Condensed Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Revenues:
Electric utility	$ 730.3	$ 743.4
Gas utility	152.2	215.8
Other utility	11.6	11.1
Non-utility	21.6	16.9
Total revenues	915.7	987.2
Operating expenses:
Electric production fuel and purchased power	184.1	218.4
Electric transmission service	122.2	123.0
Cost of gas sold	85.0	121.6
Other operation and maintenance	162.2	181.2
Depreciation and amortization	146.3	136.9
Taxes other than income taxes	27.6	29.3
Total operating expenses	727.4	810.4
Operating income	188.3	176.8
Other (income) and deductions:
Interest expense	68.9	66.3
Equity income from unconsolidated investments, net	(13.4)	(10.9)
Allowance for funds used during construction	(23.0)	(25.4)
Other	1.9	4.0
Total other (income) and deductions	34.4	34.0
Income before income taxes	153.9	142.8
Income tax expense (benefit)	(18.7)	15.1
Net income	172.6	127.7
Preferred dividend requirements of Interstate Power and Light Company	2.6	2.6
Net income attributable to common shareowners	$ 170.0	$ 125.1
Weighted average number of common shares outstanding:
Basic (in shares)	244.4	236.5
Diluted (in shares)	244.6	236.6
Earnings per weighted average common share attributable to Alliant Energy common shareowners (basic and diluted) (in dollars per share)	$ 0.70	$ 0.53
IPL [Member]
Revenues:
Electric utility	$ 424.8	$ 419.8
Gas utility	83.0	124.6
Other utility	11.1	10.7
Total revenues	518.9	555.1
Operating expenses:
Electric production fuel and purchased power	106.2	128.9
Electric transmission service	84.5	87.7
Cost of gas sold	44.2	63.3
Other operation and maintenance	86.6	108.0
Depreciation and amortization	85.9	77.1
Taxes other than income taxes	14.8	16.6
Total operating expenses	422.2	481.6
Operating income	96.7	73.5
Other (income) and deductions:
Interest expense	34.5	29.4
Allowance for funds used during construction	(9.8)	(15.8)
Other	0.9	1.9
Total other (income) and deductions	25.6	15.5
Income before income taxes	71.1	58.0
Income tax expense (benefit)	(14.1)	2.1
Net income	85.2	55.9
Preferred dividend requirements of Interstate Power and Light Company	2.6	2.6
Net income attributable to common shareowners	82.6	53.3
WPL [Member]
Revenues:
Electric utility	305.5	323.6
Gas utility	69.2	91.2
Other utility	0.5	0.4
Total revenues	375.2	415.2
Operating expenses:
Electric production fuel and purchased power	77.9	89.5
Electric transmission service	37.7	35.3
Cost of gas sold	40.8	58.3
Other operation and maintenance	54.2	63.5
Depreciation and amortization	59.1	58.6
Taxes other than income taxes	11.7	11.9
Total operating expenses	281.4	317.1
Operating income	93.8	98.1
Other (income) and deductions:
Interest expense	25.1	25.8
Allowance for funds used during construction	(13.2)	(9.6)
Other	0.5	1.6
Total other (income) and deductions	12.4	17.8
Income before income taxes	81.4	80.3
Income tax expense (benefit)	(8.2)	14.6
Net income	$ 89.6	$ 65.7