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Income Taxes (Narrative) (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended
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Mar. 31, 2014
Income Tax [Line Items] |
Increase (decrease) non-current deferred tax liabilities | $ 29.0
Deferred income tax assets [Member] |
Income Tax [Line Items] |
Increase (decrease) current deferred tax assets | (22.9)
IPL [Member] |
Income Tax [Line Items] |
Increase (decrease) non-current deferred tax liabilities | 23.0
IPL [Member] | Deferred income tax assets [Member] |
Income Tax [Line Items] |
Increase (decrease) current deferred tax assets | (9.8)
WPL [Member] |
Income Tax [Line Items] |
Increase (decrease) non-current deferred tax liabilities | 4.9
WPL [Member] | Deferred income tax assets [Member] |
Income Tax [Line Items] |
Increase (decrease) current deferred tax assets | $ (10.7)

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