Equity Compensation Plans - Summary of Stock Activity (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Number of Options/Shares
Outstanding, beginning balance (in shares)	6,432,814
Granted (in shares)	883,282	0
Dividend reinvestment (in shares)	0
Exercised or lapsed (in shares)	(449,007)
Cancelled or expired (in shares)	(49,672)
Outstanding, ending balance (in shares)	6,817,417
Options exercisable (in shares)	3,808,076		4,175,855
Nonvested (in shares)	3,008,420
Expected to vest (in shares)	2,604,017
Weighted Average Exercise Price
Outstanding, beginning balance (in dollars per share)	$ 79.51
Granted (in dollars per share)	158.63
Dividends reinvested (in dollars per share)	0
Exercised or lapsed (in dollars per share)	43.28
Cancelled or expired (in dollars per share)	113.26
Outstanding, ending balance (in dollars per share)	91.86
Options exercisable (in dollars per share)	$ 66.94		$ 65.05
Aggregate Intrinsic Value
Outstanding	$ 324.0		$ 449.2
Exercised or lapsed	50.7
Aggregate intrinsic value, options exercisable	$ 275.9		$ 352.0
Restricted stock
Number of Options/Shares
Outstanding, beginning balance (in shares)	428,729
Granted (in shares)	149,040
Dividend reinvestment (in shares)	0
Exercised or lapsed (in shares)	(2,478)
Cancelled or expired (in shares)	(8,842)
Outstanding, ending balance (in shares)	566,449
Nonvested (in shares)	566,449
Expected to vest (in shares)	487,007
Weighted Average Exercise Price
Outstanding, beginning balance (in dollars per share)	$ 107.96
Granted (in dollars per share)	158.62
Dividends reinvested (in dollars per share)	0
Exercised or lapsed (in dollars per share)	107.87
Cancelled or expired (in dollars per share)	118.60
Outstanding, ending balance (in dollars per share)	$ 121.00
Performance shares
Number of Options/Shares
Outstanding, beginning balance (in shares)	93,960
Granted (in shares)	50,736
Dividend reinvestment (in shares)	268
Exercised or lapsed (in shares)	0
Cancelled or expired (in shares)	0
Outstanding, ending balance (in shares)	144,964
Nonvested (in shares)	145,121
Expected to vest (in shares)	288,444
Weighted Average Exercise Price
Outstanding, beginning balance (in dollars per share)	$ 158.50
Granted (in dollars per share)	192.93
Outstanding, ending balance (in dollars per share)	$ 170.40