v2.4.0.6
Summary Of Significant Accounting Policies (Schedule Of Allowance For Funds Used During Construction Recovery Rate) (Details)
 12 Months Ended
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.