Interstate Power & Light (IPLDP) 10-Q 1 Nov 24 2024 Q3 Quarterly report Financial data

Document And Entity Information

Document And Entity Information	9 Months Ended
	Sep. 30, 2024 shares
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2024
Document Transition Report	false
Entity Registrant Name	ALLIANT ENERGY CORP
Entity Central Index Key	0000352541
Entity Incorporation, State or Country Code	WI
Entity Address, Address Line One	4902 N. Biltmore Lane
Entity Address, City or Town	Madison
Entity Address, State or Province	WI
Entity Address, Postal Zip Code	53718
City Area Code	608
Local Phone Number	458-3311
Entity File Number	1-9894
Entity Tax Identification Number	39-1380265
Title of 12(b) Security	Common Stock, $0.01 Par Value
Trading Symbol	LNT
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding	256,599,202
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q3
Amendment Flag	false
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 Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding	13,370,788
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 Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding	13,236,601

Condensed Consolidated Statemen

Condensed Consolidated Statements Of Income - USD ($) shares in Thousands, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Revenues:
Electric utility	$ 999	$ 995	$ 2,579	$ 2,562
Gas utility	49	47	322	400
Other utility	12	13	36	38
Non-utility	21	22	68	66
Total revenues	1,081	1,077	3,005	3,066
Operating expenses:
Electric production fuel and purchased power	192	231	493	553
Electric transmission service	165	154	464	438
Cost of gas sold	13	12	152	226
Asset valuation charge for IPL's Lansing Generating Station	0	0	60	0
Other operation and maintenance	174	160	510	499
Depreciation and amortization	195	170	571	503
Taxes other than income taxes	29	28	90	87
Total operating expenses	768	755	2,340	2,306
Operating income	313	322	665	760
Other (income) and deductions:
Interest expense	114	99	329	289
Equity income from unconsolidated investments, net	(14)	(14)	(44)	(45)
Allowance for funds used during construction	(20)	(28)	(58)	(71)
Other	0	1	2	2
Total other (income) and deductions	80	58	229	175
Income before income taxes	233	264	436	585
Income tax expense (benefit)	(62)	5	(104)	3
Net income attributable to common shareowners	$ 295	$ 259	$ 540	$ 582
Weighted average number of common shares outstanding:
Basic (in shares)	256,600	253,500	256,400	252,100
Diluted (in shares)	256,900	253,800	256,700	252,400
Earnings per weighted average common share attributable to Alliant Energy common shareowners:
Basic (in dollars per share)	$ 1.15	$ 1.02	$ 2.11	$ 2.31
Diluted (in dollars per share)	$ 1.15	$ 1.02	$ 2.10	$ 2.31
IPL [Member]
Revenues:
Electric utility	$ 523	$ 551	$ 1,318	$ 1,370
Gas utility	27	31	175	224
Other utility	11	12	34	36
Total revenues	561	594	1,527	1,630
Operating expenses:
Electric production fuel and purchased power	79	99	195	213
Electric transmission service	115	115	317	316
Cost of gas sold	8	12	85	127
Asset valuation charge for IPL's Lansing Generating Station	0	0	60	0
Other operation and maintenance	96	84	281	264
Depreciation and amortization	100	97	294	288
Taxes other than income taxes	14	14	45	43
Total operating expenses	412	421	1,277	1,251
Operating income	149	173	250	379
Other (income) and deductions:
Interest expense	44	38	128	113
Allowance for funds used during construction	(13)	(6)	(34)	(13)
Other	(4)	2	(4)	3
Total other (income) and deductions	27	34	90	103
Income before income taxes	122	139	160	276
Income tax expense (benefit)	(68)	(31)	(112)	(55)
Net income attributable to common shareowners	190	170	272	331
WPL [Member]
Revenues:
Electric utility	476	444	1,261	1,192
Gas utility	22	16	147	176
Other utility	1	1	2	2
Total revenues	499	461	1,410	1,370
Operating expenses:
Electric production fuel and purchased power	112	132	298	341
Electric transmission service	49	39	148	122
Cost of gas sold	5	0	67	99
Other operation and maintenance	72	64	200	197
Depreciation and amortization	91	71	269	208
Taxes other than income taxes	14	13	41	40
Total operating expenses	343	319	1,023	1,007
Operating income	156	142	387	363
Other (income) and deductions:
Interest expense	42	38	124	110
Allowance for funds used during construction	(7)	(22)	(24)	(58)
Other	3	(2)	4	(3)
Total other (income) and deductions	38	14	104	49
Income before income taxes	118	128	283	314
Income tax expense (benefit)	4	21	13	47
Net income attributable to common shareowners	$ 114	$ 107	$ 270	$ 267

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Current assets:
Cash and cash equivalents	$ 827	$ 62
Accounts receivable, less allowance for expected credit losses	463	475
Production fuel, at weighted average cost	60	62
Gas stored underground, at weighted average cost	60	79
Materials and supplies, at weighted average cost	200	202
Regulatory assets	214	232
Other	144	160
Total current assets	1,968	1,272
Property, plant and equipment, net	17,936	17,157
Investments:
ATC Holdings	407	386
Other	226	216
Total investments	633	602
Other assets:
Regulatory assets	2,136	2,029
Deferred charges and other	156	177
Total other assets	2,292	2,206
Total assets	22,829	21,237
Current liabilities:
Current maturities of long-term debt	1,104	809
Commercial paper	330	475
Accounts payable	473	611
Regulatory liabilities	81	107
Other	300	302
Total current liabilities	2,288	2,304
Long-term debt, net (excluding current portion)	9,245	8,225
Other liabilities:
Deferred tax liabilities	2,164	2,042
Regulatory liabilities	991	1,023
Pension and other benefit obligations	234	249
Other	939	617
Total other liabilities	4,328	3,931
Commitments and contingencies (Note 14)
Common equity:
Common stock	3	3
Additional paid-in capital	3,052	3,030
Retained earnings	3,927	3,756
Accumulated other comprehensive income (loss)	(1)	1
Shares in deferred compensation trust - 362,813 and 379,006 shares at a weighted average cost of $35.94 and $34.48 per share	(13)	(13)
Total common equity	6,968	6,777
Total liabilities and equity	22,829	21,237
IPL [Member]
Current assets:
Cash and cash equivalents	756	53
Accounts receivable, less allowance for expected credit losses	234	242
Production fuel, at weighted average cost	34	27
Gas stored underground, at weighted average cost	26	35
Materials and supplies, at weighted average cost	118	122
Regulatory assets	93	93
Other	71	51
Total current assets	1,332	623
Property, plant and equipment, net	8,801	8,298
Other assets:
Regulatory assets	1,475	1,484
Deferred charges and other	72	84
Total other assets	1,547	1,568
Total assets	11,680	10,489
Current liabilities:
Current maturities of long-term debt	800	500
Accounts payable	240	262
Accrued taxes	61	50
Accrued interest	45	40
Regulatory liabilities	34	72
Other	93	101
Total current liabilities	1,273	1,025
Long-term debt, net (excluding current portion)	3,789	3,445
Other liabilities:
Deferred tax liabilities	1,195	1,091
Regulatory liabilities	519	572
Pension and other benefit obligations	47	51
Other	437	331
Total other liabilities	2,198	2,045
Commitments and contingencies (Note 14)
Common equity:
Common stock	33	33
Additional paid-in capital	3,212	2,887
Retained earnings	1,175	1,054
Total common equity	4,420	3,974
Total liabilities and equity	11,680	10,489
WPL [Member]
Current assets:
Cash and cash equivalents	69	7
Accounts receivable, less allowance for expected credit losses	214	219
Production fuel, at weighted average cost	26	35
Gas stored underground, at weighted average cost	34	44
Materials and supplies, at weighted average cost	77	77
Regulatory assets	121	139
Prepaid gross receipts tax	37	49
Other	30	43
Total current assets	608	613
Property, plant and equipment, net	8,613	8,415
Other assets:
Regulatory assets	661	545
Deferred charges and other	56	61
Total other assets	717	606
Total assets	9,938	9,634
Current liabilities:
Commercial paper	0	318
Accounts payable	168	293
Accrued interest	41	40
Regulatory liabilities	47	35
Other	95	89
Total current liabilities	351	775
Long-term debt, net (excluding current portion)	3,369	3,070
Other liabilities:
Deferred tax liabilities	843	827
Regulatory liabilities	472	451
Pension and other benefit obligations	109	121
Other	719	493
Total other liabilities	2,143	1,892
Commitments and contingencies (Note 14)
Common equity:
Common stock	66	66
Additional paid-in capital	2,533	2,478
Retained earnings	1,476	1,353
Total common equity	4,075	3,897
Total liabilities and equity	$ 9,938	$ 9,634

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2024	Dec. 31, 2023
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	480,000,000	480,000,000
Common stock, shares outstanding (in shares)	256,599,202	256,096,848
Shares in deferred compensation trust (in shares)	362,813	379,006
Shares in deferred compensation trust, weighted average cost per share (in dollars per share)	$ 35.94	$ 34.48
IPL [Member]
Common stock, par value (in dollars per share)	$ 2.50	$ 2.50
Common stock, shares authorized (in shares)	24,000,000	24,000,000
Common stock, shares outstanding (in shares)	13,370,788	13,370,788
WPL [Member]
Common stock, par value (in dollars per share)	$ 5	$ 5
Common stock, shares authorized (in shares)	18,000,000	18,000,000
Common stock, shares outstanding (in shares)	13,236,601	13,236,601

Condensed Consolidated Statem_2

Condensed Consolidated Statements Of Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Cash flows from operating activities:
Net income	$ 540	$ 582
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	571	503
Deferred tax expense (benefit) and tax credits	(103)	(8)
Asset valuation charge for IPL's Lansing Generating Station	60	0
Other	(9)	(30)
Other changes in assets and liabilities:
Accounts receivable	(388)	(279)
Derivative assets	7	102
Accounts payable	59	(91)
Regulatory liabilities	(67)	(126)
Deferred income taxes	222	(23)
Other	21	(8)
Net cash flows from operating activities	913	622
Cash flows from (used for) investing activities:
Utility business construction and acquisition expenditures	(1,280)	(1,201)
Other construction and acquisition expenditures	(154)	(92)
Cash receipts on sold receivables	399	306
Proceeds from sales of partial ownership interests in West Riverside	123	120
Other	(28)	(85)
Net cash flows from (used for) investing activities	(940)	(952)
Cash flows from (used for) financing activities:
Common stock dividends	(369)	(341)
Proceeds from issuance of common stock, net	18	201
Proceeds from issuance of long-term debt	1,613	1,158
Payments to retire long-term debt	(305)	(404)
Net change in commercial paper and other short-term borrowings	(145)	(141)
Other	(18)	42
Net cash flows from (used for) financing activities	794	515
Net increase (decrease) in cash, cash equivalents and restricted cash	767	185
Cash, cash equivalents and restricted cash at beginning of period	63	24
Cash, cash equivalents and restricted cash at end of period	830	209
Supplemental cash flows information:
Interest	(326)	(280)
Income taxes, net	158	(6)
Significant non-cash investing and financing activities:
Accrued capital expenditures	194	287
Beneficial interest obtained in exchange for securitized accounts receivable	212	236
Indemnification Agreement [Member] | Renewable Tax Credits Transferred [Member]
Supplemental cash flows information:
Proceeds from renewable tax credits transferred to other corporate taxpayers	172
IPL [Member]
Cash flows from operating activities:
Net income	272	331
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	294	288
Deferred tax expense (benefit) and tax credits	(64)	(17)
Asset valuation charge for IPL's Lansing Generating Station	60	0
Other	(1)	(6)
Other changes in assets and liabilities:
Accounts receivable	(392)	(306)
Derivative assets	(1)	53
Regulatory assets	(36)	55
Regulatory liabilities	(65)	(90)
Deferred income taxes	166	(44)
Other	(2)	(73)
Net cash flows from operating activities	231	191
Cash flows from (used for) investing activities:
Utility business construction and acquisition expenditures	(702)	(427)
Cash receipts on sold receivables	399	306
Other	(29)	(56)
Net cash flows from (used for) investing activities	(332)	(177)
Cash flows from (used for) financing activities:
Common stock dividends	(151)	(210)
Capital contributions from parent	325	60
Proceeds from issuance of long-term debt	643	296
Other	(13)	13
Net cash flows from (used for) financing activities	804	159
Net increase (decrease) in cash, cash equivalents and restricted cash	703	173
Cash, cash equivalents and restricted cash at beginning of period	53	15
Cash, cash equivalents and restricted cash at end of period	756	188
Supplemental cash flows information:
Interest	(122)	(107)
Income taxes, net	114	36
Significant non-cash investing and financing activities:
Accrued capital expenditures	120	108
Beneficial interest obtained in exchange for securitized accounts receivable	212	236
IPL [Member] | Indemnification Agreement [Member] | Renewable Tax Credits Transferred [Member]
Supplemental cash flows information:
Proceeds from renewable tax credits transferred to other corporate taxpayers	89
WPL [Member]
Cash flows from operating activities:
Net income	270	267
Adjustments to reconcile net income to net cash flows from operating activities:
Depreciation and amortization	269	208
Other	(47)	(38)
Other changes in assets and liabilities:
Derivative assets	7	55
Regulatory assets	62	(16)
Accounts payable	28	(55)
Deferred income taxes	60	19
Other	2	(3)
Net cash flows from operating activities	651	437
Cash flows from (used for) investing activities:
Utility business construction and acquisition expenditures	(578)	(774)
Proceeds from sales of partial ownership interests in West Riverside	123	120
Other	(9)	(26)
Net cash flows from (used for) investing activities	(464)	(680)
Cash flows from (used for) financing activities:
Common stock dividends	(147)	(138)
Capital contributions from parent	55	245
Proceeds from issuance of long-term debt	297	297
Net change in commercial paper and other short-term borrowings	(318)	(170)
Other	(12)	20
Net cash flows from (used for) financing activities	(125)	254
Net increase (decrease) in cash, cash equivalents and restricted cash	62	11
Cash, cash equivalents and restricted cash at beginning of period	7	5
Cash, cash equivalents and restricted cash at end of period	69	16
Supplemental cash flows information:
Interest	(123)	(106)
Income taxes, net	36	(63)
Significant non-cash investing and financing activities:
Accrued capital expenditures	68	$ 172
WPL [Member] | Indemnification Agreement [Member] | Renewable Tax Credits Transferred [Member]
Supplemental cash flows information:
Proceeds from renewable tax credits transferred to other corporate taxpayers	$ 83

Summary Of Significant Accounti

Summary Of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2024
Summary Of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES NOTE 1(a) General - The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the 2023 Form 10-K . In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the nine months ended September 30, 2024 are not necessarily indicative of results that may be expected for the year ending December 31, 2024. A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred. Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes. NOTE 1(b) Cash and Cash Equivalents - At September 30, 2024, cash and cash equivalents included time deposits and money market fund investments of $803 million and $745 million for Alliant Energy and IPL, respectively, and money market fund investments of $58 million for WPL, with weighted average interest rates of 5%.
IPL [Member]
Summary Of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES NOTE 1(a) General - The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the 2023 Form 10-K . In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the nine months ended September 30, 2024 are not necessarily indicative of results that may be expected for the year ending December 31, 2024. A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred. Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes. NOTE 1(b) Cash and Cash Equivalents - At September 30, 2024, cash and cash equivalents included time deposits and money market fund investments of $803 million and $745 million for Alliant Energy and IPL, respectively, and money market fund investments of $58 million for WPL, with weighted average interest rates of 5%.
WPL [Member]
Summary Of Significant Accounting Policies	SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES NOTE 1(a) General - The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the 2023 Form 10-K . In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the nine months ended September 30, 2024 are not necessarily indicative of results that may be expected for the year ending December 31, 2024. A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred. Certain prior period amounts in the Financial Statements and Notes have been reclassified to conform to the current period presentation for comparative purposes. NOTE 1(b) Cash and Cash Equivalents - At September 30, 2024, cash and cash equivalents included time deposits and money market fund investments of $803 million and $745 million for Alliant Energy and IPL, respectively, and money market fund investments of $58 million for WPL, with weighted average interest rates of 5%.

Regulatory Matters

Regulatory Matters	9 Months Ended
	Sep. 30, 2024
Public Utilities, General Disclosures [Line Items]
Regulatory Matters	REGULATORY MATTERS Regulatory Assets and Regulatory Liabilities - Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $1,000 $934 $885 $831 $115 $103 AROs 418 194 223 160 195 34 Pension and OPEB costs 329 347 163 171 166 176 Assets retired early 181 273 169 259 12 14 Derivatives 80 102 24 34 56 68 Commodity cost recovery 76 120 8 12 68 108 WPL’s Western Wisconsin gas distribution expansion investments 42 44 — — 42 44 IPL’s Duane Arnold Energy Center purchased power agreement amendment 24 42 24 42 — — Other 200 205 72 68 128 137 $2,350 $2,261 $1,568 $1,577 $782 $684 AROs - Refer to Note 11 for discussion of the recognition of additional ARO regulatory assets in the second quarter of 2024, substantially resulting from the enactment of the revised CCR Rule. Assets retired early - In May 2023, IPL retired the Lansing Generating Station. IPL was previously allowed a full recovery of and a full return on this EGU from both its retail and wholesale customers. In September 2024, the IUC approved the June 2024 partial non-unanimous settlement agreement between IPL and certain stakeholders for IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period. The agreement includes a return of the remaining net book value of Lansing, but does not include a return on the remaining net book value of Lansing, effective October 1, 2024. As a result, the return on the remaining net book value is no longer recoverable from IPL’s retail electric customers, and a pre-tax non-cash charge of $60 million was recorded to “Asset valuation charge for IPL’s Lansing Generating Station” in Alliant Energy’s and IPL’s income statements for the nine months ended September 30, 2024, with a corresponding decrease in Alliant Energy’s and IPL’s assets retired early regulatory assets. Derivatives - Refer to Note 1 2 for discussion of changes in Alliant Energy’s, IPL’s and WPL’s derivative liabilities/assets during the nine months ended September 30, 2024, which resulted in comparable changes to regulatory assets/liabilities on the balance sheets. Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $589 $566 $286 $299 $303 $267 Cost of removal obligations 359 366 215 242 144 124 Derivatives 47 65 26 34 21 31 Commodity cost recovery 45 48 8 13 37 35 Other 32 85 18 56 14 29 $1,072 $1,130 $553 $644 $519 $486 Tax-related - The increase in Alliant Energy’s and WPL’s tax-related regulatory liabilities during the nine months ended September 30, 2024 was primarily due to tax benefits resulting from WPL electing investment tax credit treatment for its Cassville solar facility in the second quarter of 2024. A majority of these benefits will be addressed in a future regulatory proceeding, with a portion of the benefits passed on to WPL’s electric customers in 2024 and 2025. Rate Reviews - IPL’s Retail Electric and Gas Rate Reviews (October 2024 through September 2025 Forward-looking Test Period) - In September 2024, the IUC issued an order authorizing annual base rate increases of $185 million for IPL’s retail electric customers, with customers receiving partially offsetting credits for the first 12 months through a tax benefit rider, and $10 million for IPL’s retail gas customers, for the October 2024 through September 2025 forward-looking Test Period. Rate changes were effective October 1, 2024, and are currently subject to procedural reviews by the IUC. The IUC’s order also reflects the following: • Electric earnings sharing mechanism beginning in calendar year 2025, where IPL would apply excess earnings to the remaining net book value of IPL’s highest earning asset with advance ratemaking principles (currently the Emery Generation Station) based on its authorized return on common equity; • Investment tax credits resulting from renewable generation and battery storage projects may be utilized to offset any revenue deficiency on an annual basis up to IPL’s return on common equity threshold; any remaining investment tax credits, net of the cost of transferability, that are not used to offset any revenue deficiency, will be deferred by IPL and carried forward to offset any revenue deficiency in future years; and • Discontinuation of the renewable energy rider.
IPL [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Matters	REGULATORY MATTERS Regulatory Assets and Regulatory Liabilities - Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $1,000 $934 $885 $831 $115 $103 AROs 418 194 223 160 195 34 Pension and OPEB costs 329 347 163 171 166 176 Assets retired early 181 273 169 259 12 14 Derivatives 80 102 24 34 56 68 Commodity cost recovery 76 120 8 12 68 108 WPL’s Western Wisconsin gas distribution expansion investments 42 44 — — 42 44 IPL’s Duane Arnold Energy Center purchased power agreement amendment 24 42 24 42 — — Other 200 205 72 68 128 137 $2,350 $2,261 $1,568 $1,577 $782 $684 AROs - Refer to Note 11 for discussion of the recognition of additional ARO regulatory assets in the second quarter of 2024, substantially resulting from the enactment of the revised CCR Rule. Assets retired early - In May 2023, IPL retired the Lansing Generating Station. IPL was previously allowed a full recovery of and a full return on this EGU from both its retail and wholesale customers. In September 2024, the IUC approved the June 2024 partial non-unanimous settlement agreement between IPL and certain stakeholders for IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period. The agreement includes a return of the remaining net book value of Lansing, but does not include a return on the remaining net book value of Lansing, effective October 1, 2024. As a result, the return on the remaining net book value is no longer recoverable from IPL’s retail electric customers, and a pre-tax non-cash charge of $60 million was recorded to “Asset valuation charge for IPL’s Lansing Generating Station” in Alliant Energy’s and IPL’s income statements for the nine months ended September 30, 2024, with a corresponding decrease in Alliant Energy’s and IPL’s assets retired early regulatory assets. Derivatives - Refer to Note 1 2 for discussion of changes in Alliant Energy’s, IPL’s and WPL’s derivative liabilities/assets during the nine months ended September 30, 2024, which resulted in comparable changes to regulatory assets/liabilities on the balance sheets. Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $589 $566 $286 $299 $303 $267 Cost of removal obligations 359 366 215 242 144 124 Derivatives 47 65 26 34 21 31 Commodity cost recovery 45 48 8 13 37 35 Other 32 85 18 56 14 29 $1,072 $1,130 $553 $644 $519 $486 Tax-related - The increase in Alliant Energy’s and WPL’s tax-related regulatory liabilities during the nine months ended September 30, 2024 was primarily due to tax benefits resulting from WPL electing investment tax credit treatment for its Cassville solar facility in the second quarter of 2024. A majority of these benefits will be addressed in a future regulatory proceeding, with a portion of the benefits passed on to WPL’s electric customers in 2024 and 2025. Rate Reviews - IPL’s Retail Electric and Gas Rate Reviews (October 2024 through September 2025 Forward-looking Test Period) - In September 2024, the IUC issued an order authorizing annual base rate increases of $185 million for IPL’s retail electric customers, with customers receiving partially offsetting credits for the first 12 months through a tax benefit rider, and $10 million for IPL’s retail gas customers, for the October 2024 through September 2025 forward-looking Test Period. Rate changes were effective October 1, 2024, and are currently subject to procedural reviews by the IUC. The IUC’s order also reflects the following: • Electric earnings sharing mechanism beginning in calendar year 2025, where IPL would apply excess earnings to the remaining net book value of IPL’s highest earning asset with advance ratemaking principles (currently the Emery Generation Station) based on its authorized return on common equity; • Investment tax credits resulting from renewable generation and battery storage projects may be utilized to offset any revenue deficiency on an annual basis up to IPL’s return on common equity threshold; any remaining investment tax credits, net of the cost of transferability, that are not used to offset any revenue deficiency, will be deferred by IPL and carried forward to offset any revenue deficiency in future years; and • Discontinuation of the renewable energy rider.
WPL [Member]
Public Utilities, General Disclosures [Line Items]
Regulatory Matters	REGULATORY MATTERS Regulatory Assets and Regulatory Liabilities - Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $1,000 $934 $885 $831 $115 $103 AROs 418 194 223 160 195 34 Pension and OPEB costs 329 347 163 171 166 176 Assets retired early 181 273 169 259 12 14 Derivatives 80 102 24 34 56 68 Commodity cost recovery 76 120 8 12 68 108 WPL’s Western Wisconsin gas distribution expansion investments 42 44 — — 42 44 IPL’s Duane Arnold Energy Center purchased power agreement amendment 24 42 24 42 — — Other 200 205 72 68 128 137 $2,350 $2,261 $1,568 $1,577 $782 $684 AROs - Refer to Note 11 for discussion of the recognition of additional ARO regulatory assets in the second quarter of 2024, substantially resulting from the enactment of the revised CCR Rule. Assets retired early - In May 2023, IPL retired the Lansing Generating Station. IPL was previously allowed a full recovery of and a full return on this EGU from both its retail and wholesale customers. In September 2024, the IUC approved the June 2024 partial non-unanimous settlement agreement between IPL and certain stakeholders for IPL’s retail electric rate review for the October 2024 through September 2025 forward-looking Test Period. The agreement includes a return of the remaining net book value of Lansing, but does not include a return on the remaining net book value of Lansing, effective October 1, 2024. As a result, the return on the remaining net book value is no longer recoverable from IPL’s retail electric customers, and a pre-tax non-cash charge of $60 million was recorded to “Asset valuation charge for IPL’s Lansing Generating Station” in Alliant Energy’s and IPL’s income statements for the nine months ended September 30, 2024, with a corresponding decrease in Alliant Energy’s and IPL’s assets retired early regulatory assets. Derivatives - Refer to Note 1 2 for discussion of changes in Alliant Energy’s, IPL’s and WPL’s derivative liabilities/assets during the nine months ended September 30, 2024, which resulted in comparable changes to regulatory assets/liabilities on the balance sheets. Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $589 $566 $286 $299 $303 $267 Cost of removal obligations 359 366 215 242 144 124 Derivatives 47 65 26 34 21 31 Commodity cost recovery 45 48 8 13 37 35 Other 32 85 18 56 14 29 $1,072 $1,130 $553 $644 $519 $486 Tax-related - The increase in Alliant Energy’s and WPL’s tax-related regulatory liabilities during the nine months ended September 30, 2024 was primarily due to tax benefits resulting from WPL electing investment tax credit treatment for its Cassville solar facility in the second quarter of 2024. A majority of these benefits will be addressed in a future regulatory proceeding, with a portion of the benefits passed on to WPL’s electric customers in 2024 and 2025. Rate Reviews - IPL’s Retail Electric and Gas Rate Reviews (October 2024 through September 2025 Forward-looking Test Period) - In September 2024, the IUC issued an order authorizing annual base rate increases of $185 million for IPL’s retail electric customers, with customers receiving partially offsetting credits for the first 12 months through a tax benefit rider, and $10 million for IPL’s retail gas customers, for the October 2024 through September 2025 forward-looking Test Period. Rate changes were effective October 1, 2024, and are currently subject to procedural reviews by the IUC. The IUC’s order also reflects the following: • Electric earnings sharing mechanism beginning in calendar year 2025, where IPL would apply excess earnings to the remaining net book value of IPL’s highest earning asset with advance ratemaking principles (currently the Emery Generation Station) based on its authorized return on common equity; • Investment tax credits resulting from renewable generation and battery storage projects may be utilized to offset any revenue deficiency on an annual basis up to IPL’s return on common equity threshold; any remaining investment tax credits, net of the cost of transferability, that are not used to offset any revenue deficiency, will be deferred by IPL and carried forward to offset any revenue deficiency in future years; and • Discontinuation of the renewable energy rider.

