Summary Of Significant Accounting Policies (Schedule Of Allowance For Funds Used During Construction Recovery Rate) (Details)	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
IPL (FERC Formula-Whispering Willow-East) [Member] | IPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
AFUDC recovery rates	0.00%		0.00%		8.40%
IPL (FERC Formula-Other Projects) [Member] | IPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
AFUDC recovery rates	8.50%		4.80%		8.00%
WPL (PSCW Formula-Retail Jurisdiction) [Member] | WPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
AFUDC recovery rates	8.80%	[1]	8.80%	[1]	9.00%	[1]
WPL (FERC Formula-Wholesale Jurisdiction) [Member] | WPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
AFUDC recovery rates	6.20%		7.20%		6.70%

[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. In addition, the PSCW's order changed WPL's AFUDC recovery rate to 8.8% from 9.0% effective Jan. 1, 2010.