Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Redeemable convertible preferred stock, liquidation preference	$ 50	$ 50
Redeemable convertible preferred stock, shares outstanding	76,002	76,202
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares issued	49,697,763	52,116,390
Common stock, shares outstanding	49,697,763	52,116,390
Treasury stock, shares	8,758,267	6,211,854
Allowance for Doubtful Accounts [Member]
Allowances for receivables	$ 17.2	$ 21.1