Income Taxes (Schedule Of Effective Income Tax Rates) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Alliant Energy [Member]
Effective Tax Rate [Line Items]
Income tax rates for continuing operations	20.40%	23.50%	24.00%	16.60%
IPL [Member]
Effective Tax Rate [Line Items]
Income tax rates for continuing operations	(12.60%)	(3.30%)	(5.60%)	(1.70%)
WPL [Member]
Effective Tax Rate [Line Items]
Income tax rates for continuing operations	35.50%	34.40%	37.70%	33.00%