Stock-Based Compensation - Stock Options (Details) - Stock Options - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Stock Option Program
Balance at the beginning of the period	34,965
Granted - Annual	3,174
Exercised	(2,378)
Forfeited	(73)
Balance at the end of the period	35,688
Options exercisable	27,222
Options exercisable, exercise price	$ 120.84
Weighted average exercise price - Beginning balance	125.73
Weighted average exercise price - Granted - Annual	233.62
Weighted average exercise price - Exercised	89.67
Weighted average exercise price - Canceled	186.24
Weighted average exercise price - Ending balance	$ 137.60
Weighted average remaining contractual life for options outstanding	71 months
Weighted average remaining contractual life for options exercisable	60 months
Aggregate intrinsic value for options outstanding	$ 2,226
Aggregate intrinsic value for options exercisable	$ 2,066
Expiration of annual grants	10 years
Compensation expense yet to be recognized	$ 102
Expense recognition period	23 months
Total intrinsic value of stock options exercised	$ 345	$ 465
Cash received from options exercised	212	416
Tax benefit realized from exercise of stock options	$ 73	$ 158
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