Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Per Share data	Sep. 30, 2011	Dec. 31, 2010
Statement of Financial Position [Abstract]
Common stock, shares subject to redemption	0.2	0.2
Preferred stock, shares authorized	25.0	25.0
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, shares authorized	200.0	200.0
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares issued	67.23	66.81
Common stock, shares outstanding	67.23	66.81