Stock-Based Compensation - Stock Options (Details) - Stock Options - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Stock Option Program
Balance at the beginning of the period	35,401
Granted - Annual	3,612
Exercised	(3,514)
Forfeited	(144)
Balance at the end of the period	35,355
Options exercisable	27,628
Weighted average exercise price - Beginning balance	$ 156.23
Weighted average exercise price - Granted - Annual	175.04
Weighted average exercise price - Exercised	109.34
Weighted average exercise price - Forfeited	177.73
Weighted average exercise price - Ending balance	162.73
Options exercisable, exercise price	$ 160.24
Weighted average remaining contractual life for options outstanding	66 months
Weighted average remaining contractual life for options exercisable	55 months
Aggregate intrinsic value for options outstanding	$ 1,383
Aggregate intrinsic value for options exercisable	$ 1,172
Expiration of annual grants	10 years
Compensation expense yet to be recognized	$ 76
Expense recognition period	23 months
Total intrinsic value of stock options exercised	$ 277	$ 127
Cash received from options exercised	382	145
Tax benefit realized from exercise of stock options	$ 59	$ 27
Share- based compensation assumptions
Weighted average exercise price	$ 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	83 months
Black-Scholes fair value	$ 25.33
Maximum
Stock Option Program
Vesting period	3 years
Minimum
Stock Option Program
Vesting period	1 year