Condensed Consolidated Statements Of Income (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Utility:
Electric	$ 815.3	$ 796.9	$ 2,000.3	$ 2,037.7
Gas	46.8	46.4	263.9	342.5
Other	12.2	15.8	39.7	45.8
Non-regulated	13.3	11.8	39.7	34.6
Total operating revenues	887.6	870.9	2,343.6	2,460.6
Utility:
Electric production fuel and energy purchases	221.6	215.3	550.4	590.0
Purchased electric capacity	84.0	80.2	216.2	205.2
Electric transmission service	94.9	88.9	255.7	242.6
Cost of gas sold	17.7	19.8	141.1	211.0
Other operation and maintenance	144.7	147.1	432.6	476.6
Non-regulated operation and maintenance	3.7	4.7	8.6	13.3
Depreciation and amortization	83.6	80.7	247.4	240.0
Taxes other than income taxes	23.7	24.8	73.5	74.6
Total operating expenses	673.9	661.5	1,925.5	2,053.3
Operating income	213.7	209.4	418.1	407.3
Interest expense and other:
Interest expense	38.3	38.8	115.8	119.7
Equity income from unconsolidated investments, net	(10.4)	(10.1)	(30.4)	(29.6)
Allowance for funds used during construction	(5.8)	(2.8)	(14.4)	(8.6)
Interest income and other	(0.7)	(0.6)	(2.4)	(2.2)
Total interest expense and other	21.4	25.3	68.6	79.3
Income from continuing operations before income taxes	192.3	184.1	349.5	328.0
Income tax expense (benefit)	39.3	43.3	83.8	54.5
Income from continuing operations, net of tax	153.0	140.8	265.7	273.5
Income (loss) from discontinued operations, net of tax	1.7	(14.9)	(2.3)	(12.6)
Net income	154.7	125.9	263.4	260.9
Preferred dividend requirements of subsidiaries	4.0	3.9	11.9	14.3
Net income attributable to common shareowners	150.7	122.0	251.5	246.6
Weighted average number of common shares outstanding (basic) (000s) (in shares)	110,768	110,647	110,747	110,613
Weighted average number of common shares outstanding (diluted) (000s) (in shares)	110,779	110,695	110,763	110,668
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)	$ 1.34	$ 1.23	$ 2.29	$ 2.34
Income (loss) from discontinued operations, net of tax (in dollars per share)	$ 0.02	$ (0.13)	$ (0.02)	$ (0.11)
Net income (in dollars per share)	$ 1.36	$ 1.10	$ 2.27	$ 2.23
Amounts attributable to common shareowners:
Income from continuing operations, net of tax	149.0	136.9	253.8	259.2
Income (loss) from discontinued operations, net of tax	1.7	(14.9)	(2.3)	(12.6)
Net income attributable to common shareowners	150.7	122.0	251.5	246.6
Dividends declared per common share (in dollars per share)	$ 0.45	$ 0.425	$ 1.35	$ 1.275
IPL [Member]
Utility:
Electric	456.6	443.2	1,070.7	1,097.3
Gas	29.6	27.5	149.2	198.1
Other	11.5	13.8	37.2	40.7
Total operating revenues	497.7	484.5	1,257.1	1,336.1
Utility:
Electric production fuel and energy purchases	116.7	109.9	272.8	294.1
Purchased electric capacity	42.1	40.5	119.1	114.4
Electric transmission service	67.3	61.7	175.7	163.6
Cost of gas sold	12.9	12.7	80.5	126.2
Other operation and maintenance	86.4	84.8	257.1	282.0
Depreciation and amortization	47.3	45.2	141.1	134.1
Taxes other than income taxes	13.0	13.2	39.5	39.6
Total operating expenses	385.7	368.0	1,085.8	1,154.0
Operating income	112.0	116.5	171.3	182.1
Interest expense and other:
Interest expense	19.5	19.5	58.8	59.2
Allowance for funds used during construction	(2.1)	(1.3)	(5.3)	(4.3)
Interest income and other	0	0.1	(0.2)	(0.1)
Total interest expense and other	17.4	18.3	53.3	54.8
Income from continuing operations before income taxes	94.6	98.2	118.0	127.3
Income tax expense (benefit)	(11.9)	(3.2)	(6.6)	(2.2)
Net income	106.5	101.4	124.6	129.5
Preferred dividend requirements of subsidiaries	3.2	3.1	9.4	11.8
Net income attributable to common shareowners	103.3	98.3	115.2	117.7
Amounts attributable to common shareowners:
Net income attributable to common shareowners	103.3	98.3	115.2	117.7
WPL [Member]
Utility:
Electric	358.7	353.7	929.6	940.4
Gas	17.2	18.9	114.7	144.4
Other	0.7	2.0	2.5	5.1
Total operating revenues	376.6	374.6	1,046.8	1,089.9
Utility:
Electric production fuel and energy purchases	104.9	105.4	277.6	295.9
Purchased electric capacity	41.9	39.7	97.1	90.8
Electric transmission service	27.6	27.2	80.0	79.0
Cost of gas sold	4.8	7.1	60.6	84.8
Other operation and maintenance	58.3	62.3	175.5	194.6
Depreciation and amortization	35.8	35.0	104.8	104.5
Taxes other than income taxes	9.9	11.0	31.7	33.1
Total operating expenses	283.2	287.7	827.3	882.7
Operating income	93.4	86.9	219.5	207.2
Interest expense and other:
Interest expense	19.7	19.9	59.6	60.0
Equity income from unconsolidated investments, net	(10.5)	(9.8)	(31.2)	(28.9)
Allowance for funds used during construction	(3.7)	(1.5)	(9.1)	(4.3)
Total interest expense and other	5.5	8.6	19.3	26.8
Income from continuing operations before income taxes	87.9	78.3	200.2	180.4
Income tax expense (benefit)	31.2	26.9	75.5	59.6
Net income	56.7	51.4	124.7	120.8
Preferred dividend requirements of subsidiaries	0.8	0.8	2.5	2.5
Net income attributable to common shareowners	55.9	50.6	122.2	118.3
Amounts attributable to common shareowners:
Net income attributable to common shareowners	$ 55.9	$ 50.6	$ 122.2	$ 118.3