Condensed Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Operating revenues:
Electric utility		$ 677.6	$ 668.9
Gas utility		154.3	152.2
Other utility		11.7	13.2
Non-regulated		10.3	9.5
Total operating revenues		853.9	843.8
Operating expenses:
Electric production fuel and purchased power		207.8	200.9
Electric transmission service		124.7	127.9
Cost of gas sold		92.2	95.2
Other operation and maintenance		152.9	145.1
Depreciation and amortization		107.0	102.5
Taxes other than income taxes		26.4	26.3
Total operating expenses		711.0	697.9
Operating income		142.9	145.9
Interest expense and other:
Interest expense		52.3	48.0
Equity income from unconsolidated investments, net		(11.5)	(10.5)
Allowance for funds used during construction		(17.0)	(13.2)
Interest income and other		(0.1)	(0.2)
Total interest expense and other		23.7	24.1
Income from continuing operations before income taxes		119.2	121.8
Income tax expense (benefit)		17.6	21.6
Income from continuing operations, net of tax		101.6	100.2
Income (loss) from discontinued operations, net of tax		1.4	(1.1)
Net income		103.0	99.1
Preferred dividend requirements of Interstate Power and Light Company		2.6	2.6
Net income attributable to common shareowners		$ 100.4	$ 96.5
Weighted average number of common shares outstanding (basic and diluted) (in shares)	[1]	227.6	226.8
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]	$ 0.43	$ 0.43
Income from discontinued operations, net of tax (in dollars per share)	[1]	0.01	0.00
Net income (in dollars per share)	[1]	$ 0.44	$ 0.43
Amounts attributable to common shareowners:
Income from continuing operations, net of tax		$ 99.0	$ 97.6
Income (loss) from discontinued operations, net of tax		1.4	(1.1)
Net income attributable to common shareowners		$ 100.4	$ 96.5
Dividends declared per common share (in dollars per share)	[1]	$ 0.315	$ 0.29375
IPL [Member]
Operating revenues:
Electric utility		$ 356.2	$ 361.6
Gas utility		83.1	84.2
Other utility		11.2	12.9
Total operating revenues		450.5	458.7
Operating expenses:
Electric production fuel and purchased power		109.5	99.4
Electric transmission service		81.7	86.5
Cost of gas sold		47.8	52.4
Other operation and maintenance		94.9	92.0
Depreciation and amortization		53.6	52.7
Taxes other than income taxes		13.4	13.7
Total operating expenses		400.9	396.7
Operating income		49.6	62.0
Interest expense and other:
Interest expense		27.7	24.9
Allowance for funds used during construction		(14.3)	(10.3)
Interest income and other		0.1	0.0
Total interest expense and other		13.5	14.6
Income from continuing operations before income taxes		36.1	47.4
Income tax expense (benefit)		(3.7)	(0.8)
Net income		39.8	48.2
Preferred dividend requirements of Interstate Power and Light Company		2.6	2.6
Net income attributable to common shareowners		37.2	45.6
Amounts attributable to common shareowners:
Net income attributable to common shareowners		37.2	45.6
WPL [Member]
Operating revenues:
Electric utility		321.4	307.3
Gas utility		71.2	68.0
Other utility		0.5	0.3
Total operating revenues		393.1	375.6
Operating expenses:
Electric production fuel and purchased power		98.3	101.5
Electric transmission service		43.0	41.4
Cost of gas sold		44.4	42.8
Other operation and maintenance		57.0	52.1
Depreciation and amortization		52.4	47.4
Taxes other than income taxes		12.0	11.6
Total operating expenses		307.1	296.8
Operating income		86.0	78.8
Interest expense and other:
Interest expense		22.9	22.9
Equity income from unconsolidated investments, net		0.0	(10.7)
Allowance for funds used during construction		(2.7)	(2.9)
Interest income and other		(0.1)	(0.1)
Total interest expense and other		20.1	9.2
Income from continuing operations before income taxes		65.9	69.6
Income tax expense (benefit)		20.4	22.6
Net income		45.5	47.0
Net income attributable to noncontrolling interest		0.0	0.5
Net income attributable to common shareowners		45.5	46.5
Amounts attributable to common shareowners:
Net income attributable to common shareowners		$ 45.5	$ 46.5

[1] Amounts reflect the effects of a two-for-one common stock split distributed in May 2016.