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.