Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues:
Electric utility	$ 2,920	$ 3,064	$ 3,000
Gas utility	373	455	447
Other utility	49	46	48
Non-utility	74	83	39
Total revenues	3,416	3,648	3,534
Operating expenses:
Electric production fuel and purchased power	652	777	855
Electric transmission service	449	481	496
Cost of gas sold	182	222	232
Other operation and maintenance	670	712	646
Depreciation and amortization	615	567	507
Taxes other than income taxes	108	111	104
Total operating expenses	2,676	2,870	2,840
Operating income (loss)	740	778	694
Other (income) and deductions:
Interest expense	275	273	247
Equity income from unconsolidated investments, net	(61)	(53)	(55)
Allowance for funds used during construction	(55)	(93)	(76)
Other	14	15	8
Total other (income) and deductions	173	142	124
Income before income taxes	567	636	570
Income tax expense (benefit)	(57)	69	48
Net income	624	567	522
Preferred dividend requirements of Interstate Power and Light Company	10	10	10
Net income attributable to common shareowners	$ 614	$ 557	$ 512
Weighted average number of common shares outstanding:
Basic (in shares)	248.4	238.5	233.6
Diluted (in shares)	248.7	239.0	233.6
Earnings per weighted average common share attributable to Alliant Energy common shareowners:
Basic (in dollars per share)	$ 2.47	$ 2.34	$ 2.19
Diluted (in dollars per share)	$ 2.47	$ 2.33	$ 2.19
IPL [Member]
Revenues:
Electric utility	$ 1,695	$ 1,781	$ 1,731
Gas utility	208	264	266
Other utility	44	44	45
Total revenues	1,947	2,089	2,042
Operating expenses:
Electric production fuel and purchased power	352	435	469
Electric transmission service	298	340	353
Cost of gas sold	99	120	129
Other operation and maintenance	375	404	403
Depreciation and amortization	356	327	283
Taxes other than income taxes	57	60	54
Total operating expenses	1,537	1,686	1,691
Operating income (loss)	410	403	351
Other (income) and deductions:
Interest expense	139	127	119
Allowance for funds used during construction	(24)	(50)	(42)
Other	8	8	3
Total other (income) and deductions	123	85	80
Income before income taxes	287	318	271
Income tax expense (benefit)	(47)	24	(3)
Net income	334	294	274
Preferred dividend requirements of Interstate Power and Light Company	10	10	10
Net income attributable to common shareowners	324	284	264
WPL [Member]
Revenues:
Electric utility	1,225	1,283	1,269
Gas utility	165	191	181
Other utility	5	2	3
Total revenues	1,395	1,476	1,453
Operating expenses:
Electric production fuel and purchased power	300	342	386
Electric transmission service	151	141	143
Cost of gas sold	83	102	103
Other operation and maintenance	254	261	242
Depreciation and amortization	254	236	219
Taxes other than income taxes	47	47	47
Total operating expenses	1,089	1,129	1,140
Operating income (loss)	306	347	313
Other (income) and deductions:
Interest expense	104	102	98
Allowance for funds used during construction	(31)	(43)	(34)
Other	3	6	5
Total other (income) and deductions	76	65	69
Income before income taxes	230	282	244
Income tax expense (benefit)	(19)	49	36
Net income	$ 249	$ 233	$ 208