Stock-Based Compensation (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Stock-based compensation awards
Stock-based compensation expense, before tax (in dollars)	$ 50	$ 49
Assumptions used in determining the fair value of the stock-based awards
Weighted-average dividend yield (as a percent)	2.70%	3.42%
Weighted-average volatility (as a percent)	30.20%	29.20%
Volatilities, low end of range (as a percent)	21.50%	22.10%
Volatilities, high end of range (as a percent)	33.00%	33.00%
Risk-free interest rates, low end of range (as a percent)	2.02%	0.81%
Risk-free interest rates, high end of range (as a percent)	2.87%	2.35%
Weighted-average expected lives (in years)	8 years	8 years
Unrecognized compensation cost related to nonvested stock-based compensation awards (in dollars)	$ 327
Term of amortization of unrecognized compensation cost over weighted-average remaining requisite service periods (in years)	2 years
Stock Options
Stock-based compensation awards
Shares Granted (in shares)	1,566,788	2,701,644
Weighted-Average Fair Value Per Share (in dollars per share)	$ 46.18	$ 25.01
Weighted-Average Grant Date Stock Price (in dollars per share)	151.12	95.66
RSUs
Stock-based compensation awards
Weighted-Average Grant Date Stock Price (in dollars per share)	$ 151.12	$ 95.63
Shares Granted (in shares)	676,228	906,068
Weighted-Average Fair Value Per Share (in dollars per share)	$ 151.12	$ 89.76
PRSUs
Stock-based compensation awards
Weighted-Average Grant Date Stock Price (in dollars per share)	$ 151.12	$ 95.66
Shares Granted (in shares)	339,559	437,385
Weighted-Average Fair Value Per Share (in dollars per share)	$ 151.12	$ 86.78