Summary Of Significant Accounting Policies (Schedule Of Average Rates Of Depreciation) (Details)	1 Months Ended	12 Months Ended																		1 Months Ended	12 Months Ended
	Jan. 31, 2012 Distribution [Member]	Dec. 31, 2011 Distribution [Member] IPL [Member]	Dec. 31, 2010 Distribution [Member] IPL [Member]	Dec. 31, 2009 Distribution [Member] IPL [Member]	Dec. 31, 2011 Distribution [Member] WPL [Member]	Dec. 31, 2010 Distribution [Member] WPL [Member]	Dec. 31, 2009 Distribution [Member] WPL [Member]	Dec. 31, 2011 Gas [Member] IPL [Member]	Dec. 31, 2010 Gas [Member] IPL [Member]	Dec. 31, 2009 Gas [Member] IPL [Member]	Dec. 31, 2011 Gas [Member] WPL [Member]	Dec. 31, 2010 Gas [Member] WPL [Member]	Dec. 31, 2009 Gas [Member] WPL [Member]	Dec. 31, 2011 Other Plant In Service [Member] IPL [Member]	Dec. 31, 2010 Other Plant In Service [Member] IPL [Member]	Dec. 31, 2009 Other Plant In Service [Member] IPL [Member]	Dec. 31, 2011 Other Plant In Service [Member] WPL [Member]	Dec. 31, 2010 Other Plant In Service [Member] WPL [Member]	Dec. 31, 2009 Other Plant In Service [Member] WPL [Member]	Jan. 31, 2012 Generation [Member]	Dec. 31, 2011 Generation [Member] IPL [Member]	Dec. 31, 2010 Generation [Member] IPL [Member]	Dec. 31, 2009 Generation [Member] IPL [Member]	Dec. 31, 2011 Generation [Member] WPL [Member]	Dec. 31, 2010 Generation [Member] WPL [Member]	Dec. 31, 2009 Generation [Member] WPL [Member]
Public Utility, Property, Plant and Equipment [Line Items]
Average rate of depreciation	2.50%	2.40%	2.70%	2.70%	2.90%	2.60%	3.00%	3.50%	3.30%	3.10%	2.60%	2.20%	2.80%	4.80%	4.90%	6.00%	5.20%	6.50%	6.40%	3.80%	3.50%	3.70%	3.40%	3.30%	2.90%	3.20%