Common Equity And Preferred Stock (Narrative) (Details) (USD $)	1 Months Ended		9 Months Ended		12 Months Ended
	Apr. 30, 2011	Jul. 31, 2008	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010
Cumulative preferred stock rate	7.10%
Payments to redeem cumulative preferred stock			$ 40,000,000
IPL [Member]
Retained earnings free of dividend restrictions			315,000,000
Restricted net assets of subsidiaries			1,000,000,000
Capital contributions from parent				50,000,000
FERC order to pay common equity distributions, maximum		400,000,000
Preferred stock redeemed during the period	1,600,000
Cumulative preferred stock rate			8.375%		7.10%
Payments to redeem cumulative preferred stock	40,000,000		40,000,000
WPL [Member]
Retained earnings free of dividend restrictions			29,000,000
Restricted net assets of subsidiaries			1,400,000,000
Capital contributions from parent			25,000,000	75,000,000
Cumulative preferred stock rate			4.50%		4.50%
Alliant Energy And IPL [Member]
Preferred dividend requirements			1,500,000
Resources [Member]
Capital contributions from parent			$ 65,000,000