Stock Options and Other Share-Based Compensation - Summary of Valuation Assumptions and Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stock Option
Expected term in years	6 years 7 months 6 days	6 years 7 months 6 days	6 years 6 months
Volatility	20.80%	20.50%	21.20%
Risk-free interest rate based on zero coupon U.S. treasury note	1.50%	2.60%	2.60%
Dividend yield	4.00%	3.80%	3.80%
Weighted-average fair value per option granted (in dollars per share)	$ 13.00	$ 15.82	$ 18.18
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding, beginning balance (in shares)	86,641
Shares, Granted (in shares)	8,281
Shares, Exercised (in shares)	(2,739)
Shares, Forfeited (in shares)	(2,033)
Outstanding, ending balance (in shares)	90,150	86,641
Shares, Exercisable at December 31 (in shares)	80,860
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Weighted-Average Exercise Price, Outstanding at January 1 (in dollars per share)	$ 103.22
Weighted-Average Exercise Price, Granted (in dollars per share)	150.98
Weighted-Average Exercise Price, Exercised (in dollars per share)	78.92
Weighted-Average Exercise Price, Forfeited (in dollars per share)	110.72
Weighted-Average Exercise Price, Outstanding at December 31 (in dollars per share)	108.17	$ 103.22
Weighted-Average Exercise Price, Exercisable at December 31 (in dollars per share)	$ 107.65
Average Remaining Contractual Term, Outstanding at December 31 (in years)	4 years 1 month 9 days
Average Remaining Contractual Term, Exercisable at December 31 (in years)	3 years 7 months 2 days
Aggregate Intrinsic Value, Outstanding at December 31	$ 23
Aggregate Intrinsic Value, Exercisable at December 31	$ 23