Stock-Based Compensation - Stock Options (Details) - Stock Options - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Stock Option Program
Balance at the beginning of the period	34,965
Granted - Annual	3,211
Exercised	(2,974)
Forfeited	(106)
Balance at the end of the period	35,096
Options exercisable	26,624
Options exercisable, exercise price	$ 121.37
Weighted average exercise price - Beginning balance	125.73
Weighted average exercise price - Granted - Annual	233.19
Weighted average exercise price - Exercised	91.16
Weighted average exercise price - Canceled	187.42
Weighted average exercise price - Ending balance	$ 138.30
Weighted average remaining contractual life for options outstanding	69 months
Weighted average remaining contractual life for options exercisable	58 months
Aggregate intrinsic value for options outstanding	$ 2,613
Aggregate intrinsic value for options exercisable	$ 2,379
Expiration of annual grants	10 years
Compensation expense yet to be recognized	$ 84
Expense recognition period	22 months
Total intrinsic value of stock options exercised	$ 411	$ 526
Cash received from options exercised	270	468
Tax benefit realized from exercise of stock options	$ 87	$ 179
Share- based compensation assumptions
Weighted average exercise price	$ 233.63
Risk-free interest rate (as a percent)	2.70%
Dividend yield (as a percent)	2.40%
Expected volatility (as a percent)	21.00%
Expected life	78 months
Black-Scholes fair value	$ 41.59
Maximum
Stock Option Program
Vesting period	3 years
Minimum
Stock Option Program
Vesting period	1 year