Stockholders' Equity (Summary of Activity Related to Stock Option Plans) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Shares available for grant, beginning balances	6,111,561	8,699,941	10,739,915
Options outstanding, number of shares, beginning balance (in shares)	20,859,326	20,479,278	21,647,350
Shares available for grant, number of shares authorized (in shares)	17,500,000
Options outstanding, number of shares granted (in shares)	1,909,476	2,588,380	2,039,974
Options outstanding, number of shares, exercised (in shares)	(4,088,612)	(2,208,052)	(3,205,911)
Options outstanding, number of shares expired (in shares)	(3,380)	(280)	(2,135)
Shares available for grant, ending balances	21,702,085	6,111,561	8,699,941
Options outstanding, number of shares, ending balance (in shares)	18,676,810	20,859,326	20,479,278
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Options outstanding, weighted-average exercise price, beginning balance (dollars per share)	$ 124.28	$ 89.61	$ 61.13
Options outstanding, weighted-average exercise price, granted (dollars per share)	432.34	320.66	311.66
Options outstanding, weighted-average exercise price, exercised (dollars per share)	58.35	32.88	38.66
Options expired, weighted-average exercise price (dollars per share)	27.54	6.74	4.60
Options outstanding, weighted-average exercise price, ending balance (dollars per share)	$ 170.23	$ 124.28	$ 89.61
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Options outstanding, number of shares, vested and exercisable (in shares)	18,676,810
Options outstanding, weighted-average exercise price, vested and exercisable (in dollars per share)	$ 170.23
Weighted-average remaining contractual term (in years)	5 years 6 months 18 days
Aggregate intrinsic value, vested and exercisable	$ 6,922

Number of additional shares authorized for issuance under share-based payment arrangement.

No definition available.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.