Stock-based Compensation - Schedule of Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	6 Months Ended
	Jun. 30, 2015
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)	$ 9.38
Granted (in shares)	1.2
Granted (usd per share)	$ 31.91
Exercised (in shares)	(5.0)
Exercised (usd per share)	$ 9.45
Forfeited (in shares)	0.0
Forfeited (usd per share)	$ 0.00
Outstanding at June 30, 2015 (in shares)	13.3
Outstanding at June 30, 2015 (usd per share)	$ 11.34
Vested and expected to vest at June 30, 2015 (in shares)	13.3
Vested and expected to vest at June 30, 2015 (usd per share)	$ 11.34
Vested and expected to vest at June 30, 2015, aggregate intrinsic value	$ 289.5
Vested and expected to vest at June 30, 2015, life (in years)	8 years 3 months 4 days
Exercisable at June 30, 2015 (in shares)	12.1
Exercisable at June 30, 2015 (usd per share)	$ 9.35
Exercisable at June 30, 2015, aggregate intrinsic value	$ 288.1
Exercisable at June 30, 2015, life (in years)	8 years 1 month 10 days