Stockholders' Equity (Details) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Change in the number of shares of Class A common stock outstanding
Shares outstanding as of beginning of period	85.2	84.4
Shares issued as part of equity-based compensation plans and the ESPP, net of RSUs surrendered	1.6	1.1
Common stock repurchases	(2.0)	(0.3)
Shares outstanding as of end of period	84.8	85.2