Condensed Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Revenues:
Electric utility	$ 691.2	$ 726.3	$ 1,434.6	$ 1,435.0
Gas utility	65.2	68.6	281.0	254.2
Other utility	10.9	10.7	22.0	23.9
Non-utility	22.9	10.5	39.8	19.3
Total revenues	790.2	816.1	1,777.4	1,732.4
Operating expenses:
Electric production fuel and purchased power	164.8	208.5	383.2	411.7
Electric transmission service	112.4	119.7	235.4	246.1
Cost of gas sold	20.4	27.5	142.0	138.7
Other operation and maintenance	172.3	158.0	353.5	320.4
Depreciation and amortization	142.9	127.0	279.8	247.4
Taxes other than income taxes	27.6	24.2	56.9	51.2
Total operating expenses	640.4	664.9	1,450.8	1,415.5
Operating income	149.8	151.2	326.6	316.9
Other (income) and deductions:
Interest expense	69.2	61.3	135.5	120.5
Equity income from unconsolidated investments, net	(12.7)	(10.5)	(23.6)	(31.8)
Allowance for funds used during construction	(18.3)	(18.1)	(43.7)	(33.0)
Other	3.3	2.0	7.3	4.4
Total other (income) and deductions	41.5	34.7	75.5	60.1
Income before income taxes	108.3	116.5	251.1	256.8
Income taxes	11.2	13.6	26.3	30.4
Net income	97.1	102.9	224.8	226.4
Preferred dividend requirements of Interstate Power and Light Company	2.5	2.5	5.1	5.1
Net income attributable to common shareowners	$ 94.6	$ 100.4	$ 219.7	$ 221.3
Weighted average number of common shares outstanding (basic) (in shares)	237.5	232.0	237.0	231.7
Weighted average number of common shares outstanding (diluted) (in shares)	238.1	232.0	237.3	231.7
Earnings per weighted average common share attributable to Alliant Energy common shareowners (basic and diluted) (in dollars per share)	$ 0.40	$ 0.43	$ 0.93	$ 0.96
IPL [Member]
Revenues:
Electric utility	$ 392.3	$ 422.1	$ 812.1	$ 827.8
Gas utility	38.4	42.2	163.0	150.3
Other utility	10.5	10.5	21.2	22.5
Total revenues	441.2	474.8	996.3	1,000.6
Operating expenses:
Electric production fuel and purchased power	83.3	116.9	212.2	231.5
Electric transmission service	77.4	84.4	165.1	175.2
Cost of gas sold	10.8	16.8	74.1	77.4
Other operation and maintenance	97.4	97.0	205.4	202.5
Depreciation and amortization	82.6	70.5	159.7	135.3
Taxes other than income taxes	15.2	11.5	31.8	25.4
Total operating expenses	366.7	397.1	848.3	847.3
Operating income	74.5	77.7	148.0	153.3
Other (income) and deductions:
Interest expense	31.5	30.4	60.9	60.2
Allowance for funds used during construction	(7.9)	(9.9)	(23.7)	(17.3)
Other	1.5	0.7	3.4	1.5
Total other (income) and deductions	25.1	21.2	40.6	44.4
Income before income taxes	49.4	56.5	107.4	108.9
Income taxes	1.9	2.3	4.0	5.4
Net income	47.5	54.2	103.4	103.5
Preferred dividend requirements of Interstate Power and Light Company	2.5	2.5	5.1	5.1
Net income attributable to common shareowners	45.0	51.7	98.3	98.4
WPL [Member]
Revenues:
Electric utility	298.9	304.2	622.5	607.2
Gas utility	26.8	26.4	118.0	103.9
Other utility	0.4	0.2	0.8	1.4
Total revenues	326.1	330.8	741.3	712.5
Operating expenses:
Electric production fuel and purchased power	81.5	91.6	171.0	180.2
Electric transmission service	35.0	35.3	70.3	70.9
Cost of gas sold	9.6	10.7	67.9	61.3
Other operation and maintenance	62.4	62.3	125.9	118.6
Depreciation and amortization	59.1	55.5	117.7	110.1
Taxes other than income taxes	11.5	12.0	23.4	24.0
Total operating expenses	259.1	267.4	576.2	565.1
Operating income	67.0	63.4	165.1	147.4
Other (income) and deductions:
Interest expense	26.1	24.6	51.9	49.3
Allowance for funds used during construction	(10.4)	(8.2)	(20.0)	(15.7)
Other	1.6	1.0	3.2	2.1
Total other (income) and deductions	17.3	17.4	35.1	35.7
Income before income taxes	49.7	46.0	130.0	111.7
Income taxes	7.7	6.2	22.3	17.9
Net income			107.7	93.8
Net income attributable to common shareowners	$ 42.0	$ 39.8	$ 107.7	$ 93.8