Consolidated Statements Of Income (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Utility:
Electric	$ 2,713.6	$ 2,689.0	$ 2,589.3
Gas	517.5	464.8	396.3
Other	66.1	71.3	56.7
Non-regulated	53.1	51.7	52.2
Total operating revenues	3,350.3	3,276.8	3,094.5
Utility:
Electric production fuel and energy purchases	852.1	725.0	712.3
Purchased electric capacity	25.1	216.8	271.5
Electric transmission service	447.5	418.3	341.3
Cost of gas sold	327.8	276.7	217.2
Other operation and maintenance	658.3	620.7	590.0
Non-regulated operation and maintenance	6.7	14.9	11.9
Depreciation and amortization	388.1	370.9	332.4
Taxes other than income taxes	101.1	99.6	98.2
Total operating expenses	2,806.7	2,742.9	2,574.8
Operating income (loss)	543.6	533.9	519.7
Interest expense and other:
Interest expense	180.6	172.8	156.7
Equity (income) loss from unconsolidated investments, net	(40.4)	(43.7)	(41.3)
Allowance for funds used during construction	(34.8)	(30.8)	(21.9)
Interest income and other	(1.8)	(0.4)	(4.0)
Total interest expense and other	103.6	97.9	89.5
Income from continuing operations before income taxes	440.0	436.0	430.2
Income tax expense (benefit)	44.3	53.9	89.4
Income from continuing operations, net of tax	395.7	382.1	340.8
Loss from discontinued operations, net of tax	(2.4)	(5.9)	(5.1)
Net income	393.3	376.2	335.7
Preferred dividend requirements of subsidiaries	10.2	17.9	15.9
Net income (loss) attributable to common shareowners	383.1	358.3	319.8
Weighted average number of common shares outstanding (basic and diluted) (in shares)	110.8	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)	$ 3.48	$ 3.29	$ 2.93
Loss from discontinued operations, net of tax (in dollars per share)	$ (0.02)	$ (0.06)	$ (0.04)
Net income (in dollars per share)	$ 3.46	$ 3.23	$ 2.89
Amounts attributable to common shareowners:
Income from continuing operations, net of tax	385.5	364.2	324.9
Loss from discontinued operations, net of tax	(2.4)	(5.9)	(5.1)
Net income (loss) attributable to common shareowners	383.1	358.3	319.8
IPL [Member]
Utility:
Electric	1,493.3	1,491.8	1,371.1
Gas	296.5	273.9	226.7
Other	58.3	53.1	52.5
Total operating revenues	1,848.1	1,818.8	1,650.3
Utility:
Electric production fuel and energy purchases	472.3	382.1	344.5
Purchased electric capacity	25.0	155.2	153.7
Electric transmission service	323.4	301.4	235.0
Cost of gas sold	185.5	160.3	124.9
Other operation and maintenance	381.1	362.3	350.0
Depreciation and amortization	197.5	191.1	188.9
Taxes other than income taxes	54.1	54.4	53.0
Total operating expenses	1,638.9	1,606.8	1,450.0
Operating income (loss)	209.2	212.0	200.3
Interest expense and other:
Interest expense	89.9	81.3	78.5
Allowance for funds used during construction	(25.9)	(21.0)	(8.4)
Interest income and other	2.3	(0.3)	(0.2)
Total interest expense and other	66.3	60.0	69.9
Income from continuing operations before income taxes	142.9	152.0	130.4
Income tax expense (benefit)	(51.7)	(37.9)	(19.8)
Net income	194.6	189.9	150.2
Preferred dividend requirements of subsidiaries	10.2	16.3	12.6
Net income (loss) attributable to common shareowners	184.4	173.6	137.6
Amounts attributable to common shareowners:
Net income (loss) attributable to common shareowners	184.4	173.6	137.6
WPL [Member]
Utility:
Electric	1,220.3	1,197.2	1,218.2
Gas	221.0	190.9	169.6
Other	7.8	18.2	4.2
Total operating revenues	1,449.1	1,406.3	1,392.0
Utility:
Electric production fuel and energy purchases	379.8	342.9	367.8
Purchased electric capacity	0.1	61.6	117.8
Electric transmission service	124.1	116.9	106.3
Cost of gas sold	142.3	116.4	92.3
Other operation and maintenance	277.2	258.4	240.0
Depreciation and amortization	181.2	172.2	140.9
Taxes other than income taxes	43.4	41.8	42.1
Total operating expenses	1,148.1	1,110.2	1,107.2
Operating income (loss)	301.0	296.1	284.8
Interest expense and other:
Interest expense	86.4	85.0	80.2
Equity (income) loss from unconsolidated investments, net	(42.8)	(43.7)	(42.1)
Allowance for funds used during construction	(8.9)	(9.8)	(13.5)
Interest income and other	(0.1)	(0.1)	(0.1)
Total interest expense and other	34.6	31.4	24.5
Income from continuing operations before income taxes	266.4	264.7	260.3
Income tax expense (benefit)	85.6	87.2	94.6
Net income	180.8	177.5	165.7
Net income attributable to noncontrolling interest	0.7	0	0
Preferred dividend requirements of subsidiaries	0	1.6	3.3
Net income (loss) attributable to common shareowners	180.1	175.9	162.4
Amounts attributable to common shareowners:
Net income (loss) attributable to common shareowners	$ 180.1	$ 175.9	$ 162.4