Share-Based Compensation - Stock and Status (Details) - Stock Options - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Options
Outstanding at beginning of period (in shares)	6,299,803
Granted (in shares)	2,011,667
Exercised (in shares)	(166,508)	(174,295)
Forfeited/cancelled (in shares)	(77,200)
Outstanding at the end of period (in shares)	8,067,762
Exercisable at the end of period (in shares)	3,885,475
Unvested at the end of period (in shares)	4,182,287
Weighted-Average Exercise Price
Outstanding at beginning of period (in dollars per share)	$ 120.78
Granted (in dollars per share)	126.54
Exercised (in dollars per share)	53.10
Forfeited (in dollars per share)	130.73
Outstanding at the end of period (in dollars per share)	123.52
Exercisable at the end of period (in dollars per share)	119.05
Unvested at the end of period (in dollars per share)	$ 127.67
Weighted Average Remaining Contractual Term (in Years)
Outstanding at the end of period (in Years)	7 years
Exercisable at the end of period (in Years)	5 years 9 months 18 days
Unvested at the end of period (in Years)	8 years 1 month 6 days
Aggregate Intrinsic Value
Outstanding at the end of period)	$ 38.6
Exercisable at the end of period	32.8
Unvested at the end of period	$ 5.8
Weighted average grant date fair value of stock options (in dollars per share)	$ 40.03	$ 45.00
Aggregate grant date fair value	$ 80.5	$ 42.5
Total fair value of employee stock options that vested	$ 33.7	$ 31.1