Property, Plant and Equipment

Property, Plant and Equipment	9 Months Ended
	Sep. 30, 2024
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	PROPERTY, PLANT AND EQUIPMENT WPL currently expects construction costs associated with its approximately 1,100 MW of new solar generation will exceed the construction cost estimates previously approved by the PSCW by approximately $195 million. In February 2024, the PSCW issued an order approving deferral of the incremental solar generation construction costs. The PSCW’s order did not authorize a deferral for the return on such costs. In March 2024, WPL filed for judicial review of the PSCW’s retail electric rate review order (2024/2025 forward-looking Test Period) and solar generation construction cost deferral order related to the recovery and deferral of the return on the incremental solar generation construction costs in 2024 and 2025. In September 2024, the PSCW issued an order modifying its February 2024 order and approving the deferral of the return on the incremental solar generation construction costs, and in October 2024, WPL withdrew its filing for judicial review. Alliant Energy and WPL concluded that there was not a probable disallowance of anticipated higher rate base amounts as of September 30, 2024 given construction costs were reasonably and prudently incurred. In September 2024, the IUC approved IPL’s settlement agreement with certain stakeholders for its retail electric rate review for the October 2024 through September 2025 forward-looking Test Period. The settlement agreement allows IPL to recover construction costs associated with its 400 MW of new solar generation, including allowance for funds used during construction and transmission upgrade costs among other costs, above the original cost target of $1,650/kilowatt up to $1,837.5/kilowatt. The costs up to the original cost target of $1,650/kilowatt will earn a return on common equity of 10.25%. The costs between $1,650/kilowatt and $1,837.5/kilowatt will earn a return on common equity that is the same as other assets without advance rate-making principles, without having to establish that such costs were reasonably and prudently incurred. Alliant Energy and IPL currently do not expect these construction costs will exceed $1,837.5/kilowatt. In May 2024, WPL announced updated plans to convert the coal-fired Edgewater Unit 5 to natural gas in 2028, subject to regulatory approvals. WPL previously planned to retire the EGU by June 1, 2025. As a result, as of September 30, 2024, Alliant Energy and WPL concluded Edgewater Unit 5 (net book value of $493 million) no longer meets the criteria to be considered probable of abandonment, and $794 million was reclassified to utility electric generation plant in service from utility electric plant anticipated to be retired early. 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 May 2024, WPL renewed this financing lease through 2044. There are no lease renewal periods remaining. In June 2024, WEC Energy Group, Inc. and Madison Gas and Electric Company acquired partial ownership interests in West Riverside. The related proceeds are included in “Proceeds from sales of partial ownership interests in West Riverside” in investing activities in Alliant Energy’s and WPL’s cash flows statements for the nine months ended September 30, 2024. As a result of these transactions, WPL’s undivided current ownership interest in West Riverside is 56.6%.
IPL [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	PROPERTY, PLANT AND EQUIPMENT WPL currently expects construction costs associated with its approximately 1,100 MW of new solar generation will exceed the construction cost estimates previously approved by the PSCW by approximately $195 million. In February 2024, the PSCW issued an order approving deferral of the incremental solar generation construction costs. The PSCW’s order did not authorize a deferral for the return on such costs. In March 2024, WPL filed for judicial review of the PSCW’s retail electric rate review order (2024/2025 forward-looking Test Period) and solar generation construction cost deferral order related to the recovery and deferral of the return on the incremental solar generation construction costs in 2024 and 2025. In September 2024, the PSCW issued an order modifying its February 2024 order and approving the deferral of the return on the incremental solar generation construction costs, and in October 2024, WPL withdrew its filing for judicial review. Alliant Energy and WPL concluded that there was not a probable disallowance of anticipated higher rate base amounts as of September 30, 2024 given construction costs were reasonably and prudently incurred. In September 2024, the IUC approved IPL’s settlement agreement with certain stakeholders for its retail electric rate review for the October 2024 through September 2025 forward-looking Test Period. The settlement agreement allows IPL to recover construction costs associated with its 400 MW of new solar generation, including allowance for funds used during construction and transmission upgrade costs among other costs, above the original cost target of $1,650/kilowatt up to $1,837.5/kilowatt. The costs up to the original cost target of $1,650/kilowatt will earn a return on common equity of 10.25%. The costs between $1,650/kilowatt and $1,837.5/kilowatt will earn a return on common equity that is the same as other assets without advance rate-making principles, without having to establish that such costs were reasonably and prudently incurred. Alliant Energy and IPL currently do not expect these construction costs will exceed $1,837.5/kilowatt. In May 2024, WPL announced updated plans to convert the coal-fired Edgewater Unit 5 to natural gas in 2028, subject to regulatory approvals. WPL previously planned to retire the EGU by June 1, 2025. As a result, as of September 30, 2024, Alliant Energy and WPL concluded Edgewater Unit 5 (net book value of $493 million) no longer meets the criteria to be considered probable of abandonment, and $794 million was reclassified to utility electric generation plant in service from utility electric plant anticipated to be retired early. 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 May 2024, WPL renewed this financing lease through 2044. There are no lease renewal periods remaining. In June 2024, WEC Energy Group, Inc. and Madison Gas and Electric Company acquired partial ownership interests in West Riverside. The related proceeds are included in “Proceeds from sales of partial ownership interests in West Riverside” in investing activities in Alliant Energy’s and WPL’s cash flows statements for the nine months ended September 30, 2024. As a result of these transactions, WPL’s undivided current ownership interest in West Riverside is 56.6%.
WPL [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment	PROPERTY, PLANT AND EQUIPMENT WPL currently expects construction costs associated with its approximately 1,100 MW of new solar generation will exceed the construction cost estimates previously approved by the PSCW by approximately $195 million. In February 2024, the PSCW issued an order approving deferral of the incremental solar generation construction costs. The PSCW’s order did not authorize a deferral for the return on such costs. In March 2024, WPL filed for judicial review of the PSCW’s retail electric rate review order (2024/2025 forward-looking Test Period) and solar generation construction cost deferral order related to the recovery and deferral of the return on the incremental solar generation construction costs in 2024 and 2025. In September 2024, the PSCW issued an order modifying its February 2024 order and approving the deferral of the return on the incremental solar generation construction costs, and in October 2024, WPL withdrew its filing for judicial review. Alliant Energy and WPL concluded that there was not a probable disallowance of anticipated higher rate base amounts as of September 30, 2024 given construction costs were reasonably and prudently incurred. In September 2024, the IUC approved IPL’s settlement agreement with certain stakeholders for its retail electric rate review for the October 2024 through September 2025 forward-looking Test Period. The settlement agreement allows IPL to recover construction costs associated with its 400 MW of new solar generation, including allowance for funds used during construction and transmission upgrade costs among other costs, above the original cost target of $1,650/kilowatt up to $1,837.5/kilowatt. The costs up to the original cost target of $1,650/kilowatt will earn a return on common equity of 10.25%. The costs between $1,650/kilowatt and $1,837.5/kilowatt will earn a return on common equity that is the same as other assets without advance rate-making principles, without having to establish that such costs were reasonably and prudently incurred. Alliant Energy and IPL currently do not expect these construction costs will exceed $1,837.5/kilowatt. In May 2024, WPL announced updated plans to convert the coal-fired Edgewater Unit 5 to natural gas in 2028, subject to regulatory approvals. WPL previously planned to retire the EGU by June 1, 2025. As a result, as of September 30, 2024, Alliant Energy and WPL concluded Edgewater Unit 5 (net book value of $493 million) no longer meets the criteria to be considered probable of abandonment, and $794 million was reclassified to utility electric generation plant in service from utility electric plant anticipated to be retired early. 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 May 2024, WPL renewed this financing lease through 2044. There are no lease renewal periods remaining. In June 2024, WEC Energy Group, Inc. and Madison Gas and Electric Company acquired partial ownership interests in West Riverside. The related proceeds are included in “Proceeds from sales of partial ownership interests in West Riverside” in investing activities in Alliant Energy’s and WPL’s cash flows statements for the nine months ended September 30, 2024. As a result of these transactions, WPL’s undivided current ownership interest in West Riverside is 56.6%.

Receivables

Receivables	9 Months Ended
	Sep. 30, 2024
Receivables [Line Items]
Receivables	RECEIVABLES Sales of Accounts Receivable - IPL maintains a Receivables Purchase and Sale Agreement (Receivables Agreement) whereby it may sell its customer accounts receivables, unbilled revenues and certain other accounts receivables to a third party through wholly-owned and consolidated special purpose entities. In March 2024, IPL amended and extended through March 2026 the purchase commitment from the third party to which it sells its receivables. The transfers of receivables meet the criteria for sale accounting established by the transfer of financial assets accounting rules. Effective September 2024, the limit on cash proceeds under the Receivables Agreement was changed to $5 million. As of September 30, 2024, IPL had $4 million of available capacity under its sales of accounts receivable program. IPL’s maximum and average outstanding aggregate cash proceeds (based on daily outstanding balances) related to the sales of accounts receivable program for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2024 2023 2024 2023 Maximum outstanding aggregate cash proceeds $52 $94 $110 $110 Average outstanding aggregate cash proceeds 7 46 34 68 The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): September 30, 2024 December 31, 2023 Customer accounts receivable $141 $130 Unbilled utility revenues 81 98 Other receivables 1 1 Receivables sold to third party 223 229 Less: cash proceeds 1 1 Deferred proceeds 222 228 Less: allowance for expected credit losses 10 12 Fair value of deferred proceeds $212 $216 As of September 30, 2024, outstanding receivables past due under the Receivables Agreement were $16 million. Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2024 2023 2024 2023 Collections $565 $616 $1,578 $1,720 Write-offs, net of recoveries 4 5 9 9
IPL [Member]
Receivables [Line Items]
Receivables	RECEIVABLES Sales of Accounts Receivable - IPL maintains a Receivables Purchase and Sale Agreement (Receivables Agreement) whereby it may sell its customer accounts receivables, unbilled revenues and certain other accounts receivables to a third party through wholly-owned and consolidated special purpose entities. In March 2024, IPL amended and extended through March 2026 the purchase commitment from the third party to which it sells its receivables. The transfers of receivables meet the criteria for sale accounting established by the transfer of financial assets accounting rules. Effective September 2024, the limit on cash proceeds under the Receivables Agreement was changed to $5 million. As of September 30, 2024, IPL had $4 million of available capacity under its sales of accounts receivable program. IPL’s maximum and average outstanding aggregate cash proceeds (based on daily outstanding balances) related to the sales of accounts receivable program for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2024 2023 2024 2023 Maximum outstanding aggregate cash proceeds $52 $94 $110 $110 Average outstanding aggregate cash proceeds 7 46 34 68 The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): September 30, 2024 December 31, 2023 Customer accounts receivable $141 $130 Unbilled utility revenues 81 98 Other receivables 1 1 Receivables sold to third party 223 229 Less: cash proceeds 1 1 Deferred proceeds 222 228 Less: allowance for expected credit losses 10 12 Fair value of deferred proceeds $212 $216 As of September 30, 2024, outstanding receivables past due under the Receivables Agreement were $16 million. Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2024 2023 2024 2023 Collections $565 $616 $1,578 $1,720 Write-offs, net of recoveries 4 5 9 9

Investments

Investments	9 Months Ended
	Sep. 30, 2024
Schedule of Equity Method Investments [Line Items]
Investments	INVESTMENTS Unconsolidated Equity Investments - Alliant Energy’s equity (income) loss from unconsolidated investments accounted for under the equity method of accounting for the three and nine months ended September 30 was as follows (in millions): Three Months Nine Months 2024 2023 2024 2023 ATC Holdings ($13) ($12) ($38) ($37) Other (1) (2) (6) (8) ($14) ($14) ($44) ($45)

Common Equity

Common Equity	9 Months Ended
	Sep. 30, 2024
Common Equity [Line Items]
Common Equity	COMMON EQUITY Common Share Activity - A summary of Alliant Energy’s common stock activity was as follows: Shares outstanding, January 1, 2024 256,096,848 Shareowner Direct Plan 348,087 Equity-based compensation plans 154,267 Shares outstanding, September 30, 2024 256,599,202 Changes in Shareowners’ Equity - A summary of changes in shareowners’ equity was as follows (in millions): Alliant Energy Accumulated Shares in Additional Other Deferred Total Common Paid-In Retained Comprehensive Compensation Common Stock Capital Earnings Income (Loss) Trust Equity Three Months Ended September 30, 2024 Beginning balance, June 30, 2024 $3 $3,042 $3,755 $3 ($12) $6,791 Net income attributable to Alliant Energy common shareowners 295 295 Common stock dividends ($0.48 per share) (123) (123) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other 4 (1) 3 Other comprehensive loss, net of tax (4) (4) Ending balance, September 30, 2024 $3 $3,052 $3,927 ($1) ($13) $6,968 Three Months Ended September 30, 2023 Beginning balance, June 30, 2023 $3 $2,854 $3,606 $3 ($14) $6,452 Net income attributable to Alliant Energy common shareowners 259 259 Common stock dividends ($0.4525 per share) (115) (115) At-the-market offering program and Shareowner Direct Plan issuances 125 125 Equity-based compensation plans and other 3 1 4 Other comprehensive income, net of tax 1 1 Ending balance, September 30, 2023 $3 $2,982 $3,750 $4 ($13) $6,726 Alliant Energy Accumulated Shares in Additional Other Deferred Total Common Paid-In Retained Comprehensive Compensation Common Stock Capital Earnings Income (Loss) Trust Equity Nine Months Ended September 30, 2024 Beginning balance, December 31, 2023 $3 $3,030 $3,756 $1 ($13) $6,777 Net income attributable to Alliant Energy common shareowners 540 540 Common stock dividends ($1.44 per share) (369) (369) Shareowner Direct Plan issuances 18 18 Equity-based compensation plans and other 4 4 Other comprehensive loss, net of tax (2) (2) Ending balance, September 30, 2024 $3 $3,052 $3,927 ($1) ($13) $6,968 Nine Months Ended September 30, 2023 Beginning balance, December 31, 2022 $3 $2,777 $3,509 $— ($13) $6,276 Net income attributable to Alliant Energy common shareowners 582 582 Common stock dividends ($1.3575 per share) (341) (341) At-the-market offering program and Shareowner Direct Plan issuances 201 201 Equity-based compensation plans and other 4 4 Other comprehensive income, net of tax 4 4 Ending balance, September 30, 2023 $3 $2,982 $3,750 $4 ($13) $6,726 IPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended September 30, 2024 Beginning balance, June 30, 2024 $33 $3,012 $1,035 $4,080 Net income 190 190 Common stock dividends (50) (50) Capital contributions from parent 200 200 Ending balance, September 30, 2024 $33 $3,212 $1,175 $4,420 Three Months Ended September 30, 2023 Beginning balance, June 30, 2023 $33 $2,847 $989 $3,869 Net income 170 170 Common stock dividends (70) (70) Capital contributions from parent 20 20 Ending balance, September 30, 2023 $33 $2,867 $1,089 $3,989 IPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Nine Months Ended September 30, 2024 Beginning balance, December 31, 2023 $33 $2,887 $1,054 $3,974 Net income 272 272 Common stock dividends (151) (151) Capital contributions from parent 325 325 Ending balance, September 30, 2024 $33 $3,212 $1,175 $4,420 Nine Months Ended September 30, 2023 Beginning balance, December 31, 2022 $33 $2,807 $968 $3,808 Net income 331 331 Common stock dividends (210) (210) Capital contributions from parent 60 60 Ending balance, September 30, 2023 $33 $2,867 $1,089 $3,989 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended September 30, 2024 Beginning balance, June 30, 2024 $66 $2,533 $1,411 $4,010 Net income 114 114 Common stock dividends (49) (49) Ending balance, September 30, 2024 $66 $2,533 $1,476 $4,075 Three Months Ended September 30, 2023 Beginning balance, June 30, 2023 $66 $2,413 $1,260 $3,739 Net income 107 107 Common stock dividends (46) (46) Capital contributions from parent 65 65 Ending balance, September 30, 2023 $66 $2,478 $1,321 $3,865 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Nine Months Ended September 30, 2024 Beginning balance, December 31, 2023 $66 $2,478 $1,353 $3,897 Net income 270 270 Common stock dividends (147) (147) Capital contributions from parent 55 55 Ending balance, September 30, 2024 $66 $2,533 $1,476 $4,075 Nine Months Ended September 30, 2023 Beginning balance, December 31, 2022 $66 $2,233 $1,192 $3,491 Net income 267 267 Common stock dividends (138) (138) Capital contributions from parent 245 245 Ending balance, September 30, 2023 $66 $2,478 $1,321 $3,865
IPL [Member]
Common Equity [Line Items]
Common Equity	COMMON EQUITY Common Share Activity - A summary of Alliant Energy’s common stock activity was as follows: Shares outstanding, January 1, 2024 256,096,848 Shareowner Direct Plan 348,087 Equity-based compensation plans 154,267 Shares outstanding, September 30, 2024 256,599,202 Changes in Shareowners’ Equity - A summary of changes in shareowners’ equity was as follows (in millions): Alliant Energy Accumulated Shares in Additional Other Deferred Total Common Paid-In Retained Comprehensive Compensation Common Stock Capital Earnings Income (Loss) Trust Equity Three Months Ended September 30, 2024 Beginning balance, June 30, 2024 $3 $3,042 $3,755 $3 ($12) $6,791 Net income attributable to Alliant Energy common shareowners 295 295 Common stock dividends ($0.48 per share) (123) (123) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other 4 (1) 3 Other comprehensive loss, net of tax (4) (4) Ending balance, September 30, 2024 $3 $3,052 $3,927 ($1) ($13) $6,968 Three Months Ended September 30, 2023 Beginning balance, June 30, 2023 $3 $2,854 $3,606 $3 ($14) $6,452 Net income attributable to Alliant Energy common shareowners 259 259 Common stock dividends ($0.4525 per share) (115) (115) At-the-market offering program and Shareowner Direct Plan issuances 125 125 Equity-based compensation plans and other 3 1 4 Other comprehensive income, net of tax 1 1 Ending balance, September 30, 2023 $3 $2,982 $3,750 $4 ($13) $6,726 Alliant Energy Accumulated Shares in Additional Other Deferred Total Common Paid-In Retained Comprehensive Compensation Common Stock Capital Earnings Income (Loss) Trust Equity Nine Months Ended September 30, 2024 Beginning balance, December 31, 2023 $3 $3,030 $3,756 $1 ($13) $6,777 Net income attributable to Alliant Energy common shareowners 540 540 Common stock dividends ($1.44 per share) (369) (369) Shareowner Direct Plan issuances 18 18 Equity-based compensation plans and other 4 4 Other comprehensive loss, net of tax (2) (2) Ending balance, September 30, 2024 $3 $3,052 $3,927 ($1) ($13) $6,968 Nine Months Ended September 30, 2023 Beginning balance, December 31, 2022 $3 $2,777 $3,509 $— ($13) $6,276 Net income attributable to Alliant Energy common shareowners 582 582 Common stock dividends ($1.3575 per share) (341) (341) At-the-market offering program and Shareowner Direct Plan issuances 201 201 Equity-based compensation plans and other 4 4 Other comprehensive income, net of tax 4 4 Ending balance, September 30, 2023 $3 $2,982 $3,750 $4 ($13) $6,726 IPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended September 30, 2024 Beginning balance, June 30, 2024 $33 $3,012 $1,035 $4,080 Net income 190 190 Common stock dividends (50) (50) Capital contributions from parent 200 200 Ending balance, September 30, 2024 $33 $3,212 $1,175 $4,420 Three Months Ended September 30, 2023 Beginning balance, June 30, 2023 $33 $2,847 $989 $3,869 Net income 170 170 Common stock dividends (70) (70) Capital contributions from parent 20 20 Ending balance, September 30, 2023 $33 $2,867 $1,089 $3,989 IPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Nine Months Ended September 30, 2024 Beginning balance, December 31, 2023 $33 $2,887 $1,054 $3,974 Net income 272 272 Common stock dividends (151) (151) Capital contributions from parent 325 325 Ending balance, September 30, 2024 $33 $3,212 $1,175 $4,420 Nine Months Ended September 30, 2023 Beginning balance, December 31, 2022 $33 $2,807 $968 $3,808 Net income 331 331 Common stock dividends (210) (210) Capital contributions from parent 60 60 Ending balance, September 30, 2023 $33 $2,867 $1,089 $3,989 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended September 30, 2024 Beginning balance, June 30, 2024 $66 $2,533 $1,411 $4,010 Net income 114 114 Common stock dividends (49) (49) Ending balance, September 30, 2024 $66 $2,533 $1,476 $4,075 Three Months Ended September 30, 2023 Beginning balance, June 30, 2023 $66 $2,413 $1,260 $3,739 Net income 107 107 Common stock dividends (46) (46) Capital contributions from parent 65 65 Ending balance, September 30, 2023 $66 $2,478 $1,321 $3,865 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Nine Months Ended September 30, 2024 Beginning balance, December 31, 2023 $66 $2,478 $1,353 $3,897 Net income 270 270 Common stock dividends (147) (147) Capital contributions from parent 55 55 Ending balance, September 30, 2024 $66 $2,533 $1,476 $4,075 Nine Months Ended September 30, 2023 Beginning balance, December 31, 2022 $66 $2,233 $1,192 $3,491 Net income 267 267 Common stock dividends (138) (138) Capital contributions from parent 245 245 Ending balance, September 30, 2023 $66 $2,478 $1,321 $3,865
WPL [Member]
Common Equity [Line Items]
Common Equity	COMMON EQUITY Common Share Activity - A summary of Alliant Energy’s common stock activity was as follows: Shares outstanding, January 1, 2024 256,096,848 Shareowner Direct Plan 348,087 Equity-based compensation plans 154,267 Shares outstanding, September 30, 2024 256,599,202 Changes in Shareowners’ Equity - A summary of changes in shareowners’ equity was as follows (in millions): Alliant Energy Accumulated Shares in Additional Other Deferred Total Common Paid-In Retained Comprehensive Compensation Common Stock Capital Earnings Income (Loss) Trust Equity Three Months Ended September 30, 2024 Beginning balance, June 30, 2024 $3 $3,042 $3,755 $3 ($12) $6,791 Net income attributable to Alliant Energy common shareowners 295 295 Common stock dividends ($0.48 per share) (123) (123) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other 4 (1) 3 Other comprehensive loss, net of tax (4) (4) Ending balance, September 30, 2024 $3 $3,052 $3,927 ($1) ($13) $6,968 Three Months Ended September 30, 2023 Beginning balance, June 30, 2023 $3 $2,854 $3,606 $3 ($14) $6,452 Net income attributable to Alliant Energy common shareowners 259 259 Common stock dividends ($0.4525 per share) (115) (115) At-the-market offering program and Shareowner Direct Plan issuances 125 125 Equity-based compensation plans and other 3 1 4 Other comprehensive income, net of tax 1 1 Ending balance, September 30, 2023 $3 $2,982 $3,750 $4 ($13) $6,726 Alliant Energy Accumulated Shares in Additional Other Deferred Total Common Paid-In Retained Comprehensive Compensation Common Stock Capital Earnings Income (Loss) Trust Equity Nine Months Ended September 30, 2024 Beginning balance, December 31, 2023 $3 $3,030 $3,756 $1 ($13) $6,777 Net income attributable to Alliant Energy common shareowners 540 540 Common stock dividends ($1.44 per share) (369) (369) Shareowner Direct Plan issuances 18 18 Equity-based compensation plans and other 4 4 Other comprehensive loss, net of tax (2) (2) Ending balance, September 30, 2024 $3 $3,052 $3,927 ($1) ($13) $6,968 Nine Months Ended September 30, 2023 Beginning balance, December 31, 2022 $3 $2,777 $3,509 $— ($13) $6,276 Net income attributable to Alliant Energy common shareowners 582 582 Common stock dividends ($1.3575 per share) (341) (341) At-the-market offering program and Shareowner Direct Plan issuances 201 201 Equity-based compensation plans and other 4 4 Other comprehensive income, net of tax 4 4 Ending balance, September 30, 2023 $3 $2,982 $3,750 $4 ($13) $6,726 IPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended September 30, 2024 Beginning balance, June 30, 2024 $33 $3,012 $1,035 $4,080 Net income 190 190 Common stock dividends (50) (50) Capital contributions from parent 200 200 Ending balance, September 30, 2024 $33 $3,212 $1,175 $4,420 Three Months Ended September 30, 2023 Beginning balance, June 30, 2023 $33 $2,847 $989 $3,869 Net income 170 170 Common stock dividends (70) (70) Capital contributions from parent 20 20 Ending balance, September 30, 2023 $33 $2,867 $1,089 $3,989 IPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Nine Months Ended September 30, 2024 Beginning balance, December 31, 2023 $33 $2,887 $1,054 $3,974 Net income 272 272 Common stock dividends (151) (151) Capital contributions from parent 325 325 Ending balance, September 30, 2024 $33 $3,212 $1,175 $4,420 Nine Months Ended September 30, 2023 Beginning balance, December 31, 2022 $33 $2,807 $968 $3,808 Net income 331 331 Common stock dividends (210) (210) Capital contributions from parent 60 60 Ending balance, September 30, 2023 $33 $2,867 $1,089 $3,989 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended September 30, 2024 Beginning balance, June 30, 2024 $66 $2,533 $1,411 $4,010 Net income 114 114 Common stock dividends (49) (49) Ending balance, September 30, 2024 $66 $2,533 $1,476 $4,075 Three Months Ended September 30, 2023 Beginning balance, June 30, 2023 $66 $2,413 $1,260 $3,739 Net income 107 107 Common stock dividends (46) (46) Capital contributions from parent 65 65 Ending balance, September 30, 2023 $66 $2,478 $1,321 $3,865 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Nine Months Ended September 30, 2024 Beginning balance, December 31, 2023 $66 $2,478 $1,353 $3,897 Net income 270 270 Common stock dividends (147) (147) Capital contributions from parent 55 55 Ending balance, September 30, 2024 $66 $2,533 $1,476 $4,075 Nine Months Ended September 30, 2023 Beginning balance, December 31, 2022 $66 $2,233 $1,192 $3,491 Net income 267 267 Common stock dividends (138) (138) Capital contributions from parent 245 245 Ending balance, September 30, 2023 $66 $2,478 $1,321 $3,865

Debt

Debt	9 Months Ended
	Sep. 30, 2024
Debt [Line Items]
Debt	DEBT NOTE 7(a) Short-term Debt - In June 2024, Alliant Energy, IPL and WPL reallocated credit facility capacity amounts to $450 million for Alliant Energy at the parent company level, $250 million for IPL and $300 million for WPL, within the $1 billion total commitment. Information regarding commercial paper classified as short-term debt was as follows (dollars in millions): September 30, 2024 Alliant Energy IPL WPL Amount outstanding $330 $— $— Weighted average interest rates 5.0% —% —% Available credit facility capacity $670 $250 $300 Alliant Energy IPL WPL Three Months Ended September 30 2024 2023 2024 2023 2024 2023 Maximum amount outstanding (based on daily outstanding balances) $330 $474 $— $7 $— $125 Average amount outstanding (based on daily outstanding balances) $197 $440 $— $— $— $86 Weighted average interest rates 5.4% 5.5% —% 5.5% —% 5.4% Nine Months Ended September 30 Maximum amount outstanding (based on daily outstanding balances) $632 $793 $19 $70 $390 $349 Average amount outstanding (based on daily outstanding balances) $320 $367 $1 $2 $87 $135 Weighted average interest rates 5.5% 5.1% 5.5% 5.3% 5.5% 4.9% NOTE 7(b) Long-term Debt - In March 2024, AEF entered into a $300 million variable rate (6% as of September 30, 2024) term loan credit agreement (with Alliant Energy as guarantor), which expires in March 2025. This term loan credit agreement amends and restates the term loan credit agreement that expired in March 2024, and retired the $300 million variable rate term loan set forth therein. AEF’s restated term loan credit agreement includes an option to increase the amount outstanding with one or more additional term loans in an aggregate amount not to exceed $100 million. In June 2024, AEF issued $375 million of 5.4% senior notes due 2027 (with Alliant Energy as guarantor). The net proceeds from this issuance were used to reduce Alliant Energy’s outstanding commercial paper and for general corporate purposes. In September 2024, IPL issued $350 million of 4.95% senior debentures due 2034 and $300 million of 5.45% senior debentures due 2054. A portion of the net proceeds from this issuance were placed in time deposits and money market fund investments pending the December 2024 retirement of IPL’s $500 million 3.25% senior debentures, and the remainder of the net proceeds were used for general corporate purposes. In March 2024, WPL issued $300 million of 5.375% debentures due 2034. WPL’s 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. Convertible Senior Notes - As of September 30, 2024, the conditions allowing holders of Alliant Energy’s convertible senior notes due 2026 (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 September 30, 2024, the net carrying amount of the Notes was $570 million, with unamortized debt issuance costs of $5 million, and the estimated fair value (Level 2) of the Notes was $602 million. As of September 30, 2024, there were no shares of Alliant Energy’s common stock related to the potential conversion of the Notes included in diluted EPS based on Alliant Energy’s average stock prices and the relevant terms of the Notes.
IPL [Member]
Debt [Line Items]
Debt	DEBT NOTE 7(a) Short-term Debt - In June 2024, Alliant Energy, IPL and WPL reallocated credit facility capacity amounts to $450 million for Alliant Energy at the parent company level, $250 million for IPL and $300 million for WPL, within the $1 billion total commitment. Information regarding commercial paper classified as short-term debt was as follows (dollars in millions): September 30, 2024 Alliant Energy IPL WPL Amount outstanding $330 $— $— Weighted average interest rates 5.0% —% —% Available credit facility capacity $670 $250 $300 Alliant Energy IPL WPL Three Months Ended September 30 2024 2023 2024 2023 2024 2023 Maximum amount outstanding (based on daily outstanding balances) $330 $474 $— $7 $— $125 Average amount outstanding (based on daily outstanding balances) $197 $440 $— $— $— $86 Weighted average interest rates 5.4% 5.5% —% 5.5% —% 5.4% Nine Months Ended September 30 Maximum amount outstanding (based on daily outstanding balances) $632 $793 $19 $70 $390 $349 Average amount outstanding (based on daily outstanding balances) $320 $367 $1 $2 $87 $135 Weighted average interest rates 5.5% 5.1% 5.5% 5.3% 5.5% 4.9% NOTE 7(b) Long-term Debt - In March 2024, AEF entered into a $300 million variable rate (6% as of September 30, 2024) term loan credit agreement (with Alliant Energy as guarantor), which expires in March 2025. This term loan credit agreement amends and restates the term loan credit agreement that expired in March 2024, and retired the $300 million variable rate term loan set forth therein. AEF’s restated term loan credit agreement includes an option to increase the amount outstanding with one or more additional term loans in an aggregate amount not to exceed $100 million. In June 2024, AEF issued $375 million of 5.4% senior notes due 2027 (with Alliant Energy as guarantor). The net proceeds from this issuance were used to reduce Alliant Energy’s outstanding commercial paper and for general corporate purposes. In September 2024, IPL issued $350 million of 4.95% senior debentures due 2034 and $300 million of 5.45% senior debentures due 2054. A portion of the net proceeds from this issuance were placed in time deposits and money market fund investments pending the December 2024 retirement of IPL’s $500 million 3.25% senior debentures, and the remainder of the net proceeds were used for general corporate purposes. In March 2024, WPL issued $300 million of 5.375% debentures due 2034. WPL’s 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.
WPL [Member]
Debt [Line Items]
Debt	DEBT NOTE 7(a) Short-term Debt - In June 2024, Alliant Energy, IPL and WPL reallocated credit facility capacity amounts to $450 million for Alliant Energy at the parent company level, $250 million for IPL and $300 million for WPL, within the $1 billion total commitment. Information regarding commercial paper classified as short-term debt was as follows (dollars in millions): September 30, 2024 Alliant Energy IPL WPL Amount outstanding $330 $— $— Weighted average interest rates 5.0% —% —% Available credit facility capacity $670 $250 $300 Alliant Energy IPL WPL Three Months Ended September 30 2024 2023 2024 2023 2024 2023 Maximum amount outstanding (based on daily outstanding balances) $330 $474 $— $7 $— $125 Average amount outstanding (based on daily outstanding balances) $197 $440 $— $— $— $86 Weighted average interest rates 5.4% 5.5% —% 5.5% —% 5.4% Nine Months Ended September 30 Maximum amount outstanding (based on daily outstanding balances) $632 $793 $19 $70 $390 $349 Average amount outstanding (based on daily outstanding balances) $320 $367 $1 $2 $87 $135 Weighted average interest rates 5.5% 5.1% 5.5% 5.3% 5.5% 4.9% NOTE 7(b) Long-term Debt - In March 2024, AEF entered into a $300 million variable rate (6% as of September 30, 2024) term loan credit agreement (with Alliant Energy as guarantor), which expires in March 2025. This term loan credit agreement amends and restates the term loan credit agreement that expired in March 2024, and retired the $300 million variable rate term loan set forth therein. AEF’s restated term loan credit agreement includes an option to increase the amount outstanding with one or more additional term loans in an aggregate amount not to exceed $100 million. In June 2024, AEF issued $375 million of 5.4% senior notes due 2027 (with Alliant Energy as guarantor). The net proceeds from this issuance were used to reduce Alliant Energy’s outstanding commercial paper and for general corporate purposes. In September 2024, IPL issued $350 million of 4.95% senior debentures due 2034 and $300 million of 5.45% senior debentures due 2054. A portion of the net proceeds from this issuance were placed in time deposits and money market fund investments pending the December 2024 retirement of IPL’s $500 million 3.25% senior debentures, and the remainder of the net proceeds were used for general corporate purposes. In March 2024, WPL issued $300 million of 5.375% debentures due 2034. WPL’s 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.

