Stock-Based Compensation - Stock Options (Details) - Stock Options - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Stock Option Program
Balance at the beginning of the period	34,569
Granted - Annual	3,423
Exercised	(1,983)
Forfeited	(9)
Balance at the end of the period	36,000
Options exercisable	28,703
Options exercisable, exercise price	$ 133.67
Weighted average exercise price - Beginning balance	138.98
Weighted average exercise price - Granted - Annual	201.12
Weighted average exercise price - Exercised	82.26
Weighted average exercise price - Forfeited	205.82
Weighted average exercise price - Ending balance	$ 148.00
Weighted average remaining contractual life for options outstanding	71 months
Weighted average remaining contractual life for options exercisable	61 months
Aggregate intrinsic value for options outstanding	$ 2,233
Aggregate intrinsic value for options exercisable	$ 2,154
Expiration of annual grants	10 years
Compensation expense yet to be recognized	$ 117
Expense recognition period	25 months
Total intrinsic value of stock options exercised	$ 235	$ 283
Cash received from options exercised	162	166
Tax benefit realized from exercise of stock options	$ 49	$ 61
Share- based compensation assumptions
Weighted average exercise price	$ 201.12
Risk-free interest rate (as a percent)	2.60%
Dividend yield (as a percent)	2.50%
Expected volatility (as a percent)	20.40%
Expected life	79 months
Black-Scholes fair value	$ 34.19
Maximum
Stock Option Program
Vesting period	3 years
Minimum
Stock Option Program
Vesting period	1 year