Condensed Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Operating revenues:
Electric utility	$ 840.6	$ 864.3	$ 2,199.1	$ 2,209.1
Gas utility	45.8	39.5	262.7	248.7
Other utility	11.2	9.4	34.4	35.0
Non-regulated	9.3	11.4	29.9	30.2
Total operating revenues	906.9	924.6	2,526.1	2,523.0
Operating expenses:
Electric production fuel and purchased power	222.6	245.9	614.7	646.3
Electric transmission service	121.0	138.6	363.3	396.8
Cost of gas sold	15.0	12.5	135.5	132.3
Asset valuation charges for Franklin County wind farm	0.0	86.4	0.0	86.4
Other operation and maintenance	169.1	148.6	467.1	438.2
Depreciation and amortization	120.7	104.1	342.7	308.7
Taxes other than income taxes	27.0	25.9	79.1	77.2
Total operating expenses	675.4	762.0	2,002.4	2,085.9
Operating income	231.5	162.6	523.7	437.1
Interest expense and other:
Interest expense	53.9	48.8	159.0	144.8
Equity income from unconsolidated investments, net	(10.1)	(9.2)	(32.9)	(28.8)
Allowance for funds used during construction	(9.6)	(15.8)	(36.7)	(44.3)
Interest income and other	(0.2)	(0.1)	(0.4)	(0.3)
Total interest expense and other	34.0	23.7	89.0	71.4
Income from continuing operations before income taxes	197.5	138.9	434.7	365.7
Income tax expense (benefit)	26.1	7.5	64.9	47.2
Income from continuing operations, net of tax	171.4	131.4	369.8	318.5
Income (loss) from discontinued operations, net of tax	0.0	(0.4)	1.4	(2.0)
Net income	171.4	131.0	371.2	316.5
Preferred dividend requirements of Interstate Power and Light Company	2.6	2.6	7.7	7.7
Net income attributable to common shareowners	$ 168.8	$ 128.4	$ 363.5	$ 308.8
Weighted average number of common shares outstanding (basic and diluted) (in shares)	231.0	227.2	229.2	227.0
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)	$ 0.73	$ 0.57	$ 1.58	$ 1.37
Income (loss) from discontinued operations, net of tax (basic and diluted) (in dollars per share)	0.00	0.00	0.01	(0.01)
Earnings per weighted average common share attributable to Alliant Energy common shareowners (basic and diluted) (in dollars per share)	$ 0.73	$ 0.57	$ 1.59	$ 1.36
Amounts attributable to common shareowners:
Income from continuing operations, net of tax	$ 168.8	$ 128.8	$ 362.1	$ 310.8
Income (loss) from discontinued operations, net of tax	0.0	(0.4)	1.4	(2.0)
Net income attributable to common shareowners	$ 168.8	$ 128.4	$ 363.5	$ 308.8
Dividends declared per common share (in dollars per share)	$ 0.315	$ 0.29375	$ 0.945	$ 0.88125
IPL [Member]
Operating revenues:
Electric utility	$ 489.0	$ 483.2	$ 1,217.6	$ 1,209.2
Gas utility	27.4	23.9	147.2	142.6
Other utility	11.0	9.1	33.3	34.1
Total operating revenues	527.4	516.2	1,398.1	1,385.9
Operating expenses:
Electric production fuel and purchased power	122.5	125.0	330.0	324.8
Electric transmission service	78.2	95.9	235.0	270.7
Cost of gas sold	9.9	8.0	74.6	76.3
Other operation and maintenance	104.4	94.8	288.7	279.8
Depreciation and amortization	66.2	52.7	181.0	157.8
Taxes other than income taxes	14.4	13.9	41.1	40.6
Total operating expenses	395.6	390.3	1,150.4	1,150.0
Operating income	131.8	125.9	247.7	235.9
Interest expense and other:
Interest expense	27.9	25.5	83.5	75.4
Allowance for funds used during construction	(4.7)	(13.8)	(25.1)	(36.2)
Interest income and other	(0.1)	0.0	(0.2)	(0.1)
Total interest expense and other	23.1	11.7	58.2	39.1
Income from continuing operations before income taxes	108.7	114.2	189.5	196.8
Income tax expense (benefit)	(14.3)	(2.5)	(18.6)	(2.5)
Net income	123.0	116.7	208.1	199.3
Preferred dividend requirements of Interstate Power and Light Company	2.6	2.6	7.7	7.7
Net income attributable to common shareowners	120.4	114.1	200.4	191.6
Amounts attributable to common shareowners:
Net income attributable to common shareowners	120.4	114.1	200.4	191.6
WPL [Member]
Operating revenues:
Electric utility	351.6	381.1	981.5	999.9
Gas utility	18.4	15.6	115.5	106.1
Other utility	0.2	0.3	1.1	0.9
Total operating revenues	370.2	397.0	1,098.1	1,106.9
Operating expenses:
Electric production fuel and purchased power	100.1	120.9	284.7	321.5
Electric transmission service	42.8	42.7	128.3	126.1
Cost of gas sold	5.1	4.5	60.9	56.0
Other operation and maintenance	66.1	54.2	179.7	157.2
Depreciation and amortization	53.6	48.7	158.8	143.5
Taxes other than income taxes	11.8	11.0	35.3	33.8
Total operating expenses	279.5	282.0	847.7	838.1
Operating income	90.7	115.0	250.4	268.8
Interest expense and other:
Interest expense	23.1	22.9	69.1	68.7
Equity income from unconsolidated investments, net	(0.2)	(9.3)	(0.4)	(29.0)
Allowance for funds used during construction	(4.9)	(2.0)	(11.6)	(8.1)
Interest income and other	(0.1)	0.1	(0.2)	(0.2)
Total interest expense and other	17.9	11.7	56.9	31.4
Income from continuing operations before income taxes	72.8	103.3	193.5	237.4
Income tax expense (benefit)	23.0	33.7	60.1	77.1
Net income	49.8	69.6	133.4	160.3
Net income attributable to noncontrolling interest	0.0	0.6	0.0	1.6
Net income attributable to common shareowners	49.8	69.0	133.4	158.7
Amounts attributable to common shareowners:
Net income attributable to common shareowners	$ 49.8	$ 69.0	$ 133.4	$ 158.7