v2.4.0.6

Income Taxes (Production Tax Credits (Net Of State Tax Impacts)) (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2012 | Sep. 30, 2011 | Sep. 30, 2012 | Sep. 30, 2011
Alliant Energy [Member] |  |  |  |
Production Tax Credits [Line Items] |  |  |  |
Production tax credits (net of state tax impacts) | $ 4.5 | $ 3.8 | $ 17.7 | $ 18.1
WPL [Member] |  |  |  |
Production Tax Credits [Line Items] |  |  |  |
Production tax credits (net of state tax impacts) | 2.5 | 2.0 | 9.0 | 9.9
Cedar Ridge [Member] | WPL [Member] |  |  |  |
Production Tax Credits [Line Items] |  |  |  |
Production tax credits (net of state tax impacts) | 0.7 | 0.6 | 3.0 | 3.2
Bent Tree - Phase I [Member] | WPL [Member] |  |  |  |
Production Tax Credits [Line Items] |  |  |  |
Production tax credits (net of state tax impacts) | 1.8 | 1.4 | 6.0 | 6.7
Whispering Willow - East Wind Project [Member] | IPL [Member] |  |  |  |
Production Tax Credits [Line Items] |  |  |  |
Production tax credits (net of state tax impacts) | $ 2.0 | $ 1.8 | $ 8.7 | $ 8.2

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- Details
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- Definition Production Tax Credits Net Of State Tax Impacts + References No definition available. + Details
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