Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Consolidated Balance Sheets
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	200.0	200.0
Common stock, shares issued	101.0	99.5
Treasury stock, shares	2.2	2.2