60 6 Forward Wind Energy Center 42.6% 118 53 — 1,517 474 12 Alliant Energy $2,570 $952 $33 (a) In 2023, Madison Gas and Electric Company and WEC Energy Group, Inc. 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.
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, 2023 was as follows (dollars in millions): Ownership Electric Accumulated Provision Construction Interest % Plant for Depreciation Work in Progress IPL Ottumwa Unit 1 48.0% $632 $264 $7 George Neal Unit 4 25.7% 196 107 6 George Neal Unit 3 28.0% 181 85 8 Louisa Unit 1 4.0% 44 22 — 1,053 478 21 WPL Columbia Units 1-2 53.5% 818 361 6 West Riverside Energy Center and Solar Facility (a) 73.8% 581 60 6 Forward Wind Energy Center 42.6% 118 53 — 1,517 474 12 Alliant Energy $2,570 $952 $33 (a) In 2023, Madison Gas and Electric Company and WEC Energy Group, Inc. 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.

Receivables

Receivables	12 Months Ended
	Dec. 31, 2023
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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Customer $121 $114 $— $— $110 $102 Unbilled utility revenues 93 115 — — 93 115 Deferred proceeds 216 185 216 185 — — Other 53 109 26 74 24 34 Allowance for expected credit losses (8) (7) — — (8) (7) $475 $516 $242 $259 $219 $244 In 2023, gross write-offs for accounts receivable were as follows (in millions): Originated in 2022 Originated in 2023 Alliant Energy $12 $13 IPL 8 8 WPL 4 5 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. The purchase commitment from the third party to which IPL sells its receivables expires in March 2024. IPL currently expects to amend and extend the purchase commitment. 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 16 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, 2023, the limit on cash proceeds was $5 million and IPL had $4 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): Maximum Average 2023 2022 2021 2023 2022 2021 Outstanding aggregate cash proceeds $110 $80 $110 $51 $14 $46 As of December 31, the attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): 2023 2022 Customer accounts receivable $130 $145 Unbilled utility revenues 98 132 Other receivables 1 — Receivables sold to third party 229 277 Less: cash proceeds 1 80 Deferred proceeds 228 197 Less: allowance for expected credit losses 12 12 Fair value of deferred proceeds $216 $185 Outstanding receivables past due $22 $26 Additional attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): 2023 2022 2021 Collections $2,233 $2,302 $2,134 Write-offs, net of recoveries 12 9 9 Effective January 2024, the limit on cash proceeds under the Receivables Agreement is $110 million.
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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Customer $121 $114 $— $— $110 $102 Unbilled utility revenues 93 115 — — 93 115 Deferred proceeds 216 185 216 185 — — Other 53 109 26 74 24 34 Allowance for expected credit losses (8) (7) — — (8) (7) $475 $516 $242 $259 $219 $244 In 2023, gross write-offs for accounts receivable were as follows (in millions): Originated in 2022 Originated in 2023 Alliant Energy $12 $13 IPL 8 8 WPL 4 5 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. The purchase commitment from the third party to which IPL sells its receivables expires in March 2024. IPL currently expects to amend and extend the purchase commitment. 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 16 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, 2023, the limit on cash proceeds was $5 million and IPL had $4 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): Maximum Average 2023 2022 2021 2023 2022 2021 Outstanding aggregate cash proceeds $110 $80 $110 $51 $14 $46 As of December 31, the attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): 2023 2022 Customer accounts receivable $130 $145 Unbilled utility revenues 98 132 Other receivables 1 — Receivables sold to third party 229 277 Less: cash proceeds 1 80 Deferred proceeds 228 197 Less: allowance for expected credit losses 12 12 Fair value of deferred proceeds $216 $185 Outstanding receivables past due $22 $26 Additional attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): 2023 2022 2021 Collections $2,233 $2,302 $2,134 Write-offs, net of recoveries 12 9 9 Effective January 2024, the limit on cash proceeds under the Receivables Agreement is $110 million.
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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Customer $121 $114 $— $— $110 $102 Unbilled utility revenues 93 115 — — 93 115 Deferred proceeds 216 185 216 185 — — Other 53 109 26 74 24 34 Allowance for expected credit losses (8) (7) — — (8) (7) $475 $516 $242 $259 $219 $244 In 2023, gross write-offs for accounts receivable were as follows (in millions): Originated in 2022 Originated in 2023 Alliant Energy $12 $13 IPL 8 8 WPL 4 5

Investments

Investments	12 Months Ended
	Dec. 31, 2023
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 at Carrying Value at December 31, Equity (Income) / Loss December 31, 2023 2023 2022 2023 2022 2021 ATC Holdings 16%, 20% $386 $358 ($49) ($41) ($43) Non-utility wind farm in Oklahoma 50% 104 101 (7) (5) (4) Corporate venture investments Various 74 62 (2) (3) (13) Other Various 21 21 (3) (2) (2) $585 $542 ($61) ($51) ($62) Summary aggregate financial information from the financial statements of these holdings is as follows (in millions): Alliant Energy 2023 2022 2021 Revenues $898 $813 $802 Operating income 384 350 357 Net income 370 675 358 As of December 31: Current assets 221 227 Non-current assets 9,032 8,292 Current liabilities 528 620 Non-current liabilities 3,584 3,285 Noncontrolling interest 259 289 ATC Holdings - As of December 31, 2023, 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 17(g) for discussion of a reduction in earnings recorded in 2022 related to a court decision, which is currently expected to reduce 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 17(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 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.

Common Equity

Common Equity	12 Months Ended
	Dec. 31, 2023
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: 2023 2022 2021 Shares outstanding, January 1 251,134,966 250,474,529 249,868,415 At-the-market offering program 4,372,561 — — Shareowner Direct Plan 454,987 437,669 492,565 Equity-based compensation plans 134,334 222,768 113,549 Shares outstanding, December 31 256,096,848 251,134,966 250,474,529 At December 31, 2023, Alliant Energy had a total of 13 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. As of December 31, 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.

Preferred Stock

Preferred Stock	12 Months Ended
	Dec. 31, 2023
Preferred Stock	PREFERRED STOCK In 2021, IPL redeemed all 8,000,000 outstanding shares of its 5.1% cumulative preferred stock at the $25 per share par value for $200 million plus accrued and unpaid dividends up to the redemption date. In 2021, Alliant Energy and IPL recorded a $5 million non-cash charge related to this transaction in “Preferred dividend requirements” in their income statements.
IPL [Member]
Preferred Stock	PREFERRED STOCK In 2021, IPL redeemed all 8,000,000 outstanding shares of its 5.1% cumulative preferred stock at the $25 per share par value for $200 million plus accrued and unpaid dividends up to the redemption date. In 2021, Alliant Energy and IPL recorded a $5 million non-cash charge related to this transaction in “Preferred dividend requirements” in their income statements.

Debt

Debt	12 Months Ended
	Dec. 31, 2023
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, 2023, the short-term borrowing capacity under a single credit facility agreement totaled $1 billion ($450 million for Alliant Energy at the parent company level, $150 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 $500 million, $400 million and $500 million, respectively, within the $1 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 Energy IPL WPL December 31 2023 2022 2023 2022 2023 2022 Amount outstanding $475 $642 $— $— $318 $290 Weighted average interest rates 5.5% 4.6% N/A N/A 5.4% 4.5% Available credit facility capacity $525 $358 $150 $100 $82 $110 Alliant Energy IPL WPL For the year ended 2023 2022 2023 2022 2023 2022 Maximum amount outstanding (based on daily outstanding balances) $793 $665 $70 $— $349 $325 Average amount outstanding (based on daily outstanding balances) $386 $411 $2 $— $157 $153 Weighted average interest rates 5.2% 2.1% 5.3% —% 5.1% 1.6% In January 2024, Alliant Energy, IPL and WPL extended their single credit facility agreement, which currently expires in December 2028, and reallocated credit facility capacity amounts to $350 million for Alliant Energy at the parent company level, $150 million for IPL and $500 million for WPL, within the $1 billion total commitment. Long-term debt, net as of December 31 was as follows (dollars in millions): 2023 2022 Alliant Energy IPL WPL Alliant Energy IPL WPL Senior Debentures (a): 3.25%, due 2024 $500 $500 $— $500 $500 $— 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 (b) 300 300 — — — — 6.45%, due 2033 100 100 — 100 100 — 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 — 3,975 3,975 — 3,675 3,675 — 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 (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 3,100 — 3,100 2,800 — 2,800 Other: AEF term loan credit agreement through March 2024, 6% at December 31, 2023 (with Alliant Energy as guarantor) (d) 300 — — 400 — — 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 — — — — — 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)(f) 300 — — — — — AEF 3.6% senior notes, due 2032 (with Alliant Energy as guarantor) (a) 350 — — 350 — — Sheboygan Power, LLC 5.06% senior secured notes, due 2024 (secured by the Sheboygan Falls Energy Facility and related assets) (a) 9 — — 17 — — AEF 3.75% senior notes (with Alliant Energy as guarantor) (Retired in 2023) — — — 400 — — Other, 1% at December 31, 2023, due 2024 to 2025 — — — 1 — — 2,034 — — 1,668 — — Subtotal 9,109 3,975 3,100 8,143 3,675 2,800 Current maturities (809) (500) — (408) — — Unamortized debt issuance costs (54) (21) (19) (45) (21) (19) Unamortized debt (discount) and premium, net (21) (9) (11) (22) (8) (11) Long-term debt, net (g) $8,225 $3,445 $3,070 $7,668 $3,646 $2,770 (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 2023, IPL issued $300 million of 5.7% senior debentures due 2033. The net proceeds from the issuance were used to reduce cash amounts received from its sales of accounts receivable program, reduce commercial paper classified as long-term debt, for general corporate purposes and/or were placed in money market fund investments. (c) In March 2023, WPL issued $300 million of 4.95% debentures due 2033. 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 its solar EGUs. (d) In January 2023, AEF entered into a $300 million interest rate swap maturing in January 2026 to mitigate interest rate risk. Under the terms of the swap, AEF exchanged a variable interest rate for a fixed interest rate of 3.93% on a portion of its variable-rate term loan borrowings. In December 2023, AEF retired the remaining $100 million variable-rate term loan borrowings. Refer to Note 15 for additional information on the interest rate swap. (e) Refer to “ Convertible Senior Notes ” below for additional information. (f) In November 2023, AEF issued $300 million of 5.95% senior notes due 2029. The net proceeds from AEF’s issuance 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, 2023, the conditions allowing holders of the Notes to convert their Notes were not met, and as a result, the Notes were classified as “Long-term debt, net” on Alliant Energy’s balance sheet. As of December 31, 2023, the net carrying amount of the Notes was $568 million, with unamortized debt issuance costs of $7 million, and the estimated fair value (Level 2) of the Notes was $572 million. As of December 31, 2023, 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, 2023, long-term debt maturities for 2024 through 2028 were as follows (in millions): 2024 2025 2026 2027 2028 IPL $500 $300 $— $— $500 WPL — — — 300 — AEF 309 — 200 — 300 Alliant Energy parent company — — 575 — — Alliant Energy $809 $300 $775 $300 $800 Fair Value of Long-term Debt - Refer to Note 16 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, 2023, the short-term borrowing capacity under a single credit facility agreement totaled $1 billion ($450 million for Alliant Energy at the parent company level, $150 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 $500 million, $400 million and $500 million, respectively, within the $1 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 Energy IPL WPL December 31 2023 2022 2023 2022 2023 2022 Amount outstanding $475 $642 $— $— $318 $290 Weighted average interest rates 5.5% 4.6% N/A N/A 5.4% 4.5% Available credit facility capacity $525 $358 $150 $100 $82 $110 Alliant Energy IPL WPL For the year ended 2023 2022 2023 2022 2023 2022 Maximum amount outstanding (based on daily outstanding balances) $793 $665 $70 $— $349 $325 Average amount outstanding (based on daily outstanding balances) $386 $411 $2 $— $157 $153 Weighted average interest rates 5.2% 2.1% 5.3% —% 5.1% 1.6% In January 2024, Alliant Energy, IPL and WPL extended their single credit facility agreement, which currently expires in December 2028, and reallocated credit facility capacity amounts to $350 million for Alliant Energy at the parent company level, $150 million for IPL and $500 million for WPL, within the $1 billion total commitment. Long-term debt, net as of December 31 was as follows (dollars in millions): 2023 2022 Alliant Energy IPL WPL Alliant Energy IPL WPL Senior Debentures (a): 3.25%, due 2024 $500 $500 $— $500 $500 $— 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 (b) 300 300 — — — — 6.45%, due 2033 100 100 — 100 100 — 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 — 3,975 3,975 — 3,675 3,675 — 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 (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 3,100 — 3,100 2,800 — 2,800 Other: AEF term loan credit agreement through March 2024, 6% at December 31, 2023 (with Alliant Energy as guarantor) (d) 300 — — 400 — — 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 — — — — — 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)(f) 300 — — — — — AEF 3.6% senior notes, due 2032 (with Alliant Energy as guarantor) (a) 350 — — 350 — — Sheboygan Power, LLC 5.06% senior secured notes, due 2024 (secured by the Sheboygan Falls Energy Facility and related assets) (a) 9 — — 17 — — AEF 3.75% senior notes (with Alliant Energy as guarantor) (Retired in 2023) — — — 400 — — Other, 1% at December 31, 2023, due 2024 to 2025 — — — 1 — — 2,034 — — 1,668 — — Subtotal 9,109 3,975 3,100 8,143 3,675 2,800 Current maturities (809) (500) — (408) — — Unamortized debt issuance costs (54) (21) (19) (45) (21) (19) Unamortized debt (discount) and premium, net (21) (9) (11) (22) (8) (11) Long-term debt, net (g) $8,225 $3,445 $3,070 $7,668 $3,646 $2,770 (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 2023, IPL issued $300 million of 5.7% senior debentures due 2033. The net proceeds from the issuance were used to reduce cash amounts received from its sales of accounts receivable program, reduce commercial paper classified as long-term debt, for general corporate purposes and/or were placed in money market fund investments. (c) In March 2023, WPL issued $300 million of 4.95% debentures due 2033. 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 its solar EGUs. (d) In January 2023, AEF entered into a $300 million interest rate swap maturing in January 2026 to mitigate interest rate risk. Under the terms of the swap, AEF exchanged a variable interest rate for a fixed interest rate of 3.93% on a portion of its variable-rate term loan borrowings. In December 2023, AEF retired the remaining $100 million variable-rate term loan borrowings. Refer to Note 15 for additional information on the interest rate swap. (e) Refer to “ Convertible Senior Notes ” below for additional information. (f) In November 2023, AEF issued $300 million of 5.95% senior notes due 2029. The net proceeds from AEF’s issuance 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, 2023, the conditions allowing holders of the Notes to convert their Notes were not met, and as a result, the Notes were classified as “Long-term debt, net” on Alliant Energy’s balance sheet. As of December 31, 2023, the net carrying amount of the Notes was $568 million, with unamortized debt issuance costs of $7 million, and the estimated fair value (Level 2) of the Notes was $572 million. As of December 31, 2023, 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, 2023, long-term debt maturities for 2024 through 2028 were as follows (in millions): 2024 2025 2026 2027 2028 IPL $500 $300 $— $— $500 WPL — — — 300 — AEF 309 — 200 — 300 Alliant Energy parent company — — 575 — — Alliant Energy $809 $300 $775 $300 $800 Fair Value of Long-term Debt - Refer to Note 16 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, 2023, the short-term borrowing capacity under a single credit facility agreement totaled $1 billion ($450 million for Alliant Energy at the parent company level, $150 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 $500 million, $400 million and $500 million, respectively, within the $1 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 Energy IPL WPL December 31 2023 2022 2023 2022 2023 2022 Amount outstanding $475 $642 $— $— $318 $290 Weighted average interest rates 5.5% 4.6% N/A N/A 5.4% 4.5% Available credit facility capacity $525 $358 $150 $100 $82 $110 Alliant Energy IPL WPL For the year ended 2023 2022 2023 2022 2023 2022 Maximum amount outstanding (based on daily outstanding balances) $793 $665 $70 $— $349 $325 Average amount outstanding (based on daily outstanding balances) $386 $411 $2 $— $157 $153 Weighted average interest rates 5.2% 2.1% 5.3% —% 5.1% 1.6% In January 2024, Alliant Energy, IPL and WPL extended their single credit facility agreement, which currently expires in December 2028, and reallocated credit facility capacity amounts to $350 million for Alliant Energy at the parent company level, $150 million for IPL and $500 million for WPL, within the $1 billion total commitment. Long-term debt, net as of December 31 was as follows (dollars in millions): 2023 2022 Alliant Energy IPL WPL Alliant Energy IPL WPL Senior Debentures (a): 3.25%, due 2024 $500 $500 $— $500 $500 $— 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 (b) 300 300 — — — — 6.45%, due 2033 100 100 — 100 100 — 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 — 3,975 3,975 — 3,675 3,675 — 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 (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 3,100 — 3,100 2,800 — 2,800 Other: AEF term loan credit agreement through March 2024, 6% at December 31, 2023 (with Alliant Energy as guarantor) (d) 300 — — 400 — — 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 — — — — — 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)(f) 300 — — — — — AEF 3.6% senior notes, due 2032 (with Alliant Energy as guarantor) (a) 350 — — 350 — — Sheboygan Power, LLC 5.06% senior secured notes, due 2024 (secured by the Sheboygan Falls Energy Facility and related assets) (a) 9 — — 17 — — AEF 3.75% senior notes (with Alliant Energy as guarantor) (Retired in 2023) — — — 400 — — Other, 1% at December 31, 2023, due 2024 to 2025 — — — 1 — — 2,034 — — 1,668 — — Subtotal 9,109 3,975 3,100 8,143 3,675 2,800 Current maturities (809) (500) — (408) — — Unamortized debt issuance costs (54) (21) (19) (45) (21) (19) Unamortized debt (discount) and premium, net (21) (9) (11) (22) (8) (11) Long-term debt, net (g) $8,225 $3,445 $3,070 $7,668 $3,646 $2,770 (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 2023, IPL issued $300 million of 5.7% senior debentures due 2033. The net proceeds from the issuance were used to reduce cash amounts received from its sales of accounts receivable program, reduce commercial paper classified as long-term debt, for general corporate purposes and/or were placed in money market fund investments. (c) In March 2023, WPL issued $300 million of 4.95% debentures due 2033. 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 its solar EGUs. (d) In January 2023, AEF entered into a $300 million interest rate swap maturing in January 2026 to mitigate interest rate risk. Under the terms of the swap, AEF exchanged a variable interest rate for a fixed interest rate of 3.93% on a portion of its variable-rate term loan borrowings. In December 2023, AEF retired the remaining $100 million variable-rate term loan borrowings. Refer to Note 15 for additional information on the interest rate swap. (e) Refer to “ Convertible Senior Notes ” below for additional information. (f) In November 2023, AEF issued $300 million of 5.95% senior notes due 2029. The net proceeds from AEF’s issuance 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, 2023, the conditions allowing holders of the Notes to convert their Notes were not met, and as a result, the Notes were classified as “Long-term debt, net” on Alliant Energy’s balance sheet. As of December 31, 2023, the net carrying amount of the Notes was $568 million, with unamortized debt issuance costs of $7 million, and the estimated fair value (Level 2) of the Notes was $572 million. As of December 31, 2023, 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, 2023, long-term debt maturities for 2024 through 2028 were as follows (in millions): 2024 2025 2026 2027 2028 IPL $500 $300 $— $— $500 WPL — — — 300 — AEF 309 — 200 — 300 Alliant Energy parent company — — 575 — — Alliant Energy $809 $300 $775 $300 $800 Fair Value of Long-term Debt - Refer to Note 16 for information on the fair value of long-term debt outstanding.

Leases

Leases	12 Months Ended
	Dec. 31, 2023
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, 2023 December 31, 2022 Alliant Energy IPL WPL Alliant Energy IPL WPL Property, plant and equipment, net $23 $13 $9 $16 $9 $6 Other current liabilities $2 $1 $1 $3 $1 $1 Other liabilities 21 12 8 13 8 5 Total operating lease liabilities $23 $13 $9 $16 $9 $6 Weighted average remaining lease term 12 years 12 years 12 years 10 years 11 years 9 years Weighted average discount rate 4% 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 2023, WPL renewed this financing lease through 2039. This lease contains one remaining lease renewal period, which is not included in the finance lease obligation. 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, 2023 December 31, 2022 Alliant Energy IPL WPL Alliant Energy IPL WPL Property, plant and equipment, net: Sheboygan Falls Energy Facility N/A N/A $79 N/A N/A $15 Leased land for solar generation $172 $33 139 $133 $— 133 $172 $33 $218 $133 $— $148 Other current liabilities: Sheboygan Falls Energy Facility N/A N/A $11 N/A N/A $12 Leased land for solar generation $— $— — $5 $— 5 — — 11 5 — 17 Other liabilities: Sheboygan Falls Energy Facility N/A N/A 78 N/A N/A 19 Leased land for solar generation 172 33 139 131 — 131 172 33 217 131 — 150 Total finance lease liabilities $172 $33 $228 $136 $— $167 Weighted average remaining lease term 33 years 29 years 27 years 34 years N/A 28 years Weighted average discount rate 5% 5% 5% 5% N/A 5% Alliant Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Depreciation and amortization expenses $1 $— $— $— $— $— $6 $6 $6 Interest expense 6 3 — 1 — — 8 7 5 Total finance lease expense $7 $3 $— $1 $— $— $14 $13 $11 Finance lease liabilities arising from obtaining leased assets, which represent non-cash financing activities, were as follows (in millions): Alliant Energy IPL WPL 2023 2022 2023 2022 2023 2022 Finance lease liabilities arising from obtaining leased assets $34 $125 $33 $— $71 $125 Expected Maturities - As of December 31, 2023, expected maturities of lease liabilities were as follows (in millions): 2024 2025 2026 2027 2028 Thereafter Total Less: amount representing interest Present value of minimum lease payments Operating Leases: Alliant Energy $3 $3 $3 $3 $2 $16 $30 $7 $23 IPL 1 2 2 1 1 10 17 4 13 WPL 2 1 1 1 1 6 12 3 9 Finance Leases: Alliant Energy 8 8 8 8 8 320 360 188 172 IPL 2 2 2 2 2 59 69 36 33 WPL 21 17 13 13 13 334 411 183 228
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, 2023 December 31, 2022 Alliant Energy IPL WPL Alliant Energy IPL WPL Property, plant and equipment, net $23 $13 $9 $16 $9 $6 Other current liabilities $2 $1 $1 $3 $1 $1 Other liabilities 21 12 8 13 8 5 Total operating lease liabilities $23 $13 $9 $16 $9 $6 Weighted average remaining lease term 12 years 12 years 12 years 10 years 11 years 9 years Weighted average discount rate 4% 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 2023, WPL renewed this financing lease through 2039. This lease contains one remaining lease renewal period, which is not included in the finance lease obligation. 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, 2023 December 31, 2022 Alliant Energy IPL WPL Alliant Energy IPL WPL Property, plant and equipment, net: Sheboygan Falls Energy Facility N/A N/A $79 N/A N/A $15 Leased land for solar generation $172 $33 139 $133 $— 133 $172 $33 $218 $133 $— $148 Other current liabilities: Sheboygan Falls Energy Facility N/A N/A $11 N/A N/A $12 Leased land for solar generation $— $— — $5 $— 5 — — 11 5 — 17 Other liabilities: Sheboygan Falls Energy Facility N/A N/A 78 N/A N/A 19 Leased land for solar generation 172 33 139 131 — 131 172 33 217 131 — 150 Total finance lease liabilities $172 $33 $228 $136 $— $167 Weighted average remaining lease term 33 years 29 years 27 years 34 years N/A 28 years Weighted average discount rate 5% 5% 5% 5% N/A 5% Alliant Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Depreciation and amortization expenses $1 $— $— $— $— $— $6 $6 $6 Interest expense 6 3 — 1 — — 8 7 5 Total finance lease expense $7 $3 $— $1 $— $— $14 $13 $11 Finance lease liabilities arising from obtaining leased assets, which represent non-cash financing activities, were as follows (in millions): Alliant Energy IPL WPL 2023 2022 2023 2022 2023 2022 Finance lease liabilities arising from obtaining leased assets $34 $125 $33 $— $71 $125 Expected Maturities - As of December 31, 2023, expected maturities of lease liabilities were as follows (in millions): 2024 2025 2026 2027 2028 Thereafter Total Less: amount representing interest Present value of minimum lease payments Operating Leases: Alliant Energy $3 $3 $3 $3 $2 $16 $30 $7 $23 IPL 1 2 2 1 1 10 17 4 13 WPL 2 1 1 1 1 6 12 3 9 Finance Leases: Alliant Energy 8 8 8 8 8 320 360 188 172 IPL 2 2 2 2 2 59 69 36 33 WPL 21 17 13 13 13 334 411 183 228
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, 2023 December 31, 2022 Alliant Energy IPL WPL Alliant Energy IPL WPL Property, plant and equipment, net $23 $13 $9 $16 $9 $6 Other current liabilities $2 $1 $1 $3 $1 $1 Other liabilities 21 12 8 13 8 5 Total operating lease liabilities $23 $13 $9 $16 $9 $6 Weighted average remaining lease term 12 years 12 years 12 years 10 years 11 years 9 years Weighted average discount rate 4% 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 2023, WPL renewed this financing lease through 2039. This lease contains one remaining lease renewal period, which is not included in the finance lease obligation. 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, 2023 December 31, 2022 Alliant Energy IPL WPL Alliant Energy IPL WPL Property, plant and equipment, net: Sheboygan Falls Energy Facility N/A N/A $79 N/A N/A $15 Leased land for solar generation $172 $33 139 $133 $— 133 $172 $33 $218 $133 $— $148 Other current liabilities: Sheboygan Falls Energy Facility N/A N/A $11 N/A N/A $12 Leased land for solar generation $— $— — $5 $— 5 — — 11 5 — 17 Other liabilities: Sheboygan Falls Energy Facility N/A N/A 78 N/A N/A 19 Leased land for solar generation 172 33 139 131 — 131 172 33 217 131 — 150 Total finance lease liabilities $172 $33 $228 $136 $— $167 Weighted average remaining lease term 33 years 29 years 27 years 34 years N/A 28 years Weighted average discount rate 5% 5% 5% 5% N/A 5% Alliant Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Depreciation and amortization expenses $1 $— $— $— $— $— $6 $6 $6 Interest expense 6 3 — 1 — — 8 7 5 Total finance lease expense $7 $3 $— $1 $— $— $14 $13 $11 Finance lease liabilities arising from obtaining leased assets, which represent non-cash financing activities, were as follows (in millions): Alliant Energy IPL WPL 2023 2022 2023 2022 2023 2022 Finance lease liabilities arising from obtaining leased assets $34 $125 $33 $— $71 $125 Expected Maturities - As of December 31, 2023, expected maturities of lease liabilities were as follows (in millions): 2024 2025 2026 2027 2028 Thereafter Total Less: amount representing interest Present value of minimum lease payments Operating Leases: Alliant Energy $3 $3 $3 $3 $2 $16 $30 $7 $23 IPL 1 2 2 1 1 10 17 4 13 WPL 2 1 1 1 1 6 12 3 9 Finance Leases: Alliant Energy 8 8 8 8 8 320 360 188 172 IPL 2 2 2 2 2 59 69 36 33 WPL 21 17 13 13 13 334 411 183 228
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, 2023 December 31, 2022 Alliant Energy IPL WPL Alliant Energy IPL WPL Property, plant and equipment, net $23 $13 $9 $16 $9 $6 Other current liabilities $2 $1 $1 $3 $1 $1 Other liabilities 21 12 8 13 8 5 Total operating lease liabilities $23 $13 $9 $16 $9 $6 Weighted average remaining lease term 12 years 12 years 12 years 10 years 11 years 9 years Weighted average discount rate 4% 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 2023, WPL renewed this financing lease through 2039. This lease contains one remaining lease renewal period, which is not included in the finance lease obligation. 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, 2023 December 31, 2022 Alliant Energy IPL WPL Alliant Energy IPL WPL Property, plant and equipment, net: Sheboygan Falls Energy Facility N/A N/A $79 N/A N/A $15 Leased land for solar generation $172 $33 139 $133 $— 133 $172 $33 $218 $133 $— $148 Other current liabilities: Sheboygan Falls Energy Facility N/A N/A $11 N/A N/A $12 Leased land for solar generation $— $— — $5 $— 5 — — 11 5 — 17 Other liabilities: Sheboygan Falls Energy Facility N/A N/A 78 N/A N/A 19 Leased land for solar generation 172 33 139 131 — 131 172 33 217 131 — 150 Total finance lease liabilities $172 $33 $228 $136 $— $167 Weighted average remaining lease term 33 years 29 years 27 years 34 years N/A 28 years Weighted average discount rate 5% 5% 5% 5% N/A 5% Alliant Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Depreciation and amortization expenses $1 $— $— $— $— $— $6 $6 $6 Interest expense 6 3 — 1 — — 8 7 5 Total finance lease expense $7 $3 $— $1 $— $— $14 $13 $11 Finance lease liabilities arising from obtaining leased assets, which represent non-cash financing activities, were as follows (in millions): Alliant Energy IPL WPL 2023 2022 2023 2022 2023 2022 Finance lease liabilities arising from obtaining leased assets $34 $125 $33 $— $71 $125 Expected Maturities - As of December 31, 2023, expected maturities of lease liabilities were as follows (in millions): 2024 2025 2026 2027 2028 Thereafter Total Less: amount representing interest Present value of minimum lease payments Operating Leases: Alliant Energy $3 $3 $3 $3 $2 $16 $30 $7 $23 IPL 1 2 2 1 1 10 17 4 13 WPL 2 1 1 1 1 6 12 3 9 Finance Leases: Alliant Energy 8 8 8 8 8 320 360 188 172 IPL 2 2 2 2 2 59 69 36 33 WPL 21 17 13 13 13 334 411 183 228
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, 2023 December 31, 2022 Alliant Energy IPL WPL Alliant Energy IPL WPL Property, plant and equipment, net $23 $13 $9 $16 $9 $6 Other current liabilities $2 $1 $1 $3 $1 $1 Other liabilities 21 12 8 13 8 5 Total operating lease liabilities $23 $13 $9 $16 $9 $6 Weighted average remaining lease term 12 years 12 years 12 years 10 years 11 years 9 years Weighted average discount rate 4% 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 2023, WPL renewed this financing lease through 2039. This lease contains one remaining lease renewal period, which is not included in the finance lease obligation. 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, 2023 December 31, 2022 Alliant Energy IPL WPL Alliant Energy IPL WPL Property, plant and equipment, net: Sheboygan Falls Energy Facility N/A N/A $79 N/A N/A $15 Leased land for solar generation $172 $33 139 $133 $— 133 $172 $33 $218 $133 $— $148 Other current liabilities: Sheboygan Falls Energy Facility N/A N/A $11 N/A N/A $12 Leased land for solar generation $— $— — $5 $— 5 — — 11 5 — 17 Other liabilities: Sheboygan Falls Energy Facility N/A N/A 78 N/A N/A 19 Leased land for solar generation 172 33 139 131 — 131 172 33 217 131 — 150 Total finance lease liabilities $172 $33 $228 $136 $— $167 Weighted average remaining lease term 33 years 29 years 27 years 34 years N/A 28 years Weighted average discount rate 5% 5% 5% 5% N/A 5% Alliant Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Depreciation and amortization expenses $1 $— $— $— $— $— $6 $6 $6 Interest expense 6 3 — 1 — — 8 7 5 Total finance lease expense $7 $3 $— $1 $— $— $14 $13 $11 Finance lease liabilities arising from obtaining leased assets, which represent non-cash financing activities, were as follows (in millions): Alliant Energy IPL WPL 2023 2022 2023 2022 2023 2022 Finance lease liabilities arising from obtaining leased assets $34 $125 $33 $— $71 $125 Expected Maturities - As of December 31, 2023, expected maturities of lease liabilities were as follows (in millions): 2024 2025 2026 2027 2028 Thereafter Total Less: amount representing interest Present value of minimum lease payments Operating Leases: Alliant Energy $3 $3 $3 $3 $2 $16 $30 $7 $23 IPL 1 2 2 1 1 10 17 4 13 WPL 2 1 1 1 1 6 12 3 9 Finance Leases: Alliant Energy 8 8 8 8 8 320 360 188 172 IPL 2 2 2 2 2 59 69 36 33 WPL 21 17 13 13 13 334 411 183 228
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, 2023 December 31, 2022 Alliant Energy IPL WPL Alliant Energy IPL WPL Property, plant and equipment, net $23 $13 $9 $16 $9 $6 Other current liabilities $2 $1 $1 $3 $1 $1 Other liabilities 21 12 8 13 8 5 Total operating lease liabilities $23 $13 $9 $16 $9 $6 Weighted average remaining lease term 12 years 12 years 12 years 10 years 11 years 9 years Weighted average discount rate 4% 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 2023, WPL renewed this financing lease through 2039. This lease contains one remaining lease renewal period, which is not included in the finance lease obligation. 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, 2023 December 31, 2022 Alliant Energy IPL WPL Alliant Energy IPL WPL Property, plant and equipment, net: Sheboygan Falls Energy Facility N/A N/A $79 N/A N/A $15 Leased land for solar generation $172 $33 139 $133 $— 133 $172 $33 $218 $133 $— $148 Other current liabilities: Sheboygan Falls Energy Facility N/A N/A $11 N/A N/A $12 Leased land for solar generation $— $— — $5 $— 5 — — 11 5 — 17 Other liabilities: Sheboygan Falls Energy Facility N/A N/A 78 N/A N/A 19 Leased land for solar generation 172 33 139 131 — 131 172 33 217 131 — 150 Total finance lease liabilities $172 $33 $228 $136 $— $167 Weighted average remaining lease term 33 years 29 years 27 years 34 years N/A 28 years Weighted average discount rate 5% 5% 5% 5% N/A 5% Alliant Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Depreciation and amortization expenses $1 $— $— $— $— $— $6 $6 $6 Interest expense 6 3 — 1 — — 8 7 5 Total finance lease expense $7 $3 $— $1 $— $— $14 $13 $11 Finance lease liabilities arising from obtaining leased assets, which represent non-cash financing activities, were as follows (in millions): Alliant Energy IPL WPL 2023 2022 2023 2022 2023 2022 Finance lease liabilities arising from obtaining leased assets $34 $125 $33 $— $71 $125 Expected Maturities - As of December 31, 2023, expected maturities of lease liabilities were as follows (in millions): 2024 2025 2026 2027 2028 Thereafter Total Less: amount representing interest Present value of minimum lease payments Operating Leases: Alliant Energy $3 $3 $3 $3 $2 $16 $30 $7 $23 IPL 1 2 2 1 1 10 17 4 13 WPL 2 1 1 1 1 6 12 3 9 Finance Leases: Alliant Energy 8 8 8 8 8 320 360 188 172 IPL 2 2 2 2 2 59 69 36 33 WPL 21 17 13 13 13 334 411 183 228

Revenues

Revenues	12 Months Ended
	Dec. 31, 2023
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 IUB and PSCW, respectively. Such tariff-based services provide electricity or gas to customers without a defined contractual term. IPL and WPL have wholesale electric market-based rate authority from FERC allowing them to participate in wholesale energy markets (e.g. MISO) and transact directly with third parties. This authority from FERC allows sales of electricity referred to as bulk power sales based on current market values. FERC also allows IPL and WPL to enter into power supply agreements with municipalities and rural electric cooperatives with defined contractual terms, which include standard pricing mechanisms that are detailed in current tariffs accepted by FERC through wholesale rate review proceedings. Revenues from Alliant Energy’s non-utility business customers are primarily from its Travero business, which includes a short-line rail freight service in Iowa; a Mississippi River barge, rail and truck freight terminal in Illinois; freight brokerage services; and a rail-served warehouse in Iowa. Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Electric Utility: Retail - residential $1,220 $1,233 $1,115 $641 $673 $620 $579 $560 $495 Retail - commercial 820 821 763 519 536 508 301 285 255 Retail - industrial 968 965 893 501 538 505 467 427 388 Wholesale 213 233 187 62 64 57 151 169 130 Bulk power and other 124 169 123 38 48 62 86 121 61 Total Electric Utility 3,345 3,421 3,081 1,761 1,859 1,752 1,584 1,562 1,329 Gas Utility: Retail - residential 316 371 257 176 202 146 140 169 111 Retail - commercial 163 197 139 86 101 79 77 96 60 Retail - industrial 16 20 17 11 14 12 5 6 5 Transportation/other 45 54 43 27 34 28 18 20 15 Total Gas Utility 540 642 456 300 351 265 240 291 191 Other Utility: Steam 45 39 36 45 39 36 — — — Other utility 7 10 13 4 7 10 3 3 3 Total Other Utility 52 49 49 49 46 46 3 3 3 Non-Utility and Other: Travero and other 90 93 83 — — — — — — Total Non-Utility and Other 90 93 83 — — — — — — Total revenues $4,027 $4,205 $3,669 $2,110 $2,256 $2,063 $1,827 $1,856 $1,523
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 IUB and PSCW, respectively. Such tariff-based services provide electricity or gas to customers without a defined contractual term. IPL and WPL have wholesale electric market-based rate authority from FERC allowing them to participate in wholesale energy markets (e.g. MISO) and transact directly with third parties. This authority from FERC allows sales of electricity referred to as bulk power sales based on current market values. FERC also allows IPL and WPL to enter into power supply agreements with municipalities and rural electric cooperatives with defined contractual terms, which include standard pricing mechanisms that are detailed in current tariffs accepted by FERC through wholesale rate review proceedings. Revenues from Alliant Energy’s non-utility business customers are primarily from its Travero business, which includes a short-line rail freight service in Iowa; a Mississippi River barge, rail and truck freight terminal in Illinois; freight brokerage services; and a rail-served warehouse in Iowa. Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Electric Utility: Retail - residential $1,220 $1,233 $1,115 $641 $673 $620 $579 $560 $495 Retail - commercial 820 821 763 519 536 508 301 285 255 Retail - industrial 968 965 893 501 538 505 467 427 388 Wholesale 213 233 187 62 64 57 151 169 130 Bulk power and other 124 169 123 38 48 62 86 121 61 Total Electric Utility 3,345 3,421 3,081 1,761 1,859 1,752 1,584 1,562 1,329 Gas Utility: Retail - residential 316 371 257 176 202 146 140 169 111 Retail - commercial 163 197 139 86 101 79 77 96 60 Retail - industrial 16 20 17 11 14 12 5 6 5 Transportation/other 45 54 43 27 34 28 18 20 15 Total Gas Utility 540 642 456 300 351 265 240 291 191 Other Utility: Steam 45 39 36 45 39 36 — — — Other utility 7 10 13 4 7 10 3 3 3 Total Other Utility 52 49 49 49 46 46 3 3 3 Non-Utility and Other: Travero and other 90 93 83 — — — — — — Total Non-Utility and Other 90 93 83 — — — — — — Total revenues $4,027 $4,205 $3,669 $2,110 $2,256 $2,063 $1,827 $1,856 $1,523
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 IUB and PSCW, respectively. Such tariff-based services provide electricity or gas to customers without a defined contractual term. IPL and WPL have wholesale electric market-based rate authority from FERC allowing them to participate in wholesale energy markets (e.g. MISO) and transact directly with third parties. This authority from FERC allows sales of electricity referred to as bulk power sales based on current market values. FERC also allows IPL and WPL to enter into power supply agreements with municipalities and rural electric cooperatives with defined contractual terms, which include standard pricing mechanisms that are detailed in current tariffs accepted by FERC through wholesale rate review proceedings. Revenues from Alliant Energy’s non-utility business customers are primarily from its Travero business, which includes a short-line rail freight service in Iowa; a Mississippi River barge, rail and truck freight terminal in Illinois; freight brokerage services; and a rail-served warehouse in Iowa. Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Electric Utility: Retail - residential $1,220 $1,233 $1,115 $641 $673 $620 $579 $560 $495 Retail - commercial 820 821 763 519 536 508 301 285 255 Retail - industrial 968 965 893 501 538 505 467 427 388 Wholesale 213 233 187 62 64 57 151 169 130 Bulk power and other 124 169 123 38 48 62 86 121 61 Total Electric Utility 3,345 3,421 3,081 1,761 1,859 1,752 1,584 1,562 1,329 Gas Utility: Retail - residential 316 371 257 176 202 146 140 169 111 Retail - commercial 163 197 139 86 101 79 77 96 60 Retail - industrial 16 20 17 11 14 12 5 6 5 Transportation/other 45 54 43 27 34 28 18 20 15 Total Gas Utility 540 642 456 300 351 265 240 291 191 Other Utility: Steam 45 39 36 45 39 36 — — — Other utility 7 10 13 4 7 10 3 3 3 Total Other Utility 52 49 49 49 46 46 3 3 3 Non-Utility and Other: Travero and other 90 93 83 — — — — — — Total Non-Utility and Other 90 93 83 — — — — — — Total revenues $4,027 $4,205 $3,669 $2,110 $2,256 $2,063 $1,827 $1,856 $1,523

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2023
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 Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Current tax expense (benefit): Federal ($3) $7 $1 ($44) ($29) ($21) $48 $46 $22 State (6) 2 3 (21) (8) (1) 25 16 6 Deferred tax expense (benefit): Federal 100 109 9 87 91 73 10 10 (75) State 36 28 15 17 1 — 3 12 11 Production tax credits (121) (123) (101) (95) (105) (87) (26) (18) (14) Investment tax credits (1) (1) (1) (1) — — — — (1) Provision recorded as a change in accrued interest (1) — — (1) — — — — — $4 $22 ($74) ($58) ($50) ($36) $60 $66 ($51) 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. Alliant Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Statutory federal income tax rate 21% 21% 21% 21% 21% 21% 21% 21% 21% State income taxes, net of federal benefits 2 3 2 (2) (2) (1) 5 6 6 Production tax credits (17) (18) (17) (31) (34) (27) (7) (5) (6) Amortization of excess deferred taxes (Refer to Note 2 ) (2) (2) (18) (2) (2) (4) (2) (3) (43) Effect of rate-making on property-related differences (4) (1) (1) (5) (1) (2) (3) (2) (1) Adjustment for prior period taxes — 1 1 — 1 2 — — — Other items, net 1 (1) — — 1 — 1 — (1) Overall income tax rate 1% 3% (12%) (19%) (16%) (11%) 15% 17% (24%) 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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Deferred tax liabilities: Property $2,453 $2,442 $1,415 $1,440 $972 $938 ATC Holdings 127 125 — — — — Other 213 155 157 86 64 80 Total deferred tax liabilities 2,793 2,722 1,572 1,526 1,036 1,018 Deferred tax assets: Federal credit carryforwards 649 672 449 450 191 209 Net operating losses carryforwards - state 26 32 1 — — — Other 79 75 32 29 19 20 Subtotal deferred tax assets 754 779 482 479 210 229 Valuation allowances (3) — (1) — (1) — Total deferred tax assets 751 779 481 479 209 229 Total deferred tax liabilities, net $2,042 $1,943 $1,091 $1,047 $827 $789 Carryforwards - At December 31, 2023, carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL State net operating losses 2025-2043 $428 $6 $1 Federal tax credits 2031-2043 649 449 191 Valuation Allowances - Refer to N ote 1 (c) for discussion of valuation allowances recorded in 2023 related to the expected transfer of renewable tax credits to other corporate taxpayers. Uncertain Tax Positions - At December 31, 2023, 2022 and 2021, there were no uncertain tax positions or penalties accrued related to uncertain tax positions. As of December 31, 2023, 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) 2019 - 2022 Consolidated Iowa income tax returns (b) 2020 - 2022 Wisconsin combined tax returns (c) 2019 - 2022 (a) The 2020 and 2021 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 - In 2018, Iowa tax reform was enacted, resulting in a reduction in the Iowa income tax rate from 12% to 9.8%, effective January 1, 2021, and the elimination of the deduction for federal income taxes, effective January 1, 2022, for taxes related to 2020 and prior. In March 2022, additional Iowa tax reform was enacted. 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 certain state income tax revenue triggers are satisfied. 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 September 2022 and September 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. The reduction in tax-related regulatory assets is 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, which resulted in charges of $8 million and $10 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 and 2023, 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 Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Current tax expense (benefit): Federal ($3) $7 $1 ($44) ($29) ($21) $48 $46 $22 State (6) 2 3 (21) (8) (1) 25 16 6 Deferred tax expense (benefit): Federal 100 109 9 87 91 73 10 10 (75) State 36 28 15 17 1 — 3 12 11 Production tax credits (121) (123) (101) (95) (105) (87) (26) (18) (14) Investment tax credits (1) (1) (1) (1) — — — — (1) Provision recorded as a change in accrued interest (1) — — (1) — — — — — $4 $22 ($74) ($58) ($50) ($36) $60 $66 ($51) 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. Alliant Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Statutory federal income tax rate 21% 21% 21% 21% 21% 21% 21% 21% 21% State income taxes, net of federal benefits 2 3 2 (2) (2) (1) 5 6 6 Production tax credits (17) (18) (17) (31) (34) (27) (7) (5) (6) Amortization of excess deferred taxes (Refer to Note 2 ) (2) (2) (18) (2) (2) (4) (2) (3) (43) Effect of rate-making on property-related differences (4) (1) (1) (5) (1) (2) (3) (2) (1) Adjustment for prior period taxes — 1 1 — 1 2 — — — Other items, net 1 (1) — — 1 — 1 — (1) Overall income tax rate 1% 3% (12%) (19%) (16%) (11%) 15% 17% (24%) 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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Deferred tax liabilities: Property $2,453 $2,442 $1,415 $1,440 $972 $938 ATC Holdings 127 125 — — — — Other 213 155 157 86 64 80 Total deferred tax liabilities 2,793 2,722 1,572 1,526 1,036 1,018 Deferred tax assets: Federal credit carryforwards 649 672 449 450 191 209 Net operating losses carryforwards - state 26 32 1 — — — Other 79 75 32 29 19 20 Subtotal deferred tax assets 754 779 482 479 210 229 Valuation allowances (3) — (1) — (1) — Total deferred tax assets 751 779 481 479 209 229 Total deferred tax liabilities, net $2,042 $1,943 $1,091 $1,047 $827 $789 Carryforwards - At December 31, 2023, carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL State net operating losses 2025-2043 $428 $6 $1 Federal tax credits 2031-2043 649 449 191 Valuation Allowances - Refer to N ote 1 (c) for discussion of valuation allowances recorded in 2023 related to the expected transfer of renewable tax credits to other corporate taxpayers. Uncertain Tax Positions - At December 31, 2023, 2022 and 2021, there were no uncertain tax positions or penalties accrued related to uncertain tax positions. As of December 31, 2023, 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) 2019 - 2022 Consolidated Iowa income tax returns (b) 2020 - 2022 Wisconsin combined tax returns (c) 2019 - 2022 (a) The 2020 and 2021 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 - In 2018, Iowa tax reform was enacted, resulting in a reduction in the Iowa income tax rate from 12% to 9.8%, effective January 1, 2021, and the elimination of the deduction for federal income taxes, effective January 1, 2022, for taxes related to 2020 and prior. In March 2022, additional Iowa tax reform was enacted. 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 certain state income tax revenue triggers are satisfied. 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 September 2022 and September 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. The reduction in tax-related regulatory assets is 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, which resulted in charges of $8 million and $10 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 and 2023, 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 Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Current tax expense (benefit): Federal ($3) $7 $1 ($44) ($29) ($21) $48 $46 $22 State (6) 2 3 (21) (8) (1) 25 16 6 Deferred tax expense (benefit): Federal 100 109 9 87 91 73 10 10 (75) State 36 28 15 17 1 — 3 12 11 Production tax credits (121) (123) (101) (95) (105) (87) (26) (18) (14) Investment tax credits (1) (1) (1) (1) — — — — (1) Provision recorded as a change in accrued interest (1) — — (1) — — — — — $4 $22 ($74) ($58) ($50) ($36) $60 $66 ($51) 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. Alliant Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Statutory federal income tax rate 21% 21% 21% 21% 21% 21% 21% 21% 21% State income taxes, net of federal benefits 2 3 2 (2) (2) (1) 5 6 6 Production tax credits (17) (18) (17) (31) (34) (27) (7) (5) (6) Amortization of excess deferred taxes (Refer to Note 2 ) (2) (2) (18) (2) (2) (4) (2) (3) (43) Effect of rate-making on property-related differences (4) (1) (1) (5) (1) (2) (3) (2) (1) Adjustment for prior period taxes — 1 1 — 1 2 — — — Other items, net 1 (1) — — 1 — 1 — (1) Overall income tax rate 1% 3% (12%) (19%) (16%) (11%) 15% 17% (24%) 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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Deferred tax liabilities: Property $2,453 $2,442 $1,415 $1,440 $972 $938 ATC Holdings 127 125 — — — — Other 213 155 157 86 64 80 Total deferred tax liabilities 2,793 2,722 1,572 1,526 1,036 1,018 Deferred tax assets: Federal credit carryforwards 649 672 449 450 191 209 Net operating losses carryforwards - state 26 32 1 — — — Other 79 75 32 29 19 20 Subtotal deferred tax assets 754 779 482 479 210 229 Valuation allowances (3) — (1) — (1) — Total deferred tax assets 751 779 481 479 209 229 Total deferred tax liabilities, net $2,042 $1,943 $1,091 $1,047 $827 $789 Carryforwards - At December 31, 2023, carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL State net operating losses 2025-2043 $428 $6 $1 Federal tax credits 2031-2043 649 449 191 Valuation Allowances - Refer to N ote 1 (c) for discussion of valuation allowances recorded in 2023 related to the expected transfer of renewable tax credits to other corporate taxpayers. Uncertain Tax Positions - At December 31, 2023, 2022 and 2021, there were no uncertain tax positions or penalties accrued related to uncertain tax positions. As of December 31, 2023, 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) 2019 - 2022 Consolidated Iowa income tax returns (b) 2020 - 2022 Wisconsin combined tax returns (c) 2019 - 2022 (a) The 2020 and 2021 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 - In 2018, Iowa tax reform was enacted, resulting in a reduction in the Iowa income tax rate from 12% to 9.8%, effective January 1, 2021, and the elimination of the deduction for federal income taxes, effective January 1, 2022, for taxes related to 2020 and prior. In March 2022, additional Iowa tax reform was enacted. 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 certain state income tax revenue triggers are satisfied. 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 September 2022 and September 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. The reduction in tax-related regulatory assets is 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, which resulted in charges of $8 million and $10 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 and 2023, respectively. Alliant Energy is currently unable to predict with certainty the timing or amount of any future rate reductions.

