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Income Taxes (Production Tax Credits (Net Of State Tax Impacts)) (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2014 | Jun. 30, 2013 | Jun. 30, 2014 | Jun. 30, 2013
Production Tax Credits [Line Items] |  |  |  |
Production Tax Credits | $ 7.4 | $ 8.7 | $ 17.4 | $ 17.3
WPL [Member] |  |  |  |
Production Tax Credits [Line Items] |  |  |  |
Production Tax Credits | 4.2 | 4.6 | 9.6 | 9.3
Cedar Ridge Wind Project [Member] | WPL [Member] |  |  |  |
Production Tax Credits [Line Items] |  |  |  |
Nameplate Capacity (in megawatts) |  |  | 68 |
Production Tax Credits | 1.0 | 1.1 | 2.2 | 2.3
Bent Tree - Phase I Wind Project [Member] | WPL [Member] |  |  |  |
Production Tax Credits [Line Items] |  |  |  |
Nameplate Capacity (in megawatts) |  |  | 201 |
Production Tax Credits | 3.2 | 3.5 | 7.4 | 7.0
Whispering Willow - East Wind Project [Member] | IPL [Member] |  |  |  |
Production Tax Credits [Line Items] |  |  |  |
Nameplate Capacity (in megawatts) |  |  | 200 |
Production Tax Credits | $ 3.2 | $ 4.1 | $ 7.8 | $ 8.0

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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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