Stock-Based Compensation - Stock Options (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share- based compensation assumptions
Weighted average exercise price	$ 157.24	$ 201.12	$ 233.63
Risk-free interest rate (as a percent)	1.50%	2.60%	2.70%
Dividend yield (as a percent)	2.70%	2.50%	2.40%
Expected volatility (as a percent)	19.70%	20.40%	21.00%
Expected life	78 months	79 months	78 months
Black-Scholes fair value	$ 21.58	$ 34.19	$ 41.59
Stock Options
Stock Option Program
Balance at the beginning of the period	33,675	34,569	34,965
Granted - Annual	4,777	3,434	3,211
Exercised	(2,759)	(4,193)	(3,482)
Forfeited	(292)	(135)	(125)
Balance at the end of the period	35,401	33,675	34,569
Options exercisable	27,537	26,487	26,117
Options exercisable, exercise price	$ 149.67	$ 136.75	$ 121.98
Weighted average exercise price - Beginning balance	151.15	138.98	125.73
Weighted average exercise price - Granted - Annual	157.25	200.80	233.19
Weighted average exercise price - Exercised	93.23	89.89	91.01
Weighted average exercise price - Forfeited	181.33	201.27	188.00
Weighted average exercise price - Ending balance	$ 156.23	$ 151.15	$ 138.98
Weighted average remaining contractual life for options outstanding	63 months
Weighted average remaining contractual life for options exercisable	51 months
Aggregate intrinsic value for options outstanding	$ 929
Aggregate intrinsic value for options exercisable	$ 847
Expiration of annual grants	10 years
Compensation expense yet to be recognized	$ 56
Expense recognition period	20 months
Total intrinsic value of stock options exercised	$ 206	$ 433	$ 469
Cash received from options exercised	256	375	316
Tax benefit realized from exercise of stock options	$ 44	$ 91	$ 99
Stock Options | Maximum
Stock Option Program
Vesting period	3 years
Stock Options | Minimum
Stock Option Program
Vesting period	1 year