Benefit Plans

Benefit Plans	12 Months Ended
	Dec. 31, 2023
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 assumptions for defined benefit pension and OPEB plans at the measurement date of December 31 were as follows: Defined Benefit Pension Plans OPEB Plans Alliant Energy 2023 2022 2021 2023 2022 2021 Discount rate for benefit obligations 5.36% 5.54% 2.91% 5.40% 5.53% 2.81% Discount rate for net periodic cost 5.54% 2.91% 2.57% 5.53% 2.81% 2.31% Expected rate of return on plan assets 7.80% 7.80% 7.10% 6.50% 6.40% 4.80% Interest crediting rate for Alliant Energy Cash Balance Pension Plan 10.75% 9.22% 4.18% N/A N/A N/A Rate of compensation increase 3.30% - 4.50% 3.30% - 4.50% 3.30% - 4.50% N/A N/A N/A Qualified Defined Benefit Pension Plan OPEB Plans IPL 2023 2022 2021 2023 2022 2021 Discount rate for benefit obligations 5.35% 5.55% 2.94% 5.40% 5.53% 2.80% Discount rate for net periodic cost 5.55% 2.94% 2.61% 5.53% 2.80% 2.28% Expected rate of return on plan assets 7.80% 7.80% 7.10% 6.90% 6.50% 5.10% Rate of compensation increase 3.30% 3.30% 3.30% N/A N/A N/A Qualified Defined Benefit Pension Plan OPEB Plans WPL 2023 2022 2021 2023 2022 2021 Discount rate for benefit obligations 5.35% 5.54% 2.94% 5.40% 5.53% 2.79% Discount rate for net periodic cost 5.54% 2.94% 2.64% 5.53% 2.79% 2.27% Expected rate of return on plan assets 7.80% 7.80% 7.10% 5.65% 5.49% 4.02% Rate of compensation increase 3.30% 3.30% 3.30% N/A N/A N/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 Energy Defined Benefit Pension Plans OPEB Plans 2023 2022 2021 2023 2022 2021 Service cost $5 $9 $11 $2 $3 $4 Interest cost 47 36 34 9 6 5 Expected return on plan assets (a) (53) (69) (69) (5) (5) (5) Amortization of prior service credit (b) (1) (1) — — — — Amortization of actuarial loss (c) 28 32 39 1 2 5 Settlement losses (d) — 26 — — — — $26 $33 $15 $7 $6 $9 IPL Defined Benefit Pension Plans OPEB Plans 2023 2022 2021 2023 2022 2021 Service cost $3 $6 $7 $1 $1 $1 Interest cost 21 16 16 3 2 2 Expected return on plan assets (a) (26) (31) (32) (3) (4) (3) Amortization of actuarial loss (c) 11 13 17 1 1 2 Settlement losses (d) — 13 — — — — $9 $17 $8 $2 $— $2 WPL Defined Benefit Pension Plans OPEB Plans 2023 2022 2021 2023 2022 2021 Service cost $2 $3 $4 $1 $1 $1 Interest cost 20 16 15 3 2 2 Expected return on plan assets (a) (22) (31) (31) (1) (1) — Amortization of actuarial loss (c) 13 15 19 1 2 2 Settlement losses (d) — 13 — — — — $13 $16 $7 $4 $4 $5 (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 Plans OPEB Plans Alliant Energy 2023 2022 2023 2022 Change in benefit obligation: Net benefit obligation at January 1 $875 $1,251 $168 $210 Service cost 5 9 2 3 Interest cost 47 36 9 6 Plan participants’ contributions — — 4 4 Actuarial (gain) loss 23 (269) (3) (37) Gross benefits paid (74) (152) (20) (18) Net benefit obligation at December 31 876 875 160 168 Change in plan assets: Fair value of plan assets at January 1 706 1,011 83 106 Actual return on plan assets 86 (204) 8 (17) Employer contributions 14 51 8 8 Plan participants’ contributions — — 4 4 Gross benefits paid (74) (152) (20) (18) Fair value of plan assets at December 31 732 706 83 83 Under funded status at December 31 ($144) ($169) ($77) ($85) Defined Benefit Pension Plans OPEB Plans Alliant Energy 2023 2022 2023 2022 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $14 $9 Current liabilities (2) (2) (8) (8) Pension and other benefit obligations (142) (167) (83) (86) Net amounts recognized at December 31 ($144) ($169) ($77) ($85) Amounts recognized in Regulatory Assets consist of: Net actuarial loss $337 $376 $11 $20 Prior service credit (2) (3) — — $335 $373 $11 $20 Defined Benefit Pension Plans OPEB Plans IPL 2023 2022 2023 2022 Change in benefit obligation: Net benefit obligation at January 1 $389 $567 $68 $84 Service cost 3 6 1 1 Interest cost 21 16 3 2 Plan participants’ contributions — — 2 2 Actuarial (gain) loss 9 (123) (1) (14) Gross benefits paid (35) (77) (8) (7) Net benefit obligation at December 31 387 389 65 68 Change in plan assets: Fair value of plan assets at January 1 344 462 58 74 Actual return on plan assets 42 (92) 7 (12) Employer contributions 1 51 2 1 Plan participants’ contributions — — 2 2 Gross benefits paid (35) (77) (8) (7) Fair value of plan assets at December 31 352 344 61 58 Under funded status at December 31 ($35) ($45) ($4) ($10) Defined Benefit Pension Plans OPEB Plans IPL 2023 2022 2023 2022 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $10 $6 Current liabilities — — (1) (2) Pension and other benefit obligations (35) (45) (13) (14) Net amounts recognized at December 31 ($35) ($45) ($4) ($10) Amounts recognized in Regulatory Assets consist of: Net actuarial loss $135 $154 $9 $14 Prior service credit (1) (1) — — $134 $153 $9 $14 Defined Benefit Pension Plans OPEB Plans WPL 2023 2022 2023 2022 Change in benefit obligation: Net benefit obligation at January 1 $381 $546 $65 $81 Service cost 2 3 1 1 Interest cost 20 16 3 2 Plan participants’ contributions — — 2 2 Actuarial (gain) loss 10 (117) (2) (13) Gross benefits paid (32) (67) (8) (8) Net benefit obligation at December 31 381 381 61 65 Change in plan assets: Fair value of plan assets at January 1 291 450 14 17 Actual return on plan assets 35 (92) 1 (2) Employer contributions 12 — 5 5 Plan participants’ contributions — — 2 2 Gross benefits paid (32) (67) (8) (8) Fair value of plan assets at December 31 306 291 14 14 Under funded status at December 31 ($75) ($90) ($47) ($51) Defined Benefit Pension Plans OPEB Plans WPL 2023 2022 2023 2022 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $4 $3 Current liabilities — — (6) (5) Pension and other benefit obligations (75) (90) (45) (49) Net amounts recognized at December 31 ($75) ($90) ($47) ($51) Amounts recognized in Regulatory Assets consist of: Net actuarial loss $148 $165 $3 $6 Prior service credit — — — — $148 $165 $3 $6 In 2023, actuarial losses related to benefit obligations for defined benefit pension plans were primarily due to decreases in the discount rates. In 2022, actuarial gains related to benefit obligations for defined benefit pension and OPEB plans were primarily due to increases in the discount rates. 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 Plans OPEB Plans Alliant Energy 2023 2022 2023 2022 Accumulated benefit obligations $857 $857 $160 $168 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 857 857 160 168 Fair value of plan assets 732 706 83 83 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 876 875 N/A N/A Fair value of plan assets 732 706 N/A N/A Defined Benefit Pension Plans OPEB Plans IPL 2023 2022 2023 2022 Accumulated benefit obligations $377 $379 $65 $68 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 377 379 65 68 Fair value of plan assets 352 344 61 58 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 387 389 N/A N/A Fair value of plan assets 352 344 N/A N/A Defined Benefit Pension Plans OPEB Plans WPL 2023 2022 2023 2022 Accumulated benefit obligations $373 $373 $61 $65 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 373 373 61 65 Fair value of plan assets 306 291 14 14 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 381 381 N/A N/A Fair value of plan assets 306 291 N/A N/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): IPL WPL 2023 2022 2023 2022 Regulatory assets $28 $30 $24 $25 Estimated Future Employer Contributions and Benefit Payments - Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2024 is as follows (in millions): Alliant Energy IPL WPL Defined benefit pension plans (a) $12 $— $10 OPEB plans 8 1 6 (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 Energy 2024 2025 2026 2027 2028 2029 - 2033 Defined benefit pension benefits $73 $73 $74 $75 $75 $343 OPEB 17 17 16 16 15 65 $90 $90 $90 $91 $90 $408 IPL 2024 2025 2026 2027 2028 2029 - 2033 Defined benefit pension benefits $34 $34 $34 $33 $33 $151 OPEB 7 7 7 6 6 25 $41 $41 $41 $39 $39 $176 WPL 2024 2025 2026 2027 2028 2029 - 2033 Defined benefit pension benefits $32 $32 $31 $31 $31 $146 OPEB 7 7 6 6 6 24 $39 $39 $37 $37 $37 $170 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 diversification, including equity, fixed income and global asset strategies. Global asset strategies may include investments in global equity, global debt and currencies. Defined Benefit Pension Plan Assets - The asset mix of defined benefit pension plans 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. An overlay management service is also used to help maintain target allocations and meet liquidity needs. The overlay manager is authorized to use derivative financial instruments to facilitate this service. For separately managed accounts, prohibited investments include, but are not limited to, direct ownership of real estate, oil and gas limited partnerships, securities of the managers’ firms or affiliate firms, and Alliant Energy securities. The allocations shown below exclude market exposure obtained through the overlay management service. At December 31, 2023, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows: Target Range Actual Allocation Allocation Cash and equivalents 0% - 5% 2% Equity securities 47% - 67% 56% Global asset securities 0% - 15% 5% Fixed income securities 27% - 47% 37% 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 VEBA trusts with assets greater than $5 million and the WPL 401(h) assets, the mix among asset classes 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. At December 31, 2023, the current target ranges and actual allocations for VEBA trusts with assets greater than $5 million and the WPL 401(h) assets were as follows: Target Range Actual Allocation Allocation Cash and equivalents 0% - 5% 1% Equity securities 0% - 55% 36% Fixed income securities 40% - 100% 63% 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 16 for discussion of levels within the fair value hierarchy. Level 1 items include investments in securities held in registered investment companies and directly held equity securities, 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 and fixed income securities. Cash and equivalents include money market fund investments and cash collateral supporting derivative financial instruments. Fixed income securities include corporate and government bonds, which are valued at the closing price reported in the active market for similar assets in which the individual securities are traded or based on yields currently available on comparable securities of issuers with similar credit ratings. 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): 2023 2022 Fair Level Level Level Fair Level Level Level Alliant Energy Value 1 2 3 Value 1 2 3 Cash and equivalents $19 $— $19 $— $79 $— $79 $— Equity securities 223 223 — — 185 185 — — Global asset securities 39 39 — — 35 35 — — Fixed income securities 143 31 112 — 130 30 100 — Total assets in fair value hierarchy 424 $293 $131 $— 429 $250 $179 $— Assets measured at net asset value 306 276 Accrued investment income 2 1 Total pension plan assets $732 $706 2023 2022 Fair Level Level Level Fair Level Level Level IPL Value 1 2 3 Value 1 2 3 Cash and equivalents $9 $— $9 $— $62 $— $62 $— Equity securities 107 107 — — 83 83 — — Global asset securities 19 19 — — 16 16 — — Fixed income securities 69 15 54 — 58 13 45 — Total assets in fair value hierarchy 204 $141 $63 $— 219 $112 $107 $— Assets measured at net asset value 147 124 Accrued investment income 1 1 Total pension plan assets $352 $344 2023 2022 Fair Level Level Level Fair Level Level Level WPL Value 1 2 3 Value 1 2 3 Cash and equivalents $8 $— $8 $— $13 $— $13 $— Equity securities 93 93 — — 82 82 — — Global asset securities 16 16 — — 16 16 — — Fixed income securities 60 13 47 — 57 13 44 — Total assets in fair value hierarchy 177 $122 $55 $— 168 $111 $57 $— Assets measured at net asset value 128 122 Accrued investment income 1 1 Total pension plan assets $306 $291 At December 31, the fair values of OPEB plan assets were as follows (in millions): 2023 2022 Fair Level Level Level Fair Level Level Level Alliant Energy Value 1 2 3 Value 1 2 3 Cash and equivalents $9 $— $9 $— $3 $— $3 $— Equity securities 8 8 — — 9 9 — — Global asset securities — — — — 1 1 — — Fixed income securities 47 47 — — 47 46 1 — Total assets in fair value hierarchy 64 $55 $9 $— 60 $56 $4 $— Assets measured at net asset value 19 23 Total OPEB plan assets $83 $83 2023 2022 Fair Level Level Level Fair Level Level Level IPL Value 1 2 3 Value 1 2 3 Cash and equivalents $1 $— $1 $— $1 $— $1 $— Equity securities 6 6 — — 5 5 — — Fixed income securities 36 36 — — 34 34 — — Total assets in fair value hierarchy 43 $42 $1 $— 40 $39 $1 $— Assets measured at net asset value 18 18 Total OPEB plan assets $61 $58 2023 2022 Fair Level Level Level Fair Level Level Level WPL Value 1 2 3 Value 1 2 3 Cash and equivalents $1 $— $1 $— $— $— $— $— Equity securities 2 2 — — 1 1 — — Fixed income securities 11 11 — — 13 13 — — Total OPEB plan assets $14 $13 $1 $— $14 $14 $— $— 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, 2023 and 2022. 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 8% and 10% of total assets in the 401(k) savings plans at December 31, 2023 and 2022, 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 Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 401(k) costs $30 $28 $26 $14 $13 $13 $14 $13 $12 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, 2023, performance shares and restricted stock units (performance- and time-vesting) were outstanding under the 2020 OIP, and 8 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 Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Compensation expense $12 $13 $14 $6 $7 $8 $5 $5 $6 Income tax benefits 3 3 4 2 2 2 1 1 2 As of December 31, 2023, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $8 million, $4 million and $3 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, 2023, 429,804 shares were included in the calculation of diluted EPS related to the nonvested equity awards. Performance Shares - Equity Awards - Payouts of 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: 2023 2022 2021 Shares Weighted Shares Weighted Shares Weighted Nonvested awards, January 1 190,273 $54.13 196,429 $51.59 129,156 $54.63 Granted 108,712 55.68 74,106 54.45 73,112 46.19 Vested (53,431) 64.04 (71,101) 47.48 — — Forfeited (11,600) 53.88 (9,161) 53.99 (5,839) 51.07 Nonvested awards, December 31 233,954 52.60 190,273 54.13 196,429 51.59 Restricted Stock Units - Equity Awards - 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: 2023 2022 2021 Units Weighted Units Weighted Units Weighted Nonvested units, January 1 198,275 $54.53 217,819 $50.54 146,549 $51.54 Granted 106,124 52.77 77,122 56.88 80,152 48.65 Vested (55,345) 59.40 (82,770) 46.08 — — Forfeited (14,795) 54.53 (13,896) 55.53 (8,882) 49.84 Nonvested units, December 31 234,259 52.58 198,275 54.53 217,819 50.54 Performance Restricted Stock Units - Equity Awards - Payouts of performance restricted stock units are based upon achievement of certain performance targets during a three-year performance period, which currently includes specified growth of consolidated net income from continuing operations, as well as a diversity metric for the 2022 and 2023 grants. The actual number of units that will be paid out upon vesting is dependent upon actual performance and may range from zero to 200% of the target number of units under each award type. If minimum performance targets are not met during the performance period, these units are forfeited. Performance restricted stock units are to be paid out in shares and are accounted for as equity awards. The fair value of each performance restricted stock unit 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 a probability assessment of payouts for the awards at each reporting period. A summary of the performance restricted stock units activity, with amounts representing the target number of units, was as follows: 2023 2022 2021 Units Weighted Average Grant Date Fair Value Units Weighted Average Grant Date Fair Value Units Weighted Average Grant Date Fair Value Nonvested units, January 1 199,874 $54.74 196,429 $50.74 197,463 $47.31 Granted 124,217 52.71 84,670 57.01 73,112 48.66 Vested (53,431) 59.36 (71,101) 46.24 (68,307) 38.60 Forfeited (13,021) 55.47 (10,124) 55.92 (5,839) 50.46 Nonvested units, December 31 257,639 52.76 199,874 54.74 196,429 50.74 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 diversification 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): 2023 2022 Carrying value $13 $13 Fair market value 19 22 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, 2023 and 2022, the carrying value of Alliant Energy’s deferred compensation obligations for participants’ interest, equity and mutual fund accounts, which approximates fair market value, was $21 million and $19 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 assumptions for defined benefit pension and OPEB plans at the measurement date of December 31 were as follows: Defined Benefit Pension Plans OPEB Plans Alliant Energy 2023 2022 2021 2023 2022 2021 Discount rate for benefit obligations 5.36% 5.54% 2.91% 5.40% 5.53% 2.81% Discount rate for net periodic cost 5.54% 2.91% 2.57% 5.53% 2.81% 2.31% Expected rate of return on plan assets 7.80% 7.80% 7.10% 6.50% 6.40% 4.80% Interest crediting rate for Alliant Energy Cash Balance Pension Plan 10.75% 9.22% 4.18% N/A N/A N/A Rate of compensation increase 3.30% - 4.50% 3.30% - 4.50% 3.30% - 4.50% N/A N/A N/A Qualified Defined Benefit Pension Plan OPEB Plans IPL 2023 2022 2021 2023 2022 2021 Discount rate for benefit obligations 5.35% 5.55% 2.94% 5.40% 5.53% 2.80% Discount rate for net periodic cost 5.55% 2.94% 2.61% 5.53% 2.80% 2.28% Expected rate of return on plan assets 7.80% 7.80% 7.10% 6.90% 6.50% 5.10% Rate of compensation increase 3.30% 3.30% 3.30% N/A N/A N/A Qualified Defined Benefit Pension Plan OPEB Plans WPL 2023 2022 2021 2023 2022 2021 Discount rate for benefit obligations 5.35% 5.54% 2.94% 5.40% 5.53% 2.79% Discount rate for net periodic cost 5.54% 2.94% 2.64% 5.53% 2.79% 2.27% Expected rate of return on plan assets 7.80% 7.80% 7.10% 5.65% 5.49% 4.02% Rate of compensation increase 3.30% 3.30% 3.30% N/A N/A N/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 Energy Defined Benefit Pension Plans OPEB Plans 2023 2022 2021 2023 2022 2021 Service cost $5 $9 $11 $2 $3 $4 Interest cost 47 36 34 9 6 5 Expected return on plan assets (a) (53) (69) (69) (5) (5) (5) Amortization of prior service credit (b) (1) (1) — — — — Amortization of actuarial loss (c) 28 32 39 1 2 5 Settlement losses (d) — 26 — — — — $26 $33 $15 $7 $6 $9 IPL Defined Benefit Pension Plans OPEB Plans 2023 2022 2021 2023 2022 2021 Service cost $3 $6 $7 $1 $1 $1 Interest cost 21 16 16 3 2 2 Expected return on plan assets (a) (26) (31) (32) (3) (4) (3) Amortization of actuarial loss (c) 11 13 17 1 1 2 Settlement losses (d) — 13 — — — — $9 $17 $8 $2 $— $2 WPL Defined Benefit Pension Plans OPEB Plans 2023 2022 2021 2023 2022 2021 Service cost $2 $3 $4 $1 $1 $1 Interest cost 20 16 15 3 2 2 Expected return on plan assets (a) (22) (31) (31) (1) (1) — Amortization of actuarial loss (c) 13 15 19 1 2 2 Settlement losses (d) — 13 — — — — $13 $16 $7 $4 $4 $5 (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 Plans OPEB Plans Alliant Energy 2023 2022 2023 2022 Change in benefit obligation: Net benefit obligation at January 1 $875 $1,251 $168 $210 Service cost 5 9 2 3 Interest cost 47 36 9 6 Plan participants’ contributions — — 4 4 Actuarial (gain) loss 23 (269) (3) (37) Gross benefits paid (74) (152) (20) (18) Net benefit obligation at December 31 876 875 160 168 Change in plan assets: Fair value of plan assets at January 1 706 1,011 83 106 Actual return on plan assets 86 (204) 8 (17) Employer contributions 14 51 8 8 Plan participants’ contributions — — 4 4 Gross benefits paid (74) (152) (20) (18) Fair value of plan assets at December 31 732 706 83 83 Under funded status at December 31 ($144) ($169) ($77) ($85) Defined Benefit Pension Plans OPEB Plans Alliant Energy 2023 2022 2023 2022 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $14 $9 Current liabilities (2) (2) (8) (8) Pension and other benefit obligations (142) (167) (83) (86) Net amounts recognized at December 31 ($144) ($169) ($77) ($85) Amounts recognized in Regulatory Assets consist of: Net actuarial loss $337 $376 $11 $20 Prior service credit (2) (3) — — $335 $373 $11 $20 Defined Benefit Pension Plans OPEB Plans IPL 2023 2022 2023 2022 Change in benefit obligation: Net benefit obligation at January 1 $389 $567 $68 $84 Service cost 3 6 1 1 Interest cost 21 16 3 2 Plan participants’ contributions — — 2 2 Actuarial (gain) loss 9 (123) (1) (14) Gross benefits paid (35) (77) (8) (7) Net benefit obligation at December 31 387 389 65 68 Change in plan assets: Fair value of plan assets at January 1 344 462 58 74 Actual return on plan assets 42 (92) 7 (12) Employer contributions 1 51 2 1 Plan participants’ contributions — — 2 2 Gross benefits paid (35) (77) (8) (7) Fair value of plan assets at December 31 352 344 61 58 Under funded status at December 31 ($35) ($45) ($4) ($10) Defined Benefit Pension Plans OPEB Plans IPL 2023 2022 2023 2022 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $10 $6 Current liabilities — — (1) (2) Pension and other benefit obligations (35) (45) (13) (14) Net amounts recognized at December 31 ($35) ($45) ($4) ($10) Amounts recognized in Regulatory Assets consist of: Net actuarial loss $135 $154 $9 $14 Prior service credit (1) (1) — — $134 $153 $9 $14 Defined Benefit Pension Plans OPEB Plans WPL 2023 2022 2023 2022 Change in benefit obligation: Net benefit obligation at January 1 $381 $546 $65 $81 Service cost 2 3 1 1 Interest cost 20 16 3 2 Plan participants’ contributions — — 2 2 Actuarial (gain) loss 10 (117) (2) (13) Gross benefits paid (32) (67) (8) (8) Net benefit obligation at December 31 381 381 61 65 Change in plan assets: Fair value of plan assets at January 1 291 450 14 17 Actual return on plan assets 35 (92) 1 (2) Employer contributions 12 — 5 5 Plan participants’ contributions — — 2 2 Gross benefits paid (32) (67) (8) (8) Fair value of plan assets at December 31 306 291 14 14 Under funded status at December 31 ($75) ($90) ($47) ($51) Defined Benefit Pension Plans OPEB Plans WPL 2023 2022 2023 2022 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $4 $3 Current liabilities — — (6) (5) Pension and other benefit obligations (75) (90) (45) (49) Net amounts recognized at December 31 ($75) ($90) ($47) ($51) Amounts recognized in Regulatory Assets consist of: Net actuarial loss $148 $165 $3 $6 Prior service credit — — — — $148 $165 $3 $6 In 2023, actuarial losses related to benefit obligations for defined benefit pension plans were primarily due to decreases in the discount rates. In 2022, actuarial gains related to benefit obligations for defined benefit pension and OPEB plans were primarily due to increases in the discount rates. 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 Plans OPEB Plans Alliant Energy 2023 2022 2023 2022 Accumulated benefit obligations $857 $857 $160 $168 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 857 857 160 168 Fair value of plan assets 732 706 83 83 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 876 875 N/A N/A Fair value of plan assets 732 706 N/A N/A Defined Benefit Pension Plans OPEB Plans IPL 2023 2022 2023 2022 Accumulated benefit obligations $377 $379 $65 $68 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 377 379 65 68 Fair value of plan assets 352 344 61 58 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 387 389 N/A N/A Fair value of plan assets 352 344 N/A N/A Defined Benefit Pension Plans OPEB Plans WPL 2023 2022 2023 2022 Accumulated benefit obligations $373 $373 $61 $65 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 373 373 61 65 Fair value of plan assets 306 291 14 14 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 381 381 N/A N/A Fair value of plan assets 306 291 N/A N/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): IPL WPL 2023 2022 2023 2022 Regulatory assets $28 $30 $24 $25 Estimated Future Employer Contributions and Benefit Payments - Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2024 is as follows (in millions): Alliant Energy IPL WPL Defined benefit pension plans (a) $12 $— $10 OPEB plans 8 1 6 (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 Energy 2024 2025 2026 2027 2028 2029 - 2033 Defined benefit pension benefits $73 $73 $74 $75 $75 $343 OPEB 17 17 16 16 15 65 $90 $90 $90 $91 $90 $408 IPL 2024 2025 2026 2027 2028 2029 - 2033 Defined benefit pension benefits $34 $34 $34 $33 $33 $151 OPEB 7 7 7 6 6 25 $41 $41 $41 $39 $39 $176 WPL 2024 2025 2026 2027 2028 2029 - 2033 Defined benefit pension benefits $32 $32 $31 $31 $31 $146 OPEB 7 7 6 6 6 24 $39 $39 $37 $37 $37 $170 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 diversification, including equity, fixed income and global asset strategies. Global asset strategies may include investments in global equity, global debt and currencies. Defined Benefit Pension Plan Assets - The asset mix of defined benefit pension plans 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. An overlay management service is also used to help maintain target allocations and meet liquidity needs. The overlay manager is authorized to use derivative financial instruments to facilitate this service. For separately managed accounts, prohibited investments include, but are not limited to, direct ownership of real estate, oil and gas limited partnerships, securities of the managers’ firms or affiliate firms, and Alliant Energy securities. The allocations shown below exclude market exposure obtained through the overlay management service. At December 31, 2023, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows: Target Range Actual Allocation Allocation Cash and equivalents 0% - 5% 2% Equity securities 47% - 67% 56% Global asset securities 0% - 15% 5% Fixed income securities 27% - 47% 37% 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 VEBA trusts with assets greater than $5 million and the WPL 401(h) assets, the mix among asset classes 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. At December 31, 2023, the current target ranges and actual allocations for VEBA trusts with assets greater than $5 million and the WPL 401(h) assets were as follows: Target Range Actual Allocation Allocation Cash and equivalents 0% - 5% 1% Equity securities 0% - 55% 36% Fixed income securities 40% - 100% 63% 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 16 for discussion of levels within the fair value hierarchy. Level 1 items include investments in securities held in registered investment companies and directly held equity securities, 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 and fixed income securities. Cash and equivalents include money market fund investments and cash collateral supporting derivative financial instruments. Fixed income securities include corporate and government bonds, which are valued at the closing price reported in the active market for similar assets in which the individual securities are traded or based on yields currently available on comparable securities of issuers with similar credit ratings. 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): 2023 2022 Fair Level Level Level Fair Level Level Level Alliant Energy Value 1 2 3 Value 1 2 3 Cash and equivalents $19 $— $19 $— $79 $— $79 $— Equity securities 223 223 — — 185 185 — — Global asset securities 39 39 — — 35 35 — — Fixed income securities 143 31 112 — 130 30 100 — Total assets in fair value hierarchy 424 $293 $131 $— 429 $250 $179 $— Assets measured at net asset value 306 276 Accrued investment income 2 1 Total pension plan assets $732 $706 2023 2022 Fair Level Level Level Fair Level Level Level IPL Value 1 2 3 Value 1 2 3 Cash and equivalents $9 $— $9 $— $62 $— $62 $— Equity securities 107 107 — — 83 83 — — Global asset securities 19 19 — — 16 16 — — Fixed income securities 69 15 54 — 58 13 45 — Total assets in fair value hierarchy 204 $141 $63 $— 219 $112 $107 $— Assets measured at net asset value 147 124 Accrued investment income 1 1 Total pension plan assets $352 $344 2023 2022 Fair Level Level Level Fair Level Level Level WPL Value 1 2 3 Value 1 2 3 Cash and equivalents $8 $— $8 $— $13 $— $13 $— Equity securities 93 93 — — 82 82 — — Global asset securities 16 16 — — 16 16 — — Fixed income securities 60 13 47 — 57 13 44 — Total assets in fair value hierarchy 177 $122 $55 $— 168 $111 $57 $— Assets measured at net asset value 128 122 Accrued investment income 1 1 Total pension plan assets $306 $291 At December 31, the fair values of OPEB plan assets were as follows (in millions): 2023 2022 Fair Level Level Level Fair Level Level Level Alliant Energy Value 1 2 3 Value 1 2 3 Cash and equivalents $9 $— $9 $— $3 $— $3 $— Equity securities 8 8 — — 9 9 — — Global asset securities — — — — 1 1 — — Fixed income securities 47 47 — — 47 46 1 — Total assets in fair value hierarchy 64 $55 $9 $— 60 $56 $4 $— Assets measured at net asset value 19 23 Total OPEB plan assets $83 $83 2023 2022 Fair Level Level Level Fair Level Level Level IPL Value 1 2 3 Value 1 2 3 Cash and equivalents $1 $— $1 $— $1 $— $1 $— Equity securities 6 6 — — 5 5 — — Fixed income securities 36 36 — — 34 34 — — Total assets in fair value hierarchy 43 $42 $1 $— 40 $39 $1 $— Assets measured at net asset value 18 18 Total OPEB plan assets $61 $58 2023 2022 Fair Level Level Level Fair Level Level Level WPL Value 1 2 3 Value 1 2 3 Cash and equivalents $1 $— $1 $— $— $— $— $— Equity securities 2 2 — — 1 1 — — Fixed income securities 11 11 — — 13 13 — — Total OPEB plan assets $14 $13 $1 $— $14 $14 $— $— 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, 2023 and 2022. 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 8% and 10% of total assets in the 401(k) savings plans at December 31, 2023 and 2022, 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 Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 401(k) costs $30 $28 $26 $14 $13 $13 $14 $13 $12 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, 2023, performance shares and restricted stock units (performance- and time-vesting) were outstanding under the 2020 OIP, and 8 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 Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Compensation expense $12 $13 $14 $6 $7 $8 $5 $5 $6 Income tax benefits 3 3 4 2 2 2 1 1 2 As of December 31, 2023, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $8 million, $4 million and $3 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, 2023, 429,804 shares were included in the calculation of diluted EPS related to the nonvested equity awards. Performance Shares - Equity Awards - Payouts of 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: 2023 2022 2021 Shares Weighted Shares Weighted Shares Weighted Nonvested awards, January 1 190,273 $54.13 196,429 $51.59 129,156 $54.63 Granted 108,712 55.68 74,106 54.45 73,112 46.19 Vested (53,431) 64.04 (71,101) 47.48 — — Forfeited (11,600) 53.88 (9,161) 53.99 (5,839) 51.07 Nonvested awards, December 31 233,954 52.60 190,273 54.13 196,429 51.59 Restricted Stock Units - Equity Awards - 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: 2023 2022 2021 Units Weighted Units Weighted Units Weighted Nonvested units, January 1 198,275 $54.53 217,819 $50.54 146,549 $51.54 Granted 106,124 52.77 77,122 56.88 80,152 48.65 Vested (55,345) 59.40 (82,770) 46.08 — — Forfeited (14,795) 54.53 (13,896) 55.53 (8,882) 49.84 Nonvested units, December 31 234,259 52.58 198,275 54.53 217,819 50.54 Performance Restricted Stock Units - Equity Awards - Payouts of performance restricted stock units are based upon achievement of certain performance targets during a three-year performance period, which currently includes specified growth of consolidated net income from continuing operations, as well as a diversity metric for the 2022 and 2023 grants. The actual number of units that will be paid out upon vesting is dependent upon actual performance and may range from zero to 200% of the target number of units under each award type. If minimum performance targets are not met during the performance period, these units are forfeited. Performance restricted stock units are to be paid out in shares and are accounted for as equity awards. The fair value of each performance restricted stock unit 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 a probability assessment of payouts for the awards at each reporting period. A summary of the performance restricted stock units activity, with amounts representing the target number of units, was as follows: 2023 2022 2021 Units Weighted Average Grant Date Fair Value Units Weighted Average Grant Date Fair Value Units Weighted Average Grant Date Fair Value Nonvested units, January 1 199,874 $54.74 196,429 $50.74 197,463 $47.31 Granted 124,217 52.71 84,670 57.01 73,112 48.66 Vested (53,431) 59.36 (71,101) 46.24 (68,307) 38.60 Forfeited (13,021) 55.47 (10,124) 55.92 (5,839) 50.46 Nonvested units, December 31 257,639 52.76 199,874 54.74 196,429 50.74
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 assumptions for defined benefit pension and OPEB plans at the measurement date of December 31 were as follows: Defined Benefit Pension Plans OPEB Plans Alliant Energy 2023 2022 2021 2023 2022 2021 Discount rate for benefit obligations 5.36% 5.54% 2.91% 5.40% 5.53% 2.81% Discount rate for net periodic cost 5.54% 2.91% 2.57% 5.53% 2.81% 2.31% Expected rate of return on plan assets 7.80% 7.80% 7.10% 6.50% 6.40% 4.80% Interest crediting rate for Alliant Energy Cash Balance Pension Plan 10.75% 9.22% 4.18% N/A N/A N/A Rate of compensation increase 3.30% - 4.50% 3.30% - 4.50% 3.30% - 4.50% N/A N/A N/A Qualified Defined Benefit Pension Plan OPEB Plans IPL 2023 2022 2021 2023 2022 2021 Discount rate for benefit obligations 5.35% 5.55% 2.94% 5.40% 5.53% 2.80% Discount rate for net periodic cost 5.55% 2.94% 2.61% 5.53% 2.80% 2.28% Expected rate of return on plan assets 7.80% 7.80% 7.10% 6.90% 6.50% 5.10% Rate of compensation increase 3.30% 3.30% 3.30% N/A N/A N/A Qualified Defined Benefit Pension Plan OPEB Plans WPL 2023 2022 2021 2023 2022 2021 Discount rate for benefit obligations 5.35% 5.54% 2.94% 5.40% 5.53% 2.79% Discount rate for net periodic cost 5.54% 2.94% 2.64% 5.53% 2.79% 2.27% Expected rate of return on plan assets 7.80% 7.80% 7.10% 5.65% 5.49% 4.02% Rate of compensation increase 3.30% 3.30% 3.30% N/A N/A N/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 Energy Defined Benefit Pension Plans OPEB Plans 2023 2022 2021 2023 2022 2021 Service cost $5 $9 $11 $2 $3 $4 Interest cost 47 36 34 9 6 5 Expected return on plan assets (a) (53) (69) (69) (5) (5) (5) Amortization of prior service credit (b) (1) (1) — — — — Amortization of actuarial loss (c) 28 32 39 1 2 5 Settlement losses (d) — 26 — — — — $26 $33 $15 $7 $6 $9 IPL Defined Benefit Pension Plans OPEB Plans 2023 2022 2021 2023 2022 2021 Service cost $3 $6 $7 $1 $1 $1 Interest cost 21 16 16 3 2 2 Expected return on plan assets (a) (26) (31) (32) (3) (4) (3) Amortization of actuarial loss (c) 11 13 17 1 1 2 Settlement losses (d) — 13 — — — — $9 $17 $8 $2 $— $2 WPL Defined Benefit Pension Plans OPEB Plans 2023 2022 2021 2023 2022 2021 Service cost $2 $3 $4 $1 $1 $1 Interest cost 20 16 15 3 2 2 Expected return on plan assets (a) (22) (31) (31) (1) (1) — Amortization of actuarial loss (c) 13 15 19 1 2 2 Settlement losses (d) — 13 — — — — $13 $16 $7 $4 $4 $5 (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 Plans OPEB Plans Alliant Energy 2023 2022 2023 2022 Change in benefit obligation: Net benefit obligation at January 1 $875 $1,251 $168 $210 Service cost 5 9 2 3 Interest cost 47 36 9 6 Plan participants’ contributions — — 4 4 Actuarial (gain) loss 23 (269) (3) (37) Gross benefits paid (74) (152) (20) (18) Net benefit obligation at December 31 876 875 160 168 Change in plan assets: Fair value of plan assets at January 1 706 1,011 83 106 Actual return on plan assets 86 (204) 8 (17) Employer contributions 14 51 8 8 Plan participants’ contributions — — 4 4 Gross benefits paid (74) (152) (20) (18) Fair value of plan assets at December 31 732 706 83 83 Under funded status at December 31 ($144) ($169) ($77) ($85) Defined Benefit Pension Plans OPEB Plans Alliant Energy 2023 2022 2023 2022 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $14 $9 Current liabilities (2) (2) (8) (8) Pension and other benefit obligations (142) (167) (83) (86) Net amounts recognized at December 31 ($144) ($169) ($77) ($85) Amounts recognized in Regulatory Assets consist of: Net actuarial loss $337 $376 $11 $20 Prior service credit (2) (3) — — $335 $373 $11 $20 Defined Benefit Pension Plans OPEB Plans IPL 2023 2022 2023 2022 Change in benefit obligation: Net benefit obligation at January 1 $389 $567 $68 $84 Service cost 3 6 1 1 Interest cost 21 16 3 2 Plan participants’ contributions — — 2 2 Actuarial (gain) loss 9 (123) (1) (14) Gross benefits paid (35) (77) (8) (7) Net benefit obligation at December 31 387 389 65 68 Change in plan assets: Fair value of plan assets at January 1 344 462 58 74 Actual return on plan assets 42 (92) 7 (12) Employer contributions 1 51 2 1 Plan participants’ contributions — — 2 2 Gross benefits paid (35) (77) (8) (7) Fair value of plan assets at December 31 352 344 61 58 Under funded status at December 31 ($35) ($45) ($4) ($10) Defined Benefit Pension Plans OPEB Plans IPL 2023 2022 2023 2022 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $10 $6 Current liabilities — — (1) (2) Pension and other benefit obligations (35) (45) (13) (14) Net amounts recognized at December 31 ($35) ($45) ($4) ($10) Amounts recognized in Regulatory Assets consist of: Net actuarial loss $135 $154 $9 $14 Prior service credit (1) (1) — — $134 $153 $9 $14 Defined Benefit Pension Plans OPEB Plans WPL 2023 2022 2023 2022 Change in benefit obligation: Net benefit obligation at January 1 $381 $546 $65 $81 Service cost 2 3 1 1 Interest cost 20 16 3 2 Plan participants’ contributions — — 2 2 Actuarial (gain) loss 10 (117) (2) (13) Gross benefits paid (32) (67) (8) (8) Net benefit obligation at December 31 381 381 61 65 Change in plan assets: Fair value of plan assets at January 1 291 450 14 17 Actual return on plan assets 35 (92) 1 (2) Employer contributions 12 — 5 5 Plan participants’ contributions — — 2 2 Gross benefits paid (32) (67) (8) (8) Fair value of plan assets at December 31 306 291 14 14 Under funded status at December 31 ($75) ($90) ($47) ($51) Defined Benefit Pension Plans OPEB Plans WPL 2023 2022 2023 2022 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $4 $3 Current liabilities — — (6) (5) Pension and other benefit obligations (75) (90) (45) (49) Net amounts recognized at December 31 ($75) ($90) ($47) ($51) Amounts recognized in Regulatory Assets consist of: Net actuarial loss $148 $165 $3 $6 Prior service credit — — — — $148 $165 $3 $6 In 2023, actuarial losses related to benefit obligations for defined benefit pension plans were primarily due to decreases in the discount rates. In 2022, actuarial gains related to benefit obligations for defined benefit pension and OPEB plans were primarily due to increases in the discount rates. 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 Plans OPEB Plans Alliant Energy 2023 2022 2023 2022 Accumulated benefit obligations $857 $857 $160 $168 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 857 857 160 168 Fair value of plan assets 732 706 83 83 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 876 875 N/A N/A Fair value of plan assets 732 706 N/A N/A Defined Benefit Pension Plans OPEB Plans IPL 2023 2022 2023 2022 Accumulated benefit obligations $377 $379 $65 $68 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 377 379 65 68 Fair value of plan assets 352 344 61 58 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 387 389 N/A N/A Fair value of plan assets 352 344 N/A N/A Defined Benefit Pension Plans OPEB Plans WPL 2023 2022 2023 2022 Accumulated benefit obligations $373 $373 $61 $65 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 373 373 61 65 Fair value of plan assets 306 291 14 14 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 381 381 N/A N/A Fair value of plan assets 306 291 N/A N/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): IPL WPL 2023 2022 2023 2022 Regulatory assets $28 $30 $24 $25 Estimated Future Employer Contributions and Benefit Payments - Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2024 is as follows (in millions): Alliant Energy IPL WPL Defined benefit pension plans (a) $12 $— $10 OPEB plans 8 1 6 (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 Energy 2024 2025 2026 2027 2028 2029 - 2033 Defined benefit pension benefits $73 $73 $74 $75 $75 $343 OPEB 17 17 16 16 15 65 $90 $90 $90 $91 $90 $408 IPL 2024 2025 2026 2027 2028 2029 - 2033 Defined benefit pension benefits $34 $34 $34 $33 $33 $151 OPEB 7 7 7 6 6 25 $41 $41 $41 $39 $39 $176 WPL 2024 2025 2026 2027 2028 2029 - 2033 Defined benefit pension benefits $32 $32 $31 $31 $31 $146 OPEB 7 7 6 6 6 24 $39 $39 $37 $37 $37 $170 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 diversification, including equity, fixed income and global asset strategies. Global asset strategies may include investments in global equity, global debt and currencies. Defined Benefit Pension Plan Assets - The asset mix of defined benefit pension plans 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. An overlay management service is also used to help maintain target allocations and meet liquidity needs. The overlay manager is authorized to use derivative financial instruments to facilitate this service. For separately managed accounts, prohibited investments include, but are not limited to, direct ownership of real estate, oil and gas limited partnerships, securities of the managers’ firms or affiliate firms, and Alliant Energy securities. The allocations shown below exclude market exposure obtained through the overlay management service. At December 31, 2023, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows: Target Range Actual Allocation Allocation Cash and equivalents 0% - 5% 2% Equity securities 47% - 67% 56% Global asset securities 0% - 15% 5% Fixed income securities 27% - 47% 37% 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 VEBA trusts with assets greater than $5 million and the WPL 401(h) assets, the mix among asset classes 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. At December 31, 2023, the current target ranges and actual allocations for VEBA trusts with assets greater than $5 million and the WPL 401(h) assets were as follows: Target Range Actual Allocation Allocation Cash and equivalents 0% - 5% 1% Equity securities 0% - 55% 36% Fixed income securities 40% - 100% 63% 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 16 for discussion of levels within the fair value hierarchy. Level 1 items include investments in securities held in registered investment companies and directly held equity securities, 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 and fixed income securities. Cash and equivalents include money market fund investments and cash collateral supporting derivative financial instruments. Fixed income securities include corporate and government bonds, which are valued at the closing price reported in the active market for similar assets in which the individual securities are traded or based on yields currently available on comparable securities of issuers with similar credit ratings. 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): 2023 2022 Fair Level Level Level Fair Level Level Level Alliant Energy Value 1 2 3 Value 1 2 3 Cash and equivalents $19 $— $19 $— $79 $— $79 $— Equity securities 223 223 — — 185 185 — — Global asset securities 39 39 — — 35 35 — — Fixed income securities 143 31 112 — 130 30 100 — Total assets in fair value hierarchy 424 $293 $131 $— 429 $250 $179 $— Assets measured at net asset value 306 276 Accrued investment income 2 1 Total pension plan assets $732 $706 2023 2022 Fair Level Level Level Fair Level Level Level IPL Value 1 2 3 Value 1 2 3 Cash and equivalents $9 $— $9 $— $62 $— $62 $— Equity securities 107 107 — — 83 83 — — Global asset securities 19 19 — — 16 16 — — Fixed income securities 69 15 54 — 58 13 45 — Total assets in fair value hierarchy 204 $141 $63 $— 219 $112 $107 $— Assets measured at net asset value 147 124 Accrued investment income 1 1 Total pension plan assets $352 $344 2023 2022 Fair Level Level Level Fair Level Level Level WPL Value 1 2 3 Value 1 2 3 Cash and equivalents $8 $— $8 $— $13 $— $13 $— Equity securities 93 93 — — 82 82 — — Global asset securities 16 16 — — 16 16 — — Fixed income securities 60 13 47 — 57 13 44 — Total assets in fair value hierarchy 177 $122 $55 $— 168 $111 $57 $— Assets measured at net asset value 128 122 Accrued investment income 1 1 Total pension plan assets $306 $291 At December 31, the fair values of OPEB plan assets were as follows (in millions): 2023 2022 Fair Level Level Level Fair Level Level Level Alliant Energy Value 1 2 3 Value 1 2 3 Cash and equivalents $9 $— $9 $— $3 $— $3 $— Equity securities 8 8 — — 9 9 — — Global asset securities — — — — 1 1 — — Fixed income securities 47 47 — — 47 46 1 — Total assets in fair value hierarchy 64 $55 $9 $— 60 $56 $4 $— Assets measured at net asset value 19 23 Total OPEB plan assets $83 $83 2023 2022 Fair Level Level Level Fair Level Level Level IPL Value 1 2 3 Value 1 2 3 Cash and equivalents $1 $— $1 $— $1 $— $1 $— Equity securities 6 6 — — 5 5 — — Fixed income securities 36 36 — — 34 34 — — Total assets in fair value hierarchy 43 $42 $1 $— 40 $39 $1 $— Assets measured at net asset value 18 18 Total OPEB plan assets $61 $58 2023 2022 Fair Level Level Level Fair Level Level Level WPL Value 1 2 3 Value 1 2 3 Cash and equivalents $1 $— $1 $— $— $— $— $— Equity securities 2 2 — — 1 1 — — Fixed income securities 11 11 — — 13 13 — — Total OPEB plan assets $14 $13 $1 $— $14 $14 $— $— 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, 2023 and 2022. 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 8% and 10% of total assets in the 401(k) savings plans at December 31, 2023 and 2022, 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 Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 401(k) costs $30 $28 $26 $14 $13 $13 $14 $13 $12 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, 2023, performance shares and restricted stock units (performance- and time-vesting) were outstanding under the 2020 OIP, and 8 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 Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Compensation expense $12 $13 $14 $6 $7 $8 $5 $5 $6 Income tax benefits 3 3 4 2 2 2 1 1 2 As of December 31, 2023, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $8 million, $4 million and $3 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, 2023, 429,804 shares were included in the calculation of diluted EPS related to the nonvested equity awards. Performance Shares - Equity Awards - Payouts of 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: 2023 2022 2021 Shares Weighted Shares Weighted Shares Weighted Nonvested awards, January 1 190,273 $54.13 196,429 $51.59 129,156 $54.63 Granted 108,712 55.68 74,106 54.45 73,112 46.19 Vested (53,431) 64.04 (71,101) 47.48 — — Forfeited (11,600) 53.88 (9,161) 53.99 (5,839) 51.07 Nonvested awards, December 31 233,954 52.60 190,273 54.13 196,429 51.59 Restricted Stock Units - Equity Awards - 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: 2023 2022 2021 Units Weighted Units Weighted Units Weighted Nonvested units, January 1 198,275 $54.53 217,819 $50.54 146,549 $51.54 Granted 106,124 52.77 77,122 56.88 80,152 48.65 Vested (55,345) 59.40 (82,770) 46.08 — — Forfeited (14,795) 54.53 (13,896) 55.53 (8,882) 49.84 Nonvested units, December 31 234,259 52.58 198,275 54.53 217,819 50.54 Performance Restricted Stock Units - Equity Awards - Payouts of performance restricted stock units are based upon achievement of certain performance targets during a three-year performance period, which currently includes specified growth of consolidated net income from continuing operations, as well as a diversity metric for the 2022 and 2023 grants. The actual number of units that will be paid out upon vesting is dependent upon actual performance and may range from zero to 200% of the target number of units under each award type. If minimum performance targets are not met during the performance period, these units are forfeited. Performance restricted stock units are to be paid out in shares and are accounted for as equity awards. The fair value of each performance restricted stock unit 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 a probability assessment of payouts for the awards at each reporting period. A summary of the performance restricted stock units activity, with amounts representing the target number of units, was as follows: 2023 2022 2021 Units Weighted Average Grant Date Fair Value Units Weighted Average Grant Date Fair Value Units Weighted Average Grant Date Fair Value Nonvested units, January 1 199,874 $54.74 196,429 $50.74 197,463 $47.31 Granted 124,217 52.71 84,670 57.01 73,112 48.66 Vested (53,431) 59.36 (71,101) 46.24 (68,307) 38.60 Forfeited (13,021) 55.47 (10,124) 55.92 (5,839) 50.46 Nonvested units, December 31 257,639 52.76 199,874 54.74 196,429 50.74

