Condensed Consolidated Statements Of Income (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Utility:
Electric	$ 620.5	$ 627.3	$ 1,240.8	$ 1,232.2
Gas	67.1	59.5	296.1	284.4
Other	13.3	15.4	30.0	33.0
Non-regulated	118.6	39.4	197.6	82.2
Total operating revenues	819.5	741.6	1,764.5	1,631.8
Utility:
Electric production fuel and energy purchases	180.7	193.2	374.7	403.6
Purchased electric capacity	67.2	72.5	125.0	135.8
Electric transmission service	80.1	71.1	153.7	133.4
Cost of gas sold	34.8	28.7	191.2	185.1
Other operation and maintenance	168.9	152.2	329.5	302.7
Non-regulated operation and maintenance	108.0	33.1	177.9	71.3
Depreciation and amortization	82.2	65.1	161.0	139.5
Taxes other than income taxes	25.6	25.0	51.7	50.7
Total operating expenses	747.5	640.9	1,564.7	1,422.1
Operating income	72.0	100.7	199.8	209.7
Interest expense and other:
Interest expense	40.4	39.6	81.0	80.3
Equity income from unconsolidated investments, net	(9.6)	(9.6)	(19.5)	(19.4)
Allowance for funds used during construction	(2.7)	(5.5)	(5.8)	(9.4)
Interest income and other	(0.8)	0.5	(1.6)	(0.3)
Total interest expense and other	27.3	25.0	54.1	51.2
Income from continuing operations before income taxes	44.7	75.7	145.7	158.5
Income tax expense (benefit)	(10.6)	23.0	12.0	57.7
Income from continuing operations, net of tax	55.3	52.7	133.7	100.8
Income (loss) from discontinued operations, net of tax		(0.2)	1.3	(0.2)
Net income	55.3	52.5	135.0	100.6
Preferred dividend requirements of subsidiaries	4.2	4.7	10.4	9.4
Net income attributable to common shareowners	51.1	47.8	124.6	91.2
Weighted average number of common shares outstanding (basic) (000s)	110,624	110,409	110,596	110,389
Earnings per weighted average common share attributable to Alliant Energy common shareowners (basic):
Income from continuing operations, net of tax	$ 0.46	$ 0.43	$ 1.12	$ 0.83
Income from discontinued operations, net of tax			$ 0.01
Net income	$ 0.46	$ 0.43	$ 1.13	$ 0.83
Weighted average number of common shares outstanding (diluted) (000s)	110,677	110,490	110,654	110,471
Earnings per weighted average common share attributable to Alliant Energy common shareowners (diluted):
Income from continuing operations, net of tax	$ 0.46	$ 0.43	$ 1.12	$ 0.83
Income from discontinued operations, net of tax			$ 0.01
Net income	$ 0.46	$ 0.43	$ 1.13	$ 0.83
Amounts attributable to Alliant Energy common shareowners:
Income from continuing operations, net of tax	51.1	48.0	123.3	91.4
Income (loss) from discontinued operations, net of tax		(0.2)	1.3	(0.2)
Net income attributable to common shareowners	51.1	47.8	124.6	91.2
Dividends declared per common share	$ 0.425	$ 0.395	$ 0.85	$ 0.79
IPL [Member]
Utility:
Electric	323.9	344.8	654.1	654.4
Gas	38.7	31.1	170.6	159.8
Other	11.5	13.4	26.9	29.6
Total operating revenues	374.1	389.3	851.6	843.8
Utility:
Electric production fuel and energy purchases	87.4	101.3	184.2	201.8
Purchased electric capacity	34.6	33.8	73.9	72.4
Electric transmission service	54.0	45.9	101.9	83.5
Cost of gas sold	20.9	14.6	113.5	105.8
Other operation and maintenance	100.5	91.9	197.2	184.2
Depreciation and amortization	45.0	43.6	88.9	86.6
Taxes other than income taxes	13.2	13.0	26.4	26.0
Total operating expenses	355.6	344.1	786.0	760.3
Operating income	18.5	45.2	65.6	83.5
Interest expense and other:
Interest expense	19.8	20.3	39.7	40.6
Allowance for funds used during construction	(1.6)	(2.4)	(3.0)	(3.7)
Interest income and other		0.3	(0.2)
Total interest expense and other	18.2	18.2	36.5	36.9
Income from continuing operations before income taxes	0.3	27.0	29.1	46.6
Income tax expense (benefit)	(0.7)	5.8	1.0	15.7
Net income	1.0	21.2	28.1	30.9
Preferred dividend requirements of subsidiaries	3.3	3.8	8.7	7.7
Net income attributable to common shareowners	(2.3)	17.4	19.4	23.2
Amounts attributable to Alliant Energy common shareowners:
Net income attributable to common shareowners	(2.3)	17.4	19.4	23.2
WPL [Member]
Utility:
Electric	296.6	282.5	586.7	577.8
Gas	28.4	28.4	125.5	124.6
Other	1.8	2.0	3.1	3.4
Total operating revenues	326.8	312.9	715.3	705.8
Utility:
Electric production fuel and energy purchases	93.3	91.9	190.5	201.8
Purchased electric capacity	32.6	38.7	51.1	63.4
Electric transmission service	26.1	25.2	51.8	49.9
Cost of gas sold	13.9	14.1	77.7	79.3
Other operation and maintenance	68.4	60.3	132.3	118.5
Depreciation and amortization	36.1	19.9	69.5	49.8
Taxes other than income taxes	10.9	10.5	22.1	21.1
Total operating expenses	281.3	260.6	595.0	583.8
Operating income	45.5	52.3	120.3	122.0
Interest expense and other:
Interest expense	20.0	18.7	40.1	38.5
Equity income from unconsolidated investments, net	(9.7)	(9.6)	(19.1)	(19.1)
Allowance for funds used during construction	(1.1)	(3.1)	(2.8)	(5.7)
Interest income and other		(0.1)		(0.1)
Total interest expense and other	9.2	5.9	18.2	13.6
Income from continuing operations before income taxes	36.3	46.4	102.1	108.4
Income tax expense (benefit)	11.3	16.2	32.7	41.2
Net income	25.0	30.2	69.4	67.2
Preferred dividend requirements of subsidiaries	0.9	0.9	1.7	1.7
Net income attributable to common shareowners	24.1	29.3	67.7	65.5
Amounts attributable to Alliant Energy common shareowners:
Net income attributable to common shareowners	$ 24.1	$ 29.3	$ 67.7	$ 65.5