Condensed Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenues:
Electric utility	$ 861.2	$ 840.6	$ 2,296.2	$ 2,199.1
Gas utility	44.8	45.8	299.0	262.7
Other utility	12.3	11.2	36.2	34.4
Non-utility	10.3	9.3	29.6	29.9
Total revenues	928.6	906.9	2,661.0	2,526.1
Operating expenses:
Electric production fuel and purchased power	227.8	222.6	639.5	614.7
Electric transmission service	129.1	121.0	375.2	363.3
Cost of gas sold	11.3	15.0	150.0	135.5
Other operation and maintenance	148.4	164.3	468.8	453.6
Depreciation and amortization	129.0	120.7	376.4	342.7
Taxes other than income taxes	26.9	27.0	78.1	79.1
Total operating expenses	672.5	670.6	2,088.0	1,988.9
Operating income	256.1	236.3	573.0	537.2
Other (income) and deductions:
Interest expense	63.3	53.9	183.8	159.0
Equity income from unconsolidated investments, net	(9.8)	(10.1)	(41.6)	(32.9)
Allowance for funds used during construction	(18.8)	(9.6)	(51.8)	(36.7)
Other	1.6	4.6	6.0	13.1
Total other (income) and deductions	36.3	38.8	96.4	102.5
Income from continuing operations before income taxes	219.8	197.5	476.6	434.7
Income tax expense (benefit)	11.7	26.1	42.1	64.9
Income from continuing operations, net of tax	208.1	171.4	434.5	369.8
Income from discontinued operations, net of tax	0.0	0.0	0.0	1.4
Net income	208.1	171.4	434.5	371.2
Preferred dividend requirements of Interstate Power and Light Company	2.6	2.6	7.7	7.7
Net income attributable to common shareowners	$ 205.5	$ 168.8	$ 426.8	$ 363.5
Weighted average number of common shares outstanding (basic and diluted) (in shares)	235.2	231.0	232.9	229.2
Earnings per weighted average common share attributable to Alliant Energy common shareowners (basic and diluted):
Income from continuing operations, net of tax (basic and diluted) (in dollars per share)	$ 0.87	$ 0.73	$ 1.83	$ 1.58
Income from discontinued operations, net of tax (basic and diluted) (in dollars per share)	0.00	0.00	0.00	0.01
Earnings per weighted average common share attributable to Alliant Energy common shareowners (basic and diluted) (in dollars per share)	$ 0.87	$ 0.73	$ 1.83	$ 1.59
Amounts attributable to common shareowners:
Income from continuing operations, net of tax	$ 205.5	$ 168.8	$ 426.8	$ 362.1
Income from discontinued operations, net of tax	0.0	0.0	0.0	1.4
Net income attributable to common shareowners	205.5	168.8	426.8	363.5
IPL [Member]
Revenues:
Electric utility	509.2	489.0	1,337.0	1,217.6
Gas utility	26.7	27.4	177.0	147.2
Other utility	11.7	11.0	34.2	33.3
Total revenues	547.6	527.4	1,548.2	1,398.1
Operating expenses:
Electric production fuel and purchased power	122.5	122.5	354.0	330.0
Electric transmission service	92.8	78.2	268.0	235.0
Cost of gas sold	6.4	9.9	83.8	74.6
Other operation and maintenance	94.6	102.4	297.1	283.2
Depreciation and amortization	73.9	66.2	209.2	181.0
Taxes other than income taxes	14.3	14.4	39.7	41.1
Total operating expenses	404.5	393.6	1,251.8	1,144.9
Operating income	143.1	133.8	296.4	253.2
Other (income) and deductions:
Interest expense	30.4	27.9	90.6	83.5
Allowance for funds used during construction	(11.0)	(4.7)	(28.3)	(25.1)
Other	0.5	1.9	2.0	5.3
Total other (income) and deductions	19.9	25.1	64.3	63.7
Income from continuing operations before income taxes	123.2	108.7	232.1	189.5
Income tax expense (benefit)	(5.9)	(14.3)	(0.5)	(18.6)
Net income	129.1	123.0	232.6	208.1
Preferred dividend requirements of Interstate Power and Light Company	2.6	2.6	7.7	7.7
Net income attributable to common shareowners	126.5	120.4	224.9	200.4
Amounts attributable to common shareowners:
Net income attributable to common shareowners	126.5	120.4	224.9	200.4
WPL [Member]
Revenues:
Electric utility	352.0	351.6	959.2	981.5
Gas utility	18.1	18.4	122.0	115.5
Other utility	0.6	0.2	2.0	1.1
Total revenues	370.7	370.2	1,083.2	1,098.1
Operating expenses:
Electric production fuel and purchased power	105.3	100.1	285.5	284.7
Electric transmission service	36.3	42.8	107.2	128.3
Cost of gas sold	4.9	5.1	66.2	60.9
Other operation and maintenance	54.2	63.3	172.8	171.8
Depreciation and amortization	54.1	53.6	164.2	158.8
Taxes other than income taxes	11.7	11.8	35.7	35.3
Total operating expenses	266.5	276.7	831.6	839.8
Operating income	104.2	93.5	251.6	258.3
Other (income) and deductions:
Interest expense	24.2	23.1	73.5	69.1
Allowance for funds used during construction	(7.8)	(4.9)	(23.5)	(11.6)
Other	1.3	2.5	3.4	7.3
Total other (income) and deductions	17.7	20.7	53.4	64.8
Income from continuing operations before income taxes	86.5	72.8	198.2	193.5
Income tax expense (benefit)	10.2	23.0	28.1	60.1
Net income			170.1	133.4
Net income attributable to common shareowners	76.3	49.8	170.1	133.4
Amounts attributable to common shareowners:
Net income attributable to common shareowners	$ 76.3	$ 49.8	$ 170.1	$ 133.4