Stock-Based Compensation - Summary of the Company's Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Options
Options outstanding at the beginning of the period (in shares)	3.6
Granted (in shares)	0.3
Exercised (in shares)	(0.6)
Forfeited (in shares)	(0.1)
Canceled (in shares)	(0.5)
Options outstanding at the end of the period (in shares)	2.7	3.6
Options vested and expected to vest (in shares)	2.7
Options exercisable (in shares)	2.2
Weighted Average Exercise Price
Options outstanding at the beginning of the period (in dollars per share)	$ 15.62
Granted (in dollars per share)	18.67
Exercised (in dollars per share)	8.19
Forfeited (in dollars per share)	16.54
Canceled (in dollars per share)	24.34
Options outstanding at the end of the period (in dollars per share)	15.95	$ 15.62
Options vested and expected to vest (in dollars per share)	15.94
Options exercisable (in dollars per share)	$ 15.81
Weighted Average Remaining Contractual Life (Years)
Options outstanding	4 years 10 months 24 days	4 years 6 months
Options vested and expected to vest	4 years 9 months 18 days
Options exercisable	4 years
Aggregate Intrinsic Value
Options outstanding	$ 22.9	$ 0.0
Options vested and expected to vest	0.0
Options exercisable	$ 18.8
Exercise Price, low end of range (in dollars per share)	$ 3.51
Exercise Price, high end of range (in dollars per share)	$ 31.14