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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, 2014 | Sep. 30, 2013 | Sep. 30, 2014 | Sep. 30, 2013
Production Tax Credits [Line Items] |  |  |  |
Production Tax Credits | $ 4.6 | $ 5.1 | $ 22.0 | $ 22.4
WPL [Member] |  |  |  |
Production Tax Credits [Line Items] |  |  |  |
Production Tax Credits | 2.6 | 2.8 | 12.2 | 12.1
Cedar Ridge Wind Project [Member] | WPL [Member] |  |  |  |
Production Tax Credits [Line Items] |  |  |  |
Nameplate Capacity (in megawatts) |  |  | 68 |
Production Tax Credits | 0.6 | 0.6 | 2.8 | 2.9
Bent Tree - Phase I Wind Project [Member] | WPL [Member] |  |  |  |
Production Tax Credits [Line Items] |  |  |  |
Nameplate Capacity (in megawatts) |  |  | 201 |
Production Tax Credits | 2.0 | 2.2 | 9.4 | 9.2
Whispering Willow - East Wind Project [Member] | IPL [Member] |  |  |  |
Production Tax Credits [Line Items] |  |  |  |
Nameplate Capacity (in megawatts) |  |  | 200 |
Production Tax Credits | $ 2.0 | $ 2.3 | $ 9.8 | $ 10.3

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- Definition Electric Capacity Of Wind Project + References No definition available. + Details
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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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