Consolidated Balance Sheets (Parenthetical) (USD $) In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Preferred stock, par value	$ 0.01	$ 0.01
Preferred stock, shares authorized	100.0	100.0
Preferred stock, shares issued
Preferred stock, shares outstanding
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	500.0	500.0
Common stock, shares issued	189.5	186.6
Treasury stock, shares	23.8	19.3

Face amount or stated value of common stock per share; generally not indicative of the fair market value per share.

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