Asset Retirement Obligations

Asset Retirement Obligations	12 Months Ended
	Dec. 31, 2023
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, wind farms, active ash landfills, ash ponds, solar generation, 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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Balance, January 1 $279 $294 $195 $213 $84 $81 Revisions in estimated cash flows (6) 19 (9) 15 3 4 Liabilities settled (51) (48) (44) (39) (7) (9) Liabilities incurred 16 6 1 — 15 6 Accretion expense 8 8 5 6 3 2 Balance, December 31 $246 $279 $148 $195 $98 $84
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, wind farms, active ash landfills, ash ponds, solar generation, 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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Balance, January 1 $279 $294 $195 $213 $84 $81 Revisions in estimated cash flows (6) 19 (9) 15 3 4 Liabilities settled (51) (48) (44) (39) (7) (9) Liabilities incurred 16 6 1 — 15 6 Accretion expense 8 8 5 6 3 2 Balance, December 31 $246 $279 $148 $195 $98 $84
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, wind farms, active ash landfills, ash ponds, solar generation, 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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Balance, January 1 $279 $294 $195 $213 $84 $81 Revisions in estimated cash flows (6) 19 (9) 15 3 4 Liabilities settled (51) (48) (44) (39) (7) (9) Liabilities incurred 16 6 1 — 15 6 Accretion expense 8 8 5 6 3 2 Balance, December 31 $246 $279 $148 $195 $98 $84

Derivative Instruments

Derivative Instruments	12 Months Ended
	Dec. 31, 2023
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, 2023, 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): Electricity FTRs Natural Gas MWhs Years MWhs Years Dths Years Alliant Energy 1,640 2024-2026 11,927 2024 176,349 2024-2032 IPL 673 2024-2026 5,336 2024 74,360 2024-2030 WPL 967 2024-2026 6,591 2024 101,989 2024-2032 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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Current derivative assets $44 $111 $30 $69 $14 $42 Non-current derivative assets 44 126 24 69 20 57 Current derivative liabilities 51 59 22 40 29 19 Non-current derivative liabilities 47 20 8 6 39 14 In 2023, Alliant Energy’s, IPL’s and WPL’s derivative assets decreased primarily due to settlements of natural gas and electricity contracts, and lower natural gas prices. Alliant Energy’s, IPL’s and WPL’s non-current derivative liabilities increased primarily due to lower natural gas prices. Alliant Energy’s and IPL’s current derivative liabilities decreased primarily due to settlements of natural gas contracts. 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, 2023 and 2022, 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 Energy IPL WPL Gross Gross Gross (as reported) Net (as reported) Net (as reported) Net 2023 Derivative assets $88 $47 $54 $32 $34 $15 Derivative liabilities 98 57 30 8 68 49 2022 Derivative assets 237 193 138 108 99 85 Derivative liabilities 79 35 46 16 33 19 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 December 31, 2023, $1 million of non-current interest rate derivative assets was recorded in “Deferred charges and other” on Alliant Energy’s balance sheet. This interest rate derivative was designated as a cash flow hedge, with changes in fair value recorded as other comprehensive income/loss. As of December 31, 2023, accumulated other comprehensive income included $1 million of income related to the interest rate swap. In 2023, $3 million 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, 2023, 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): Electricity FTRs Natural Gas MWhs Years MWhs Years Dths Years Alliant Energy 1,640 2024-2026 11,927 2024 176,349 2024-2032 IPL 673 2024-2026 5,336 2024 74,360 2024-2030 WPL 967 2024-2026 6,591 2024 101,989 2024-2032 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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Current derivative assets $44 $111 $30 $69 $14 $42 Non-current derivative assets 44 126 24 69 20 57 Current derivative liabilities 51 59 22 40 29 19 Non-current derivative liabilities 47 20 8 6 39 14 In 2023, Alliant Energy’s, IPL’s and WPL’s derivative assets decreased primarily due to settlements of natural gas and electricity contracts, and lower natural gas prices. Alliant Energy’s, IPL’s and WPL’s non-current derivative liabilities increased primarily due to lower natural gas prices. Alliant Energy’s and IPL’s current derivative liabilities decreased primarily due to settlements of natural gas contracts. 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, 2023 and 2022, 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 Energy IPL WPL Gross Gross Gross (as reported) Net (as reported) Net (as reported) Net 2023 Derivative assets $88 $47 $54 $32 $34 $15 Derivative liabilities 98 57 30 8 68 49 2022 Derivative assets 237 193 138 108 99 85 Derivative liabilities 79 35 46 16 33 19 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 December 31, 2023, $1 million of non-current interest rate derivative assets was recorded in “Deferred charges and other” on Alliant Energy’s balance sheet. This interest rate derivative was designated as a cash flow hedge, with changes in fair value recorded as other comprehensive income/loss. As of December 31, 2023, accumulated other comprehensive income included $1 million of income related to the interest rate swap. In 2023, $3 million 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, 2023, 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): Electricity FTRs Natural Gas MWhs Years MWhs Years Dths Years Alliant Energy 1,640 2024-2026 11,927 2024 176,349 2024-2032 IPL 673 2024-2026 5,336 2024 74,360 2024-2030 WPL 967 2024-2026 6,591 2024 101,989 2024-2032 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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Current derivative assets $44 $111 $30 $69 $14 $42 Non-current derivative assets 44 126 24 69 20 57 Current derivative liabilities 51 59 22 40 29 19 Non-current derivative liabilities 47 20 8 6 39 14 In 2023, Alliant Energy’s, IPL’s and WPL’s derivative assets decreased primarily due to settlements of natural gas and electricity contracts, and lower natural gas prices. Alliant Energy’s, IPL’s and WPL’s non-current derivative liabilities increased primarily due to lower natural gas prices. Alliant Energy’s and IPL’s current derivative liabilities decreased primarily due to settlements of natural gas contracts. 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, 2023 and 2022, 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 Energy IPL WPL Gross Gross Gross (as reported) Net (as reported) Net (as reported) Net 2023 Derivative assets $88 $47 $54 $32 $34 $15 Derivative liabilities 98 57 30 8 68 49 2022 Derivative assets 237 193 138 108 99 85 Derivative liabilities 79 35 46 16 33 19 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 December 31, 2023, $1 million of non-current interest rate derivative assets was recorded in “Deferred charges and other” on Alliant Energy’s balance sheet. This interest rate derivative was designated as a cash flow hedge, with changes in fair value recorded as other comprehensive income/loss. As of December 31, 2023, accumulated other comprehensive income included $1 million of income related to the interest rate swap. In 2023, $3 million of reductions to interest expense were recorded in Alliant Energy’s income statement related to the interest rate swap.

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2023
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 15 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 substantially classified as Level 2. Refer to Note 9(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 the related estimated fair values of other financial instruments at December 31 were as follows (in millions): Alliant Energy 2023 2022 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $45 $45 $— $— $45 $10 $10 $— $— $10 Commodity derivatives 88 — 59 29 88 237 — 206 31 237 Interest rate derivatives 1 — 1 — 1 — — — — — Deferred proceeds 216 — — 216 216 185 — — 185 185 Liabilities and equity: Commodity derivatives 98 — 93 5 98 79 — 67 12 79 Long-term debt (incl. current maturities) 9,034 — 8,677 — 8,677 8,076 — 7,338 1 7,339 IPL 2023 2022 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $45 $45 $— $— $45 $10 $10 $— $— $10 Commodity derivatives 54 — 30 24 54 138 — 111 27 138 Deferred proceeds 216 — — 216 216 185 — — 185 185 Liabilities and equity: Commodity derivatives 30 — 25 5 30 46 — 35 11 46 Long-term debt (incl. current maturities) 3,945 — 3,664 — 3,664 3,646 — 3,228 — 3,228 WPL 2023 2022 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Commodity derivatives $34 $— $29 $5 $34 $99 $— $95 $4 $99 Liabilities and equity: Commodity derivatives 68 — 68 — 68 33 — 32 1 33 Long-term debt 3,070 — 2,933 — 2,933 2,770 — 2,542 — 2,542 Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions): Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds 2023 2022 2023 2022 Beginning balance, January 1 $19 $29 $185 $214 Total net gains (losses) included in changes in net assets (realized/unrealized) 3 (18) — — Purchases 62 79 — — Sales (3) (2) — — Settlements (a) (57) (69) 31 (29) Ending balance, December 31 $24 $19 $216 $185 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 ($18) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds 2023 2022 2023 2022 Beginning balance, January 1 $16 $18 $185 $214 Total net losses included in changes in net assets (realized/unrealized) (3) (12) — — Purchases 51 58 — — Sales (3) (1) — — Settlements (a) (42) (47) 31 (29) Ending balance, December 31 $19 $16 $216 $185 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 ($3) ($13) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net 2023 2022 Beginning balance, January 1 $3 $11 Total net gains (losses) included in changes in net assets (realized/unrealized) 6 (6) Purchases 11 21 Sales — (1) Settlements (a) (15) (22) Ending balance, December 31 $5 $3 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31 $6 ($5) (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 (liabilities) at December 31 as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs 2023 $3 $21 $3 $16 $— $5 2022 (10) 29 (9) 25 (1) 4
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 15 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 substantially classified as Level 2. Refer to Note 9(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 the related estimated fair values of other financial instruments at December 31 were as follows (in millions): Alliant Energy 2023 2022 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $45 $45 $— $— $45 $10 $10 $— $— $10 Commodity derivatives 88 — 59 29 88 237 — 206 31 237 Interest rate derivatives 1 — 1 — 1 — — — — — Deferred proceeds 216 — — 216 216 185 — — 185 185 Liabilities and equity: Commodity derivatives 98 — 93 5 98 79 — 67 12 79 Long-term debt (incl. current maturities) 9,034 — 8,677 — 8,677 8,076 — 7,338 1 7,339 IPL 2023 2022 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $45 $45 $— $— $45 $10 $10 $— $— $10 Commodity derivatives 54 — 30 24 54 138 — 111 27 138 Deferred proceeds 216 — — 216 216 185 — — 185 185 Liabilities and equity: Commodity derivatives 30 — 25 5 30 46 — 35 11 46 Long-term debt (incl. current maturities) 3,945 — 3,664 — 3,664 3,646 — 3,228 — 3,228 WPL 2023 2022 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Commodity derivatives $34 $— $29 $5 $34 $99 $— $95 $4 $99 Liabilities and equity: Commodity derivatives 68 — 68 — 68 33 — 32 1 33 Long-term debt 3,070 — 2,933 — 2,933 2,770 — 2,542 — 2,542 Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions): Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds 2023 2022 2023 2022 Beginning balance, January 1 $19 $29 $185 $214 Total net gains (losses) included in changes in net assets (realized/unrealized) 3 (18) — — Purchases 62 79 — — Sales (3) (2) — — Settlements (a) (57) (69) 31 (29) Ending balance, December 31 $24 $19 $216 $185 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 ($18) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds 2023 2022 2023 2022 Beginning balance, January 1 $16 $18 $185 $214 Total net losses included in changes in net assets (realized/unrealized) (3) (12) — — Purchases 51 58 — — Sales (3) (1) — — Settlements (a) (42) (47) 31 (29) Ending balance, December 31 $19 $16 $216 $185 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 ($3) ($13) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net 2023 2022 Beginning balance, January 1 $3 $11 Total net gains (losses) included in changes in net assets (realized/unrealized) 6 (6) Purchases 11 21 Sales — (1) Settlements (a) (15) (22) Ending balance, December 31 $5 $3 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31 $6 ($5) (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 (liabilities) at December 31 as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs 2023 $3 $21 $3 $16 $— $5 2022 (10) 29 (9) 25 (1) 4
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 15 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 substantially classified as Level 2. Refer to Note 9(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 the related estimated fair values of other financial instruments at December 31 were as follows (in millions): Alliant Energy 2023 2022 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $45 $45 $— $— $45 $10 $10 $— $— $10 Commodity derivatives 88 — 59 29 88 237 — 206 31 237 Interest rate derivatives 1 — 1 — 1 — — — — — Deferred proceeds 216 — — 216 216 185 — — 185 185 Liabilities and equity: Commodity derivatives 98 — 93 5 98 79 — 67 12 79 Long-term debt (incl. current maturities) 9,034 — 8,677 — 8,677 8,076 — 7,338 1 7,339 IPL 2023 2022 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $45 $45 $— $— $45 $10 $10 $— $— $10 Commodity derivatives 54 — 30 24 54 138 — 111 27 138 Deferred proceeds 216 — — 216 216 185 — — 185 185 Liabilities and equity: Commodity derivatives 30 — 25 5 30 46 — 35 11 46 Long-term debt (incl. current maturities) 3,945 — 3,664 — 3,664 3,646 — 3,228 — 3,228 WPL 2023 2022 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Commodity derivatives $34 $— $29 $5 $34 $99 $— $95 $4 $99 Liabilities and equity: Commodity derivatives 68 — 68 — 68 33 — 32 1 33 Long-term debt 3,070 — 2,933 — 2,933 2,770 — 2,542 — 2,542 Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions): Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds 2023 2022 2023 2022 Beginning balance, January 1 $19 $29 $185 $214 Total net gains (losses) included in changes in net assets (realized/unrealized) 3 (18) — — Purchases 62 79 — — Sales (3) (2) — — Settlements (a) (57) (69) 31 (29) Ending balance, December 31 $24 $19 $216 $185 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 ($18) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds 2023 2022 2023 2022 Beginning balance, January 1 $16 $18 $185 $214 Total net losses included in changes in net assets (realized/unrealized) (3) (12) — — Purchases 51 58 — — Sales (3) (1) — — Settlements (a) (42) (47) 31 (29) Ending balance, December 31 $19 $16 $216 $185 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 ($3) ($13) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net 2023 2022 Beginning balance, January 1 $3 $11 Total net gains (losses) included in changes in net assets (realized/unrealized) 6 (6) Purchases 11 21 Sales — (1) Settlements (a) (15) (22) Ending balance, December 31 $5 $3 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31 $6 ($5) (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 (liabilities) at December 31 as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs 2023 $3 $21 $3 $16 $— $5 2022 (10) 29 (9) 25 (1) 4

Commitments And Contingencies

Commitments And Contingencies	12 Months Ended
	Dec. 31, 2023
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 solar generation, WPL’s expansion of battery storage, and IPL’s repowering of the existing Franklin County wind farm. At December 31, 2023, Alliant Energy’s, IPL’s, and WPL’s minimum future commitments in 2024 for these projects were $188 million, $131 million, and $57 million, respectively. 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, 2023, 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 Energy 2024 2025 2026 2027 2028 Thereafter Total Natural gas $301 $187 $123 $78 $49 $142 $880 Coal 94 49 8 8 6 — 165 Other (a) 61 17 14 9 2 22 125 $456 $253 $145 $95 $57 $164 $1,170 IPL 2024 2025 2026 2027 2028 Thereafter Total Natural gas $165 $86 $47 $35 $14 $25 $372 Coal 49 35 8 8 6 — 106 Other (a) 23 2 2 2 2 22 53 $237 $123 $57 $45 $22 $47 $531 WPL 2024 2025 2026 2027 2028 Thereafter Total Natural gas $136 $101 $76 $43 $35 $117 $508 Coal 45 14 — — — — 59 Other (a) 23 1 1 — — — 25 $204 $116 $77 $43 $35 $117 $592 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2023. 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. Whiting Petroleum - Whiting Petroleum is an independent oil and gas company. In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum. Alliant Energy Resources, LLC, as the successor to a predecessor entity that owned Whiting Petroleum, and a wholly-owned subsidiary of AEF, continues to guarantee 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. As of December 31, 2023, the currently known partnership obligations for the abandonment obligations are estimated at $49 million, which represents Alliant Energy’s currently estimated maximum exposure under the guarantees. Alliant Energy estimates its expected loss to be a portion of the $49 million of known partnership abandonment obligations of the Whiting Petroleum affiliate and the other partners. Alliant Energy is not aware of any material liabilities related to these guarantees 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, 2023 and 2022. Whiting Petroleum completed a business combination with Oasis Petroleum Inc. in 2022. The combined operations are now known as Chord Energy Corporation. The business combination is not expected to affect the scope of the Whiting Petroleum affiliate’s obligations to Alliant Energy or Alliant Energy’s related guarantees. 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 $51 million as of December 31, 2023 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, 2023 and 2022. Transfers of Renewable Tax Credits - 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. IPL and WPL provided indemnifications associated with $76 million and $22 million, respectively, of proceeds for renewable tax credits transferred to other corporate taxpayers in 2023 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. 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, 2023, 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 Energy IPL WPL Range of estimated future costs $9 - $36 $5 - $11 $4 - $25 Current and non-current environmental liabilities $18 $8 $10 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. 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 diverse 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 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, diversification of 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 counterparty diversification, 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 15 for details of allowances for expected credit losses and credit risk-related contingent features, respectively. 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, which may result in additional changes to the base return on equity authorized for the MISO transmission owners. 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 anticipated reduction in the base return on equity authorized for the MISO transmission owners. Any further changes in FERC’s decisions may have an impact on Alliant Energy’s share of ATC’s future earnings and customer costs. - At December 31, 2023, employees covered by collective bargaining agreements represented 53%, 69% and 83% of total employees of Alliant Energy, IPL and WPL, respectively. In August 2024, IPL’s collective bargaining agreement with International Brotherhood of Electrical Workers Local 204 (Cedar Rapids) expires, representing 18% and 53% of total employees of Alliant Energy and IPL, respectively.
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 solar generation, WPL’s expansion of battery storage, and IPL’s repowering of the existing Franklin County wind farm. At December 31, 2023, Alliant Energy’s, IPL’s, and WPL’s minimum future commitments in 2024 for these projects were $188 million, $131 million, and $57 million, respectively. 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, 2023, 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 Energy 2024 2025 2026 2027 2028 Thereafter Total Natural gas $301 $187 $123 $78 $49 $142 $880 Coal 94 49 8 8 6 — 165 Other (a) 61 17 14 9 2 22 125 $456 $253 $145 $95 $57 $164 $1,170 IPL 2024 2025 2026 2027 2028 Thereafter Total Natural gas $165 $86 $47 $35 $14 $25 $372 Coal 49 35 8 8 6 — 106 Other (a) 23 2 2 2 2 22 53 $237 $123 $57 $45 $22 $47 $531 WPL 2024 2025 2026 2027 2028 Thereafter Total Natural gas $136 $101 $76 $43 $35 $117 $508 Coal 45 14 — — — — 59 Other (a) 23 1 1 — — — 25 $204 $116 $77 $43 $35 $117 $592 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2023. 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. Whiting Petroleum - Whiting Petroleum is an independent oil and gas company. In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum. Alliant Energy Resources, LLC, as the successor to a predecessor entity that owned Whiting Petroleum, and a wholly-owned subsidiary of AEF, continues to guarantee 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. As of December 31, 2023, the currently known partnership obligations for the abandonment obligations are estimated at $49 million, which represents Alliant Energy’s currently estimated maximum exposure under the guarantees. Alliant Energy estimates its expected loss to be a portion of the $49 million of known partnership abandonment obligations of the Whiting Petroleum affiliate and the other partners. Alliant Energy is not aware of any material liabilities related to these guarantees 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, 2023 and 2022. Whiting Petroleum completed a business combination with Oasis Petroleum Inc. in 2022. The combined operations are now known as Chord Energy Corporation. The business combination is not expected to affect the scope of the Whiting Petroleum affiliate’s obligations to Alliant Energy or Alliant Energy’s related guarantees. 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 $51 million as of December 31, 2023 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, 2023 and 2022. Transfers of Renewable Tax Credits - 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. IPL and WPL provided indemnifications associated with $76 million and $22 million, respectively, of proceeds for renewable tax credits transferred to other corporate taxpayers in 2023 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. 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, 2023, 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 Energy IPL WPL Range of estimated future costs $9 - $36 $5 - $11 $4 - $25 Current and non-current environmental liabilities $18 $8 $10 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. 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 diverse 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 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, diversification of 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 counterparty diversification, 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 15 for details of allowances for expected credit losses and credit risk-related contingent features, respectively. 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, which may result in additional changes to the base return on equity authorized for the MISO transmission owners. 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 anticipated reduction in the base return on equity authorized for the MISO transmission owners. Any further changes in FERC’s decisions may have an impact on Alliant Energy’s share of ATC’s future earnings and customer costs. - At December 31, 2023, employees covered by collective bargaining agreements represented 53%, 69% and 83% of total employees of Alliant Energy, IPL and WPL, respectively. In August 2024, IPL’s collective bargaining agreement with International Brotherhood of Electrical Workers Local 204 (Cedar Rapids) expires, representing 18% and 53% of total employees of Alliant Energy and IPL, respectively.
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 solar generation, WPL’s expansion of battery storage, and IPL’s repowering of the existing Franklin County wind farm. At December 31, 2023, Alliant Energy’s, IPL’s, and WPL’s minimum future commitments in 2024 for these projects were $188 million, $131 million, and $57 million, respectively. 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, 2023, 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 Energy 2024 2025 2026 2027 2028 Thereafter Total Natural gas $301 $187 $123 $78 $49 $142 $880 Coal 94 49 8 8 6 — 165 Other (a) 61 17 14 9 2 22 125 $456 $253 $145 $95 $57 $164 $1,170 IPL 2024 2025 2026 2027 2028 Thereafter Total Natural gas $165 $86 $47 $35 $14 $25 $372 Coal 49 35 8 8 6 — 106 Other (a) 23 2 2 2 2 22 53 $237 $123 $57 $45 $22 $47 $531 WPL 2024 2025 2026 2027 2028 Thereafter Total Natural gas $136 $101 $76 $43 $35 $117 $508 Coal 45 14 — — — — 59 Other (a) 23 1 1 — — — 25 $204 $116 $77 $43 $35 $117 $592 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2023. 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. Whiting Petroleum - Whiting Petroleum is an independent oil and gas company. In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum. Alliant Energy Resources, LLC, as the successor to a predecessor entity that owned Whiting Petroleum, and a wholly-owned subsidiary of AEF, continues to guarantee 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. As of December 31, 2023, the currently known partnership obligations for the abandonment obligations are estimated at $49 million, which represents Alliant Energy’s currently estimated maximum exposure under the guarantees. Alliant Energy estimates its expected loss to be a portion of the $49 million of known partnership abandonment obligations of the Whiting Petroleum affiliate and the other partners. Alliant Energy is not aware of any material liabilities related to these guarantees 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, 2023 and 2022. Whiting Petroleum completed a business combination with Oasis Petroleum Inc. in 2022. The combined operations are now known as Chord Energy Corporation. The business combination is not expected to affect the scope of the Whiting Petroleum affiliate’s obligations to Alliant Energy or Alliant Energy’s related guarantees. 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 $51 million as of December 31, 2023 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, 2023 and 2022. Transfers of Renewable Tax Credits - 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. IPL and WPL provided indemnifications associated with $76 million and $22 million, respectively, of proceeds for renewable tax credits transferred to other corporate taxpayers in 2023 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. 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, 2023, 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 Energy IPL WPL Range of estimated future costs $9 - $36 $5 - $11 $4 - $25 Current and non-current environmental liabilities $18 $8 $10 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. 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 diverse 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 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, diversification of 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 counterparty diversification, 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 15 for details of allowances for expected credit losses and credit risk-related contingent features, respectively. 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, which may result in additional changes to the base return on equity authorized for the MISO transmission owners. 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 anticipated reduction in the base return on equity authorized for the MISO transmission owners. Any further changes in FERC’s decisions may have an impact on Alliant Energy’s share of ATC’s future earnings and customer costs. - At December 31, 2023, employees covered by collective bargaining agreements represented 53%, 69% and 83% of total employees of Alliant Energy, IPL and WPL, respectively. In August 2024, IPL’s collective bargaining agreement with International Brotherhood of Electrical Workers Local 204 (Cedar Rapids) expires, representing 18% and 53% of total employees of Alliant Energy and IPL, respectively.

Segments Of Business

Segments Of Business	12 Months Ended
	Dec. 31, 2023
Segment Reporting Information [Line Items]
Segments Of Business	SEGMENTS OF BUSINESS Alliant Energy - Alliant Energy’s principal businesses as of December 31, 2023 are: • Utility - includes the operations of IPL and WPL, which primarily serve retail customers in Iowa and Wisconsin. The utility business has three reportable segments: a) utility electric operations; b) utility gas operations; and c) utility other, which includes steam operations and the unallocated portions of the utility business. Various line items in the following tables are not allocated to the electric and gas segments for management reporting purposes, and therefore, are included only in “Total Utility.” • ATC Holdings, Non-utility, Parent and Other - 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. 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. Intersegment revenues were not material to Alliant Energy’s operations and there was no single customer whose revenues were 10% or more of Alliant Energy’s consolidated revenues. All of Alliant Energy’s operations and assets are located in the U.S. Certain financial information relating to Alliant Energy’s business segments, which represent the services provided to its customers, was as follows (in millions): ATC Holdings, Utility Non-utility, Alliant Energy 2023 Electric Gas Other Total Parent and Other Consolidated Revenues $3,345 $540 $52 $3,937 $90 $4,027 Depreciation and amortization 602 60 6 668 8 676 Operating income 827 70 19 916 27 943 Interest expense 304 90 394 Equity income from unconsolidated investments, net (3) — — (3) (58) (61) Income taxes 2 2 4 Net income (loss) attributable to Alliant Energy common shareowners 711 (8) 703 Total assets 17,833 1,684 606 20,123 1,114 21,237 Investments in equity method subsidiaries 21 — — 21 564 585 Construction and acquisition expenditures 1,641 90 — 1,731 123 1,854 ATC Holdings, Utility Non-utility, Alliant Energy 2022 Electric Gas Other Total Parent and Other Consolidated Revenues $3,421 $642 $49 $4,112 $93 $4,205 Depreciation and amortization 601 56 7 664 7 671 Operating income 805 97 3 905 23 928 Interest expense 269 56 325 Equity income from unconsolidated investments, net (1) — — (1) (50) (51) Income taxes 16 6 22 Net income attributable to Alliant Energy common shareowners 675 11 686 Total assets 16,571 1,631 860 19,062 1,101 20,163 Investments in equity method subsidiaries 20 — — 20 522 542 Construction and acquisition expenditures 1,318 74 — 1,392 92 1,484 ATC Holdings, Utility Non-utility, Alliant Energy 2021 Electric Gas Other Total Parent and Other Consolidated Revenues $3,081 $456 $49 $3,586 $83 $3,669 Depreciation and amortization 591 54 6 651 6 657 Operating income (loss) 716 63 (11) 768 27 795 Interest expense 244 33 277 Equity income from unconsolidated investments, net (2) — — (2) (60) (62) Income tax expense (benefit) (87) 13 (74) Net income attributable to Alliant Energy common shareowners 618 41 659 Total assets 14,924 1,487 1,103 17,514 1,039 18,553 Investments in equity method subsidiaries 17 — — 17 491 508 Construction and acquisition expenditures 980 90 — 1,070 99 1,169 IPL - IPL is a utility primarily serving retail customers in Iowa and includes three reportable segments: a) electric operations; b) gas operations; and c) other, which includes steam operations and the unallocated portions of the utility business. Various line items in the following tables are not allocated to the electric and gas segments for management reporting purposes, and therefore, are included only in “Total.” Intersegment revenues were not material to IPL’s operations and there was no single customer whose revenues were 10% or more of IPL’s consolidated revenues. All of IPL’s operations and assets are located in the U.S. Certain financial information relating to IPL’s business segments, which represent the services provided to its customers, was as follows (in millions): 2023 Electric Gas Other Total Revenues $1,761 $300 $49 $2,110 Depreciation and amortization 348 34 6 388 Operating income 390 35 19 444 Interest expense 155 Income tax benefit (58) Net income available for common stock 366 Total assets 9,311 921 257 10,489 Construction and acquisition expenditures 671 41 — 712 2022 Electric Gas Other Total Revenues $1,859 $351 $46 $2,256 Depreciation and amortization 342 32 7 381 Operating income 397 53 3 453 Interest expense 148 Income tax benefit (50) Net income available for common stock 360 Total assets 8,686 872 517 10,075 Construction and acquisition expenditures 336 36 — 372 2021 Electric Gas Other Total Revenues $1,752 $265 $46 $2,063 Depreciation and amortization 338 31 6 375 Operating income (loss) 420 43 (3) 460 Interest expense 139 Income tax benefit (36) Net income available for common stock 350 Total assets 8,602 819 575 9,996 Construction and acquisition expenditures 342 42 — 384 WPL - WPL is a utility serving customers in Wisconsin and includes three reportable segments: a) electric operations; b) gas operations; and c) other, which includes the unallocated portions of the utility business. Various line items in the following tables are not allocated to the electric and gas segments for management reporting purposes, and therefore, are included only in “Total.” Intersegment revenues were not material to WPL’s operations and there was no single customer whose revenues were 10% or more of WPL’s consolidated revenues. All of WPL’s operations and assets are located in the U.S. Certain financial information relating to WPL’s business segments, which represent the services provided to its customers, was as follows (in millions): 2023 Electric Gas Other Total Revenues $1,584 $240 $3 $1,827 Depreciation and amortization 254 26 — 280 Operating income 437 35 — 472 Interest expense 149 Income taxes 60 Net income 345 Total assets 8,522 763 349 9,634 Construction and acquisition expenditures 970 49 — 1,019 2022 Electric Gas Other Total Revenues $1,562 $291 $3 $1,856 Depreciation and amortization 259 24 — 283 Operating income 408 44 — 452 Interest expense 121 Income taxes 66 Net income 315 Total assets 7,885 759 343 8,987 Construction and acquisition expenditures 982 38 — 1,020 2021 Electric Gas Other Total Revenues $1,329 $191 $3 $1,523 Depreciation and amortization 253 23 — 276 Operating income (loss) 296 20 (8) 308 Interest expense 105 Income tax benefit (51) Net income 268 Total assets 6,322 668 528 7,518 Construction and acquisition expenditures 638 48 — 686
IPL [Member]
Segment Reporting Information [Line Items]
Segments Of Business	SEGMENTS OF BUSINESS Alliant Energy - Alliant Energy’s principal businesses as of December 31, 2023 are: • Utility - includes the operations of IPL and WPL, which primarily serve retail customers in Iowa and Wisconsin. The utility business has three reportable segments: a) utility electric operations; b) utility gas operations; and c) utility other, which includes steam operations and the unallocated portions of the utility business. Various line items in the following tables are not allocated to the electric and gas segments for management reporting purposes, and therefore, are included only in “Total Utility.” • ATC Holdings, Non-utility, Parent and Other - 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. 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. Intersegment revenues were not material to Alliant Energy’s operations and there was no single customer whose revenues were 10% or more of Alliant Energy’s consolidated revenues. All of Alliant Energy’s operations and assets are located in the U.S. Certain financial information relating to Alliant Energy’s business segments, which represent the services provided to its customers, was as follows (in millions): ATC Holdings, Utility Non-utility, Alliant Energy 2023 Electric Gas Other Total Parent and Other Consolidated Revenues $3,345 $540 $52 $3,937 $90 $4,027 Depreciation and amortization 602 60 6 668 8 676 Operating income 827 70 19 916 27 943 Interest expense 304 90 394 Equity income from unconsolidated investments, net (3) — — (3) (58) (61) Income taxes 2 2 4 Net income (loss) attributable to Alliant Energy common shareowners 711 (8) 703 Total assets 17,833 1,684 606 20,123 1,114 21,237 Investments in equity method subsidiaries 21 — — 21 564 585 Construction and acquisition expenditures 1,641 90 — 1,731 123 1,854 ATC Holdings, Utility Non-utility, Alliant Energy 2022 Electric Gas Other Total Parent and Other Consolidated Revenues $3,421 $642 $49 $4,112 $93 $4,205 Depreciation and amortization 601 56 7 664 7 671 Operating income 805 97 3 905 23 928 Interest expense 269 56 325 Equity income from unconsolidated investments, net (1) — — (1) (50) (51) Income taxes 16 6 22 Net income attributable to Alliant Energy common shareowners 675 11 686 Total assets 16,571 1,631 860 19,062 1,101 20,163 Investments in equity method subsidiaries 20 — — 20 522 542 Construction and acquisition expenditures 1,318 74 — 1,392 92 1,484 ATC Holdings, Utility Non-utility, Alliant Energy 2021 Electric Gas Other Total Parent and Other Consolidated Revenues $3,081 $456 $49 $3,586 $83 $3,669 Depreciation and amortization 591 54 6 651 6 657 Operating income (loss) 716 63 (11) 768 27 795 Interest expense 244 33 277 Equity income from unconsolidated investments, net (2) — — (2) (60) (62) Income tax expense (benefit) (87) 13 (74) Net income attributable to Alliant Energy common shareowners 618 41 659 Total assets 14,924 1,487 1,103 17,514 1,039 18,553 Investments in equity method subsidiaries 17 — — 17 491 508 Construction and acquisition expenditures 980 90 — 1,070 99 1,169 IPL - IPL is a utility primarily serving retail customers in Iowa and includes three reportable segments: a) electric operations; b) gas operations; and c) other, which includes steam operations and the unallocated portions of the utility business. Various line items in the following tables are not allocated to the electric and gas segments for management reporting purposes, and therefore, are included only in “Total.” Intersegment revenues were not material to IPL’s operations and there was no single customer whose revenues were 10% or more of IPL’s consolidated revenues. All of IPL’s operations and assets are located in the U.S. Certain financial information relating to IPL’s business segments, which represent the services provided to its customers, was as follows (in millions): 2023 Electric Gas Other Total Revenues $1,761 $300 $49 $2,110 Depreciation and amortization 348 34 6 388 Operating income 390 35 19 444 Interest expense 155 Income tax benefit (58) Net income available for common stock 366 Total assets 9,311 921 257 10,489 Construction and acquisition expenditures 671 41 — 712 2022 Electric Gas Other Total Revenues $1,859 $351 $46 $2,256 Depreciation and amortization 342 32 7 381 Operating income 397 53 3 453 Interest expense 148 Income tax benefit (50) Net income available for common stock 360 Total assets 8,686 872 517 10,075 Construction and acquisition expenditures 336 36 — 372 2021 Electric Gas Other Total Revenues $1,752 $265 $46 $2,063 Depreciation and amortization 338 31 6 375 Operating income (loss) 420 43 (3) 460 Interest expense 139 Income tax benefit (36) Net income available for common stock 350 Total assets 8,602 819 575 9,996 Construction and acquisition expenditures 342 42 — 384 WPL - WPL is a utility serving customers in Wisconsin and includes three reportable segments: a) electric operations; b) gas operations; and c) other, which includes the unallocated portions of the utility business. Various line items in the following tables are not allocated to the electric and gas segments for management reporting purposes, and therefore, are included only in “Total.” Intersegment revenues were not material to WPL’s operations and there was no single customer whose revenues were 10% or more of WPL’s consolidated revenues. All of WPL’s operations and assets are located in the U.S. Certain financial information relating to WPL’s business segments, which represent the services provided to its customers, was as follows (in millions): 2023 Electric Gas Other Total Revenues $1,584 $240 $3 $1,827 Depreciation and amortization 254 26 — 280 Operating income 437 35 — 472 Interest expense 149 Income taxes 60 Net income 345 Total assets 8,522 763 349 9,634 Construction and acquisition expenditures 970 49 — 1,019 2022 Electric Gas Other Total Revenues $1,562 $291 $3 $1,856 Depreciation and amortization 259 24 — 283 Operating income 408 44 — 452 Interest expense 121 Income taxes 66 Net income 315 Total assets 7,885 759 343 8,987 Construction and acquisition expenditures 982 38 — 1,020 2021 Electric Gas Other Total Revenues $1,329 $191 $3 $1,523 Depreciation and amortization 253 23 — 276 Operating income (loss) 296 20 (8) 308 Interest expense 105 Income tax benefit (51) Net income 268 Total assets 6,322 668 528 7,518 Construction and acquisition expenditures 638 48 — 686
WPL [Member]
Segment Reporting Information [Line Items]
Segments Of Business	SEGMENTS OF BUSINESS Alliant Energy - Alliant Energy’s principal businesses as of December 31, 2023 are: • Utility - includes the operations of IPL and WPL, which primarily serve retail customers in Iowa and Wisconsin. The utility business has three reportable segments: a) utility electric operations; b) utility gas operations; and c) utility other, which includes steam operations and the unallocated portions of the utility business. Various line items in the following tables are not allocated to the electric and gas segments for management reporting purposes, and therefore, are included only in “Total Utility.” • ATC Holdings, Non-utility, Parent and Other - 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. 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. Intersegment revenues were not material to Alliant Energy’s operations and there was no single customer whose revenues were 10% or more of Alliant Energy’s consolidated revenues. All of Alliant Energy’s operations and assets are located in the U.S. Certain financial information relating to Alliant Energy’s business segments, which represent the services provided to its customers, was as follows (in millions): ATC Holdings, Utility Non-utility, Alliant Energy 2023 Electric Gas Other Total Parent and Other Consolidated Revenues $3,345 $540 $52 $3,937 $90 $4,027 Depreciation and amortization 602 60 6 668 8 676 Operating income 827 70 19 916 27 943 Interest expense 304 90 394 Equity income from unconsolidated investments, net (3) — — (3) (58) (61) Income taxes 2 2 4 Net income (loss) attributable to Alliant Energy common shareowners 711 (8) 703 Total assets 17,833 1,684 606 20,123 1,114 21,237 Investments in equity method subsidiaries 21 — — 21 564 585 Construction and acquisition expenditures 1,641 90 — 1,731 123 1,854 ATC Holdings, Utility Non-utility, Alliant Energy 2022 Electric Gas Other Total Parent and Other Consolidated Revenues $3,421 $642 $49 $4,112 $93 $4,205 Depreciation and amortization 601 56 7 664 7 671 Operating income 805 97 3 905 23 928 Interest expense 269 56 325 Equity income from unconsolidated investments, net (1) — — (1) (50) (51) Income taxes 16 6 22 Net income attributable to Alliant Energy common shareowners 675 11 686 Total assets 16,571 1,631 860 19,062 1,101 20,163 Investments in equity method subsidiaries 20 — — 20 522 542 Construction and acquisition expenditures 1,318 74 — 1,392 92 1,484 ATC Holdings, Utility Non-utility, Alliant Energy 2021 Electric Gas Other Total Parent and Other Consolidated Revenues $3,081 $456 $49 $3,586 $83 $3,669 Depreciation and amortization 591 54 6 651 6 657 Operating income (loss) 716 63 (11) 768 27 795 Interest expense 244 33 277 Equity income from unconsolidated investments, net (2) — — (2) (60) (62) Income tax expense (benefit) (87) 13 (74) Net income attributable to Alliant Energy common shareowners 618 41 659 Total assets 14,924 1,487 1,103 17,514 1,039 18,553 Investments in equity method subsidiaries 17 — — 17 491 508 Construction and acquisition expenditures 980 90 — 1,070 99 1,169 IPL - IPL is a utility primarily serving retail customers in Iowa and includes three reportable segments: a) electric operations; b) gas operations; and c) other, which includes steam operations and the unallocated portions of the utility business. Various line items in the following tables are not allocated to the electric and gas segments for management reporting purposes, and therefore, are included only in “Total.” Intersegment revenues were not material to IPL’s operations and there was no single customer whose revenues were 10% or more of IPL’s consolidated revenues. All of IPL’s operations and assets are located in the U.S. Certain financial information relating to IPL’s business segments, which represent the services provided to its customers, was as follows (in millions): 2023 Electric Gas Other Total Revenues $1,761 $300 $49 $2,110 Depreciation and amortization 348 34 6 388 Operating income 390 35 19 444 Interest expense 155 Income tax benefit (58) Net income available for common stock 366 Total assets 9,311 921 257 10,489 Construction and acquisition expenditures 671 41 — 712 2022 Electric Gas Other Total Revenues $1,859 $351 $46 $2,256 Depreciation and amortization 342 32 7 381 Operating income 397 53 3 453 Interest expense 148 Income tax benefit (50) Net income available for common stock 360 Total assets 8,686 872 517 10,075 Construction and acquisition expenditures 336 36 — 372 2021 Electric Gas Other Total Revenues $1,752 $265 $46 $2,063 Depreciation and amortization 338 31 6 375 Operating income (loss) 420 43 (3) 460 Interest expense 139 Income tax benefit (36) Net income available for common stock 350 Total assets 8,602 819 575 9,996 Construction and acquisition expenditures 342 42 — 384 WPL - WPL is a utility serving customers in Wisconsin and includes three reportable segments: a) electric operations; b) gas operations; and c) other, which includes the unallocated portions of the utility business. Various line items in the following tables are not allocated to the electric and gas segments for management reporting purposes, and therefore, are included only in “Total.” Intersegment revenues were not material to WPL’s operations and there was no single customer whose revenues were 10% or more of WPL’s consolidated revenues. All of WPL’s operations and assets are located in the U.S. Certain financial information relating to WPL’s business segments, which represent the services provided to its customers, was as follows (in millions): 2023 Electric Gas Other Total Revenues $1,584 $240 $3 $1,827 Depreciation and amortization 254 26 — 280 Operating income 437 35 — 472 Interest expense 149 Income taxes 60 Net income 345 Total assets 8,522 763 349 9,634 Construction and acquisition expenditures 970 49 — 1,019 2022 Electric Gas Other Total Revenues $1,562 $291 $3 $1,856 Depreciation and amortization 259 24 — 283 Operating income 408 44 — 452 Interest expense 121 Income taxes 66 Net income 315 Total assets 7,885 759 343 8,987 Construction and acquisition expenditures 982 38 — 1,020 2021 Electric Gas Other Total Revenues $1,329 $191 $3 $1,523 Depreciation and amortization 253 23 — 276 Operating income (loss) 296 20 (8) 308 Interest expense 105 Income tax benefit (51) Net income 268 Total assets 6,322 668 528 7,518 Construction and acquisition expenditures 638 48 — 686

Related Parties

Related Parties	12 Months Ended
	Dec. 31, 2023
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): IPL WPL 2023 2022 2021 2023 2022 2021 Corporate Services billings $181 $181 $180 $163 $155 $154 Sales credited 11 19 22 55 74 23 Purchases billed 431 435 441 35 174 116 As of December 31, net intercompany payables to Corporate Services were as follows (in millions): 2023 2022 IPL $129 $103 WPL 72 56 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): 2023 2022 2021 ATC billings to WPL $159 $140 $122 WPL billings to ATC 20 18 18 As of December 31, 2023 and 2022, WPL owed ATC net amounts of $10 million and $10 million, respectively. WPL’s Sheboygan Falls Energy Facility Lease - Refer to Note 10 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): IPL WPL 2023 2022 2021 2023 2022 2021 Corporate Services billings $181 $181 $180 $163 $155 $154 Sales credited 11 19 22 55 74 23 Purchases billed 431 435 441 35 174 116 As of December 31, net intercompany payables to Corporate Services were as follows (in millions): 2023 2022 IPL $129 $103 WPL 72 56
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): IPL WPL 2023 2022 2021 2023 2022 2021 Corporate Services billings $181 $181 $180 $163 $155 $154 Sales credited 11 19 22 55 74 23 Purchases billed 431 435 441 35 174 116 As of December 31, net intercompany payables to Corporate Services were as follows (in millions): 2023 2022 IPL $129 $103 WPL 72 56 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): 2023 2022 2021 ATC billings to WPL $159 $140 $122 WPL billings to ATC 20 18 18 As of December 31, 2023 and 2022, WPL owed ATC net amounts of $10 million and $10 million, respectively. WPL’s Sheboygan Falls Energy Facility Lease - Refer to Note 10 for discussion of WPL’s Sheboygan Falls Energy Facility lease.

