Consolidated Statements Of Income - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating revenues:
Electric utility	$ 2,770.5	$ 2,713.6	$ 2,689.0
Gas utility	381.2	517.5	464.8
Other utility	57.9	66.1	71.3
Non-regulated	44.0	53.1	51.7
Total operating revenues	3,253.6	3,350.3	3,276.8
Operating expenses:
Electric production fuel and purchased power	837.7	877.2	941.8
Electric transmission service	485.3	447.5	418.3
Cost of gas sold	219.1	327.8	276.7
Other operation and maintenance	629.5	665.0	635.6
Depreciation and amortization	401.3	388.1	370.9
Taxes other than income taxes	103.7	101.1	99.6
Total operating expenses	2,676.6	2,806.7	2,742.9
Operating income (loss)	577.0	543.6	533.9
Interest expense and other:
Interest expense	187.1	180.6	172.8
Equity (income) loss from unconsolidated investments, net	(33.8)	(40.4)	(43.7)
Allowance for funds used during construction	(36.9)	(34.8)	(30.8)
Interest income and other	(0.7)	(1.8)	(0.4)
Total interest expense and other	115.7	103.6	97.9
Income from continuing operations before income taxes	461.3	440.0	436.0
Income tax expense (benefit)	70.4	44.3	53.9
Income from continuing operations, net of tax	390.9	395.7	382.1
Loss from discontinued operations, net of tax	(2.5)	(2.4)	(5.9)
Net income	388.4	393.3	376.2
Preferred dividend requirements of subsidiaries	10.2	10.2	17.9
Net income (loss) attributable to common shareowners	$ 378.2	$ 383.1	$ 358.3
Weighted average number of common shares outstanding (basic and diluted) (in shares)	112.7	110.8	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)	$ 3.38	$ 3.48	$ 3.29
Loss from discontinued operations, net of tax (in dollars per share)	(0.02)	(0.02)	(0.06)
Net income (in dollars per share)	$ 3.36	$ 3.46	$ 3.23
Amounts attributable to common shareowners:
Income from continuing operations, net of tax	$ 380.7	$ 385.5	$ 364.2
Loss from discontinued operations, net of tax	(2.5)	(2.4)	(5.9)
Net income (loss)	378.2	383.1	358.3
IPL [Member]
Operating revenues:
Electric utility	1,503.8	1,493.3	1,491.8
Gas utility	217.3	296.5	273.9
Other utility	53.4	58.3	53.1
Total operating revenues	1,774.5	1,848.1	1,818.8
Operating expenses:
Electric production fuel and purchased power	428.4	497.3	537.3
Electric transmission service	328.2	323.4	301.4
Cost of gas sold	123.3	185.5	160.3
Other operation and maintenance	389.9	381.1	362.3
Depreciation and amortization	207.2	197.5	191.1
Taxes other than income taxes	55.6	54.1	54.4
Total operating expenses	1,532.6	1,638.9	1,606.8
Operating income (loss)	241.9	209.2	212.0
Interest expense and other:
Interest expense	96.8	89.9	81.3
Allowance for funds used during construction	(28.2)	(25.9)	(21.0)
Interest income and other	(0.2)	2.3	(0.3)
Total interest expense and other	68.4	66.3	60.0
Income from continuing operations before income taxes	173.5	142.9	152.0
Income tax expense (benefit)	(22.7)	(48.9)	(36.3)
Net income	196.2	191.8	188.3
Preferred dividend requirements of subsidiaries	10.2	10.2	16.3
Net income (loss) attributable to common shareowners	186.0	181.6	172.0
Amounts attributable to common shareowners:
Net income (loss)	186.0	181.6	172.0
WPL [Member]
Operating revenues:
Electric utility	1,266.7	1,220.3	1,197.2
Gas utility	163.9	221.0	190.9
Other utility	4.5	7.8	18.2
Total operating revenues	1,435.1	1,449.1	1,406.3
Operating expenses:
Electric production fuel and purchased power	409.3	379.9	404.5
Electric transmission service	157.1	124.1	116.9
Cost of gas sold	95.8	142.3	116.4
Other operation and maintenance	235.4	277.2	258.4
Depreciation and amortization	184.3	181.2	172.2
Taxes other than income taxes	44.5	43.4	41.8
Total operating expenses	1,126.4	1,148.1	1,110.2
Operating income (loss)	308.7	301.0	296.1
Interest expense and other:
Interest expense	92.4	86.4	85.0
Equity (income) loss from unconsolidated investments, net	(35.1)	(42.8)	(43.7)
Allowance for funds used during construction	(8.7)	(8.9)	(9.8)
Interest income and other	(0.4)	(0.1)	(0.1)
Total interest expense and other	48.2	34.6	31.4
Income from continuing operations before income taxes	260.5	266.4	264.7
Income tax expense (benefit)	82.9	85.3	85.6
Net income	177.6	181.1	179.1
Net income attributable to noncontrolling interest	1.3	0.7	0.0
Preferred dividend requirements of subsidiaries	0.0	0.0	1.6
Net income (loss) attributable to common shareowners	176.3	180.4	177.5
Amounts attributable to common shareowners:
Net income (loss)	$ 176.3	$ 180.4	$ 177.5