Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues:
Electric utility	$ 3,063.6	$ 3,000.3	$ 2,894.7
Gas utility	455.2	446.6	400.9
Other utility	46.5	48.0	47.5
Non-utility	82.4	39.6	39.1
Total revenues	3,647.7	3,534.5	3,382.2
Operating expenses:
Electric production fuel and purchased power	776.7	855.0	818.1
Electric transmission service	481.4	495.7	480.9
Cost of gas sold	221.7	232.3	211.4
Other operation and maintenance	712.2	645.8	633.2
Depreciation and amortization	567.2	506.9	461.8
Taxes other than income taxes	110.8	104.4	105.6
Total operating expenses	2,870.0	2,840.1	2,711.0
Operating income (loss)	777.7	694.4	671.2
Other (income) and deductions:
Interest expense	272.9	247.0	215.6
Equity income from unconsolidated investments, net	(53.0)	(54.6)	(44.8)
Allowance for funds used during construction	(92.7)	(75.6)	(49.7)
Other	14.4	7.6	17.3
Total other (income) and deductions	141.6	124.4	138.4
Income from continuing operations before income taxes	636.1	570.0	532.8
Income tax expense (benefit)	68.7	47.7	66.7
Income from continuing operations, net of tax	567.4	522.3	466.1
Income from discontinued operations, net of tax	0.0	0.0	1.4
Net income	567.4	522.3	467.5
Preferred dividend requirements of Interstate Power and Light Company	10.2	10.2	10.2
Net income attributable to common shareowners	$ 557.2	$ 512.1	$ 457.3
Weighted average number of common shares outstanding:
Basic (in shares)	238.5	233.6	229.7
Diluted (in shares)	239.0	233.6	229.7
Earnings per weighted average common share attributable to Alliant Energy common shareowners:
Basic (in dollars per share)	$ 2.34	$ 2.19	$ 1.99
Diluted (in dollars per share)	$ 2.33	$ 2.19	$ 1.99
Amounts attributable to common shareowners:
Income from continuing operations, net of tax	$ 557.2	$ 512.1	$ 455.9
Income from discontinued operations, net of tax	0.0	0.0	1.4
Net income	557.2	512.1	457.3
IPL [Member]
Revenues:
Electric utility	1,781.2	1,731.1	1,598.9
Gas utility	264.2	266.2	226.0
Other utility	44.2	45.0	45.4
Total revenues	2,089.6	2,042.3	1,870.3
Operating expenses:
Electric production fuel and purchased power	434.5	469.0	443.6
Electric transmission service	340.2	352.9	310.4
Cost of gas sold	119.9	129.6	115.6
Other operation and maintenance	404.6	402.6	396.6
Depreciation and amortization	326.7	283.5	245.0
Taxes other than income taxes	60.9	53.9	55.0
Total operating expenses	1,686.8	1,691.5	1,566.2
Operating income (loss)	402.8	350.8	304.1
Other (income) and deductions:
Interest expense	126.9	119.4	112.4
Allowance for funds used during construction	(49.4)	(42.2)	(31.4)
Other	6.9	2.6	7.0
Total other (income) and deductions	84.4	79.8	88.0
Income from continuing operations before income taxes	318.4	271.0	216.1
Income tax expense (benefit)	24.1	(3.2)	(10.9)
Net income	294.3	274.2	227.0
Preferred dividend requirements of Interstate Power and Light Company	10.2	10.2	10.2
Net income attributable to common shareowners	284.1	264.0	216.8
Amounts attributable to common shareowners:
Net income	284.1	264.0	216.8
WPL [Member]
Revenues:
Electric utility	1,282.4	1,269.2	1,295.8
Gas utility	191.0	180.4	174.9
Other utility	2.3	3.0	2.1
Total revenues	1,475.7	1,452.6	1,472.8
Operating expenses:
Electric production fuel and purchased power	342.2	386.0	374.5
Electric transmission service	141.2	142.8	170.5
Cost of gas sold	101.8	102.7	95.8
Other operation and maintenance	260.9	241.6	238.5
Depreciation and amortization	235.6	219.4	212.9
Taxes other than income taxes	46.8	47.2	46.9
Total operating expenses	1,128.5	1,139.7	1,139.1
Operating income (loss)	347.2	312.9	333.7
Other (income) and deductions:
Interest expense	102.2	97.8	93.8
Allowance for funds used during construction	(43.3)	(33.4)	(18.3)
Other	6.0	4.2	9.7
Total other (income) and deductions	64.9	68.6	85.2
Income from continuing operations before income taxes	282.3	244.3	248.5
Income tax expense (benefit)	49.3	36.2	61.9
Net income	$ 233.0	$ 208.1	$ 186.6