Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating revenues:
Electric utility		$ 2,875.5	$ 2,770.5	$ 2,713.6
Gas utility		355.4	381.2	517.5
Other utility		48.6	57.9	66.1
Non-regulated		40.5	44.0	53.1
Total operating revenues		3,320.0	3,253.6	3,350.3
Operating expenses:
Electric production fuel and purchased power		854.0	837.7	877.2
Electric transmission service		527.9	485.3	447.5
Cost of gas sold		194.3	219.1	327.8
Asset valuation charges for Franklin County wind farm		86.4	0.0	0.0
Other operation and maintenance		606.5	629.5	665.0
Depreciation and amortization		411.6	401.3	388.1
Taxes other than income taxes		102.3	103.7	101.1
Total operating expenses		2,783.0	2,676.6	2,806.7
Operating income (loss)		537.0	577.0	543.6
Interest expense and other:
Interest expense		196.2	187.1	180.6
Equity (income) loss from unconsolidated investments, net		(39.6)	(33.8)	(40.4)
Allowance for funds used during construction		(62.5)	(36.9)	(34.8)
Interest income and other		(0.5)	(0.7)	(1.8)
Total interest expense and other		93.6	115.7	103.6
Income from continuing operations before income taxes		443.4	461.3	440.0
Income tax expense (benefit)		59.4	70.4	44.3
Income from continuing operations, net of tax		384.0	390.9	395.7
Loss from discontinued operations, net of tax		(2.3)	(2.5)	(2.4)
Net income		381.7	388.4	393.3
Preferred dividend requirements of Interstate Power and Light Company		10.2	10.2	10.2
Net income attributable to common shareowners		$ 371.5	$ 378.2	$ 383.1
Weighted average number of common shares outstanding (basic and diluted) (in shares)	[1]	227.1	225.4	221.7
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]	$ 1.65	$ 1.69	$ 1.74
Loss from discontinued operations, net of tax (in dollars per share)	[1]	(0.01)	(0.01)	(0.01)
Net income (in dollars per share)	[1]	$ 1.64	$ 1.68	$ 1.73
Amounts attributable to common shareowners:
Income from continuing operations, net of tax		$ 373.8	$ 380.7	$ 385.5
Loss from discontinued operations, net of tax		(2.3)	(2.5)	(2.4)
Net income		371.5	378.2	383.1
IPL [Member]
Operating revenues:
Electric utility		1,569.7	1,503.8	1,493.3
Gas utility		204.0	217.3	296.5
Other utility		46.7	53.4	58.3
Total operating revenues		1,820.4	1,774.5	1,848.1
Operating expenses:
Electric production fuel and purchased power		430.5	428.4	497.3
Electric transmission service		359.7	328.2	323.4
Cost of gas sold		111.0	123.3	185.5
Other operation and maintenance		383.7	389.9	381.1
Depreciation and amortization		210.8	207.2	197.5
Taxes other than income taxes		53.9	55.6	54.1
Total operating expenses		1,549.6	1,532.6	1,638.9
Operating income (loss)		270.8	241.9	209.2
Interest expense and other:
Interest expense		103.2	96.8	89.9
Allowance for funds used during construction		(52.0)	(28.2)	(25.9)
Interest income and other		(0.3)	(0.2)	2.3
Total interest expense and other		50.9	68.4	66.3
Income from continuing operations before income taxes		219.9	173.5	142.9
Income tax expense (benefit)		(5.9)	(22.7)	(48.9)
Net income		225.8	196.2	191.8
Preferred dividend requirements of Interstate Power and Light Company		10.2	10.2	10.2
Net income attributable to common shareowners		215.6	186.0	181.6
Amounts attributable to common shareowners:
Net income		215.6	186.0	181.6
WPL [Member]
Operating revenues:
Electric utility		1,305.8	1,266.7	1,220.3
Gas utility		151.4	163.9	221.0
Other utility		1.9	4.5	7.8
Total operating revenues		1,459.1	1,435.1	1,449.1
Operating expenses:
Electric production fuel and purchased power		423.5	409.3	379.9
Electric transmission service		168.2	157.1	124.1
Cost of gas sold		83.3	95.8	142.3
Other operation and maintenance		219.8	235.4	277.2
Depreciation and amortization		192.5	184.3	181.2
Taxes other than income taxes		44.8	44.5	43.4
Total operating expenses		1,132.1	1,126.4	1,148.1
Operating income (loss)		327.0	308.7	301.0
Interest expense and other:
Interest expense		91.4	92.4	86.4
Equity (income) loss from unconsolidated investments, net		(39.8)	(35.1)	(42.8)
Allowance for funds used during construction		(10.5)	(8.7)	(8.9)
Interest income and other		(0.2)	(0.4)	(0.1)
Total interest expense and other		40.9	48.2	34.6
Income from continuing operations before income taxes		286.1	260.5	266.4
Income tax expense (benefit)		93.3	82.9	85.3
Net income		192.8	177.6	181.1
Net income attributable to noncontrolling interest		2.4	1.3	0.7
Net income attributable to common shareowners		190.4	176.3	180.4
Amounts attributable to common shareowners:
Net income		$ 190.4	$ 176.3	$ 180.4

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