Condensed Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Revenues:
Electric utility	$ 939	$ 852	$ 2,357	$ 2,257
Gas utility	50	42	289	253
Other utility	13	10	36	32
Non-utility	22	16	60	57
Total revenues	1,024	920	2,742	2,599
Operating expenses:
Electric production fuel and purchased power	207	179	478	527
Electric transmission service	148	132	403	326
Cost of gas sold	18	11	149	117
Other operation and maintenance	171	143	477	465
Depreciation and amortization	165	156	494	454
Taxes other than income taxes	26	27	78	82
Total operating expenses	735	648	2,079	1,971
Operating income	289	272	663	628
Other (income) and deductions:
Interest expense	68	68	206	207
Equity income from unconsolidated investments, net	(13)	(15)	(47)	(46)
Allowance for funds used during construction	(7)	(13)	(16)	(51)
Other	3	3	7	7
Total other (income) and deductions	51	43	150	117
Income before income taxes	238	229	513	511
Income tax benefit	(21)	(20)	(66)	(47)
Net income	259	249	579	558
Preferred dividend requirements of Interstate Power and Light Company	3	3	8	8
Net income attributable to common shareowners	$ 256	$ 246	$ 571	$ 550
Weighted average number of common shares outstanding:
Basic (in shares)	250.3	249.7	250.2	247.9
Diluted (in shares)	250.8	250.0	250.6	248.1
Earnings per weighted average common share attributable to Alliant Energy common shareowners:
Basic (in dollars per share)	$ 1.02	$ 0.99	$ 2.28	$ 2.22
Diluted (in dollars per share)	$ 1.02	$ 0.98	$ 2.28	$ 2.22
IPL [Member]
Revenues:
Electric utility	$ 555	$ 519	$ 1,343	$ 1,332
Gas utility	31	24	165	141
Other utility	13	10	35	31
Total revenues	599	553	1,543	1,504
Operating expenses:
Electric production fuel and purchased power	101	102	215	304
Electric transmission service	103	93	274	212
Cost of gas sold	12	6	84	63
Other operation and maintenance	95	85	253	269
Depreciation and amortization	94	89	281	264
Taxes other than income taxes	14	16	42	45
Total operating expenses	419	391	1,149	1,157
Operating income	180	162	394	347
Other (income) and deductions:
Interest expense	34	35	103	104
Allowance for funds used during construction	(2)	(6)	(7)	(21)
Other	0	1	2	3
Total other (income) and deductions	32	30	98	86
Income before income taxes	148	132	296	261
Income tax benefit	(12)	(19)	(34)	(37)
Net income	160	151	330	298
Preferred dividend requirements of Interstate Power and Light Company	3	3	8	8
Net income attributable to common shareowners	157	148	322	290
WPL [Member]
Revenues:
Electric utility	384	333	1,014	925
Gas utility	19	18	124	112
Other utility	0	0	1	1
Total revenues	403	351	1,139	1,038
Operating expenses:
Electric production fuel and purchased power	105	78	263	223
Electric transmission service	44	39	128	114
Cost of gas sold	6	4	65	53
Other operation and maintenance	66	65	194	172
Depreciation and amortization	70	65	209	186
Taxes other than income taxes	12	11	35	35
Total operating expenses	303	262	894	783
Operating income	100	89	245	255
Other (income) and deductions:
Interest expense	25	26	77	78
Allowance for funds used during construction	(5)	(6)	(9)	(29)
Other	2	1	3	3
Total other (income) and deductions	22	21	71	52
Income before income taxes	78	68	174	203
Income tax benefit	(15)	(5)	(41)	(17)
Net income	$ 93	$ 73	$ 215	$ 220