Condensed Consolidated Statements Of Income (USD $) In Millions, except Share data in Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Utility:
Electric	$ 798.1	$ 815.3	$ 2,043.4	$ 2,000.3
Gas	39.8	46.8	310.5	263.9
Other	17.4	12.2	52.4	39.7
Non-regulated	11.3	13.3	37.9	39.7
Total operating revenues	866.6	887.6	2,444.2	2,343.6
Utility:
Electric production fuel and energy purchases	205.4	221.6	542.5	550.4
Purchased electric capacity	58.6	84.0	167.6	216.2
Electric transmission service	110.5	94.9	313.8	255.7
Cost of gas sold	14.3	17.7	181.2	141.1
Other operation and maintenance	156.3	144.7	453.7	432.6
Non-regulated operation and maintenance	3.1	3.7	8.4	8.6
Depreciation and amortization	92.1	83.6	277.4	247.4
Taxes other than income taxes	24.9	23.7	74.3	73.5
Total operating expenses	665.2	673.9	2,018.9	1,925.5
Operating income	201.4	213.7	425.3	418.1
Interest expense and other:
Interest expense	42.5	38.3	127.6	115.8
Equity income from unconsolidated investments, net	(11.1)	(10.4)	(32.7)	(30.4)
Allowance for funds used during construction	(8.5)	(5.8)	(21.1)	(14.4)
Interest income and other	(0.6)	(0.7)	(1.7)	(2.4)
Total interest expense and other	22.3	21.4	72.1	68.6
Income from continuing operations before income taxes	179.1	192.3	353.2	349.5
Income tax expense (benefit)	17.6	39.3	40.2	83.8
Income from continuing operations, net of tax	161.5	153.0	313.0	265.7
Income (loss) from discontinued operations, net of tax	(1.3)	1.7	(4.9)	(2.3)
Net income (loss)	160.2	154.7	308.1	263.4
Preferred dividend requirements of subsidiaries	2.6	4.0	15.3	11.9
Net income (loss) attributable to common shareowners	157.6	150.7	292.8	251.5
Weighted average number of common shares outstanding (basic) (000s) (in shares)	110,783	110,768	110,775	110,747
Weighted average number of common shares outstanding (diluted) (000s) (in shares)	110,785	110,779	110,780	110,763
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)	$ 1.43	$ 1.34	$ 2.69	$ 2.29
Income (loss) from discontinued operations, net of tax (in dollars per share)	$ (0.01)	$ 0.02	$ (0.05)	$ (0.02)
Net income (in dollars per share)	$ 1.42	$ 1.36	$ 2.64	$ 2.27
Amounts attributable to common shareowners:
Income from continuing operations, net of tax	158.9	149.0	297.7	253.8
Income (loss) from discontinued operations, net of tax	(1.3)	1.7	(4.9)	(2.3)
Net income (loss) attributable to common shareowners	157.6	150.7	292.8	251.5
Dividends declared per common share (in dollars per share)	$ 0.47	$ 0.45	$ 1.41	$ 1.35
IPL [Member]
Utility:
Electric	457.6	456.6	1,137.4	1,070.7
Gas	24.6	29.6	180.9	149.2
Other	12.2	11.5	37.4	37.2
Total operating revenues	494.4	497.7	1,355.7	1,257.1
Utility:
Electric production fuel and energy purchases	110.9	116.7	282.5	272.8
Purchased electric capacity	42.7	42.1	120.3	119.1
Electric transmission service	80.0	67.3	226.0	175.7
Cost of gas sold	9.3	12.9	103.2	80.5
Other operation and maintenance	90.5	86.4	264.2	257.1
Depreciation and amortization	47.6	47.3	142.8	141.1
Taxes other than income taxes	13.4	13.0	40.9	39.5
Total operating expenses	394.4	385.7	1,179.9	1,085.8
Operating income	100.0	112.0	175.8	171.3
Interest expense and other:
Interest expense	19.6	19.5	58.9	58.8
Allowance for funds used during construction	(5.8)	(2.1)	(14.3)	(5.3)
Interest income and other	0	0	(0.2)	(0.2)
Total interest expense and other	13.8	17.4	44.4	53.3
Income from continuing operations before income taxes	86.2	94.6	131.4	118.0
Income tax expense (benefit)	(26.4)	(11.9)	(37.4)	(6.6)
Net income (loss)	112.6	106.5	168.8	124.6
Preferred dividend requirements of subsidiaries	2.6	3.2	13.7	9.4
Net income (loss) attributable to common shareowners	110.0	103.3	155.1	115.2
Amounts attributable to common shareowners:
Net income (loss) attributable to common shareowners	110.0	103.3	155.1	115.2
WPL [Member]
Utility:
Electric	340.5	358.7	906.0	929.6
Gas	15.2	17.2	129.6	114.7
Other	5.2	0.7	15.0	2.5
Total operating revenues	360.9	376.6	1,050.6	1,046.8
Utility:
Electric production fuel and energy purchases	94.5	104.9	260.0	277.6
Purchased electric capacity	15.9	41.9	47.3	97.1
Electric transmission service	30.5	27.6	87.8	80.0
Cost of gas sold	5.0	4.8	78.0	60.6
Other operation and maintenance	65.8	58.3	189.5	175.5
Depreciation and amortization	42.7	35.8	129.0	104.8
Taxes other than income taxes	10.6	9.9	30.7	31.7
Total operating expenses	265.0	283.2	822.3	827.3
Operating income	95.9	93.4	228.3	219.5
Interest expense and other:
Interest expense	21.2	19.7	63.8	59.6
Equity income from unconsolidated investments, net	(11.1)	(10.5)	(32.7)	(31.2)
Allowance for funds used during construction	(2.7)	(3.7)	(6.8)	(9.1)
Total interest expense and other	7.4	5.5	24.3	19.3
Income from continuing operations before income taxes	88.5	87.9	204.0	200.2
Income tax expense (benefit)	27.2	31.2	64.7	75.5
Net income (loss)	61.3	56.7	139.3	124.7
Preferred dividend requirements of subsidiaries	0	0.8	1.6	2.5
Net income (loss) attributable to common shareowners	61.3	55.9	137.7	122.2
Amounts attributable to common shareowners:
Net income (loss) attributable to common shareowners	$ 61.3	$ 55.9	$ 137.7	$ 122.2