Stock-Based Compensation Option Activity (Details) $ / shares in Units, shares in Millions, $ in Millions	6 Months Ended
	Jun. 30, 2017 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options outstanding, beginning of period (in shares) | shares	10.7
Options granted (in shares) | shares	1.8
Options exercised (in shares) | shares	(0.7)
Options canceled/forfeited (in shares) | shares	(0.2)
Options outstanding, end of period (in shares) | shares	11.6
Options vested and expected to vest (in shares) | shares	11.2	[1]
Options vested (in shares) | shares	5.1
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Options outstanding, beginning of period (in dollars per share) | $ / shares	$ 33.23
Options granted (in dollars per share) | $ / shares	57.41
Options exercised (in dollars per share) | $ / shares	23.50
Options canceled/forfeited (in dollars per share) | $ / shares	42.51
Options outstanding, end of period (in dollars per share) | $ / shares	37.40
Options vested and expected to vest (in dollars per share) | $ / shares	36.16	[1]
Options vested (in dollars per share) | $ / shares	$ 27.25
Weighted average remaining contractual term, outstanding	6 years 8 months
Weighted average remaining contractual term, vested and expected to vest	6 years 6 months	[1]
Weighted average remaining contractual term, vested	4 years 8 months
Aggregate intrinsic value, outstanding | $	$ 302.4
Aggregate intrinsic value, vested and expected to vest | $	295.8	[1]
Aggregate intrinsic value, vested | $	$ 183.8

[1] The “expected to vest” options are the net unvested options that remain after applying the forfeiture rate assumption to total unvested options.