Revenues

Revenues	9 Months Ended
	Sep. 30, 2024
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	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 Three Months Ended September 30 2024 2023 2024 2023 2024 2023 Electric Utility: Retail - residential $378 $374 $202 $209 $176 $165 Retail - commercial 239 241 153 158 86 83 Retail - industrial 270 280 142 153 128 127 Wholesale 58 59 19 21 39 38 Bulk power and other 54 41 7 10 47 31 Total Electric Utility 999 995 523 551 476 444 Gas Utility: Retail - residential 24 23 13 14 11 9 Retail - commercial 13 12 7 9 6 3 Retail - industrial 1 2 1 2 — — Transportation/other 11 10 6 6 5 4 Total Gas Utility 49 47 27 31 22 16 Other Utility: Steam 9 11 9 11 — — Other utility 3 2 2 1 1 1 Total Other Utility 12 13 11 12 1 1 Non-Utility and Other: Travero and other 21 22 — — — — Total Non-Utility and Other 21 22 — — — — Total revenues $1,081 $1,077 $561 $594 $499 $461 Alliant Energy IPL WPL Nine Months Ended September 30 2024 2023 2024 2023 2024 2023 Electric Utility: Retail - residential $966 $943 $502 $503 $464 $440 Retail - commercial 616 627 385 399 231 228 Retail - industrial 730 740 372 389 358 351 Wholesale 147 154 45 47 102 107 Bulk power and other 120 98 14 32 106 66 Total Electric Utility 2,579 2,562 1,318 1,370 1,261 1,192 Gas Utility: Retail - residential 189 233 103 131 86 102 Retail - commercial 92 122 48 65 44 57 Retail - industrial 8 12 5 8 3 4 Transportation/other 33 33 19 20 14 13 Total Gas Utility 322 400 175 224 147 176 Other Utility: Steam 29 32 29 32 — — Other utility 7 6 5 4 2 2 Total Other Utility 36 38 34 36 2 2 Non-Utility and Other: Travero and other 68 66 — — — — Total Non-Utility and Other 68 66 — — — — Total revenues $3,005 $3,066 $1,527 $1,630 $1,410 $1,370
IPL [Member]
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	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 Three Months Ended September 30 2024 2023 2024 2023 2024 2023 Electric Utility: Retail - residential $378 $374 $202 $209 $176 $165 Retail - commercial 239 241 153 158 86 83 Retail - industrial 270 280 142 153 128 127 Wholesale 58 59 19 21 39 38 Bulk power and other 54 41 7 10 47 31 Total Electric Utility 999 995 523 551 476 444 Gas Utility: Retail - residential 24 23 13 14 11 9 Retail - commercial 13 12 7 9 6 3 Retail - industrial 1 2 1 2 — — Transportation/other 11 10 6 6 5 4 Total Gas Utility 49 47 27 31 22 16 Other Utility: Steam 9 11 9 11 — — Other utility 3 2 2 1 1 1 Total Other Utility 12 13 11 12 1 1 Non-Utility and Other: Travero and other 21 22 — — — — Total Non-Utility and Other 21 22 — — — — Total revenues $1,081 $1,077 $561 $594 $499 $461 Alliant Energy IPL WPL Nine Months Ended September 30 2024 2023 2024 2023 2024 2023 Electric Utility: Retail - residential $966 $943 $502 $503 $464 $440 Retail - commercial 616 627 385 399 231 228 Retail - industrial 730 740 372 389 358 351 Wholesale 147 154 45 47 102 107 Bulk power and other 120 98 14 32 106 66 Total Electric Utility 2,579 2,562 1,318 1,370 1,261 1,192 Gas Utility: Retail - residential 189 233 103 131 86 102 Retail - commercial 92 122 48 65 44 57 Retail - industrial 8 12 5 8 3 4 Transportation/other 33 33 19 20 14 13 Total Gas Utility 322 400 175 224 147 176 Other Utility: Steam 29 32 29 32 — — Other utility 7 6 5 4 2 2 Total Other Utility 36 38 34 36 2 2 Non-Utility and Other: Travero and other 68 66 — — — — Total Non-Utility and Other 68 66 — — — — Total revenues $3,005 $3,066 $1,527 $1,630 $1,410 $1,370
WPL [Member]
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	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 Three Months Ended September 30 2024 2023 2024 2023 2024 2023 Electric Utility: Retail - residential $378 $374 $202 $209 $176 $165 Retail - commercial 239 241 153 158 86 83 Retail - industrial 270 280 142 153 128 127 Wholesale 58 59 19 21 39 38 Bulk power and other 54 41 7 10 47 31 Total Electric Utility 999 995 523 551 476 444 Gas Utility: Retail - residential 24 23 13 14 11 9 Retail - commercial 13 12 7 9 6 3 Retail - industrial 1 2 1 2 — — Transportation/other 11 10 6 6 5 4 Total Gas Utility 49 47 27 31 22 16 Other Utility: Steam 9 11 9 11 — — Other utility 3 2 2 1 1 1 Total Other Utility 12 13 11 12 1 1 Non-Utility and Other: Travero and other 21 22 — — — — Total Non-Utility and Other 21 22 — — — — Total revenues $1,081 $1,077 $561 $594 $499 $461 Alliant Energy IPL WPL Nine Months Ended September 30 2024 2023 2024 2023 2024 2023 Electric Utility: Retail - residential $966 $943 $502 $503 $464 $440 Retail - commercial 616 627 385 399 231 228 Retail - industrial 730 740 372 389 358 351 Wholesale 147 154 45 47 102 107 Bulk power and other 120 98 14 32 106 66 Total Electric Utility 2,579 2,562 1,318 1,370 1,261 1,192 Gas Utility: Retail - residential 189 233 103 131 86 102 Retail - commercial 92 122 48 65 44 57 Retail - industrial 8 12 5 8 3 4 Transportation/other 33 33 19 20 14 13 Total Gas Utility 322 400 175 224 147 176 Other Utility: Steam 29 32 29 32 — — Other utility 7 6 5 4 2 2 Total Other Utility 36 38 34 36 2 2 Non-Utility and Other: Travero and other 68 66 — — — — Total Non-Utility and Other 68 66 — — — — Total revenues $3,005 $3,066 $1,527 $1,630 $1,410 $1,370

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2024
Income Taxes [Line Items]
Income Taxes	INCOME TAXES Income Tax Rates - Overall effective income tax rates for the three and nine months ended September 30, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, investment tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. Also impacting Alliant Energy’s and IPL’s effective income tax rates for the nine months ended September 30, 2024 were the pre-tax non-cash charge of $60 million for IPL’s Lansing Generation Station discussed in Note 2 and the pre-tax non-cash charge of $20 million for the portion of recorded AROs allocated to IPL’s steam business discussed in Note 11 . Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 Overall income tax rate (27%) 2% (24%) 1% (56%) (22%) (70%) (20%) 3% 16% 5% 15% Deferred Tax Assets and Liabilities - Carryforwards - At September 30, 2024, the carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL State net operating losses 2025-2044 $367 $6 $1 Federal tax credits 2033-2044 622 435 175 Iowa Tax Reform - Pursuant to Iowa tax reform enacted in 2022, and based on the remeasurement of Alliant Energy parent company’s deferred tax assets in the third quarter of 2023 for the Iowa corporate income tax rate of 7.1% effective January 1, 2024, a charge of $8 million was recorded to income tax expense in Alliant Energy’s income statement in the third quarter of 2023.
IPL [Member]
Income Taxes [Line Items]
Income Taxes	INCOME TAXES Income Tax Rates - Overall effective income tax rates for the three and nine months ended September 30, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, investment tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. Also impacting Alliant Energy’s and IPL’s effective income tax rates for the nine months ended September 30, 2024 were the pre-tax non-cash charge of $60 million for IPL’s Lansing Generation Station discussed in Note 2 and the pre-tax non-cash charge of $20 million for the portion of recorded AROs allocated to IPL’s steam business discussed in Note 11 . Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 Overall income tax rate (27%) 2% (24%) 1% (56%) (22%) (70%) (20%) 3% 16% 5% 15% Deferred Tax Assets and Liabilities - Carryforwards - At September 30, 2024, the carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL State net operating losses 2025-2044 $367 $6 $1 Federal tax credits 2033-2044 622 435 175
WPL [Member]
Income Taxes [Line Items]
Income Taxes	INCOME TAXES Income Tax Rates - Overall effective income tax rates for the three and nine months ended September 30, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, investment tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. Also impacting Alliant Energy’s and IPL’s effective income tax rates for the nine months ended September 30, 2024 were the pre-tax non-cash charge of $60 million for IPL’s Lansing Generation Station discussed in Note 2 and the pre-tax non-cash charge of $20 million for the portion of recorded AROs allocated to IPL’s steam business discussed in Note 11 . Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 Overall income tax rate (27%) 2% (24%) 1% (56%) (22%) (70%) (20%) 3% 16% 5% 15% Deferred Tax Assets and Liabilities - Carryforwards - At September 30, 2024, the carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL State net operating losses 2025-2044 $367 $6 $1 Federal tax credits 2033-2044 622 435 175

Benefit Plans

Benefit Plans	9 Months Ended
	Sep. 30, 2024
Benefit Plans	BENEFIT PLANS NOTE 10(a) Pension and OPEB Plans - Net Periodic Benefit Costs - The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and nine months ended September 30 are included below (in millions). For IPL and WPL, amounts are 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. Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months Alliant Energy 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $1 $2 $3 $4 $1 $1 $2 $2 Interest cost 12 12 34 35 2 3 6 7 Expected return on plan assets (14) (14) (41) (40) (2) (2) (4) (4) Amortization of prior service credit — (1) — (1) — — — — Amortization of actuarial loss 6 7 18 21 — — — 1 $5 $6 $14 $19 $1 $2 $4 $6 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months IPL 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $1 $— $2 $2 $— $— $— $— Interest cost 5 6 15 16 1 1 3 3 Expected return on plan assets (7) (6) (20) (19) (1) (1) (3) (3) Amortization of actuarial loss 2 2 7 8 — — — 1 $1 $2 $4 $7 $— $— $— $1 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months WPL 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $— $— $1 $1 $— $1 $— $1 Interest cost 5 5 15 15 1 1 3 3 Expected return on plan assets (6) (5) (18) (16) (1) (1) (1) (1) Amortization of actuarial loss 3 3 9 10 — — — — $2 $3 $7 $10 $— $1 $2 $3 NOTE 10(b) Equity-based Compensation Plans - A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three and nine months ended September 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 Compensation expense $3 $4 $10 $10 $2 $2 $5 $5 $1 $2 $4 $4 Income tax benefits 1 1 3 3 — 1 1 1 — — 1 1 As of September 30, 2024, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $15 million, $7 million and $7 million, respectively, which is expected to be recognized over a weighted average period of between 1 year and 2 years. For the nine months ended September 30, 2024, performance shares and restricted stock units were granted to key employees under the equity-based compensation plans as follows. These shares and units will be paid out in shares of common stock, and are therefore accounted for as equity awards. Weighted Average Grants Grant Date Fair Value Performance shares (total shareowner return metric) 127,267 $46.04 Performance shares (net income and diversity metrics) (formerly granted as performance restricted stock units) 145,449 48.49 Restricted stock units 128,620 48.57 As of September 30, 2024, 392,649 shares were included in the calculation of diluted EPS related to the nonvested equity awards.
IPL [Member]
Benefit Plans	BENEFIT PLANS NOTE 10(a) Pension and OPEB Plans - Net Periodic Benefit Costs - The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and nine months ended September 30 are included below (in millions). For IPL and WPL, amounts are 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. Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months Alliant Energy 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $1 $2 $3 $4 $1 $1 $2 $2 Interest cost 12 12 34 35 2 3 6 7 Expected return on plan assets (14) (14) (41) (40) (2) (2) (4) (4) Amortization of prior service credit — (1) — (1) — — — — Amortization of actuarial loss 6 7 18 21 — — — 1 $5 $6 $14 $19 $1 $2 $4 $6 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months IPL 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $1 $— $2 $2 $— $— $— $— Interest cost 5 6 15 16 1 1 3 3 Expected return on plan assets (7) (6) (20) (19) (1) (1) (3) (3) Amortization of actuarial loss 2 2 7 8 — — — 1 $1 $2 $4 $7 $— $— $— $1 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months WPL 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $— $— $1 $1 $— $1 $— $1 Interest cost 5 5 15 15 1 1 3 3 Expected return on plan assets (6) (5) (18) (16) (1) (1) (1) (1) Amortization of actuarial loss 3 3 9 10 — — — — $2 $3 $7 $10 $— $1 $2 $3 NOTE 10(b) Equity-based Compensation Plans - A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three and nine months ended September 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 Compensation expense $3 $4 $10 $10 $2 $2 $5 $5 $1 $2 $4 $4 Income tax benefits 1 1 3 3 — 1 1 1 — — 1 1 As of September 30, 2024, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $15 million, $7 million and $7 million, respectively, which is expected to be recognized over a weighted average period of between 1 year and 2 years. For the nine months ended September 30, 2024, performance shares and restricted stock units were granted to key employees under the equity-based compensation plans as follows. These shares and units will be paid out in shares of common stock, and are therefore accounted for as equity awards. Weighted Average Grants Grant Date Fair Value Performance shares (total shareowner return metric) 127,267 $46.04 Performance shares (net income and diversity metrics) (formerly granted as performance restricted stock units) 145,449 48.49 Restricted stock units 128,620 48.57 As of September 30, 2024, 392,649 shares were included in the calculation of diluted EPS related to the nonvested equity awards.
WPL [Member]
Benefit Plans	BENEFIT PLANS NOTE 10(a) Pension and OPEB Plans - Net Periodic Benefit Costs - The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and nine months ended September 30 are included below (in millions). For IPL and WPL, amounts are 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. Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months Alliant Energy 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $1 $2 $3 $4 $1 $1 $2 $2 Interest cost 12 12 34 35 2 3 6 7 Expected return on plan assets (14) (14) (41) (40) (2) (2) (4) (4) Amortization of prior service credit — (1) — (1) — — — — Amortization of actuarial loss 6 7 18 21 — — — 1 $5 $6 $14 $19 $1 $2 $4 $6 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months IPL 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $1 $— $2 $2 $— $— $— $— Interest cost 5 6 15 16 1 1 3 3 Expected return on plan assets (7) (6) (20) (19) (1) (1) (3) (3) Amortization of actuarial loss 2 2 7 8 — — — 1 $1 $2 $4 $7 $— $— $— $1 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months WPL 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $— $— $1 $1 $— $1 $— $1 Interest cost 5 5 15 15 1 1 3 3 Expected return on plan assets (6) (5) (18) (16) (1) (1) (1) (1) Amortization of actuarial loss 3 3 9 10 — — — — $2 $3 $7 $10 $— $1 $2 $3 NOTE 10(b) Equity-based Compensation Plans - A summary of compensation expense, including amounts allocated to IPL and WPL, and the related income tax benefits recognized for share-based compensation awards for the three and nine months ended September 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 Compensation expense $3 $4 $10 $10 $2 $2 $5 $5 $1 $2 $4 $4 Income tax benefits 1 1 3 3 — 1 1 1 — — 1 1 As of September 30, 2024, Alliant Energy’s, IPL’s and WPL’s total unrecognized compensation cost related to share-based compensation awards was $15 million, $7 million and $7 million, respectively, which is expected to be recognized over a weighted average period of between 1 year and 2 years. For the nine months ended September 30, 2024, performance shares and restricted stock units were granted to key employees under the equity-based compensation plans as follows. These shares and units will be paid out in shares of common stock, and are therefore accounted for as equity awards. Weighted Average Grants Grant Date Fair Value Performance shares (total shareowner return metric) 127,267 $46.04 Performance shares (net income and diversity metrics) (formerly granted as performance restricted stock units) 145,449 48.49 Restricted stock units 128,620 48.57 As of September 30, 2024, 392,649 shares were included in the calculation of diluted EPS related to the nonvested equity awards.

Asset Retirement Obligations

Asset Retirement Obligations	9 Months Ended
	Sep. 30, 2024
Asset Retirement Obligations [Line Items]
Asset Retirement Obligations	ASSET RETIREMENT OBLIGATIONS A reconciliation of the changes in AROs associated with long-lived assets for the nine months ended September 30, 2024 is as follows (in millions): Alliant Energy IPL WPL Balance, January 1 $246 $148 $98 Revisions in estimated cash flows (2) — (2) Liabilities settled (4) (2) (2) Liabilities incurred (a) 356 103 253 Accretion expense 12 6 6 Balance, September 30 $608 $255 $353 (a) In the second quarter of 2024, substantially due to the enactment of the revised CCR Rule, which significantly expands the scope of regulation to include coal ash ponds at sites that no longer produce electricity and inactive landfills, including some IPL and WPL facilities, Alliant Energy, IPL and WPL recorded additional AROs, additional ARO regulatory assets for EGUs no longer in operation, additional property, plant and equipment for EGUs still in operation, and a pre-tax non-cash charge of $20 million recorded to “Other operation and maintenance” in Alliant Energy’s and IPL’s income statements for the nine months ended September 30, 2024 for the portion allocated to IPL’s steam business for IPL’s Prairie Creek Generating Station and the retired Sixth Street Generating Station as established in prior rate reviews. The amounts recorded in the second quarter of 2024 are expected to be adjusted in the future as additional information is obtained for the specific site closure plans, including the determination of whether or not individual sites are considered legal obligations and the acceptance and approval of compliance approaches, which could change management assumptions and result in a material change to the recorded amounts.
IPL [Member]
Asset Retirement Obligations [Line Items]
Asset Retirement Obligations	ASSET RETIREMENT OBLIGATIONS A reconciliation of the changes in AROs associated with long-lived assets for the nine months ended September 30, 2024 is as follows (in millions): Alliant Energy IPL WPL Balance, January 1 $246 $148 $98 Revisions in estimated cash flows (2) — (2) Liabilities settled (4) (2) (2) Liabilities incurred (a) 356 103 253 Accretion expense 12 6 6 Balance, September 30 $608 $255 $353 (a) In the second quarter of 2024, substantially due to the enactment of the revised CCR Rule, which significantly expands the scope of regulation to include coal ash ponds at sites that no longer produce electricity and inactive landfills, including some IPL and WPL facilities, Alliant Energy, IPL and WPL recorded additional AROs, additional ARO regulatory assets for EGUs no longer in operation, additional property, plant and equipment for EGUs still in operation, and a pre-tax non-cash charge of $20 million recorded to “Other operation and maintenance” in Alliant Energy’s and IPL’s income statements for the nine months ended September 30, 2024 for the portion allocated to IPL’s steam business for IPL’s Prairie Creek Generating Station and the retired Sixth Street Generating Station as established in prior rate reviews. The amounts recorded in the second quarter of 2024 are expected to be adjusted in the future as additional information is obtained for the specific site closure plans, including the determination of whether or not individual sites are considered legal obligations and the acceptance and approval of compliance approaches, which could change management assumptions and result in a material change to the recorded amounts.
WPL [Member]
Asset Retirement Obligations [Line Items]
Asset Retirement Obligations	ASSET RETIREMENT OBLIGATIONS A reconciliation of the changes in AROs associated with long-lived assets for the nine months ended September 30, 2024 is as follows (in millions): Alliant Energy IPL WPL Balance, January 1 $246 $148 $98 Revisions in estimated cash flows (2) — (2) Liabilities settled (4) (2) (2) Liabilities incurred (a) 356 103 253 Accretion expense 12 6 6 Balance, September 30 $608 $255 $353 (a) In the second quarter of 2024, substantially due to the enactment of the revised CCR Rule, which significantly expands the scope of regulation to include coal ash ponds at sites that no longer produce electricity and inactive landfills, including some IPL and WPL facilities, Alliant Energy, IPL and WPL recorded additional AROs, additional ARO regulatory assets for EGUs no longer in operation, additional property, plant and equipment for EGUs still in operation, and a pre-tax non-cash charge of $20 million recorded to “Other operation and maintenance” in Alliant Energy’s and IPL’s income statements for the nine months ended September 30, 2024 for the portion allocated to IPL’s steam business for IPL’s Prairie Creek Generating Station and the retired Sixth Street Generating Station as established in prior rate reviews. The amounts recorded in the second quarter of 2024 are expected to be adjusted in the future as additional information is obtained for the specific site closure plans, including the determination of whether or not individual sites are considered legal obligations and the acceptance and approval of compliance approaches, which could change management assumptions and result in a material change to the recorded amounts.

