Condensed Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Operating revenues:
Electric utility	$ 668.9	$ 671.3
Gas utility	152.2	198.4
Other utility	13.2	16.4
Non-regulated	9.5	11.3
Total operating revenues	843.8	897.4
Operating expenses:
Electric production fuel and purchased power	200.9	215.9
Electric transmission service	127.9	123.2
Cost of gas sold	95.2	130.8
Other operation and maintenance	145.1	147.9
Depreciation and amortization	102.5	100.2
Taxes other than income taxes	26.3	26.5
Total operating expenses	697.9	744.5
Operating income	145.9	152.9
Interest expense and other:
Interest expense	48.0	46.6
Equity income from unconsolidated investments, net	(10.5)	(6.5)
Allowance for funds used during construction	(13.2)	(6.8)
Interest income and other	(0.2)	(0.1)
Total interest expense and other	24.1	33.2
Income from continuing operations before income taxes	121.8	119.7
Income tax expense (benefit)	21.6	20.5
Income from continuing operations, net of tax	100.2	99.2
Loss from discontinued operations, net of tax	(1.1)	0.0
Net income	99.1	99.2
Preferred dividend requirements of Interstate Power and Light Company	2.6	2.6
Net income (loss) attributable to common shareowners	$ 96.5	$ 96.6
Weighted average number of common shares outstanding (basic and diluted) (in shares)	113.4	111.1
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)	$ 0.86	$ 0.87
Loss from discontinued operations, net of tax (in dollars per share)	(0.01)	0.00
Net income (in dollars per share)	$ 0.85	$ 0.87
Amounts attributable to common shareowners:
Income from continuing operations, net of tax	$ 97.6	$ 96.6
Loss from discontinued operations, net of tax	(1.1)	0.0
Net income (loss) attributable to common shareowners	$ 96.5	$ 96.6
Dividends declared per common share (in dollars per share)	$ 0.5875	$ 0.55
IPL [Member]
Operating revenues:
Electric utility	$ 361.6	$ 362.6
Gas utility	84.2	111.2
Other utility	12.9	15.2
Total operating revenues	458.7	489.0
Operating expenses:
Electric production fuel and purchased power	99.4	110.1
Electric transmission service	86.5	83.9
Cost of gas sold	52.4	71.0
Other operation and maintenance	92.0	92.6
Depreciation and amortization	52.7	51.8
Taxes other than income taxes	13.7	14.1
Total operating expenses	396.7	423.5
Operating income	62.0	65.5
Interest expense and other:
Interest expense	24.9	24.1
Allowance for funds used during construction	(10.3)	(5.3)
Interest income and other	0.0	(0.1)
Total interest expense and other	14.6	18.7
Income from continuing operations before income taxes	47.4	46.8
Income tax expense (benefit)	(0.8)	(3.3)
Net income	48.2	50.1
Preferred dividend requirements of Interstate Power and Light Company	2.6	2.6
Net income (loss) attributable to common shareowners	45.6	47.5
Amounts attributable to common shareowners:
Net income (loss) attributable to common shareowners	45.6	47.5
WPL [Member]
Operating revenues:
Electric utility	307.3	308.7
Gas utility	68.0	87.2
Other utility	0.3	1.2
Total operating revenues	375.6	397.1
Operating expenses:
Electric production fuel and purchased power	101.5	105.8
Electric transmission service	41.4	39.3
Cost of gas sold	42.8	59.8
Other operation and maintenance	52.1	54.0
Depreciation and amortization	47.4	46.0
Taxes other than income taxes	11.6	11.4
Total operating expenses	296.8	316.3
Operating income	78.8	80.8
Interest expense and other:
Interest expense	22.9	23.1
Equity income from unconsolidated investments, net	(10.7)	(7.8)
Allowance for funds used during construction	(2.9)	(1.5)
Interest income and other	(0.1)	0.1
Total interest expense and other	9.2	13.9
Income from continuing operations before income taxes	69.6	66.9
Income tax expense (benefit)	22.6	21.8
Net income	47.0	45.1
Net income attributable to noncontrolling interest	0.5	0.2
Net income (loss) attributable to common shareowners	46.5	44.9
Amounts attributable to common shareowners:
Net income (loss) attributable to common shareowners	$ 46.5	$ 44.9