Income Taxes (Schedule Of Effective Income Tax Rates) (Details)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Alliant Energy Corporation [Member]
Effective Tax Rate [Line Items]
Income tax rates for continuing operations	39.00%	22.30%
IPL [Member]
Effective Tax Rate [Line Items]
Income tax rates for continuing operations	125.40%	5.90%
WPL [Member]
Effective Tax Rate [Line Items]
Income tax rates for continuing operations	44.10%	32.50%