Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Revenues:
Electric utility	$ 3,697	$ 3,372	$ 3,345
Gas utility	525	465	540
Other utility	51	54	52
Non-utility	89	90	90
Total revenues	4,362	3,981	4,027
Operating expenses:
Electric production fuel and purchased power	742	628	736
Electric transmission service	625	613	583
Cost of gas sold	263	224	299
Asset valuation charge for IPL's Lansing Generating Station	0	60	0
Other operation and maintenance	740	676	675
Depreciation and amortization	846	772	676
Taxes other than income taxes	121	122	115
Total operating expenses	3,337	3,095	3,084
Operating income (loss)	1,025	886	943
Other (income) and deductions:
Interest expense	512	449	394
Equity income from unconsolidated investments, net	(60)	(61)	(61)
Allowance for funds used during construction	(89)	(75)	(100)
Other	1	(3)	3
Total other (income) and deductions	364	310	236
Income before income taxes	661	576	707
Income tax expense (benefit)	(149)	(114)	4
Net income attributable to common shareowners	$ 810	$ 690	$ 703
Weighted average number of common shares outstanding:
Basic (in shares)	257.0	256.5	253.0
Diluted (in shares)	257.8	256.8	253.3
Earnings per weighted average common share attributable to Alliant Energy common shareowners:
Basic (in dollars per share)	$ 3.15	$ 2.69	$ 2.78
Diluted (in dollars per share)	$ 3.14	$ 2.69	$ 2.78
IPL [Member]
Revenues:
Electric utility	$ 1,896	$ 1,747	$ 1,761
Gas utility	265	250	300
Other utility	47	49	49
Total revenues	2,208	2,046	2,110
Operating expenses:
Electric production fuel and purchased power	283	269	282
Electric transmission service	422	417	420
Cost of gas sold	130	123	166
Asset valuation charge for IPL's Lansing Generating Station	0	60	0
Other operation and maintenance	373	358	353
Depreciation and amortization	463	404	388
Taxes other than income taxes	59	60	57
Total operating expenses	1,730	1,691	1,666
Operating income (loss)	478	355	444
Other (income) and deductions:
Interest expense	211	177	155
Allowance for funds used during construction	(56)	(43)	(21)
Other	(7)	(12)	2
Total other (income) and deductions	148	122	136
Income before income taxes	330	233	308
Income tax expense (benefit)	(127)	(129)	(58)
Net income attributable to common shareowners	457	362	366
WPL [Member]
Revenues:
Electric utility	1,801	1,625	1,584
Gas utility	260	215	240
Other utility	4	5	3
Total revenues	2,065	1,845	1,827
Operating expenses:
Electric production fuel and purchased power	459	359	455
Electric transmission service	203	196	163
Cost of gas sold	133	101	134
Other operation and maintenance	306	279	271
Depreciation and amortization	370	357	280
Taxes other than income taxes	55	56	52
Total operating expenses	1,526	1,348	1,355
Operating income (loss)	539	497	472
Other (income) and deductions:
Interest expense	173	165	149
Allowance for funds used during construction	(33)	(32)	(79)
Other	12	8	(3)
Total other (income) and deductions	152	141	67
Income before income taxes	387	356	405
Income tax expense (benefit)	(14)	11	60
Net income attributable to common shareowners	$ 401	$ 345	$ 345