Stock-based Compensation - Schedule of Stock Option Activity (Details) $ / shares in Units, shares in Millions, $ in Millions	9 Months Ended
	Sep. 30, 2015 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding at January 1, 2015 (in shares)	17.1
Outstanding at January 1, 2015 (usd per share) | $ / shares	$ 9.38
Granted (in shares)	1.2
Granted (usd per share) | $ / shares	$ 31.45
Exercised (in shares)	(7.0)
Exercised (usd per share) | $ / shares	$ 8.91
Forfeited (in shares)	0.0
Forfeited (usd per share) | $ / shares	$ 0.00
Outstanding at September 30, 2015 (in shares)	11.3
Outstanding at September 30, 2015 (usd per share) | $ / shares	$ 12.01
Vested and expected to vest at September 30, 2015 (in shares)	11.3
Vested and expected to vest at September 30, 2015 (usd per share) | $ / shares	$ 12.01
Vested and expected to vest at September 30, 2015, aggregate intrinsic value | $	$ 158.5
Vested and expected to vest at September 30, 2015, life (in years)	8 years 18 days
Exercisable at September 30, 2015 (in shares)	10.1
Exercisable at September 30, 2015 (usd per share) | $ / shares	$ 9.70
Exercisable at September 30, 2015, aggregate intrinsic value | $	$ 158.2
Exercisable at September 30, 2015, life (in years)	7 years 10 months 9 days