CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $)	Sep. 30, 2014	Dec. 31, 2013
Statement of Financial Position [Abstract]
Class A common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Class A common stock, shares authorized	199,300,000.0	199,300,000.0
Class A common stock, shares issued	102,000,000	100,400,000
Class A common stock, shares outstanding	84,800,000	85,200,000
Treasury stock, at cost, shares held	17,200,000	15,200,000