Stock-Based Incentive Compensation Plans (Total unrecognized compensation expense for all stock-based incentive compensation plans) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based compensation arrangement by share-based payment award [Line Items]
Expense	$ 59	$ 66	$ 73
Stock Options [Member]
Share-based compensation arrangement by share-based payment award [Line Items]
Expense	$ 8	$ 9	$ 9
Weighted average period (in years)	8 months 12 days	10 months 24 days	1 year 1 month 6 days
Performance Shares [Member]
Share-based compensation arrangement by share-based payment award [Line Items]
Expense	$ 14	$ 15	$ 14
Weighted average period (in years)	1 year 3 months 18 days	1 year 3 months 18 days	10 months 24 days
RSUs [Member]
Share-based compensation arrangement by share-based payment award [Line Items]
Expense	$ 37	$ 42	$ 50
Weighted average period (in years)	1 year 2 months 12 days	1 year 4 months 24 days	1 year 2 months 12 days

Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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 (i)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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