Condensed Consolidated Statements Of Income (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Utility:
Electric	$ 612.6	$ 620.5	$ 1,185.0	$ 1,240.8
Gas	50.0	67.1	217.1	296.1
Other	13.8	13.3	27.5	30.0
Non-regulated	13.9	11.6	26.4	22.8
Total operating revenues	690.3	712.5	1,456.0	1,589.7
Utility:
Electric production fuel and energy purchases	168.9	180.7	328.8	374.7
Purchased electric capacity	70.7	67.2	132.2	125.0
Electric transmission service	79.4	80.1	160.8	153.7
Cost of gas sold	18.6	34.8	123.4	191.2
Other operation and maintenance	137.9	168.9	287.9	329.5
Non-regulated operation and maintenance	0.7	4.0	4.9	8.6
Depreciation and amortization	80.8	81.5	163.8	159.3
Taxes other than income taxes	24.5	24.7	49.8	49.8
Total operating expenses	581.5	641.9	1,251.6	1,391.8
Operating income	108.8	70.6	204.4	197.9
Interest expense and other:
Interest expense	38.6	40.4	77.5	80.9
Equity income from unconsolidated investments, net	(10.6)	(9.6)	(20.0)	(19.5)
Allowance for funds used during construction	(4.8)	(2.7)	(8.6)	(5.8)
Interest income and other	(0.6)	(0.8)	(1.7)	(1.6)
Total interest expense and other	22.6	27.3	47.2	54.0
Income from continuing operations before income taxes	86.2	43.3	157.2	143.9
Income tax expense (benefit)	16.8	(11.2)	44.5	11.2
Income from continuing operations, net of tax	69.4	54.5	112.7	132.7
Income (loss) from discontinued operations, net of tax	0.4	0.8	(4.0)	2.3
Net income	69.8	55.3	108.7	135.0
Preferred dividend requirements of subsidiaries	3.9	4.2	7.9	10.4
Net income attributable to common shareowners	65.9	51.1	100.8	124.6
Weighted average number of common shares outstanding (basic) (000s) (in shares)	110,756	110,624	110,736	110,596
Weighted average number of common shares outstanding (diluted) (000s) (in shares)	110,769	110,677	110,755	110,654
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)	$ 0.60	$ 0.45	$ 0.95	$ 1.11
Income (loss) from discontinued operations, net of tax (in dollars per share)	$ 0.00	$ 0.01	$ (0.04)	$ 0.02
Net income (in dollars per share)	$ 0.60	$ 0.46	$ 0.91	$ 1.13
Amounts attributable to common shareowners:
Income from continuing operations, net of tax	65.5	50.3	104.8	122.3
Income (loss) from discontinued operations, net of tax	0.4	0.8	(4.0)	2.3
Net income attributable to common shareowners	65.9	51.1	100.8	124.6
Dividends declared per common share (in dollars per share)	$ 0.45	$ 0.425	$ 0.9	$ 0.85
IPL [Member]
Utility:
Electric	321.0	323.9	614.1	654.1
Gas	26.8	38.7	119.6	170.6
Other	12.9	11.5	25.7	26.9
Total operating revenues	360.7	374.1	759.4	851.6
Utility:
Electric production fuel and energy purchases	82.0	87.4	156.1	184.2
Purchased electric capacity	36.0	34.6	77.0	73.9
Electric transmission service	52.9	54.0	108.4	101.9
Cost of gas sold	10.3	20.9	67.6	113.5
Other operation and maintenance	83.8	100.5	170.7	197.2
Depreciation and amortization	47.1	45.0	93.8	88.9
Taxes other than income taxes	13.2	13.2	26.5	26.4
Total operating expenses	325.3	355.6	700.1	786.0
Operating income	35.4	18.5	59.3	65.6
Interest expense and other:
Interest expense	19.6	19.8	39.3	39.7
Allowance for funds used during construction	(1.7)	(1.6)	(3.2)	(3.0)
Interest income and other	0	0	(0.2)	(0.2)
Total interest expense and other	17.9	18.2	35.9	36.5
Income from continuing operations before income taxes	17.5	0.3	23.4	29.1
Income tax expense (benefit)	(2.1)	(0.7)	5.3	1.0
Net income	19.6	1.0	18.1	28.1
Preferred dividend requirements of subsidiaries	3.0	3.3	6.2	8.7
Net income attributable to common shareowners	16.6	(2.3)	11.9	19.4
Amounts attributable to common shareowners:
Net income attributable to common shareowners	16.6	(2.3)	11.9	19.4
WPL [Member]
Utility:
Electric	291.6	296.6	570.9	586.7
Gas	23.2	28.4	97.5	125.5
Other	0.9	1.8	1.8	3.1
Total operating revenues	315.7	326.8	670.2	715.3
Utility:
Electric production fuel and energy purchases	86.9	93.3	172.7	190.5
Purchased electric capacity	34.7	32.6	55.2	51.1
Electric transmission service	26.5	26.1	52.4	51.8
Cost of gas sold	8.3	13.9	55.8	77.7
Other operation and maintenance	54.1	68.4	117.2	132.3
Depreciation and amortization	33.2	36.1	69.0	69.5
Taxes other than income taxes	10.5	10.9	21.8	22.1
Total operating expenses	254.2	281.3	544.1	595.0
Operating income	61.5	45.5	126.1	120.3
Interest expense and other:
Interest expense	19.9	20.0	39.9	40.1
Equity income from unconsolidated investments, net	(10.6)	(9.7)	(20.7)	(19.1)
Allowance for funds used during construction	(3.1)	(1.1)	(5.4)	(2.8)
Interest income and other	0.1	0	0	0
Total interest expense and other	6.3	9.2	13.8	18.2
Income from continuing operations before income taxes	55.2	36.3	112.3	102.1
Income tax expense (benefit)	19.1	11.3	44.3	32.7
Net income	36.1	25.0	68.0	69.4
Preferred dividend requirements of subsidiaries	0.9	0.9	1.7	1.7
Net income attributable to common shareowners	35.2	24.1	66.3	67.7
Amounts attributable to common shareowners:
Net income attributable to common shareowners	$ 35.2	$ 24.1	$ 66.3	$ 67.7