Stock-Based Compensation - Stock Options (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Number of Options
Beginning balance (in shares)	35,401
Granted (in shares)	3,612
Exercised (in shares)	(3,880)
Forfeited (in shares)	(206)
Ending balance (in shares)	34,927
Options exercisable (in shares)	27,271
Weighted Average Exercise Price
Beginning balance (in dollars per share)	$ 156.23
Granted (in dollars per share)	175.04
Exercised (in dollars per share)	110.14
Forfeited (in dollars per share)	179.50
Ending balance (in dollars per share)	163.16
Options exercisable (in dollars per share)	$ 160.79
Weighted Average Remaining Contractual Life (months)
Weighted average remaining contractual life for options outstanding (in months)	64 months
Weighted average remaining contractual life for options exercisable (in months)	52 months
Aggregate Intrinsic Value (millions)
Aggregate intrinsic value for options outstanding	$ 691
Aggregate intrinsic value for options exercisable	$ 634
Stock Options
Aggregate Intrinsic Value (millions)
Expiration of annual grants (in years)	10 years
Compensation expense yet to be recognized	$ 62
Expense recognition period (in months)	21 months
Total intrinsic value of stock options exercised	$ 306	$ 160
Cash received from options exercised	425	193
Tax benefit realized from exercise of stock options	$ 65	$ 34
Share- based compensation assumptions
Weighted average exercise price (in dollars per share)	$ 175.04
Risk-free interest rate (as a percent)	0.80%
Dividend yield (as a percent)	2.80%
Expected volatility (as a percent)	22.60%
Expected life (in months)	83 months
Black-Scholes fair value (in dollars per share)	$ 25.33
Stock Options | Minimum
Aggregate Intrinsic Value (millions)
Vesting period (in years)	1 year
Stock Options | Maximum
Aggregate Intrinsic Value (millions)
Vesting period (in years)	3 years