Condensed Consolidated Statements Of Income (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Utility:
Electric	$ 796.9	$ 842.0	$ 2,037.7	$ 2,074.2
Gas	46.4	46.5	342.5	330.9
Other	15.8	15.9	45.8	48.9
Non-regulated	162.5	47.3	360.1	129.5
Total operating revenues	1,021.6	951.7	2,786.1	2,583.5
Utility:
Electric production fuel and energy purchases	215.3	238.8	590.0	642.4
Purchased electric capacity	80.2	86.0	205.2	221.8
Electric transmission service	88.9	77.1	242.6	210.5
Cost of gas sold	19.8	19.8	211.0	204.9
Other operation and maintenance	147.1	143.4	476.6	446.1
Non-regulated operation and maintenance	178.5	40.4	356.4	111.7
Depreciation and amortization	81.3	75.4	242.3	214.9
Taxes other than income taxes	25.4	24.2	77.1	74.9
Total operating expenses	836.5	705.1	2,401.2	2,127.2
Operating income	185.1	246.6	384.9	456.3
Interest expense and other:
Interest expense	38.7	41.9	119.7	122.2
Equity income from unconsolidated investments, net	(10.1)	(9.3)	(29.6)	(28.7)
Allowance for funds used during construction	(2.8)	(5.0)	(8.6)	(14.4)
Interest income and other	(0.7)	(0.6)	(2.3)	(0.9)
Total interest expense and other	25.1	27.0	79.2	78.2
Income from continuing operations before income taxes	160.0	219.6	305.7	378.1
Income tax expense (benefit)	34.1	64.1	46.1	121.8
Income from continuing operations, net of tax	125.9	155.5	259.6	256.3
Income (loss) from discontinued operations, net of tax		(1.8)	1.3	(2.0)
Net income	125.9	153.7	260.9	254.3
Preferred dividend requirements of subsidiaries	3.9	4.6	14.3	14.0
Net income attributable to common shareowners	122.0	149.1	246.6	240.3
Weighted average number of common shares outstanding (basic) (000s)	110,647	110,469	110,613	110,415
Earnings per weighted average common share attributable to Alliant Energy common shareowners (basic):
Income from continuing operations, net of tax	$ 1.10	$ 1.37	$ 2.22	$ 2.19
Income (loss) from discontinued operations, net of tax		$ (0.02)	$ 0.01	$ (0.02)
Net income	$ 1.10	$ 1.35	$ 2.23	$ 2.17
Weighted average number of common shares outstanding (diluted) (000s)	110,695	110,544	110,668	110,495
Earnings per weighted average common share attributable to Alliant Energy common shareowners (diluted):
Income from continuing operations, net of tax	$ 1.10	$ 1.37	$ 2.22	$ 2.19
Income (loss) from discontinued operations, net of tax		$ (0.02)	$ 0.01	$ (0.02)
Net income	$ 1.10	$ 1.35	$ 2.23	$ 2.17
Amounts attributable to Alliant Energy common shareowners:
Income from continuing operations, net of tax	122.0	150.9	245.3	242.3
Income (loss) from discontinued operations, net of tax		(1.8)	1.3	(2.0)
Net income attributable to common shareowners	122.0	149.1	246.6	240.3
Dividends declared per common share	$ 0.425	$ 0.395	$ 1.275	$ 1.185
IPL [Member]
Utility:
Electric	443.2	492.4	1,097.3	1,146.8
Gas	27.5	28.1	198.1	187.9
Other	13.8	14.3	40.7	43.9
Total operating revenues	484.5	534.8	1,336.1	1,378.6
Utility:
Electric production fuel and energy purchases	109.9	130.2	294.1	332.0
Purchased electric capacity	40.5	39.9	114.4	112.3
Electric transmission service	61.7	51.4	163.6	134.9
Cost of gas sold	12.7	13.3	126.2	119.1
Other operation and maintenance	84.8	86.9	282.0	271.1
Depreciation and amortization	45.2	44.8	134.1	131.4
Taxes other than income taxes	13.2	12.6	39.6	38.6
Total operating expenses	368.0	379.1	1,154.0	1,139.4
Operating income	116.5	155.7	182.1	239.2
Interest expense and other:
Interest expense	19.5	21.4	59.2	62.0
Allowance for funds used during construction	(1.3)	(1.1)	(4.3)	(4.8)
Interest income and other	0.1	(0.2)	(0.1)	(0.2)
Total interest expense and other	18.3	20.1	54.8	57.0
Income from continuing operations before income taxes	98.2	135.6	127.3	182.2
Income tax expense (benefit)	(3.2)	35.0	(2.2)	50.7
Net income	101.4	100.6	129.5	131.5
Preferred dividend requirements of subsidiaries	3.1	3.8	11.8	11.5
Net income attributable to common shareowners	98.3	96.8	117.7	120.0
Amounts attributable to Alliant Energy common shareowners:
Net income attributable to common shareowners	98.3	96.8	117.7	120.0
WPL [Member]
Utility:
Electric	353.7	349.6	940.4	927.4
Gas	18.9	18.4	144.4	143.0
Other	2.0	1.6	5.1	5.0
Total operating revenues	374.6	369.6	1,089.9	1,075.4
Utility:
Electric production fuel and energy purchases	105.4	108.6	295.9	310.4
Purchased electric capacity	39.7	46.1	90.8	109.5
Electric transmission service	27.2	25.7	79.0	75.6
Cost of gas sold	7.1	6.5	84.8	85.8
Other operation and maintenance	62.3	56.5	194.6	175.0
Depreciation and amortization	35.0	29.2	104.5	79.0
Taxes other than income taxes	11.0	10.3	33.1	31.4
Total operating expenses	287.7	282.9	882.7	866.7
Operating income	86.9	86.7	207.2	208.7
Interest expense and other:
Interest expense	19.9	20.0	60.0	58.5
Equity income from unconsolidated investments, net	(9.8)	(9.3)	(28.9)	(28.4)
Allowance for funds used during construction	(1.5)	(3.9)	(4.3)	(9.6)
Interest income and other		0.1
Total interest expense and other	8.6	6.9	26.8	20.5
Income from continuing operations before income taxes	78.3	79.8	180.4	188.2
Income tax expense (benefit)	26.9	29.8	59.6	71.0
Net income	51.4	50.0	120.8	117.2
Preferred dividend requirements of subsidiaries	0.8	0.8	2.5	2.5
Net income attributable to common shareowners	50.6	49.2	118.3	114.7
Amounts attributable to Alliant Energy common shareowners:
Net income attributable to common shareowners	$ 50.6	$ 49.2	$ 118.3	$ 114.7