Condensed Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Utility:
Electric	$ 835.8	$ 771.2	$ 2,147.5	$ 2,090.9
Gas	38.0	47.2	288.1	364.8
Other	13.4	12.2	44.6	50.6
Non-regulated	11.7	12.5	33.3	39.9
Total operating revenues	898.9	843.1	2,513.5	2,546.2
Operating expenses:
Electric production fuel and purchased power	245.8	230.8	646.9	683.6
Electric transmission service	127.6	114.0	367.7	333.6
Cost of gas sold	13.6	21.8	166.3	228.7
Other operation and maintenance	151.1	159.0	456.3	483.8
Depreciation and amortization	99.3	97.1	299.9	288.4
Taxes other than income taxes	25.6	25.6	78.6	75.8
Total operating expenses	663.0	648.3	2,015.7	2,093.9
Operating income	235.9	194.8	497.8	452.3
Interest expense and other:
Interest expense	46.4	44.6	139.5	134.9
Equity income from unconsolidated investments, net	(11.1)	(11.5)	(28.9)	(34.2)
Allowance for funds used during construction	(9.7)	(8.3)	(25.1)	(25.8)
Interest income and other	(0.1)	(0.2)	(0.4)	(1.8)
Total interest expense and other	25.5	24.6	85.1	73.1
Income from continuing operations before income taxes	210.4	170.2	412.7	379.2
Income tax expense (benefit)	27.8	12.4	59.5	46.2
Income from continuing operations, net of tax	182.6	157.8	353.2	333.0
Loss from discontinued operations, net of tax	(0.1)	(1.9)	(1.4)	(2.2)
Net income (loss)	182.5	155.9	351.8	330.8
Preferred dividend requirements of Interstate Power and Light Company	2.6	2.6	7.7	7.7
Net income (loss) attributable to common shareowners	$ 179.9	$ 153.3	$ 344.1	$ 323.1
Weighted average number of common shares outstanding (basic and diluted) (in shares)	113.2	110.8	112.5	110.8
Earnings per weighted average common share attributable to Alliant Energy common shareowners (basic and diluted):
Income from continuing operations, net of tax (in dollars per share)	$ 1.59	$ 1.40	$ 3.07	$ 2.94
Loss from discontinued operations, net of tax (in dollars per share)	0.00	(0.02)	(0.01)	(0.02)
Net income (in dollars per share)	$ 1.59	$ 1.38	$ 3.06	$ 2.92
Amounts attributable to common shareowners:
Income from continuing operations, net of tax	$ 180.0	$ 155.2	$ 345.5	$ 325.3
Loss from discontinued operations, net of tax	(0.1)	(1.9)	(1.4)	(2.2)
Net income (loss) attributable to common shareowners	$ 179.9	$ 153.3	$ 344.1	$ 323.1
Dividends declared per common share (in dollars per share)	$ 0.55	$ 0.51	$ 1.65	$ 1.53
IPL [Member]
Utility:
Electric	$ 468.6	$ 435.9	$ 1,170.6	$ 1,164.7
Gas	23.1	28.7	164.1	208.1
Other	12.9	11.6	41.1	44.2
Total operating revenues	504.6	476.2	1,375.8	1,417.0
Operating expenses:
Electric production fuel and purchased power	131.4	132.2	332.0	395.1
Electric transmission service	87.5	82.7	249.3	241.7
Cost of gas sold	9.4	14.6	93.4	128.4
Other operation and maintenance	94.3	89.8	287.5	279.1
Depreciation and amortization	51.2	49.3	155.1	146.9
Taxes other than income taxes	13.8	13.7	42.2	40.4
Total operating expenses	387.6	382.3	1,159.5	1,231.6
Operating income	117.0	93.9	216.3	185.4
Interest expense and other:
Interest expense	23.8	21.9	71.8	67.0
Allowance for funds used during construction	(7.3)	(6.6)	(19.3)	(18.6)
Interest income and other	0.1	0.0	0.0	(0.1)
Total interest expense and other	16.6	15.3	52.5	48.3
Income from continuing operations before income taxes	100.4	78.6	163.8	137.1
Income tax expense (benefit)	(19.6)	(26.5)	(25.8)	(34.9)
Net income (loss)	120.0	105.1	189.6	172.0
Preferred dividend requirements of Interstate Power and Light Company	2.6	2.6	7.7	7.7
Net income (loss) attributable to common shareowners	117.4	102.5	181.9	164.3
Amounts attributable to common shareowners:
Net income (loss) attributable to common shareowners	117.4	102.5	181.9	164.3
WPL [Member]
Utility:
Electric	367.2	335.3	976.9	926.2
Gas	14.9	18.5	124.0	156.7
Other	0.5	0.6	3.5	6.4
Total operating revenues	382.6	354.4	1,104.4	1,089.3
Operating expenses:
Electric production fuel and purchased power	114.4	98.6	314.9	288.5
Electric transmission service	40.1	31.3	118.4	91.9
Cost of gas sold	4.2	7.2	72.9	100.3
Other operation and maintenance	57.0	66.9	167.7	199.3
Depreciation and amortization	45.7	45.6	137.5	135.0
Taxes other than income taxes	10.9	10.9	33.6	32.7
Total operating expenses	272.3	260.5	845.0	847.7
Operating income	110.3	93.9	259.4	241.6
Interest expense and other:
Interest expense	23.1	21.0	69.5	63.2
Equity income from unconsolidated investments, net	(11.1)	(11.4)	(30.2)	(34.2)
Allowance for funds used during construction	(2.4)	(1.7)	(5.8)	(7.2)
Interest income and other	(0.3)	0.5	(0.3)	0.8
Total interest expense and other	9.3	8.4	33.2	22.6
Income from continuing operations before income taxes	101.0	85.5	226.2	219.0
Income tax expense (benefit)	33.1	23.9	74.0	68.0
Net income (loss)	67.9	61.6	152.2	151.0
Net income attributable to noncontrolling interest	0.4	0.0	1.1	0.0
Net income (loss) attributable to common shareowners	67.5	61.6	151.1	151.0
Amounts attributable to common shareowners:
Net income (loss) attributable to common shareowners	$ 67.5	$ 61.6	$ 151.1	$ 151.0