Condensed Consolidated Statements Of Income (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Utility:
Electric	$ 572.4	$ 620.3
Gas	167.1	229.0
Other	13.7	16.7
Non-regulated	12.5	11.2
Total operating revenues	765.7	877.2
Utility:
Electric production fuel and energy purchases	159.9	194.0
Purchased electric capacity	61.5	57.8
Electric transmission service	81.4	73.6
Cost of gas sold	104.8	156.4
Other operation and maintenance	150.0	160.6
Non-regulated operation and maintenance	4.2	4.6
Depreciation and amortization	83.0	77.8
Taxes other than income taxes	25.3	25.1
Total operating expenses	670.1	749.9
Operating income	95.6	127.3
Interest expense and other:
Interest expense	38.9	40.5
Equity income from unconsolidated investments, net	(9.4)	(9.9)
Allowance for funds used during construction	(3.8)	(3.1)
Interest income and other	(1.1)	(0.8)
Total interest expense and other	24.6	26.7
Income from continuing operations before income taxes	71.0	100.6
Income taxes	27.7	22.4
Income from continuing operations, net of tax	43.3	78.2
Income (loss) from discontinued operations, net of tax	(4.4)	1.5
Net income (loss)	38.9	79.7
Preferred dividend requirements of subsidiaries	4.0	6.2
Net income attributable to common shareowners	34.9	73.5
Weighted average number of common shares outstanding (basic) (000s)	110,716	110,569
Earnings per weighted average common share attributable to Alliant Energy common shareowners (basic and diluted):
Income from continuing operations, net of tax	$ 0.36	$ 0.65
Income (loss) from discontinued operations, net of tax	$ (0.04)	$ 0.01
Net income	$ 0.32	$ 0.66
Weighted average number of common shares outstanding (diluted) (000s)	110,741	110,632
Amounts attributable to Alliant Energy common shareowners:
Income from continuing operations, net of tax	39.3	72.0
Income (loss) from discontinued operations, net of tax	(4.4)	1.5
Net income attributable to common shareowners	34.9	73.5
Dividends declared per common share	$ 0.45	$ 0.425
IPL [Member]
Utility:
Electric	293.1	330.2
Gas	92.8	131.9
Other	12.8	15.4
Total operating revenues	398.7	477.5
Utility:
Electric production fuel and energy purchases	74.1	96.8
Purchased electric capacity	41.0	39.3
Electric transmission service	55.5	47.9
Cost of gas sold	57.3	92.6
Other operation and maintenance	86.9	96.7
Depreciation and amortization	46.7	43.9
Taxes other than income taxes	13.3	13.2
Total operating expenses	374.8	430.4
Operating income	23.9	47.1
Interest expense and other:
Interest expense	19.7	19.9
Allowance for funds used during construction	(1.5)	(1.4)
Interest income and other	(0.2)	(0.2)
Total interest expense and other	18.0	18.3
Income from continuing operations before income taxes	5.9	28.8
Income taxes	7.4	1.7
Net income (loss)	(1.5)	27.1
Preferred dividend requirements of subsidiaries	3.2	5.4
Net income attributable to common shareowners	(4.7)	21.7
Amounts attributable to Alliant Energy common shareowners:
Net income attributable to common shareowners	(4.7)	21.7
WPL [Member]
Utility:
Electric	279.3	290.1
Gas	74.3	97.1
Other	0.9	1.3
Total operating revenues	354.5	388.5
Utility:
Electric production fuel and energy purchases	85.8	97.2
Purchased electric capacity	20.5	18.5
Electric transmission service	25.9	25.7
Cost of gas sold	47.5	63.8
Other operation and maintenance	63.1	63.9
Depreciation and amortization	35.8	33.4
Taxes other than income taxes	11.3	11.2
Total operating expenses	289.9	313.7
Operating income	64.6	74.8
Interest expense and other:
Interest expense	20.0	20.1
Equity income from unconsolidated investments, net	(10.1)	(9.4)
Allowance for funds used during construction	(2.3)	(1.7)
Interest income and other	(0.1)
Total interest expense and other	7.5	9.0
Income from continuing operations before income taxes	57.1	65.8
Income taxes	25.2	21.4
Net income (loss)	31.9	44.4
Preferred dividend requirements of subsidiaries	0.8	0.8
Net income attributable to common shareowners	31.1	43.6
Amounts attributable to Alliant Energy common shareowners:
Net income attributable to common shareowners	$ 31.1	$ 43.6