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Income Taxes (Narrative) (Details) $ in Millions | 6 Months Ended
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Jun. 30, 2016 USD ($)
Income Taxes [Line Items] |
Increase (decrease) in non-current deferred tax liabilities | $ 92.9
IPL [Member] |
Income Taxes [Line Items] |
Increase (decrease) in non-current deferred tax liabilities | 62.1
WPL [Member] |
Income Taxes [Line Items] |
Increase (decrease) in non-current deferred tax liabilities | $ 44.1

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