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Income Taxes (Narrative) (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2016 | Dec. 31, 2015
Income Tax [Line Items] |  |
Net operating loss carryforwards, percentage expiring |  | 99.00%
Scenario, Forecast [Member] |  |
Income Tax [Line Items] |  |
Deductions in income tax return | $ 200 |
IPL [Member] |  |
Income Tax [Line Items] |  |
Net operating loss carryforwards, percentage expiring |  | 95.00%
IPL [Member] | Scenario, Forecast [Member] |  |
Income Tax [Line Items] |  |
Deductions in income tax return | 100 |
WPL [Member] |  |
Income Tax [Line Items] |  |
Net operating loss carryforwards, percentage expiring |  | 96.00%
WPL [Member] | Scenario, Forecast [Member] |  |
Income Tax [Line Items] |  |
Deductions in income tax return | $ 50 |

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- Definition The difference between tax and book deductions that are expected to be reflected on income tax returns as applicable federal and state laws allow. + References No definition available. + Details
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