Derivative Instruments

Derivative Instruments	9 Months Ended
	Sep. 30, 2024
Derivative Instruments [Line Items]
Derivative Instruments	DERIVATIVE INSTRUMENTS Commodity Derivatives - Notional Amounts - As of September 30, 2024, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands): Electricity FTRs Natural Gas Diesel Fuel MWhs Years MWhs Years Dths Years Gallons Years Alliant Energy 1,841 2024-2026 15,595 2024-2025 156,626 2024-2032 3,150 2024-2025 IPL 675 2024-2026 5,385 2024-2025 67,817 2024-2030 — — WPL 1,166 2024-2026 10,210 2024-2025 88,809 2024-2032 3,150 2024-2025 Financial Statement Presentation - Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities as follows (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Current derivative assets $51 $44 $37 $30 $14 $14 Non-current derivative assets 31 44 18 24 13 20 Current derivative liabilities 31 51 14 22 17 29 Non-current derivative liabilities 45 47 6 8 39 39 Based on IPL’s and WPL’s cost recovery mechanisms, the majority of changes in the fair value of derivative liabilities/assets result 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 September 30, 2024 and December 31, 2023, the aggregate fair value of all derivative instruments with credit risk-related contingent features in a net liability position was not materially different than amounts that would be required to be posted as credit support to counterparties by Alliant Energy, IPL or WPL if the most restrictive credit risk-related contingent features for derivative agreements in a net liability position were triggered. Balance Sheet Offsetting - The fair value amounts of derivative instruments subject to a master netting arrangement are not netted by counterparty on the balance sheets. However, if the fair value amounts of derivative instruments by counterparty were netted, derivative assets and derivative liabilities related to commodity contracts would have been presented on the balance sheets as follows (in millions): Alliant Energy IPL WPL Gross Gross Gross (as reported) Net (as reported) Net (as reported) Net September 30, 2024 Derivative assets $82 $63 $55 $45 $27 $18 Derivative liabilities 76 57 20 10 56 47 December 31, 2023 Derivative assets 88 47 54 32 34 15 Derivative liabilities 98 57 30 8 68 49 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 - The interest rate derivative associated with AEF’s interest rate swap maturing in January 2026 was valued based on quoted prices that utilize current market interest rate forecasts. As of September 30, 2024, $1 million of non-current interest rate derivative liabilities was recorded in “Other liabilities” 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 September 30, 2024, accumulated other comprehensive loss included $1 million of losses related to the interest rate swap. Reductions to interest expense of $1 million and $3 million for the three and nine months ended September 30, 2024, respectively, and $1 million and $2 million for the three and nine months ended September 30, 2023, respectively, were recorded in Alliant Energy’s income statement related to the interest rate swap.
IPL [Member]
Derivative Instruments [Line Items]
Derivative Instruments	DERIVATIVE INSTRUMENTS Commodity Derivatives - Notional Amounts - As of September 30, 2024, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands): Electricity FTRs Natural Gas Diesel Fuel MWhs Years MWhs Years Dths Years Gallons Years Alliant Energy 1,841 2024-2026 15,595 2024-2025 156,626 2024-2032 3,150 2024-2025 IPL 675 2024-2026 5,385 2024-2025 67,817 2024-2030 — — WPL 1,166 2024-2026 10,210 2024-2025 88,809 2024-2032 3,150 2024-2025 Financial Statement Presentation - Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities as follows (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Current derivative assets $51 $44 $37 $30 $14 $14 Non-current derivative assets 31 44 18 24 13 20 Current derivative liabilities 31 51 14 22 17 29 Non-current derivative liabilities 45 47 6 8 39 39 Based on IPL’s and WPL’s cost recovery mechanisms, the majority of changes in the fair value of derivative liabilities/assets result 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 September 30, 2024 and December 31, 2023, the aggregate fair value of all derivative instruments with credit risk-related contingent features in a net liability position was not materially different than amounts that would be required to be posted as credit support to counterparties by Alliant Energy, IPL or WPL if the most restrictive credit risk-related contingent features for derivative agreements in a net liability position were triggered. Balance Sheet Offsetting - The fair value amounts of derivative instruments subject to a master netting arrangement are not netted by counterparty on the balance sheets. However, if the fair value amounts of derivative instruments by counterparty were netted, derivative assets and derivative liabilities related to commodity contracts would have been presented on the balance sheets as follows (in millions): Alliant Energy IPL WPL Gross Gross Gross (as reported) Net (as reported) Net (as reported) Net September 30, 2024 Derivative assets $82 $63 $55 $45 $27 $18 Derivative liabilities 76 57 20 10 56 47 December 31, 2023 Derivative assets 88 47 54 32 34 15 Derivative liabilities 98 57 30 8 68 49 Fair value amounts recognized for the right to reclaim cash collateral (receivable) or the obligation to return cash collateral (payable) are not offset against fair value amounts recognized for derivative instruments executed with the same counterparty under the same master netting arrangement.
WPL [Member]
Derivative Instruments [Line Items]
Derivative Instruments	DERIVATIVE INSTRUMENTS Commodity Derivatives - Notional Amounts - As of September 30, 2024, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands): Electricity FTRs Natural Gas Diesel Fuel MWhs Years MWhs Years Dths Years Gallons Years Alliant Energy 1,841 2024-2026 15,595 2024-2025 156,626 2024-2032 3,150 2024-2025 IPL 675 2024-2026 5,385 2024-2025 67,817 2024-2030 — — WPL 1,166 2024-2026 10,210 2024-2025 88,809 2024-2032 3,150 2024-2025 Financial Statement Presentation - Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities as follows (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Current derivative assets $51 $44 $37 $30 $14 $14 Non-current derivative assets 31 44 18 24 13 20 Current derivative liabilities 31 51 14 22 17 29 Non-current derivative liabilities 45 47 6 8 39 39 Based on IPL’s and WPL’s cost recovery mechanisms, the majority of changes in the fair value of derivative liabilities/assets result 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 September 30, 2024 and December 31, 2023, the aggregate fair value of all derivative instruments with credit risk-related contingent features in a net liability position was not materially different than amounts that would be required to be posted as credit support to counterparties by Alliant Energy, IPL or WPL if the most restrictive credit risk-related contingent features for derivative agreements in a net liability position were triggered. Balance Sheet Offsetting - The fair value amounts of derivative instruments subject to a master netting arrangement are not netted by counterparty on the balance sheets. However, if the fair value amounts of derivative instruments by counterparty were netted, derivative assets and derivative liabilities related to commodity contracts would have been presented on the balance sheets as follows (in millions): Alliant Energy IPL WPL Gross Gross Gross (as reported) Net (as reported) Net (as reported) Net September 30, 2024 Derivative assets $82 $63 $55 $45 $27 $18 Derivative liabilities 76 57 20 10 56 47 December 31, 2023 Derivative assets 88 47 54 32 34 15 Derivative liabilities 98 57 30 8 68 49 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.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2024
Fair Value Measurements	FAIR VALUE MEASUREMENTS Fair Value of Financial Instruments - The carrying amounts of current assets and current liabilities approximate fair value because of the short maturity of such financial instruments. Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions): Alliant Energy September 30, 2024 December 31, 2023 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Time deposits and money market fund investments $803 $803 $— $— $803 $45 $45 $— $— $45 Commodity derivatives 82 — 42 40 82 88 — 59 29 88 Interest rate derivatives — — — — — 1 — 1 — 1 Deferred proceeds 212 — — 212 212 216 — — 216 216 Liabilities: Commodity derivatives 76 — 73 3 76 98 — 93 5 98 Interest rate derivatives 1 — 1 — 1 — — — — — Long-term debt (incl. current maturities) 10,349 — 10,444 — 10,444 9,034 — 8,677 — 8,677 IPL September 30, 2024 December 31, 2023 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Time deposits and money market fund investments $745 $745 $— $— $745 $45 $45 $— $— $45 Commodity derivatives 55 — 23 32 55 54 — 30 24 54 Deferred proceeds 212 — — 212 212 216 — — 216 216 Liabilities: Commodity derivatives 20 — 17 3 20 30 — 25 5 30 Long-term debt (incl. current maturities) 4,589 — 4,407 — 4,407 3,945 — 3,664 — 3,664 WPL September 30, 2024 December 31, 2023 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 $58 $58 $— $— $58 $— $— $— $— $— Commodity derivatives 27 — 19 8 27 34 — 29 5 34 Liabilities: Commodity derivatives 56 — 56 — 56 68 — 68 — 68 Long-term debt 3,369 — 3,322 — 3,322 3,070 — 2,933 — 2,933 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 Three Months Ended September 30 2024 2023 2024 2023 Beginning balance, July 1 $51 $54 $171 $175 Total net gains included in changes in net assets (realized/unrealized) 2 17 — — Sales — (1) — — Settlements (a) (16) (27) 41 61 Ending balance, September 30 $37 $43 $212 $236 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $2 $17 $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2024 2023 2024 2023 Beginning balance, January 1 $24 $19 $216 $185 Total net gains (losses) included in changes in net assets (realized/unrealized) (7) 6 — — Purchases 59 62 — — Sales (1) (2) — — Settlements (a) (38) (42) (4) 51 Ending balance, September 30 $37 $43 $212 $236 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 September 30 ($7) $6 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2024 2023 2024 2023 Beginning balance, July 1 $40 $41 $171 $175 Total net gains included in changes in net assets (realized/unrealized) — 12 — — Sales — (1) — — Settlements (a) (11) (17) 41 61 Ending balance, September 30 $29 $35 $212 $236 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $— $12 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2024 2023 2024 2023 Beginning balance, January 1 $19 $16 $216 $185 Total net losses included in changes in net assets (realized/unrealized) (7) — — — Purchases 45 51 — — Sales (1) (2) — — Settlements (a) (27) (30) (4) 51 Ending balance, September 30 $29 $35 $212 $236 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 September 30 ($7) $— $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended September 30 2024 2023 Beginning balance, July 1 $11 $13 Total net gains included in changes in net assets (realized/unrealized) 2 5 Settlements (5) (10) Ending balance, September 30 $8 $8 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $2 $5 WPL Commodity Contract Derivative Assets and (Liabilities), net Nine Months Ended September 30 2024 2023 Beginning balance, January 1 $5 $3 Total net gains included in changes in net assets (realized/unrealized) — 6 Purchases 14 11 Settlements (11) (12) Ending balance, September 30 $8 $8 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $— $6 (a) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for expected credit losses associated with the receivables sold and cash amounts received from the receivables sold. Commodity Contracts - The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs September 30, 2024 $— $37 $— $29 $— $8 December 31, 2023 3 21 3 16 — 5
IPL [Member]
Fair Value Measurements	FAIR VALUE MEASUREMENTS Fair Value of Financial Instruments - The carrying amounts of current assets and current liabilities approximate fair value because of the short maturity of such financial instruments. Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions): Alliant Energy September 30, 2024 December 31, 2023 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Time deposits and money market fund investments $803 $803 $— $— $803 $45 $45 $— $— $45 Commodity derivatives 82 — 42 40 82 88 — 59 29 88 Interest rate derivatives — — — — — 1 — 1 — 1 Deferred proceeds 212 — — 212 212 216 — — 216 216 Liabilities: Commodity derivatives 76 — 73 3 76 98 — 93 5 98 Interest rate derivatives 1 — 1 — 1 — — — — — Long-term debt (incl. current maturities) 10,349 — 10,444 — 10,444 9,034 — 8,677 — 8,677 IPL September 30, 2024 December 31, 2023 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Time deposits and money market fund investments $745 $745 $— $— $745 $45 $45 $— $— $45 Commodity derivatives 55 — 23 32 55 54 — 30 24 54 Deferred proceeds 212 — — 212 212 216 — — 216 216 Liabilities: Commodity derivatives 20 — 17 3 20 30 — 25 5 30 Long-term debt (incl. current maturities) 4,589 — 4,407 — 4,407 3,945 — 3,664 — 3,664 WPL September 30, 2024 December 31, 2023 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 $58 $58 $— $— $58 $— $— $— $— $— Commodity derivatives 27 — 19 8 27 34 — 29 5 34 Liabilities: Commodity derivatives 56 — 56 — 56 68 — 68 — 68 Long-term debt 3,369 — 3,322 — 3,322 3,070 — 2,933 — 2,933 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 Three Months Ended September 30 2024 2023 2024 2023 Beginning balance, July 1 $51 $54 $171 $175 Total net gains included in changes in net assets (realized/unrealized) 2 17 — — Sales — (1) — — Settlements (a) (16) (27) 41 61 Ending balance, September 30 $37 $43 $212 $236 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $2 $17 $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2024 2023 2024 2023 Beginning balance, January 1 $24 $19 $216 $185 Total net gains (losses) included in changes in net assets (realized/unrealized) (7) 6 — — Purchases 59 62 — — Sales (1) (2) — — Settlements (a) (38) (42) (4) 51 Ending balance, September 30 $37 $43 $212 $236 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 September 30 ($7) $6 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2024 2023 2024 2023 Beginning balance, July 1 $40 $41 $171 $175 Total net gains included in changes in net assets (realized/unrealized) — 12 — — Sales — (1) — — Settlements (a) (11) (17) 41 61 Ending balance, September 30 $29 $35 $212 $236 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $— $12 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2024 2023 2024 2023 Beginning balance, January 1 $19 $16 $216 $185 Total net losses included in changes in net assets (realized/unrealized) (7) — — — Purchases 45 51 — — Sales (1) (2) — — Settlements (a) (27) (30) (4) 51 Ending balance, September 30 $29 $35 $212 $236 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 September 30 ($7) $— $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended September 30 2024 2023 Beginning balance, July 1 $11 $13 Total net gains included in changes in net assets (realized/unrealized) 2 5 Settlements (5) (10) Ending balance, September 30 $8 $8 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $2 $5 WPL Commodity Contract Derivative Assets and (Liabilities), net Nine Months Ended September 30 2024 2023 Beginning balance, January 1 $5 $3 Total net gains included in changes in net assets (realized/unrealized) — 6 Purchases 14 11 Settlements (11) (12) Ending balance, September 30 $8 $8 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $— $6 (a) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for expected credit losses associated with the receivables sold and cash amounts received from the receivables sold. Commodity Contracts - The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs September 30, 2024 $— $37 $— $29 $— $8 December 31, 2023 3 21 3 16 — 5
WPL [Member]
Fair Value Measurements	FAIR VALUE MEASUREMENTS Fair Value of Financial Instruments - The carrying amounts of current assets and current liabilities approximate fair value because of the short maturity of such financial instruments. Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions): Alliant Energy September 30, 2024 December 31, 2023 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Time deposits and money market fund investments $803 $803 $— $— $803 $45 $45 $— $— $45 Commodity derivatives 82 — 42 40 82 88 — 59 29 88 Interest rate derivatives — — — — — 1 — 1 — 1 Deferred proceeds 212 — — 212 212 216 — — 216 216 Liabilities: Commodity derivatives 76 — 73 3 76 98 — 93 5 98 Interest rate derivatives 1 — 1 — 1 — — — — — Long-term debt (incl. current maturities) 10,349 — 10,444 — 10,444 9,034 — 8,677 — 8,677 IPL September 30, 2024 December 31, 2023 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Time deposits and money market fund investments $745 $745 $— $— $745 $45 $45 $— $— $45 Commodity derivatives 55 — 23 32 55 54 — 30 24 54 Deferred proceeds 212 — — 212 212 216 — — 216 216 Liabilities: Commodity derivatives 20 — 17 3 20 30 — 25 5 30 Long-term debt (incl. current maturities) 4,589 — 4,407 — 4,407 3,945 — 3,664 — 3,664 WPL September 30, 2024 December 31, 2023 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 $58 $58 $— $— $58 $— $— $— $— $— Commodity derivatives 27 — 19 8 27 34 — 29 5 34 Liabilities: Commodity derivatives 56 — 56 — 56 68 — 68 — 68 Long-term debt 3,369 — 3,322 — 3,322 3,070 — 2,933 — 2,933 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 Three Months Ended September 30 2024 2023 2024 2023 Beginning balance, July 1 $51 $54 $171 $175 Total net gains included in changes in net assets (realized/unrealized) 2 17 — — Sales — (1) — — Settlements (a) (16) (27) 41 61 Ending balance, September 30 $37 $43 $212 $236 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $2 $17 $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2024 2023 2024 2023 Beginning balance, January 1 $24 $19 $216 $185 Total net gains (losses) included in changes in net assets (realized/unrealized) (7) 6 — — Purchases 59 62 — — Sales (1) (2) — — Settlements (a) (38) (42) (4) 51 Ending balance, September 30 $37 $43 $212 $236 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 September 30 ($7) $6 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2024 2023 2024 2023 Beginning balance, July 1 $40 $41 $171 $175 Total net gains included in changes in net assets (realized/unrealized) — 12 — — Sales — (1) — — Settlements (a) (11) (17) 41 61 Ending balance, September 30 $29 $35 $212 $236 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $— $12 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2024 2023 2024 2023 Beginning balance, January 1 $19 $16 $216 $185 Total net losses included in changes in net assets (realized/unrealized) (7) — — — Purchases 45 51 — — Sales (1) (2) — — Settlements (a) (27) (30) (4) 51 Ending balance, September 30 $29 $35 $212 $236 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 September 30 ($7) $— $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended September 30 2024 2023 Beginning balance, July 1 $11 $13 Total net gains included in changes in net assets (realized/unrealized) 2 5 Settlements (5) (10) Ending balance, September 30 $8 $8 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $2 $5 WPL Commodity Contract Derivative Assets and (Liabilities), net Nine Months Ended September 30 2024 2023 Beginning balance, January 1 $5 $3 Total net gains included in changes in net assets (realized/unrealized) — 6 Purchases 14 11 Settlements (11) (12) Ending balance, September 30 $8 $8 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $— $6 (a) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for expected credit losses associated with the receivables sold and cash amounts received from the receivables sold. Commodity Contracts - The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs September 30, 2024 $— $37 $— $29 $— $8 December 31, 2023 3 21 3 16 — 5

Commitments And Contingencies

Commitments And Contingencies	9 Months Ended
	Sep. 30, 2024
Commitments and Contingencies Disclosure	COMMITMENTS AND CONTINGENCIES NOTE 14(a) Capital Purchase Commitments - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects, including WPL’s expansion of battery storage, IPL’s repowering of the existing Franklin County wind farm, and IPL’s expansion of solar generation. At September 30, 2024, Alliant Energy’s, IPL’s and WPL’s minimum future commitments for these projects were $99 million, $24 million and $72 million, respectively. NOTE 14(b) Other Purchase Commitments - Various commodity supply, transportation and storage contracts help meet obligations to provide electricity and natural gas to utility customers. In addition, there are various purchase commitments associated with other goods and services. At September 30, 2024, the related minimum future commitments, excluding amounts for purchased power commitments that do not have minimum thresholds but will require payment when electricity is generated by the provider, were as follows (in millions): Alliant Energy IPL WPL Natural gas $746 $322 $424 Coal 139 80 59 Other (a) 110 46 22 $995 $448 $505 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2024. NOTE 14(c) Guarantees and Indemnifications - Whiting Petroleum Corporation (Whiting Petroleum) - In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum, an independent oil and gas company. Alliant Energy Resources, LLC, as the successor to a predecessor entity that owned Whiting Petroleum, and a wholly-owned subsidiary of AEF, has guaranteed the partnership obligations of an affiliate of Whiting Petroleum under multiple general partnership agreements in the oil and gas industry. The guarantees do not include a maximum limit. Based on information made available to Alliant Energy by Whiting Petroleum, the Whiting Petroleum affiliate holds an approximate 6% share in the partnerships, and currently known obligations include costs associated with the future abandonment of certain facilities owned by the partnerships. The general partnerships were formed under California law, and Alliant Energy Resources, LLC may need to perform under the guarantees if the affiliate of Whiting Petroleum is unable to meet its partnership obligations. Whiting Petroleum previously completed bankruptcy proceedings and business combinations, which substantially reduce the likelihood that Alliant Energy will be obligated to make any payments under these guarantees. As of September 30, 2024, 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 is not currently aware of, nor does it currently expect to incur in the future, any material liabilities related to these guarantees and therefore has not recognized any material liabilities related to these guarantees as of September 30, 2024 and December 31, 2023. Non-utility Wind Farm in Oklahoma - In 2017, a wholly-owned subsidiary of AEF acquired a cash equity ownership interest in a non-utility wind farm located in Oklahoma. The wind farm provides electricity to a third party under a long-term purchased power agreement (PPA). Alliant Energy provided a parent guarantee of its subsidiary’s indemnification obligations under the related operating agreement and PPA. Alliant Energy’s obligations under the operating agreement were $43 million as of September 30, 2024 and will reduce annually until expiring in July 2047. Alliant Energy’s obligations under the PPA are subject to a maximum limit of $17 million and expire in December 2031, subject to potential extension. Alliant Energy is not aware of any material liabilities related to this guarantee that it is probable that it will be obligated to pay and therefore has not recognized any material liabilities related to this guarantee as of September 30, 2024 and December 31, 2023. Transfers of Renewable Tax Credits - In 2023 and 2024, IPL and WPL entered into agreements to transfer renewable tax credits from certain wind, solar and battery storage facilities to other corporate taxpayers in exchange for cash. As of September 30, 2024, IPL and WPL provided indemnifications associated with $165 million and $105 million, respectively, of proceeds for renewable tax credits transferred to other corporate taxpayers in the event of an adverse interpretation of tax law, including whether the related tax credits meet the qualification requirements. Alliant Energy, IPL and WPL believe the likelihood of having to make any material cash payments under these indemnifications is remote. NOTE 14(d) Environmental Matters - Manufactured Gas Plant (MGP) 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 September 30, 2024, estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, which are not discounted, were as follows (in millions): Alliant Energy IPL WPL Range of estimated future costs $7 - $28 $5 - $17 $2 - $11 Current and non-current environmental liabilities $13 $8 $5 IPL Consent Decree - In 2015, the U.S. District Court for the Northern District of Iowa approved a Consent Decree that IPL entered into with the EPA, the Sierra Club, the State of Iowa and Linn County in Iowa, thereby resolving potential Clean Air Act 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: Cross-State Air Pollution Rule, Effluent Limitation Guidelines, CCR Rule, and various legislation and EPA regulations to monitor and regulate the emission of greenhouse gases, including the Clean Air Act. NOTE 14(e) MISO Transmission Owner Return on Equity Complaints - A group of stakeholders, including MISO cooperative and municipal utilities, previously filed complaints with the Federal Energy Regulatory Commission (FERC) requesting a reduction to the base return on equity authorized for MISO transmission owners, including ITC Midwest LLC 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. In October 2024, FERC issued an order reducing the base return on equity authorized for MISO transmission owners to 9.98%, effective September 28, 2016. As a result, the MISO transmission owners will provide refunds based on the 9.98% base return on equity, with interest, for November 12, 2013 through February 11, 2015, and subsequent to September 28, 2016, which is not expected to result in any material impacts on Alliant Energy’s results of operations or financial condition. Any further changes in FERC’s decisions may have an impact on Alliant Energy’s share of ATC’s future earnings and customer costs; however, Alliant Energy is currently unable to predict with certainty the future outcome or impact of any further changes. NOTE 14(f) Collective Bargaining Agreements - In August 2024, IPL’s collective bargaining agreement with International Brotherhood of Electrical Workers Local 204 (Cedar Rapids) expired. A new agreement was reached in September 2024, which expires August 31, 2028.
IPL [Member]
Commitments and Contingencies Disclosure	COMMITMENTS AND CONTINGENCIES NOTE 14(a) Capital Purchase Commitments - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects, including WPL’s expansion of battery storage, IPL’s repowering of the existing Franklin County wind farm, and IPL’s expansion of solar generation. At September 30, 2024, Alliant Energy’s, IPL’s and WPL’s minimum future commitments for these projects were $99 million, $24 million and $72 million, respectively. NOTE 14(b) Other Purchase Commitments - Various commodity supply, transportation and storage contracts help meet obligations to provide electricity and natural gas to utility customers. In addition, there are various purchase commitments associated with other goods and services. At September 30, 2024, the related minimum future commitments, excluding amounts for purchased power commitments that do not have minimum thresholds but will require payment when electricity is generated by the provider, were as follows (in millions): Alliant Energy IPL WPL Natural gas $746 $322 $424 Coal 139 80 59 Other (a) 110 46 22 $995 $448 $505 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2024. NOTE 14(c) Guarantees and Indemnifications - Whiting Petroleum Corporation (Whiting Petroleum) - In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum, an independent oil and gas company. Alliant Energy Resources, LLC, as the successor to a predecessor entity that owned Whiting Petroleum, and a wholly-owned subsidiary of AEF, has guaranteed the partnership obligations of an affiliate of Whiting Petroleum under multiple general partnership agreements in the oil and gas industry. The guarantees do not include a maximum limit. Based on information made available to Alliant Energy by Whiting Petroleum, the Whiting Petroleum affiliate holds an approximate 6% share in the partnerships, and currently known obligations include costs associated with the future abandonment of certain facilities owned by the partnerships. The general partnerships were formed under California law, and Alliant Energy Resources, LLC may need to perform under the guarantees if the affiliate of Whiting Petroleum is unable to meet its partnership obligations. Whiting Petroleum previously completed bankruptcy proceedings and business combinations, which substantially reduce the likelihood that Alliant Energy will be obligated to make any payments under these guarantees. As of September 30, 2024, 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 is not currently aware of, nor does it currently expect to incur in the future, any material liabilities related to these guarantees and therefore has not recognized any material liabilities related to these guarantees as of September 30, 2024 and December 31, 2023. Non-utility Wind Farm in Oklahoma - In 2017, a wholly-owned subsidiary of AEF acquired a cash equity ownership interest in a non-utility wind farm located in Oklahoma. The wind farm provides electricity to a third party under a long-term purchased power agreement (PPA). Alliant Energy provided a parent guarantee of its subsidiary’s indemnification obligations under the related operating agreement and PPA. Alliant Energy’s obligations under the operating agreement were $43 million as of September 30, 2024 and will reduce annually until expiring in July 2047. Alliant Energy’s obligations under the PPA are subject to a maximum limit of $17 million and expire in December 2031, subject to potential extension. Alliant Energy is not aware of any material liabilities related to this guarantee that it is probable that it will be obligated to pay and therefore has not recognized any material liabilities related to this guarantee as of September 30, 2024 and December 31, 2023. Transfers of Renewable Tax Credits - In 2023 and 2024, IPL and WPL entered into agreements to transfer renewable tax credits from certain wind, solar and battery storage facilities to other corporate taxpayers in exchange for cash. As of September 30, 2024, IPL and WPL provided indemnifications associated with $165 million and $105 million, respectively, of proceeds for renewable tax credits transferred to other corporate taxpayers in the event of an adverse interpretation of tax law, including whether the related tax credits meet the qualification requirements. Alliant Energy, IPL and WPL believe the likelihood of having to make any material cash payments under these indemnifications is remote. NOTE 14(d) Environmental Matters - Manufactured Gas Plant (MGP) 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 September 30, 2024, estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, which are not discounted, were as follows (in millions): Alliant Energy IPL WPL Range of estimated future costs $7 - $28 $5 - $17 $2 - $11 Current and non-current environmental liabilities $13 $8 $5 IPL Consent Decree - In 2015, the U.S. District Court for the Northern District of Iowa approved a Consent Decree that IPL entered into with the EPA, the Sierra Club, the State of Iowa and Linn County in Iowa, thereby resolving potential Clean Air Act 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: Cross-State Air Pollution Rule, Effluent Limitation Guidelines, CCR Rule, and various legislation and EPA regulations to monitor and regulate the emission of greenhouse gases, including the Clean Air Act. NOTE 14(e) MISO Transmission Owner Return on Equity Complaints - A group of stakeholders, including MISO cooperative and municipal utilities, previously filed complaints with the Federal Energy Regulatory Commission (FERC) requesting a reduction to the base return on equity authorized for MISO transmission owners, including ITC Midwest LLC 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. In October 2024, FERC issued an order reducing the base return on equity authorized for MISO transmission owners to 9.98%, effective September 28, 2016. As a result, the MISO transmission owners will provide refunds based on the 9.98% base return on equity, with interest, for November 12, 2013 through February 11, 2015, and subsequent to September 28, 2016, which is not expected to result in any material impacts on Alliant Energy’s results of operations or financial condition. Any further changes in FERC’s decisions may have an impact on Alliant Energy’s share of ATC’s future earnings and customer costs; however, Alliant Energy is currently unable to predict with certainty the future outcome or impact of any further changes. NOTE 14(f) Collective Bargaining Agreements - In August 2024, IPL’s collective bargaining agreement with International Brotherhood of Electrical Workers Local 204 (Cedar Rapids) expired. A new agreement was reached in September 2024, which expires August 31, 2028.
WPL [Member]
Commitments and Contingencies Disclosure	COMMITMENTS AND CONTINGENCIES NOTE 14(a) Capital Purchase Commitments - Various contractual obligations contain minimum future commitments related to capital expenditures for certain construction projects, including WPL’s expansion of battery storage, IPL’s repowering of the existing Franklin County wind farm, and IPL’s expansion of solar generation. At September 30, 2024, Alliant Energy’s, IPL’s and WPL’s minimum future commitments for these projects were $99 million, $24 million and $72 million, respectively. NOTE 14(b) Other Purchase Commitments - Various commodity supply, transportation and storage contracts help meet obligations to provide electricity and natural gas to utility customers. In addition, there are various purchase commitments associated with other goods and services. At September 30, 2024, the related minimum future commitments, excluding amounts for purchased power commitments that do not have minimum thresholds but will require payment when electricity is generated by the provider, were as follows (in millions): Alliant Energy IPL WPL Natural gas $746 $322 $424 Coal 139 80 59 Other (a) 110 46 22 $995 $448 $505 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2024. NOTE 14(c) Guarantees and Indemnifications - Whiting Petroleum Corporation (Whiting Petroleum) - In 2004, Alliant Energy sold its remaining interest in Whiting Petroleum, an independent oil and gas company. Alliant Energy Resources, LLC, as the successor to a predecessor entity that owned Whiting Petroleum, and a wholly-owned subsidiary of AEF, has guaranteed the partnership obligations of an affiliate of Whiting Petroleum under multiple general partnership agreements in the oil and gas industry. The guarantees do not include a maximum limit. Based on information made available to Alliant Energy by Whiting Petroleum, the Whiting Petroleum affiliate holds an approximate 6% share in the partnerships, and currently known obligations include costs associated with the future abandonment of certain facilities owned by the partnerships. The general partnerships were formed under California law, and Alliant Energy Resources, LLC may need to perform under the guarantees if the affiliate of Whiting Petroleum is unable to meet its partnership obligations. Whiting Petroleum previously completed bankruptcy proceedings and business combinations, which substantially reduce the likelihood that Alliant Energy will be obligated to make any payments under these guarantees. As of September 30, 2024, 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 is not currently aware of, nor does it currently expect to incur in the future, any material liabilities related to these guarantees and therefore has not recognized any material liabilities related to these guarantees as of September 30, 2024 and December 31, 2023. Non-utility Wind Farm in Oklahoma - In 2017, a wholly-owned subsidiary of AEF acquired a cash equity ownership interest in a non-utility wind farm located in Oklahoma. The wind farm provides electricity to a third party under a long-term purchased power agreement (PPA). Alliant Energy provided a parent guarantee of its subsidiary’s indemnification obligations under the related operating agreement and PPA. Alliant Energy’s obligations under the operating agreement were $43 million as of September 30, 2024 and will reduce annually until expiring in July 2047. Alliant Energy’s obligations under the PPA are subject to a maximum limit of $17 million and expire in December 2031, subject to potential extension. Alliant Energy is not aware of any material liabilities related to this guarantee that it is probable that it will be obligated to pay and therefore has not recognized any material liabilities related to this guarantee as of September 30, 2024 and December 31, 2023. Transfers of Renewable Tax Credits - In 2023 and 2024, IPL and WPL entered into agreements to transfer renewable tax credits from certain wind, solar and battery storage facilities to other corporate taxpayers in exchange for cash. As of September 30, 2024, IPL and WPL provided indemnifications associated with $165 million and $105 million, respectively, of proceeds for renewable tax credits transferred to other corporate taxpayers in the event of an adverse interpretation of tax law, including whether the related tax credits meet the qualification requirements. Alliant Energy, IPL and WPL believe the likelihood of having to make any material cash payments under these indemnifications is remote. NOTE 14(d) Environmental Matters - Manufactured Gas Plant (MGP) 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 September 30, 2024, estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, which are not discounted, were as follows (in millions): Alliant Energy IPL WPL Range of estimated future costs $7 - $28 $5 - $17 $2 - $11 Current and non-current environmental liabilities $13 $8 $5 IPL Consent Decree - In 2015, the U.S. District Court for the Northern District of Iowa approved a Consent Decree that IPL entered into with the EPA, the Sierra Club, the State of Iowa and Linn County in Iowa, thereby resolving potential Clean Air Act 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: Cross-State Air Pollution Rule, Effluent Limitation Guidelines, CCR Rule, and various legislation and EPA regulations to monitor and regulate the emission of greenhouse gases, including the Clean Air Act. NOTE 14(e) MISO Transmission Owner Return on Equity Complaints - A group of stakeholders, including MISO cooperative and municipal utilities, previously filed complaints with the Federal Energy Regulatory Commission (FERC) requesting a reduction to the base return on equity authorized for MISO transmission owners, including ITC Midwest LLC 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. In October 2024, FERC issued an order reducing the base return on equity authorized for MISO transmission owners to 9.98%, effective September 28, 2016. As a result, the MISO transmission owners will provide refunds based on the 9.98% base return on equity, with interest, for November 12, 2013 through February 11, 2015, and subsequent to September 28, 2016, which is not expected to result in any material impacts on Alliant Energy’s results of operations or financial condition. Any further changes in FERC’s decisions may have an impact on Alliant Energy’s share of ATC’s future earnings and customer costs; however, Alliant Energy is currently unable to predict with certainty the future outcome or impact of any further changes. NOTE 14(f) Collective Bargaining Agreements - In August 2024, IPL’s collective bargaining agreement with International Brotherhood of Electrical Workers Local 204 (Cedar Rapids) expired. A new agreement was reached in September 2024, which expires August 31, 2028.

