Stock-Based Compensation - Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Number of shares
Outstanding, beginning balance (in shares)	3,205	3,196
Granted (in shares)	764	723
Exercised (in shares)	(527)	(650)
Canceled (in shares)	(93)	(64)
Outstanding, ending balance (in shares)	3,349	3,205
Exercisable (in shares)	1,611
Weighted-average exercise price per share
Outstanding, beginning balance (in dollars per share)	$ 180.69	$ 140.68
Granted (in dollars per share)	320.65	279.10
Exercised (in dollars per share)	122.94	90.43
Canceled (in dollars per share)	273.64	211.57
Outstanding, ending balance (in dollars per share)	219.14	$ 180.69
Exercisable (in dollars per share)	$ 150.31
Weighted-average contractual term, outstanding	6 years 7 months 28 days	6 years 6 months 29 days
Weighted-average contractual term, exercisable	4 years 8 months 26 days
Aggregate intrinsic value, outstanding	$ 452.8	$ 284.0
Aggregate intrinsic value, exercisable	$ 328.6

The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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Period Type:	instant

- Definition

The weighted-average price as of the balance sheet date at which grantees can acquire the shares reserved for issuance on vested portions of options outstanding and currently exercisable under the stock option plan.