Income Taxes (Schedule Of Effective Income Tax Rates) (Details)	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Alliant Energy [Member]
Effective Tax Rate [Line Items]
Income tax rates for continuing operations	19.50%	(25.90%)	28.30%	7.80%
IPL [Member]
Effective Tax Rate [Line Items]
Income tax rates for continuing operations	(12.00%)	(233.30%)	22.60%	3.40%
WPL [Member]
Effective Tax Rate [Line Items]
Income tax rates for continuing operations	34.60%	31.10%	39.40%	32.00%