Condensed Consolidated Statements Of Income (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Utility:
Electric	$ 671.3	$ 675.8
Gas	198.4	240.7
Other	16.4	22.8
Non-regulated	11.3	13.5
Total operating revenues	897.4	952.8
Utility:
Electric production fuel and purchased power	215.9	238.7
Electric transmission service	123.2	114.1
Cost of gas sold	130.8	161.9
Other operation and maintenance	146.6	161.0
Non-regulated operation and maintenance	1.3	1.3
Depreciation and amortization	100.2	95.5
Taxes other than income taxes	26.5	26.1
Total operating expenses	744.5	798.6
Operating income	152.9	154.2
Interest expense and other:
Interest expense	46.6	45.2
Equity income from unconsolidated investments, net	(6.5)	(11.4)
Allowance for funds used during construction	(6.8)	(9.1)
Interest income and other	(0.1)	(1.7)
Total interest expense and other	33.2	23.0
Income before income taxes	119.7	131.2
Income tax expense (benefit)	20.5	20.6
Net income (loss)	99.2	110.6
Preferred dividend requirements of IPL	2.6	2.6
Net income (loss) attributable to common shareowners	96.6	108.0
Weighted average number of common shares outstanding (basic and diluted) (in shares)	111.1	110.8
Earnings per weighted average common share attributable to Alliant Energy common shareowners (basic and diluted) (in dollars per share)	$ 0.87	$ 0.97
Dividends declared per common share (in dollars per share)	$ 0.55	$ 0.51
IPL [Member]
Utility:
Electric	362.6	374.2
Gas	111.2	135.7
Other	15.2	19.0
Total operating revenues	489.0	528.9
Utility:
Electric production fuel and purchased power	110.1	140.0
Electric transmission service	83.9	83.6
Cost of gas sold	71.0	88.1
Other operation and maintenance	92.6	97.2
Depreciation and amortization	51.8	48.7
Taxes other than income taxes	14.1	13.8
Total operating expenses	423.5	471.4
Operating income	65.5	57.5
Interest expense and other:
Interest expense	24.1	22.5
Allowance for funds used during construction	(5.3)	(6.0)
Interest income and other	(0.1)	0
Total interest expense and other	18.7	16.5
Income before income taxes	46.8	41.0
Income tax expense (benefit)	(3.6)	(5.0)
Net income (loss)	50.4	46.0
Preferred dividend requirements of IPL	2.6	2.6
Net income (loss) attributable to common shareowners	47.8	43.4
WPL [Member]
Utility:
Electric	308.7	301.6
Gas	87.2	105.0
Other	1.2	3.8
Total operating revenues	397.1	410.4
Utility:
Electric production fuel and purchased power	105.8	98.7
Electric transmission service	39.3	30.5
Cost of gas sold	59.8	73.8
Other operation and maintenance	54.0	63.8
Depreciation and amortization	46.0	44.7
Taxes other than income taxes	11.4	11.2
Total operating expenses	316.3	322.7
Operating income	80.8	87.7
Interest expense and other:
Interest expense	23.1	21.1
Equity income from unconsolidated investments, net	(7.8)	(11.4)
Allowance for funds used during construction	(1.5)	(3.1)
Interest income and other	0.1	0
Total interest expense and other	13.9	6.6
Income before income taxes	66.9	81.1
Income tax expense (benefit)	22.1	26.3
Net income (loss)	44.8	54.8
Net income attributable to noncontrolling interest	0.2	0
Net income (loss) attributable to common shareowners	$ 44.6	$ 54.8