Condensed Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Revenues:
Electric utility	$ 701	$ 730
Gas utility	170	152
Other utility	13	12
Non-utility	17	22
Total revenues	901	916
Operating expenses:
Electric production fuel and purchased power	133	184
Electric transmission service	134	122
Cost of gas sold	100	85
Other operation and maintenance	146	163
Depreciation and amortization	164	146
Taxes other than income taxes	26	28
Total operating expenses	703	728
Operating income	198	188
Other (income) and deductions:
Interest expense	69	69
Equity income from unconsolidated investments, net	(15)	(13)
Allowance for funds used during construction	(4)	(23)
Other	2	1
Total other (income) and deductions	52	34
Income before income taxes	146	154
Income tax benefit	(28)	(19)
Net income	174	173
Preferred dividend requirements of Interstate Power and Light Company	3	3
Net income attributable to common shareowners	$ 171	$ 170
Weighted average number of common shares outstanding:
Basic (in shares)	250.0	244.4
Diluted (in shares)	250.4	244.6
Earnings per weighted average common share attributable to Alliant Energy common shareowners (basic and diluted)	$ 0.68	$ 0.70
IPL [Member]
Revenues:
Electric utility	$ 386	$ 425
Gas utility	91	83
Other utility	12	11
Total revenues	489	519
Operating expenses:
Electric production fuel and purchased power	59	106
Electric transmission service	92	84
Cost of gas sold	50	44
Other operation and maintenance	77	87
Depreciation and amortization	94	86
Taxes other than income taxes	14	15
Total operating expenses	386	422
Operating income	103	97
Other (income) and deductions:
Interest expense	35	34
Allowance for funds used during construction	(2)	(10)
Other	0	1
Total other (income) and deductions	33	25
Income before income taxes	70	72
Income tax benefit	(12)	(14)
Net income	82	86
Preferred dividend requirements of Interstate Power and Light Company	3	3
Net income attributable to common shareowners	79	83
WPL [Member]
Revenues:
Electric utility	315	305
Gas utility	79	69
Other utility	1	1
Total revenues	395	375
Operating expenses:
Electric production fuel and purchased power	74	78
Electric transmission service	42	38
Cost of gas sold	50	41
Other operation and maintenance	59	54
Depreciation and amortization	69	59
Taxes other than income taxes	11	11
Total operating expenses	305	281
Operating income	90	94
Other (income) and deductions:
Interest expense	26	25
Allowance for funds used during construction	(2)	(13)
Other	1	0
Total other (income) and deductions	25	12
Income before income taxes	65	82
Income tax benefit	(19)	(8)
Net income	$ 84	$ 90