Segments Of Business

Segments Of Business	9 Months Ended
	Sep. 30, 2024
Segment Reporting Information [Line Items]
Segments Of Business	SEGMENTS OF BUSINESS Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s business segments is as follows. Intersegment revenues were not material to their respective operations. Refer to Note 2 for discussion of asset valuation charges recorded in the second quarter of 2024 related to IPL’s Lansing Generating Station, which decreased the assets for “Utility - Electric,” and N ote 11 for discussion of additional AROs recorded in the second quarter of 2024 substantially due to the enactment of the revised CCR Rule, which primarily increased the assets for “Utility - Electric.” Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended September 30, 2024 Revenues $999 $49 $12 $1,060 $21 $1,081 Operating income (loss) 305 (4) 4 305 8 313 Net income (loss) attributable to Alliant Energy common shareowners 304 (9) 295 Three Months Ended September 30, 2023 Revenues $995 $47 $13 $1,055 $22 $1,077 Operating income (loss) 319 (4) — 315 7 322 Net income (loss) attributable to Alliant Energy common shareowners 277 (18) 259 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Nine Months Ended September 30, 2024 Revenues $2,579 $322 $36 $2,937 $68 $3,005 Operating income (loss) 600 44 (7) 637 28 665 Net income (loss) attributable to Alliant Energy common shareowners 542 (2) 540 Nine Months Ended September 30, 2023 Revenues $2,562 $400 $38 $3,000 $66 $3,066 Operating income 682 48 12 742 18 760 Net income (loss) attributable to Alliant Energy common shareowners 598 (16) 582 IPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2024 Revenues $523 $27 $11 $561 Operating income (loss) 148 (3) 4 149 Net income 190 Three Months Ended September 30, 2023 Revenues $551 $31 $12 $594 Operating income (loss) 171 (2) 4 173 Net income 170 Nine Months Ended September 30, 2024 Revenues $1,318 $175 $34 $1,527 Operating income (loss) 239 18 (7) 250 Net income 272 Nine Months Ended September 30, 2023 Revenues $1,370 $224 $36 $1,630 Operating income 342 25 12 379 Net income 331 WPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2024 Revenues $476 $22 $1 $499 Operating income (loss) 157 (1) — 156 Net income 114 Three Months Ended September 30, 2023 Revenues $444 $16 $1 $461 Operating income (loss) 148 (2) (4) 142 Net income 107 Nine Months Ended September 30, 2024 Revenues $1,261 $147 $2 $1,410 Operating income 361 26 — 387 Net income 270 Nine Months Ended September 30, 2023 Revenues $1,192 $176 $2 $1,370 Operating income 340 23 — 363 Net income 267
IPL [Member]
Segment Reporting Information [Line Items]
Segments Of Business	SEGMENTS OF BUSINESS Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s business segments is as follows. Intersegment revenues were not material to their respective operations. Refer to Note 2 for discussion of asset valuation charges recorded in the second quarter of 2024 related to IPL’s Lansing Generating Station, which decreased the assets for “Utility - Electric,” and N ote 11 for discussion of additional AROs recorded in the second quarter of 2024 substantially due to the enactment of the revised CCR Rule, which primarily increased the assets for “Utility - Electric.” Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended September 30, 2024 Revenues $999 $49 $12 $1,060 $21 $1,081 Operating income (loss) 305 (4) 4 305 8 313 Net income (loss) attributable to Alliant Energy common shareowners 304 (9) 295 Three Months Ended September 30, 2023 Revenues $995 $47 $13 $1,055 $22 $1,077 Operating income (loss) 319 (4) — 315 7 322 Net income (loss) attributable to Alliant Energy common shareowners 277 (18) 259 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Nine Months Ended September 30, 2024 Revenues $2,579 $322 $36 $2,937 $68 $3,005 Operating income (loss) 600 44 (7) 637 28 665 Net income (loss) attributable to Alliant Energy common shareowners 542 (2) 540 Nine Months Ended September 30, 2023 Revenues $2,562 $400 $38 $3,000 $66 $3,066 Operating income 682 48 12 742 18 760 Net income (loss) attributable to Alliant Energy common shareowners 598 (16) 582 IPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2024 Revenues $523 $27 $11 $561 Operating income (loss) 148 (3) 4 149 Net income 190 Three Months Ended September 30, 2023 Revenues $551 $31 $12 $594 Operating income (loss) 171 (2) 4 173 Net income 170 Nine Months Ended September 30, 2024 Revenues $1,318 $175 $34 $1,527 Operating income (loss) 239 18 (7) 250 Net income 272 Nine Months Ended September 30, 2023 Revenues $1,370 $224 $36 $1,630 Operating income 342 25 12 379 Net income 331 WPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2024 Revenues $476 $22 $1 $499 Operating income (loss) 157 (1) — 156 Net income 114 Three Months Ended September 30, 2023 Revenues $444 $16 $1 $461 Operating income (loss) 148 (2) (4) 142 Net income 107 Nine Months Ended September 30, 2024 Revenues $1,261 $147 $2 $1,410 Operating income 361 26 — 387 Net income 270 Nine Months Ended September 30, 2023 Revenues $1,192 $176 $2 $1,370 Operating income 340 23 — 363 Net income 267
WPL [Member]
Segment Reporting Information [Line Items]
Segments Of Business	SEGMENTS OF BUSINESS Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s business segments is as follows. Intersegment revenues were not material to their respective operations. Refer to Note 2 for discussion of asset valuation charges recorded in the second quarter of 2024 related to IPL’s Lansing Generating Station, which decreased the assets for “Utility - Electric,” and N ote 11 for discussion of additional AROs recorded in the second quarter of 2024 substantially due to the enactment of the revised CCR Rule, which primarily increased the assets for “Utility - Electric.” Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended September 30, 2024 Revenues $999 $49 $12 $1,060 $21 $1,081 Operating income (loss) 305 (4) 4 305 8 313 Net income (loss) attributable to Alliant Energy common shareowners 304 (9) 295 Three Months Ended September 30, 2023 Revenues $995 $47 $13 $1,055 $22 $1,077 Operating income (loss) 319 (4) — 315 7 322 Net income (loss) attributable to Alliant Energy common shareowners 277 (18) 259 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Nine Months Ended September 30, 2024 Revenues $2,579 $322 $36 $2,937 $68 $3,005 Operating income (loss) 600 44 (7) 637 28 665 Net income (loss) attributable to Alliant Energy common shareowners 542 (2) 540 Nine Months Ended September 30, 2023 Revenues $2,562 $400 $38 $3,000 $66 $3,066 Operating income 682 48 12 742 18 760 Net income (loss) attributable to Alliant Energy common shareowners 598 (16) 582 IPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2024 Revenues $523 $27 $11 $561 Operating income (loss) 148 (3) 4 149 Net income 190 Three Months Ended September 30, 2023 Revenues $551 $31 $12 $594 Operating income (loss) 171 (2) 4 173 Net income 170 Nine Months Ended September 30, 2024 Revenues $1,318 $175 $34 $1,527 Operating income (loss) 239 18 (7) 250 Net income 272 Nine Months Ended September 30, 2023 Revenues $1,370 $224 $36 $1,630 Operating income 342 25 12 379 Net income 331 WPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2024 Revenues $476 $22 $1 $499 Operating income (loss) 157 (1) — 156 Net income 114 Three Months Ended September 30, 2023 Revenues $444 $16 $1 $461 Operating income (loss) 148 (2) (4) 142 Net income 107 Nine Months Ended September 30, 2024 Revenues $1,261 $147 $2 $1,410 Operating income 361 26 — 387 Net income 270 Nine Months Ended September 30, 2023 Revenues $1,192 $176 $2 $1,370 Operating income 340 23 — 363 Net income 267

Related Parties

Related Parties	9 Months Ended
	Sep. 30, 2024
Related Party Transactions [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 for the three and nine months ended September 30 were as follows (in millions): IPL WPL Three Months Nine Months Three Months Nine Months 2024 2023 2024 2023 2024 2023 2024 2023 Corporate Services billings $42 $46 $134 $134 $38 $40 $124 $120 Sales credited — 3 — 11 29 23 66 45 Purchases billed 130 133 332 320 18 5 41 21 Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL September 30, 2024 December 31, 2023 September 30, 2024 December 31, 2023 Net payables to Corporate Services $131 $129 $72 $72 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 for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2024 2023 2024 2023 ATC billings to WPL $39 $41 $115 $119 WPL billings to ATC 5 5 12 16 WPL owed ATC net amounts of $11 million as of September 30, 2024 and $10 million as of December 31, 2023.
IPL [Member]
Related Party Transactions [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 for the three and nine months ended September 30 were as follows (in millions): IPL WPL Three Months Nine Months Three Months Nine Months 2024 2023 2024 2023 2024 2023 2024 2023 Corporate Services billings $42 $46 $134 $134 $38 $40 $124 $120 Sales credited — 3 — 11 29 23 66 45 Purchases billed 130 133 332 320 18 5 41 21 Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL September 30, 2024 December 31, 2023 September 30, 2024 December 31, 2023 Net payables to Corporate Services $131 $129 $72 $72
WPL [Member]
Related Party Transactions [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 for the three and nine months ended September 30 were as follows (in millions): IPL WPL Three Months Nine Months Three Months Nine Months 2024 2023 2024 2023 2024 2023 2024 2023 Corporate Services billings $42 $46 $134 $134 $38 $40 $124 $120 Sales credited — 3 — 11 29 23 66 45 Purchases billed 130 133 332 320 18 5 41 21 Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL September 30, 2024 December 31, 2023 September 30, 2024 December 31, 2023 Net payables to Corporate Services $131 $129 $72 $72 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 for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2024 2023 2024 2023 ATC billings to WPL $39 $41 $115 $119 WPL billings to ATC 5 5 12 16 WPL owed ATC net amounts of $11 million as of September 30, 2024 and $10 million as of December 31, 2023.

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Pay vs Performance Disclosure
Net income	$ 540	$ 582

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Sep. 30, 2024
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

Summary Of Significant Accoun_2

Summary Of Significant Accounting Policies (Policy)	9 Months Ended
	Sep. 30, 2024
General, Basis of Accounting	The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the 2023 Form 10-K . In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the nine months ended September 30, 2024 are not necessarily indicative of results that may be expected for the year ending December 31, 2024.
General, Use of Estimates	A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred.
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.
Cash and Cash Equivalents	At September 30, 2024, cash and cash equivalents included time deposits and money market fund investments of $803 million and $745 million for Alliant Energy and IPL, respectively, and money market fund investments of $58 million for WPL, with weighted average interest rates of 5%.
IPL [Member]
General, Basis of Accounting	The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the 2023 Form 10-K . In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the nine months ended September 30, 2024 are not necessarily indicative of results that may be expected for the year ending December 31, 2024.
General, Use of Estimates	A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred.
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.
Cash and Cash Equivalents	At September 30, 2024, cash and cash equivalents included time deposits and money market fund investments of $803 million and $745 million for Alliant Energy and IPL, respectively, and money market fund investments of $58 million for WPL, with weighted average interest rates of 5%.
WPL [Member]
General, Basis of Accounting	The interim unaudited Financial Statements included herein have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. Accordingly, certain information and note disclosures normally included in financial statements prepared in accordance with GAAP have been condensed or omitted, although management believes that the disclosures are adequate to make the information presented not misleading. These Financial Statements should be read in conjunction with the financial statements and the notes thereto included in the 2023 Form 10-K . In the opinion of management, all adjustments, which unless otherwise noted are normal and recurring in nature, necessary for a fair presentation of the results of operations, financial position and cash flows have been made. Results for the nine months ended September 30, 2024 are not necessarily indicative of results that may be expected for the year ending December 31, 2024.
General, Use of Estimates	A change in management’s estimates or assumptions could have a material impact on financial condition and results of operations during the period in which such change occurred.
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.
Cash and Cash Equivalents	At September 30, 2024, cash and cash equivalents included time deposits and money market fund investments of $803 million and $745 million for Alliant Energy and IPL, respectively, and money market fund investments of $58 million for WPL, with weighted average interest rates of 5%.

Regulatory Matters (Tables)

Regulatory Matters (Tables)	9 Months Ended
	Sep. 30, 2024
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $1,000 $934 $885 $831 $115 $103 AROs 418 194 223 160 195 34 Pension and OPEB costs 329 347 163 171 166 176 Assets retired early 181 273 169 259 12 14 Derivatives 80 102 24 34 56 68 Commodity cost recovery 76 120 8 12 68 108 WPL’s Western Wisconsin gas distribution expansion investments 42 44 — — 42 44 IPL’s Duane Arnold Energy Center purchased power agreement amendment 24 42 24 42 — — Other 200 205 72 68 128 137 $2,350 $2,261 $1,568 $1,577 $782 $684
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $589 $566 $286 $299 $303 $267 Cost of removal obligations 359 366 215 242 144 124 Derivatives 47 65 26 34 21 31 Commodity cost recovery 45 48 8 13 37 35 Other 32 85 18 56 14 29 $1,072 $1,130 $553 $644 $519 $486
IPL [Member]
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $1,000 $934 $885 $831 $115 $103 AROs 418 194 223 160 195 34 Pension and OPEB costs 329 347 163 171 166 176 Assets retired early 181 273 169 259 12 14 Derivatives 80 102 24 34 56 68 Commodity cost recovery 76 120 8 12 68 108 WPL’s Western Wisconsin gas distribution expansion investments 42 44 — — 42 44 IPL’s Duane Arnold Energy Center purchased power agreement amendment 24 42 24 42 — — Other 200 205 72 68 128 137 $2,350 $2,261 $1,568 $1,577 $782 $684
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $589 $566 $286 $299 $303 $267 Cost of removal obligations 359 366 215 242 144 124 Derivatives 47 65 26 34 21 31 Commodity cost recovery 45 48 8 13 37 35 Other 32 85 18 56 14 29 $1,072 $1,130 $553 $644 $519 $486
WPL [Member]
Regulatory Assets [Line Items]
Regulatory Assets	Regulatory assets were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $1,000 $934 $885 $831 $115 $103 AROs 418 194 223 160 195 34 Pension and OPEB costs 329 347 163 171 166 176 Assets retired early 181 273 169 259 12 14 Derivatives 80 102 24 34 56 68 Commodity cost recovery 76 120 8 12 68 108 WPL’s Western Wisconsin gas distribution expansion investments 42 44 — — 42 44 IPL’s Duane Arnold Energy Center purchased power agreement amendment 24 42 24 42 — — Other 200 205 72 68 128 137 $2,350 $2,261 $1,568 $1,577 $782 $684
Regulatory Liabilities	Regulatory liabilities were comprised of the following items (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Tax-related $589 $566 $286 $299 $303 $267 Cost of removal obligations 359 366 215 242 144 124 Derivatives 47 65 26 34 21 31 Commodity cost recovery 45 48 8 13 37 35 Other 32 85 18 56 14 29 $1,072 $1,130 $553 $644 $519 $486

Receivables (Tables)

Receivables (Tables)	9 Months Ended
	Sep. 30, 2024
Receivables [Line Items]
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 for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2024 2023 2024 2023 Maximum outstanding aggregate cash proceeds $52 $94 $110 $110 Average outstanding aggregate cash proceeds 7 46 34 68
Attributes of Receivables Sold Under the Receivables Agreement	The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): September 30, 2024 December 31, 2023 Customer accounts receivable $141 $130 Unbilled utility revenues 81 98 Other receivables 1 1 Receivables sold to third party 223 229 Less: cash proceeds 1 1 Deferred proceeds 222 228 Less: allowance for expected credit losses 10 12 Fair value of deferred proceeds $212 $216
Additional Attributes Of Receivables Sold Under The Receivables Agreement	Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2024 2023 2024 2023 Collections $565 $616 $1,578 $1,720 Write-offs, net of recoveries 4 5 9 9
IPL [Member]
Receivables [Line Items]
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 for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2024 2023 2024 2023 Maximum outstanding aggregate cash proceeds $52 $94 $110 $110 Average outstanding aggregate cash proceeds 7 46 34 68
Attributes of Receivables Sold Under the Receivables Agreement	The attributes of IPL’s receivables sold under the Receivables Agreement were as follows (in millions): September 30, 2024 December 31, 2023 Customer accounts receivable $141 $130 Unbilled utility revenues 81 98 Other receivables 1 1 Receivables sold to third party 223 229 Less: cash proceeds 1 1 Deferred proceeds 222 228 Less: allowance for expected credit losses 10 12 Fair value of deferred proceeds $212 $216
Additional Attributes Of Receivables Sold Under The Receivables Agreement	Additional attributes of IPL’s receivables sold under the Receivables Agreement for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2024 2023 2024 2023 Collections $565 $616 $1,578 $1,720 Write-offs, net of recoveries 4 5 9 9

Investments (Tables)

Investments (Tables)	9 Months Ended
	Sep. 30, 2024
Schedule of Equity Method Investments [Line Items]
Unconsolidated Equity Investments	Alliant Energy’s equity (income) loss from unconsolidated investments accounted for under the equity method of accounting for the three and nine months ended September 30 was as follows (in millions): Three Months Nine Months 2024 2023 2024 2023 ATC Holdings ($13) ($12) ($38) ($37) Other (1) (2) (6) (8) ($14) ($14) ($44) ($45)

Common Equity (Tables)

Common Equity (Tables)	9 Months Ended
	Sep. 30, 2024
Schedule of Capitalization, Equity [Line Items]
Common Share Activity	A summary of Alliant Energy’s common stock activity was as follows: Shares outstanding, January 1, 2024 256,096,848 Shareowner Direct Plan 348,087 Equity-based compensation plans 154,267 Shares outstanding, September 30, 2024 256,599,202
Changes in Shareowners' Equity	A summary of changes in shareowners’ equity was as follows (in millions): Alliant Energy Accumulated Shares in Additional Other Deferred Total Common Paid-In Retained Comprehensive Compensation Common Stock Capital Earnings Income (Loss) Trust Equity Three Months Ended September 30, 2024 Beginning balance, June 30, 2024 $3 $3,042 $3,755 $3 ($12) $6,791 Net income attributable to Alliant Energy common shareowners 295 295 Common stock dividends ($0.48 per share) (123) (123) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other 4 (1) 3 Other comprehensive loss, net of tax (4) (4) Ending balance, September 30, 2024 $3 $3,052 $3,927 ($1) ($13) $6,968 Three Months Ended September 30, 2023 Beginning balance, June 30, 2023 $3 $2,854 $3,606 $3 ($14) $6,452 Net income attributable to Alliant Energy common shareowners 259 259 Common stock dividends ($0.4525 per share) (115) (115) At-the-market offering program and Shareowner Direct Plan issuances 125 125 Equity-based compensation plans and other 3 1 4 Other comprehensive income, net of tax 1 1 Ending balance, September 30, 2023 $3 $2,982 $3,750 $4 ($13) $6,726 Alliant Energy Accumulated Shares in Additional Other Deferred Total Common Paid-In Retained Comprehensive Compensation Common Stock Capital Earnings Income (Loss) Trust Equity Nine Months Ended September 30, 2024 Beginning balance, December 31, 2023 $3 $3,030 $3,756 $1 ($13) $6,777 Net income attributable to Alliant Energy common shareowners 540 540 Common stock dividends ($1.44 per share) (369) (369) Shareowner Direct Plan issuances 18 18 Equity-based compensation plans and other 4 4 Other comprehensive loss, net of tax (2) (2) Ending balance, September 30, 2024 $3 $3,052 $3,927 ($1) ($13) $6,968 Nine Months Ended September 30, 2023 Beginning balance, December 31, 2022 $3 $2,777 $3,509 $— ($13) $6,276 Net income attributable to Alliant Energy common shareowners 582 582 Common stock dividends ($1.3575 per share) (341) (341) At-the-market offering program and Shareowner Direct Plan issuances 201 201 Equity-based compensation plans and other 4 4 Other comprehensive income, net of tax 4 4 Ending balance, September 30, 2023 $3 $2,982 $3,750 $4 ($13) $6,726 IPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended September 30, 2024 Beginning balance, June 30, 2024 $33 $3,012 $1,035 $4,080 Net income 190 190 Common stock dividends (50) (50) Capital contributions from parent 200 200 Ending balance, September 30, 2024 $33 $3,212 $1,175 $4,420 Three Months Ended September 30, 2023 Beginning balance, June 30, 2023 $33 $2,847 $989 $3,869 Net income 170 170 Common stock dividends (70) (70) Capital contributions from parent 20 20 Ending balance, September 30, 2023 $33 $2,867 $1,089 $3,989 IPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Nine Months Ended September 30, 2024 Beginning balance, December 31, 2023 $33 $2,887 $1,054 $3,974 Net income 272 272 Common stock dividends (151) (151) Capital contributions from parent 325 325 Ending balance, September 30, 2024 $33 $3,212 $1,175 $4,420 Nine Months Ended September 30, 2023 Beginning balance, December 31, 2022 $33 $2,807 $968 $3,808 Net income 331 331 Common stock dividends (210) (210) Capital contributions from parent 60 60 Ending balance, September 30, 2023 $33 $2,867 $1,089 $3,989 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended September 30, 2024 Beginning balance, June 30, 2024 $66 $2,533 $1,411 $4,010 Net income 114 114 Common stock dividends (49) (49) Ending balance, September 30, 2024 $66 $2,533 $1,476 $4,075 Three Months Ended September 30, 2023 Beginning balance, June 30, 2023 $66 $2,413 $1,260 $3,739 Net income 107 107 Common stock dividends (46) (46) Capital contributions from parent 65 65 Ending balance, September 30, 2023 $66 $2,478 $1,321 $3,865 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Nine Months Ended September 30, 2024 Beginning balance, December 31, 2023 $66 $2,478 $1,353 $3,897 Net income 270 270 Common stock dividends (147) (147) Capital contributions from parent 55 55 Ending balance, September 30, 2024 $66 $2,533 $1,476 $4,075 Nine Months Ended September 30, 2023 Beginning balance, December 31, 2022 $66 $2,233 $1,192 $3,491 Net income 267 267 Common stock dividends (138) (138) Capital contributions from parent 245 245 Ending balance, September 30, 2023 $66 $2,478 $1,321 $3,865
IPL [Member]
Schedule of Capitalization, Equity [Line Items]
Changes in Shareowners' Equity	A summary of changes in shareowners’ equity was as follows (in millions): Alliant Energy Accumulated Shares in Additional Other Deferred Total Common Paid-In Retained Comprehensive Compensation Common Stock Capital Earnings Income (Loss) Trust Equity Three Months Ended September 30, 2024 Beginning balance, June 30, 2024 $3 $3,042 $3,755 $3 ($12) $6,791 Net income attributable to Alliant Energy common shareowners 295 295 Common stock dividends ($0.48 per share) (123) (123) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other 4 (1) 3 Other comprehensive loss, net of tax (4) (4) Ending balance, September 30, 2024 $3 $3,052 $3,927 ($1) ($13) $6,968 Three Months Ended September 30, 2023 Beginning balance, June 30, 2023 $3 $2,854 $3,606 $3 ($14) $6,452 Net income attributable to Alliant Energy common shareowners 259 259 Common stock dividends ($0.4525 per share) (115) (115) At-the-market offering program and Shareowner Direct Plan issuances 125 125 Equity-based compensation plans and other 3 1 4 Other comprehensive income, net of tax 1 1 Ending balance, September 30, 2023 $3 $2,982 $3,750 $4 ($13) $6,726 Alliant Energy Accumulated Shares in Additional Other Deferred Total Common Paid-In Retained Comprehensive Compensation Common Stock Capital Earnings Income (Loss) Trust Equity Nine Months Ended September 30, 2024 Beginning balance, December 31, 2023 $3 $3,030 $3,756 $1 ($13) $6,777 Net income attributable to Alliant Energy common shareowners 540 540 Common stock dividends ($1.44 per share) (369) (369) Shareowner Direct Plan issuances 18 18 Equity-based compensation plans and other 4 4 Other comprehensive loss, net of tax (2) (2) Ending balance, September 30, 2024 $3 $3,052 $3,927 ($1) ($13) $6,968 Nine Months Ended September 30, 2023 Beginning balance, December 31, 2022 $3 $2,777 $3,509 $— ($13) $6,276 Net income attributable to Alliant Energy common shareowners 582 582 Common stock dividends ($1.3575 per share) (341) (341) At-the-market offering program and Shareowner Direct Plan issuances 201 201 Equity-based compensation plans and other 4 4 Other comprehensive income, net of tax 4 4 Ending balance, September 30, 2023 $3 $2,982 $3,750 $4 ($13) $6,726 IPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended September 30, 2024 Beginning balance, June 30, 2024 $33 $3,012 $1,035 $4,080 Net income 190 190 Common stock dividends (50) (50) Capital contributions from parent 200 200 Ending balance, September 30, 2024 $33 $3,212 $1,175 $4,420 Three Months Ended September 30, 2023 Beginning balance, June 30, 2023 $33 $2,847 $989 $3,869 Net income 170 170 Common stock dividends (70) (70) Capital contributions from parent 20 20 Ending balance, September 30, 2023 $33 $2,867 $1,089 $3,989 IPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Nine Months Ended September 30, 2024 Beginning balance, December 31, 2023 $33 $2,887 $1,054 $3,974 Net income 272 272 Common stock dividends (151) (151) Capital contributions from parent 325 325 Ending balance, September 30, 2024 $33 $3,212 $1,175 $4,420 Nine Months Ended September 30, 2023 Beginning balance, December 31, 2022 $33 $2,807 $968 $3,808 Net income 331 331 Common stock dividends (210) (210) Capital contributions from parent 60 60 Ending balance, September 30, 2023 $33 $2,867 $1,089 $3,989 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended September 30, 2024 Beginning balance, June 30, 2024 $66 $2,533 $1,411 $4,010 Net income 114 114 Common stock dividends (49) (49) Ending balance, September 30, 2024 $66 $2,533 $1,476 $4,075 Three Months Ended September 30, 2023 Beginning balance, June 30, 2023 $66 $2,413 $1,260 $3,739 Net income 107 107 Common stock dividends (46) (46) Capital contributions from parent 65 65 Ending balance, September 30, 2023 $66 $2,478 $1,321 $3,865 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Nine Months Ended September 30, 2024 Beginning balance, December 31, 2023 $66 $2,478 $1,353 $3,897 Net income 270 270 Common stock dividends (147) (147) Capital contributions from parent 55 55 Ending balance, September 30, 2024 $66 $2,533 $1,476 $4,075 Nine Months Ended September 30, 2023 Beginning balance, December 31, 2022 $66 $2,233 $1,192 $3,491 Net income 267 267 Common stock dividends (138) (138) Capital contributions from parent 245 245 Ending balance, September 30, 2023 $66 $2,478 $1,321 $3,865
WPL [Member]
Schedule of Capitalization, Equity [Line Items]
Changes in Shareowners' Equity	A summary of changes in shareowners’ equity was as follows (in millions): Alliant Energy Accumulated Shares in Additional Other Deferred Total Common Paid-In Retained Comprehensive Compensation Common Stock Capital Earnings Income (Loss) Trust Equity Three Months Ended September 30, 2024 Beginning balance, June 30, 2024 $3 $3,042 $3,755 $3 ($12) $6,791 Net income attributable to Alliant Energy common shareowners 295 295 Common stock dividends ($0.48 per share) (123) (123) Shareowner Direct Plan issuances 6 6 Equity-based compensation plans and other 4 (1) 3 Other comprehensive loss, net of tax (4) (4) Ending balance, September 30, 2024 $3 $3,052 $3,927 ($1) ($13) $6,968 Three Months Ended September 30, 2023 Beginning balance, June 30, 2023 $3 $2,854 $3,606 $3 ($14) $6,452 Net income attributable to Alliant Energy common shareowners 259 259 Common stock dividends ($0.4525 per share) (115) (115) At-the-market offering program and Shareowner Direct Plan issuances 125 125 Equity-based compensation plans and other 3 1 4 Other comprehensive income, net of tax 1 1 Ending balance, September 30, 2023 $3 $2,982 $3,750 $4 ($13) $6,726 Alliant Energy Accumulated Shares in Additional Other Deferred Total Common Paid-In Retained Comprehensive Compensation Common Stock Capital Earnings Income (Loss) Trust Equity Nine Months Ended September 30, 2024 Beginning balance, December 31, 2023 $3 $3,030 $3,756 $1 ($13) $6,777 Net income attributable to Alliant Energy common shareowners 540 540 Common stock dividends ($1.44 per share) (369) (369) Shareowner Direct Plan issuances 18 18 Equity-based compensation plans and other 4 4 Other comprehensive loss, net of tax (2) (2) Ending balance, September 30, 2024 $3 $3,052 $3,927 ($1) ($13) $6,968 Nine Months Ended September 30, 2023 Beginning balance, December 31, 2022 $3 $2,777 $3,509 $— ($13) $6,276 Net income attributable to Alliant Energy common shareowners 582 582 Common stock dividends ($1.3575 per share) (341) (341) At-the-market offering program and Shareowner Direct Plan issuances 201 201 Equity-based compensation plans and other 4 4 Other comprehensive income, net of tax 4 4 Ending balance, September 30, 2023 $3 $2,982 $3,750 $4 ($13) $6,726 IPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended September 30, 2024 Beginning balance, June 30, 2024 $33 $3,012 $1,035 $4,080 Net income 190 190 Common stock dividends (50) (50) Capital contributions from parent 200 200 Ending balance, September 30, 2024 $33 $3,212 $1,175 $4,420 Three Months Ended September 30, 2023 Beginning balance, June 30, 2023 $33 $2,847 $989 $3,869 Net income 170 170 Common stock dividends (70) (70) Capital contributions from parent 20 20 Ending balance, September 30, 2023 $33 $2,867 $1,089 $3,989 IPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Nine Months Ended September 30, 2024 Beginning balance, December 31, 2023 $33 $2,887 $1,054 $3,974 Net income 272 272 Common stock dividends (151) (151) Capital contributions from parent 325 325 Ending balance, September 30, 2024 $33 $3,212 $1,175 $4,420 Nine Months Ended September 30, 2023 Beginning balance, December 31, 2022 $33 $2,807 $968 $3,808 Net income 331 331 Common stock dividends (210) (210) Capital contributions from parent 60 60 Ending balance, September 30, 2023 $33 $2,867 $1,089 $3,989 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Three Months Ended September 30, 2024 Beginning balance, June 30, 2024 $66 $2,533 $1,411 $4,010 Net income 114 114 Common stock dividends (49) (49) Ending balance, September 30, 2024 $66 $2,533 $1,476 $4,075 Three Months Ended September 30, 2023 Beginning balance, June 30, 2023 $66 $2,413 $1,260 $3,739 Net income 107 107 Common stock dividends (46) (46) Capital contributions from parent 65 65 Ending balance, September 30, 2023 $66 $2,478 $1,321 $3,865 WPL Additional Total Common Paid-In Retained Common Stock Capital Earnings Equity Nine Months Ended September 30, 2024 Beginning balance, December 31, 2023 $66 $2,478 $1,353 $3,897 Net income 270 270 Common stock dividends (147) (147) Capital contributions from parent 55 55 Ending balance, September 30, 2024 $66 $2,533 $1,476 $4,075 Nine Months Ended September 30, 2023 Beginning balance, December 31, 2022 $66 $2,233 $1,192 $3,491 Net income 267 267 Common stock dividends (138) (138) Capital contributions from parent 245 245 Ending balance, September 30, 2023 $66 $2,478 $1,321 $3,865

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 2024
Short-term Debt [Line Items]
Other Short-Term Borrowings	Information regarding commercial paper classified as short-term debt was as follows (dollars in millions): September 30, 2024 Alliant Energy IPL WPL Amount outstanding $330 $— $— Weighted average interest rates 5.0% —% —% Available credit facility capacity $670 $250 $300 Alliant Energy IPL WPL Three Months Ended September 30 2024 2023 2024 2023 2024 2023 Maximum amount outstanding (based on daily outstanding balances) $330 $474 $— $7 $— $125 Average amount outstanding (based on daily outstanding balances) $197 $440 $— $— $— $86 Weighted average interest rates 5.4% 5.5% —% 5.5% —% 5.4% Nine Months Ended September 30 Maximum amount outstanding (based on daily outstanding balances) $632 $793 $19 $70 $390 $349 Average amount outstanding (based on daily outstanding balances) $320 $367 $1 $2 $87 $135 Weighted average interest rates 5.5% 5.1% 5.5% 5.3% 5.5% 4.9%
IPL [Member]
Short-term Debt [Line Items]
Other Short-Term Borrowings	Information regarding commercial paper classified as short-term debt was as follows (dollars in millions): September 30, 2024 Alliant Energy IPL WPL Amount outstanding $330 $— $— Weighted average interest rates 5.0% —% —% Available credit facility capacity $670 $250 $300 Alliant Energy IPL WPL Three Months Ended September 30 2024 2023 2024 2023 2024 2023 Maximum amount outstanding (based on daily outstanding balances) $330 $474 $— $7 $— $125 Average amount outstanding (based on daily outstanding balances) $197 $440 $— $— $— $86 Weighted average interest rates 5.4% 5.5% —% 5.5% —% 5.4% Nine Months Ended September 30 Maximum amount outstanding (based on daily outstanding balances) $632 $793 $19 $70 $390 $349 Average amount outstanding (based on daily outstanding balances) $320 $367 $1 $2 $87 $135 Weighted average interest rates 5.5% 5.1% 5.5% 5.3% 5.5% 4.9%
WPL [Member]
Short-term Debt [Line Items]
Other Short-Term Borrowings	Information regarding commercial paper classified as short-term debt was as follows (dollars in millions): September 30, 2024 Alliant Energy IPL WPL Amount outstanding $330 $— $— Weighted average interest rates 5.0% —% —% Available credit facility capacity $670 $250 $300 Alliant Energy IPL WPL Three Months Ended September 30 2024 2023 2024 2023 2024 2023 Maximum amount outstanding (based on daily outstanding balances) $330 $474 $— $7 $— $125 Average amount outstanding (based on daily outstanding balances) $197 $440 $— $— $— $86 Weighted average interest rates 5.4% 5.5% —% 5.5% —% 5.4% Nine Months Ended September 30 Maximum amount outstanding (based on daily outstanding balances) $632 $793 $19 $70 $390 $349 Average amount outstanding (based on daily outstanding balances) $320 $367 $1 $2 $87 $135 Weighted average interest rates 5.5% 5.1% 5.5% 5.3% 5.5% 4.9%

