Condensed Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Revenues:
Electric utility	$ 852	$ 916	$ 2,257	$ 2,350
Gas utility	42	42	253	323
Other utility	10	11	32	33
Non-utility	16	21	57	62
Total revenues	920	990	2,599	2,768
Operating expenses:
Electric production fuel and purchased power	179	219	527	602
Electric transmission service	132	127	326	363
Cost of gas sold	11	9	117	151
Other operation and maintenance	143	174	465	527
Depreciation and amortization	156	144	454	424
Taxes other than income taxes	27	27	82	84
Total operating expenses	648	700	1,971	2,151
Operating income	272	290	628	617
Other (income) and deductions:
Interest expense	68	68	207	204
Equity income from unconsolidated investments, net	(15)	(12)	(46)	(35)
Allowance for funds used during construction	(13)	(22)	(51)	(66)
Other	3	4	7	11
Total other (income) and deductions	43	38	117	114
Income before income taxes	229	252	511	503
Income tax expense (benefit)	(20)	23	(47)	49
Net income	249	229	558	454
Preferred dividend requirements of Interstate Power and Light Company	3	3	8	8
Net income attributable to common shareowners	$ 246	$ 226	$ 550	$ 446
Weighted average number of common shares outstanding:
Basic (in shares)	249.7	239.1	247.9	237.7
Diluted (in shares)	250.0	239.9	248.1	238.2
Earnings per weighted average common share attributable to Alliant Energy common shareowners:
Basic (in dollars per share)	$ 0.99	$ 0.95	$ 2.22	$ 1.88
Diluted (in dollars per share)	$ 0.98	$ 0.94	$ 2.22	$ 1.87
IPL [Member]
Revenues:
Electric utility	$ 519	$ 561	$ 1,332	$ 1,373
Gas utility	24	25	141	188
Other utility	10	11	31	32
Total revenues	553	597	1,504	1,593
Operating expenses:
Electric production fuel and purchased power	102	127	304	339
Electric transmission service	93	92	212	257
Cost of gas sold	6	6	63	80
Other operation and maintenance	85	100	269	306
Depreciation and amortization	89	84	264	243
Taxes other than income taxes	16	14	45	46
Total operating expenses	391	423	1,157	1,271
Operating income	162	174	347	322
Other (income) and deductions:
Interest expense	35	32	104	93
Allowance for funds used during construction	(6)	(11)	(21)	(34)
Other	1	2	3	5
Total other (income) and deductions	30	23	86	64
Income before income taxes	132	151	261	258
Income tax expense (benefit)	(19)	7	(37)	11
Net income	151	144	298	247
Preferred dividend requirements of Interstate Power and Light Company	3	3	8	8
Net income attributable to common shareowners	148	141	290	239
WPL [Member]
Revenues:
Electric utility	333	355	925	977
Gas utility	18	17	112	135
Other utility	0	0	1	1
Total revenues	351	372	1,038	1,113
Operating expenses:
Electric production fuel and purchased power	78	92	223	263
Electric transmission service	39	36	114	106
Cost of gas sold	4	3	53	71
Other operation and maintenance	65	62	172	188
Depreciation and amortization	65	59	186	177
Taxes other than income taxes	11	12	35	35
Total operating expenses	262	264	783	840
Operating income	89	108	255	273
Other (income) and deductions:
Interest expense	26	25	78	77
Allowance for funds used during construction	(6)	(11)	(29)	(31)
Other	1	1	3	4
Total other (income) and deductions	21	15	52	50
Income before income taxes	68	93	203	223
Income tax expense (benefit)	(5)	17	(17)	40
Net income	$ 73	$ 76	$ 220	$ 183