Condensed Consolidated Statements Of Income (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Utility:
Electric	$ 633.2	$ 572.4
Gas	197.3	167.1
Other	17.2	13.7
Non-regulated	11.9	12.5
Total operating revenues	859.6	765.7
Utility:
Electric production fuel and energy purchases	179.1	159.9
Purchased electric capacity	57.0	61.5
Electric transmission service	103.7	81.4
Cost of gas sold	128.0	104.8
Other operation and maintenance	150.2	150.0
Non-regulated operation and maintenance	2.2	4.2
Depreciation and amortization	92.6	83.0
Taxes other than income taxes	26.1	25.3
Total operating expenses	738.9	670.1
Operating income	120.7	95.6
Interest expense and other:
Interest expense	42.6	38.9
Equity income from unconsolidated investments, net	(10.7)	(9.4)
Allowance for funds used during construction	(5.6)	(3.8)
Interest income and other	(0.8)	(1.1)
Total interest expense and other	25.5	24.6
Income from continuing operations before income taxes	95.2	71.0
Income tax expense (benefit)	12.1	27.7
Income from continuing operations, net of tax	83.1	43.3
Income (loss) from discontinued operations, net of tax	(3.0)	(4.4)
Net income (loss)	80.1	38.9
Preferred dividend requirements of subsidiaries	10.2	4.0
Net income (loss) attributable to common shareowners	69.9	34.9
Weighted average number of common shares outstanding (basic) (000s) (in shares)	110,767	110,716
Weighted average number of common shares outstanding (diluted) (000s) (in shares)	110,776	110,741
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)	$ 0.66	$ 0.36
Income (loss) from discontinued operations, net of tax (in dollars per share)	$ (0.03)	$ (0.04)
Net income (in dollars per share)	$ 0.63	$ 0.32
Amounts attributable to common shareowners:
Income from continuing operations, net of tax	72.9	39.3
Income (loss) from discontinued operations, net of tax	(3.0)	(4.4)
Net income (loss) attributable to common shareowners	69.9	34.9
Dividends declared per common share (in dollars per share)	$ 0.47	$ 0.45
IPL [Member]
Utility:
Electric	350.2	293.1
Gas	114.3	92.8
Other	13.4	12.8
Total operating revenues	477.9	398.7
Utility:
Electric production fuel and energy purchases	96.7	74.1
Purchased electric capacity	41.4	41.0
Electric transmission service	74.6	55.5
Cost of gas sold	72.1	57.3
Other operation and maintenance	90.5	86.9
Depreciation and amortization	47.6	46.7
Taxes other than income taxes	13.9	13.3
Total operating expenses	436.8	374.8
Operating income	41.1	23.9
Interest expense and other:
Interest expense	19.6	19.7
Allowance for funds used during construction	(3.8)	(1.5)
Interest income and other	(0.1)	(0.2)
Total interest expense and other	15.7	18.0
Income from continuing operations before income taxes	25.4	5.9
Income tax expense (benefit)	(6.1)	7.4
Net income (loss)	31.5	(1.5)
Preferred dividend requirements of subsidiaries	8.6	3.2
Net income (loss) attributable to common shareowners	22.9	(4.7)
Amounts attributable to common shareowners:
Net income (loss) attributable to common shareowners	22.9	(4.7)
WPL [Member]
Utility:
Electric	283.0	279.3
Gas	83.0	74.3
Other	3.8	0.9
Total operating revenues	369.8	354.5
Utility:
Electric production fuel and energy purchases	82.4	85.8
Purchased electric capacity	15.6	20.5
Electric transmission service	29.1	25.9
Cost of gas sold	55.9	47.5
Other operation and maintenance	59.7	63.1
Depreciation and amortization	43.1	35.8
Taxes other than income taxes	11.3	11.3
Total operating expenses	297.1	289.9
Operating income	72.7	64.6
Interest expense and other:
Interest expense	21.3	20.0
Equity income from unconsolidated investments, net	(10.8)	(10.1)
Allowance for funds used during construction	(1.8)	(2.3)
Interest income and other	(0.1)	(0.1)
Total interest expense and other	8.6	7.5
Income from continuing operations before income taxes	64.1	57.1
Income tax expense (benefit)	20.5	25.2
Net income (loss)	43.6	31.9
Preferred dividend requirements of subsidiaries	1.6	0.8
Net income (loss) attributable to common shareowners	42.0	31.1
Amounts attributable to common shareowners:
Net income (loss) attributable to common shareowners	$ 42.0	$ 31.1