Condensed Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenues:
Electric utility	$ 675.2	$ 691.2	$ 1,405.5	$ 1,434.6
Gas utility	58.9	65.2	211.1	281.0
Other utility	10.1	10.9	21.7	22.0
Non-utility	18.9	22.9	40.5	39.8
Total revenues	763.1	790.2	1,678.8	1,777.4
Operating expenses:
Electric production fuel and purchased power	163.5	164.8	347.6	383.2
Electric transmission service	71.6	112.4	193.8	235.4
Cost of gas sold	20.9	20.4	105.9	142.0
Other operation and maintenance	159.8	172.3	322.0	353.5
Depreciation and amortization	152.1	142.9	298.4	279.8
Taxes other than income taxes	27.1	27.6	54.7	56.9
Total operating expenses	595.0	640.4	1,322.4	1,450.8
Operating income	168.1	149.8	356.4	326.6
Other (income) and deductions:
Interest expense	69.6	69.2	138.5	135.5
Equity income from unconsolidated investments, net	(17.4)	(12.7)	(30.8)	(23.6)
Allowance for funds used during construction	(15.2)	(18.3)	(38.2)	(43.7)
Other	2.5	3.3	4.4	7.3
Total other (income) and deductions	39.5	41.5	73.9	75.5
Income before income taxes	128.6	108.3	282.5	251.1
Income tax expense (benefit)	(8.3)	11.2	(27.0)	26.3
Net income	136.9	97.1	309.5	224.8
Preferred dividend requirements of Interstate Power and Light Company	2.5	2.5	5.1	5.1
Net income attributable to common shareowners	$ 134.4	$ 94.6	$ 304.4	$ 219.7
Weighted average number of common shares outstanding:
Basic (in shares)	249.6	237.5	247.0	237.0
Diluted (in shares)	249.8	238.1	247.2	237.3
Earnings per weighted average common share attributable to Alliant Energy common shareowners (basic and diluted) (in dollars per share)	$ 0.54	$ 0.40	$ 1.23	$ 0.93
IPL [Member]
Revenues:
Electric utility	$ 388.4	$ 392.3	$ 813.2	$ 812.1
Gas utility	33.9	38.4	116.9	163.0
Other utility	9.6	10.5	20.7	21.2
Total revenues	431.9	441.2	950.8	996.3
Operating expenses:
Electric production fuel and purchased power	96.0	83.3	202.2	212.2
Electric transmission service	34.0	77.4	118.5	165.1
Cost of gas sold	12.4	10.8	56.6	74.1
Other operation and maintenance	97.5	97.4	184.1	205.4
Depreciation and amortization	88.7	82.6	174.6	159.7
Taxes other than income taxes	14.6	15.2	29.4	31.8
Total operating expenses	343.2	366.7	765.4	848.3
Operating income	88.7	74.5	185.4	148.0
Other (income) and deductions:
Interest expense	34.8	31.5	69.3	60.9
Allowance for funds used during construction	(5.6)	(7.9)	(15.4)	(23.7)
Other	1.0	1.5	1.9	3.4
Total other (income) and deductions	30.2	25.1	55.8	40.6
Income before income taxes	58.5	49.4	129.6	107.4
Income tax expense (benefit)	(3.8)	1.9	(17.9)	4.0
Net income	62.3	47.5	147.5	103.4
Preferred dividend requirements of Interstate Power and Light Company	2.5	2.5	5.1	5.1
Net income attributable to common shareowners	59.8	45.0	142.4	98.3
WPL [Member]
Revenues:
Electric utility	286.8	298.9	592.3	622.5
Gas utility	25.0	26.8	94.2	118.0
Other utility	0.5	0.4	1.0	0.8
Total revenues	312.3	326.1	687.5	741.3
Operating expenses:
Electric production fuel and purchased power	67.5	81.5	145.4	171.0
Electric transmission service	37.6	35.0	75.3	70.3
Cost of gas sold	8.5	9.6	49.3	67.9
Other operation and maintenance	53.2	62.4	107.4	125.9
Depreciation and amortization	62.0	59.1	121.1	117.7
Taxes other than income taxes	11.8	11.5	23.5	23.4
Total operating expenses	240.6	259.1	522.0	576.2
Operating income	71.7	67.0	165.5	165.1
Other (income) and deductions:
Interest expense	27.3	26.1	52.4	51.9
Allowance for funds used during construction	(9.5)	(10.4)	(22.7)	(20.0)
Other	0.8	1.6	1.3	3.2
Total other (income) and deductions	18.6	17.3	31.0	35.1
Income before income taxes	53.1	49.7	134.5	130.0
Income tax expense (benefit)	(4.5)	7.7	(12.7)	22.3
Net income	$ 57.6	$ 42.0	$ 147.2	$ 107.7