Condensed Parent Company Financ

Condensed Parent Company Financial Statements	12 Months Ended
	Dec. 31, 2023
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 INCOME 2023 2022 2021 (in millions) Operating expenses $3 $9 $5 Operating loss (3) (9) (5) Other (income) and deductions: Equity earnings from consolidated subsidiaries (742) (707) (664) Interest expense 34 6 1 Other 4 1 1 Total other (income) and deductions (704) (700) (662) Income before income taxes 701 691 657 Income tax expense (benefit) (5) 2 (5) Net income $706 $689 $662 Refer to accompanying Notes to Condensed Financial Statements. ALLIANT ENERGY CORPORATION (Parent Company Only) December 31, CONDENSED BALANCE SHEETS 2023 2022 (in millions) ASSETS Current assets: Notes receivable from affiliated companies $96 $65 Other 1 1 Total current assets 97 66 Investments: Investments in consolidated subsidiaries 8,405 7,801 Other 2 2 Total investments 8,407 7,803 Other assets 90 97 Total assets $8,594 $7,966 LIABILITIES AND EQUITY Current liabilities: Commercial paper $157 $352 Notes payable to affiliated companies 1,068 1,318 Other 10 10 Total current liabilities 1,235 1,680 Long-term debt, net 568 — Other liabilities 2 1 Common equity: Common stock and additional paid-in capital 3,033 2,780 Retained earnings 3,768 3,518 Accumulated other comprehensive income 1 — Shares in deferred compensation trust (13) (13) Total common equity 6,789 6,285 Total liabilities and equity $8,594 $7,966 Refer to accompanying Notes to Condensed Financial Statements. ALLIANT ENERGY CORPORATION (Parent Company Only) Year Ended December 31, CONDENSED STATEMENTS OF CASH FLOWS 2023 2022 2021 (in millions) Net cash flows from operating activities $445 $492 $494 Cash flows used for investing activities: Capital contributions to consolidated subsidiaries (325) (530) (295) Net change in notes receivable from and payable to affiliates (281) 369 (21) Dividends from consolidated subsidiaries in excess of equity earnings — — 50 Net cash flows used for investing activities (606) (161) (266) Cash flows from (used for) financing activities: Common stock dividends (456) (428) (403) Proceeds from issuance of common stock, net 246 25 28 Proceeds from issuance of long-term debt 565 — — Net change in commercial paper (195) 73 147 Other 1 (1) — Net cash flows from (used for) financing activities 161 (331) (228) 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) refunded during the period for: Interest ($27) ($6) ($1) Income taxes, net $22 $15 $4 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 2023 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.

Valuation and Qualifying Accoun

Valuation and Qualifying Accounts And Reserves	12 Months Ended
	Dec. 31, 2023
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 to Balance, Description January 1 Expense) 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, 2023 $7 $20 $19 $8 Year ended December 31, 2022 11 17 21 7 Year ended December 31, 2021 18 12 19 11 IPL (b) Year ended December 31, 2023 $— $11 $11 $— Year ended December 31, 2022 1 7 8 — Year ended December 31, 2021 1 6 6 1 WPL Year ended December 31, 2023 $7 $9 $8 $8 Year ended December 31, 2022 10 10 13 7 Year ended December 31, 2021 17 6 13 10 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 to Balance, Description January 1 Expense) 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, 2023 $7 $20 $19 $8 Year ended December 31, 2022 11 17 21 7 Year ended December 31, 2021 18 12 19 11 IPL (b) Year ended December 31, 2023 $— $11 $11 $— Year ended December 31, 2022 1 7 8 — Year ended December 31, 2021 1 6 6 1 WPL Year ended December 31, 2023 $7 $9 $8 $8 Year ended December 31, 2022 10 10 13 7 Year ended December 31, 2021 17 6 13 10 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 to Balance, Description January 1 Expense) 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, 2023 $7 $20 $19 $8 Year ended December 31, 2022 11 17 21 7 Year ended December 31, 2021 18 12 19 11 IPL (b) Year ended December 31, 2023 $— $11 $11 $— Year ended December 31, 2022 1 7 8 — Year ended December 31, 2021 1 6 6 1 WPL Year ended December 31, 2023 $7 $9 $8 $8 Year ended December 31, 2022 10 10 13 7 Year ended December 31, 2021 17 6 13 10 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.

Summary Of Significant Accoun_2

Summary Of Significant Accounting Policies (Policy)	12 Months Ended
	Dec. 31, 2023
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, 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.
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.
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: 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.
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.
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.
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 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]
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, 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.
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.
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: 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.
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.
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.
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 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.
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, 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.
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.
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: 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.
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.
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.
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 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.

Summary Of Significant Accoun_3

Summary Of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2023
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: 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%
Schedule of Allowance for Funds Used During Construction Rate	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%
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: 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%
Schedule of Allowance for Funds Used During Construction Rate	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%
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: 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%
Schedule of Allowance for Funds Used During Construction Rate	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%

Regulatory Matters (Tables)

Regulatory Matters (Tables)	12 Months Ended
	Dec. 31, 2023
Regulatory Assets [Line Items]
Schedule of Regulatory Assets	At December 31, regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL 2023 2022 2023 2022 2023 2022 Tax-related $934 $929 $831 $848 $103 $81 Pension and OPEB costs 347 392 171 197 176 195 Assets retired early 273 70 259 53 14 17 AROs 194 151 160 110 34 41 Commodity cost recovery 120 160 12 1 108 159 Derivatives 102 84 34 48 68 36 WPL’s Western Wisconsin gas distribution expansion investments 44 48 — — 44 48 IPL’s DAEC PPA amendment 42 66 42 66 — — Other 205 146 68 63 137 83 $2,261 $2,046 $1,577 $1,386 $684 $660
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): Entity Asset Retirement Date Regulatory Asset Balance as of Dec. 31, 2023 Recovery Regulatory Approval IPL Lansing 2023 $216 Return of and return on remaining net book value through 2037 FERC and pending with the IUB (a) IPL Analog electric meters 2019 20 Return of remaining net book value through 2028 IUB and FERC IPL Sutherland Units 1 and 3 2017 12 Return of and return on remaining net book value through 2027 IUB and FERC IPL M.L. Kapp Unit 2 2018 11 Return of and return on remaining net book value through 2029 IUB and FERC WPL Edgewater Unit 4 2018 14 Return of and return on remaining net book value through 2028 PSCW and FERC (a) IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period includes a request with the IUB for continued recovery of the remaining net book value of Lansing through 2037.
Schedule of Regulatory Liabilities	At December 31, regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL 2023 2022 2023 2022 2023 2022 Tax-related $566 $579 $299 $303 $267 $276 Cost of removal obligations 366 398 242 259 124 139 Derivatives 65 210 34 115 31 95 Commodity cost recovery 48 40 13 38 35 2 WPL’s West Riverside liquidated damages 1 32 — — 1 32 Other 84 65 56 39 28 26 $1,130 $1,324 $644 $754 $486 $570
IPL [Member]
Regulatory Assets [Line Items]
Schedule of Regulatory Assets	At December 31, regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL 2023 2022 2023 2022 2023 2022 Tax-related $934 $929 $831 $848 $103 $81 Pension and OPEB costs 347 392 171 197 176 195 Assets retired early 273 70 259 53 14 17 AROs 194 151 160 110 34 41 Commodity cost recovery 120 160 12 1 108 159 Derivatives 102 84 34 48 68 36 WPL’s Western Wisconsin gas distribution expansion investments 44 48 — — 44 48 IPL’s DAEC PPA amendment 42 66 42 66 — — Other 205 146 68 63 137 83 $2,261 $2,046 $1,577 $1,386 $684 $660
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): Entity Asset Retirement Date Regulatory Asset Balance as of Dec. 31, 2023 Recovery Regulatory Approval IPL Lansing 2023 $216 Return of and return on remaining net book value through 2037 FERC and pending with the IUB (a) IPL Analog electric meters 2019 20 Return of remaining net book value through 2028 IUB and FERC IPL Sutherland Units 1 and 3 2017 12 Return of and return on remaining net book value through 2027 IUB and FERC IPL M.L. Kapp Unit 2 2018 11 Return of and return on remaining net book value through 2029 IUB and FERC WPL Edgewater Unit 4 2018 14 Return of and return on remaining net book value through 2028 PSCW and FERC (a) IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period includes a request with the IUB for continued recovery of the remaining net book value of Lansing through 2037.
Schedule of Regulatory Liabilities	At December 31, regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL 2023 2022 2023 2022 2023 2022 Tax-related $566 $579 $299 $303 $267 $276 Cost of removal obligations 366 398 242 259 124 139 Derivatives 65 210 34 115 31 95 Commodity cost recovery 48 40 13 38 35 2 WPL’s West Riverside liquidated damages 1 32 — — 1 32 Other 84 65 56 39 28 26 $1,130 $1,324 $644 $754 $486 $570
WPL [Member]
Regulatory Assets [Line Items]
Schedule of Regulatory Assets	At December 31, regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL 2023 2022 2023 2022 2023 2022 Tax-related $934 $929 $831 $848 $103 $81 Pension and OPEB costs 347 392 171 197 176 195 Assets retired early 273 70 259 53 14 17 AROs 194 151 160 110 34 41 Commodity cost recovery 120 160 12 1 108 159 Derivatives 102 84 34 48 68 36 WPL’s Western Wisconsin gas distribution expansion investments 44 48 — — 44 48 IPL’s DAEC PPA amendment 42 66 42 66 — — Other 205 146 68 63 137 83 $2,261 $2,046 $1,577 $1,386 $684 $660
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): Entity Asset Retirement Date Regulatory Asset Balance as of Dec. 31, 2023 Recovery Regulatory Approval IPL Lansing 2023 $216 Return of and return on remaining net book value through 2037 FERC and pending with the IUB (a) IPL Analog electric meters 2019 20 Return of remaining net book value through 2028 IUB and FERC IPL Sutherland Units 1 and 3 2017 12 Return of and return on remaining net book value through 2027 IUB and FERC IPL M.L. Kapp Unit 2 2018 11 Return of and return on remaining net book value through 2029 IUB and FERC WPL Edgewater Unit 4 2018 14 Return of and return on remaining net book value through 2028 PSCW and FERC (a) IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period includes a request with the IUB for continued recovery of the remaining net book value of Lansing through 2037.
Schedule of Regulatory Liabilities	At December 31, regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL 2023 2022 2023 2022 2023 2022 Tax-related $566 $579 $299 $303 $267 $276 Cost of removal obligations 366 398 242 259 124 139 Derivatives 65 210 34 115 31 95 Commodity cost recovery 48 40 13 38 35 2 WPL’s West Riverside liquidated damages 1 32 — — 1 32 Other 84 65 56 39 28 26 $1,130 $1,324 $644 $754 $486 $570

Property, Plant and Equipment (

Property, Plant and Equipment (Tables)	12 Months Ended
	Dec. 31, 2023
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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Utility: Electric plant: Generation in service (a) $9,180 $8,060 $5,025 $4,962 $4,155 $3,098 Distribution in service 7,314 6,912 4,091 3,876 3,223 3,036 Other in service 567 543 356 354 211 189 Anticipated to be retired early (b) 1,629 2,103 — 491 1,629 1,612 Total electric plant 18,690 17,618 9,472 9,683 9,218 7,935 Gas plant in service 1,791 1,705 951 910 840 795 Other plant in service 653 624 411 402 242 222 Accumulated depreciation (b) (5,924) (5,690) (3,180) (3,149) (2,744) (2,541) Net plant 15,210 14,257 7,654 7,846 7,556 6,411 Leased Sheboygan Falls Energy Facility, net (c) — — — — 79 15 Leased land for solar generation, net 172 133 33 — 139 133 Construction work in progress 1,245 1,357 605 194 640 1,163 Other, net 7 6 6 6 1 — Total utility 16,634 15,753 8,298 8,046 8,415 7,722 Non-utility and other: Non-utility Generation, net (d) 68 71 — — — — Corporate Services and other, net (e) 455 423 — — — — Total non-utility and other 523 494 — — — — Total property, plant and equipment $17,157 $16,247 $8,298 $8,046 $8,415 $7,722 (a) Alliant Energy and WPL currently expect estimated construction costs associated with WPL’s approximately 1,100 MW of new solar generation will exceed amounts previously approved by the PSCW by approximately $180 million. In February 2024, the PSCW issued an oral decision approving WPL’s deferral request to seek recovery of these costs in a future regulatory proceeding. Alliant Energy and IPL currently expect the estimated construction costs associated with IPL’s 400 MW of new solar generation will exceed the cost target of $1,650/kilowatt, including AFUDC and transmission upgrade costs among other costs, approved in the IUB’s advance rate-making principles by approximately 10%. Alliant Energy, IPL and WPL concluded that there was not a probable disallowance of anticipated higher rate base amounts as of December 31, 2023 given construction costs were reasonably and prudently incurred. (b) In 2023, IPL retired Lansing and reclassified the remaining net book value of this EGU from property, plant and equipment to a regulatory asset on Alliant Energy’s and IPL’s balance sheets. In 2020 and 2021, WPL received approval from MISO to retire Edgewater Unit 5, and Columbia Units 1 and 2, respectively. WPL currently anticipates retiring Edgewater Unit 5 by June 1, 2025, and Columbia Units 1 and 2 by June 1, 2026. Alliant Energy and WPL concluded that Edgewater Unit 5 and Columbia Units 1 and 2 met the criteria to be considered probable of abandonment as of December 31, 2023. 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, Alliant Energy and WPL concluded that no disallowance was required as of December 31, 2023. As of December 31, 2023, net book values were $504 million for Edgewater Unit 5, and $428 million for Columbia Units 1 and 2 in aggregate. (c) Less accumulated amortization of $112 million and $106 million for WPL as of December 31, 2023 and 2022, respectively. Refer to Note 10 for discussion of WPL’s renewal of this lease in 2023. 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. (d) Less accumulated depreciation of $75 million and $71 million for Alliant Energy as of December 31, 2023 and 2022, respectively. (e) Less accumulated depreciation of $275 million and $269 million for Alliant Energy as of December 31, 2023 and 2022, respectively.
Allowance For Funds Used During Construction	The amount of AFUDC generated by equity and debt components was as follows (in millions): Alliant Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Equity $74 $44 $18 $15 $8 $7 $59 $36 $11 Debt 26 16 7 6 3 2 20 13 5 $100 $60 $25 $21 $11 $9 $79 $49 $16
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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Utility: Electric plant: Generation in service (a) $9,180 $8,060 $5,025 $4,962 $4,155 $3,098 Distribution in service 7,314 6,912 4,091 3,876 3,223 3,036 Other in service 567 543 356 354 211 189 Anticipated to be retired early (b) 1,629 2,103 — 491 1,629 1,612 Total electric plant 18,690 17,618 9,472 9,683 9,218 7,935 Gas plant in service 1,791 1,705 951 910 840 795 Other plant in service 653 624 411 402 242 222 Accumulated depreciation (b) (5,924) (5,690) (3,180) (3,149) (2,744) (2,541) Net plant 15,210 14,257 7,654 7,846 7,556 6,411 Leased Sheboygan Falls Energy Facility, net (c) — — — — 79 15 Leased land for solar generation, net 172 133 33 — 139 133 Construction work in progress 1,245 1,357 605 194 640 1,163 Other, net 7 6 6 6 1 — Total utility 16,634 15,753 8,298 8,046 8,415 7,722 Non-utility and other: Non-utility Generation, net (d) 68 71 — — — — Corporate Services and other, net (e) 455 423 — — — — Total non-utility and other 523 494 — — — — Total property, plant and equipment $17,157 $16,247 $8,298 $8,046 $8,415 $7,722 (a) Alliant Energy and WPL currently expect estimated construction costs associated with WPL’s approximately 1,100 MW of new solar generation will exceed amounts previously approved by the PSCW by approximately $180 million. In February 2024, the PSCW issued an oral decision approving WPL’s deferral request to seek recovery of these costs in a future regulatory proceeding. Alliant Energy and IPL currently expect the estimated construction costs associated with IPL’s 400 MW of new solar generation will exceed the cost target of $1,650/kilowatt, including AFUDC and transmission upgrade costs among other costs, approved in the IUB’s advance rate-making principles by approximately 10%. Alliant Energy, IPL and WPL concluded that there was not a probable disallowance of anticipated higher rate base amounts as of December 31, 2023 given construction costs were reasonably and prudently incurred. (b) In 2023, IPL retired Lansing and reclassified the remaining net book value of this EGU from property, plant and equipment to a regulatory asset on Alliant Energy’s and IPL’s balance sheets. In 2020 and 2021, WPL received approval from MISO to retire Edgewater Unit 5, and Columbia Units 1 and 2, respectively. WPL currently anticipates retiring Edgewater Unit 5 by June 1, 2025, and Columbia Units 1 and 2 by June 1, 2026. Alliant Energy and WPL concluded that Edgewater Unit 5 and Columbia Units 1 and 2 met the criteria to be considered probable of abandonment as of December 31, 2023. 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, Alliant Energy and WPL concluded that no disallowance was required as of December 31, 2023. As of December 31, 2023, net book values were $504 million for Edgewater Unit 5, and $428 million for Columbia Units 1 and 2 in aggregate. (c) Less accumulated amortization of $112 million and $106 million for WPL as of December 31, 2023 and 2022, respectively. Refer to Note 10 for discussion of WPL’s renewal of this lease in 2023. 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. (d) Less accumulated depreciation of $75 million and $71 million for Alliant Energy as of December 31, 2023 and 2022, respectively. (e) Less accumulated depreciation of $275 million and $269 million for Alliant Energy as of December 31, 2023 and 2022, respectively.
Allowance For Funds Used During Construction	The amount of AFUDC generated by equity and debt components was as follows (in millions): Alliant Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Equity $74 $44 $18 $15 $8 $7 $59 $36 $11 Debt 26 16 7 6 3 2 20 13 5 $100 $60 $25 $21 $11 $9 $79 $49 $16
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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Utility: Electric plant: Generation in service (a) $9,180 $8,060 $5,025 $4,962 $4,155 $3,098 Distribution in service 7,314 6,912 4,091 3,876 3,223 3,036 Other in service 567 543 356 354 211 189 Anticipated to be retired early (b) 1,629 2,103 — 491 1,629 1,612 Total electric plant 18,690 17,618 9,472 9,683 9,218 7,935 Gas plant in service 1,791 1,705 951 910 840 795 Other plant in service 653 624 411 402 242 222 Accumulated depreciation (b) (5,924) (5,690) (3,180) (3,149) (2,744) (2,541) Net plant 15,210 14,257 7,654 7,846 7,556 6,411 Leased Sheboygan Falls Energy Facility, net (c) — — — — 79 15 Leased land for solar generation, net 172 133 33 — 139 133 Construction work in progress 1,245 1,357 605 194 640 1,163 Other, net 7 6 6 6 1 — Total utility 16,634 15,753 8,298 8,046 8,415 7,722 Non-utility and other: Non-utility Generation, net (d) 68 71 — — — — Corporate Services and other, net (e) 455 423 — — — — Total non-utility and other 523 494 — — — — Total property, plant and equipment $17,157 $16,247 $8,298 $8,046 $8,415 $7,722 (a) Alliant Energy and WPL currently expect estimated construction costs associated with WPL’s approximately 1,100 MW of new solar generation will exceed amounts previously approved by the PSCW by approximately $180 million. In February 2024, the PSCW issued an oral decision approving WPL’s deferral request to seek recovery of these costs in a future regulatory proceeding. Alliant Energy and IPL currently expect the estimated construction costs associated with IPL’s 400 MW of new solar generation will exceed the cost target of $1,650/kilowatt, including AFUDC and transmission upgrade costs among other costs, approved in the IUB’s advance rate-making principles by approximately 10%. Alliant Energy, IPL and WPL concluded that there was not a probable disallowance of anticipated higher rate base amounts as of December 31, 2023 given construction costs were reasonably and prudently incurred. (b) In 2023, IPL retired Lansing and reclassified the remaining net book value of this EGU from property, plant and equipment to a regulatory asset on Alliant Energy’s and IPL’s balance sheets. In 2020 and 2021, WPL received approval from MISO to retire Edgewater Unit 5, and Columbia Units 1 and 2, respectively. WPL currently anticipates retiring Edgewater Unit 5 by June 1, 2025, and Columbia Units 1 and 2 by June 1, 2026. Alliant Energy and WPL concluded that Edgewater Unit 5 and Columbia Units 1 and 2 met the criteria to be considered probable of abandonment as of December 31, 2023. 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, Alliant Energy and WPL concluded that no disallowance was required as of December 31, 2023. As of December 31, 2023, net book values were $504 million for Edgewater Unit 5, and $428 million for Columbia Units 1 and 2 in aggregate. (c) Less accumulated amortization of $112 million and $106 million for WPL as of December 31, 2023 and 2022, respectively. Refer to Note 10 for discussion of WPL’s renewal of this lease in 2023. 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. (d) Less accumulated depreciation of $75 million and $71 million for Alliant Energy as of December 31, 2023 and 2022, respectively. (e) Less accumulated depreciation of $275 million and $269 million for Alliant Energy as of December 31, 2023 and 2022, respectively.
Allowance For Funds Used During Construction	The amount of AFUDC generated by equity and debt components was as follows (in millions): Alliant Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Equity $74 $44 $18 $15 $8 $7 $59 $36 $11 Debt 26 16 7 6 3 2 20 13 5 $100 $60 $25 $21 $11 $9 $79 $49 $16

Jointly-Owned Electric Utilit_2

Jointly-Owned Electric Utility Plant (Tables)	12 Months Ended
	Dec. 31, 2023
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, 2023 was as follows (dollars in millions): Ownership Electric Accumulated Provision Construction Interest % Plant for Depreciation Work in Progress IPL Ottumwa Unit 1 48.0% $632 $264 $7 George Neal Unit 4 25.7% 196 107 6 George Neal Unit 3 28.0% 181 85 8 Louisa Unit 1 4.0% 44 22 — 1,053 478 21 WPL Columbia Units 1-2 53.5% 818 361 6 West Riverside Energy Center and Solar Facility (a) 73.8% 581 60 6 Forward Wind Energy Center 42.6% 118 53 — 1,517 474 12 Alliant Energy $2,570 $952 $33 (a) In 2023, Madison Gas and Electric Company and WEC Energy Group, Inc. 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.
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, 2023 was as follows (dollars in millions): Ownership Electric Accumulated Provision Construction Interest % Plant for Depreciation Work in Progress IPL Ottumwa Unit 1 48.0% $632 $264 $7 George Neal Unit 4 25.7% 196 107 6 George Neal Unit 3 28.0% 181 85 8 Louisa Unit 1 4.0% 44 22 — 1,053 478 21 WPL Columbia Units 1-2 53.5% 818 361 6 West Riverside Energy Center and Solar Facility (a) 73.8% 581 60 6 Forward Wind Energy Center 42.6% 118 53 — 1,517 474 12 Alliant Energy $2,570 $952 $33 (a) In 2023, Madison Gas and Electric Company and WEC Energy Group, Inc. 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.
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, 2023 was as follows (dollars in millions): Ownership Electric Accumulated Provision Construction Interest % Plant for Depreciation Work in Progress IPL Ottumwa Unit 1 48.0% $632 $264 $7 George Neal Unit 4 25.7% 196 107 6 George Neal Unit 3 28.0% 181 85 8 Louisa Unit 1 4.0% 44 22 — 1,053 478 21 WPL Columbia Units 1-2 53.5% 818 361 6 West Riverside Energy Center and Solar Facility (a) 73.8% 581 60 6 Forward Wind Energy Center 42.6% 118 53 — 1,517 474 12 Alliant Energy $2,570 $952 $33 (a) In 2023, Madison Gas and Electric Company and WEC Energy Group, Inc. 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.

Receivables (Tables)

Receivables (Tables)	12 Months Ended
	Dec. 31, 2023
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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Customer $121 $114 $— $— $110 $102 Unbilled utility revenues 93 115 — — 93 115 Deferred proceeds 216 185 216 185 — — Other 53 109 26 74 24 34 Allowance for expected credit losses (8) (7) — — (8) (7) $475 $516 $242 $259 $219 $244
Gross Write-offs for Accounts Receivable	In 2023, gross write-offs for accounts receivable were as follows (in millions): Originated in 2022 Originated in 2023 Alliant Energy $12 $13 IPL 8 8 WPL 4 5
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): Maximum Average 2023 2022 2021 2023 2022 2021 Outstanding aggregate cash proceeds $110 $80 $110 $51 $14 $46
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): 2023 2022 Customer accounts receivable $130 $145 Unbilled utility revenues 98 132 Other receivables 1 — Receivables sold to third party 229 277 Less: cash proceeds 1 80 Deferred proceeds 228 197 Less: allowance for expected credit losses 12 12 Fair value of deferred proceeds $216 $185 Outstanding receivables past due $22 $26
Additional Attributes Of Receivables Sold Under The Agreement	Additional attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): 2023 2022 2021 Collections $2,233 $2,302 $2,134 Write-offs, net of recoveries 12 9 9
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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Customer $121 $114 $— $— $110 $102 Unbilled utility revenues 93 115 — — 93 115 Deferred proceeds 216 185 216 185 — — Other 53 109 26 74 24 34 Allowance for expected credit losses (8) (7) — — (8) (7) $475 $516 $242 $259 $219 $244
Gross Write-offs for Accounts Receivable	In 2023, gross write-offs for accounts receivable were as follows (in millions): Originated in 2022 Originated in 2023 Alliant Energy $12 $13 IPL 8 8 WPL 4 5
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): Maximum Average 2023 2022 2021 2023 2022 2021 Outstanding aggregate cash proceeds $110 $80 $110 $51 $14 $46
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): 2023 2022 Customer accounts receivable $130 $145 Unbilled utility revenues 98 132 Other receivables 1 — Receivables sold to third party 229 277 Less: cash proceeds 1 80 Deferred proceeds 228 197 Less: allowance for expected credit losses 12 12 Fair value of deferred proceeds $216 $185 Outstanding receivables past due $22 $26
Additional Attributes Of Receivables Sold Under The Agreement	Additional attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): 2023 2022 2021 Collections $2,233 $2,302 $2,134 Write-offs, net of recoveries 12 9 9
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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Customer $121 $114 $— $— $110 $102 Unbilled utility revenues 93 115 — — 93 115 Deferred proceeds 216 185 216 185 — — Other 53 109 26 74 24 34 Allowance for expected credit losses (8) (7) — — (8) (7) $475 $516 $242 $259 $219 $244
Gross Write-offs for Accounts Receivable	In 2023, gross write-offs for accounts receivable were as follows (in millions): Originated in 2022 Originated in 2023 Alliant Energy $12 $13 IPL 8 8 WPL 4 5

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2023
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 at Carrying Value at December 31, Equity (Income) / Loss December 31, 2023 2023 2022 2023 2022 2021 ATC Holdings 16%, 20% $386 $358 ($49) ($41) ($43) Non-utility wind farm in Oklahoma 50% 104 101 (7) (5) (4) Corporate venture investments Various 74 62 (2) (3) (13) Other Various 21 21 (3) (2) (2) $585 $542 ($61) ($51) ($62)
Summary Financial Information	Summary aggregate financial information from the financial statements of these holdings is as follows (in millions): Alliant Energy 2023 2022 2021 Revenues $898 $813 $802 Operating income 384 350 357 Net income 370 675 358 As of December 31: Current assets 221 227 Non-current assets 9,032 8,292 Current liabilities 528 620 Non-current liabilities 3,584 3,285 Noncontrolling interest 259 289

Common Equity (Tables)

Common Equity (Tables)	12 Months Ended
	Dec. 31, 2023
Schedule of Common Equity [Line Items]
Common Stock Activity	A summary of Alliant Energy’s common stock activity was as follows: 2023 2022 2021 Shares outstanding, January 1 251,134,966 250,474,529 249,868,415 At-the-market offering program 4,372,561 — — Shareowner Direct Plan 454,987 437,669 492,565 Equity-based compensation plans 134,334 222,768 113,549 Shares outstanding, December 31 256,096,848 251,134,966 250,474,529

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2023
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 Energy IPL WPL December 31 2023 2022 2023 2022 2023 2022 Amount outstanding $475 $642 $— $— $318 $290 Weighted average interest rates 5.5% 4.6% N/A N/A 5.4% 4.5% Available credit facility capacity $525 $358 $150 $100 $82 $110 Alliant Energy IPL WPL For the year ended 2023 2022 2023 2022 2023 2022 Maximum amount outstanding (based on daily outstanding balances) $793 $665 $70 $— $349 $325 Average amount outstanding (based on daily outstanding balances) $386 $411 $2 $— $157 $153 Weighted average interest rates 5.2% 2.1% 5.3% —% 5.1% 1.6%
Schedule of Long-term Debt	Long-term debt, net as of December 31 was as follows (dollars in millions): 2023 2022 Alliant Energy IPL WPL Alliant Energy IPL WPL Senior Debentures (a): 3.25%, due 2024 $500 $500 $— $500 $500 $— 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 (b) 300 300 — — — — 6.45%, due 2033 100 100 — 100 100 — 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 — 3,975 3,975 — 3,675 3,675 — 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 (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 3,100 — 3,100 2,800 — 2,800 Other: AEF term loan credit agreement through March 2024, 6% at December 31, 2023 (with Alliant Energy as guarantor) (d) 300 — — 400 — — 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 — — — — — 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)(f) 300 — — — — — AEF 3.6% senior notes, due 2032 (with Alliant Energy as guarantor) (a) 350 — — 350 — — Sheboygan Power, LLC 5.06% senior secured notes, due 2024 (secured by the Sheboygan Falls Energy Facility and related assets) (a) 9 — — 17 — — AEF 3.75% senior notes (with Alliant Energy as guarantor) (Retired in 2023) — — — 400 — — Other, 1% at December 31, 2023, due 2024 to 2025 — — — 1 — — 2,034 — — 1,668 — — Subtotal 9,109 3,975 3,100 8,143 3,675 2,800 Current maturities (809) (500) — (408) — — Unamortized debt issuance costs (54) (21) (19) (45) (21) (19) Unamortized debt (discount) and premium, net (21) (9) (11) (22) (8) (11) Long-term debt, net (g) $8,225 $3,445 $3,070 $7,668 $3,646 $2,770 (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 2023, IPL issued $300 million of 5.7% senior debentures due 2033. The net proceeds from the issuance were used to reduce cash amounts received from its sales of accounts receivable program, reduce commercial paper classified as long-term debt, for general corporate purposes and/or were placed in money market fund investments. (c) In March 2023, WPL issued $300 million of 4.95% debentures due 2033. 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 its solar EGUs. (d) In January 2023, AEF entered into a $300 million interest rate swap maturing in January 2026 to mitigate interest rate risk. Under the terms of the swap, AEF exchanged a variable interest rate for a fixed interest rate of 3.93% on a portion of its variable-rate term loan borrowings. In December 2023, AEF retired the remaining $100 million variable-rate term loan borrowings. Refer to Note 15 for additional information on the interest rate swap. (e) Refer to “ Convertible Senior Notes ” below for additional information. (f) In November 2023, AEF issued $300 million of 5.95% senior notes due 2029. The net proceeds from AEF’s issuance 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, 2023, long-term debt maturities for 2024 through 2028 were as follows (in millions): 2024 2025 2026 2027 2028 IPL $500 $300 $— $— $500 WPL — — — 300 — AEF 309 — 200 — 300 Alliant Energy parent company — — 575 — — Alliant Energy $809 $300 $775 $300 $800
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 Energy IPL WPL December 31 2023 2022 2023 2022 2023 2022 Amount outstanding $475 $642 $— $— $318 $290 Weighted average interest rates 5.5% 4.6% N/A N/A 5.4% 4.5% Available credit facility capacity $525 $358 $150 $100 $82 $110 Alliant Energy IPL WPL For the year ended 2023 2022 2023 2022 2023 2022 Maximum amount outstanding (based on daily outstanding balances) $793 $665 $70 $— $349 $325 Average amount outstanding (based on daily outstanding balances) $386 $411 $2 $— $157 $153 Weighted average interest rates 5.2% 2.1% 5.3% —% 5.1% 1.6%
Schedule of Long-term Debt	Long-term debt, net as of December 31 was as follows (dollars in millions): 2023 2022 Alliant Energy IPL WPL Alliant Energy IPL WPL Senior Debentures (a): 3.25%, due 2024 $500 $500 $— $500 $500 $— 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 (b) 300 300 — — — — 6.45%, due 2033 100 100 — 100 100 — 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 — 3,975 3,975 — 3,675 3,675 — 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 (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 3,100 — 3,100 2,800 — 2,800 Other: AEF term loan credit agreement through March 2024, 6% at December 31, 2023 (with Alliant Energy as guarantor) (d) 300 — — 400 — — 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 — — — — — 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)(f) 300 — — — — — AEF 3.6% senior notes, due 2032 (with Alliant Energy as guarantor) (a) 350 — — 350 — — Sheboygan Power, LLC 5.06% senior secured notes, due 2024 (secured by the Sheboygan Falls Energy Facility and related assets) (a) 9 — — 17 — — AEF 3.75% senior notes (with Alliant Energy as guarantor) (Retired in 2023) — — — 400 — — Other, 1% at December 31, 2023, due 2024 to 2025 — — — 1 — — 2,034 — — 1,668 — — Subtotal 9,109 3,975 3,100 8,143 3,675 2,800 Current maturities (809) (500) — (408) — — Unamortized debt issuance costs (54) (21) (19) (45) (21) (19) Unamortized debt (discount) and premium, net (21) (9) (11) (22) (8) (11) Long-term debt, net (g) $8,225 $3,445 $3,070 $7,668 $3,646 $2,770 (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 2023, IPL issued $300 million of 5.7% senior debentures due 2033. The net proceeds from the issuance were used to reduce cash amounts received from its sales of accounts receivable program, reduce commercial paper classified as long-term debt, for general corporate purposes and/or were placed in money market fund investments. (c) In March 2023, WPL issued $300 million of 4.95% debentures due 2033. 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 its solar EGUs. (d) In January 2023, AEF entered into a $300 million interest rate swap maturing in January 2026 to mitigate interest rate risk. Under the terms of the swap, AEF exchanged a variable interest rate for a fixed interest rate of 3.93% on a portion of its variable-rate term loan borrowings. In December 2023, AEF retired the remaining $100 million variable-rate term loan borrowings. Refer to Note 15 for additional information on the interest rate swap. (e) Refer to “ Convertible Senior Notes ” below for additional information. (f) In November 2023, AEF issued $300 million of 5.95% senior notes due 2029. The net proceeds from AEF’s issuance 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, 2023, long-term debt maturities for 2024 through 2028 were as follows (in millions): 2024 2025 2026 2027 2028 IPL $500 $300 $— $— $500 WPL — — — 300 — AEF 309 — 200 — 300 Alliant Energy parent company — — 575 — — Alliant Energy $809 $300 $775 $300 $800
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 Energy IPL WPL December 31 2023 2022 2023 2022 2023 2022 Amount outstanding $475 $642 $— $— $318 $290 Weighted average interest rates 5.5% 4.6% N/A N/A 5.4% 4.5% Available credit facility capacity $525 $358 $150 $100 $82 $110 Alliant Energy IPL WPL For the year ended 2023 2022 2023 2022 2023 2022 Maximum amount outstanding (based on daily outstanding balances) $793 $665 $70 $— $349 $325 Average amount outstanding (based on daily outstanding balances) $386 $411 $2 $— $157 $153 Weighted average interest rates 5.2% 2.1% 5.3% —% 5.1% 1.6%
Schedule of Long-term Debt	Long-term debt, net as of December 31 was as follows (dollars in millions): 2023 2022 Alliant Energy IPL WPL Alliant Energy IPL WPL Senior Debentures (a): 3.25%, due 2024 $500 $500 $— $500 $500 $— 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 (b) 300 300 — — — — 6.45%, due 2033 100 100 — 100 100 — 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 — 3,975 3,975 — 3,675 3,675 — 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 (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 3,100 — 3,100 2,800 — 2,800 Other: AEF term loan credit agreement through March 2024, 6% at December 31, 2023 (with Alliant Energy as guarantor) (d) 300 — — 400 — — 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 — — — — — 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)(f) 300 — — — — — AEF 3.6% senior notes, due 2032 (with Alliant Energy as guarantor) (a) 350 — — 350 — — Sheboygan Power, LLC 5.06% senior secured notes, due 2024 (secured by the Sheboygan Falls Energy Facility and related assets) (a) 9 — — 17 — — AEF 3.75% senior notes (with Alliant Energy as guarantor) (Retired in 2023) — — — 400 — — Other, 1% at December 31, 2023, due 2024 to 2025 — — — 1 — — 2,034 — — 1,668 — — Subtotal 9,109 3,975 3,100 8,143 3,675 2,800 Current maturities (809) (500) — (408) — — Unamortized debt issuance costs (54) (21) (19) (45) (21) (19) Unamortized debt (discount) and premium, net (21) (9) (11) (22) (8) (11) Long-term debt, net (g) $8,225 $3,445 $3,070 $7,668 $3,646 $2,770 (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 2023, IPL issued $300 million of 5.7% senior debentures due 2033. The net proceeds from the issuance were used to reduce cash amounts received from its sales of accounts receivable program, reduce commercial paper classified as long-term debt, for general corporate purposes and/or were placed in money market fund investments. (c) In March 2023, WPL issued $300 million of 4.95% debentures due 2033. 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 its solar EGUs. (d) In January 2023, AEF entered into a $300 million interest rate swap maturing in January 2026 to mitigate interest rate risk. Under the terms of the swap, AEF exchanged a variable interest rate for a fixed interest rate of 3.93% on a portion of its variable-rate term loan borrowings. In December 2023, AEF retired the remaining $100 million variable-rate term loan borrowings. Refer to Note 15 for additional information on the interest rate swap. (e) Refer to “ Convertible Senior Notes ” below for additional information. (f) In November 2023, AEF issued $300 million of 5.95% senior notes due 2029. The net proceeds from AEF’s issuance 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, 2023, long-term debt maturities for 2024 through 2028 were as follows (in millions): 2024 2025 2026 2027 2028 IPL $500 $300 $— $— $500 WPL — — — 300 — AEF 309 — 200 — 300 Alliant Energy parent company — — 575 — — Alliant Energy $809 $300 $775 $300 $800

