Condensed Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Revenues:
Electric utility	$ 717	$ 675	$ 1,418	$ 1,405
Gas utility	69	59	239	211
Other utility	10	10	23	22
Non-utility	21	19	38	41
Total revenues	817	763	1,718	1,679
Operating expenses:
Electric production fuel and purchased power	138	164	271	348
Electric transmission service	121	72	255	194
Cost of gas sold	31	21	131	106
Other operation and maintenance	160	159	306	322
Depreciation and amortization	165	152	329	298
Taxes other than income taxes	26	27	52	55
Total operating expenses	641	595	1,344	1,323
Operating income	176	168	374	356
Other (income) and deductions:
Interest expense	69	70	138	139
Equity income from unconsolidated investments, net	(19)	(18)	(34)	(31)
Allowance for funds used during construction	(5)	(15)	(9)	(38)
Other	2	3	4	4
Total other (income) and deductions	47	40	99	74
Income before income taxes	129	128	275	282
Income tax benefit	(17)	(8)	(45)	(27)
Net income	146	136	320	309
Preferred dividend requirements of Interstate Power and Light Company	2	2	5	5
Net income attributable to common shareowners	$ 144	$ 134	$ 315	$ 304
Weighted average number of common shares outstanding:
Basic (in shares)	250.2	249.6	250.1	247.0
Diluted (in shares)	250.6	249.8	250.5	247.2
Earnings per weighted average common share attributable to Alliant Energy common shareowners:
Basic (in dollars per share)	$ 0.58	$ 0.54	$ 1.26	$ 1.23
Diluted (in dollars per share)	$ 0.57	$ 0.54	$ 1.26	$ 1.23
IPL [Member]
Revenues:
Electric utility	$ 402	$ 388	$ 788	$ 813
Gas utility	43	34	134	117
Other utility	10	10	22	21
Total revenues	455	432	944	951
Operating expenses:
Electric production fuel and purchased power	55	96	114	202
Electric transmission service	79	35	171	119
Cost of gas sold	22	13	72	57
Other operation and maintenance	81	97	158	184
Depreciation and amortization	93	89	187	175
Taxes other than income taxes	14	14	28	29
Total operating expenses	344	344	730	766
Operating income	111	88	214	185
Other (income) and deductions:
Interest expense	34	35	69	69
Allowance for funds used during construction	(3)	(5)	(5)	(15)
Other	2	0	2	2
Total other (income) and deductions	33	30	66	56
Income before income taxes	78	58	148	129
Income tax benefit	(10)	(4)	(22)	(18)
Net income	88	62	170	147
Preferred dividend requirements of Interstate Power and Light Company	2	2	5	5
Net income attributable to common shareowners	86	60	165	142
WPL [Member]
Revenues:
Electric utility	315	287	630	592
Gas utility	26	25	105	94
Other utility	0	0	1	1
Total revenues	341	312	736	687
Operating expenses:
Electric production fuel and purchased power	84	67	158	145
Electric transmission service	42	37	84	75
Cost of gas sold	9	8	59	49
Other operation and maintenance	69	53	128	107
Depreciation and amortization	70	62	139	121
Taxes other than income taxes	12	13	23	24
Total operating expenses	286	240	591	521
Operating income	55	72	145	166
Other (income) and deductions:
Interest expense	26	27	52	52
Allowance for funds used during construction	(2)	(10)	(4)	(23)
Other	0	2	1	2
Total other (income) and deductions	24	19	49	31
Income before income taxes	31	53	96	135
Income tax benefit	(7)	(5)	(26)	(12)
Net income	$ 38	$ 58	$ 122	$ 147