Stock-based Compensation (Schedule of Stock Option Exercises) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Stock Option Aggregate Disclosures [Abstract]
Intrinsic value of stock options exercised	$ 9	$ 17	$ 32	$ 65
Cash received from option exercises	4	18	34	51
Treasury shares repurchased for employee payroll taxes	(1)	(4)	(7)	(12)
Tax benefit realized from option exercises	2	3	6	14
Aggregate grant-date fair value of stock options vested			$ 14	$ 14

Aggregate grant-date fair value of stock options vested.

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Value of treasury shares repurchased during period for employee payroll taxes related to share-based compensation awards.

+ References

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Amount of tax benefit from exercise of option under share-based payment arrangement.

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Amount of cash inflow from exercise of option under share-based payment arrangement.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=SL79508275-113901

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3255-108585

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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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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (d)(2)
-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

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