Share-Based Compensation Plans - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Shares
Outstanding at beginning of period (in shares)	723	672	574
Granted (in shares)	156	174	122
Exercised (in shares)	(90)	(79)	(24)
Expired or cancelled (in shares)	(1)	(44)
Outstanding at end of period (in shares)	788	723	672
Exercisable (in shares)	455	426	401
Wtd. Avg. Exercise Price Per Share
Outstanding at beginning of period (in dollars per share)	$ 87	$ 85	$ 77
Granted (in dollars per share)	93	84	123
Exercised (in dollars per share)	59	65	78
Expired or cancelled (in dollars per share)	54	91
Outstanding at end of period (in dollars per share)	91	87	85
Exercisable (in dollars per share)	$ 90	$ 82	$ 76
Wtd. Avg. Remaining Contractual Term and Aggregate Intrinsic Value
Outstanding (in years)	6 years 2 months 12 days	6 years 1 month 6 days	5 years 10 months 24 days
Exercisable (in years)	4 years 6 months	4 years 6 months	4 years 6 months
Outstanding	$ 4	$ 10	$ 1
Exercised	3	2	1
Exercisable	$ 3	$ 8	$ 1