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Summary Of Significant Accounting Policies (Schedule Of Allowance For Funds Used During Construction Recovery Rate) (Details) - MW | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
IPL [Member] | IPL (Marshalltown CWIP) [Member] |  |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |  |
Recovery rates | [1] | 7.80% | 7.90% | 7.90%
IPL [Member] | IPL (Wind generation CWIP) [Member] |  |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |  |
Recovery rates | [2] | 7.60% |  |
IPL [Member] | IPL (other CWIP) [Member] |  |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |  |
Recovery rates |  | 7.60% | 7.70% | 7.70%
IPL [Member] | Marshalltown Generating Station [Member] |  |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |  |
Return on common equity for calculation of AFUDC |  | 10.30% |  |
IPL [Member] | Expansion of Wind Generation [Member] |  |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |  |
Return on common equity for calculation of AFUDC |  | 10.00% |  |
Electric capacity of wind farm (in megawatts) |  | 500 |  |
WPL [Member] | WPL (retail jurisdiction) [Member] |  |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |  |
Recovery rates |  | 7.60% | 8.20% | 8.20%
WPL [Member] | WPL (wholesale jurisdiction) [Member] |  |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |  |
Recovery rates |  | 6.00% | 6.70% | 7.90%
WPL [Member] | Expansion of Wind Generation [Member] |  |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |  |
Electric capacity of wind farm (in megawatts) |  | 129 |  |
[1] | In 2013, the IUB issued an order establishing rate-making principles that require a 10.3% return on common equity for the calculation of AFUDC related to the construction of Marshalltown.
[2] | In 2016, the IUB issued an order establishing rate-making principles that require a return on common equity for the calculation of AFUDC related to the construction of up to 500 MW of new wind generation equal to the greater of 10.0% or whatever percentage the IUB finds reasonable during IPL’s most recent retail electric rate proceeding.

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- Definition Effective rate, including composite rate, of cost of financing additions to qualifying regulated assets, commonly called allowance for funds used during construction. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 835 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6501662&loc=d3e56162-110433 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 835 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6501569&loc=d3e55921-110430 + Details
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