Share-Based Compensation Plans (Summary of Stock Option Activity) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Options
Outstanding at January 1, 2019 (in shares)	4,752,808
Granted (in shares)	830,900
Forfeited (in shares)	(553)
Exercised (in shares)	(803,751)
Outstanding at December 31, 2019 (in shares)	4,779,404	4,752,808
Vested at December 31, 2019 (in shares)	3,603,296
Exercisable at December 31, 2019 (in shares)	3,267,111
Weighted- Average Exercise Price
Outstanding at January 1, 2019 (in dollars per share)	$ 63.11
Granted (in dollars per share)	94.97
Forfeited (in dollars per share)	94.85
Exercised (in dollars per share)	39.90
Outstanding at December 31, 2019 (in dollars per share)	72.55	$ 63.11
Vested at December 31, 2019 (in dollars per share)	65.69
Exercisable at December 31, 2019 (in dollars per share)	63.57
Weighted-Average Grant-Date Fair Value (in dollars per share)	$ 17.58	$ 20.69	$ 16.95
Aggregate Intrinsic Value, Exercised	$ 51	$ 37	$ 62
Aggregate Intrinsic Value, Exercisable	162
Aggregate Intrinsic Value, Vested	$ 154

Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The number of shares under options that were cancelled during the reporting period as a result of occurrence of a terminating event specified in contractual agreements pertaining to the stock option plan.