Share-Based Compensation - Stock and Status (Details) - Stock Options - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Options
Outstanding at beginning of period (in shares)		6,299,803
Granted (in shares)		2,081,047
Exercised (in shares)	(4,857)	(191,508)	(287,760)
Forfeited/canceled (in shares)		(95,016)
Outstanding at the end of period (in shares)		8,094,326
Exercisable at the end of period (in shares)		3,915,462
Unvested at the end of period (in shares)		4,178,864
Weighted-Average Exercise Price
Outstanding at beginning of period (in dollars per share)		$ 120.78
Granted (in dollars per share)		124.87
Exercised (in dollars per share)		51.53
Forfeited (in dollars per share)		131.04
Outstanding at the end of period (in dollars per share)		123.35
Exercisable at the end of period (in dollars per share)		119.40
Unvested at the end of period (in dollars per share)		$ 127.05
Weighted Average Remaining Contractual Term (in Years)
Outstanding at the end of period (in Years)		6 years 6 months
Exercisable at the end of period (in Years)		5 years 4 months 24 days
Unvested at the end of period (in Years)		7 years 7 months 6 days
Outstanding at the end of period)		$ 8.4
Exercisable at the end of period		8.2
Unvested at the end of period		$ 0.2
Share-based Compensation Arrangement by Share-based Payment Award, Options, Aggregate Intrinsic Value Disclosures [Abstract]
Weighted average grant date fair value of stock options (in dollars per share)		$ 39.63	$ 45.02
Aggregate grant date fair value		$ 82.5	$ 44.3
Total grant date fair value of employee stock options that vested		$ 36.4	$ 33.9