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2023
Leases [Line Items]
Schedule of Lease Details	Operating lease details are as follows (dollars in millions): December 31, 2023 December 31, 2022 Alliant Energy IPL WPL Alliant Energy IPL WPL Property, plant and equipment, net $23 $13 $9 $16 $9 $6 Other current liabilities $2 $1 $1 $3 $1 $1 Other liabilities 21 12 8 13 8 5 Total operating lease liabilities $23 $13 $9 $16 $9 $6 Weighted average remaining lease term 12 years 12 years 12 years 10 years 11 years 9 years Weighted average discount rate 4% 4% 4% 4% 4% 4% Finance lease details are as follows (dollars in millions): December 31, 2023 December 31, 2022 Alliant Energy IPL WPL Alliant Energy IPL WPL Property, plant and equipment, net: Sheboygan Falls Energy Facility N/A N/A $79 N/A N/A $15 Leased land for solar generation $172 $33 139 $133 $— 133 $172 $33 $218 $133 $— $148 Other current liabilities: Sheboygan Falls Energy Facility N/A N/A $11 N/A N/A $12 Leased land for solar generation $— $— — $5 $— 5 — — 11 5 — 17 Other liabilities: Sheboygan Falls Energy Facility N/A N/A 78 N/A N/A 19 Leased land for solar generation 172 33 139 131 — 131 172 33 217 131 — 150 Total finance lease liabilities $172 $33 $228 $136 $— $167 Weighted average remaining lease term 33 years 29 years 27 years 34 years N/A 28 years Weighted average discount rate 5% 5% 5% 5% N/A 5% Alliant Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Depreciation and amortization expenses $1 $— $— $— $— $— $6 $6 $6 Interest expense 6 3 — 1 — — 8 7 5 Total finance lease expense $7 $3 $— $1 $— $— $14 $13 $11 Finance lease liabilities arising from obtaining leased assets, which represent non-cash financing activities, were as follows (in millions): Alliant Energy IPL WPL 2023 2022 2023 2022 2023 2022 Finance lease liabilities arising from obtaining leased assets $34 $125 $33 $— $71 $125
Schedule of Operating Lease Liability Maturities	As of December 31, 2023, expected maturities of lease liabilities were as follows (in millions): 2024 2025 2026 2027 2028 Thereafter Total Less: amount representing interest Present value of minimum lease payments Operating Leases: Alliant Energy $3 $3 $3 $3 $2 $16 $30 $7 $23 IPL 1 2 2 1 1 10 17 4 13 WPL 2 1 1 1 1 6 12 3 9 Finance Leases: Alliant Energy 8 8 8 8 8 320 360 188 172 IPL 2 2 2 2 2 59 69 36 33 WPL 21 17 13 13 13 334 411 183 228
Schedule of Finance Lease Liability Maturities	As of December 31, 2023, expected maturities of lease liabilities were as follows (in millions): 2024 2025 2026 2027 2028 Thereafter Total Less: amount representing interest Present value of minimum lease payments Operating Leases: Alliant Energy $3 $3 $3 $3 $2 $16 $30 $7 $23 IPL 1 2 2 1 1 10 17 4 13 WPL 2 1 1 1 1 6 12 3 9 Finance Leases: Alliant Energy 8 8 8 8 8 320 360 188 172 IPL 2 2 2 2 2 59 69 36 33 WPL 21 17 13 13 13 334 411 183 228
IPL [Member]
Leases [Line Items]
Schedule of Lease Details	Operating lease details are as follows (dollars in millions): December 31, 2023 December 31, 2022 Alliant Energy IPL WPL Alliant Energy IPL WPL Property, plant and equipment, net $23 $13 $9 $16 $9 $6 Other current liabilities $2 $1 $1 $3 $1 $1 Other liabilities 21 12 8 13 8 5 Total operating lease liabilities $23 $13 $9 $16 $9 $6 Weighted average remaining lease term 12 years 12 years 12 years 10 years 11 years 9 years Weighted average discount rate 4% 4% 4% 4% 4% 4% Finance lease details are as follows (dollars in millions): December 31, 2023 December 31, 2022 Alliant Energy IPL WPL Alliant Energy IPL WPL Property, plant and equipment, net: Sheboygan Falls Energy Facility N/A N/A $79 N/A N/A $15 Leased land for solar generation $172 $33 139 $133 $— 133 $172 $33 $218 $133 $— $148 Other current liabilities: Sheboygan Falls Energy Facility N/A N/A $11 N/A N/A $12 Leased land for solar generation $— $— — $5 $— 5 — — 11 5 — 17 Other liabilities: Sheboygan Falls Energy Facility N/A N/A 78 N/A N/A 19 Leased land for solar generation 172 33 139 131 — 131 172 33 217 131 — 150 Total finance lease liabilities $172 $33 $228 $136 $— $167 Weighted average remaining lease term 33 years 29 years 27 years 34 years N/A 28 years Weighted average discount rate 5% 5% 5% 5% N/A 5% Alliant Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Depreciation and amortization expenses $1 $— $— $— $— $— $6 $6 $6 Interest expense 6 3 — 1 — — 8 7 5 Total finance lease expense $7 $3 $— $1 $— $— $14 $13 $11 Finance lease liabilities arising from obtaining leased assets, which represent non-cash financing activities, were as follows (in millions): Alliant Energy IPL WPL 2023 2022 2023 2022 2023 2022 Finance lease liabilities arising from obtaining leased assets $34 $125 $33 $— $71 $125
Schedule of Operating Lease Liability Maturities	As of December 31, 2023, expected maturities of lease liabilities were as follows (in millions): 2024 2025 2026 2027 2028 Thereafter Total Less: amount representing interest Present value of minimum lease payments Operating Leases: Alliant Energy $3 $3 $3 $3 $2 $16 $30 $7 $23 IPL 1 2 2 1 1 10 17 4 13 WPL 2 1 1 1 1 6 12 3 9 Finance Leases: Alliant Energy 8 8 8 8 8 320 360 188 172 IPL 2 2 2 2 2 59 69 36 33 WPL 21 17 13 13 13 334 411 183 228
Schedule of Finance Lease Liability Maturities	As of December 31, 2023, expected maturities of lease liabilities were as follows (in millions): 2024 2025 2026 2027 2028 Thereafter Total Less: amount representing interest Present value of minimum lease payments Operating Leases: Alliant Energy $3 $3 $3 $3 $2 $16 $30 $7 $23 IPL 1 2 2 1 1 10 17 4 13 WPL 2 1 1 1 1 6 12 3 9 Finance Leases: Alliant Energy 8 8 8 8 8 320 360 188 172 IPL 2 2 2 2 2 59 69 36 33 WPL 21 17 13 13 13 334 411 183 228
WPL [Member]
Leases [Line Items]
Schedule of Lease Details	Operating lease details are as follows (dollars in millions): December 31, 2023 December 31, 2022 Alliant Energy IPL WPL Alliant Energy IPL WPL Property, plant and equipment, net $23 $13 $9 $16 $9 $6 Other current liabilities $2 $1 $1 $3 $1 $1 Other liabilities 21 12 8 13 8 5 Total operating lease liabilities $23 $13 $9 $16 $9 $6 Weighted average remaining lease term 12 years 12 years 12 years 10 years 11 years 9 years Weighted average discount rate 4% 4% 4% 4% 4% 4% Finance lease details are as follows (dollars in millions): December 31, 2023 December 31, 2022 Alliant Energy IPL WPL Alliant Energy IPL WPL Property, plant and equipment, net: Sheboygan Falls Energy Facility N/A N/A $79 N/A N/A $15 Leased land for solar generation $172 $33 139 $133 $— 133 $172 $33 $218 $133 $— $148 Other current liabilities: Sheboygan Falls Energy Facility N/A N/A $11 N/A N/A $12 Leased land for solar generation $— $— — $5 $— 5 — — 11 5 — 17 Other liabilities: Sheboygan Falls Energy Facility N/A N/A 78 N/A N/A 19 Leased land for solar generation 172 33 139 131 — 131 172 33 217 131 — 150 Total finance lease liabilities $172 $33 $228 $136 $— $167 Weighted average remaining lease term 33 years 29 years 27 years 34 years N/A 28 years Weighted average discount rate 5% 5% 5% 5% N/A 5% Alliant Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Depreciation and amortization expenses $1 $— $— $— $— $— $6 $6 $6 Interest expense 6 3 — 1 — — 8 7 5 Total finance lease expense $7 $3 $— $1 $— $— $14 $13 $11 Finance lease liabilities arising from obtaining leased assets, which represent non-cash financing activities, were as follows (in millions): Alliant Energy IPL WPL 2023 2022 2023 2022 2023 2022 Finance lease liabilities arising from obtaining leased assets $34 $125 $33 $— $71 $125
Schedule of Operating Lease Liability Maturities	As of December 31, 2023, expected maturities of lease liabilities were as follows (in millions): 2024 2025 2026 2027 2028 Thereafter Total Less: amount representing interest Present value of minimum lease payments Operating Leases: Alliant Energy $3 $3 $3 $3 $2 $16 $30 $7 $23 IPL 1 2 2 1 1 10 17 4 13 WPL 2 1 1 1 1 6 12 3 9 Finance Leases: Alliant Energy 8 8 8 8 8 320 360 188 172 IPL 2 2 2 2 2 59 69 36 33 WPL 21 17 13 13 13 334 411 183 228
Schedule of Finance Lease Liability Maturities	As of December 31, 2023, expected maturities of lease liabilities were as follows (in millions): 2024 2025 2026 2027 2028 Thereafter Total Less: amount representing interest Present value of minimum lease payments Operating Leases: Alliant Energy $3 $3 $3 $3 $2 $16 $30 $7 $23 IPL 1 2 2 1 1 10 17 4 13 WPL 2 1 1 1 1 6 12 3 9 Finance Leases: Alliant Energy 8 8 8 8 8 320 360 188 172 IPL 2 2 2 2 2 59 69 36 33 WPL 21 17 13 13 13 334 411 183 228

Revenues (Tables)

Revenues (Tables)	12 Months Ended
	Dec. 31, 2023
Disaggregation of Revenue [Line Items]
Disaggregation of Revenues	Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Electric Utility: Retail - residential $1,220 $1,233 $1,115 $641 $673 $620 $579 $560 $495 Retail - commercial 820 821 763 519 536 508 301 285 255 Retail - industrial 968 965 893 501 538 505 467 427 388 Wholesale 213 233 187 62 64 57 151 169 130 Bulk power and other 124 169 123 38 48 62 86 121 61 Total Electric Utility 3,345 3,421 3,081 1,761 1,859 1,752 1,584 1,562 1,329 Gas Utility: Retail - residential 316 371 257 176 202 146 140 169 111 Retail - commercial 163 197 139 86 101 79 77 96 60 Retail - industrial 16 20 17 11 14 12 5 6 5 Transportation/other 45 54 43 27 34 28 18 20 15 Total Gas Utility 540 642 456 300 351 265 240 291 191 Other Utility: Steam 45 39 36 45 39 36 — — — Other utility 7 10 13 4 7 10 3 3 3 Total Other Utility 52 49 49 49 46 46 3 3 3 Non-Utility and Other: Travero and other 90 93 83 — — — — — — Total Non-Utility and Other 90 93 83 — — — — — — Total revenues $4,027 $4,205 $3,669 $2,110 $2,256 $2,063 $1,827 $1,856 $1,523
IPL [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenues	Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Electric Utility: Retail - residential $1,220 $1,233 $1,115 $641 $673 $620 $579 $560 $495 Retail - commercial 820 821 763 519 536 508 301 285 255 Retail - industrial 968 965 893 501 538 505 467 427 388 Wholesale 213 233 187 62 64 57 151 169 130 Bulk power and other 124 169 123 38 48 62 86 121 61 Total Electric Utility 3,345 3,421 3,081 1,761 1,859 1,752 1,584 1,562 1,329 Gas Utility: Retail - residential 316 371 257 176 202 146 140 169 111 Retail - commercial 163 197 139 86 101 79 77 96 60 Retail - industrial 16 20 17 11 14 12 5 6 5 Transportation/other 45 54 43 27 34 28 18 20 15 Total Gas Utility 540 642 456 300 351 265 240 291 191 Other Utility: Steam 45 39 36 45 39 36 — — — Other utility 7 10 13 4 7 10 3 3 3 Total Other Utility 52 49 49 49 46 46 3 3 3 Non-Utility and Other: Travero and other 90 93 83 — — — — — — Total Non-Utility and Other 90 93 83 — — — — — — Total revenues $4,027 $4,205 $3,669 $2,110 $2,256 $2,063 $1,827 $1,856 $1,523
WPL [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenues	Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Electric Utility: Retail - residential $1,220 $1,233 $1,115 $641 $673 $620 $579 $560 $495 Retail - commercial 820 821 763 519 536 508 301 285 255 Retail - industrial 968 965 893 501 538 505 467 427 388 Wholesale 213 233 187 62 64 57 151 169 130 Bulk power and other 124 169 123 38 48 62 86 121 61 Total Electric Utility 3,345 3,421 3,081 1,761 1,859 1,752 1,584 1,562 1,329 Gas Utility: Retail - residential 316 371 257 176 202 146 140 169 111 Retail - commercial 163 197 139 86 101 79 77 96 60 Retail - industrial 16 20 17 11 14 12 5 6 5 Transportation/other 45 54 43 27 34 28 18 20 15 Total Gas Utility 540 642 456 300 351 265 240 291 191 Other Utility: Steam 45 39 36 45 39 36 — — — Other utility 7 10 13 4 7 10 3 3 3 Total Other Utility 52 49 49 49 46 46 3 3 3 Non-Utility and Other: Travero and other 90 93 83 — — — — — — Total Non-Utility and Other 90 93 83 — — — — — — Total revenues $4,027 $4,205 $3,669 $2,110 $2,256 $2,063 $1,827 $1,856 $1,523

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2023
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 Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Current tax expense (benefit): Federal ($3) $7 $1 ($44) ($29) ($21) $48 $46 $22 State (6) 2 3 (21) (8) (1) 25 16 6 Deferred tax expense (benefit): Federal 100 109 9 87 91 73 10 10 (75) State 36 28 15 17 1 — 3 12 11 Production tax credits (121) (123) (101) (95) (105) (87) (26) (18) (14) Investment tax credits (1) (1) (1) (1) — — — — (1) Provision recorded as a change in accrued interest (1) — — (1) — — — — — $4 $22 ($74) ($58) ($50) ($36) $60 $66 ($51)
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. Alliant Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Statutory federal income tax rate 21% 21% 21% 21% 21% 21% 21% 21% 21% State income taxes, net of federal benefits 2 3 2 (2) (2) (1) 5 6 6 Production tax credits (17) (18) (17) (31) (34) (27) (7) (5) (6) Amortization of excess deferred taxes (Refer to Note 2 ) (2) (2) (18) (2) (2) (4) (2) (3) (43) Effect of rate-making on property-related differences (4) (1) (1) (5) (1) (2) (3) (2) (1) Adjustment for prior period taxes — 1 1 — 1 2 — — — Other items, net 1 (1) — — 1 — 1 — (1) Overall income tax rate 1% 3% (12%) (19%) (16%) (11%) 15% 17% (24%)
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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Deferred tax liabilities: Property $2,453 $2,442 $1,415 $1,440 $972 $938 ATC Holdings 127 125 — — — — Other 213 155 157 86 64 80 Total deferred tax liabilities 2,793 2,722 1,572 1,526 1,036 1,018 Deferred tax assets: Federal credit carryforwards 649 672 449 450 191 209 Net operating losses carryforwards - state 26 32 1 — — — Other 79 75 32 29 19 20 Subtotal deferred tax assets 754 779 482 479 210 229 Valuation allowances (3) — (1) — (1) — Total deferred tax assets 751 779 481 479 209 229 Total deferred tax liabilities, net $2,042 $1,943 $1,091 $1,047 $827 $789
Summary Of Tax Credit Carryforwards	At December 31, 2023, carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL State net operating losses 2025-2043 $428 $6 $1 Federal tax credits 2031-2043 649 449 191
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) 2019 - 2022 Consolidated Iowa income tax returns (b) 2020 - 2022 Wisconsin combined tax returns (c) 2019 - 2022 (a) The 2020 and 2021 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 Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Current tax expense (benefit): Federal ($3) $7 $1 ($44) ($29) ($21) $48 $46 $22 State (6) 2 3 (21) (8) (1) 25 16 6 Deferred tax expense (benefit): Federal 100 109 9 87 91 73 10 10 (75) State 36 28 15 17 1 — 3 12 11 Production tax credits (121) (123) (101) (95) (105) (87) (26) (18) (14) Investment tax credits (1) (1) (1) (1) — — — — (1) Provision recorded as a change in accrued interest (1) — — (1) — — — — — $4 $22 ($74) ($58) ($50) ($36) $60 $66 ($51)
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. Alliant Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Statutory federal income tax rate 21% 21% 21% 21% 21% 21% 21% 21% 21% State income taxes, net of federal benefits 2 3 2 (2) (2) (1) 5 6 6 Production tax credits (17) (18) (17) (31) (34) (27) (7) (5) (6) Amortization of excess deferred taxes (Refer to Note 2 ) (2) (2) (18) (2) (2) (4) (2) (3) (43) Effect of rate-making on property-related differences (4) (1) (1) (5) (1) (2) (3) (2) (1) Adjustment for prior period taxes — 1 1 — 1 2 — — — Other items, net 1 (1) — — 1 — 1 — (1) Overall income tax rate 1% 3% (12%) (19%) (16%) (11%) 15% 17% (24%)
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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Deferred tax liabilities: Property $2,453 $2,442 $1,415 $1,440 $972 $938 ATC Holdings 127 125 — — — — Other 213 155 157 86 64 80 Total deferred tax liabilities 2,793 2,722 1,572 1,526 1,036 1,018 Deferred tax assets: Federal credit carryforwards 649 672 449 450 191 209 Net operating losses carryforwards - state 26 32 1 — — — Other 79 75 32 29 19 20 Subtotal deferred tax assets 754 779 482 479 210 229 Valuation allowances (3) — (1) — (1) — Total deferred tax assets 751 779 481 479 209 229 Total deferred tax liabilities, net $2,042 $1,943 $1,091 $1,047 $827 $789
Summary Of Tax Credit Carryforwards	At December 31, 2023, carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL State net operating losses 2025-2043 $428 $6 $1 Federal tax credits 2031-2043 649 449 191
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) 2019 - 2022 Consolidated Iowa income tax returns (b) 2020 - 2022 Wisconsin combined tax returns (c) 2019 - 2022 (a) The 2020 and 2021 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 Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Current tax expense (benefit): Federal ($3) $7 $1 ($44) ($29) ($21) $48 $46 $22 State (6) 2 3 (21) (8) (1) 25 16 6 Deferred tax expense (benefit): Federal 100 109 9 87 91 73 10 10 (75) State 36 28 15 17 1 — 3 12 11 Production tax credits (121) (123) (101) (95) (105) (87) (26) (18) (14) Investment tax credits (1) (1) (1) (1) — — — — (1) Provision recorded as a change in accrued interest (1) — — (1) — — — — — $4 $22 ($74) ($58) ($50) ($36) $60 $66 ($51)
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. Alliant Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Statutory federal income tax rate 21% 21% 21% 21% 21% 21% 21% 21% 21% State income taxes, net of federal benefits 2 3 2 (2) (2) (1) 5 6 6 Production tax credits (17) (18) (17) (31) (34) (27) (7) (5) (6) Amortization of excess deferred taxes (Refer to Note 2 ) (2) (2) (18) (2) (2) (4) (2) (3) (43) Effect of rate-making on property-related differences (4) (1) (1) (5) (1) (2) (3) (2) (1) Adjustment for prior period taxes — 1 1 — 1 2 — — — Other items, net 1 (1) — — 1 — 1 — (1) Overall income tax rate 1% 3% (12%) (19%) (16%) (11%) 15% 17% (24%)
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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Deferred tax liabilities: Property $2,453 $2,442 $1,415 $1,440 $972 $938 ATC Holdings 127 125 — — — — Other 213 155 157 86 64 80 Total deferred tax liabilities 2,793 2,722 1,572 1,526 1,036 1,018 Deferred tax assets: Federal credit carryforwards 649 672 449 450 191 209 Net operating losses carryforwards - state 26 32 1 — — — Other 79 75 32 29 19 20 Subtotal deferred tax assets 754 779 482 479 210 229 Valuation allowances (3) — (1) — (1) — Total deferred tax assets 751 779 481 479 209 229 Total deferred tax liabilities, net $2,042 $1,943 $1,091 $1,047 $827 $789
Summary Of Tax Credit Carryforwards	At December 31, 2023, carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL State net operating losses 2025-2043 $428 $6 $1 Federal tax credits 2031-2043 649 449 191
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) 2019 - 2022 Consolidated Iowa income tax returns (b) 2020 - 2022 Wisconsin combined tax returns (c) 2019 - 2022 (a) The 2020 and 2021 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.

Benefit Plans (Tables)

Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2023
Defined Benefit Plan Disclosure [Line Items]
Assumptions Used To Measure Benefit Plans	The assumptions for defined benefit pension and OPEB plans at the measurement date of December 31 were as follows: Defined Benefit Pension Plans OPEB Plans Alliant Energy 2023 2022 2021 2023 2022 2021 Discount rate for benefit obligations 5.36% 5.54% 2.91% 5.40% 5.53% 2.81% Discount rate for net periodic cost 5.54% 2.91% 2.57% 5.53% 2.81% 2.31% Expected rate of return on plan assets 7.80% 7.80% 7.10% 6.50% 6.40% 4.80% Interest crediting rate for Alliant Energy Cash Balance Pension Plan 10.75% 9.22% 4.18% N/A N/A N/A Rate of compensation increase 3.30% - 4.50% 3.30% - 4.50% 3.30% - 4.50% N/A N/A N/A Qualified Defined Benefit Pension Plan OPEB Plans IPL 2023 2022 2021 2023 2022 2021 Discount rate for benefit obligations 5.35% 5.55% 2.94% 5.40% 5.53% 2.80% Discount rate for net periodic cost 5.55% 2.94% 2.61% 5.53% 2.80% 2.28% Expected rate of return on plan assets 7.80% 7.80% 7.10% 6.90% 6.50% 5.10% Rate of compensation increase 3.30% 3.30% 3.30% N/A N/A N/A Qualified Defined Benefit Pension Plan OPEB Plans WPL 2023 2022 2021 2023 2022 2021 Discount rate for benefit obligations 5.35% 5.54% 2.94% 5.40% 5.53% 2.79% Discount rate for net periodic cost 5.54% 2.94% 2.64% 5.53% 2.79% 2.27% Expected rate of return on plan assets 7.80% 7.80% 7.10% 5.65% 5.49% 4.02% Rate of compensation increase 3.30% 3.30% 3.30% N/A N/A N/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 Energy Defined Benefit Pension Plans OPEB Plans 2023 2022 2021 2023 2022 2021 Service cost $5 $9 $11 $2 $3 $4 Interest cost 47 36 34 9 6 5 Expected return on plan assets (a) (53) (69) (69) (5) (5) (5) Amortization of prior service credit (b) (1) (1) — — — — Amortization of actuarial loss (c) 28 32 39 1 2 5 Settlement losses (d) — 26 — — — — $26 $33 $15 $7 $6 $9 IPL Defined Benefit Pension Plans OPEB Plans 2023 2022 2021 2023 2022 2021 Service cost $3 $6 $7 $1 $1 $1 Interest cost 21 16 16 3 2 2 Expected return on plan assets (a) (26) (31) (32) (3) (4) (3) Amortization of actuarial loss (c) 11 13 17 1 1 2 Settlement losses (d) — 13 — — — — $9 $17 $8 $2 $— $2 WPL Defined Benefit Pension Plans OPEB Plans 2023 2022 2021 2023 2022 2021 Service cost $2 $3 $4 $1 $1 $1 Interest cost 20 16 15 3 2 2 Expected return on plan assets (a) (22) (31) (31) (1) (1) — Amortization of actuarial loss (c) 13 15 19 1 2 2 Settlement losses (d) — 13 — — — — $13 $16 $7 $4 $4 $5 (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 Plans OPEB Plans Alliant Energy 2023 2022 2023 2022 Change in benefit obligation: Net benefit obligation at January 1 $875 $1,251 $168 $210 Service cost 5 9 2 3 Interest cost 47 36 9 6 Plan participants’ contributions — — 4 4 Actuarial (gain) loss 23 (269) (3) (37) Gross benefits paid (74) (152) (20) (18) Net benefit obligation at December 31 876 875 160 168 Change in plan assets: Fair value of plan assets at January 1 706 1,011 83 106 Actual return on plan assets 86 (204) 8 (17) Employer contributions 14 51 8 8 Plan participants’ contributions — — 4 4 Gross benefits paid (74) (152) (20) (18) Fair value of plan assets at December 31 732 706 83 83 Under funded status at December 31 ($144) ($169) ($77) ($85) Defined Benefit Pension Plans OPEB Plans Alliant Energy 2023 2022 2023 2022 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $14 $9 Current liabilities (2) (2) (8) (8) Pension and other benefit obligations (142) (167) (83) (86) Net amounts recognized at December 31 ($144) ($169) ($77) ($85) Amounts recognized in Regulatory Assets consist of: Net actuarial loss $337 $376 $11 $20 Prior service credit (2) (3) — — $335 $373 $11 $20 Defined Benefit Pension Plans OPEB Plans IPL 2023 2022 2023 2022 Change in benefit obligation: Net benefit obligation at January 1 $389 $567 $68 $84 Service cost 3 6 1 1 Interest cost 21 16 3 2 Plan participants’ contributions — — 2 2 Actuarial (gain) loss 9 (123) (1) (14) Gross benefits paid (35) (77) (8) (7) Net benefit obligation at December 31 387 389 65 68 Change in plan assets: Fair value of plan assets at January 1 344 462 58 74 Actual return on plan assets 42 (92) 7 (12) Employer contributions 1 51 2 1 Plan participants’ contributions — — 2 2 Gross benefits paid (35) (77) (8) (7) Fair value of plan assets at December 31 352 344 61 58 Under funded status at December 31 ($35) ($45) ($4) ($10) Defined Benefit Pension Plans OPEB Plans IPL 2023 2022 2023 2022 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $10 $6 Current liabilities — — (1) (2) Pension and other benefit obligations (35) (45) (13) (14) Net amounts recognized at December 31 ($35) ($45) ($4) ($10) Amounts recognized in Regulatory Assets consist of: Net actuarial loss $135 $154 $9 $14 Prior service credit (1) (1) — — $134 $153 $9 $14 Defined Benefit Pension Plans OPEB Plans WPL 2023 2022 2023 2022 Change in benefit obligation: Net benefit obligation at January 1 $381 $546 $65 $81 Service cost 2 3 1 1 Interest cost 20 16 3 2 Plan participants’ contributions — — 2 2 Actuarial (gain) loss 10 (117) (2) (13) Gross benefits paid (32) (67) (8) (8) Net benefit obligation at December 31 381 381 61 65 Change in plan assets: Fair value of plan assets at January 1 291 450 14 17 Actual return on plan assets 35 (92) 1 (2) Employer contributions 12 — 5 5 Plan participants’ contributions — — 2 2 Gross benefits paid (32) (67) (8) (8) Fair value of plan assets at December 31 306 291 14 14 Under funded status at December 31 ($75) ($90) ($47) ($51) Defined Benefit Pension Plans OPEB Plans WPL 2023 2022 2023 2022 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $4 $3 Current liabilities — — (6) (5) Pension and other benefit obligations (75) (90) (45) (49) Net amounts recognized at December 31 ($75) ($90) ($47) ($51) Amounts recognized in Regulatory Assets consist of: Net actuarial loss $148 $165 $3 $6 Prior service credit — — — — $148 $165 $3 $6
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 Plans OPEB Plans Alliant Energy 2023 2022 2023 2022 Accumulated benefit obligations $857 $857 $160 $168 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 857 857 160 168 Fair value of plan assets 732 706 83 83 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 876 875 N/A N/A Fair value of plan assets 732 706 N/A N/A Defined Benefit Pension Plans OPEB Plans IPL 2023 2022 2023 2022 Accumulated benefit obligations $377 $379 $65 $68 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 377 379 65 68 Fair value of plan assets 352 344 61 58 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 387 389 N/A N/A Fair value of plan assets 352 344 N/A N/A Defined Benefit Pension Plans OPEB Plans WPL 2023 2022 2023 2022 Accumulated benefit obligations $373 $373 $61 $65 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 373 373 61 65 Fair value of plan assets 306 291 14 14 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 381 381 N/A N/A Fair value of plan assets 306 291 N/A N/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): IPL WPL 2023 2022 2023 2022 Regulatory assets $28 $30 $24 $25
Estimated Future Employer Contributions	Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2024 is as follows (in millions): Alliant Energy IPL WPL Defined benefit pension plans (a) $12 $— $10 OPEB plans 8 1 6 (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 Energy 2024 2025 2026 2027 2028 2029 - 2033 Defined benefit pension benefits $73 $73 $74 $75 $75 $343 OPEB 17 17 16 16 15 65 $90 $90 $90 $91 $90 $408 IPL 2024 2025 2026 2027 2028 2029 - 2033 Defined benefit pension benefits $34 $34 $34 $33 $33 $151 OPEB 7 7 7 6 6 25 $41 $41 $41 $39 $39 $176 WPL 2024 2025 2026 2027 2028 2029 - 2033 Defined benefit pension benefits $32 $32 $31 $31 $31 $146 OPEB 7 7 6 6 6 24 $39 $39 $37 $37 $37 $170
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 Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Compensation expense $12 $13 $14 $6 $7 $8 $5 $5 $6 Income tax benefits 3 3 4 2 2 2 1 1 2
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): 2023 2022 Carrying value $13 $13 Fair market value 19 22
IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Assumptions Used To Measure Benefit Plans	The assumptions for defined benefit pension and OPEB plans at the measurement date of December 31 were as follows: Defined Benefit Pension Plans OPEB Plans Alliant Energy 2023 2022 2021 2023 2022 2021 Discount rate for benefit obligations 5.36% 5.54% 2.91% 5.40% 5.53% 2.81% Discount rate for net periodic cost 5.54% 2.91% 2.57% 5.53% 2.81% 2.31% Expected rate of return on plan assets 7.80% 7.80% 7.10% 6.50% 6.40% 4.80% Interest crediting rate for Alliant Energy Cash Balance Pension Plan 10.75% 9.22% 4.18% N/A N/A N/A Rate of compensation increase 3.30% - 4.50% 3.30% - 4.50% 3.30% - 4.50% N/A N/A N/A Qualified Defined Benefit Pension Plan OPEB Plans IPL 2023 2022 2021 2023 2022 2021 Discount rate for benefit obligations 5.35% 5.55% 2.94% 5.40% 5.53% 2.80% Discount rate for net periodic cost 5.55% 2.94% 2.61% 5.53% 2.80% 2.28% Expected rate of return on plan assets 7.80% 7.80% 7.10% 6.90% 6.50% 5.10% Rate of compensation increase 3.30% 3.30% 3.30% N/A N/A N/A Qualified Defined Benefit Pension Plan OPEB Plans WPL 2023 2022 2021 2023 2022 2021 Discount rate for benefit obligations 5.35% 5.54% 2.94% 5.40% 5.53% 2.79% Discount rate for net periodic cost 5.54% 2.94% 2.64% 5.53% 2.79% 2.27% Expected rate of return on plan assets 7.80% 7.80% 7.10% 5.65% 5.49% 4.02% Rate of compensation increase 3.30% 3.30% 3.30% N/A N/A N/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 Energy Defined Benefit Pension Plans OPEB Plans 2023 2022 2021 2023 2022 2021 Service cost $5 $9 $11 $2 $3 $4 Interest cost 47 36 34 9 6 5 Expected return on plan assets (a) (53) (69) (69) (5) (5) (5) Amortization of prior service credit (b) (1) (1) — — — — Amortization of actuarial loss (c) 28 32 39 1 2 5 Settlement losses (d) — 26 — — — — $26 $33 $15 $7 $6 $9 IPL Defined Benefit Pension Plans OPEB Plans 2023 2022 2021 2023 2022 2021 Service cost $3 $6 $7 $1 $1 $1 Interest cost 21 16 16 3 2 2 Expected return on plan assets (a) (26) (31) (32) (3) (4) (3) Amortization of actuarial loss (c) 11 13 17 1 1 2 Settlement losses (d) — 13 — — — — $9 $17 $8 $2 $— $2 WPL Defined Benefit Pension Plans OPEB Plans 2023 2022 2021 2023 2022 2021 Service cost $2 $3 $4 $1 $1 $1 Interest cost 20 16 15 3 2 2 Expected return on plan assets (a) (22) (31) (31) (1) (1) — Amortization of actuarial loss (c) 13 15 19 1 2 2 Settlement losses (d) — 13 — — — — $13 $16 $7 $4 $4 $5 (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 Plans OPEB Plans Alliant Energy 2023 2022 2023 2022 Change in benefit obligation: Net benefit obligation at January 1 $875 $1,251 $168 $210 Service cost 5 9 2 3 Interest cost 47 36 9 6 Plan participants’ contributions — — 4 4 Actuarial (gain) loss 23 (269) (3) (37) Gross benefits paid (74) (152) (20) (18) Net benefit obligation at December 31 876 875 160 168 Change in plan assets: Fair value of plan assets at January 1 706 1,011 83 106 Actual return on plan assets 86 (204) 8 (17) Employer contributions 14 51 8 8 Plan participants’ contributions — — 4 4 Gross benefits paid (74) (152) (20) (18) Fair value of plan assets at December 31 732 706 83 83 Under funded status at December 31 ($144) ($169) ($77) ($85) Defined Benefit Pension Plans OPEB Plans Alliant Energy 2023 2022 2023 2022 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $14 $9 Current liabilities (2) (2) (8) (8) Pension and other benefit obligations (142) (167) (83) (86) Net amounts recognized at December 31 ($144) ($169) ($77) ($85) Amounts recognized in Regulatory Assets consist of: Net actuarial loss $337 $376 $11 $20 Prior service credit (2) (3) — — $335 $373 $11 $20 Defined Benefit Pension Plans OPEB Plans IPL 2023 2022 2023 2022 Change in benefit obligation: Net benefit obligation at January 1 $389 $567 $68 $84 Service cost 3 6 1 1 Interest cost 21 16 3 2 Plan participants’ contributions — — 2 2 Actuarial (gain) loss 9 (123) (1) (14) Gross benefits paid (35) (77) (8) (7) Net benefit obligation at December 31 387 389 65 68 Change in plan assets: Fair value of plan assets at January 1 344 462 58 74 Actual return on plan assets 42 (92) 7 (12) Employer contributions 1 51 2 1 Plan participants’ contributions — — 2 2 Gross benefits paid (35) (77) (8) (7) Fair value of plan assets at December 31 352 344 61 58 Under funded status at December 31 ($35) ($45) ($4) ($10) Defined Benefit Pension Plans OPEB Plans IPL 2023 2022 2023 2022 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $10 $6 Current liabilities — — (1) (2) Pension and other benefit obligations (35) (45) (13) (14) Net amounts recognized at December 31 ($35) ($45) ($4) ($10) Amounts recognized in Regulatory Assets consist of: Net actuarial loss $135 $154 $9 $14 Prior service credit (1) (1) — — $134 $153 $9 $14 Defined Benefit Pension Plans OPEB Plans WPL 2023 2022 2023 2022 Change in benefit obligation: Net benefit obligation at January 1 $381 $546 $65 $81 Service cost 2 3 1 1 Interest cost 20 16 3 2 Plan participants’ contributions — — 2 2 Actuarial (gain) loss 10 (117) (2) (13) Gross benefits paid (32) (67) (8) (8) Net benefit obligation at December 31 381 381 61 65 Change in plan assets: Fair value of plan assets at January 1 291 450 14 17 Actual return on plan assets 35 (92) 1 (2) Employer contributions 12 — 5 5 Plan participants’ contributions — — 2 2 Gross benefits paid (32) (67) (8) (8) Fair value of plan assets at December 31 306 291 14 14 Under funded status at December 31 ($75) ($90) ($47) ($51) Defined Benefit Pension Plans OPEB Plans WPL 2023 2022 2023 2022 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $4 $3 Current liabilities — — (6) (5) Pension and other benefit obligations (75) (90) (45) (49) Net amounts recognized at December 31 ($75) ($90) ($47) ($51) Amounts recognized in Regulatory Assets consist of: Net actuarial loss $148 $165 $3 $6 Prior service credit — — — — $148 $165 $3 $6
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 Plans OPEB Plans Alliant Energy 2023 2022 2023 2022 Accumulated benefit obligations $857 $857 $160 $168 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 857 857 160 168 Fair value of plan assets 732 706 83 83 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 876 875 N/A N/A Fair value of plan assets 732 706 N/A N/A Defined Benefit Pension Plans OPEB Plans IPL 2023 2022 2023 2022 Accumulated benefit obligations $377 $379 $65 $68 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 377 379 65 68 Fair value of plan assets 352 344 61 58 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 387 389 N/A N/A Fair value of plan assets 352 344 N/A N/A Defined Benefit Pension Plans OPEB Plans WPL 2023 2022 2023 2022 Accumulated benefit obligations $373 $373 $61 $65 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 373 373 61 65 Fair value of plan assets 306 291 14 14 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 381 381 N/A N/A Fair value of plan assets 306 291 N/A N/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): IPL WPL 2023 2022 2023 2022 Regulatory assets $28 $30 $24 $25
Estimated Future Employer Contributions	Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2024 is as follows (in millions): Alliant Energy IPL WPL Defined benefit pension plans (a) $12 $— $10 OPEB plans 8 1 6 (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 Energy 2024 2025 2026 2027 2028 2029 - 2033 Defined benefit pension benefits $73 $73 $74 $75 $75 $343 OPEB 17 17 16 16 15 65 $90 $90 $90 $91 $90 $408 IPL 2024 2025 2026 2027 2028 2029 - 2033 Defined benefit pension benefits $34 $34 $34 $33 $33 $151 OPEB 7 7 7 6 6 25 $41 $41 $41 $39 $39 $176 WPL 2024 2025 2026 2027 2028 2029 - 2033 Defined benefit pension benefits $32 $32 $31 $31 $31 $146 OPEB 7 7 6 6 6 24 $39 $39 $37 $37 $37 $170
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 Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Compensation expense $12 $13 $14 $6 $7 $8 $5 $5 $6 Income tax benefits 3 3 4 2 2 2 1 1 2
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Assumptions Used To Measure Benefit Plans	The assumptions for defined benefit pension and OPEB plans at the measurement date of December 31 were as follows: Defined Benefit Pension Plans OPEB Plans Alliant Energy 2023 2022 2021 2023 2022 2021 Discount rate for benefit obligations 5.36% 5.54% 2.91% 5.40% 5.53% 2.81% Discount rate for net periodic cost 5.54% 2.91% 2.57% 5.53% 2.81% 2.31% Expected rate of return on plan assets 7.80% 7.80% 7.10% 6.50% 6.40% 4.80% Interest crediting rate for Alliant Energy Cash Balance Pension Plan 10.75% 9.22% 4.18% N/A N/A N/A Rate of compensation increase 3.30% - 4.50% 3.30% - 4.50% 3.30% - 4.50% N/A N/A N/A Qualified Defined Benefit Pension Plan OPEB Plans IPL 2023 2022 2021 2023 2022 2021 Discount rate for benefit obligations 5.35% 5.55% 2.94% 5.40% 5.53% 2.80% Discount rate for net periodic cost 5.55% 2.94% 2.61% 5.53% 2.80% 2.28% Expected rate of return on plan assets 7.80% 7.80% 7.10% 6.90% 6.50% 5.10% Rate of compensation increase 3.30% 3.30% 3.30% N/A N/A N/A Qualified Defined Benefit Pension Plan OPEB Plans WPL 2023 2022 2021 2023 2022 2021 Discount rate for benefit obligations 5.35% 5.54% 2.94% 5.40% 5.53% 2.79% Discount rate for net periodic cost 5.54% 2.94% 2.64% 5.53% 2.79% 2.27% Expected rate of return on plan assets 7.80% 7.80% 7.10% 5.65% 5.49% 4.02% Rate of compensation increase 3.30% 3.30% 3.30% N/A N/A N/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 Energy Defined Benefit Pension Plans OPEB Plans 2023 2022 2021 2023 2022 2021 Service cost $5 $9 $11 $2 $3 $4 Interest cost 47 36 34 9 6 5 Expected return on plan assets (a) (53) (69) (69) (5) (5) (5) Amortization of prior service credit (b) (1) (1) — — — — Amortization of actuarial loss (c) 28 32 39 1 2 5 Settlement losses (d) — 26 — — — — $26 $33 $15 $7 $6 $9 IPL Defined Benefit Pension Plans OPEB Plans 2023 2022 2021 2023 2022 2021 Service cost $3 $6 $7 $1 $1 $1 Interest cost 21 16 16 3 2 2 Expected return on plan assets (a) (26) (31) (32) (3) (4) (3) Amortization of actuarial loss (c) 11 13 17 1 1 2 Settlement losses (d) — 13 — — — — $9 $17 $8 $2 $— $2 WPL Defined Benefit Pension Plans OPEB Plans 2023 2022 2021 2023 2022 2021 Service cost $2 $3 $4 $1 $1 $1 Interest cost 20 16 15 3 2 2 Expected return on plan assets (a) (22) (31) (31) (1) (1) — Amortization of actuarial loss (c) 13 15 19 1 2 2 Settlement losses (d) — 13 — — — — $13 $16 $7 $4 $4 $5 (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 Plans OPEB Plans Alliant Energy 2023 2022 2023 2022 Change in benefit obligation: Net benefit obligation at January 1 $875 $1,251 $168 $210 Service cost 5 9 2 3 Interest cost 47 36 9 6 Plan participants’ contributions — — 4 4 Actuarial (gain) loss 23 (269) (3) (37) Gross benefits paid (74) (152) (20) (18) Net benefit obligation at December 31 876 875 160 168 Change in plan assets: Fair value of plan assets at January 1 706 1,011 83 106 Actual return on plan assets 86 (204) 8 (17) Employer contributions 14 51 8 8 Plan participants’ contributions — — 4 4 Gross benefits paid (74) (152) (20) (18) Fair value of plan assets at December 31 732 706 83 83 Under funded status at December 31 ($144) ($169) ($77) ($85) Defined Benefit Pension Plans OPEB Plans Alliant Energy 2023 2022 2023 2022 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $14 $9 Current liabilities (2) (2) (8) (8) Pension and other benefit obligations (142) (167) (83) (86) Net amounts recognized at December 31 ($144) ($169) ($77) ($85) Amounts recognized in Regulatory Assets consist of: Net actuarial loss $337 $376 $11 $20 Prior service credit (2) (3) — — $335 $373 $11 $20 Defined Benefit Pension Plans OPEB Plans IPL 2023 2022 2023 2022 Change in benefit obligation: Net benefit obligation at January 1 $389 $567 $68 $84 Service cost 3 6 1 1 Interest cost 21 16 3 2 Plan participants’ contributions — — 2 2 Actuarial (gain) loss 9 (123) (1) (14) Gross benefits paid (35) (77) (8) (7) Net benefit obligation at December 31 387 389 65 68 Change in plan assets: Fair value of plan assets at January 1 344 462 58 74 Actual return on plan assets 42 (92) 7 (12) Employer contributions 1 51 2 1 Plan participants’ contributions — — 2 2 Gross benefits paid (35) (77) (8) (7) Fair value of plan assets at December 31 352 344 61 58 Under funded status at December 31 ($35) ($45) ($4) ($10) Defined Benefit Pension Plans OPEB Plans IPL 2023 2022 2023 2022 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $10 $6 Current liabilities — — (1) (2) Pension and other benefit obligations (35) (45) (13) (14) Net amounts recognized at December 31 ($35) ($45) ($4) ($10) Amounts recognized in Regulatory Assets consist of: Net actuarial loss $135 $154 $9 $14 Prior service credit (1) (1) — — $134 $153 $9 $14 Defined Benefit Pension Plans OPEB Plans WPL 2023 2022 2023 2022 Change in benefit obligation: Net benefit obligation at January 1 $381 $546 $65 $81 Service cost 2 3 1 1 Interest cost 20 16 3 2 Plan participants’ contributions — — 2 2 Actuarial (gain) loss 10 (117) (2) (13) Gross benefits paid (32) (67) (8) (8) Net benefit obligation at December 31 381 381 61 65 Change in plan assets: Fair value of plan assets at January 1 291 450 14 17 Actual return on plan assets 35 (92) 1 (2) Employer contributions 12 — 5 5 Plan participants’ contributions — — 2 2 Gross benefits paid (32) (67) (8) (8) Fair value of plan assets at December 31 306 291 14 14 Under funded status at December 31 ($75) ($90) ($47) ($51) Defined Benefit Pension Plans OPEB Plans WPL 2023 2022 2023 2022 Amounts recognized on the balance sheets consist of: Non-current assets $— $— $4 $3 Current liabilities — — (6) (5) Pension and other benefit obligations (75) (90) (45) (49) Net amounts recognized at December 31 ($75) ($90) ($47) ($51) Amounts recognized in Regulatory Assets consist of: Net actuarial loss $148 $165 $3 $6 Prior service credit — — — — $148 $165 $3 $6
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 Plans OPEB Plans Alliant Energy 2023 2022 2023 2022 Accumulated benefit obligations $857 $857 $160 $168 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 857 857 160 168 Fair value of plan assets 732 706 83 83 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 876 875 N/A N/A Fair value of plan assets 732 706 N/A N/A Defined Benefit Pension Plans OPEB Plans IPL 2023 2022 2023 2022 Accumulated benefit obligations $377 $379 $65 $68 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 377 379 65 68 Fair value of plan assets 352 344 61 58 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 387 389 N/A N/A Fair value of plan assets 352 344 N/A N/A Defined Benefit Pension Plans OPEB Plans WPL 2023 2022 2023 2022 Accumulated benefit obligations $373 $373 $61 $65 Plans with accumulated benefit obligations in excess of plan assets: Accumulated benefit obligations 373 373 61 65 Fair value of plan assets 306 291 14 14 Plans with projected benefit obligations in excess of plan assets: Projected benefit obligations 381 381 N/A N/A Fair value of plan assets 306 291 N/A N/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): IPL WPL 2023 2022 2023 2022 Regulatory assets $28 $30 $24 $25
Estimated Future Employer Contributions	Estimated funding for the qualified and non-qualified defined benefit pension and OPEB plans for 2024 is as follows (in millions): Alliant Energy IPL WPL Defined benefit pension plans (a) $12 $— $10 OPEB plans 8 1 6 (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 Energy 2024 2025 2026 2027 2028 2029 - 2033 Defined benefit pension benefits $73 $73 $74 $75 $75 $343 OPEB 17 17 16 16 15 65 $90 $90 $90 $91 $90 $408 IPL 2024 2025 2026 2027 2028 2029 - 2033 Defined benefit pension benefits $34 $34 $34 $33 $33 $151 OPEB 7 7 7 6 6 25 $41 $41 $41 $39 $39 $176 WPL 2024 2025 2026 2027 2028 2029 - 2033 Defined benefit pension benefits $32 $32 $31 $31 $31 $146 OPEB 7 7 6 6 6 24 $39 $39 $37 $37 $37 $170
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 Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 Compensation expense $12 $13 $14 $6 $7 $8 $5 $5 $6 Income tax benefits 3 3 4 2 2 2 1 1 2
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, 2023, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows: Target Range Actual Allocation Allocation Cash and equivalents 0% - 5% 2% Equity securities 47% - 67% 56% Global asset securities 0% - 15% 5% Fixed income securities 27% - 47% 37% At December 31, the fair values of qualified and non-qualified defined benefit pension plan assets were as follows (in millions): 2023 2022 Fair Level Level Level Fair Level Level Level Alliant Energy Value 1 2 3 Value 1 2 3 Cash and equivalents $19 $— $19 $— $79 $— $79 $— Equity securities 223 223 — — 185 185 — — Global asset securities 39 39 — — 35 35 — — Fixed income securities 143 31 112 — 130 30 100 — Total assets in fair value hierarchy 424 $293 $131 $— 429 $250 $179 $— Assets measured at net asset value 306 276 Accrued investment income 2 1 Total pension plan assets $732 $706 2023 2022 Fair Level Level Level Fair Level Level Level IPL Value 1 2 3 Value 1 2 3 Cash and equivalents $9 $— $9 $— $62 $— $62 $— Equity securities 107 107 — — 83 83 — — Global asset securities 19 19 — — 16 16 — — Fixed income securities 69 15 54 — 58 13 45 — Total assets in fair value hierarchy 204 $141 $63 $— 219 $112 $107 $— Assets measured at net asset value 147 124 Accrued investment income 1 1 Total pension plan assets $352 $344 2023 2022 Fair Level Level Level Fair Level Level Level WPL Value 1 2 3 Value 1 2 3 Cash and equivalents $8 $— $8 $— $13 $— $13 $— Equity securities 93 93 — — 82 82 — — Global asset securities 16 16 — — 16 16 — — Fixed income securities 60 13 47 — 57 13 44 — Total assets in fair value hierarchy 177 $122 $55 $— 168 $111 $57 $— Assets measured at net asset value 128 122 Accrued investment income 1 1 Total pension plan assets $306 $291
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, 2023, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows: Target Range Actual Allocation Allocation Cash and equivalents 0% - 5% 2% Equity securities 47% - 67% 56% Global asset securities 0% - 15% 5% Fixed income securities 27% - 47% 37% At December 31, the fair values of qualified and non-qualified defined benefit pension plan assets were as follows (in millions): 2023 2022 Fair Level Level Level Fair Level Level Level Alliant Energy Value 1 2 3 Value 1 2 3 Cash and equivalents $19 $— $19 $— $79 $— $79 $— Equity securities 223 223 — — 185 185 — — Global asset securities 39 39 — — 35 35 — — Fixed income securities 143 31 112 — 130 30 100 — Total assets in fair value hierarchy 424 $293 $131 $— 429 $250 $179 $— Assets measured at net asset value 306 276 Accrued investment income 2 1 Total pension plan assets $732 $706 2023 2022 Fair Level Level Level Fair Level Level Level IPL Value 1 2 3 Value 1 2 3 Cash and equivalents $9 $— $9 $— $62 $— $62 $— Equity securities 107 107 — — 83 83 — — Global asset securities 19 19 — — 16 16 — — Fixed income securities 69 15 54 — 58 13 45 — Total assets in fair value hierarchy 204 $141 $63 $— 219 $112 $107 $— Assets measured at net asset value 147 124 Accrued investment income 1 1 Total pension plan assets $352 $344 2023 2022 Fair Level Level Level Fair Level Level Level WPL Value 1 2 3 Value 1 2 3 Cash and equivalents $8 $— $8 $— $13 $— $13 $— Equity securities 93 93 — — 82 82 — — Global asset securities 16 16 — — 16 16 — — Fixed income securities 60 13 47 — 57 13 44 — Total assets in fair value hierarchy 177 $122 $55 $— 168 $111 $57 $— Assets measured at net asset value 128 122 Accrued investment income 1 1 Total pension plan assets $306 $291
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, 2023, the current target ranges and actual allocations for the defined benefit pension plan assets were as follows: Target Range Actual Allocation Allocation Cash and equivalents 0% - 5% 2% Equity securities 47% - 67% 56% Global asset securities 0% - 15% 5% Fixed income securities 27% - 47% 37% At December 31, the fair values of qualified and non-qualified defined benefit pension plan assets were as follows (in millions): 2023 2022 Fair Level Level Level Fair Level Level Level Alliant Energy Value 1 2 3 Value 1 2 3 Cash and equivalents $19 $— $19 $— $79 $— $79 $— Equity securities 223 223 — — 185 185 — — Global asset securities 39 39 — — 35 35 — — Fixed income securities 143 31 112 — 130 30 100 — Total assets in fair value hierarchy 424 $293 $131 $— 429 $250 $179 $— Assets measured at net asset value 306 276 Accrued investment income 2 1 Total pension plan assets $732 $706 2023 2022 Fair Level Level Level Fair Level Level Level IPL Value 1 2 3 Value 1 2 3 Cash and equivalents $9 $— $9 $— $62 $— $62 $— Equity securities 107 107 — — 83 83 — — Global asset securities 19 19 — — 16 16 — — Fixed income securities 69 15 54 — 58 13 45 — Total assets in fair value hierarchy 204 $141 $63 $— 219 $112 $107 $— Assets measured at net asset value 147 124 Accrued investment income 1 1 Total pension plan assets $352 $344 2023 2022 Fair Level Level Level Fair Level Level Level WPL Value 1 2 3 Value 1 2 3 Cash and equivalents $8 $— $8 $— $13 $— $13 $— Equity securities 93 93 — — 82 82 — — Global asset securities 16 16 — — 16 16 — — Fixed income securities 60 13 47 — 57 13 44 — Total assets in fair value hierarchy 177 $122 $55 $— 168 $111 $57 $— Assets measured at net asset value 128 122 Accrued investment income 1 1 Total pension plan assets $306 $291
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, 2023, the current target ranges and actual allocations for VEBA trusts with assets greater than $5 million and the WPL 401(h) assets were as follows: Target Range Actual Allocation Allocation Cash and equivalents 0% - 5% 1% Equity securities 0% - 55% 36% Fixed income securities 40% - 100% 63% At December 31, the fair values of OPEB plan assets were as follows (in millions): 2023 2022 Fair Level Level Level Fair Level Level Level Alliant Energy Value 1 2 3 Value 1 2 3 Cash and equivalents $9 $— $9 $— $3 $— $3 $— Equity securities 8 8 — — 9 9 — — Global asset securities — — — — 1 1 — — Fixed income securities 47 47 — — 47 46 1 — Total assets in fair value hierarchy 64 $55 $9 $— 60 $56 $4 $— Assets measured at net asset value 19 23 Total OPEB plan assets $83 $83 2023 2022 Fair Level Level Level Fair Level Level Level IPL Value 1 2 3 Value 1 2 3 Cash and equivalents $1 $— $1 $— $1 $— $1 $— Equity securities 6 6 — — 5 5 — — Fixed income securities 36 36 — — 34 34 — — Total assets in fair value hierarchy 43 $42 $1 $— 40 $39 $1 $— Assets measured at net asset value 18 18 Total OPEB plan assets $61 $58 2023 2022 Fair Level Level Level Fair Level Level Level WPL Value 1 2 3 Value 1 2 3 Cash and equivalents $1 $— $1 $— $— $— $— $— Equity securities 2 2 — — 1 1 — — Fixed income securities 11 11 — — 13 13 — — Total OPEB plan assets $14 $13 $1 $— $14 $14 $— $—
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, 2023, the current target ranges and actual allocations for VEBA trusts with assets greater than $5 million and the WPL 401(h) assets were as follows: Target Range Actual Allocation Allocation Cash and equivalents 0% - 5% 1% Equity securities 0% - 55% 36% Fixed income securities 40% - 100% 63% At December 31, the fair values of OPEB plan assets were as follows (in millions): 2023 2022 Fair Level Level Level Fair Level Level Level Alliant Energy Value 1 2 3 Value 1 2 3 Cash and equivalents $9 $— $9 $— $3 $— $3 $— Equity securities 8 8 — — 9 9 — — Global asset securities — — — — 1 1 — — Fixed income securities 47 47 — — 47 46 1 — Total assets in fair value hierarchy 64 $55 $9 $— 60 $56 $4 $— Assets measured at net asset value 19 23 Total OPEB plan assets $83 $83 2023 2022 Fair Level Level Level Fair Level Level Level IPL Value 1 2 3 Value 1 2 3 Cash and equivalents $1 $— $1 $— $1 $— $1 $— Equity securities 6 6 — — 5 5 — — Fixed income securities 36 36 — — 34 34 — — Total assets in fair value hierarchy 43 $42 $1 $— 40 $39 $1 $— Assets measured at net asset value 18 18 Total OPEB plan assets $61 $58 2023 2022 Fair Level Level Level Fair Level Level Level WPL Value 1 2 3 Value 1 2 3 Cash and equivalents $1 $— $1 $— $— $— $— $— Equity securities 2 2 — — 1 1 — — Fixed income securities 11 11 — — 13 13 — — Total OPEB plan assets $14 $13 $1 $— $14 $14 $— $—
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, 2023, the current target ranges and actual allocations for VEBA trusts with assets greater than $5 million and the WPL 401(h) assets were as follows: Target Range Actual Allocation Allocation Cash and equivalents 0% - 5% 1% Equity securities 0% - 55% 36% Fixed income securities 40% - 100% 63% At December 31, the fair values of OPEB plan assets were as follows (in millions): 2023 2022 Fair Level Level Level Fair Level Level Level Alliant Energy Value 1 2 3 Value 1 2 3 Cash and equivalents $9 $— $9 $— $3 $— $3 $— Equity securities 8 8 — — 9 9 — — Global asset securities — — — — 1 1 — — Fixed income securities 47 47 — — 47 46 1 — Total assets in fair value hierarchy 64 $55 $9 $— 60 $56 $4 $— Assets measured at net asset value 19 23 Total OPEB plan assets $83 $83 2023 2022 Fair Level Level Level Fair Level Level Level IPL Value 1 2 3 Value 1 2 3 Cash and equivalents $1 $— $1 $— $1 $— $1 $— Equity securities 6 6 — — 5 5 — — Fixed income securities 36 36 — — 34 34 — — Total assets in fair value hierarchy 43 $42 $1 $— 40 $39 $1 $— Assets measured at net asset value 18 18 Total OPEB plan assets $61 $58 2023 2022 Fair Level Level Level Fair Level Level Level WPL Value 1 2 3 Value 1 2 3 Cash and equivalents $1 $— $1 $— $— $— $— $— Equity securities 2 2 — — 1 1 — — Fixed income securities 11 11 — — 13 13 — — Total OPEB plan assets $14 $13 $1 $— $14 $14 $— $—
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 Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 401(k) costs $30 $28 $26 $14 $13 $13 $14 $13 $12
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 Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 401(k) costs $30 $28 $26 $14 $13 $13 $14 $13 $12
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 Energy IPL WPL 2023 2022 2021 2023 2022 2021 2023 2022 2021 401(k) costs $30 $28 $26 $14 $13 $13 $14 $13 $12
Performance Shares Equity Awards [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: 2023 2022 2021 Shares Weighted Shares Weighted Shares Weighted Nonvested awards, January 1 190,273 $54.13 196,429 $51.59 129,156 $54.63 Granted 108,712 55.68 74,106 54.45 73,112 46.19 Vested (53,431) 64.04 (71,101) 47.48 — — Forfeited (11,600) 53.88 (9,161) 53.99 (5,839) 51.07 Nonvested awards, December 31 233,954 52.60 190,273 54.13 196,429 51.59
Restricted Stock Units Equity Awards [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: 2023 2022 2021 Units Weighted Units Weighted Units Weighted Nonvested units, January 1 198,275 $54.53 217,819 $50.54 146,549 $51.54 Granted 106,124 52.77 77,122 56.88 80,152 48.65 Vested (55,345) 59.40 (82,770) 46.08 — — Forfeited (14,795) 54.53 (13,896) 55.53 (8,882) 49.84 Nonvested units, December 31 234,259 52.58 198,275 54.53 217,819 50.54
Performance Restricted Stock Units Equity Awards [Member]
Defined Benefit Plan Disclosure [Line Items]
Schedule Of Equity-based Compensation Plans Activity	A summary of the performance restricted stock units activity, with amounts representing the target number of units, was as follows: 2023 2022 2021 Units Weighted Average Grant Date Fair Value Units Weighted Average Grant Date Fair Value Units Weighted Average Grant Date Fair Value Nonvested units, January 1 199,874 $54.74 196,429 $50.74 197,463 $47.31 Granted 124,217 52.71 84,670 57.01 73,112 48.66 Vested (53,431) 59.36 (71,101) 46.24 (68,307) 38.60 Forfeited (13,021) 55.47 (10,124) 55.92 (5,839) 50.46 Nonvested units, December 31 257,639 52.76 199,874 54.74 196,429 50.74

