v2.4.0.6

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, 2012 | Dec. 31, 2011 | Dec. 31, 2010
IPL [Member] | IPL (FERC formula) [Member] |  |  |  |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |  |  |  |
Recovery rates | 8.20% |  | 8.50% |  | 4.80% |
WPL [Member] | WPL (PSCW formula - retail jurisdiction) [Member] |  |  |  |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |  |  |  |
Recovery rates | 8.80% | [1] | 8.80% | [1] | 8.80% | [1]
WPL [Member] | WPL (FERC formula - wholesale jurisdiction) [Member] |  |  |  |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |  |  |  |
Recovery rates | 7.90% |  | 6.20% |  | 7.20% |
WPL [Member] | Bent Tree - Phase I Wind Project [Member] |  |  |  |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |  |  |  |
Current return earned, percentage of estimated CWIP |  |  |  |  | 50.00% |
Accrual recorded, percentage of estimated CWIP |  |  |  |  | 50.00% |
WPL [Member] | Edgewater Unit 5 and Columbia Units 1 and 2 [Member] |  |  |  |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |  |  |  |
Accrual recorded, percentage of estimated CWIP | 100.00% |  |  |  |  |
WPL [Member] | Columbia Units 1-2 [Member] |  |  |  |  |  |
Public Utility, Property, Plant and Equipment [Line Items] |  |  |  |  |  |
Return earned, expected percentage of estimated CWIP, next twelve months | 50.00% |  |  |  |  |
Accrual recorded, expected percentage of estimated CWIP, next twelve months | 50.00% |  |  |  |  |
[1] | Consistent with the PSCW’s retail rate case order issued in 2009, WPL earned a current return on 50% of the estimated CWIP related to its Bent Tree - Phase I wind project for 2010 and accrued AFUDC on the remaining 50% in 2010. Consistent with the PSCW’s retail order issued in 2009, WPL accrued AFUDC on 100% of CWIP related to the Edgewater Unit 5 emission controls project and the Columbia Units 1 and 2 emission controls project in 2012, 2011 and 2010. Consistent with the PSCW’s retail rate case order issued in 2012, WPL will earn a return on 50% of the estimated CWIP related to its Columbia Units 1 and 2 emission controls project for 2013 and will accrue AFUDC on the remaining 50% in 2013.

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- Definition Public Utilities, Allowance for Funds Used During Construction, Accrual Recorded, Percentage of Estimated Construction Work-in-process + References No definition available. + Details
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- Definition Public Utilities, Allowance for Funds Used During Construction, Current Return Earned, Percentage of Estimated Construction Work-in-process + References No definition available. + Details
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- Definition Public Utilities, Allowance for Funds Used During Construction, Return Earned, Expected Percentage of Estimated Construction Work-in-process, Next Twelve Months + References No definition available. + Details
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- Definition Disclosure of the effective rate for the period representing (a) total additions to qualifying regulated assets for allowance for funds used during construction, (b) divided by the sum of debt and equity funds used for construction. + References Reference 1: 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 Reference 2: 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 + Details
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