Condensed Consolidated Statements Of Income (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Utility:
Electric	$ 612.1	$ 612.6	$ 1,245.3	$ 1,185.0
Gas	73.4	50.0	270.7	217.1
Other	17.8	13.8	35.0	27.5
Non-regulated	14.7	13.9	26.6	26.4
Total operating revenues	718.0	690.3	1,577.6	1,456.0
Utility:
Electric production fuel and energy purchases	158.0	168.9	337.1	328.8
Purchased electric capacity	52.0	70.7	109.0	132.2
Electric transmission service	99.6	79.4	203.3	160.8
Cost of gas sold	38.9	18.6	166.9	123.4
Other operation and maintenance	147.2	137.9	297.4	287.9
Non-regulated operation and maintenance	3.1	0.7	5.3	4.9
Depreciation and amortization	92.7	80.8	185.3	163.8
Taxes other than income taxes	23.3	24.5	49.4	49.8
Total operating expenses	614.8	581.5	1,353.7	1,251.6
Operating income	103.2	108.8	223.9	204.4
Interest expense and other:
Interest expense	42.5	38.6	85.1	77.5
Equity income from unconsolidated investments, net	(10.9)	(10.6)	(21.6)	(20.0)
Allowance for funds used during construction	(7.0)	(4.8)	(12.6)	(8.6)
Interest income and other	(0.3)	(0.6)	(1.1)	(1.7)
Total interest expense and other	24.3	22.6	49.8	47.2
Income from continuing operations before income taxes	78.9	86.2	174.1	157.2
Income tax expense (benefit)	10.5	16.8	22.6	44.5
Income from continuing operations, net of tax	68.4	69.4	151.5	112.7
Income (loss) from discontinued operations, net of tax	(0.6)	0.4	(3.6)	(4.0)
Net income (loss)	67.8	69.8	147.9	108.7
Preferred dividend requirements of subsidiaries	2.5	3.9	12.7	7.9
Net income (loss) attributable to common shareowners	65.3	65.9	135.2	100.8
Weighted average number of common shares outstanding (basic) (000s) (in shares)	110,776	110,756	110,772	110,736
Weighted average number of common shares outstanding (diluted) (000s) (in shares)	110,780	110,769	110,778	110,755
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)	$ 0.59	$ 0.60	$ 1.25	$ 0.95
Income (loss) from discontinued operations, net of tax (in dollars per share)	$ 0.00	$ 0.00	$ (0.03)	$ (0.04)
Net income (in dollars per share)	$ 0.59	$ 0.60	$ 1.22	$ 0.91
Amounts attributable to common shareowners:
Income from continuing operations, net of tax	65.9	65.5	138.8	104.8
Income (loss) from discontinued operations, net of tax	(0.6)	0.4	(3.6)	(4.0)
Net income (loss) attributable to common shareowners	65.3	65.9	135.2	100.8
Dividends declared per common share (in dollars per share)	$ 0.47	$ 0.45	$ 0.94	$ 0.90
IPL [Member]
Utility:
Electric	329.6	321.0	679.8	614.1
Gas	42.0	26.8	156.3	119.6
Other	11.8	12.9	25.2	25.7
Total operating revenues	383.4	360.7	861.3	759.4
Utility:
Electric production fuel and energy purchases	74.9	82.0	171.6	156.1
Purchased electric capacity	36.2	36.0	77.6	77.0
Electric transmission service	71.4	52.9	146.0	108.4
Cost of gas sold	21.8	10.3	93.9	67.6
Other operation and maintenance	83.2	83.8	173.7	170.7
Depreciation and amortization	47.6	47.1	95.2	93.8
Taxes other than income taxes	13.6	13.2	27.5	26.5
Total operating expenses	348.7	325.3	785.5	700.1
Operating income	34.7	35.4	75.8	59.3
Interest expense and other:
Interest expense	19.7	19.6	39.3	39.3
Allowance for funds used during construction	(4.7)	(1.7)	(8.5)	(3.2)
Interest income and other	(0.1)	0	(0.2)	(0.2)
Total interest expense and other	14.9	17.9	30.6	35.9
Income from continuing operations before income taxes	19.8	17.5	45.2	23.4
Income tax expense (benefit)	(4.9)	(2.1)	(11.0)	5.3
Net income (loss)	24.7	19.6	56.2	18.1
Preferred dividend requirements of subsidiaries	2.5	3.0	11.1	6.2
Net income (loss) attributable to common shareowners	22.2	16.6	45.1	11.9
Amounts attributable to common shareowners:
Net income (loss) attributable to common shareowners	22.2	16.6	45.1	11.9
WPL [Member]
Utility:
Electric	282.5	291.6	565.5	570.9
Gas	31.4	23.2	114.4	97.5
Other	6.0	0.9	9.8	1.8
Total operating revenues	319.9	315.7	689.7	670.2
Utility:
Electric production fuel and energy purchases	83.1	86.9	165.5	172.7
Purchased electric capacity	15.8	34.7	31.4	55.2
Electric transmission service	28.2	26.5	57.3	52.4
Cost of gas sold	17.1	8.3	73.0	55.8
Other operation and maintenance	64.0	54.1	123.7	117.2
Depreciation and amortization	43.2	33.2	86.3	69.0
Taxes other than income taxes	8.8	10.5	20.1	21.8
Total operating expenses	260.2	254.2	557.3	544.1
Operating income	59.7	61.5	132.4	126.1
Interest expense and other:
Interest expense	21.3	19.9	42.6	39.9
Equity income from unconsolidated investments, net	(10.8)	(10.6)	(21.6)	(20.7)
Allowance for funds used during construction	(2.3)	(3.1)	(4.1)	(5.4)
Interest income and other	0.1	0.1	0	0
Total interest expense and other	8.3	6.3	16.9	13.8
Income from continuing operations before income taxes	51.4	55.2	115.5	112.3
Income tax expense (benefit)	17.0	19.1	37.5	44.3
Net income (loss)	34.4	36.1	78.0	68.0
Preferred dividend requirements of subsidiaries	0	0.9	1.6	1.7
Net income (loss) attributable to common shareowners	34.4	35.2	76.4	66.3
Amounts attributable to common shareowners:
Net income (loss) attributable to common shareowners	$ 34.4	$ 35.2	$ 76.4	$ 66.3