Stock-Based Compensation - Stock Options (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Stock Option Program
Balance at the beginning of the period	34,965	36,196
Balance at the end of the period		34,965	36,196
Weighted average exercise price - Beginning balance	$ 125.73	$ 112.07
Weighted average exercise price - Ending balance		125.73	$ 112.07
Share- based compensation assumptions
Weighted average exercise price	$ 233.63	$ 175.76	$ 147.87
Risk-free interest rate (as a percent)	2.70%	2.10%	1.50%
Dividend yield (as a percent)	2.40%	2.50%	2.50%
Expected volatility (as a percent)	21.00%	17.30%	20.80%
Expected life	78 months	78 months	77 months
Black-Scholes fair value	$ 41.59	$ 23.51	$ 22.47
Stock Options
Stock Option Program
Balance at the beginning of the period	34,965	36,196	38,552
Granted - Annual	3,211	5,410	5,592
Exercised	(3,482)	(6,474)	(7,716)
Forfeited	(125)	(167)	(232)
Balance at the end of the period	34,569	34,965	36,196
Options exercisable	26,117	24,281	25,241
Options exercisable, exercise price	$ 121.98	$ 108.50	$ 95.65
Weighted average exercise price - Beginning balance	125.73	112.07	102.01
Weighted average exercise price - Granted - Annual	233.19	175.93	147.99
Weighted average exercise price - Exercised	91.01	90.37	86.76
Weighted average exercise price - Canceled	188.00	162.36	148.43
Weighted average exercise price - Ending balance	$ 138.98	$ 125.73	$ 112.07
Weighted average remaining contractual life for options outstanding	66 months
Weighted average remaining contractual life for options exercisable	55 months
Aggregate intrinsic value for options outstanding	$ 1,918.0
Aggregate intrinsic value for options exercisable	$ 1,791.0
Expiration of annual grants	10 years
Compensation expense yet to be recognized	$ 66.0
Expense recognition period	20 months
Total intrinsic value of stock options exercised	$ 469.0	$ 703.0	$ 608.0
Cash received from options exercised	316.0	585.0	665.0
Tax benefit realized from exercise of stock options	$ 99.0	$ 238.0	$ 224.0
Stock Options | Maximum
Stock Option Program
Vesting period	3 years
Stock Options | Minimum
Stock Option Program
Vesting period	1 year