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	12 Months Ended
	Dec. 31, 2023
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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Balance, January 1 $279 $294 $195 $213 $84 $81 Revisions in estimated cash flows (6) 19 (9) 15 3 4 Liabilities settled (51) (48) (44) (39) (7) (9) Liabilities incurred 16 6 1 — 15 6 Accretion expense 8 8 5 6 3 2 Balance, December 31 $246 $279 $148 $195 $98 $84
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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Balance, January 1 $279 $294 $195 $213 $84 $81 Revisions in estimated cash flows (6) 19 (9) 15 3 4 Liabilities settled (51) (48) (44) (39) (7) (9) Liabilities incurred 16 6 1 — 15 6 Accretion expense 8 8 5 6 3 2 Balance, December 31 $246 $279 $148 $195 $98 $84
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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Balance, January 1 $279 $294 $195 $213 $84 $81 Revisions in estimated cash flows (6) 19 (9) 15 3 4 Liabilities settled (51) (48) (44) (39) (7) (9) Liabilities incurred 16 6 1 — 15 6 Accretion expense 8 8 5 6 3 2 Balance, December 31 $246 $279 $148 $195 $98 $84

Derivative Instruments (Tables)

Derivative Instruments (Tables)	12 Months Ended
	Dec. 31, 2023
Derivative [Line Items]
Notional Amounts of Derivative Instruments	As of December 31, 2023, 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): Electricity FTRs Natural Gas MWhs Years MWhs Years Dths Years Alliant Energy 1,640 2024-2026 11,927 2024 176,349 2024-2032 IPL 673 2024-2026 5,336 2024 74,360 2024-2030 WPL 967 2024-2026 6,591 2024 101,989 2024-2032
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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Current derivative assets $44 $111 $30 $69 $14 $42 Non-current derivative assets 44 126 24 69 20 57 Current derivative liabilities 51 59 22 40 29 19 Non-current derivative liabilities 47 20 8 6 39 14
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 Energy IPL WPL Gross Gross Gross (as reported) Net (as reported) Net (as reported) Net 2023 Derivative assets $88 $47 $54 $32 $34 $15 Derivative liabilities 98 57 30 8 68 49 2022 Derivative assets 237 193 138 108 99 85 Derivative liabilities 79 35 46 16 33 19
IPL [Member]
Derivative [Line Items]
Notional Amounts of Derivative Instruments	As of December 31, 2023, 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): Electricity FTRs Natural Gas MWhs Years MWhs Years Dths Years Alliant Energy 1,640 2024-2026 11,927 2024 176,349 2024-2032 IPL 673 2024-2026 5,336 2024 74,360 2024-2030 WPL 967 2024-2026 6,591 2024 101,989 2024-2032
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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Current derivative assets $44 $111 $30 $69 $14 $42 Non-current derivative assets 44 126 24 69 20 57 Current derivative liabilities 51 59 22 40 29 19 Non-current derivative liabilities 47 20 8 6 39 14
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 Energy IPL WPL Gross Gross Gross (as reported) Net (as reported) Net (as reported) Net 2023 Derivative assets $88 $47 $54 $32 $34 $15 Derivative liabilities 98 57 30 8 68 49 2022 Derivative assets 237 193 138 108 99 85 Derivative liabilities 79 35 46 16 33 19
WPL [Member]
Derivative [Line Items]
Notional Amounts of Derivative Instruments	As of December 31, 2023, 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): Electricity FTRs Natural Gas MWhs Years MWhs Years Dths Years Alliant Energy 1,640 2024-2026 11,927 2024 176,349 2024-2032 IPL 673 2024-2026 5,336 2024 74,360 2024-2030 WPL 967 2024-2026 6,591 2024 101,989 2024-2032
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 Energy IPL WPL 2023 2022 2023 2022 2023 2022 Current derivative assets $44 $111 $30 $69 $14 $42 Non-current derivative assets 44 126 24 69 20 57 Current derivative liabilities 51 59 22 40 29 19 Non-current derivative liabilities 47 20 8 6 39 14
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 Energy IPL WPL Gross Gross Gross (as reported) Net (as reported) Net (as reported) Net 2023 Derivative assets $88 $47 $54 $32 $34 $15 Derivative liabilities 98 57 30 8 68 49 2022 Derivative assets 237 193 138 108 99 85 Derivative liabilities 79 35 46 16 33 19

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2023
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Recurring Fair Value Measurements	Carrying amounts and the related estimated fair values of other financial instruments at December 31 were as follows (in millions): Alliant Energy 2023 2022 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $45 $45 $— $— $45 $10 $10 $— $— $10 Commodity derivatives 88 — 59 29 88 237 — 206 31 237 Interest rate derivatives 1 — 1 — 1 — — — — — Deferred proceeds 216 — — 216 216 185 — — 185 185 Liabilities and equity: Commodity derivatives 98 — 93 5 98 79 — 67 12 79 Long-term debt (incl. current maturities) 9,034 — 8,677 — 8,677 8,076 — 7,338 1 7,339 IPL 2023 2022 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $45 $45 $— $— $45 $10 $10 $— $— $10 Commodity derivatives 54 — 30 24 54 138 — 111 27 138 Deferred proceeds 216 — — 216 216 185 — — 185 185 Liabilities and equity: Commodity derivatives 30 — 25 5 30 46 — 35 11 46 Long-term debt (incl. current maturities) 3,945 — 3,664 — 3,664 3,646 — 3,228 — 3,228 WPL 2023 2022 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Commodity derivatives $34 $— $29 $5 $34 $99 $— $95 $4 $99 Liabilities and equity: Commodity derivatives 68 — 68 — 68 33 — 32 1 33 Long-term debt 3,070 — 2,933 — 2,933 2,770 — 2,542 — 2,542
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 Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds 2023 2022 2023 2022 Beginning balance, January 1 $19 $29 $185 $214 Total net gains (losses) included in changes in net assets (realized/unrealized) 3 (18) — — Purchases 62 79 — — Sales (3) (2) — — Settlements (a) (57) (69) 31 (29) Ending balance, December 31 $24 $19 $216 $185 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 ($18) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds 2023 2022 2023 2022 Beginning balance, January 1 $16 $18 $185 $214 Total net losses included in changes in net assets (realized/unrealized) (3) (12) — — Purchases 51 58 — — Sales (3) (1) — — Settlements (a) (42) (47) 31 (29) Ending balance, December 31 $19 $16 $216 $185 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 ($3) ($13) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net 2023 2022 Beginning balance, January 1 $3 $11 Total net gains (losses) included in changes in net assets (realized/unrealized) 6 (6) Purchases 11 21 Sales — (1) Settlements (a) (15) (22) Ending balance, December 31 $5 $3 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31 $6 ($5) (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 (liabilities) at December 31 as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs 2023 $3 $21 $3 $16 $— $5 2022 (10) 29 (9) 25 (1) 4
IPL [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Recurring Fair Value Measurements	Carrying amounts and the related estimated fair values of other financial instruments at December 31 were as follows (in millions): Alliant Energy 2023 2022 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $45 $45 $— $— $45 $10 $10 $— $— $10 Commodity derivatives 88 — 59 29 88 237 — 206 31 237 Interest rate derivatives 1 — 1 — 1 — — — — — Deferred proceeds 216 — — 216 216 185 — — 185 185 Liabilities and equity: Commodity derivatives 98 — 93 5 98 79 — 67 12 79 Long-term debt (incl. current maturities) 9,034 — 8,677 — 8,677 8,076 — 7,338 1 7,339 IPL 2023 2022 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $45 $45 $— $— $45 $10 $10 $— $— $10 Commodity derivatives 54 — 30 24 54 138 — 111 27 138 Deferred proceeds 216 — — 216 216 185 — — 185 185 Liabilities and equity: Commodity derivatives 30 — 25 5 30 46 — 35 11 46 Long-term debt (incl. current maturities) 3,945 — 3,664 — 3,664 3,646 — 3,228 — 3,228 WPL 2023 2022 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Commodity derivatives $34 $— $29 $5 $34 $99 $— $95 $4 $99 Liabilities and equity: Commodity derivatives 68 — 68 — 68 33 — 32 1 33 Long-term debt 3,070 — 2,933 — 2,933 2,770 — 2,542 — 2,542
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 Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds 2023 2022 2023 2022 Beginning balance, January 1 $19 $29 $185 $214 Total net gains (losses) included in changes in net assets (realized/unrealized) 3 (18) — — Purchases 62 79 — — Sales (3) (2) — — Settlements (a) (57) (69) 31 (29) Ending balance, December 31 $24 $19 $216 $185 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 ($18) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds 2023 2022 2023 2022 Beginning balance, January 1 $16 $18 $185 $214 Total net losses included in changes in net assets (realized/unrealized) (3) (12) — — Purchases 51 58 — — Sales (3) (1) — — Settlements (a) (42) (47) 31 (29) Ending balance, December 31 $19 $16 $216 $185 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 ($3) ($13) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net 2023 2022 Beginning balance, January 1 $3 $11 Total net gains (losses) included in changes in net assets (realized/unrealized) 6 (6) Purchases 11 21 Sales — (1) Settlements (a) (15) (22) Ending balance, December 31 $5 $3 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31 $6 ($5) (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 (liabilities) at December 31 as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs 2023 $3 $21 $3 $16 $— $5 2022 (10) 29 (9) 25 (1) 4
WPL [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Recurring Fair Value Measurements	Carrying amounts and the related estimated fair values of other financial instruments at December 31 were as follows (in millions): Alliant Energy 2023 2022 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $45 $45 $— $— $45 $10 $10 $— $— $10 Commodity derivatives 88 — 59 29 88 237 — 206 31 237 Interest rate derivatives 1 — 1 — 1 — — — — — Deferred proceeds 216 — — 216 216 185 — — 185 185 Liabilities and equity: Commodity derivatives 98 — 93 5 98 79 — 67 12 79 Long-term debt (incl. current maturities) 9,034 — 8,677 — 8,677 8,076 — 7,338 1 7,339 IPL 2023 2022 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Money market fund investments $45 $45 $— $— $45 $10 $10 $— $— $10 Commodity derivatives 54 — 30 24 54 138 — 111 27 138 Deferred proceeds 216 — — 216 216 185 — — 185 185 Liabilities and equity: Commodity derivatives 30 — 25 5 30 46 — 35 11 46 Long-term debt (incl. current maturities) 3,945 — 3,664 — 3,664 3,646 — 3,228 — 3,228 WPL 2023 2022 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Commodity derivatives $34 $— $29 $5 $34 $99 $— $95 $4 $99 Liabilities and equity: Commodity derivatives 68 — 68 — 68 33 — 32 1 33 Long-term debt 3,070 — 2,933 — 2,933 2,770 — 2,542 — 2,542
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 Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds 2023 2022 2023 2022 Beginning balance, January 1 $19 $29 $185 $214 Total net gains (losses) included in changes in net assets (realized/unrealized) 3 (18) — — Purchases 62 79 — — Sales (3) (2) — — Settlements (a) (57) (69) 31 (29) Ending balance, December 31 $24 $19 $216 $185 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 ($18) $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds 2023 2022 2023 2022 Beginning balance, January 1 $16 $18 $185 $214 Total net losses included in changes in net assets (realized/unrealized) (3) (12) — — Purchases 51 58 — — Sales (3) (1) — — Settlements (a) (42) (47) 31 (29) Ending balance, December 31 $19 $16 $216 $185 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 ($3) ($13) $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net 2023 2022 Beginning balance, January 1 $3 $11 Total net gains (losses) included in changes in net assets (realized/unrealized) 6 (6) Purchases 11 21 Sales — (1) Settlements (a) (15) (22) Ending balance, December 31 $5 $3 The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31 $6 ($5) (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 (liabilities) at December 31 as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs 2023 $3 $21 $3 $16 $— $5 2022 (10) 29 (9) 25 (1) 4

Commitments And Contingencies (

Commitments And Contingencies (Tables)	12 Months Ended
	Dec. 31, 2023
Long-term Purchase Commitment [Line Items]
Other Purchase Commitments	At December 31, 2023, 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 Energy 2024 2025 2026 2027 2028 Thereafter Total Natural gas $301 $187 $123 $78 $49 $142 $880 Coal 94 49 8 8 6 — 165 Other (a) 61 17 14 9 2 22 125 $456 $253 $145 $95 $57 $164 $1,170 IPL 2024 2025 2026 2027 2028 Thereafter Total Natural gas $165 $86 $47 $35 $14 $25 $372 Coal 49 35 8 8 6 — 106 Other (a) 23 2 2 2 2 22 53 $237 $123 $57 $45 $22 $47 $531 WPL 2024 2025 2026 2027 2028 Thereafter Total Natural gas $136 $101 $76 $43 $35 $117 $508 Coal 45 14 — — — — 59 Other (a) 23 1 1 — — — 25 $204 $116 $77 $43 $35 $117 $592 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2023.
Schedule of Environmental Liabilities	At December 31, 2023, 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 Energy IPL WPL Range of estimated future costs $9 - $36 $5 - $11 $4 - $25 Current and non-current environmental liabilities $18 $8 $10
IPL [Member]
Long-term Purchase Commitment [Line Items]
Other Purchase Commitments	At December 31, 2023, 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 Energy 2024 2025 2026 2027 2028 Thereafter Total Natural gas $301 $187 $123 $78 $49 $142 $880 Coal 94 49 8 8 6 — 165 Other (a) 61 17 14 9 2 22 125 $456 $253 $145 $95 $57 $164 $1,170 IPL 2024 2025 2026 2027 2028 Thereafter Total Natural gas $165 $86 $47 $35 $14 $25 $372 Coal 49 35 8 8 6 — 106 Other (a) 23 2 2 2 2 22 53 $237 $123 $57 $45 $22 $47 $531 WPL 2024 2025 2026 2027 2028 Thereafter Total Natural gas $136 $101 $76 $43 $35 $117 $508 Coal 45 14 — — — — 59 Other (a) 23 1 1 — — — 25 $204 $116 $77 $43 $35 $117 $592 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2023.
Schedule of Environmental Liabilities	At December 31, 2023, 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 Energy IPL WPL Range of estimated future costs $9 - $36 $5 - $11 $4 - $25 Current and non-current environmental liabilities $18 $8 $10
WPL [Member]
Long-term Purchase Commitment [Line Items]
Other Purchase Commitments	At December 31, 2023, 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 Energy 2024 2025 2026 2027 2028 Thereafter Total Natural gas $301 $187 $123 $78 $49 $142 $880 Coal 94 49 8 8 6 — 165 Other (a) 61 17 14 9 2 22 125 $456 $253 $145 $95 $57 $164 $1,170 IPL 2024 2025 2026 2027 2028 Thereafter Total Natural gas $165 $86 $47 $35 $14 $25 $372 Coal 49 35 8 8 6 — 106 Other (a) 23 2 2 2 2 22 53 $237 $123 $57 $45 $22 $47 $531 WPL 2024 2025 2026 2027 2028 Thereafter Total Natural gas $136 $101 $76 $43 $35 $117 $508 Coal 45 14 — — — — 59 Other (a) 23 1 1 — — — 25 $204 $116 $77 $43 $35 $117 $592 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at December 31, 2023.

Segments Of Business (Tables)

Segments Of Business (Tables)	12 Months Ended
	Dec. 31, 2023
Segment Reporting Information [Line Items]
Schedule of Segments of Business	Certain financial information relating to Alliant Energy’s business segments, which represent the services provided to its customers, was as follows (in millions): ATC Holdings, Utility Non-utility, Alliant Energy 2023 Electric Gas Other Total Parent and Other Consolidated Revenues $3,345 $540 $52 $3,937 $90 $4,027 Depreciation and amortization 602 60 6 668 8 676 Operating income 827 70 19 916 27 943 Interest expense 304 90 394 Equity income from unconsolidated investments, net (3) — — (3) (58) (61) Income taxes 2 2 4 Net income (loss) attributable to Alliant Energy common shareowners 711 (8) 703 Total assets 17,833 1,684 606 20,123 1,114 21,237 Investments in equity method subsidiaries 21 — — 21 564 585 Construction and acquisition expenditures 1,641 90 — 1,731 123 1,854 ATC Holdings, Utility Non-utility, Alliant Energy 2022 Electric Gas Other Total Parent and Other Consolidated Revenues $3,421 $642 $49 $4,112 $93 $4,205 Depreciation and amortization 601 56 7 664 7 671 Operating income 805 97 3 905 23 928 Interest expense 269 56 325 Equity income from unconsolidated investments, net (1) — — (1) (50) (51) Income taxes 16 6 22 Net income attributable to Alliant Energy common shareowners 675 11 686 Total assets 16,571 1,631 860 19,062 1,101 20,163 Investments in equity method subsidiaries 20 — — 20 522 542 Construction and acquisition expenditures 1,318 74 — 1,392 92 1,484 ATC Holdings, Utility Non-utility, Alliant Energy 2021 Electric Gas Other Total Parent and Other Consolidated Revenues $3,081 $456 $49 $3,586 $83 $3,669 Depreciation and amortization 591 54 6 651 6 657 Operating income (loss) 716 63 (11) 768 27 795 Interest expense 244 33 277 Equity income from unconsolidated investments, net (2) — — (2) (60) (62) Income tax expense (benefit) (87) 13 (74) Net income attributable to Alliant Energy common shareowners 618 41 659 Total assets 14,924 1,487 1,103 17,514 1,039 18,553 Investments in equity method subsidiaries 17 — — 17 491 508 Construction and acquisition expenditures 980 90 — 1,070 99 1,169
IPL [Member]
Segment Reporting Information [Line Items]
Schedule of Segments of Business	Certain financial information relating to IPL’s business segments, which represent the services provided to its customers, was as follows (in millions): 2023 Electric Gas Other Total Revenues $1,761 $300 $49 $2,110 Depreciation and amortization 348 34 6 388 Operating income 390 35 19 444 Interest expense 155 Income tax benefit (58) Net income available for common stock 366 Total assets 9,311 921 257 10,489 Construction and acquisition expenditures 671 41 — 712 2022 Electric Gas Other Total Revenues $1,859 $351 $46 $2,256 Depreciation and amortization 342 32 7 381 Operating income 397 53 3 453 Interest expense 148 Income tax benefit (50) Net income available for common stock 360 Total assets 8,686 872 517 10,075 Construction and acquisition expenditures 336 36 — 372 2021 Electric Gas Other Total Revenues $1,752 $265 $46 $2,063 Depreciation and amortization 338 31 6 375 Operating income (loss) 420 43 (3) 460 Interest expense 139 Income tax benefit (36) Net income available for common stock 350 Total assets 8,602 819 575 9,996 Construction and acquisition expenditures 342 42 — 384
WPL [Member]
Segment Reporting Information [Line Items]
Schedule of Segments of Business	Certain financial information relating to WPL’s business segments, which represent the services provided to its customers, was as follows (in millions): 2023 Electric Gas Other Total Revenues $1,584 $240 $3 $1,827 Depreciation and amortization 254 26 — 280 Operating income 437 35 — 472 Interest expense 149 Income taxes 60 Net income 345 Total assets 8,522 763 349 9,634 Construction and acquisition expenditures 970 49 — 1,019 2022 Electric Gas Other Total Revenues $1,562 $291 $3 $1,856 Depreciation and amortization 259 24 — 283 Operating income 408 44 — 452 Interest expense 121 Income taxes 66 Net income 315 Total assets 7,885 759 343 8,987 Construction and acquisition expenditures 982 38 — 1,020 2021 Electric Gas Other Total Revenues $1,329 $191 $3 $1,523 Depreciation and amortization 253 23 — 276 Operating income (loss) 296 20 (8) 308 Interest expense 105 Income tax benefit (51) Net income 268 Total assets 6,322 668 528 7,518 Construction and acquisition expenditures 638 48 — 686

Related Parties (Tables)

Related Parties (Tables)	12 Months Ended
	Dec. 31, 2023
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): IPL WPL 2023 2022 2021 2023 2022 2021 Corporate Services billings $181 $181 $180 $163 $155 $154 Sales credited 11 19 22 55 74 23 Purchases billed 431 435 441 35 174 116
Net Intercompany Payables	As of December 31, net intercompany payables to Corporate Services were as follows (in millions): 2023 2022 IPL $129 $103 WPL 72 56
Related Amounts Billed Between Parties	The related amounts billed between the parties were as follows (in millions): 2023 2022 2021 ATC billings to WPL $159 $140 $122 WPL billings to ATC 20 18 18
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): IPL WPL 2023 2022 2021 2023 2022 2021 Corporate Services billings $181 $181 $180 $163 $155 $154 Sales credited 11 19 22 55 74 23 Purchases billed 431 435 441 35 174 116
Net Intercompany Payables	As of December 31, net intercompany payables to Corporate Services were as follows (in millions): 2023 2022 IPL $129 $103 WPL 72 56
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): IPL WPL 2023 2022 2021 2023 2022 2021 Corporate Services billings $181 $181 $180 $163 $155 $154 Sales credited 11 19 22 55 74 23 Purchases billed 431 435 441 35 174 116
Net Intercompany Payables	As of December 31, net intercompany payables to Corporate Services were as follows (in millions): 2023 2022 IPL $129 $103 WPL 72 56
Related Amounts Billed Between Parties	The related amounts billed between the parties were as follows (in millions): 2023 2022 2021 ATC billings to WPL $159 $140 $122 WPL billings to ATC 20 18 18

Condensed Parent Company Fina_2

Condensed Parent Company Financial Statements (Tables)	12 Months Ended
	Dec. 31, 2023
Condensed Financial Information Disclosure [Abstract]
Condensed Statements of Income	ALLIANT ENERGY CORPORATION (Parent Company Only) Year Ended December 31, CONDENSED STATEMENTS OF INCOME 2023 2022 2021 (in millions) Operating expenses $3 $9 $5 Operating loss (3) (9) (5) Other (income) and deductions: Equity earnings from consolidated subsidiaries (742) (707) (664) Interest expense 34 6 1 Other 4 1 1 Total other (income) and deductions (704) (700) (662) Income before income taxes 701 691 657 Income tax expense (benefit) (5) 2 (5) Net income $706 $689 $662 Refer to accompanying Notes to Condensed Financial Statements.
Condensed Balance Sheets	ALLIANT ENERGY CORPORATION (Parent Company Only) December 31, CONDENSED BALANCE SHEETS 2023 2022 (in millions) ASSETS Current assets: Notes receivable from affiliated companies $96 $65 Other 1 1 Total current assets 97 66 Investments: Investments in consolidated subsidiaries 8,405 7,801 Other 2 2 Total investments 8,407 7,803 Other assets 90 97 Total assets $8,594 $7,966 LIABILITIES AND EQUITY Current liabilities: Commercial paper $157 $352 Notes payable to affiliated companies 1,068 1,318 Other 10 10 Total current liabilities 1,235 1,680 Long-term debt, net 568 — Other liabilities 2 1 Common equity: Common stock and additional paid-in capital 3,033 2,780 Retained earnings 3,768 3,518 Accumulated other comprehensive income 1 — Shares in deferred compensation trust (13) (13) Total common equity 6,789 6,285 Total liabilities and equity $8,594 $7,966 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 FLOWS 2023 2022 2021 (in millions) Net cash flows from operating activities $445 $492 $494 Cash flows used for investing activities: Capital contributions to consolidated subsidiaries (325) (530) (295) Net change in notes receivable from and payable to affiliates (281) 369 (21) Dividends from consolidated subsidiaries in excess of equity earnings — — 50 Net cash flows used for investing activities (606) (161) (266) Cash flows from (used for) financing activities: Common stock dividends (456) (428) (403) Proceeds from issuance of common stock, net 246 25 28 Proceeds from issuance of long-term debt 565 — — Net change in commercial paper (195) 73 147 Other 1 (1) — Net cash flows from (used for) financing activities 161 (331) (228) 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) refunded during the period for: Interest ($27) ($6) ($1) Income taxes, net $22 $15 $4 Refer to accompanying Notes to Condensed Financial Statements.

Summary Of Significant Accoun_4

Summary Of Significant Accounting Policies (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($) customer MW	Dec. 31, 2022 USD ($)
Cash, Cash Equivalents and Restricted Cash:
Money market fund investments | $	$ 45	$ 10
Money market fund investments interest rate, percentage	5%
Non-utility wind farm in Oklahoma [Member]
General:
Ownership interest	50%
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 | $	$ 45	$ 10
Money market fund investments interest rate, percentage	5%
Property, Plant and Equipment:
AFUDC accrual recorded, percentage of estimated CWIP	100%
WPL [Member]
Property, Plant and Equipment:
AFUDC accrual recorded, percentage of estimated CWIP	50%
AFUDC accrual recorded, percentage earning a return as part of rate base	50%
AFUDC rates, projects with approval	100%
Alliant Energy Finance, LLC [Member]
General:
Electric capacity of wind farm (in megawatts) | MW	225
Alliant Energy Finance, LLC [Member] | Non-utility wind farm in Oklahoma [Member]
General:
Ownership interest	50%
Sheboygan Falls Energy Facility [Member]
General:
Fossil-fueled EGU capacity (in megawatts) | MW	347

Summary Of Significant Accoun_5

Summary Of Significant Accounting Policies (Schedule Of Average Rates Of Depreciation) (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Electric - generation [Member] | IPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	3.30%	3.40%	3.40%
Electric - generation [Member] | WPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	3%	3.40%	3.50%
Electric - distribution [Member] | IPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	2.80%	2.80%	2.90%
Electric - distribution [Member] | WPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	2.70%	2.50%	2.60%
Electric - other [Member] | IPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	5.60%	5.70%	5.70%
Electric - other [Member] | WPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	6.30%	6.80%	7.40%
Gas [Member] | IPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	3.30%	3.30%	3.30%
Gas [Member] | WPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	2.50%	2.40%	2.40%
Other [Member] | IPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	6.20%	6.10%	6.10%
Other [Member] | WPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	4.60%	4.90%	5.40%

Summary Of Significant Accoun_6

Summary Of Significant Accounting Policies (Schedule Of Allowance For Funds Used During Construction Recovery Rate) (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
IPL [Member] | IPL (Wind generation CWIP) [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Recovery rates	6.90%	6.90%	7%
IPL [Member] | IPL (other CWIP) [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Recovery rates	7%	7%	7.20%
WPL [Member] | WPL (retail jurisdiction) [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Recovery rates	7.40%	7%	7%
WPL [Member] | WPL (wholesale jurisdiction) [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Recovery rates	7.10%	6.20%	5.60%

Regulatory Matters (Narrative)

Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Regulatory Matters [Line Items]
Regulatory assets			$ 2,261	$ 2,046
Collected from retail electric customers			3,345	3,421	$ 3,081
Regulatory liabilities			1,130	1,324
IPL [Member]
Regulatory Matters [Line Items]
Regulatory assets not earning a return			74
Regulatory assets			1,577	1,386
Collected from retail electric customers			1,761	1,859	1,752
Regulatory liabilities			644	754
WPL [Member]
Regulatory Matters [Line Items]
Regulatory assets not earning a return			32
Regulatory assets			684	660
Collected from retail electric customers			1,584	1,562	$ 1,329
Regulatory liabilities			486	570
2021 Test Period Fuel-related Costs [Member] | WPL [Member]
Regulatory Matters [Line Items]
Regulatory assets				37
2022 Test Period Fuel-related Costs [Member] | WPL [Member]
Regulatory Matters [Line Items]
Regulatory assets				117
Collected from retail electric customers			12
2023 Test Period Fuel-related Costs | WPL [Member]
Regulatory Matters [Line Items]
Regulatory liabilities			34
2022 Test Period Retail Electric [Member] | WPL [Member]
Regulatory Matters [Line Items]
Authorized increase (decrease) in final rates, amount				114
2022 Test Period Retail Gas [Member] | WPL [Member]
Regulatory Matters [Line Items]
Authorized increase (decrease) in final rates, amount				$ 15
2023 Test Period Retail Gas [Member] | WPL [Member]
Regulatory Matters [Line Items]
Authorized increase (decrease) in final rates, amount			$ 9
DAEC PPA [Member]
Regulatory Matters [Line Items]
Buyout payment						$ 110
PPA term amendment			5 years
Forecast [Member] | 2024 Test Period Retail Electric [Member] | WPL [Member]
Regulatory Matters [Line Items]
Authorized increase (decrease) in final rates, amount		$ 49
Forecast [Member] | 2024 Test Period Retail Gas [Member] | WPL [Member]
Regulatory Matters [Line Items]
Authorized increase (decrease) in final rates, amount		$ 13
Forecast [Member] | 2025 Test Period Retail Electric [Member] | WPL [Member]
Regulatory Matters [Line Items]
Authorized increase (decrease) in final rates, amount	$ 60

Regulatory Matters (Regulatory

Regulatory Matters (Regulatory Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Regulatory Assets [Line Items]
Regulatory assets	$ 2,261	$ 2,046
Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	934	929
Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	347	392
Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	273	70
AROs [Member]
Regulatory Assets [Line Items]
Regulatory assets	194	151
Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	120	160
Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	102	84
WPL's Western Wisconsin gas distribution expansion investments [Member]
Regulatory Assets [Line Items]
Regulatory assets	44	48
IPL's DAEC PPA amendment [Member]
Regulatory Assets [Line Items]
Regulatory assets	42	66
Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	205	146
IPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,577	1,386
IPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	831	848
IPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	171	197
IPL [Member] | Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	259	53
IPL [Member] | AROs [Member]
Regulatory Assets [Line Items]
Regulatory assets	160	110
IPL [Member] | Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	12	1
IPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	34	48
IPL [Member] | IPL's DAEC PPA amendment [Member]
Regulatory Assets [Line Items]
Regulatory assets	42	66
IPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	68	63
WPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	684	660
WPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	103	81
WPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	176	195
WPL [Member] | Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	14	17
WPL [Member] | AROs [Member]
Regulatory Assets [Line Items]
Regulatory assets	34	41
WPL [Member] | Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	108	159
WPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	68	36
WPL [Member] | WPL's Western Wisconsin gas distribution expansion investments [Member]
Regulatory Assets [Line Items]
Regulatory assets	44	48
WPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 137	$ 83

Regulatory Matters (Assets Reti

Regulatory Matters (Assets Retired Early) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Regulatory Assets [Line Items]
Regulatory assets	$ 2,261	$ 2,046
Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	273	70
IPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,577	1,386
IPL [Member] | Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	259	53
IPL [Member] | Assets retired early [Member] | Lansing [Member]
Regulatory Assets [Line Items]
Regulatory assets	216
IPL [Member] | Assets retired early [Member] | Analog Electric Meters [Member]
Regulatory Assets [Line Items]
Regulatory assets	20
IPL [Member] | Assets retired early [Member] | Sutherland Units 1 and 3 [Member]
Regulatory Assets [Line Items]
Regulatory assets	12
IPL [Member] | Assets retired early [Member] | M.L. Kapp Unit 2 [Member]
Regulatory Assets [Line Items]
Regulatory assets	11
WPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	684	660
WPL [Member] | Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	14	$ 17
WPL [Member] | Assets retired early [Member] | Edgewater Unit 4 [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 14

Regulatory Matters (Regulator_2

Regulatory Matters (Regulatory Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 1,130	$ 1,324
Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	566	579
Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	366	398
Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	65	210
Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	48	40
West Riverside liquidated damages [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	1	32
Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	84	65
IPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	644	754
IPL [Member] | Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	299	303
IPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	242	259
IPL [Member] | Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	34	115
IPL [Member] | Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	13	38
IPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	56	39
WPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	486	570
WPL [Member] | Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	267	276
WPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	124	139
WPL [Member] | Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	31	95
WPL [Member] | Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	35	2
WPL [Member] | West Riverside liquidated damages [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	1	32
WPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 28	$ 26

Property, Plant and Equipment_2

Property, Plant and Equipment (Narrative) (Details)	Dec. 31, 2023
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
Customer Billing And Information System [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	12 years
Software [Member]
Property, Plant and Equipment [Line Items]
Property, plant and equipment, useful life	5 years