Revenues (Tables)

Revenues (Tables)	9 Months Ended
	Sep. 30, 2024
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL Three Months Ended September 30 2024 2023 2024 2023 2024 2023 Electric Utility: Retail - residential $378 $374 $202 $209 $176 $165 Retail - commercial 239 241 153 158 86 83 Retail - industrial 270 280 142 153 128 127 Wholesale 58 59 19 21 39 38 Bulk power and other 54 41 7 10 47 31 Total Electric Utility 999 995 523 551 476 444 Gas Utility: Retail - residential 24 23 13 14 11 9 Retail - commercial 13 12 7 9 6 3 Retail - industrial 1 2 1 2 — — Transportation/other 11 10 6 6 5 4 Total Gas Utility 49 47 27 31 22 16 Other Utility: Steam 9 11 9 11 — — Other utility 3 2 2 1 1 1 Total Other Utility 12 13 11 12 1 1 Non-Utility and Other: Travero and other 21 22 — — — — Total Non-Utility and Other 21 22 — — — — Total revenues $1,081 $1,077 $561 $594 $499 $461 Alliant Energy IPL WPL Nine Months Ended September 30 2024 2023 2024 2023 2024 2023 Electric Utility: Retail - residential $966 $943 $502 $503 $464 $440 Retail - commercial 616 627 385 399 231 228 Retail - industrial 730 740 372 389 358 351 Wholesale 147 154 45 47 102 107 Bulk power and other 120 98 14 32 106 66 Total Electric Utility 2,579 2,562 1,318 1,370 1,261 1,192 Gas Utility: Retail - residential 189 233 103 131 86 102 Retail - commercial 92 122 48 65 44 57 Retail - industrial 8 12 5 8 3 4 Transportation/other 33 33 19 20 14 13 Total Gas Utility 322 400 175 224 147 176 Other Utility: Steam 29 32 29 32 — — Other utility 7 6 5 4 2 2 Total Other Utility 36 38 34 36 2 2 Non-Utility and Other: Travero and other 68 66 — — — — Total Non-Utility and Other 68 66 — — — — Total revenues $3,005 $3,066 $1,527 $1,630 $1,410 $1,370
IPL [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL Three Months Ended September 30 2024 2023 2024 2023 2024 2023 Electric Utility: Retail - residential $378 $374 $202 $209 $176 $165 Retail - commercial 239 241 153 158 86 83 Retail - industrial 270 280 142 153 128 127 Wholesale 58 59 19 21 39 38 Bulk power and other 54 41 7 10 47 31 Total Electric Utility 999 995 523 551 476 444 Gas Utility: Retail - residential 24 23 13 14 11 9 Retail - commercial 13 12 7 9 6 3 Retail - industrial 1 2 1 2 — — Transportation/other 11 10 6 6 5 4 Total Gas Utility 49 47 27 31 22 16 Other Utility: Steam 9 11 9 11 — — Other utility 3 2 2 1 1 1 Total Other Utility 12 13 11 12 1 1 Non-Utility and Other: Travero and other 21 22 — — — — Total Non-Utility and Other 21 22 — — — — Total revenues $1,081 $1,077 $561 $594 $499 $461 Alliant Energy IPL WPL Nine Months Ended September 30 2024 2023 2024 2023 2024 2023 Electric Utility: Retail - residential $966 $943 $502 $503 $464 $440 Retail - commercial 616 627 385 399 231 228 Retail - industrial 730 740 372 389 358 351 Wholesale 147 154 45 47 102 107 Bulk power and other 120 98 14 32 106 66 Total Electric Utility 2,579 2,562 1,318 1,370 1,261 1,192 Gas Utility: Retail - residential 189 233 103 131 86 102 Retail - commercial 92 122 48 65 44 57 Retail - industrial 8 12 5 8 3 4 Transportation/other 33 33 19 20 14 13 Total Gas Utility 322 400 175 224 147 176 Other Utility: Steam 29 32 29 32 — — Other utility 7 6 5 4 2 2 Total Other Utility 36 38 34 36 2 2 Non-Utility and Other: Travero and other 68 66 — — — — Total Non-Utility and Other 68 66 — — — — Total revenues $3,005 $3,066 $1,527 $1,630 $1,410 $1,370
WPL [Member]
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue	Disaggregation of revenues from contracts with customers, which correlates to revenues for each reportable segment, was as follows (in millions): Alliant Energy IPL WPL Three Months Ended September 30 2024 2023 2024 2023 2024 2023 Electric Utility: Retail - residential $378 $374 $202 $209 $176 $165 Retail - commercial 239 241 153 158 86 83 Retail - industrial 270 280 142 153 128 127 Wholesale 58 59 19 21 39 38 Bulk power and other 54 41 7 10 47 31 Total Electric Utility 999 995 523 551 476 444 Gas Utility: Retail - residential 24 23 13 14 11 9 Retail - commercial 13 12 7 9 6 3 Retail - industrial 1 2 1 2 — — Transportation/other 11 10 6 6 5 4 Total Gas Utility 49 47 27 31 22 16 Other Utility: Steam 9 11 9 11 — — Other utility 3 2 2 1 1 1 Total Other Utility 12 13 11 12 1 1 Non-Utility and Other: Travero and other 21 22 — — — — Total Non-Utility and Other 21 22 — — — — Total revenues $1,081 $1,077 $561 $594 $499 $461 Alliant Energy IPL WPL Nine Months Ended September 30 2024 2023 2024 2023 2024 2023 Electric Utility: Retail - residential $966 $943 $502 $503 $464 $440 Retail - commercial 616 627 385 399 231 228 Retail - industrial 730 740 372 389 358 351 Wholesale 147 154 45 47 102 107 Bulk power and other 120 98 14 32 106 66 Total Electric Utility 2,579 2,562 1,318 1,370 1,261 1,192 Gas Utility: Retail - residential 189 233 103 131 86 102 Retail - commercial 92 122 48 65 44 57 Retail - industrial 8 12 5 8 3 4 Transportation/other 33 33 19 20 14 13 Total Gas Utility 322 400 175 224 147 176 Other Utility: Steam 29 32 29 32 — — Other utility 7 6 5 4 2 2 Total Other Utility 36 38 34 36 2 2 Non-Utility and Other: Travero and other 68 66 — — — — Total Non-Utility and Other 68 66 — — — — Total revenues $3,005 $3,066 $1,527 $1,630 $1,410 $1,370

Income Taxes (Tables)

Income Taxes (Tables)	9 Months Ended
	Sep. 30, 2024
Income Taxes [Line Items]
Schedule Of Effective Income Tax Rates	Overall effective income tax rates for the three and nine months ended September 30, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, investment tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. Also impacting Alliant Energy’s and IPL’s effective income tax rates for the nine months ended September 30, 2024 were the pre-tax non-cash charge of $60 million for IPL’s Lansing Generation Station discussed in Note 2 and the pre-tax non-cash charge of $20 million for the portion of recorded AROs allocated to IPL’s steam business discussed in Note 11 . Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 Overall income tax rate (27%) 2% (24%) 1% (56%) (22%) (70%) (20%) 3% 16% 5% 15%
Summary Of Tax Credit Carryforwards	At September 30, 2024, the carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL State net operating losses 2025-2044 $367 $6 $1 Federal tax credits 2033-2044 622 435 175
IPL [Member]
Income Taxes [Line Items]
Schedule Of Effective Income Tax Rates	Overall effective income tax rates for the three and nine months ended September 30, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, investment tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. Also impacting Alliant Energy’s and IPL’s effective income tax rates for the nine months ended September 30, 2024 were the pre-tax non-cash charge of $60 million for IPL’s Lansing Generation Station discussed in Note 2 and the pre-tax non-cash charge of $20 million for the portion of recorded AROs allocated to IPL’s steam business discussed in Note 11 . Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 Overall income tax rate (27%) 2% (24%) 1% (56%) (22%) (70%) (20%) 3% 16% 5% 15%
Summary Of Tax Credit Carryforwards	At September 30, 2024, the carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL State net operating losses 2025-2044 $367 $6 $1 Federal tax credits 2033-2044 622 435 175
WPL [Member]
Income Taxes [Line Items]
Schedule Of Effective Income Tax Rates	Overall effective income tax rates for the three and nine months ended September 30, which were computed by dividing income tax expense (benefit) by income before income taxes, were as follows. The effective income tax rates were different than the federal statutory rate primarily due to state income taxes, production tax credits, investment tax credits, amortization of excess deferred taxes and the effect of rate-making on property-related differences. Also impacting Alliant Energy’s and IPL’s effective income tax rates for the nine months ended September 30, 2024 were the pre-tax non-cash charge of $60 million for IPL’s Lansing Generation Station discussed in Note 2 and the pre-tax non-cash charge of $20 million for the portion of recorded AROs allocated to IPL’s steam business discussed in Note 11 . Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 Overall income tax rate (27%) 2% (24%) 1% (56%) (22%) (70%) (20%) 3% 16% 5% 15%
Summary Of Tax Credit Carryforwards	At September 30, 2024, the carryforwards and expiration dates were estimated as follows (in millions): Range of Expiration Dates Alliant Energy IPL WPL State net operating losses 2025-2044 $367 $6 $1 Federal tax credits 2033-2044 622 435 175

Benefit Plans (Tables)

Benefit Plans (Tables)	9 Months Ended
	Sep. 30, 2024
Defined Benefit Plan Disclosure [Line Items]
Net Periodic Benefit Costs	The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and nine months ended September 30 are included below (in millions). For IPL and WPL, amounts are 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. Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months Alliant Energy 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $1 $2 $3 $4 $1 $1 $2 $2 Interest cost 12 12 34 35 2 3 6 7 Expected return on plan assets (14) (14) (41) (40) (2) (2) (4) (4) Amortization of prior service credit — (1) — (1) — — — — Amortization of actuarial loss 6 7 18 21 — — — 1 $5 $6 $14 $19 $1 $2 $4 $6 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months IPL 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $1 $— $2 $2 $— $— $— $— Interest cost 5 6 15 16 1 1 3 3 Expected return on plan assets (7) (6) (20) (19) (1) (1) (3) (3) Amortization of actuarial loss 2 2 7 8 — — — 1 $1 $2 $4 $7 $— $— $— $1 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months WPL 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $— $— $1 $1 $— $1 $— $1 Interest cost 5 5 15 15 1 1 3 3 Expected return on plan assets (6) (5) (18) (16) (1) (1) (1) (1) Amortization of actuarial loss 3 3 9 10 — — — — $2 $3 $7 $10 $— $1 $2 $3
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 for the three and nine months ended September 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 Compensation expense $3 $4 $10 $10 $2 $2 $5 $5 $1 $2 $4 $4 Income tax benefits 1 1 3 3 — 1 1 1 — — 1 1
Schedule Of Equity-based Compensation Plans Activity	For the nine months ended September 30, 2024, performance shares and restricted stock units were granted to key employees under the equity-based compensation plans as follows. These shares and units will be paid out in shares of common stock, and are therefore accounted for as equity awards. Weighted Average Grants Grant Date Fair Value Performance shares (total shareowner return metric) 127,267 $46.04 Performance shares (net income and diversity metrics) (formerly granted as performance restricted stock units) 145,449 48.49 Restricted stock units 128,620 48.57
IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Net Periodic Benefit Costs	The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and nine months ended September 30 are included below (in millions). For IPL and WPL, amounts are 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. Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months Alliant Energy 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $1 $2 $3 $4 $1 $1 $2 $2 Interest cost 12 12 34 35 2 3 6 7 Expected return on plan assets (14) (14) (41) (40) (2) (2) (4) (4) Amortization of prior service credit — (1) — (1) — — — — Amortization of actuarial loss 6 7 18 21 — — — 1 $5 $6 $14 $19 $1 $2 $4 $6 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months IPL 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $1 $— $2 $2 $— $— $— $— Interest cost 5 6 15 16 1 1 3 3 Expected return on plan assets (7) (6) (20) (19) (1) (1) (3) (3) Amortization of actuarial loss 2 2 7 8 — — — 1 $1 $2 $4 $7 $— $— $— $1 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months WPL 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $— $— $1 $1 $— $1 $— $1 Interest cost 5 5 15 15 1 1 3 3 Expected return on plan assets (6) (5) (18) (16) (1) (1) (1) (1) Amortization of actuarial loss 3 3 9 10 — — — — $2 $3 $7 $10 $— $1 $2 $3
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 for the three and nine months ended September 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 Compensation expense $3 $4 $10 $10 $2 $2 $5 $5 $1 $2 $4 $4 Income tax benefits 1 1 3 3 — 1 1 1 — — 1 1
Schedule Of Equity-based Compensation Plans Activity	For the nine months ended September 30, 2024, performance shares and restricted stock units were granted to key employees under the equity-based compensation plans as follows. These shares and units will be paid out in shares of common stock, and are therefore accounted for as equity awards. Weighted Average Grants Grant Date Fair Value Performance shares (total shareowner return metric) 127,267 $46.04 Performance shares (net income and diversity metrics) (formerly granted as performance restricted stock units) 145,449 48.49 Restricted stock units 128,620 48.57
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Net Periodic Benefit Costs	The components of net periodic benefit costs for sponsored defined benefit pension and OPEB plans for the three and nine months ended September 30 are included below (in millions). For IPL and WPL, amounts are 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. Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months Alliant Energy 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $1 $2 $3 $4 $1 $1 $2 $2 Interest cost 12 12 34 35 2 3 6 7 Expected return on plan assets (14) (14) (41) (40) (2) (2) (4) (4) Amortization of prior service credit — (1) — (1) — — — — Amortization of actuarial loss 6 7 18 21 — — — 1 $5 $6 $14 $19 $1 $2 $4 $6 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months IPL 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $1 $— $2 $2 $— $— $— $— Interest cost 5 6 15 16 1 1 3 3 Expected return on plan assets (7) (6) (20) (19) (1) (1) (3) (3) Amortization of actuarial loss 2 2 7 8 — — — 1 $1 $2 $4 $7 $— $— $— $1 Defined Benefit Pension Plans OPEB Plans Three Months Nine Months Three Months Nine Months WPL 2024 2023 2024 2023 2024 2023 2024 2023 Service cost $— $— $1 $1 $— $1 $— $1 Interest cost 5 5 15 15 1 1 3 3 Expected return on plan assets (6) (5) (18) (16) (1) (1) (1) (1) Amortization of actuarial loss 3 3 9 10 — — — — $2 $3 $7 $10 $— $1 $2 $3
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 for the three and nine months ended September 30 was as follows (in millions): Alliant Energy IPL WPL Three Months Nine Months Three Months Nine Months Three Months Nine Months 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 2024 2023 Compensation expense $3 $4 $10 $10 $2 $2 $5 $5 $1 $2 $4 $4 Income tax benefits 1 1 3 3 — 1 1 1 — — 1 1
Schedule Of Equity-based Compensation Plans Activity	For the nine months ended September 30, 2024, performance shares and restricted stock units were granted to key employees under the equity-based compensation plans as follows. These shares and units will be paid out in shares of common stock, and are therefore accounted for as equity awards. Weighted Average Grants Grant Date Fair Value Performance shares (total shareowner return metric) 127,267 $46.04 Performance shares (net income and diversity metrics) (formerly granted as performance restricted stock units) 145,449 48.49 Restricted stock units 128,620 48.57

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	9 Months Ended
	Sep. 30, 2024
Schedule of Asset Retirement Obligations [Line Items]
Reconciliation of Changes in Asset Retirement Obligations	A reconciliation of the changes in AROs associated with long-lived assets for the nine months ended September 30, 2024 is as follows (in millions): Alliant Energy IPL WPL Balance, January 1 $246 $148 $98 Revisions in estimated cash flows (2) — (2) Liabilities settled (4) (2) (2) Liabilities incurred (a) 356 103 253 Accretion expense 12 6 6 Balance, September 30 $608 $255 $353 (a) In the second quarter of 2024, substantially due to the enactment of the revised CCR Rule, which significantly expands the scope of regulation to include coal ash ponds at sites that no longer produce electricity and inactive landfills, including some IPL and WPL facilities, Alliant Energy, IPL and WPL recorded additional AROs, additional ARO regulatory assets for EGUs no longer in operation, additional property, plant and equipment for EGUs still in operation, and a pre-tax non-cash charge of $20 million recorded to “Other operation and maintenance” in Alliant Energy’s and IPL’s income statements for the nine months ended September 30, 2024 for the portion allocated to IPL’s steam business for IPL’s Prairie Creek Generating Station and the retired Sixth Street Generating Station as established in prior rate reviews. The amounts recorded in the second quarter of 2024 are expected to be adjusted in the future as additional information is obtained for the specific site closure plans, including the determination of whether or not individual sites are considered legal obligations and the acceptance and approval of compliance approaches, which could change management assumptions and result in a material change to the recorded amounts.
IPL [Member]
Schedule of Asset Retirement Obligations [Line Items]
Reconciliation of Changes in Asset Retirement Obligations	A reconciliation of the changes in AROs associated with long-lived assets for the nine months ended September 30, 2024 is as follows (in millions): Alliant Energy IPL WPL Balance, January 1 $246 $148 $98 Revisions in estimated cash flows (2) — (2) Liabilities settled (4) (2) (2) Liabilities incurred (a) 356 103 253 Accretion expense 12 6 6 Balance, September 30 $608 $255 $353 (a) In the second quarter of 2024, substantially due to the enactment of the revised CCR Rule, which significantly expands the scope of regulation to include coal ash ponds at sites that no longer produce electricity and inactive landfills, including some IPL and WPL facilities, Alliant Energy, IPL and WPL recorded additional AROs, additional ARO regulatory assets for EGUs no longer in operation, additional property, plant and equipment for EGUs still in operation, and a pre-tax non-cash charge of $20 million recorded to “Other operation and maintenance” in Alliant Energy’s and IPL’s income statements for the nine months ended September 30, 2024 for the portion allocated to IPL’s steam business for IPL’s Prairie Creek Generating Station and the retired Sixth Street Generating Station as established in prior rate reviews. The amounts recorded in the second quarter of 2024 are expected to be adjusted in the future as additional information is obtained for the specific site closure plans, including the determination of whether or not individual sites are considered legal obligations and the acceptance and approval of compliance approaches, which could change management assumptions and result in a material change to the recorded amounts.
WPL [Member]
Schedule of Asset Retirement Obligations [Line Items]
Reconciliation of Changes in Asset Retirement Obligations	A reconciliation of the changes in AROs associated with long-lived assets for the nine months ended September 30, 2024 is as follows (in millions): Alliant Energy IPL WPL Balance, January 1 $246 $148 $98 Revisions in estimated cash flows (2) — (2) Liabilities settled (4) (2) (2) Liabilities incurred (a) 356 103 253 Accretion expense 12 6 6 Balance, September 30 $608 $255 $353 (a) In the second quarter of 2024, substantially due to the enactment of the revised CCR Rule, which significantly expands the scope of regulation to include coal ash ponds at sites that no longer produce electricity and inactive landfills, including some IPL and WPL facilities, Alliant Energy, IPL and WPL recorded additional AROs, additional ARO regulatory assets for EGUs no longer in operation, additional property, plant and equipment for EGUs still in operation, and a pre-tax non-cash charge of $20 million recorded to “Other operation and maintenance” in Alliant Energy’s and IPL’s income statements for the nine months ended September 30, 2024 for the portion allocated to IPL’s steam business for IPL’s Prairie Creek Generating Station and the retired Sixth Street Generating Station as established in prior rate reviews. The amounts recorded in the second quarter of 2024 are expected to be adjusted in the future as additional information is obtained for the specific site closure plans, including the determination of whether or not individual sites are considered legal obligations and the acceptance and approval of compliance approaches, which could change management assumptions and result in a material change to the recorded amounts.

Derivative Instruments (Tables)

Derivative Instruments (Tables)	9 Months Ended
	Sep. 30, 2024
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of September 30, 2024, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands): Electricity FTRs Natural Gas Diesel Fuel MWhs Years MWhs Years Dths Years Gallons Years Alliant Energy 1,841 2024-2026 15,595 2024-2025 156,626 2024-2032 3,150 2024-2025 IPL 675 2024-2026 5,385 2024-2025 67,817 2024-2030 — — WPL 1,166 2024-2026 10,210 2024-2025 88,809 2024-2032 3,150 2024-2025
Fair Value Of Financial Instruments	Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities as follows (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Current derivative assets $51 $44 $37 $30 $14 $14 Non-current derivative assets 31 44 18 24 13 20 Current derivative liabilities 31 51 14 22 17 29 Non-current derivative liabilities 45 47 6 8 39 39
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 as follows (in millions): Alliant Energy IPL WPL Gross Gross Gross (as reported) Net (as reported) Net (as reported) Net September 30, 2024 Derivative assets $82 $63 $55 $45 $27 $18 Derivative liabilities 76 57 20 10 56 47 December 31, 2023 Derivative assets 88 47 54 32 34 15 Derivative liabilities 98 57 30 8 68 49
IPL [Member]
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of September 30, 2024, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands): Electricity FTRs Natural Gas Diesel Fuel MWhs Years MWhs Years Dths Years Gallons Years Alliant Energy 1,841 2024-2026 15,595 2024-2025 156,626 2024-2032 3,150 2024-2025 IPL 675 2024-2026 5,385 2024-2025 67,817 2024-2030 — — WPL 1,166 2024-2026 10,210 2024-2025 88,809 2024-2032 3,150 2024-2025
Fair Value Of Financial Instruments	Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities as follows (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Current derivative assets $51 $44 $37 $30 $14 $14 Non-current derivative assets 31 44 18 24 13 20 Current derivative liabilities 31 51 14 22 17 29 Non-current derivative liabilities 45 47 6 8 39 39
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 as follows (in millions): Alliant Energy IPL WPL Gross Gross Gross (as reported) Net (as reported) Net (as reported) Net September 30, 2024 Derivative assets $82 $63 $55 $45 $27 $18 Derivative liabilities 76 57 20 10 56 47 December 31, 2023 Derivative assets 88 47 54 32 34 15 Derivative liabilities 98 57 30 8 68 49
WPL [Member]
Derivative Instruments [Line Items]
Notional Amounts Of Derivative Instruments	As of September 30, 2024, gross notional amounts and settlement/delivery years related to outstanding swap contracts, option contracts, physical forward contracts and FTRs that were accounted for as commodity derivative instruments were as follows (units in thousands): Electricity FTRs Natural Gas Diesel Fuel MWhs Years MWhs Years Dths Years Gallons Years Alliant Energy 1,841 2024-2026 15,595 2024-2025 156,626 2024-2032 3,150 2024-2025 IPL 675 2024-2026 5,385 2024-2025 67,817 2024-2030 — — WPL 1,166 2024-2026 10,210 2024-2025 88,809 2024-2032 3,150 2024-2025
Fair Value Of Financial Instruments	Derivative instruments are recorded at fair value each reporting date on the balance sheets as assets or liabilities as follows (in millions): Alliant Energy IPL WPL September 30, December 31, September 30, December 31, September 30, December 31, Current derivative assets $51 $44 $37 $30 $14 $14 Non-current derivative assets 31 44 18 24 13 20 Current derivative liabilities 31 51 14 22 17 29 Non-current derivative liabilities 45 47 6 8 39 39
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 as follows (in millions): Alliant Energy IPL WPL Gross Gross Gross (as reported) Net (as reported) Net (as reported) Net September 30, 2024 Derivative assets $82 $63 $55 $45 $27 $18 Derivative liabilities 76 57 20 10 56 47 December 31, 2023 Derivative assets 88 47 54 32 34 15 Derivative liabilities 98 57 30 8 68 49

