Condensed Consolidated Balance Sheets (Parenthetical) (USD $)	Mar. 31, 2012	Dec. 31, 2011
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	240,000,000	240,000,000
Common stock, shares outstanding	110,962,089	111,018,821
Shares in deferred compensation trust, shares	249,298	262,735
Shares in deferred compensation trust, weighted average cost per share	$ 32.10	$ 31.68
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