Discontinued Operations (Components Of Discontinued Operations In Condensed Consolidated Statements Of Income) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Operating revenues	$ 1.1		$ 6.3		$ 5.5
Operating expenses	0.6	[1]	8.9	[1]	4.5	[1]
Gain on sale of IEA	(2.5)
Interest expense and other			0.2		0.3
Income (loss) before income taxes	3.0		(2.8)		0.7
Income tax expense (benefit)	1.7		(1.1)		(0.2)
Income (loss) from discontinued operations, net of tax	1.3		(1.7)		0.9
Non cash valuation charge			5.4
RMT [Member]
Net proceeds	12
IEA [Member]
Net proceeds	$ 5

[1] In 2010, Alliant Energy recorded pre-tax, non-cash valuation charges of $5.4 million as a result of declines in the fair value of IEA during 2010. The fair value was estimated using updated market information from bids received from potential buyers for IEA.