Stock-based Compensation - Schedule of Stock Option Activity (Details) $ / shares in Units, shares in Millions, $ in Millions	9 Months Ended
	Sep. 30, 2017 USD ($) $ / shares shares
Awards (in millions)
Beginning Balance | shares	9.6
Grants in period | shares	0.9
Exercises in period | shares	(1.9)
Forfeitures in period | shares	(0.1)
Ending Balance | shares	8.5
Weighted Average Exercise Price (usd per share)
Beginning Balance | $ / shares	$ 14.40
Grants in period (usd per share) | $ / shares	29.56
Exercised (usd per share) | $ / shares	10.76
Forfeited (usd per share) | $ / shares	25.61
Ending Balance | $ / shares	$ 16.58
Vested and Expected to Vest
Vested and expected to vest, in shares | shares	8.5
Vested and expected to vest, weighted average exercise price (usd) | $ / shares	$ 16.58
Vested and expected to vest, aggregate intrinsic value | $	$ 108.9
Vested and expected to vest, weighted average contractual life (in years)	6 years 9 months 8 days
Exercisable
Exercisable, in shares | shares	6.6
Exercisable, usd per share | $ / shares	$ 13.33
Exercisable, aggregate intrinsic value | $	$ 105.1
Exercisable, weighted average contractual life (in years)	6 years 2 months 23 days