v2.4.0.6

Income Taxes (Production Tax Credits (Net Of State Tax Impacts)) (Details) (USD $) In Millions, unless otherwise specified | 12 Months Ended
--- | ---
Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010
Production Tax Credits [Line Items] |  |  |  |  |  |
Production tax credits, net of state tax impacts | $ 24.8 |  | $ 27.1 |  | $ 11.2 |
IPL [Member] |  |  |  |  |  |
Production Tax Credits [Line Items] |  |  |  |  |  |
Production tax credits, net of state tax impacts | 12.5 |  | 12.3 |  | 7.7 |
WPL [Member] |  |  |  |  |  |
Production Tax Credits [Line Items] |  |  |  |  |  |
Production tax credits, net of state tax impacts | 12.3 |  | 14.8 |  | 3.5 |
Whispering Willow - East Wind Project [Member] |  |  |  |  |  |
Production Tax Credits [Line Items] |  |  |  |  |  |
Production tax credits, net of state tax impacts | 12.5 |  | 12.3 |  | 7.7 |
Whispering Willow - East Wind Project [Member] | IPL [Member] |  |  |  |  |  |
Production Tax Credits [Line Items] |  |  |  |  |  |
Production tax credits, net of state tax impacts | 12.5 |  | 12.3 |  | 7.7 |
Whispering Willow - East Wind Project [Member] | WPL [Member] |  |  |  |  |  |
Production Tax Credits [Line Items] |  |  |  |  |  |
Production tax credits, net of state tax impacts | 0 |  | 0 |  | 0 |
Bent Tree - Phase I Wind Project [Member] |  |  |  |  |  |
Production Tax Credits [Line Items] |  |  |  |  |  |
Production tax credits, net of state tax impacts | 9.3 | [1] | 9.3 | [1] | 1.2 | [1]
Bent Tree - Phase I Wind Project [Member] | IPL [Member] |  |  |  |  |  |
Production Tax Credits [Line Items] |  |  |  |  |  |
Production tax credits, net of state tax impacts | 0 | [1] | 0 | [1] | 0 | [1]
Bent Tree - Phase I Wind Project [Member] | WPL [Member] |  |  |  |  |  |
Production Tax Credits [Line Items] |  |  |  |  |  |
Production tax credits, net of state tax impacts | 9.3 | [1] | 9.3 | [1] | 1.2 | [1]
Cedar Ridge Wind Project [Member] |  |  |  |  |  |
Production Tax Credits [Line Items] |  |  |  |  |  |
Production tax credits, net of state tax impacts | 4.0 |  | 4.5 |  | 3.3 |
Cedar Ridge Wind Project [Member] | IPL [Member] |  |  |  |  |  |
Production Tax Credits [Line Items] |  |  |  |  |  |
Production tax credits, net of state tax impacts | 0 |  | 0 |  | 0 |
Cedar Ridge Wind Project [Member] | WPL [Member] |  |  |  |  |  |
Production Tax Credits [Line Items] |  |  |  |  |  |
Production tax credits, net of state tax impacts | 4.0 |  | 4.5 |  | 3.3 |
Subtotal [Member] |  |  |  |  |  |
Production Tax Credits [Line Items] |  |  |  |  |  |
Production tax credits, net of state tax impacts | 25.8 |  | 26.1 |  | 12.2 |
Subtotal [Member] | IPL [Member] |  |  |  |  |  |
Production Tax Credits [Line Items] |  |  |  |  |  |
Production tax credits, net of state tax impacts | 12.5 |  | 12.3 |  | 7.7 |
Subtotal [Member] | WPL [Member] |  |  |  |  |  |
Production Tax Credits [Line Items] |  |  |  |  |  |
Production tax credits, net of state tax impacts | 13.3 |  | 13.8 |  | 4.5 |
Deferral [Member] |  |  |  |  |  |
Production Tax Credits [Line Items] |  |  |  |  |  |
Production tax credits, net of state tax impacts | (1.0) | [1] | 1.0 | [1] | (1.0) | [1]
Deferral [Member] | IPL [Member] |  |  |  |  |  |
Production Tax Credits [Line Items] |  |  |  |  |  |
Production tax credits, net of state tax impacts | 0 | [1] | 0 | [1] | 0 | [1]
Deferral [Member] | WPL [Member] |  |  |  |  |  |
Production Tax Credits [Line Items] |  |  |  |  |  |
Production tax credits, net of state tax impacts | $ (1.0) | [1] | $ 1.0 | [1] | $ (1.0) | [1]
[1] | In 2010 and 2012, WPL deferred the retail portion of the production tax credits generated in 2010 from its Bent Tree - Phase I wind project pursuant to orders issued by the PSCW in December 2009 and July 2012, respectively. As a result of a regulatory assessment completed in 2011, the retail portion of the production tax credit deferral recorded in 2010 was reversed.

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