Stockholders' Equity (Details) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Change in the number of shares of Class A common stock outstanding
Shares outstanding as of beginning of period	85.1	85.2
Shares issued as part of equity-based compensation plans and the ESPP, net of RSUs surrendered	0.7	1.9
Common stock repurchases	0	(2.0)
Shares outstanding as of end of period	85.8	85.1