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Summary Of Significant Accounting Policies (Schedule Of Allowance For Funds Used During Construction Recovery Rate) (Details) | 12 Months Ended
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Dec. 31, 2015 | Dec. 31, 2014 | Dec. 31, 2013
IPL [Member] | IPL (Marshalltown CWIP) [Member] |  |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |  |
Recovery rates | [1] | 7.90% | 8.00% | 0.00%
IPL [Member] | IPL (other CWIP) [Member] |  |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |  |
Recovery rates |  | 7.70% | 7.80% | 8.20%
IPL [Member] | Marshalltown Generating Station [Member] |  |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |  |
Return on common equity for calculation of AFUDC |  | 10.30% |  |
WPL [Member] | WPL (retail jurisdiction) [Member] |  |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |  |
Recovery rates |  | 8.20% | 8.20% | 8.20%
WPL [Member] | WPL (wholesale jurisdiction) [Member] |  |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |  |
Recovery rates |  | 7.90% | 4.10% | 4.50%
[1] | In 2013, the IUB issued an order establishing rate-making principles for Marshalltown that requires a 10.3% return on common equity for the calculation of AFUDC related to the construction of such facility.

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