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2024
Statement [Line Items]
Fair Value Measurements	Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions): Alliant Energy September 30, 2024 December 31, 2023 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Time deposits and money market fund investments $803 $803 $— $— $803 $45 $45 $— $— $45 Commodity derivatives 82 — 42 40 82 88 — 59 29 88 Interest rate derivatives — — — — — 1 — 1 — 1 Deferred proceeds 212 — — 212 212 216 — — 216 216 Liabilities: Commodity derivatives 76 — 73 3 76 98 — 93 5 98 Interest rate derivatives 1 — 1 — 1 — — — — — Long-term debt (incl. current maturities) 10,349 — 10,444 — 10,444 9,034 — 8,677 — 8,677 IPL September 30, 2024 December 31, 2023 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Time deposits and money market fund investments $745 $745 $— $— $745 $45 $45 $— $— $45 Commodity derivatives 55 — 23 32 55 54 — 30 24 54 Deferred proceeds 212 — — 212 212 216 — — 216 216 Liabilities: Commodity derivatives 20 — 17 3 20 30 — 25 5 30 Long-term debt (incl. current maturities) 4,589 — 4,407 — 4,407 3,945 — 3,664 — 3,664 WPL September 30, 2024 December 31, 2023 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 $58 $58 $— $— $58 $— $— $— $— $— Commodity derivatives 27 — 19 8 27 34 — 29 5 34 Liabilities: Commodity derivatives 56 — 56 — 56 68 — 68 — 68 Long-term debt 3,369 — 3,322 — 3,322 3,070 — 2,933 — 2,933
Fair Value Measurements Using Significant Unobservable Inputs	Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions): Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2024 2023 2024 2023 Beginning balance, July 1 $51 $54 $171 $175 Total net gains included in changes in net assets (realized/unrealized) 2 17 — — Sales — (1) — — Settlements (a) (16) (27) 41 61 Ending balance, September 30 $37 $43 $212 $236 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $2 $17 $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2024 2023 2024 2023 Beginning balance, January 1 $24 $19 $216 $185 Total net gains (losses) included in changes in net assets (realized/unrealized) (7) 6 — — Purchases 59 62 — — Sales (1) (2) — — Settlements (a) (38) (42) (4) 51 Ending balance, September 30 $37 $43 $212 $236 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 September 30 ($7) $6 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2024 2023 2024 2023 Beginning balance, July 1 $40 $41 $171 $175 Total net gains included in changes in net assets (realized/unrealized) — 12 — — Sales — (1) — — Settlements (a) (11) (17) 41 61 Ending balance, September 30 $29 $35 $212 $236 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $— $12 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2024 2023 2024 2023 Beginning balance, January 1 $19 $16 $216 $185 Total net losses included in changes in net assets (realized/unrealized) (7) — — — Purchases 45 51 — — Sales (1) (2) — — Settlements (a) (27) (30) (4) 51 Ending balance, September 30 $29 $35 $212 $236 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 September 30 ($7) $— $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended September 30 2024 2023 Beginning balance, July 1 $11 $13 Total net gains included in changes in net assets (realized/unrealized) 2 5 Settlements (5) (10) Ending balance, September 30 $8 $8 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $2 $5 WPL Commodity Contract Derivative Assets and (Liabilities), net Nine Months Ended September 30 2024 2023 Beginning balance, January 1 $5 $3 Total net gains included in changes in net assets (realized/unrealized) — 6 Purchases 14 11 Settlements (11) (12) Ending balance, September 30 $8 $8 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $— $6 (a) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for expected credit losses associated with the receivables sold and cash amounts received from the receivables sold.
Fair Value Of Net Derivative Assets (Liabilities)	The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs September 30, 2024 $— $37 $— $29 $— $8 December 31, 2023 3 21 3 16 — 5
IPL [Member]
Statement [Line Items]
Fair Value Measurements	Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions): Alliant Energy September 30, 2024 December 31, 2023 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Time deposits and money market fund investments $803 $803 $— $— $803 $45 $45 $— $— $45 Commodity derivatives 82 — 42 40 82 88 — 59 29 88 Interest rate derivatives — — — — — 1 — 1 — 1 Deferred proceeds 212 — — 212 212 216 — — 216 216 Liabilities: Commodity derivatives 76 — 73 3 76 98 — 93 5 98 Interest rate derivatives 1 — 1 — 1 — — — — — Long-term debt (incl. current maturities) 10,349 — 10,444 — 10,444 9,034 — 8,677 — 8,677 IPL September 30, 2024 December 31, 2023 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Time deposits and money market fund investments $745 $745 $— $— $745 $45 $45 $— $— $45 Commodity derivatives 55 — 23 32 55 54 — 30 24 54 Deferred proceeds 212 — — 212 212 216 — — 216 216 Liabilities: Commodity derivatives 20 — 17 3 20 30 — 25 5 30 Long-term debt (incl. current maturities) 4,589 — 4,407 — 4,407 3,945 — 3,664 — 3,664 WPL September 30, 2024 December 31, 2023 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 $58 $58 $— $— $58 $— $— $— $— $— Commodity derivatives 27 — 19 8 27 34 — 29 5 34 Liabilities: Commodity derivatives 56 — 56 — 56 68 — 68 — 68 Long-term debt 3,369 — 3,322 — 3,322 3,070 — 2,933 — 2,933
Fair Value Measurements Using Significant Unobservable Inputs	Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions): Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2024 2023 2024 2023 Beginning balance, July 1 $51 $54 $171 $175 Total net gains included in changes in net assets (realized/unrealized) 2 17 — — Sales — (1) — — Settlements (a) (16) (27) 41 61 Ending balance, September 30 $37 $43 $212 $236 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $2 $17 $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2024 2023 2024 2023 Beginning balance, January 1 $24 $19 $216 $185 Total net gains (losses) included in changes in net assets (realized/unrealized) (7) 6 — — Purchases 59 62 — — Sales (1) (2) — — Settlements (a) (38) (42) (4) 51 Ending balance, September 30 $37 $43 $212 $236 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 September 30 ($7) $6 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2024 2023 2024 2023 Beginning balance, July 1 $40 $41 $171 $175 Total net gains included in changes in net assets (realized/unrealized) — 12 — — Sales — (1) — — Settlements (a) (11) (17) 41 61 Ending balance, September 30 $29 $35 $212 $236 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $— $12 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2024 2023 2024 2023 Beginning balance, January 1 $19 $16 $216 $185 Total net losses included in changes in net assets (realized/unrealized) (7) — — — Purchases 45 51 — — Sales (1) (2) — — Settlements (a) (27) (30) (4) 51 Ending balance, September 30 $29 $35 $212 $236 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 September 30 ($7) $— $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended September 30 2024 2023 Beginning balance, July 1 $11 $13 Total net gains included in changes in net assets (realized/unrealized) 2 5 Settlements (5) (10) Ending balance, September 30 $8 $8 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $2 $5 WPL Commodity Contract Derivative Assets and (Liabilities), net Nine Months Ended September 30 2024 2023 Beginning balance, January 1 $5 $3 Total net gains included in changes in net assets (realized/unrealized) — 6 Purchases 14 11 Settlements (11) (12) Ending balance, September 30 $8 $8 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $— $6 (a) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for expected credit losses associated with the receivables sold and cash amounts received from the receivables sold.
Fair Value Of Net Derivative Assets (Liabilities)	The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs September 30, 2024 $— $37 $— $29 $— $8 December 31, 2023 3 21 3 16 — 5
WPL [Member]
Statement [Line Items]
Fair Value Measurements	Carrying amounts and related estimated fair values of other financial instruments were as follows (in millions): Alliant Energy September 30, 2024 December 31, 2023 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Time deposits and money market fund investments $803 $803 $— $— $803 $45 $45 $— $— $45 Commodity derivatives 82 — 42 40 82 88 — 59 29 88 Interest rate derivatives — — — — — 1 — 1 — 1 Deferred proceeds 212 — — 212 212 216 — — 216 216 Liabilities: Commodity derivatives 76 — 73 3 76 98 — 93 5 98 Interest rate derivatives 1 — 1 — 1 — — — — — Long-term debt (incl. current maturities) 10,349 — 10,444 — 10,444 9,034 — 8,677 — 8,677 IPL September 30, 2024 December 31, 2023 Fair Value Fair Value Carrying Level Level Level Carrying Level Level Level Amount 1 2 3 Total Amount 1 2 3 Total Assets: Time deposits and money market fund investments $745 $745 $— $— $745 $45 $45 $— $— $45 Commodity derivatives 55 — 23 32 55 54 — 30 24 54 Deferred proceeds 212 — — 212 212 216 — — 216 216 Liabilities: Commodity derivatives 20 — 17 3 20 30 — 25 5 30 Long-term debt (incl. current maturities) 4,589 — 4,407 — 4,407 3,945 — 3,664 — 3,664 WPL September 30, 2024 December 31, 2023 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 $58 $58 $— $— $58 $— $— $— $— $— Commodity derivatives 27 — 19 8 27 34 — 29 5 34 Liabilities: Commodity derivatives 56 — 56 — 56 68 — 68 — 68 Long-term debt 3,369 — 3,322 — 3,322 3,070 — 2,933 — 2,933
Fair Value Measurements Using Significant Unobservable Inputs	Information for fair value measurements using significant unobservable inputs (Level 3 inputs) was as follows (in millions): Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2024 2023 2024 2023 Beginning balance, July 1 $51 $54 $171 $175 Total net gains included in changes in net assets (realized/unrealized) 2 17 — — Sales — (1) — — Settlements (a) (16) (27) 41 61 Ending balance, September 30 $37 $43 $212 $236 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $2 $17 $— $— Alliant Energy Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2024 2023 2024 2023 Beginning balance, January 1 $24 $19 $216 $185 Total net gains (losses) included in changes in net assets (realized/unrealized) (7) 6 — — Purchases 59 62 — — Sales (1) (2) — — Settlements (a) (38) (42) (4) 51 Ending balance, September 30 $37 $43 $212 $236 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 September 30 ($7) $6 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Three Months Ended September 30 2024 2023 2024 2023 Beginning balance, July 1 $40 $41 $171 $175 Total net gains included in changes in net assets (realized/unrealized) — 12 — — Sales — (1) — — Settlements (a) (11) (17) 41 61 Ending balance, September 30 $29 $35 $212 $236 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $— $12 $— $— IPL Commodity Contract Derivative Assets and (Liabilities), net Deferred Proceeds Nine Months Ended September 30 2024 2023 2024 2023 Beginning balance, January 1 $19 $16 $216 $185 Total net losses included in changes in net assets (realized/unrealized) (7) — — — Purchases 45 51 — — Sales (1) (2) — — Settlements (a) (27) (30) (4) 51 Ending balance, September 30 $29 $35 $212 $236 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 September 30 ($7) $— $— $— WPL Commodity Contract Derivative Assets and (Liabilities), net Three Months Ended September 30 2024 2023 Beginning balance, July 1 $11 $13 Total net gains included in changes in net assets (realized/unrealized) 2 5 Settlements (5) (10) Ending balance, September 30 $8 $8 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $2 $5 WPL Commodity Contract Derivative Assets and (Liabilities), net Nine Months Ended September 30 2024 2023 Beginning balance, January 1 $5 $3 Total net gains included in changes in net assets (realized/unrealized) — 6 Purchases 14 11 Settlements (11) (12) Ending balance, September 30 $8 $8 The amount of total net gains for the period included in changes in net assets attributable to the change in unrealized gains relating to assets and liabilities held at September 30 $— $6 (a) Settlements related to deferred proceeds are due to the change in the carrying amount of receivables sold less the allowance for expected credit losses associated with the receivables sold and cash amounts received from the receivables sold.
Fair Value Of Net Derivative Assets (Liabilities)	The fair value of FTR and natural gas commodity contracts categorized as Level 3 was recognized as net derivative assets as follows (in millions): Alliant Energy IPL WPL Excluding FTRs FTRs Excluding FTRs FTRs Excluding FTRs FTRs September 30, 2024 $— $37 $— $29 $— $8 December 31, 2023 3 21 3 16 — 5

Commitments And Contingencies (

Commitments And Contingencies (Tables)	9 Months Ended
	Sep. 30, 2024
Commitments and Contingencies [Line Items]
Other Purchase Commitments	At September 30, 2024, the related minimum future commitments, excluding amounts for purchased power commitments that do not have minimum thresholds but will require payment when electricity is generated by the provider, were as follows (in millions): Alliant Energy IPL WPL Natural gas $746 $322 $424 Coal 139 80 59 Other (a) 110 46 22 $995 $448 $505 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2024.
MGP Site Estimated Future Costs And Recorded Liabilities	At September 30, 2024, estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, which are not discounted, were as follows (in millions): Alliant Energy IPL WPL Range of estimated future costs $7 - $28 $5 - $17 $2 - $11 Current and non-current environmental liabilities $13 $8 $5
IPL [Member]
Commitments and Contingencies [Line Items]
Other Purchase Commitments	At September 30, 2024, the related minimum future commitments, excluding amounts for purchased power commitments that do not have minimum thresholds but will require payment when electricity is generated by the provider, were as follows (in millions): Alliant Energy IPL WPL Natural gas $746 $322 $424 Coal 139 80 59 Other (a) 110 46 22 $995 $448 $505 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2024.
MGP Site Estimated Future Costs And Recorded Liabilities	At September 30, 2024, estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, which are not discounted, were as follows (in millions): Alliant Energy IPL WPL Range of estimated future costs $7 - $28 $5 - $17 $2 - $11 Current and non-current environmental liabilities $13 $8 $5
WPL [Member]
Commitments and Contingencies [Line Items]
Other Purchase Commitments	At September 30, 2024, the related minimum future commitments, excluding amounts for purchased power commitments that do not have minimum thresholds but will require payment when electricity is generated by the provider, were as follows (in millions): Alliant Energy IPL WPL Natural gas $746 $322 $424 Coal 139 80 59 Other (a) 110 46 22 $995 $448 $505 (a) Includes individual commitments incurred during the normal course of business that exceeded $1 million at September 30, 2024.
MGP Site Estimated Future Costs And Recorded Liabilities	At September 30, 2024, estimated future costs expected to be incurred for the investigation, remediation and monitoring of the MGP sites, as well as environmental liabilities recorded on the balance sheets for these sites, which are not discounted, were as follows (in millions): Alliant Energy IPL WPL Range of estimated future costs $7 - $28 $5 - $17 $2 - $11 Current and non-current environmental liabilities $13 $8 $5

Segments Of Business (Tables)

Segments Of Business (Tables)	9 Months Ended
	Sep. 30, 2024
Segment Reporting Information [Line Items]
Schedule Of Segments Of Business	Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s business segments is as follows. Intersegment revenues were not material to their respective operations. Refer to Note 2 for discussion of asset valuation charges recorded in the second quarter of 2024 related to IPL’s Lansing Generating Station, which decreased the assets for “Utility - Electric,” and N ote 11 for discussion of additional AROs recorded in the second quarter of 2024 substantially due to the enactment of the revised CCR Rule, which primarily increased the assets for “Utility - Electric.” Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended September 30, 2024 Revenues $999 $49 $12 $1,060 $21 $1,081 Operating income (loss) 305 (4) 4 305 8 313 Net income (loss) attributable to Alliant Energy common shareowners 304 (9) 295 Three Months Ended September 30, 2023 Revenues $995 $47 $13 $1,055 $22 $1,077 Operating income (loss) 319 (4) — 315 7 322 Net income (loss) attributable to Alliant Energy common shareowners 277 (18) 259 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Nine Months Ended September 30, 2024 Revenues $2,579 $322 $36 $2,937 $68 $3,005 Operating income (loss) 600 44 (7) 637 28 665 Net income (loss) attributable to Alliant Energy common shareowners 542 (2) 540 Nine Months Ended September 30, 2023 Revenues $2,562 $400 $38 $3,000 $66 $3,066 Operating income 682 48 12 742 18 760 Net income (loss) attributable to Alliant Energy common shareowners 598 (16) 582 IPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2024 Revenues $523 $27 $11 $561 Operating income (loss) 148 (3) 4 149 Net income 190 Three Months Ended September 30, 2023 Revenues $551 $31 $12 $594 Operating income (loss) 171 (2) 4 173 Net income 170 Nine Months Ended September 30, 2024 Revenues $1,318 $175 $34 $1,527 Operating income (loss) 239 18 (7) 250 Net income 272 Nine Months Ended September 30, 2023 Revenues $1,370 $224 $36 $1,630 Operating income 342 25 12 379 Net income 331 WPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2024 Revenues $476 $22 $1 $499 Operating income (loss) 157 (1) — 156 Net income 114 Three Months Ended September 30, 2023 Revenues $444 $16 $1 $461 Operating income (loss) 148 (2) (4) 142 Net income 107 Nine Months Ended September 30, 2024 Revenues $1,261 $147 $2 $1,410 Operating income 361 26 — 387 Net income 270 Nine Months Ended September 30, 2023 Revenues $1,192 $176 $2 $1,370 Operating income 340 23 — 363 Net income 267
IPL [Member]
Segment Reporting Information [Line Items]
Schedule Of Segments Of Business	Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s business segments is as follows. Intersegment revenues were not material to their respective operations. Refer to Note 2 for discussion of asset valuation charges recorded in the second quarter of 2024 related to IPL’s Lansing Generating Station, which decreased the assets for “Utility - Electric,” and N ote 11 for discussion of additional AROs recorded in the second quarter of 2024 substantially due to the enactment of the revised CCR Rule, which primarily increased the assets for “Utility - Electric.” Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended September 30, 2024 Revenues $999 $49 $12 $1,060 $21 $1,081 Operating income (loss) 305 (4) 4 305 8 313 Net income (loss) attributable to Alliant Energy common shareowners 304 (9) 295 Three Months Ended September 30, 2023 Revenues $995 $47 $13 $1,055 $22 $1,077 Operating income (loss) 319 (4) — 315 7 322 Net income (loss) attributable to Alliant Energy common shareowners 277 (18) 259 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Nine Months Ended September 30, 2024 Revenues $2,579 $322 $36 $2,937 $68 $3,005 Operating income (loss) 600 44 (7) 637 28 665 Net income (loss) attributable to Alliant Energy common shareowners 542 (2) 540 Nine Months Ended September 30, 2023 Revenues $2,562 $400 $38 $3,000 $66 $3,066 Operating income 682 48 12 742 18 760 Net income (loss) attributable to Alliant Energy common shareowners 598 (16) 582 IPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2024 Revenues $523 $27 $11 $561 Operating income (loss) 148 (3) 4 149 Net income 190 Three Months Ended September 30, 2023 Revenues $551 $31 $12 $594 Operating income (loss) 171 (2) 4 173 Net income 170 Nine Months Ended September 30, 2024 Revenues $1,318 $175 $34 $1,527 Operating income (loss) 239 18 (7) 250 Net income 272 Nine Months Ended September 30, 2023 Revenues $1,370 $224 $36 $1,630 Operating income 342 25 12 379 Net income 331 WPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2024 Revenues $476 $22 $1 $499 Operating income (loss) 157 (1) — 156 Net income 114 Three Months Ended September 30, 2023 Revenues $444 $16 $1 $461 Operating income (loss) 148 (2) (4) 142 Net income 107 Nine Months Ended September 30, 2024 Revenues $1,261 $147 $2 $1,410 Operating income 361 26 — 387 Net income 270 Nine Months Ended September 30, 2023 Revenues $1,192 $176 $2 $1,370 Operating income 340 23 — 363 Net income 267
WPL [Member]
Segment Reporting Information [Line Items]
Schedule Of Segments Of Business	Certain financial information relating to Alliant Energy’s, IPL’s and WPL’s business segments is as follows. Intersegment revenues were not material to their respective operations. Refer to Note 2 for discussion of asset valuation charges recorded in the second quarter of 2024 related to IPL’s Lansing Generating Station, which decreased the assets for “Utility - Electric,” and N ote 11 for discussion of additional AROs recorded in the second quarter of 2024 substantially due to the enactment of the revised CCR Rule, which primarily increased the assets for “Utility - Electric.” Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Three Months Ended September 30, 2024 Revenues $999 $49 $12 $1,060 $21 $1,081 Operating income (loss) 305 (4) 4 305 8 313 Net income (loss) attributable to Alliant Energy common shareowners 304 (9) 295 Three Months Ended September 30, 2023 Revenues $995 $47 $13 $1,055 $22 $1,077 Operating income (loss) 319 (4) — 315 7 322 Net income (loss) attributable to Alliant Energy common shareowners 277 (18) 259 Alliant Energy ATC Holdings, Alliant Utility Non-Utility, Energy Electric Gas Other Total Parent and Other Consolidated (in millions) Nine Months Ended September 30, 2024 Revenues $2,579 $322 $36 $2,937 $68 $3,005 Operating income (loss) 600 44 (7) 637 28 665 Net income (loss) attributable to Alliant Energy common shareowners 542 (2) 540 Nine Months Ended September 30, 2023 Revenues $2,562 $400 $38 $3,000 $66 $3,066 Operating income 682 48 12 742 18 760 Net income (loss) attributable to Alliant Energy common shareowners 598 (16) 582 IPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2024 Revenues $523 $27 $11 $561 Operating income (loss) 148 (3) 4 149 Net income 190 Three Months Ended September 30, 2023 Revenues $551 $31 $12 $594 Operating income (loss) 171 (2) 4 173 Net income 170 Nine Months Ended September 30, 2024 Revenues $1,318 $175 $34 $1,527 Operating income (loss) 239 18 (7) 250 Net income 272 Nine Months Ended September 30, 2023 Revenues $1,370 $224 $36 $1,630 Operating income 342 25 12 379 Net income 331 WPL Electric Gas Other Total (in millions) Three Months Ended September 30, 2024 Revenues $476 $22 $1 $499 Operating income (loss) 157 (1) — 156 Net income 114 Three Months Ended September 30, 2023 Revenues $444 $16 $1 $461 Operating income (loss) 148 (2) (4) 142 Net income 107 Nine Months Ended September 30, 2024 Revenues $1,261 $147 $2 $1,410 Operating income 361 26 — 387 Net income 270 Nine Months Ended September 30, 2023 Revenues $1,192 $176 $2 $1,370 Operating income 340 23 — 363 Net income 267

Related Parties (Tables)

Related Parties (Tables)	9 Months Ended
	Sep. 30, 2024
Related Party Transactions [Line Items]
Services Provided, Sales Credited And Purchases	The amounts billed for services provided, sales credited and purchases for the three and nine months ended September 30 were as follows (in millions): IPL WPL Three Months Nine Months Three Months Nine Months 2024 2023 2024 2023 2024 2023 2024 2023 Corporate Services billings $42 $46 $134 $134 $38 $40 $124 $120 Sales credited — 3 — 11 29 23 66 45 Purchases billed 130 133 332 320 18 5 41 21
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL September 30, 2024 December 31, 2023 September 30, 2024 December 31, 2023 Net payables to Corporate Services $131 $129 $72 $72
Related Amounts Billed Between Parties	The related amounts billed between the parties for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2024 2023 2024 2023 ATC billings to WPL $39 $41 $115 $119 WPL billings to ATC 5 5 12 16
IPL [Member]
Related Party Transactions [Line Items]
Services Provided, Sales Credited And Purchases	The amounts billed for services provided, sales credited and purchases for the three and nine months ended September 30 were as follows (in millions): IPL WPL Three Months Nine Months Three Months Nine Months 2024 2023 2024 2023 2024 2023 2024 2023 Corporate Services billings $42 $46 $134 $134 $38 $40 $124 $120 Sales credited — 3 — 11 29 23 66 45 Purchases billed 130 133 332 320 18 5 41 21
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL September 30, 2024 December 31, 2023 September 30, 2024 December 31, 2023 Net payables to Corporate Services $131 $129 $72 $72
WPL [Member]
Related Party Transactions [Line Items]
Services Provided, Sales Credited And Purchases	The amounts billed for services provided, sales credited and purchases for the three and nine months ended September 30 were as follows (in millions): IPL WPL Three Months Nine Months Three Months Nine Months 2024 2023 2024 2023 2024 2023 2024 2023 Corporate Services billings $42 $46 $134 $134 $38 $40 $124 $120 Sales credited — 3 — 11 29 23 66 45 Purchases billed 130 133 332 320 18 5 41 21
Net Intercompany Payables	Net intercompany payables to Corporate Services were as follows (in millions): IPL WPL September 30, 2024 December 31, 2023 September 30, 2024 December 31, 2023 Net payables to Corporate Services $131 $129 $72 $72
Related Amounts Billed Between Parties	The related amounts billed between the parties for the three and nine months ended September 30 were as follows (in millions): Three Months Nine Months 2024 2023 2024 2023 ATC billings to WPL $39 $41 $115 $119 WPL billings to ATC 5 5 12 16

Summary Of Significant Accoun_3

Summary Of Significant Accounting Policies (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash equivalents	$ 803	$ 45
Cash equivalents weighted-average interest rate, percentage	5%
IPL [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash equivalents	$ 745	45
Cash equivalents weighted-average interest rate, percentage	5%
WPL [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cash equivalents	$ 58	$ 0
Cash equivalents weighted-average interest rate, percentage	5%

Regulatory Matters (Narrative)

Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Regulatory Matters [Line Items]
Asset valuation charge for IPL's Lansing Generating Station	$ 0	$ 0	$ 60	$ 0
IPL [Member]
Regulatory Matters [Line Items]
Asset valuation charge for IPL's Lansing Generating Station	$ 0	$ 0	60	$ 0
October 2024 Through September 2025 Test Period Retail Electric [Member] | IPL [Member]
Regulatory Matters [Line Items]
Authorized increase (decrease) in final rates, amount			185
October 2024 Through September 2025 Test Period Retail Gas [Member] | IPL [Member]
Regulatory Matters [Line Items]
Authorized increase (decrease) in final rates, amount			$ 10

Regulatory Matters (Regulatory

Regulatory Matters (Regulatory Assets) (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Regulatory Assets [Line Items]
Regulatory assets	$ 2,350	$ 2,261
Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,000	934
Asset retirement obligations (AROs) [Member]
Regulatory Assets [Line Items]
Regulatory assets	418	194
Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	329	347
Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	181	273
Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	80	102
Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	76	120
WPL's Western Wisconsin gas distribution expansion investments [Member]
Regulatory Assets [Line Items]
Regulatory assets	42	44
IPL's Duane Arnold Energy Center purchased power agreement amendment [Member]
Regulatory Assets [Line Items]
Regulatory assets	24	42
Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	200	205
IPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	1,568	1,577
IPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	885	831
IPL [Member] | Asset retirement obligations (AROs) [Member]
Regulatory Assets [Line Items]
Regulatory assets	223	160
IPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	163	171
IPL [Member] | Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	169	259
IPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	24	34
IPL [Member] | Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	8	12
IPL [Member] | IPL's Duane Arnold Energy Center purchased power agreement amendment [Member]
Regulatory Assets [Line Items]
Regulatory assets	24	42
IPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	72	68
WPL [Member]
Regulatory Assets [Line Items]
Regulatory assets	782	684
WPL [Member] | Tax-related [Member]
Regulatory Assets [Line Items]
Regulatory assets	115	103
WPL [Member] | Asset retirement obligations (AROs) [Member]
Regulatory Assets [Line Items]
Regulatory assets	195	34
WPL [Member] | Pension and OPEB costs [Member]
Regulatory Assets [Line Items]
Regulatory assets	166	176
WPL [Member] | Assets retired early [Member]
Regulatory Assets [Line Items]
Regulatory assets	12	14
WPL [Member] | Derivatives [Member]
Regulatory Assets [Line Items]
Regulatory assets	56	68
WPL [Member] | Commodity cost recovery [Member]
Regulatory Assets [Line Items]
Regulatory assets	68	108
WPL [Member] | WPL's Western Wisconsin gas distribution expansion investments [Member]
Regulatory Assets [Line Items]
Regulatory assets	42	44
WPL [Member] | Other [Member]
Regulatory Assets [Line Items]
Regulatory assets	$ 128	$ 137

Regulatory Matters (Regulator_2

Regulatory Matters (Regulatory Liabilities) (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 1,072	$ 1,130
Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	589	566
Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	359	366
Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	47	65
Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	45	48
Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	32	85
IPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	553	644
IPL [Member] | Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	286	299
IPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	215	242
IPL [Member] | Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	26	34
IPL [Member] | Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	8	13
IPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	18	56
WPL [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	519	486
WPL [Member] | Tax-related [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	303	267
WPL [Member] | Cost of removal obligations [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	144	124
WPL [Member] | Derivatives [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	21	31
WPL [Member] | Commodity cost recovery [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	37	35
WPL [Member] | Other [Member]
Regulatory Liabilities [Line Items]
Regulatory liabilities	$ 14	$ 29

Property, Plant and Equipment (

Property, Plant and Equipment (Narrative) (Details)	9 Months Ended
	Sep. 30, 2024 USD ($) lease_renewal_period_option MW
IPL [Member]
Property, Plant and Equipment [Line Items]
Electric capacity of solar project | MW	400
Construction project cost target, exceedance	$ 1,837.5
Construction project cost target, original	$ 1,650
Solar project cost return on equity, percentage	10.25%
WPL [Member]
Property, Plant and Equipment [Line Items]
Electric capacity of solar project | MW	1,100
Construction project cost target, exceedance	$ 195,000,000
WPL [Member] | Sheboygan Falls Energy Facility
Property, Plant and Equipment [Line Items]
Financing lease, lease renewal periods remaining | lease_renewal_period_option	0
WPL [Member] | West Riverside Energy Center [Member]
Property, Plant and Equipment [Line Items]
Ownership interest, percent	56.60%
Electric Generation | WPL [Member] | Edgewater Unit 5
Property, Plant and Equipment [Line Items]
Net book value, Edgewater Unit 5	$ 493,000,000
Utility electric generation plant in service, Edgewater Unit 5	$ 794,000,000

Receivables (Narrative) (Detail

Receivables (Narrative) (Details) - Receivables Sold [Member] - IPL [Member] $ in Millions	Sep. 30, 2024 USD ($)
Receivables [Line Items]
Available capacity	$ 4
Maximum [Member]
Receivables [Line Items]
Limit on cash proceeds to be received from third-party	5
Financial Asset, Past Due [Member]
Receivables [Line Items]
Outstanding receivables past due	$ 16

Receivables (Maximum And Averag

Receivables (Maximum And Average Outstanding Cash Proceeds) (Details) - IPL [Member] - Receivables Sold [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Maximum [Member]
Receivables [Line Items]
Outstanding aggregate cash proceeds (based on daily outstanding balances)	$ 52	$ 94	$ 110	$ 110
Average [Member]
Receivables [Line Items]
Outstanding aggregate cash proceeds (based on daily outstanding balances)	$ 7	$ 46	$ 34	$ 68

Receivables (Receivables Sold U

Receivables (Receivables Sold Under The Agreement) (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Receivables [Line Items]
Fair value of deferred proceeds	$ 212	$ 216
IPL [Member]
Receivables [Line Items]
Fair value of deferred proceeds	212	216
Receivables Sold [Member] | IPL [Member]
Receivables [Line Items]
Customer accounts receivable	141	130
Unbilled utility revenues	81	98
Other receivables	1	1
Receivables sold to third party	223	229
Less: cash proceeds	1	1
Deferred proceeds	222	228
Less: allowance for expected credit losses	10	12
Fair value of deferred proceeds	$ 212	$ 216

Receivables (Additional Attribu

Receivables (Additional Attributes Of Receivables Sold Under The Agreement) (Details) - IPL [Member] - Receivables Sold [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Receivables [Line Items]
Collections	$ 565	$ 616	$ 1,578	$ 1,720
Write-offs, net of recoveries	$ 4	$ 5	$ 9	$ 9

Investments (Unconsolidated Equ

Investments (Unconsolidated Equity Investments) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Schedule of Equity Method Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	$ (14)	$ (14)	$ (44)	$ (45)
ATC Holdings [Member]
Schedule of Equity Method Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	(13)	(12)	(38)	(37)
Other [Member]
Schedule of Equity Method Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	(1)	(2)	(6)	(8)
Total [Member]
Schedule of Equity Method Investments [Line Items]
Equity (income) loss from unconsolidated investments, net	$ (14)	$ (14)	$ (44)	$ (45)

Common Equity (Common Share Act

Common Equity (Common Share Activity) (Details)	9 Months Ended
	Sep. 30, 2024 shares
Common Stock Oustanding [Roll Forward]
Shares outstanding, January 1, 2024 (in shares)	256,096,848
Shareowner Direct Plan (in shares)	348,087
Equity-based compensation plans (in shares)	154,267
Shares outstanding, September 30, 2024 (in shares)	256,599,202

Common Equity (Changes in Share

Common Equity (Changes in Shareowners' Equity) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance			$ 6,777
Beginning balance	$ 6,791	$ 6,452	6,777	$ 6,276
Net income attributable to common shareowners	295	259	540	582
Net income			540	582
Common stock dividends	(123)	(115)	(369)	(341)
At-the-market offering program and Shareowner Direct Plan issuances	6	125	18	201
Equity-based compensation plans and other	3	4	4	4
Other comprehensive income (loss), net of tax	(4)	1	(2)	4
Ending balance	6,968		6,968
Ending balance	$ 6,968	$ 6,726	$ 6,968	$ 6,726
Common stock dividends (in dollars per share)	$ 0.48	$ 0.4525	$ 1.44	$ 1.3575
Common Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	$ 3	$ 3	$ 3	$ 3
Ending balance	3	3	3	3
Additional Paid-in Capital [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	3,042	2,854	3,030	2,777
At-the-market offering program and Shareowner Direct Plan issuances	6	125	18	201
Equity-based compensation plans and other	4	3	4	4
Ending balance	3,052	2,982	3,052	2,982
Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	3,755	3,606	3,756	3,509
Net income attributable to common shareowners	295	259	540	582
Common stock dividends	(123)	(115)	(369)	(341)
Ending balance	3,927	3,750	3,927	3,750
Accumulated Other Comprehensive Income (Loss) [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	3	3	1	0
Other comprehensive income (loss), net of tax	(4)	1	(2)	4
Ending balance	(1)	4	(1)	4
Shares in Deferred Compensation Trust [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	(12)	(14)	(13)	(13)
Equity-based compensation plans and other	(1)	1
Ending balance	(13)	(13)	(13)	(13)
IPL [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance			3,974
Beginning balance	4,080	3,869	3,974	3,808
Net income attributable to common shareowners	190	170	272	331
Net income	190	170	272	331
Common stock dividends	(50)	(70)	(151)	(210)
Capital contributions from parent	200	20	325	60
Ending balance	4,420		4,420
Ending balance	4,420	3,989	4,420	3,989
IPL [Member] | Common Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	33	33	33	33
Ending balance	33	33	33	33
IPL [Member] | Additional Paid-in Capital [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	3,012	2,847	2,887	2,807
Capital contributions from parent	200	20	325	60
Ending balance	3,212	2,867	3,212	2,867
IPL [Member] | Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	1,035	989	1,054	968
Net income	190	170	272	331
Common stock dividends	(50)	(70)	(151)	(210)
Ending balance	1,175	1,089	1,175	1,089
WPL [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance			3,897
Beginning balance	4,010	3,739	3,897	3,491
Net income attributable to common shareowners	114	107	270	267
Net income	114	107	270	267
Common stock dividends	(49)	(46)	(147)	(138)
Capital contributions from parent		65	55	245
Ending balance	4,075		4,075
Ending balance	4,075	3,865	4,075	3,865
WPL [Member] | Common Stock [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	66	66	66	66
Ending balance	66	66	66	66
WPL [Member] | Additional Paid-in Capital [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	2,533	2,413	2,478	2,233
Capital contributions from parent		65	55	245
Ending balance	2,533	2,478	2,533	2,478
WPL [Member] | Retained Earnings [Member]
Changes in Shareowners' Equity Roll Forward [Line Items]
Beginning balance	1,411	1,260	1,353	1,192
Net income	114	107	270	267
Common stock dividends	(49)	(46)	(147)	(138)
Ending balance	$ 1,476	$ 1,321	$ 1,476	$ 1,321