Property, Plant and Equipment_3

Property, Plant and Equipment (Property, Plant and Equipment) (Details) $ in Millions	Dec. 31, 2023 USD ($) MW	Dec. 31, 2022 USD ($)
Property, Plant and Equipment [Line Items]
Electric plant anticipated to be retired early	$ 1,629	$ 2,103
Total electric plant	18,690	17,618
Gas plant in service	1,791	1,705
Other plant in service	653	624
Accumulated depreciation	(5,924)	(5,690)
Net plant	15,210	14,257
Leased land for solar generation, net	172	133
Construction work in progress	1,245	1,357
Other, net	7	6
Total utility	16,634	15,753
Non-utility Generation, net	68	71
Corporate Services and other, net	455	423
Total non-utility and other	523	494
Total property, plant and equipment	17,157	16,247
Non-utility Generation, accumulated depreciation	75	71
Corporate Services and other, accumulated depreciation	275	269
Generation [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service	9,180	8,060
Distribution [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service	7,314	6,912
Other [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service	567	543
IPL [Member]
Property, Plant and Equipment [Line Items]
Electric plant anticipated to be retired early	0	491
Total electric plant	9,472	9,683
Gas plant in service	951	910
Other plant in service	411	402
Accumulated depreciation	(3,180)	(3,149)
Net plant	7,654	7,846
Leased land for solar generation, net	33	0
Construction work in progress	605	194
Other, net	6	6
Total utility	8,298	8,046
Total property, plant and equipment	$ 8,298	8,046
Electric capacity of solar project | MW	400
Construction project cost target	$ 1,650
Construction project cost target exceedance, percentage	10%
IPL [Member] | Generation [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service	$ 5,025	4,962
IPL [Member] | Distribution [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service	4,091	3,876
IPL [Member] | Other [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service	356	354
WPL [Member]
Property, Plant and Equipment [Line Items]
Electric plant anticipated to be retired early	1,629	1,612
Total electric plant	9,218	7,935
Gas plant in service	840	795
Other plant in service	242	222
Accumulated depreciation	(2,744)	(2,541)
Net plant	7,556	6,411
Leased Sheboygan Falls Energy Facility, net	79	15
Leased land for solar generation, net	139	133
Construction work in progress	640	1,163
Other, net	1	0
Total utility	8,415	7,722
Total property, plant and equipment	$ 8,415	7,722
Electric capacity of solar project | MW	1,100
Construction project cost target exceedance	$ 180
Leased Sheboygan Falls Energy Facility, accumulated depreciation	112	106
WPL [Member] | Edgewater Unit 5 [Member]
Property, Plant and Equipment [Line Items]
Electric plant anticipated to be retired early	504
WPL [Member] | Columbia Units 1-2 [Member]
Property, Plant and Equipment [Line Items]
Electric plant anticipated to be retired early	428
WPL [Member] | Generation [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service	4,155	3,098
WPL [Member] | Distribution [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service	3,223	3,036
WPL [Member] | Other [Member]
Property, Plant and Equipment [Line Items]
Electric plant in service	$ 211	$ 189

Property, Plant and Equipment_4

Property, Plant and Equipment (Equity and Debt AFUDC) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	$ 100	$ 60	$ 25
Equity [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	74	44	18
Debt [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	26	16	7
IPL [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	21	11	9
IPL [Member] | Equity [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	15	8	7
IPL [Member] | Debt [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	6	3	2
WPL [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	79	49	16
WPL [Member] | Equity [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	59	36	11
WPL [Member] | Debt [Member]
Property, Plant and Equipment [Line Items]
Allowance for funds used during construction	$ 20	$ 13	$ 5

Jointly-Owned Electric Utilit_3

Jointly-Owned Electric Utility Plant (Details) $ in Millions	Dec. 31, 2023 USD ($)
Jointly Owned Electric Utility Plant [Line Items]
Electric Plant	$ 2,570
Accumulated Provision for Depreciation	952
Construction Work in Progress	33
IPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Electric Plant	1,053
Accumulated Provision for Depreciation	478
Construction Work in Progress	21
WPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Electric Plant	1,517
Accumulated Provision for Depreciation	474
Construction Work in Progress	$ 12
Ottumwa Unit 1 [Member] | IPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Ownership Interest %	48%
Electric Plant	$ 632
Accumulated Provision for Depreciation	264
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	$ 196
Accumulated Provision for Depreciation	107
Construction Work in Progress	$ 6
George Neal Unit 3 [Member] | IPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Ownership Interest %	28%
Electric Plant	$ 181
Accumulated Provision for Depreciation	85
Construction Work in Progress	$ 8
Louisa Unit 1 [Member] | IPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Ownership Interest %	4%
Electric Plant	$ 44
Accumulated Provision for Depreciation	22
Construction Work in Progress	$ 0
Columbia Units 1-2 [Member] | WPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Ownership Interest %	53.50%
Electric Plant	$ 818
Accumulated Provision for Depreciation	361
Construction Work in Progress	$ 6
West Riverside Energy Center and Solar Facility [Member] | WPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Ownership Interest %	73.80%
Electric Plant	$ 581
Accumulated Provision for Depreciation	60
Construction Work in Progress	$ 6
Forward Wind Energy Center [Member] | WPL [Member]
Jointly Owned Electric Utility Plant [Line Items]
Ownership Interest %	42.60%
Electric Plant	$ 118
Accumulated Provision for Depreciation	53
Construction Work in Progress	$ 0

Receivables (Narrative) (Detail

Receivables (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
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
Maximum [Member] | Subsequent Event
Receivables [Line Items]
Limit on cash proceeds to be received from third-party	$ 110
Receivables Sold [Member] | IPL [Member]
Receivables [Line Items]
Available capacity		$ 4

Receivables (Details of Account

Receivables (Details of Accounts Receivable) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Receivables [Line Items]
Customer	$ 121	$ 114
Unbilled utility revenues	93	115
Deferred proceeds	216	185
Other	53	109
Allowance for expected credit losses	(8)	(7)
Accounts receivable, less allowance for expected credit losses	475	516
IPL [Member]
Receivables [Line Items]
Customer	0	0
Unbilled utility revenues	0	0
Deferred proceeds	216	185
Other	26	74
Allowance for expected credit losses	0	0
Accounts receivable, less allowance for expected credit losses	242	259
WPL [Member]
Receivables [Line Items]
Customer	110	102
Unbilled utility revenues	93	115
Other	24	34
Allowance for expected credit losses	(8)	(7)
Accounts receivable, less allowance for expected credit losses	$ 219	$ 244

Receivables (Gross Write-offs f

Receivables (Gross Write-offs for Accounts Receivable (Details) $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($)
Financing Receivable, Credit Quality Indicator [Line Items]
Gross write-offs for accounts receivable, originated in 2022	$ 12
Gross write-offs for accounts receivable, originated in 2023	13
IPL [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Gross write-offs for accounts receivable, originated in 2022	8
Gross write-offs for accounts receivable, originated in 2023	8
WPL [Member]
Financing Receivable, Credit Quality Indicator [Line Items]
Gross write-offs for accounts receivable, originated in 2022	4
Gross write-offs for accounts receivable, originated in 2023	$ 5

Receivables (Maximum And Averag

Receivables (Maximum And Average Outstanding Cash Proceeds) (Details) - IPL [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Maximum [Member]
Receivables [Line Items]
Outstanding aggregate cash proceeds (based on daily outstanding balances)	$ 110	$ 80	$ 110
Average [Member]
Receivables [Line Items]
Outstanding aggregate cash proceeds (based on daily outstanding balances)	$ 51	$ 14	$ 46

Receivables (Receivables Sold U

Receivables (Receivables Sold Under The Agreement) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Receivables [Line Items]
Fair value of deferred proceeds	$ 216	$ 185
IPL [Member]
Receivables [Line Items]
Fair value of deferred proceeds	216	185
Receivables Sold [Member] | IPL [Member]
Receivables [Line Items]
Customer accounts receivable	130	145
Unbilled utility revenues	98	132
Other receivables	1	0
Receivables sold to third party	229	277
Less: cash proceeds	1	80
Deferred proceeds	228	197
Less: allowance for expected credit losses	12	12
Fair value of deferred proceeds	216	185
Outstanding receivables past due	$ 22	$ 26

Receivables (Additional Attribu

Receivables (Additional Attributes Of Receivables Sold Under The Agreement) (Details) - IPL [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Receivables [Line Items]
Collections	$ 2,233	$ 2,302	$ 2,134
Write-offs, net of recoveries	$ 12	$ 9	$ 9

Investments (Narrative) (Detail

Investments (Narrative) (Details)	Dec. 31, 2023
ATC LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest	16%
ATC Holdco LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest	20%

Investments (Unconsolidated Equ

Investments (Unconsolidated Equity Investments) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Schedule of Equity Method Investments [Line Items]
Carrying value	$ 585	$ 542	$ 508
Equity (income) / loss	(61)	(51)	(62)
ATC Holdings [Member]
Schedule of Equity Method Investments [Line Items]
Carrying value	386	358
Equity (income) / loss	$ (49)	(41)	(43)
ATC LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest	16%
ATC Holdco LLC [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest	20%
Non-utility wind farm in Oklahoma [Member]
Schedule of Equity Method Investments [Line Items]
Ownership interest	50%
Carrying value	$ 104	101
Equity (income) / loss	(7)	(5)	(4)
Corporate venture investments [Member]
Schedule of Equity Method Investments [Line Items]
Carrying value	74	62
Equity (income) / loss	(2)	(3)	(13)
Other [Member]
Schedule of Equity Method Investments [Line Items]
Carrying value	21	21
Equity (income) / loss	(3)	(2)	(2)
Total [Member]
Schedule of Equity Method Investments [Line Items]
Carrying value	585	542
Equity (income) / loss	$ (61)	$ (51)	$ (62)

Investments (Summary Financial

Investments (Summary Financial Information) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Revenues	$ 4,027	$ 4,205	$ 3,669
Current assets	1,272	1,250
Current liabilities	2,304	2,363
Equity Method Investment, Nonconsolidated Investee or Group of Investees [Member]
Revenues	898	813	802
Operating income	384	350	357
Net income	370	675	$ 358
Current assets	221	227
Non-current assets	9,032	8,292
Current liabilities	528	620
Non-current liabilities	3,584	3,285
Noncontrolling interest	$ 259	$ 289

Common Equity (Narrative) (Deta

Common Equity (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Schedule of Common Equity [Line Items]
Shares available for issuance under the 2020 OIP, Shareowner Direct Plan and 401(k) Savings Plan (in shares)	13,000,000
Proceeds from issuance of common stock, net	$ 246	$ 25	$ 28
At-the-market Offering Program [Member]
Schedule of Common Equity [Line Items]
Proceeds from issuance of common stock, net	$ 223	$ 225
Common stock issued during the period, At-the-market offering program (in shares)	4,372,561	0	0
Fees and commissions from issuance of common stock	$ 2

Common Equity (Common Share Act

Common Equity (Common Share Activity) (Details) - shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Common Stock Oustanding [Roll Forward]
Shares outstanding, January 1 (in shares)	251,134,966	250,474,529	249,868,415
Common stock issued during the period, Shareowner Direct Plan (in shares)	454,987	437,669	492,565
Common stock issued during the period, Equity-based compensation plans (in shares)	134,334	222,768	113,549
Shares outstanding, December 31 (in shares)	256,096,848	251,134,966	250,474,529
At-the-market Offering Program [Member]
Common Stock Oustanding [Roll Forward]
Common stock issued during the period, At-the-market offering program (in shares)	4,372,561	0	0

Preferred Stock (Narrative) (De

Preferred Stock (Narrative) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Temporary Equity [Line Items]
Redemption of IPL's cumulative preferred stock	$ 0	$ 0	$ 200
IPL [Member]
Temporary Equity [Line Items]
Redemption of IPL's cumulative preferred stock	$ 0	$ 0	200
IPL [Member] | Cumulative Preferred Stock [Member]
Temporary Equity [Line Items]
Shares outstanding (in shares)				8,000
Cumulative preferred stock rate				5.10%
Preferred stock redemption price per share (in dollars per share)				$ 25
Redemption of IPL's cumulative preferred stock			200
Non-cash charge, preferred stock redemption			$ 5

Debt (Narrative) (Details)

Debt (Narrative) (Details)	12 Months Ended
	Dec. 31, 2023 USD ($) Integer $ / shares shares	Dec. 31, 2024 USD ($)	Dec. 31, 2022 USD ($)
Debt Instrument [Line Items]
Line of credit facility, current borrowing capacity	$ 1,000,000,000
Long-term debt	9,109,000,000		$ 8,143,000,000
Long-term debt, fair value	$ 8,677,000,000		7,339,000,000
Subsequent Event
Debt Instrument [Line Items]
Line of credit facility, current borrowing capacity		$ 350,000,000
Convertible Debt
Debt Instrument [Line Items]
Trading days | Integer	20
Trading days consecutive | Integer	30
3.875% senior notes, due 2026 [Member] | Convertible Debt
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%
Long-term debt, carrying value	$ 568,000,000
Unamortized debt issuance costs	7,000,000
Long-term debt, fair value	$ 572,000,000
Shares included in diluted earnings per share (in shares) | shares	0
3.875% senior notes, due 2026 [Member] | Convertible Debt | Maximum [Member]
Debt Instrument [Line Items]
Conversion price, percent	130%
Parent Company [Member]
Debt Instrument [Line Items]
Line of credit facility, current borrowing capacity	$ 450,000,000
IPL [Member]
Debt Instrument [Line Items]
Line of credit facility, current borrowing capacity	150,000,000
Long-term debt	3,975,000,000		3,675,000,000
Long-term debt, fair value	3,664,000,000		3,228,000,000
IPL [Member] | Subsequent Event
Debt Instrument [Line Items]
Line of credit facility, current borrowing capacity		150,000,000
WPL [Member]
Debt Instrument [Line Items]
Line of credit facility, current borrowing capacity	400,000,000
Long-term debt	3,100,000,000		2,800,000,000
Long-term debt, fair value	$ 2,933,000,000		$ 2,542,000,000
WPL [Member] | Subsequent Event
Debt Instrument [Line Items]
Line of credit facility, current borrowing capacity		500,000,000
Forecast [Member] | Parent Company [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum borrowing capacity		500,000,000
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

Debt (Credit Facilities) (Detai

Debt (Credit Facilities) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Commercial paper and borrowings under the single credit facility:
Amount outstanding	$ 475	$ 642
Weighted average interest rates	5.50%	4.60%
Available credit facility capacity	$ 525	$ 358
IPL [Member]
Commercial paper and borrowings under the single credit facility:
Amount outstanding	0	0
Available credit facility capacity	150	100
WPL [Member]
Commercial paper and borrowings under the single credit facility:
Amount outstanding	$ 318	$ 290
Weighted average interest rates	5.40%	4.50%
Available credit facility capacity	$ 82	$ 110

Debt (Other Short-Term Borrowin

Debt (Other Short-Term Borrowings) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 793	$ 665
Average amount outstanding (based on daily outstanding balances)	$ 386	$ 411
Weighted average interest rates	5.20%	2.10%
IPL [Member]
Debt Instrument [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 70	$ 0
Average amount outstanding (based on daily outstanding balances)	$ 2	$ 0
Weighted average interest rates	5.30%	0%
WPL [Member]
Debt Instrument [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 349	$ 325
Average amount outstanding (based on daily outstanding balances)	$ 157	$ 153
Weighted average interest rates	5.10%	1.60%

Debt (Long-term Debt) (Details)

Debt (Long-term Debt) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Long-term debt	$ 9,109	$ 8,143
Current maturities	(809)	(408)
Unamortized debt issuance costs	(54)	(45)
Unamortized debt (discount) and premium, net	(21)	(22)
Long-term debt, net	8,225	7,668
Senior Debentures [Member]
Debt Instrument [Line Items]
Long-term debt	3,975	3,675
Senior Debentures [Member] | 3.25% senior debenture, due 2024 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 500	$ 500
Interest rate, percent	3.25%	3.25%
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	$ 0
Interest rate, percent	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] | 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%
Debentures [Member]
Debt Instrument [Line Items]
Long-term debt	$ 3,100	$ 2,800
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%	3%
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% debentures, due 2033 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 300	$ 0
Interest rate, percent	4.95%
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%
Other Long Term Debt [Member]
Debt Instrument [Line Items]
Long-term debt	$ 2,034	$ 1,668
Senior Notes [Member] | 3.875% senior notes, due 2026 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 575	0
Interest rate, percent	3.875%
Other [Member] | Other, 1% at December 31, 2022, due 2024 to 2025 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 0	1
Interest rate, percent	1%
IPL [Member]
Debt Instrument [Line Items]
Long-term debt	$ 3,975	3,675
Current maturities	(500)	0
Unamortized debt issuance costs	(21)	(21)
Unamortized debt (discount) and premium, net	(9)	(8)
Long-term debt, net	3,445	3,646
IPL [Member] | Senior Debentures [Member]
Debt Instrument [Line Items]
Long-term debt	3,975	3,675
IPL [Member] | Senior Debentures [Member] | 3.25% senior debenture, due 2024 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 500	$ 500
Interest rate, percent	3.25%	3.25%
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	$ 0
Interest rate, percent	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] | 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%
WPL [Member]
Debt Instrument [Line Items]
Long-term debt	$ 3,100	$ 2,800
Current maturities	0	0
Unamortized debt issuance costs	(19)	(19)
Unamortized debt (discount) and premium, net	(11)	(11)
Long-term debt, net	3,070	2,770
WPL [Member] | Debentures [Member]
Debt Instrument [Line Items]
Long-term debt	3,100	2,800
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%	3%
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% debentures, due 2033 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 300	$ 0
Interest rate, percent	4.95%
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 2024, Variable Rate [Member]
Debt Instrument [Line Items]
Long-term debt	$ 300	$ 400
Interest rate, percent	6%
Payments to retire long-term debt	$ 100
Alliant Energy Finance, LLC [Member] | Term Loan Credit Agreement [Member] | Term loan credit agreement through March 2024, Fixed Rate [Member]
Debt Instrument [Line Items]
Interest rate, percent	3.93%
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] | 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	$ 0
Interest rate, percent	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%
Alliant Energy Finance, LLC [Member] | Senior Notes [Member] | 3.75% senior notes, retired in 2023 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 0	$ 400
Interest rate, percent		3.75%
Sheboygan Power, LLC [Member] | Senior Secured Notes [Member] | 5.06% senior secured notes, due 2024 [Member]
Debt Instrument [Line Items]
Long-term debt	$ 9	$ 17
Interest rate, percent	5.06%	5.06%

Debt (Schedule Of Debt Maturiti

Debt (Schedule Of Debt Maturities) (Details) $ in Millions	Dec. 31, 2023 USD ($)
2024	$ 809
2025	300
2026	775
2027	300
2028	800
Parent Company [Member]
2024	0
2025	0
2026	575
2027	0
2028	0
IPL [Member]
2024	500
2025	300
2026	0
2027	0
2028	500
WPL [Member]
2024	0
2025	0
2026	0
2027	300
2028	0
Alliant Energy Finance, LLC [Member]
2024	309
2025	0
2026	200
2027	0
2028	$ 300

Leases (Narrative) (Details)

Leases (Narrative) (Details)	12 Months Ended
	Dec. 31, 2023 lease_renewal_period_option
Sheboygan Falls Energy Facility [Member] | WPL [Member]
Leases [Line Items]
Finance lease, renewal options (in number of renewal periods)	1

Leases (Operating Leases) (Deta

Leases (Operating Leases) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Leases [Line Items]
Operating leases assets, Property, plant and equipment, net	$ 23	$ 16
Operating leases liabilities, Other current liabilities	2	3
Operating leases liabilities, Other liabilities	21	13
Operating leases liabilities, Total	$ 23	$ 16
Operating leases, Weighted average remaining lease term	12 years	10 years
Operating leases, Weighted average discount rate, percent	4%	4%
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	$ 13	$ 9
Operating leases liabilities, Other current liabilities	1	1
Operating leases liabilities, Other liabilities	12	8
Operating leases liabilities, Total	$ 13	$ 9
Operating leases, Weighted average remaining lease term	12 years	11 years
Operating leases, Weighted average discount rate, percent	4%	4%
WPL [Member]
Leases [Line Items]
Operating leases assets, Property, plant and equipment, net	$ 9	$ 6
Operating leases liabilities, Other current liabilities	1	1
Operating leases liabilities, Other liabilities	8	5
Operating leases liabilities, Total	$ 9	$ 6
Operating leases, Weighted average remaining lease term	12 years	9 years
Operating leases, Weighted average discount rate, percent	4%	4%

Leases (Finance Lease) (Details

Leases (Finance Lease) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Leases [Line Items]
Finance lease assets, Property, plant and equipment, net	$ 172	$ 133
Finance lease liabilities, Other current liabilities	0	5
Finance lease liabilities, Other liabilities	172	131
Finance lease liabilities, Total	$ 172	$ 136
Finance lease, Remaining lease term	33 years	34 years
Finance lease, Discount rate, percent	5%	5%
Finance lease, Depreciation expense	$ 1	$ 0	$ 0
Finance lease, Interest expense	6	3	0
Finance lease, Total expense	$ 7	$ 3	0
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	$ 172	$ 133
Finance lease liabilities, Other current liabilities	0	5
Finance lease liabilities, Other liabilities	$ 172	$ 131
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	$ 33	$ 0
Finance lease liabilities, Other current liabilities	0
Finance lease liabilities, Other liabilities	33	0
Finance lease liabilities, Total	$ 33	0
Finance lease, Remaining lease term	29 years
Finance lease, Discount rate, percent	5%
Finance lease, Depreciation expense	$ 0	0	0
Finance lease, Interest expense	1	0	0
Finance lease, Total expense	1	0	0
IPL [Member] | Leased land for solar generation [Member]
Leases [Line Items]
Finance lease assets, Property, plant and equipment, net	33	0
Finance lease liabilities, Other current liabilities	0	0
Finance lease liabilities, Other liabilities	33	0
WPL [Member]
Leases [Line Items]
Finance lease assets, Property, plant and equipment, net	218	148
Finance lease liabilities, Other current liabilities	11	17
Finance lease liabilities, Other liabilities	217	150
Finance lease liabilities, Total	$ 228	$ 167
Finance lease, Remaining lease term	27 years	28 years
Finance lease, Discount rate, percent	5%	5%
Finance lease, Depreciation expense	$ 6	$ 6	6
Finance lease, Interest expense	8	7	5
Finance lease, Total expense	14	13	$ 11
WPL [Member] | Sheboygan Falls Energy Facility [Member]
Leases [Line Items]
Finance lease assets, Property, plant and equipment, net	79	15
Finance lease liabilities, Other current liabilities	11	12
Finance lease liabilities, Other liabilities	78	19
WPL [Member] | Leased land for solar generation [Member]
Leases [Line Items]
Finance lease assets, Property, plant and equipment, net	139	133
Finance lease liabilities, Other current liabilities	0	5
Finance lease liabilities, Other liabilities	$ 139	$ 131

Leases (Liabilities Arising fro

Leases (Liabilities Arising from Obtaining Leased Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Leases [Line Items]
Finance lease liabilities arising from obtaining leased assets	$ 34	$ 125
IPL [Member]
Leases [Line Items]
Finance lease liabilities arising from obtaining leased assets	33	0
WPL [Member]
Leases [Line Items]
Finance lease liabilities arising from obtaining leased assets	$ 71	$ 125

Leases (Expected Maturities of

Leases (Expected Maturities of Operating and Finance Lease Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Leases [Line Items]
Operating Leases Liability, 2024	$ 3
Operating Leases Liability, 2025	3
Operating Leases Liability, 2026	3
Operating Leases Liability, 2027	3
Operating Leases Liability, 2028	2
Operating Leases Liability, Thereafter	16
Operating Leases Liability, Total	30
Operating Leases Liability, Less: amount representing interest	7
Operating Leases Liability, Present value of minimum lease payments	23	$ 16
Finance Lease Liability, 2024	8
Finance Lease Liability, 2025	8
Finance Lease Liability, 2026	8
Finance Lease Liability, 2027	8
Finance Lease Liability, 2028	8
Finance Lease Liability, Thereafter	320
Finance Lease Liability, Total	360
Finance Lease Liability, Less: amount representing interest	188
Finance Lease Liability, Present value of minimum lease payments	172	136
IPL [Member]
Leases [Line Items]
Operating Leases Liability, 2024	1
Operating Leases Liability, 2025	2
Operating Leases Liability, 2026	2
Operating Leases Liability, 2027	1
Operating Leases Liability, 2028	1
Operating Leases Liability, Thereafter	10
Operating Leases Liability, Total	17
Operating Leases Liability, Less: amount representing interest	4
Operating Leases Liability, Present value of minimum lease payments	13	9
Finance Lease Liability, 2024	2
Finance Lease Liability, 2025	2
Finance Lease Liability, 2026	2
Finance Lease Liability, 2027	2
Finance Lease Liability, 2028	2
Finance Lease Liability, Thereafter	59
Finance Lease Liability, Total	69
Finance Lease Liability, Less: amount representing interest	36
Finance Lease Liability, Present value of minimum lease payments	33	0
WPL [Member]
Leases [Line Items]
Operating Leases Liability, 2024	2
Operating Leases Liability, 2025	1
Operating Leases Liability, 2026	1
Operating Leases Liability, 2027	1
Operating Leases Liability, 2028	1
Operating Leases Liability, Thereafter	6
Operating Leases Liability, Total	12
Operating Leases Liability, Less: amount representing interest	3
Operating Leases Liability, Present value of minimum lease payments	9	6
Finance Lease Liability, 2024	21
Finance Lease Liability, 2025	17
Finance Lease Liability, 2026	13
Finance Lease Liability, 2027	13
Finance Lease Liability, 2028	13
Finance Lease Liability, Thereafter	334
Finance Lease Liability, Total	411
Finance Lease Liability, Less: amount representing interest	183
Finance Lease Liability, Present value of minimum lease payments	$ 228	$ 167

Disaggregation of Revenues (Det

Disaggregation of Revenues (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Disaggregation of Revenue [Line Items]
Revenues	$ 4,027	$ 4,205	$ 3,669
IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	2,110	2,256	2,063
WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,827	1,856	1,523
Electric [Member]
Disaggregation of Revenue [Line Items]
Revenues	3,345	3,421	3,081
Electric [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,761	1,859	1,752
Electric [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,584	1,562	1,329
Electric [Member] | Retail - Residential [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,220	1,233	1,115
Electric [Member] | Retail - Residential [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	641	673	620
Electric [Member] | Retail - Residential [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	579	560	495
Electric [Member] | Retail - Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenues	820	821	763
Electric [Member] | Retail - Commercial [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	519	536	508
Electric [Member] | Retail - Commercial [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	301	285	255
Electric [Member] | Retail - Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenues	968	965	893
Electric [Member] | Retail - Industrial [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	501	538	505
Electric [Member] | Retail - Industrial [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	467	427	388
Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenues	213	233	187
Electric [Member] | Wholesale [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	62	64	57
Electric [Member] | Wholesale [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	151	169	130
Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	124	169	123
Electric [Member] | Other [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	38	48	62
Electric [Member] | Other [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	86	121	61
Gas [Member]
Disaggregation of Revenue [Line Items]
Revenues	540	642	456
Gas [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	300	351	265
Gas [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	240	291	191
Gas [Member] | Retail - Residential [Member]
Disaggregation of Revenue [Line Items]
Revenues	316	371	257
Gas [Member] | Retail - Residential [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	176	202	146
Gas [Member] | Retail - Residential [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	140	169	111
Gas [Member] | Retail - Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenues	163	197	139
Gas [Member] | Retail - Commercial [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	86	101	79
Gas [Member] | Retail - Commercial [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	77	96	60
Gas [Member] | Retail - Industrial [Member]
Disaggregation of Revenue [Line Items]
Revenues	16	20	17
Gas [Member] | Retail - Industrial [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	11	14	12
Gas [Member] | Retail - Industrial [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	5	6	5
Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	45	54	43
Gas [Member] | Other [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	27	34	28
Gas [Member] | Other [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	18	20	15
Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenues	52	49	49
Other Utility [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	49	46	46
Other Utility [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	3	3	3
Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	7	10	13
Other Utility [Member] | Other [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	4	7	10
Other Utility [Member] | Other [Member] | WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	3	3	3
Other Utility [Member] | Steam [Member]
Disaggregation of Revenue [Line Items]
Revenues	45	39	36
Other Utility [Member] | Steam [Member] | IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues	45	39	36
Non-Utility and Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	90	93	83
Non-Utility and Other [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenues	$ 90	$ 93	$ 83

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Tax [Line Items]
Overall income tax rate			1%	3%	(12.00%)
State income tax rate, percent			2%	3%	2%
Reduction of tax-related regulatory assets			$ 24	$ (108)	$ 51
Income tax expense (benefit)			4	22	$ (74)
Tax-related [Member]
Income Tax [Line Items]
Reduction of tax-related regulatory assets			74	77
Income tax expense (benefit)			$ 10	$ 8
IPL [Member]
Income Tax [Line Items]
Overall income tax rate			(19.00%)	(16.00%)	(11.00%)
State income tax rate, percent			(2.00%)	(2.00%)	(1.00%)
Reduction of tax-related regulatory assets			$ 58	$ 56	$ 30
Income tax expense (benefit)			(58)	(50)	$ (36)
IPL [Member] | Tax-related [Member]
Income Tax [Line Items]
Reduction of tax-related regulatory assets			$ 74	$ 77
WPL [Member]
Income Tax [Line Items]
Overall income tax rate			15%	17%	(24.00%)
State income tax rate, percent			5%	6%	6%
Reduction of tax-related regulatory assets			$ (34)	$ (163)	$ 21
Income tax expense (benefit)			$ 60	$ 66	$ (51)
State [Member]
Income Tax [Line Items]
Overall income tax rate					9.80%	12%
State income tax rate, percent			8.40%
State [Member] | Forecast [Member]
Income Tax [Line Items]
State income tax rate, percent	5.50%	7.10%

Income Taxes (Schedule Of Compo

Income Taxes (Schedule Of Components Of Income Tax) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Current tax expense (benefit):
Federal	$ (3)	$ 7	$ 1
State	(6)	2	3
Deferred tax expense (benefit):
Federal	100	109	9
State	36	28	15
Production tax credits	(121)	(123)	(101)
Investment tax credits	(1)	(1)	(1)
Provision recorded as a change in accrued interest	(1)	0	0
Income tax expense (benefit)	4	22	(74)
IPL [Member]
Current tax expense (benefit):
Federal	(44)	(29)	(21)
State	(21)	(8)	(1)
Deferred tax expense (benefit):
Federal	87	91	73
State	17	1	0
Production tax credits	(95)	(105)	(87)
Investment tax credits	(1)	0	0
Provision recorded as a change in accrued interest	(1)	0	0
Income tax expense (benefit)	(58)	(50)	(36)
WPL [Member]
Current tax expense (benefit):
Federal	48	46	22
State	25	16	6
Deferred tax expense (benefit):
Federal	10	10	(75)
State	3	12	11
Production tax credits	(26)	(18)	(14)
Investment tax credits	0	0	(1)
Provision recorded as a change in accrued interest	0	0	0
Income tax expense (benefit)	$ 60	$ 66	$ (51)

Income Taxes (Schedule Of Effec

Income Taxes (Schedule Of Effective Income Tax Rates) (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Effective Tax Rate [Line Items]
Statutory federal income tax rate	21%	21%	21%
State income taxes, net of federal benefits	2%	3%	2%
Production tax credits	(17.00%)	(18.00%)	(17.00%)
Amortization of excess deferred taxes	(2.00%)	(2.00%)	(18.00%)
Effect of rate-making on property-related differences	(4.00%)	(1.00%)	(1.00%)
Adjustment for prior period taxes	0%	1%	1%
Other items, net	1%	(1.00%)	0%
Overall income tax rate	1%	3%	(12.00%)
IPL [Member]
Effective Tax Rate [Line Items]
Statutory federal income tax rate	21%	21%	21%
State income taxes, net of federal benefits	(2.00%)	(2.00%)	(1.00%)
Production tax credits	(31.00%)	(34.00%)	(27.00%)
Amortization of excess deferred taxes	(2.00%)	(2.00%)	(4.00%)
Effect of rate-making on property-related differences	(5.00%)	(1.00%)	(2.00%)
Adjustment for prior period taxes	0%	1%	2%
Other items, net	0%	1%	0%
Overall income tax rate	(19.00%)	(16.00%)	(11.00%)
WPL [Member]
Effective Tax Rate [Line Items]
Statutory federal income tax rate	21%	21%	21%
State income taxes, net of federal benefits	5%	6%	6%
Production tax credits	(7.00%)	(5.00%)	(6.00%)
Amortization of excess deferred taxes	(2.00%)	(3.00%)	(43.00%)
Effect of rate-making on property-related differences	(3.00%)	(2.00%)	(1.00%)
Adjustment for prior period taxes	0%	0%	0%
Other items, net	1%	0%	(1.00%)
Overall income tax rate	15%	17%	(24.00%)

Income Taxes (Schedule Of Defer

Income Taxes (Schedule Of Deferred Tax Assets And Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Deferred tax liabilities, property	$ 2,453	$ 2,442
Deferred tax liabilities, other	213	155
Total deferred tax liabilities	2,793	2,722
Deferred tax assets, federal credit carryforwards	649	672
Deferred tax assets, net operating losses carryforwards - state	26	32
Deferred tax assets, other	79	75
Subtotal deferred tax assets	754	779
Deferred tax assets, valuation allowances	(3)	0
Total deferred tax assets	751	779
Total deferred tax liabilities, net	2,042	1,943
IPL [Member]
Deferred tax liabilities, property	1,415	1,440
Deferred tax liabilities, other	157	86
Total deferred tax liabilities	1,572	1,526
Deferred tax assets, federal credit carryforwards	449	450
Deferred tax assets, net operating losses carryforwards - state	1	0
Deferred tax assets, other	32	29
Subtotal deferred tax assets	482	479
Deferred tax assets, valuation allowances	(1)	0
Total deferred tax assets	481	479
Total deferred tax liabilities, net	1,091	1,047
WPL [Member]
Deferred tax liabilities, property	972	938
Deferred tax liabilities, other	64	80
Total deferred tax liabilities	1,036	1,018
Deferred tax assets, federal credit carryforwards	191	209
Deferred tax assets, net operating losses carryforwards - state	0	0
Deferred tax assets, other	19	20
Subtotal deferred tax assets	210	229
Deferred tax assets, valuation allowances	(1)	0
Total deferred tax assets	209	229
Total deferred tax liabilities, net	827	789
ATC Holdings [Member]
Deferred tax liabilities, ATC Holdings	127	125
ATC Holdings [Member] | IPL [Member]
Deferred tax liabilities, ATC Holdings	0	0
ATC Holdings [Member] | WPL [Member]
Deferred tax liabilities, ATC Holdings	$ 0	$ 0

Income Taxes (Summary Of Tax Cr

Income Taxes (Summary Of Tax Credit Carryforwards) (Details) $ in Millions	Dec. 31, 2023 USD ($)
State [Member]
Tax carryforwards, net operating losses	$ 428
State [Member] | IPL [Member]
Tax carryforwards, net operating losses	6
State [Member] | WPL [Member]
Tax carryforwards, net operating losses	1
Federal [Member]
Tax carryforwards, tax credits	649
Federal [Member] | IPL [Member]
Tax carryforwards, tax credits	449
Federal [Member] | WPL [Member]
Tax carryforwards, tax credits	$ 191

Income Taxes (Schedule Of Uncer

Income Taxes (Schedule Of Uncertain Tax Positions) (Details)	12 Months Ended
	Dec. 31, 2023
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

Benefit Plans (Narrative) (Deta

Benefit Plans (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Benefit Plans [Line Items]
Total plan assets (less than 1%), percentage of common stock	1%	1%
Common stock percentage in assets held in 401(k) saving plans	8%	10%
Unrecognized compensation cost	$ 8
Percentage of base salary and short-term cash incentive compensation	100%
Carrying value of deferred compensation obligations	$ 21	$ 19
Performance Shares Equity Awards [Member]
Benefit Plans [Line Items]
Performance period	3 years
Restricted Stock Units Equity Awards [Member]
Benefit Plans [Line Items]
Performance period	3 years
Instrument valuation based on shares of common stock, number of shares	1
Performance Restricted Stock Units Equity Awards [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 Equity Awards [Member]
Benefit Plans [Line Items]
Actual number of shares paid out upon vesting, percentage of target shares	0%
Minimum [Member] | Performance Restricted Stock Units Equity Awards [Member]
Benefit Plans [Line Items]
Actual number of shares paid out upon vesting, percentage of target shares	0%
Maximum [Member]
Benefit Plans [Line Items]
Unrecognized compensation cost recognized over a weighted average period	2 years
Maximum [Member] | Performance Shares Equity Awards [Member]
Benefit Plans [Line Items]
Actual number of shares paid out upon vesting, percentage of target shares	200%
Maximum [Member] | Performance Restricted Stock Units Equity Awards [Member]
Benefit Plans [Line Items]
Actual number of shares paid out upon vesting, percentage of target shares	200%
IPL [Member]
Benefit Plans [Line Items]
Unrecognized compensation cost	$ 4
WPL [Member]
Benefit Plans [Line Items]
Unrecognized compensation cost	3
Other Postretirement Benefits Plans [Member]
Benefit Plans [Line Items]
Plan asset threshold for long-term allocation targets	5
Other Postretirement Benefits Plans [Member] | IPL [Member]
Benefit Plans [Line Items]
Plan asset threshold for long-term allocation targets	5
Other Postretirement Benefits Plans [Member] | WPL [Member]
Benefit Plans [Line Items]
Plan asset threshold for long-term allocation targets	$ 5
Omnibus Incentive Plan [Member]
Benefit Plans [Line Items]
Shares available for issuance under the Amended and Restated OIP (in shares)	8,000,000
Shares included in diluted earnings per share (in shares)	429,804

Benefit Plans (Assumptions Used

Benefit Plans (Assumptions Used To Measure Benefit Plans) (Details)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations	5.36%	5.54%	2.91%
Discount rate for net periodic cost	5.54%	2.91%	2.57%
Expected rate of return on plan assets	7.80%	7.80%	7.10%
Interest crediting rate for Alliant Energy Cash Balance Pension Plan	10.75%	9.22%	4.18%
Pension Plans, Defined Benefit [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations	5.35%	5.55%	2.94%
Discount rate for net periodic cost	5.55%	2.94%	2.61%
Expected rate of return on plan assets	7.80%	7.80%	7.10%
Rate of compensation increase	3.30%	3.30%	3.30%
Pension Plans, Defined Benefit [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations	5.35%	5.54%	2.94%
Discount rate for net periodic cost	5.54%	2.94%	2.64%
Expected rate of return on plan assets	7.80%	7.80%	7.10%
Rate of compensation increase	3.30%	3.30%	3.30%
Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations	5.40%	5.53%	2.81%
Discount rate for net periodic cost	5.53%	2.81%	2.31%
Expected rate of return on plan assets	6.50%	6.40%	4.80%
Other Postretirement Benefits Plans [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations	5.40%	5.53%	2.80%
Discount rate for net periodic cost	5.53%	2.80%	2.28%
Expected rate of return on plan assets	6.90%	6.50%	5.10%
Other Postretirement Benefits Plans [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate for benefit obligations	5.40%	5.53%	2.79%
Discount rate for net periodic cost	5.53%	2.79%	2.27%
Expected rate of return on plan assets	5.65%	5.49%	4.02%
Minimum [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Rate of compensation increase	3.30%	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%

Benefit Plans (Net Periodic Ben

Benefit Plans (Net Periodic Benefit Costs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Defined Benefit Plan Disclosure [Line Items]
Pension settlement losses	$ (3)	$ (6)	$ (5)
Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	5	9	11
Interest cost	47	36	34
Expected return on plan assets	(53)	(69)	(69)
Amortization of prior service cost (credit)	(1)	(1)	0
Amortization of actuarial loss	28	32	39
Settlement losses	0	26	0
Total	26	33	15
Pension settlement losses	7
Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	2	3	4
Interest cost	9	6	5
Expected return on plan assets	(5)	(5)	(5)
Amortization of prior service cost (credit)	0	0	0
Amortization of actuarial loss	1	2	5
Settlement losses	0	0	0
Total	7	6	9
IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension settlement losses	(2)	(6)	(1)
IPL [Member] | Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	3	6	7
Interest cost	21	16	16
Expected return on plan assets	(26)	(31)	(32)
Amortization of actuarial loss	11	13	17
Settlement losses	0	13	0
Total	9	17	8
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	2	2
Expected return on plan assets	(3)	(4)	(3)
Amortization of actuarial loss	1	1	2
Settlement losses	0	0	0
Total	2	0	2
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension settlement losses	3	1	(2)
WPL [Member] | Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	2	3	4
Interest cost	20	16	15
Expected return on plan assets	(22)	(31)	(31)
Amortization of actuarial loss	13	15	19
Settlement losses	0	13	0
Total	13	16	7
WPL [Member] | Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1	1
Interest cost	3	2	2
Expected return on plan assets	(1)	(1)	0
Amortization of actuarial loss	1	2	2
Settlement losses	0	0	0
Total	$ 4	$ 4	$ 5

Benefit Plans (Funded Status of

Benefit Plans (Funded Status of Benefits Plans) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligations	$ 876	$ 875
Change in benefit obligation:
Net benefit obligation at January 1	875	1,251
Service cost	5	9	$ 11
Interest cost	47	36	34
Plan participants' contributions	0	0
Actuarial (gain) loss	23	(269)
Gross benefits paid	(74)	(152)
Net benefit obligation at December 31	876	875	1,251
Change in plan assets:
Fair value of plan assets at January 1	706	1,011
Actual return on plan assets	86	(204)
Employer contributions	14	51
Plan participants' contributions	0	0
Gross benefits paid	(74)	(152)
Fair value of plan assets at December 31	732	706	1,011
Under funded status at December 31	(144)	(169)
Fair value of plan assets	732	706
Pension Plans, Defined Benefit [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligations	387	389
Change in benefit obligation:
Net benefit obligation at January 1	389	567
Service cost	3	6	7
Interest cost	21	16	16
Plan participants' contributions	0	0
Actuarial (gain) loss	9	(123)
Gross benefits paid	(35)	(77)
Net benefit obligation at December 31	387	389	567
Change in plan assets:
Fair value of plan assets at January 1	344	462
Actual return on plan assets	42	(92)
Employer contributions	1	51
Plan participants' contributions	0	0
Gross benefits paid	(35)	(77)
Fair value of plan assets at December 31	352	344	462
Under funded status at December 31	(35)	(45)
Fair value of plan assets	352	344
Pension Plans, Defined Benefit [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligations	381	381
Change in benefit obligation:
Net benefit obligation at January 1	381	546
Service cost	2	3	4
Interest cost	20	16	15
Plan participants' contributions	0	0
Actuarial (gain) loss	10	(117)
Gross benefits paid	(32)	(67)
Net benefit obligation at December 31	381	381	546
Change in plan assets:
Fair value of plan assets at January 1	291	450
Actual return on plan assets	35	(92)
Employer contributions	12	0
Plan participants' contributions	0	0
Gross benefits paid	(32)	(67)
Fair value of plan assets at December 31	306	291	450
Under funded status at December 31	(75)	(90)
Fair value of plan assets	306	291
Other Postretirement Benefits Plans [Member]
Change in benefit obligation:
Net benefit obligation at January 1	168	210
Service cost	2	3	4
Interest cost	9	6	5
Plan participants' contributions	4	4
Actuarial (gain) loss	(3)	(37)
Gross benefits paid	(20)	(18)
Net benefit obligation at December 31	160	168	210
Change in plan assets:
Fair value of plan assets at January 1	83	106
Actual return on plan assets	8	(17)
Employer contributions	8	8
Plan participants' contributions	4	4
Gross benefits paid	(20)	(18)
Fair value of plan assets at December 31	83	83	106
Under funded status at December 31	(77)	(85)
Other Postretirement Benefits Plans [Member] | IPL [Member]
Change in benefit obligation:
Net benefit obligation at January 1	68	84
Service cost	1	1	1
Interest cost	3	2	2
Plan participants' contributions	2	2
Actuarial (gain) loss	(1)	(14)
Gross benefits paid	(8)	(7)
Net benefit obligation at December 31	65	68	84
Change in plan assets:
Fair value of plan assets at January 1	58	74
Actual return on plan assets	7	(12)
Employer contributions	2	1
Plan participants' contributions	2	2
Gross benefits paid	(8)	(7)
Fair value of plan assets at December 31	61	58	74
Under funded status at December 31	(4)	(10)
Other Postretirement Benefits Plans [Member] | WPL [Member]
Change in benefit obligation:
Net benefit obligation at January 1	65	81
Service cost	1	1	1
Interest cost	3	2	2
Plan participants' contributions	2	2
Actuarial (gain) loss	(2)	(13)
Gross benefits paid	(8)	(8)
Net benefit obligation at December 31	61	65	81
Change in plan assets:
Fair value of plan assets at January 1	14	17
Actual return on plan assets	1	(2)
Employer contributions	5	5
Plan participants' contributions	2	2
Gross benefits paid	(8)	(8)
Fair value of plan assets at December 31	14	14	$ 17
Under funded status at December 31	$ (47)	$ (51)

