Condensed Consolidated Balance Sheets (Parenthetical) (USD $)	Sep. 30, 2011	Dec. 31, 2010
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	240,000,000	240,000,000
Common stock, shares outstanding	110,981,511	110,893,901
Shares in deferred compensation trust, shares	259,247	246,301
Shares in deferred compensation trust, weighted average cost per share	$ 31.47	$ 30.75
IPL [Member]
Common stock, par value	$ 2.5	$ 2.5
Common stock, shares authorized	24,000,000	24,000,000
Common stock, shares outstanding	13,370,788	13,370,788
WPL [Member]
Common stock, par value	$ 5	$ 5
Common stock, shares authorized	18,000,000	18,000,000
Common stock, shares outstanding	13,236,601	13,236,601