Stock-Based Compensation - Stock Options (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
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
Stock Options
Stock Option Program
Balance at the beginning of the period	35,401
Granted - Annual	3,612
Exercised	(2,323)
Forfeited	(104)
Balance at the end of the period	36,586
Options exercisable	28,819
Weighted average exercise price - Beginning balance	$ 156.23
Weighted average exercise price - Granted - Annual	175.04
Weighted average exercise price - Exercised	104.16
Weighted average exercise price - Forfeited	174.71
Weighted average exercise price - Ending balance	161.34
Options exercisable, exercise price	$ 158.58
Weighted average remaining contractual life for options outstanding	68 months
Weighted average remaining contractual life for options exercisable	57 months
Aggregate intrinsic value for options outstanding	$ 1,299
Aggregate intrinsic value for options exercisable	$ 1,126
Expiration of annual grants	10 years
Compensation expense yet to be recognized	$ 93
Expense recognition period	25 months
Total intrinsic value of stock options exercised	$ 180	$ 98
Cash received from options exercised	240	100
Tax benefit realized from exercise of stock options	$ 38	$ 20
Stock Options | Maximum
Stock Option Program
Vesting period	3 years
Stock Options | Minimum
Stock Option Program
Vesting period	1 year