CONSOLIDATED BALANCE SHEETS (Parenthetical) (USD $) In Millions, except Per Share data, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Statement of Financial Position [Abstract]
Software accumulated amortization	$ 138.0	$ 114.2
Class A common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Class A common stock, shares authorized	199.3	199.3
Class A common stock, shares issued	101.4	100.4
Class A common stock, shares outstanding	84.2	85.2
Treasury stock, at cost, shares held	17.2	15.2