Stock-Based Compensation - Stock Options (Details) - Stock Options - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Stock Option Program
Balance at the beginning of the period	33,675
Granted - Annual	4,741
Exercised	(1,159)
Forfeited	(41)
Balance at the end of the period	37,216
Options exercisable	29,173
Options exercisable, exercise price	$ 146.86
Weighted average exercise price - Beginning balance	151.15
Weighted average exercise price - Granted - Annual	157.26
Weighted average exercise price - Exercised	87.25
Weighted average exercise price - Forfeited	193.77
Weighted average exercise price - Ending balance	$ 153.87
Weighted average remaining contractual life for options outstanding	70 months
Weighted average remaining contractual life for options exercisable	58 months
Aggregate intrinsic value for options outstanding	$ 359
Aggregate intrinsic value for options exercisable	$ 359
Expiration of annual grants	10 years
Compensation expense yet to be recognized	$ 107
Expense recognition period	25 months
Total intrinsic value of stock options exercised	$ 98	$ 235
Cash received from options exercised	100	162
Tax benefit realized from exercise of stock options	$ 20	$ 49
Share- based compensation assumptions
Weighted average exercise price	$ 157.24
Risk-free interest rate (as a percent)	1.50%
Dividend yield (as a percent)	2.70%
Expected volatility (as a percent)	19.70%
Expected life	78 months
Black-Scholes fair value	$ 21.58
Maximum
Stock Option Program
Vesting period	3 years
Minimum
Stock Option Program
Vesting period	1 year