Benefit Plans (Amounts Recogniz

Benefit Plans (Amounts Recognized On The Consolidated Balance Sheets) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Amounts recognized on the balance sheets consist of:
Pension and other benefit obligations	$ (249)	$ (277)
Pension Plans, Defined Benefit [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets	0	0
Current liabilities	(2)	(2)
Pension and other benefit obligations	(142)	(167)
Net amounts recognized at December 31	(144)	(169)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	337	376
Prior service credit	(2)	(3)
Net amount recognized at December 31	335	373
Other Postretirement Benefits Plans [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets	14	9
Current liabilities	(8)	(8)
Pension and other benefit obligations	(83)	(86)
Net amounts recognized at December 31	(77)	(85)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	11	20
Prior service credit	0	0
Net amount recognized at December 31	11	20
IPL [Member]
Amounts recognized on the balance sheets consist of:
Pension and other benefit obligations	(51)	(62)
IPL [Member] | Pension Plans, Defined Benefit [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets	0	0
Current liabilities	0	0
Pension and other benefit obligations	(35)	(45)
Net amounts recognized at December 31	(35)	(45)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	135	154
Prior service credit	(1)	(1)
Net amount recognized at December 31	134	153
IPL [Member] | Other Postretirement Benefits Plans [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets	10	6
Current liabilities	(1)	(2)
Pension and other benefit obligations	(13)	(14)
Net amounts recognized at December 31	(4)	(10)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	9	14
Prior service credit	0	0
Net amount recognized at December 31	9	14
WPL [Member]
Amounts recognized on the balance sheets consist of:
Pension and other benefit obligations	(121)	(140)
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	(75)	(90)
Net amounts recognized at December 31	(75)	(90)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	148	165
Prior service credit	0	0
Net amount recognized at December 31	148	165
WPL [Member] | Other Postretirement Benefits Plans [Member]
Amounts recognized on the balance sheets consist of:
Non-current assets	4	3
Current liabilities	(6)	(5)
Pension and other benefit obligations	(45)	(49)
Net amounts recognized at December 31	(47)	(51)
Amounts recognized in Regulatory Assets consist of:
Net actuarial loss	3	6
Prior service credit	0	0
Net amount recognized at December 31	$ 3	$ 6

Benefit Plans (Accumulated Bene

Benefit Plans (Accumulated Benefit Obligations) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations	$ 857	$ 857
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	857	857
Fair value of plan assets	732	706
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	876	875
Fair value of plan assets	732	706
Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations	160	168
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	160	168
Fair value of plan assets	83	83
IPL [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations	377	379
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	377	379
Fair value of plan assets	352	344
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	387	389
Fair value of plan assets	352	344
IPL [Member] | Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations	65	68
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	65	68
Fair value of plan assets	61	58
WPL [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations	373	373
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	373	373
Fair value of plan assets	306	291
Plans with projected benefit obligations in excess of plan assets:
Projected benefit obligations	381	381
Fair value of plan assets	306	291
WPL [Member] | Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations	61	65
Plans with accumulated benefit obligations in excess of plan assets:
Accumulated benefit obligations	61	65
Fair value of plan assets	$ 14	$ 14

Benefit Plans (Regulatory Asset

Benefit Plans (Regulatory Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory assets	$ 28	$ 30
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Regulatory assets	$ 24	$ 25

Benefit Plans (Estimated Future

Benefit Plans (Estimated Future Funding) (Details) - Forecast [Member] $ in Millions	Dec. 31, 2024 USD ($)
Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated funding for calendar year 2024	$ 12
Defined Benefit Pension Plans [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated funding for calendar year 2024	0
Defined Benefit Pension Plans [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated funding for calendar year 2024	10
Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated funding for calendar year 2024	8
Other Postretirement Benefits Plans [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated funding for calendar year 2024	1
Other Postretirement Benefits Plans [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated funding for calendar year 2024	$ 6

Benefit Plans (Expected Benefit

Benefit Plans (Expected Benefit Payments) (Details) $ in Millions	Dec. 31, 2023 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2024	$ 90
Expected benefit payments, 2025	90
Expected benefit payments, 2026	90
Expected benefit payments, 2027	91
Expected benefit payments, 2028	90
Expected benefit payments, 2029 - 2033	408
Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2024	73
Expected benefit payments, 2025	73
Expected benefit payments, 2026	74
Expected benefit payments, 2027	75
Expected benefit payments, 2028	75
Expected benefit payments, 2029 - 2033	343
Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2024	17
Expected benefit payments, 2025	17
Expected benefit payments, 2026	16
Expected benefit payments, 2027	16
Expected benefit payments, 2028	15
Expected benefit payments, 2029 - 2033	65
IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2024	41
Expected benefit payments, 2025	41
Expected benefit payments, 2026	41
Expected benefit payments, 2027	39
Expected benefit payments, 2028	39
Expected benefit payments, 2029 - 2033	176
IPL [Member] | Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2024	34
Expected benefit payments, 2025	34
Expected benefit payments, 2026	34
Expected benefit payments, 2027	33
Expected benefit payments, 2028	33
Expected benefit payments, 2029 - 2033	151
IPL [Member] | Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2024	7
Expected benefit payments, 2025	7
Expected benefit payments, 2026	7
Expected benefit payments, 2027	6
Expected benefit payments, 2028	6
Expected benefit payments, 2029 - 2033	25
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2024	39
Expected benefit payments, 2025	39
Expected benefit payments, 2026	37
Expected benefit payments, 2027	37
Expected benefit payments, 2028	37
Expected benefit payments, 2029 - 2033	170
WPL [Member] | Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2024	32
Expected benefit payments, 2025	32
Expected benefit payments, 2026	31
Expected benefit payments, 2027	31
Expected benefit payments, 2028	31
Expected benefit payments, 2029 - 2033	146
WPL [Member] | Other Postretirement Benefits Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected benefit payments, 2024	7
Expected benefit payments, 2025	7
Expected benefit payments, 2026	6
Expected benefit payments, 2027	6
Expected benefit payments, 2028	6
Expected benefit payments, 2029 - 2033	$ 24

Benefit Plans (Allocation Of Pl

Benefit Plans (Allocation Of Plan Assets) (Details)	Dec. 31, 2023
Pension Plans, Defined Benefit [Member] | Cash and equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Actual allocation, percentage	2%
Pension Plans, Defined Benefit [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Actual allocation, percentage	56%
Pension Plans, Defined Benefit [Member] | Global asset securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Actual allocation, percentage	5%
Pension Plans, Defined Benefit [Member] | Fixed income securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Actual allocation, percentage	37%
Other Postretirement Benefits Plans [Member] | Cash and equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Actual allocation, percentage	1%
Other Postretirement Benefits Plans [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Actual allocation, percentage	36%
Other Postretirement Benefits Plans [Member] | Fixed income securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Actual allocation, percentage	63%
Minimum [Member] | Pension Plans, Defined Benefit [Member] | Cash and equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Target range allocation, percentage	0%
Minimum [Member] | Pension Plans, Defined Benefit [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target range allocation, percentage	47%
Minimum [Member] | Pension Plans, Defined Benefit [Member] | Global asset securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target range allocation, percentage	0%
Minimum [Member] | Pension Plans, Defined Benefit [Member] | Fixed income securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target range allocation, percentage	27%
Minimum [Member] | Other Postretirement Benefits Plans [Member] | Cash and equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Target range allocation, percentage	0%
Minimum [Member] | Other Postretirement Benefits Plans [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target range allocation, percentage	0%
Minimum [Member] | Other Postretirement Benefits Plans [Member] | Fixed income securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target range allocation, percentage	40%
Maximum [Member] | Pension Plans, Defined Benefit [Member] | Cash and equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Target range allocation, percentage	5%
Maximum [Member] | Pension Plans, Defined Benefit [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target range allocation, percentage	67%
Maximum [Member] | Pension Plans, Defined Benefit [Member] | Global asset securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target range allocation, percentage	15%
Maximum [Member] | Pension Plans, Defined Benefit [Member] | Fixed income securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target range allocation, percentage	47%
Maximum [Member] | Other Postretirement Benefits Plans [Member] | Cash and equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Target range allocation, percentage	5%
Maximum [Member] | Other Postretirement Benefits Plans [Member] | Equity securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target range allocation, percentage	55%
Maximum [Member] | Other Postretirement Benefits Plans [Member] | Fixed income securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Target range allocation, percentage	100%

Benefit Plans (Fair Value Of Pl

Benefit Plans (Fair Value Of Plan Assets By Asset Category And Fair Value Hierarchy Level) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 732	$ 706	$ 1,011
Pension Plans, Defined Benefit [Member] | Level 1, Level 2, and Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	424	429
Pension Plans, Defined Benefit [Member] | Assets Measured at Net Asset Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	306	276
Pension Plans, Defined Benefit [Member] | Cash and equivalents [Member] | Level 1, Level 2, and Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	19	79
Pension Plans, Defined Benefit [Member] | Cash and equivalents [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | Cash and equivalents [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	19	79
Pension Plans, Defined Benefit [Member] | Cash and equivalents [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | Equity securities [Member] | Level 1, Level 2, and Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	223	185
Pension Plans, Defined Benefit [Member] | Equity securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	223	185
Pension Plans, Defined Benefit [Member] | Equity securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	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
Pension Plans, Defined Benefit [Member] | Global asset securities [Member] | Level 1, Level 2, and Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	39	35
Pension Plans, Defined Benefit [Member] | Global asset securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	39	35
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
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
Pension Plans, Defined Benefit [Member] | Fixed income securities [Member] | Level 1, Level 2, and Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	143	130
Pension Plans, Defined Benefit [Member] | Fixed income securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	31	30
Pension Plans, Defined Benefit [Member] | Fixed income securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	112	100
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
Pension Plans, Defined Benefit [Member] | Subtotal [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	293	250
Pension Plans, Defined Benefit [Member] | Subtotal [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	131	179
Pension Plans, Defined Benefit [Member] | Subtotal [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | Accrued investment income [Member] | Level 1, Level 2, and Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2	1
Pension Plans, Defined Benefit [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	352	344	462
Pension Plans, Defined Benefit [Member] | IPL [Member] | Level 1, Level 2, and Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	204	219
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	147	124
Pension Plans, Defined Benefit [Member] | IPL [Member] | Cash and equivalents [Member] | Level 1, Level 2, and Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	9	62
Pension Plans, Defined Benefit [Member] | IPL [Member] | Cash and equivalents [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | IPL [Member] | Cash and equivalents [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	9	62
Pension Plans, Defined Benefit [Member] | IPL [Member] | Cash and equivalents [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | IPL [Member] | Equity securities [Member] | Level 1, Level 2, and Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	107	83
Pension Plans, Defined Benefit [Member] | IPL [Member] | Equity securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	107	83
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
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
Pension Plans, Defined Benefit [Member] | IPL [Member] | Global asset securities [Member] | Level 1, Level 2, and Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	19	16
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	19	16
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
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
Pension Plans, Defined Benefit [Member] | IPL [Member] | Fixed income securities [Member] | Level 1, Level 2, and Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	69	58
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	15	13
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	54	45
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
Pension Plans, Defined Benefit [Member] | IPL [Member] | Subtotal [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	141	112
Pension Plans, Defined Benefit [Member] | IPL [Member] | Subtotal [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	63	107
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
Pension Plans, Defined Benefit [Member] | IPL [Member] | Accrued investment income [Member] | Level 1, Level 2, and Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1	1
Pension Plans, Defined Benefit [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	306	291	450
Pension Plans, Defined Benefit [Member] | WPL [Member] | Level 1, Level 2, and Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	177	168
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	128	122
Pension Plans, Defined Benefit [Member] | WPL [Member] | Cash and equivalents [Member] | Level 1, Level 2, and Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	8	13
Pension Plans, Defined Benefit [Member] | WPL [Member] | Cash and equivalents [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plans, Defined Benefit [Member] | WPL [Member] | Cash and equivalents [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	8	13
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
Pension Plans, Defined Benefit [Member] | WPL [Member] | Equity securities [Member] | Level 1, Level 2, and Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	93	82
Pension Plans, Defined Benefit [Member] | WPL [Member] | Equity securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	93	82
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
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
Pension Plans, Defined Benefit [Member] | WPL [Member] | Global asset securities [Member] | Level 1, Level 2, and Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	16	16
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	16	16
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
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
Pension Plans, Defined Benefit [Member] | WPL [Member] | Fixed income securities [Member] | Level 1, Level 2, and Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	60	57
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	13	13
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	47	44
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
Pension Plans, Defined Benefit [Member] | WPL [Member] | Subtotal [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	122	111
Pension Plans, Defined Benefit [Member] | WPL [Member] | Subtotal [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	55	57
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
Pension Plans, Defined Benefit [Member] | WPL [Member] | Accrued investment income [Member] | Level 1, Level 2, and Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1	1
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	83	83	106
Other Postretirement Benefit Plans, Defined Benefit [Member] | Level 1, Level 2, and Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	64	60
Other Postretirement Benefit Plans, Defined Benefit [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	55	56
Other Postretirement Benefit Plans, Defined Benefit [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	9	4
Other Postretirement Benefit Plans, Defined Benefit [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Assets Measured at Net Asset Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	19	23
Other Postretirement Benefit Plans, Defined Benefit [Member] | Cash and equivalents [Member] | Level 1, Level 2, and Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	9	3
Other Postretirement Benefit Plans, Defined Benefit [Member] | Cash and equivalents [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Cash and equivalents [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	9	3
Other Postretirement Benefit Plans, Defined Benefit [Member] | Cash and equivalents [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity securities [Member] | Level 1, Level 2, and Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	8	9
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	8	9
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Equity securities [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Global asset securities [Member] | Level 1, Level 2, and Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	1
Other Postretirement Benefit Plans, Defined Benefit [Member] | Global asset securities [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	1
Other Postretirement Benefit Plans, Defined Benefit [Member] | Global asset securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Global asset securities [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fixed income securities [Member] | Level 1, Level 2, and Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	47	47
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	47	46
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	1
Other Postretirement Benefit Plans, Defined Benefit [Member] | Fixed income securities [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	61	58	74
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Level 1, Level 2, and Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	43	40
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	42	39
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1	1
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Assets Measured at Net Asset Value [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	18	18
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Cash and equivalents [Member] | Level 1, Level 2, and Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1	1
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Cash and equivalents [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Cash and equivalents [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1	1
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Cash and equivalents [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Equity securities [Member] | Level 1, Level 2, and Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6	5
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	6	5
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Equity securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Equity securities [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Fixed income securities [Member] | Level 1, Level 2, and Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	36	34
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	36	34
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Fixed income securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | IPL [Member] | Fixed income securities [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14	14	$ 17
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	13	14
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	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
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Cash and equivalents [Member] | Level 1, Level 2, and Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	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
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	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
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Equity securities [Member] | Level 1, Level 2, and Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2	1
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	1
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Equity securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Equity securities [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Fixed income securities [Member] | Level 1, Level 2, and Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11	13
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	13
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Fixed income securities [Member] | Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Postretirement Benefit Plans, Defined Benefit [Member] | WPL [Member] | Fixed income securities [Member] | Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0	$ 0

Benefit Plans (Employees Partic

Benefit Plans (Employees Participate In Defined Contribution Retirement Plans) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
401(k) costs	$ 30	$ 28	$ 26
IPL [Member]
401(k) costs	14	13	13
WPL [Member]
401(k) costs	$ 14	$ 13	$ 12

Benefit Plans (Recognized Compe

Benefit Plans (Recognized Compensation Expense And Income Tax Benefits) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Compensation expense	$ 12	$ 13	$ 14
Income tax benefits	3	3	4
IPL [Member]
Compensation expense	6	7	8
Income tax benefits	2	2	2
WPL [Member]
Compensation expense	5	5	6
Income tax benefits	$ 1	$ 1	$ 2

Benefit Plans (Summary Of Perfo

Benefit Plans (Summary Of Performance Shares Activity) (Details) - Performance Shares Equity Awards [Member] - $ / shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Nonvested, January 1 (in shares/awards)	190,273	196,429	129,156
Nonvested, January 1, weighted average grant date fair value (in dollars per share)	$ 54.13	$ 51.59	$ 54.63
Granted (in shares/awards)	108,712	74,106	73,112
Granted, weighted average grant date fair value (in dollars per share)	$ 55.68	$ 54.45	$ 46.19
Vested (in shares/awards)	(53,431)	(71,101)	0
Vested, weighted average grant date fair value (in dollars per share)	$ 64.04	$ 47.48	$ 0
Forfeited (in shares/awards)	(11,600)	(9,161)	(5,839)
Forfeited, weighted average grant date fair value (in dollars per share)	$ 53.88	$ 53.99	$ 51.07
Nonvested, December 31 (in shares/awards)	233,954	190,273	196,429
Nonvested, December 31, weighted average grant date fair value (in dollars per share)	$ 52.60	$ 54.13	$ 51.59

Benefit Plans (Summary of Restr

Benefit Plans (Summary of Restricted Stock Units) (Details) - Restricted Stock Units Equity Awards [Member] - $ / shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Nonvested, January 1 (in shares/awards)	198,275	217,819	146,549
Nonvested, January 1, weighted average grant date fair value (in dollars per share)	$ 54.53	$ 50.54	$ 51.54
Granted (in shares/awards)	106,124	77,122	80,152
Granted, weighted average grant date fair value (in dollars per share)	$ 52.77	$ 56.88	$ 48.65
Vested (in shares/awards)	(55,345)	(82,770)	0
Vested, weighted average grant date fair value (in dollars per share)	$ 59.40	$ 46.08	$ 0
Forfeited (in shares/awards)	(14,795)	(13,896)	(8,882)
Forfeited, weighted average grant date fair value (in dollars per share)	$ 54.53	$ 55.53	$ 49.84
Nonvested, December 31 (in shares/awards)	234,259	198,275	217,819
Nonvested, December 31, weighted average grant date fair value (in dollars per share)	$ 52.58	$ 54.53	$ 50.54

Benefit Plans (Summary of Per_2

Benefit Plans (Summary of Performance Restricted Stock Units) (Details) - Performance Restricted Stock Units Equity Awards [Member] - $ / shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Nonvested, January 1 (in shares/awards)	199,874	196,429	197,463
Nonvested, January 1, weighted average grant date fair value (in dollars per share)	$ 54.74	$ 50.74	$ 47.31
Granted (in shares/awards)	124,217	84,670	73,112
Granted, weighted average grant date fair value (in dollars per share)	$ 52.71	$ 57.01	$ 48.66
Vested (in shares/awards)	(53,431)	(71,101)	(68,307)
Vested, weighted average grant date fair value (in dollars per share)	$ 59.36	$ 46.24	$ 38.60
Forfeited (in shares/awards)	(13,021)	(10,124)	(5,839)
Forfeited, weighted average grant date fair value (in dollars per share)	$ 55.47	$ 55.92	$ 50.46
Nonvested, December 31 (in shares/awards)	257,639	199,874	196,429
Nonvested, December 31, weighted average grant date fair value (in dollars per share)	$ 52.76	$ 54.74	$ 50.74

Benefit Plans (Carrying Value A

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, 2023	Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
Carrying value of deferred compensation obligation	$ 13	$ 13
Fair market value of deferred compensation obligation	$ 19	$ 22

Asset Retirement Obligations (R

Asset Retirement Obligations (Reconciliation Of Changes In Asset Retirement Obligations) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1	$ 279	$ 294
Revisions in estimated cash flows	(6)	19
Liabilities settled	(51)	(48)
Liabilities incurred	16	6
Accretion expense	8	8
Balance, December 31	246	279
IPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1	195	213
Revisions in estimated cash flows	(9)	15
Liabilities settled	(44)	(39)
Liabilities incurred	1	0
Accretion expense	5	6
Balance, December 31	148	195
WPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1	84	81
Revisions in estimated cash flows	3	4
Liabilities settled	(7)	(9)
Liabilities incurred	15	6
Accretion expense	3	2
Balance, December 31	$ 98	$ 84

Derivative Instruments (Narrati

Derivative Instruments (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Derivative [Line Items]
Interest rate swap	$ 9,109	$ 8,143
Non-current interest rate swap assets	177	227
Accumulated other comprehensive income	1	0
Interest expense, interest rate swap	394	325	$ 277
IPL [Member]
Derivative [Line Items]
Interest rate swap	3,975	3,675
Non-current interest rate swap assets	84	110
Interest expense, interest rate swap	155	148	139
WPL [Member]
Derivative [Line Items]
Interest rate swap	3,100	2,800
Non-current interest rate swap assets	61	98
Interest expense, interest rate swap	149	$ 121	$ 105
Alliant Energy Finance, LLC [Member] | Interest Rate Swap | 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
Accumulated other comprehensive income	1
Interest expense, interest rate swap	$ 3

Derivative Instruments (Notiona

Derivative Instruments (Notional Amounts Of Derivative Instruments) (Details) - Commodity [Member]	12 Months Ended
	Dec. 31, 2023 Dekatherms MWh
Electricity (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	1,640
Electricity (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	673
Electricity (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	967
FTRs (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	11,927
FTRs (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	5,336
FTRs (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	6,591
Gas (Dths) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	176,349
Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	74,360
Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	101,989

Derivative Instruments (Fair Va

Derivative Instruments (Fair Value Of Financial Instruments) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Derivatives, Fair Value [Line Items]
Current derivative assets	$ 44	$ 111
Non-current derivative assets	44	126
Current derivative liabilities	51	59
Non-current derivative liabilities	47	20
IPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	30	69
Non-current derivative assets	24	69
Current derivative liabilities	22	40
Non-current derivative liabilities	8	6
WPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	14	42
Non-current derivative assets	20	57
Current derivative liabilities	29	19
Non-current derivative liabilities	$ 39	$ 14

Derivative Instruments (Balance

Derivative Instruments (Balance Sheet Offsetting) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Derivative [Line Items]
Derivative assets, Gross (as reported)	$ 88	$ 237
Derivative assets, net	47	193
Derivative liabilities, gross (as reported)	98	79
Derivative liabilities, net	57	35
IPL [Member]
Derivative [Line Items]
Derivative assets, Gross (as reported)	54	138
Derivative assets, net	32	108
Derivative liabilities, gross (as reported)	30	46
Derivative liabilities, net	8	16
WPL [Member]
Derivative [Line Items]
Derivative assets, Gross (as reported)	34	99
Derivative assets, net	15	85
Derivative liabilities, gross (as reported)	68	33
Derivative liabilities, net	$ 49	$ 19

Fair Value Measurements (Recurr

Fair Value Measurements (Recurring Fair Value Measurements) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Carrying Amount [Member]
Assets:
Money market fund investments	$ 45	$ 10
Deferred proceeds	216	185
Liabilities and equity:
Long-term debt (including current maturities)	9,034	8,076
Carrying Amount [Member] | Commodity Contracts [Member]
Assets:
Derivatives	88	237
Liabilities and equity:
Derivatives	98	79
Carrying Amount [Member] | Interest Rate Swap
Assets:
Derivatives	1	0
Money market fund investments	45	10
Deferred proceeds	216	185
Liabilities and equity:
Long-Term Debt, Fair Value	8,677	7,339
Commodity Contracts [Member]
Assets:
Derivatives	88	237
Liabilities and equity:
Derivatives	98	79
Interest Rate Swap
Assets:
Derivatives	1	0
Level 1 [Member]
Assets:
Money market fund investments	45	10
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
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	8,677	7,338
Level 2 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	59	206
Liabilities and equity:
Derivatives	93	67
Level 2 [Member] | Interest Rate Swap
Assets:
Derivatives	1	0
Level 3 [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	216	185
Liabilities and equity:
Long-Term Debt, Fair Value	0	1
Level 3 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	29	31
Liabilities and equity:
Derivatives	5	12
Level 3 [Member] | Interest Rate Swap
Assets:
Derivatives	0	0
IPL [Member] | Carrying Amount [Member]
Assets:
Money market fund investments	45	10
Deferred proceeds	216	185
Liabilities and equity:
Long-term debt (including current maturities)	3,945	3,646
IPL [Member] | Carrying Amount [Member] | Commodity Contracts [Member]
Assets:
Derivatives	54	138
Liabilities and equity:
Derivatives	30	46
IPL [Member]
Assets:
Money market fund investments	45	10
Deferred proceeds	216	185
Liabilities and equity:
Long-Term Debt, Fair Value	3,664	3,228
IPL [Member] | Commodity Contracts [Member]
Assets:
Derivatives	54	138
Liabilities and equity:
Derivatives	30	46
IPL [Member] | Level 1 [Member]
Assets:
Money market fund investments	45	10
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	3,664	3,228
IPL [Member] | Level 2 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	30	111
Liabilities and equity:
Derivatives	25	35
IPL [Member] | Level 3 [Member]
Assets:
Money market fund investments	0	0
Deferred proceeds	216	185
Liabilities and equity:
Long-Term Debt, Fair Value	0	0
IPL [Member] | Level 3 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	24	27
Liabilities and equity:
Derivatives	5	11
WPL [Member] | Carrying Amount [Member]
Liabilities and equity:
Long-term debt (including current maturities)	3,070	2,770
WPL [Member] | Carrying Amount [Member] | Commodity Contracts [Member]
Assets:
Derivatives	34	99
Liabilities and equity:
Derivatives	68	33
WPL [Member]
Liabilities and equity:
Long-Term Debt, Fair Value	2,933	2,542
WPL [Member] | Commodity Contracts [Member]
Assets:
Derivatives	34	99
Liabilities and equity:
Derivatives	68	33
WPL [Member] | Level 1 [Member]
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]
Liabilities and equity:
Long-Term Debt, Fair Value	2,933	2,542
WPL [Member] | Level 2 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	29	95
Liabilities and equity:
Derivatives	68	32
WPL [Member] | Level 3 [Member]
Liabilities and equity:
Long-Term Debt, Fair Value	0	0
WPL [Member] | Level 3 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	5	4
Liabilities and equity:
Derivatives	$ 0	$ 1

Fair Value Measurements (Fair V

Fair Value Measurements (Fair Value Measurements Using Significant Unobservable Inputs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
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	$ 19	$ 29
Total net gains (losses) included in changes in net assets (realized/unrealized)	3	(18)
Purchases	62	79
Sales	(3)	(2)
Settlements	(57)	(69)
Ending balance, December 31	24	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	3	(18)
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	16	18
Total net gains (losses) included in changes in net assets (realized/unrealized)	(3)	(12)
Purchases	51	58
Sales	(3)	(1)
Settlements	(42)	(47)
Ending balance, December 31	19	16
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)	(13)
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	3	11
Total net gains (losses) included in changes in net assets (realized/unrealized)	6	(6)
Purchases	11	21
Sales	0	(1)
Settlements	(15)	(22)
Ending balance, December 31	5	3
The amount of total net gains (losses) for the period included in changes in net assets attributable to the change in unrealized gains (losses) relating to assets and liabilities held at December 31	6	(5)
Deferred Proceeds [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance, January 1	185	214
Total net gains (losses) included in changes in net assets (realized/unrealized)	0	0
Purchases	0	0
Sales	0	0
Settlements	31	(29)
Ending balance, December 31	216	185
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	185	214
Total net gains (losses) included in changes in net assets (realized/unrealized)	0	0
Purchases	0	0
Sales	0	0
Settlements	31	(29)
Ending balance, December 31	216	185
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

Fair Value Measurements (Fair_2

Fair Value Measurements (Fair Value Of Net Derivative Assets (Liabilities)) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative assets	$ 24	$ 19	$ 29
Excluding FTRs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative assets	3
Fair value, net derivative liabilities		(10)
FTRs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative assets	21	29
IPL [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative assets	19	16	18
IPL [Member] | Excluding FTRs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative assets	3
Fair value, net derivative liabilities		(9)
IPL [Member] | FTRs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative assets	16	25
WPL [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative assets	5	3	$ 11
WPL [Member] | Excluding FTRs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative assets	0
Fair value, net derivative liabilities		(1)
WPL [Member] | FTRs [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net derivative assets	$ 5	$ 4

Commitments And Contingencies_2

Commitments And Contingencies (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Long-term Purchase Commitment [Line Items]
Equity income from unconsolidated investments, net	$ 61	$ 51	$ 62
Workforce Subject to Collective Bargaining Arrangements [Member]
Long-term Purchase Commitment [Line Items]
Employees covered by collective bargaining agreement	53%
Workforce Subject to Collective Bargaining Arrangements Expiring within One Year [Member]
Long-term Purchase Commitment [Line Items]
Employees covered by collective bargaining agreement	18%
Whiting Petroleum Affiliate [Member]
Long-term Purchase Commitment [Line Items]
Partnership share, percent	6%
Obligations, maximum	$ 49
Capital Purchase Commitment [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	$ 188
IPL [Member] | Workforce Subject to Collective Bargaining Arrangements [Member]
Long-term Purchase Commitment [Line Items]
Employees covered by collective bargaining agreement	69%
IPL [Member] | Workforce Subject to Collective Bargaining Arrangements Expiring within One Year [Member]
Long-term Purchase Commitment [Line Items]
Employees covered by collective bargaining agreement	53%
IPL [Member] | Capital Purchase Commitment [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	$ 131
WPL [Member] | Workforce Subject to Collective Bargaining Arrangements [Member]
Long-term Purchase Commitment [Line Items]
Employees covered by collective bargaining agreement	83%
WPL [Member] | Capital Purchase Commitment [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments	$ 57
Indemnification Agreement [Member]
Long-term Purchase Commitment [Line Items]
Obligations, maximum	51
Indemnification Agreement [Member] | Purchased Power [Member]
Long-term Purchase Commitment [Line Items]
Obligations, maximum	17
Indemnification Agreement [Member] | Renewable Tax Credits Transferred [Member]
Long-term Purchase Commitment [Line Items]
Guarantor Obligations, Liquidation Proceeds, Monetary Amount	98
Indemnification Agreement [Member] | IPL [Member] | Renewable Tax Credits Transferred [Member]
Long-term Purchase Commitment [Line Items]
Guarantor Obligations, Liquidation Proceeds, Monetary Amount	76
Indemnification Agreement [Member] | WPL [Member] | Renewable Tax Credits Transferred [Member]
Long-term Purchase Commitment [Line Items]
Guarantor Obligations, Liquidation Proceeds, Monetary Amount	$ 22
FERC [Member]
Long-term Purchase Commitment [Line Items]
Base return on equity, percentage				10.02%	9.88%
Equity income from unconsolidated investments, net		$ 6

Commitments And Contingencies_3

Commitments And Contingencies (Other Purchase Commitments) (Details) $ in Millions	Dec. 31, 2023 USD ($)
Long-term Purchase Commitment [Line Items]
Minimum future commitments, 2023	$ 456
Minimum future commitments, 2024	253
Minimum future commitments, 2025	145
Minimum future commitments, 2026	95
Minimum future commitments, 2027	57
Minimum future commitments, Thereafter	164
Minimum future commitments, Total	1,170
Individual commitments incurred	1
Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments, 2023	301
Minimum future commitments, 2024	187
Minimum future commitments, 2025	123
Minimum future commitments, 2026	78
Minimum future commitments, 2027	49
Minimum future commitments, Thereafter	142
Minimum future commitments, Total	880
Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments, 2023	94
Minimum future commitments, 2024	49
Minimum future commitments, 2025	8
Minimum future commitments, 2026	8
Minimum future commitments, 2027	6
Minimum future commitments, Thereafter	0
Minimum future commitments, Total	165
Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments, 2023	61
Minimum future commitments, 2024	17
Minimum future commitments, 2025	14
Minimum future commitments, 2026	9
Minimum future commitments, 2027	2
Minimum future commitments, Thereafter	22
Minimum future commitments, Total	125
IPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments, 2023	237
Minimum future commitments, 2024	123
Minimum future commitments, 2025	57
Minimum future commitments, 2026	45
Minimum future commitments, 2027	22
Minimum future commitments, Thereafter	47
Minimum future commitments, Total	531
IPL [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments, 2023	165
Minimum future commitments, 2024	86
Minimum future commitments, 2025	47
Minimum future commitments, 2026	35
Minimum future commitments, 2027	14
Minimum future commitments, Thereafter	25
Minimum future commitments, Total	372
IPL [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments, 2023	49
Minimum future commitments, 2024	35
Minimum future commitments, 2025	8
Minimum future commitments, 2026	8
Minimum future commitments, 2027	6
Minimum future commitments, Thereafter	0
Minimum future commitments, Total	106
IPL [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments, 2023	23
Minimum future commitments, 2024	2
Minimum future commitments, 2025	2
Minimum future commitments, 2026	2
Minimum future commitments, 2027	2
Minimum future commitments, Thereafter	22
Minimum future commitments, Total	53
WPL [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments, 2023	204
Minimum future commitments, 2024	116
Minimum future commitments, 2025	77
Minimum future commitments, 2026	43
Minimum future commitments, 2027	35
Minimum future commitments, Thereafter	117
Minimum future commitments, Total	592
WPL [Member] | Natural Gas [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments, 2023	136
Minimum future commitments, 2024	101
Minimum future commitments, 2025	76
Minimum future commitments, 2026	43
Minimum future commitments, 2027	35
Minimum future commitments, Thereafter	117
Minimum future commitments, Total	508
WPL [Member] | Coal [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments, 2023	45
Minimum future commitments, 2024	14
Minimum future commitments, 2025	0
Minimum future commitments, 2026	0
Minimum future commitments, 2027	0
Minimum future commitments, Thereafter	0
Minimum future commitments, Total	59
WPL [Member] | Other [Member]
Long-term Purchase Commitment [Line Items]
Minimum future commitments, 2023	23
Minimum future commitments, 2024	1
Minimum future commitments, 2025	1
Minimum future commitments, 2026	0
Minimum future commitments, 2027	0
Minimum future commitments, Thereafter	0
Minimum future commitments, Total	$ 25

Commitments And Contingencies_4

Commitments And Contingencies (Schedule Of Environmental Liabilities) (Details) - Natural Gas Processing Plant [Member] $ in Millions	12 Months Ended
	Dec. 31, 2023 USD ($)
Current and non-current environmental liabilities	$ 18
IPL [Member]
Current and non-current environmental liabilities	8
WPL [Member]
Current and non-current environmental liabilities	10
Minimum [Member]
Range of estimated future costs	9
Minimum [Member] | IPL [Member]
Range of estimated future costs	5
Minimum [Member] | WPL [Member]
Range of estimated future costs	4
Maximum [Member]
Range of estimated future costs	36
Maximum [Member] | IPL [Member]
Range of estimated future costs	11
Maximum [Member] | WPL [Member]
Range of estimated future costs	$ 25

Segments Of Business (Narrative

Segments Of Business (Narrative) (Details)	12 Months Ended
	Dec. 31, 2023 segment
Utility Business [Member]
Segment Reporting Information [Line Items]
Number of reportable segments (in segments)	3
IPL [Member]
Segment Reporting Information [Line Items]
Number of reportable segments (in segments)	3
WPL [Member]
Segment Reporting Information [Line Items]
Number of reportable segments (in segments)	3

Segments Of Business (Schedule

Segments Of Business (Schedule Of Segment Of Business) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Segment Reporting Information [Line Items]
Revenues	$ 4,027	$ 4,205	$ 3,669
Depreciation and amortization	676	671	657
Operating income (loss)	943	928	795
Interest expense	394	325	277
Equity income from unconsolidated investments, net	(61)	(51)	(62)
Income tax expense (benefit)	4	22	(74)
Net income attributable to common shareowners	703	686	659
Total assets	21,237	20,163	18,553
Investments in equity method subsidiaries	585	542	508
Construction and acquisition expenditures	1,854	1,484	1,169
IPL [Member]
Segment Reporting Information [Line Items]
Revenues	2,110	2,256	2,063
Operating income (loss)	444	453	460
Interest expense	155	148	139
Income tax expense (benefit)	(58)	(50)	(36)
Net income attributable to common shareowners	366	360	350
Total assets	10,489	10,075
WPL [Member]
Segment Reporting Information [Line Items]
Revenues	1,827	1,856	1,523
Operating income (loss)	472	452	308
Interest expense	149	121	105
Income tax expense (benefit)	60	66	(51)
Total assets	9,634	8,987
Electric [Member]
Segment Reporting Information [Line Items]
Revenues	3,345	3,421	3,081
Depreciation and amortization	602	601	591
Operating income (loss)	827	805	716
Equity income from unconsolidated investments, net	(3)	(1)	(2)
Total assets	17,833	16,571	14,924
Investments in equity method subsidiaries	21	20	17
Construction and acquisition expenditures	1,641	1,318	980
Electric [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	1,761	1,859	1,752
Depreciation and amortization	348	342	338
Operating income (loss)	390	397	420
Total assets	9,311	8,686	8,602
Construction and acquisition expenditures	671	336	342
Electric [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	1,584	1,562	1,329
Depreciation and amortization	254	259	253
Operating income (loss)	437	408	296
Total assets	8,522	7,885	6,322
Construction and acquisition expenditures	970	982	638
Gas [Member]
Segment Reporting Information [Line Items]
Revenues	540	642	456
Depreciation and amortization	60	56	54
Operating income (loss)	70	97	63
Equity income from unconsolidated investments, net	0	0	0
Total assets	1,684	1,631	1,487
Investments in equity method subsidiaries	0	0	0
Construction and acquisition expenditures	90	74	90
Gas [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	300	351	265
Depreciation and amortization	34	32	31
Operating income (loss)	35	53	43
Total assets	921	872	819
Construction and acquisition expenditures	41	36	42
Gas [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	240	291	191
Depreciation and amortization	26	24	23
Operating income (loss)	35	44	20
Total assets	763	759	668
Construction and acquisition expenditures	49	38	48
Other Utility [Member]
Segment Reporting Information [Line Items]
Revenues	52	49	49
Depreciation and amortization	6	7	6
Operating income (loss)	19	3	(11)
Equity income from unconsolidated investments, net	0	0	0
Total assets	606	860	1,103
Investments in equity method subsidiaries	0	0	0
Construction and acquisition expenditures	0	0	0
Other Utility [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	49	46	46
Depreciation and amortization	6	7	6
Operating income (loss)	19	3	(3)
Total assets	257	517	575
Construction and acquisition expenditures	0	0	0
Other Utility [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	3	3	3
Depreciation and amortization	0	0	0
Operating income (loss)	0	0	(8)
Total assets	349	343	528
Construction and acquisition expenditures	0	0	0
ATC Holdings, Non-utility, Parent and Other [Member]
Segment Reporting Information [Line Items]
Revenues	90	93	83
Depreciation and amortization	8	7	6
Operating income (loss)	27	23	27
Interest expense	90	56	33
Equity income from unconsolidated investments, net	(58)	(50)	(60)
Income tax expense (benefit)	2	6	13
Net income attributable to common shareowners	(8)	11	41
Total assets	1,114	1,101	1,039
Investments in equity method subsidiaries	564	522	491
Construction and acquisition expenditures	123	92	99
Utility Business [Member]
Segment Reporting Information [Line Items]
Revenues	3,937	4,112	3,586
Depreciation and amortization	668	664	651
Operating income (loss)	916	905	768
Interest expense	304	269	244
Equity income from unconsolidated investments, net	(3)	(1)	(2)
Income tax expense (benefit)	2	16	(87)
Net income attributable to common shareowners	711	675	618
Total assets	20,123	19,062	17,514
Investments in equity method subsidiaries	21	20	17
Construction and acquisition expenditures	1,731	1,392	1,070
Utility Business [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	2,110	2,256	2,063
Depreciation and amortization	388	381	375
Operating income (loss)	444	453	460
Interest expense	155	148	139
Income tax expense (benefit)	(58)	(50)	(36)
Net income attributable to common shareowners	366	360	350
Total assets	10,489	10,075	9,996
Construction and acquisition expenditures	712	372	384
Utility Business [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	1,827	1,856	1,523
Depreciation and amortization	280	283	276
Operating income (loss)	472	452	308
Interest expense	149	121	105
Income tax expense (benefit)	60	66	(51)
Net income attributable to common shareowners	345	315	268
Total assets	9,634	8,987	7,518
Construction and acquisition expenditures	$ 1,019	$ 1,020	$ 686

Related Parties (Narrative) (De

Related Parties (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
WPL [Member] | Related Party [Member] | WPL Owed ATC LLC [Member] | ATC LLC [Member]
Related Party Transaction [Line Items]
Net amounts owed	$ 10	$ 10

Related Parties (Service Agreem

Related Parties (Service Agreements) (Details) - Corporate Services [Member] - Subsidiary of Common Parent [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Administrative and General Services Billings [Member] | IPL [Member]
Related Party Transaction [Line Items]
Amounts billed between related parties	$ 181	$ 181	$ 180
Administrative and General Services Billings [Member] | WPL [Member]
Related Party Transaction [Line Items]
Amounts billed between related parties	163	155	154
Transmission Sales Credited [Member] | IPL [Member]
Related Party Transaction [Line Items]
Amounts billed between related parties	11	19	22
Transmission Sales Credited [Member] | WPL [Member]
Related Party Transaction [Line Items]
Amounts billed between related parties	55	74	23
Transmission Purchases Billed [Member] | IPL [Member]
Related Party Transaction [Line Items]
Amounts billed between related parties	431	435	441
Transmission Purchases Billed [Member] | WPL [Member]
Related Party Transaction [Line Items]
Amounts billed between related parties	$ 35	$ 174	$ 116

Related Parties (Net Intercompa

Related Parties (Net Intercompany Payables) (Details) - Corporate Services [Member] - Related Party [Member] - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
IPL [Member]
Related Party Transaction [Line Items]
Net amounts owed	$ 129	$ 103
WPL [Member]
Related Party Transaction [Line Items]
Net amounts owed	$ 72	$ 56

Related Parties (Related Amount

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, 2023	Dec. 31, 2022	Dec. 31, 2021
ATC Billings To WPL [Member]
Related Party Transaction [Line Items]
Amounts billed between related parties	$ 159	$ 140	$ 122
WPL Billings To ATC [Member]
Related Party Transaction [Line Items]
Amounts billed between related parties	$ 20	$ 18	$ 18

Condensed Parent Company Fina_3

Condensed Parent Company Financial Statements (Condensed Statements Of Income) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Operating expenses	$ 3,084	$ 3,277	$ 2,874
Operating income (loss)	943	928	795
Other (income) and deductions:
Equity earnings from consolidated subsidiaries	(61)	(51)	(62)
Interest expense	394	325	277
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
Parent Company [Member]
Operating expenses	3	9	5
Operating income (loss)	(3)	(9)	(5)
Other (income) and deductions:
Equity earnings from consolidated subsidiaries	(742)	(707)	(664)
Interest expense	34	6	1
Other	4	1	1
Total other (income) and deductions	(704)	(700)	(662)
Income before income taxes	701	691	657
Income tax expense (benefit)	(5)	2	(5)
Net income	$ 706	$ 689	$ 662

Condensed Parent Company Fina_4

Condensed Parent Company Financial Statements (Condensed Balance Sheets) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Current assets:
Other	$ 160	$ 223
Total current assets	1,272	1,250
Investments:
Other	216	201
Total investments	602	559
Other assets	2,206	2,107
Total assets	21,237	20,163	$ 18,553
Current liabilities:
Commercial paper	475	642
Other	302	351
Total current liabilities	2,304	2,363
Long-term debt, net	8,225	7,668
Other liabilities	617	518
Common Equity:
Retained earnings	3,756	3,509
Accumulated other comprehensive income	1	0
Shares in deferred compensation trust	(13)	(13)
Total common equity	6,777	6,276
Total liabilities and equity	21,237	20,163
Parent Company [Member]
Current assets:
Notes receivable from affiliated companies	96	65
Other	1	1
Total current assets	97	66
Investments:
Investments in consolidated subsidiaries	8,405	7,801
Other	2	2
Total investments	8,407	7,803
Other assets	90	97
Total assets	8,594	7,966
Current liabilities:
Commercial paper	157	352
Notes payable to affiliated companies	1,068	1,318
Other	10	10
Total current liabilities	1,235	1,680
Long-term debt, net	568	0
Other liabilities	2	1
Common Equity:
Common stock and additional paid-in capital	3,033	2,780
Retained earnings	3,768	3,518
Accumulated other comprehensive income	1	0
Shares in deferred compensation trust	(13)	(13)
Total common equity	6,789	6,285
Total liabilities and equity	$ 8,594	$ 7,966

Condensed Parent Company Fina_5

Condensed Parent Company Financial Statements (Condensed Statements of Cash Flows) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Net cash flows from operating activities	$ 867	$ 486	$ 582
Cash flows from (used for) investing activities:
Dividends from consolidated subsidiaries in excess of equity earnings	(120)	(47)	(61)
Net cash flows from (used for) investing activities	(1,401)	(933)	(728)
Cash flows used for financing activities:
Common stock dividends	(456)	(428)	(403)
Proceeds from issuance of common stock, net	246	25	28
Proceeds from issuance of long-term debt	1,455	1,338	600
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)
Parent Company [Member]
Net cash flows from operating activities	445	492	494
Cash flows from (used for) investing activities:
Capital contributions to consolidated subsidiaries	(325)	(530)	(295)
Net change in notes receivable from and payable to affiliates	(281)	369	(21)
Dividends from consolidated subsidiaries in excess of equity earnings	0	0	50
Net cash flows from (used for) investing activities	(606)	(161)	(266)
Cash flows used for financing activities:
Common stock dividends	(456)	(428)	(403)
Proceeds from issuance of common stock, net	246	25	28
Proceeds from issuance of long-term debt	565	0	0
Net change in commercial paper	(195)	73	147
Other	1	(1)	0
Net cash flows from (used for) financing activities	161	(331)	(228)
Net increase (decrease) in cash, cash equivalents and restricted cash	0	0	0
Cash, cash equivalents and restricted cash at beginning of period	0	0	0
Cash, cash equivalents and restricted cash at end of period	0	0	0
Supplemental cash flows information:
Interest	(27)	(6)	(1)
Income taxes, net	$ 22	$ 15	$ 4

Valuation And Qualifying Acco_2

Valuation And Qualifying Accounts and Reserves (Details) - Accumulated Provision for Uncollectible Accounts [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	$ 7	$ 11	$ 18
Charged to Expense	20	17	12
Deductions	19	21	19
Ending Balance	8	7	11
IPL [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	0	1	1
Charged to Expense	11	7	6
Deductions	11	8	6
Ending Balance	0	0	1
WPL [Member]
SEC Schedule, 12-09, Valuation and Qualifying Accounts Disclosure [Line Items]
Beginning Balance	7	10	17
Charged to Expense	9	10	6
Deductions	8	13	13
Ending Balance	$ 8	$ 7	$ 10