Stockholders' Deficit - Changes in Class A Common Stock (Details) - shares shares in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Change in the number of shares of Class A common stock outstanding [Roll Forward]
Shares outstanding as of beginning of period (in shares)	88.0
Shares outstanding as of end of period (in shares)	89.9	88.0
Class A Common Stock
Change in the number of shares of Class A common stock outstanding [Roll Forward]
Shares outstanding as of beginning of period (in shares)	88.0	86.5
Shares issued as part of equity-based compensation plans and the ESPP, net of shares surrendered (in shares)	1.9	1.5
Shares outstanding as of end of period (in shares)	89.9	88.0