Debt (Narrative) (Details)

Debt (Narrative) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2025	Dec. 31, 2023
Debt [Line Items]
Line of credit facility, current borrowing capacity	$ 1,000
Payments to retire long-term debt	305	$ 404
Long-term debt, fair value	10,444			$ 8,677
Parent Company [Member]
Debt [Line Items]
Line of credit facility, current borrowing capacity	450
IPL [Member]
Debt [Line Items]
Line of credit facility, current borrowing capacity	250
Long-term debt, fair value	4,407			3,664
WPL [Member]
Debt [Line Items]
Line of credit facility, current borrowing capacity	300
Long-term debt, fair value	3,322			$ 2,933
Term Loan Credit Agreement [Member] | Term loan credit agreement through March 2025 [Member] | Alliant Energy Finance LLC [Member]
Debt [Line Items]
Long-term debt	$ 300
Interest rate, percent	6%
Term Loan Credit Agreement [Member] | Term loan credit agreement through March 2025 [Member] | Alliant Energy Finance LLC [Member] | Forecast [Member]
Debt [Line Items]
Long-term debt			$ 100
Term Loan Credit Agreement [Member] | Term loan credit agreement through March 2024 [Member] | Alliant Energy Finance LLC [Member]
Debt [Line Items]
Payments to retire long-term debt	$ 300
Senior Notes [Member] | 5.4% senior notes, due 2027 [Member] | Alliant Energy Finance LLC [Member]
Debt [Line Items]
Long-term debt	$ 375
Interest rate, percent	5.40%
Senior Debentures [Member] | 4.95% senior debenture, due 2034 [Member] | IPL [Member]
Debt [Line Items]
Long-term debt	$ 350
Interest rate, percent	4.95%
Senior Debentures [Member] | 5.45% senior debenture, due 2054 [Member] | IPL [Member]
Debt [Line Items]
Long-term debt	$ 300
Interest rate, percent	5.45%
Senior Debentures [Member] | 3.25% senior debenture, due 2024 [Member] | IPL [Member]
Debt [Line Items]
Long-term debt	$ 500
Interest rate, percent	3.25%
Debentures [Member] | 5.375% debenture, due 2034 [Member] | WPL [Member]
Debt [Line Items]
Long-term debt	$ 300
Interest rate, percent	5.375%
Convertible Senior Notes [Member] | 3.875% convertible senior notes, due 2026 [Member]
Debt [Line Items]
Long-term debt, carrying value	$ 570
Unamortized debt issuance costs	5
Long-term debt, fair value	$ 602
Shares included in diluted earnings per share (in shares)	0

Debt (Credit Facilities) (Detai

Debt (Credit Facilities) (Details) $ in Millions	Sep. 30, 2024 USD ($)
Debt [Line Items]
Amount outstanding	$ 330
Weighted average interest rates	5%
Available credit facility capacity	$ 670
IPL [Member]
Debt [Line Items]
Amount outstanding	$ 0
Weighted average interest rates	0%
Available credit facility capacity	$ 250
WPL [Member]
Debt [Line Items]
Amount outstanding	$ 0
Weighted average interest rates	0%
Available credit facility capacity	$ 300

Debt (Other Short-Term Borrowin

Debt (Other Short-Term Borrowings) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 330	$ 474	$ 632	$ 793
Average amount outstanding (based on daily outstanding balances)	$ 197	$ 440	$ 320	$ 367
Weighted average interest rates	5.40%	5.50%	5.50%	5.10%
IPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 0	$ 7	$ 19	$ 70
Average amount outstanding (based on daily outstanding balances)	$ 0	$ 0	$ 1	$ 2
Weighted average interest rates	0%	5.50%	5.50%	5.30%
WPL [Member]
Debt [Line Items]
Maximum amount outstanding (based on daily outstanding balances)	$ 0	$ 125	$ 390	$ 349
Average amount outstanding (based on daily outstanding balances)	$ 0	$ 86	$ 87	$ 135
Weighted average interest rates	0%	5.40%	5.50%	4.90%

Revenue (Disaggregation of Reve

Revenue (Disaggregation of Revenues) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 1,081	$ 1,077	$ 3,005	$ 3,066
Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	999	995	2,579	2,562
Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	378	374	966	943
Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	239	241	616	627
Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	270	280	730	740
Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	58	59	147	154
Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	54	41	120	98
Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	49	47	322	400
Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	24	23	189	233
Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	13	12	92	122
Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	2	8	12
Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	11	10	33	33
Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	12	13	36	38
Other Utility [Member] | Steam [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	9	11	29	32
Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3	2	7	6
Non-utility and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	21	22	68	66
Non-utility and Other [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	21	22	68	66
IPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	561	594	1,527	1,630
IPL [Member] | Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	523	551	1,318	1,370
IPL [Member] | Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	202	209	502	503
IPL [Member] | Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	153	158	385	399
IPL [Member] | Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	142	153	372	389
IPL [Member] | Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	19	21	45	47
IPL [Member] | Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	7	10	14	32
IPL [Member] | Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	27	31	175	224
IPL [Member] | Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	13	14	103	131
IPL [Member] | Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	7	9	48	65
IPL [Member] | Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	2	5	8
IPL [Member] | Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	6	6	19	20
IPL [Member] | Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	11	12	34	36
IPL [Member] | Other Utility [Member] | Steam [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	9	11	29	32
IPL [Member] | Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2	1	5	4
WPL [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	499	461	1,410	1,370
WPL [Member] | Electric [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	476	444	1,261	1,192
WPL [Member] | Electric [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	176	165	464	440
WPL [Member] | Electric [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	86	83	231	228
WPL [Member] | Electric [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	128	127	358	351
WPL [Member] | Electric [Member] | Wholesale [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	39	38	102	107
WPL [Member] | Electric [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	47	31	106	66
WPL [Member] | Gas [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	22	16	147	176
WPL [Member] | Gas [Member] | Retail - residential [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	11	9	86	102
WPL [Member] | Gas [Member] | Retail - commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	6	3	44	57
WPL [Member] | Gas [Member] | Retail - industrial [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0	3	4
WPL [Member] | Gas [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	5	4	14	13
WPL [Member] | Other Utility [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1	1	2	2
WPL [Member] | Other Utility [Member] | Other [Member]
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 1	$ 1	$ 2	$ 2

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2024
Income Taxes [Line Items]
Asset valuation charge for IPL's Lansing Generating Station	$ 0	$ 0	$ 60	$ 0
Income tax expense (benefit)	(62)	5	(104)	3
Steam Plant
Income Taxes [Line Items]
Asset retirement obligation charge for IPL's steam assets			20
Tax-related [Member]
Income Taxes [Line Items]
Income tax expense (benefit)		8
Forecast [Member]
Income Taxes [Line Items]
State income tax rate, percent					7.10%
IPL [Member]
Income Taxes [Line Items]
Asset valuation charge for IPL's Lansing Generating Station	0	0	60	0
Asset retirement obligation charge for IPL's steam assets	96	84	281	264
Income tax expense (benefit)	(68)	(31)	(112)	(55)
IPL [Member] | Steam Plant
Income Taxes [Line Items]
Asset retirement obligation charge for IPL's steam assets			20
WPL [Member]
Income Taxes [Line Items]
Asset retirement obligation charge for IPL's steam assets	72	64	200	197
Income tax expense (benefit)	$ 4	$ 21	$ 13	$ 47

Income Taxes (Schedule Of Effec

Income Taxes (Schedule Of Effective Income Tax Rates) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Effective Tax Rate [Line Items]
Overall income tax rate	(27.00%)	2%	(24.00%)	1%
IPL [Member]
Effective Tax Rate [Line Items]
Overall income tax rate	(56.00%)	(22.00%)	(70.00%)	(20.00%)
WPL [Member]
Effective Tax Rate [Line Items]
Overall income tax rate	3%	16%	5%	15%

Income Taxes (Summary Of Tax Cr

Income Taxes (Summary Of Tax Credit Carryforwards) (Details) $ in Millions	Sep. 30, 2024 USD ($)
State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	$ 367
Federal [Member]
Carryforwards [Line Items]
Tax credits, carryforward amount	622
IPL [Member] | State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	6
IPL [Member] | Federal [Member]
Carryforwards [Line Items]
Tax credits, carryforward amount	435
WPL [Member] | State [Member]
Carryforwards [Line Items]
Net operating losses, carryforward amount	1
WPL [Member] | Federal [Member]
Carryforwards [Line Items]
Tax credits, carryforward amount	$ 175

Benefit Plans (Narrative) (Deta

Benefit Plans (Narrative) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2024 USD ($) shares
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost	$ 15
Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost recognized over a weighted average period	1 year
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost recognized over a weighted average period	2 years
IPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost	$ 7
WPL [Member]
Defined Benefit Plan Disclosure [Line Items]
Unrecognized compensation cost	$ 7
Omnibus Incentive Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Shares included in diluted earnings per share (in shares) | shares	392,649

Benefit Plans (Defined Benefit

Benefit Plans (Defined Benefit Pension And Other Postretirement Benefits Plans) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1	$ 2	$ 3	$ 4
Interest cost	12	12	34	35
Expected return on plan assets	(14)	(14)	(41)	(40)
Amortization of prior service credit	0	(1)	0	(1)
Amortization of actuarial loss	6	7	18	21
Total	5	6	14	19
OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	1	2	2
Interest cost	2	3	6	7
Expected return on plan assets	(2)	(2)	(4)	(4)
Amortization of prior service credit	0	0	0	0
Amortization of actuarial loss	0	0	0	1
Total	1	2	4	6
IPL [Member] | Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1	0	2	2
Interest cost	5	6	15	16
Expected return on plan assets	(7)	(6)	(20)	(19)
Amortization of actuarial loss	2	2	7	8
Total	1	2	4	7
IPL [Member] | OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0
Interest cost	1	1	3	3
Expected return on plan assets	(1)	(1)	(3)	(3)
Amortization of actuarial loss	0	0	0	1
Total	0	0	0	1
WPL [Member] | Defined benefit pension plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	1	1
Interest cost	5	5	15	15
Expected return on plan assets	(6)	(5)	(18)	(16)
Amortization of actuarial loss	3	3	9	10
Total	2	3	7	10
WPL [Member] | OPEB Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	1	0	1
Interest cost	1	1	3	3
Expected return on plan assets	(1)	(1)	(1)	(1)
Amortization of actuarial loss	0	0	0	0
Total	$ 0	$ 1	$ 2	$ 3

Benefit Plans (Recognized Compe

Benefit Plans (Recognized Compensation Expense And Income Tax Benefits) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Compensation expense	$ 3	$ 4	$ 10	$ 10
Income tax benefits	1	1	3	3
IPL [Member]
Compensation expense	2	2	5	5
Income tax benefits	0	1	1	1
WPL [Member]
Compensation expense	1	2	4	4
Income tax benefits	$ 0	$ 0	$ 1	$ 1

Benefit Plans (Summary Of Equit

Benefit Plans (Summary Of Equity-based Compensation Plans Grants) (Details)	9 Months Ended
	Sep. 30, 2024 $ / shares shares
Performance Shares (total shareowner return metric) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants (in shares/units) | shares	127,267
Weighted average grant date fair value (in dollars per share/unit) | $ / shares	$ 46.04
Performance Shares (net income and diversity metrics) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants (in shares/units) | shares	145,449
Weighted average grant date fair value (in dollars per share/unit) | $ / shares	$ 48.49
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Grants (in shares/units) | shares	128,620
Weighted average grant date fair value (in dollars per share/unit) | $ / shares	$ 48.57

Asset Retirement Obligations (R

Asset Retirement Obligations (Reconciliation Of Changes In Asset Retirement Obligations) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1			$ 246
Revisions in estimated cash flows			(2)
Liabilities settled			(4)
Liabilities incurred			356
Accretion expense			12
Balance, September 30	$ 608		608
Steam Plant
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset retirement obligation charge for IPL's steam assets			20
IPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1			148
Revisions in estimated cash flows			0
Liabilities settled			(2)
Liabilities incurred			103
Accretion expense			6
Balance, September 30	255		255
Asset retirement obligation charge for IPL's steam assets	96	$ 84	281	$ 264
IPL [Member] | Steam Plant
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Asset retirement obligation charge for IPL's steam assets			20
WPL [Member]
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance, January 1			98
Revisions in estimated cash flows			(2)
Liabilities settled			(2)
Liabilities incurred			253
Accretion expense			6
Balance, September 30	353		353
Asset retirement obligation charge for IPL's steam assets	$ 72	$ 64	$ 200	$ 197

Derivative Instruments (Narrati

Derivative Instruments (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Derivative Instruments [Line Items]
Non-current interest rate derivative liabilities	$ 939		$ 939		$ 617
Accumulated other comprehensive loss, interest rate swap	1		1		$ (1)
Alliant Energy Finance LLC [Member] | Interest Rate Swap [Member] | Term Loan Credit Agreement [Member]
Derivative Instruments [Line Items]
Non-current interest rate derivative liabilities	1		1
Accumulated other comprehensive loss, interest rate swap	1		1
Interest expense, interest rate swap	$ 1	$ 1	$ 3	$ 2

Derivative Instruments (Notiona

Derivative Instruments (Notional Amounts Of Derivative Instruments) (Details) - Commodity [Member] gal in Thousands	9 Months Ended
	Sep. 30, 2024 Dekatherms MWh gal
Electricity (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	1,841
Electricity (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	675
Electricity (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	1,166
FTRs (MWhs) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	15,595
FTRs (MWhs) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	5,385
FTRs (MWhs) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in MWhs)	10,210
Natural Gas (Dths) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	156,626
Natural Gas (Dths) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	67,817
Natural Gas (Dths) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Dths) | Dekatherms	88,809
Diesel Fuel (Gallons) [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Gallons) | gal	3,150
Diesel Fuel (Gallons) [Member] | IPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Gallons) | gal	0
Diesel Fuel (Gallons) [Member] | WPL [Member]
Notional Amount of Derivatives [Line Items]
Notional unit amount of derivatives (in Gallons) | gal	3,150

Derivative Instruments (Fair Va

Derivative Instruments (Fair Value Of Financial Instruments) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Derivatives, Fair Value [Line Items]
Current derivative assets	$ 51	$ 44
Non-current derivative assets	31	44
Current derivative liabilities	31	51
Non-current derivative liabilities	45	47
IPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	37	30
Non-current derivative assets	18	24
Current derivative liabilities	14	22
Non-current derivative liabilities	6	8
WPL [Member]
Derivatives, Fair Value [Line Items]
Current derivative assets	14	14
Non-current derivative assets	13	20
Current derivative liabilities	17	29
Non-current derivative liabilities	$ 39	$ 39

Derivative Instruments (Balance

Derivative Instruments (Balance Sheet Offsetting) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Derivative Instruments [Line Items]
Derivative assets, Gross (as reported)	$ 82	$ 88
Derivative assets, Net	63	47
Derivative liabilities, Gross (as reported)	76	98
Derivative liabilities, Net	57	57
IPL [Member]
Derivative Instruments [Line Items]
Derivative assets, Gross (as reported)	55	54
Derivative assets, Net	45	32
Derivative liabilities, Gross (as reported)	20	30
Derivative liabilities, Net	10	8
WPL [Member]
Derivative Instruments [Line Items]
Derivative assets, Gross (as reported)	27	34
Derivative assets, Net	18	15
Derivative liabilities, Gross (as reported)	56	68
Derivative liabilities, Net	$ 47	$ 49

Fair Value Measurements (Fair V

Fair Value Measurements (Fair Value Measurements) (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Carrying Amount [Member]
Assets:
Time deposits and/or money market fund investments	$ 803	$ 45
Deferred proceeds	212	216
Liabilities:
Long-term debt (incl. current maturities)	10,349	9,034
Carrying Amount [Member] | IPL [Member]
Assets:
Time deposits and/or money market fund investments	745	45
Deferred proceeds	212	216
Liabilities:
Long-term debt (incl. current maturities)	4,589	3,945
Carrying Amount [Member] | WPL [Member]
Assets:
Time deposits and/or money market fund investments	58	0
Liabilities:
Long-term debt (incl. current maturities)	3,369	3,070
Carrying Amount [Member] | Commodity Contracts [Member]
Assets:
Derivatives	82	88
Liabilities:
Derivatives	76	98
Carrying Amount [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	55	54
Liabilities:
Derivatives	20	30
Carrying Amount [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	27	34
Liabilities:
Derivatives	56	68
Carrying Amount [Member] | Interest Rate Swap [Member]
Assets:
Derivatives	0	1
Liabilities:
Derivatives	1	0
Time deposits and/or money market fund investments	803	45
Deferred proceeds	212	216
Long-term debt (incl. current maturities)	10,444	8,677
IPL [Member]
Assets:
Time deposits and/or money market fund investments	745	45
Deferred proceeds	212	216
Liabilities:
Long-term debt (incl. current maturities)	4,407	3,664
WPL [Member]
Assets:
Time deposits and/or money market fund investments	58	0
Liabilities:
Long-term debt (incl. current maturities)	3,322	2,933
Commodity Contracts [Member]
Assets:
Derivatives	82	88
Liabilities:
Derivatives	76	98
Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	55	54
Liabilities:
Derivatives	20	30
Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	27	34
Liabilities:
Derivatives	56	68
Interest Rate Swap [Member]
Assets:
Derivatives	0	1
Liabilities:
Derivatives	1	0
Level 1 [Member]
Assets:
Time deposits and/or money market fund investments	803	45
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 1 [Member] | IPL [Member]
Assets:
Time deposits and/or money market fund investments	745	45
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 1 [Member] | WPL [Member]
Assets:
Time deposits and/or money market fund investments	58	0
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 1 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	0	0
Liabilities:
Derivatives	0	0
Level 1 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	0	0
Liabilities:
Derivatives	0	0
Level 1 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	0	0
Liabilities:
Derivatives	0	0
Level 1 [Member] | Interest Rate Swap [Member]
Assets:
Derivatives	0	0
Liabilities:
Derivatives	0	0
Level 2 [Member]
Assets:
Time deposits and/or money market fund investments	0	0
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	10,444	8,677
Level 2 [Member] | IPL [Member]
Assets:
Time deposits and/or money market fund investments	0	0
Deferred proceeds	0	0
Liabilities:
Long-term debt (incl. current maturities)	4,407	3,664
Level 2 [Member] | WPL [Member]
Assets:
Time deposits and/or money market fund investments	0	0
Liabilities:
Long-term debt (incl. current maturities)	3,322	2,933
Level 2 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	42	59
Liabilities:
Derivatives	73	93
Level 2 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	23	30
Liabilities:
Derivatives	17	25
Level 2 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	19	29
Liabilities:
Derivatives	56	68
Level 2 [Member] | Interest Rate Swap [Member]
Assets:
Derivatives	0	1
Liabilities:
Derivatives	1	0
Level 3 [Member]
Assets:
Time deposits and/or money market fund investments	0	0
Deferred proceeds	212	216
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 3 [Member] | IPL [Member]
Assets:
Time deposits and/or money market fund investments	0	0
Deferred proceeds	212	216
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 3 [Member] | WPL [Member]
Assets:
Time deposits and/or money market fund investments	0	0
Liabilities:
Long-term debt (incl. current maturities)	0	0
Level 3 [Member] | Commodity Contracts [Member]
Assets:
Derivatives	40	29
Liabilities:
Derivatives	3	5
Level 3 [Member] | Commodity Contracts [Member] | IPL [Member]
Assets:
Derivatives	32	24
Liabilities:
Derivatives	3	5
Level 3 [Member] | Commodity Contracts [Member] | WPL [Member]
Assets:
Derivatives	8	5
Liabilities:
Derivatives	0	0
Level 3 [Member] | Interest Rate Swap [Member]
Assets:
Derivatives	0	0
Liabilities:
Derivatives	$ 0	$ 0

Fair Value Measurements (Fair_2

Fair Value Measurements (Fair Value Measurements Using Significant Unobservable Inputs) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Commodity Contracts [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ 51	$ 54	$ 24	$ 19
Total net gains (losses) included in changes in net assets (realized/unrealized)	2	17	(7)	6
Purchases			59	62
Sales	0	(1)	(1)	(2)
Settlements	(16)	(27)	(38)	(42)
Ending balance	37	43	37	43
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 September 30	2	17	(7)	6
Commodity Contracts [Member] | IPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	40	41	19	16
Total net gains (losses) included in changes in net assets (realized/unrealized)	0	12	(7)	0
Purchases			45	51
Sales	0	(1)	(1)	(2)
Settlements	(11)	(17)	(27)	(30)
Ending balance	29	35	29	35
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 September 30	0	12	(7)	0
Commodity Contracts [Member] | WPL [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	11	13	5	3
Total net gains (losses) included in changes in net assets (realized/unrealized)	2	5	0	6
Purchases			14	11
Settlements	(5)	(10)	(11)	(12)
Ending balance	8	8	8	8
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 September 30	2	5	0	6
Deferred Proceeds [Member]
Fair Value, Assets and Liabilities, Net, Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	171	175	216	185
Total net gains (losses) included in changes in net assets (realized/unrealized)	0	0	0	0
Purchases			0	0
Sales	0	0	0	0
Settlements	41	61	(4)	51
Ending balance	212	236	212	236
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 September 30	0	0	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	171	175	216	185
Total net gains (losses) included in changes in net assets (realized/unrealized)	0	0	0	0
Purchases			0	0
Sales	0	0	0	0
Settlements	41	61	(4)	51
Ending balance	212	236	212	236
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 September 30	$ 0	$ 0	$ 0	$ 0

Fair Value Measurements (Fair_3

Fair Value Measurements (Fair Value Of Net Derivative Assets (Liabilities)) (Details) - Commodity Contracts [Member] - USD ($) $ in Millions	Sep. 30, 2024	Jun. 30, 2024	Dec. 31, 2023	Sep. 30, 2023	Jun. 30, 2023	Dec. 31, 2022
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	$ 37	$ 51	$ 24	$ 43	$ 54	$ 19
Excluding Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets			3
Fair value, net derivative liabilities	0
Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	37		21
IPL [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	29	40	19	35	41	16
IPL [Member] | Excluding Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets			3
Fair value, net derivative liabilities	0
IPL [Member] | Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	29		16
WPL [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	8	$ 11	5	$ 8	$ 13	$ 3
WPL [Member] | Excluding Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative liabilities	0		0
WPL [Member] | Financial Transmission Rights [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Fair value, net derivative assets	$ 8		$ 5

Commitments And Contingencies_2

Commitments And Contingencies (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Sep. 30, 2024
Commitments and Contingencies [Line Items]
Minimum future commitments			$ 995
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments			$ 448
MISO base return on equity, percentage			10.25%
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments			$ 505
Federal Energy Regulatory Commission [Member]
Commitments and Contingencies [Line Items]
MISO base return on equity, percentage	10.02%	9.88%	9.98%
Indemnification Agreement [Member]
Commitments and Contingencies [Line Items]
Obligations, maximum			$ 43
Whiting Petroleum Affiliate [Member]
Commitments and Contingencies [Line Items]
Partnership share, percent			6%
Obligations, maximum			$ 49
Capital Purchase Commitment [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments			99
Capital Purchase Commitment [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments			24
Capital Purchase Commitment [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments			72
Purchased Power [Member] | Indemnification Agreement [Member]
Commitments and Contingencies [Line Items]
Obligations, maximum			17
Renewable Tax Credits Transferred [Member] | Indemnification Agreement [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Obligations, maximum			165
Renewable Tax Credits Transferred [Member] | Indemnification Agreement [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Obligations, maximum			$ 105

Commitments And Contingencies_3

Commitments And Contingencies (Other Purchase Commitments) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2024 USD ($)
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 995
Individual commitments incurred	1
IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	448
Individual commitments incurred	1
WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	505
Individual commitments incurred	1
Natural gas [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	746
Natural gas [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	322
Natural gas [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	424
Coal [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	139
Coal [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	80
Coal [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	59
Other [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	110
Other [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	46
Other [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Minimum future commitments	$ 22

Commitments And Contingencies_4

Commitments And Contingencies (MPG Site Estimated Future Costs And Recorded Liabilities) (Details) - Natural Gas Processing Plant [Member] $ in Millions	9 Months Ended
	Sep. 30, 2024 USD ($)
Commitments and Contingencies [Line Items]
Current and non-current environmental liabilities	$ 13
IPL [Member]
Commitments and Contingencies [Line Items]
Current and non-current environmental liabilities	8
WPL [Member]
Commitments and Contingencies [Line Items]
Current and non-current environmental liabilities	5
Minimum [Member]
Commitments and Contingencies [Line Items]
Range of estimated future costs	7
Minimum [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Range of estimated future costs	5
Minimum [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Range of estimated future costs	2
Maximum [Member]
Commitments and Contingencies [Line Items]
Range of estimated future costs	28
Maximum [Member] | IPL [Member]
Commitments and Contingencies [Line Items]
Range of estimated future costs	17
Maximum [Member] | WPL [Member]
Commitments and Contingencies [Line Items]
Range of estimated future costs	$ 11

Segments Of Business (Schedule

Segments Of Business (Schedule Of Segments Of Business) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Segment Reporting Information [Line Items]
Revenues	$ 1,081	$ 1,077	$ 3,005	$ 3,066
Operating income (loss)	313	322	665	760
Net income (loss) attributable to common shareowners	295	259	540	582
Net income			540	582
IPL [Member]
Segment Reporting Information [Line Items]
Revenues	561	594	1,527	1,630
Operating income (loss)	149	173	250	379
Net income (loss) attributable to common shareowners	190	170	272	331
Net income	190	170	272	331
WPL [Member]
Segment Reporting Information [Line Items]
Revenues	499	461	1,410	1,370
Operating income (loss)	156	142	387	363
Net income (loss) attributable to common shareowners	114	107	270	267
Net income	114	107	270	267
Electric [Member]
Segment Reporting Information [Line Items]
Revenues	999	995	2,579	2,562
Operating income (loss)	305	319	600	682
Electric [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	523	551	1,318	1,370
Operating income (loss)	148	171	239	342
Electric [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	476	444	1,261	1,192
Operating income (loss)	157	148	361	340
Gas [Member]
Segment Reporting Information [Line Items]
Revenues	49	47	322	400
Operating income (loss)	(4)	(4)	44	48
Gas [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	27	31	175	224
Operating income (loss)	(3)	(2)	18	25
Gas [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	22	16	147	176
Operating income (loss)	(1)	(2)	26	23
Other Utility [Member]
Segment Reporting Information [Line Items]
Revenues	12	13	36	38
Operating income (loss)	4	0	(7)	12
Other Utility [Member] | IPL [Member]
Segment Reporting Information [Line Items]
Revenues	11	12	34	36
Operating income (loss)	4	4	(7)	12
Other Utility [Member] | WPL [Member]
Segment Reporting Information [Line Items]
Revenues	1	1	2	2
Operating income (loss)	0	(4)	0	0
Non-utility and Other [Member]
Segment Reporting Information [Line Items]
Revenues	21	22	68	66
Operating income (loss)	8	7	28	18
Net income (loss) attributable to common shareowners	(9)	(18)	(2)	(16)
Utility Business [Member]
Segment Reporting Information [Line Items]
Revenues	1,060	1,055	2,937	3,000
Operating income (loss)	305	315	637	742
Net income (loss) attributable to common shareowners	$ 304	$ 277	$ 542	$ 598

Related Parties (Narrative) (De

Related Parties (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
WPL [Member] | WPL Owed ATC LLC [Member] | Related Party [Member]
Related Party Transactions [Line Items]
Net amounts owed	$ 11	$ 10

Related Parties (Service Agreem

Related Parties (Service Agreements) (Details) - Corporate Services [Member] - Subsidiary of Common Parent [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Corporate Services Billings [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 42	$ 46	$ 134	$ 134
Corporate Services Billings [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	38	40	124	120
Sales Credited [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	0	3	0	11
Sales Credited [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	29	23	66	45
Purchases Billed [Member] | IPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	130	133	332	320
Purchases Billed [Member] | WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 18	$ 5	$ 41	$ 21

Related Parties (Net Intercompa

Related Parties (Net Intercompany Payables) (Details) - Related Party [Member] - Corporate Services [Member] - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
IPL [Member]
Related Party Transactions [Line Items]
Net amounts owed	$ 131	$ 129
WPL [Member]
Related Party Transactions [Line Items]
Net amounts owed	$ 72	$ 72

Related Parties (Amounts Billed

Related Parties (Amounts Billed Between Parties) (Details) - ATC LLC [Member] - WPL [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
ATC Billings To WPL [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 39	$ 41	$ 115	$ 119
WPL Billings To ATC [Member]
Related Party Transactions [Line Items]
Amounts billed between related parties	$ 5	$ 5	$ 12	$ 16