Share-Based Compensation (Stock Option Compensation Expense) (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]
Pretax compensation expense	$ 21	$ 22	$ 20
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Pretax compensation expense	10	10	11
Tax benefit	(2)	(1)	(2)
Compensation expense, net of tax	$ 8	$ 9	$ 9
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition	1 year 9 months 18 days

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
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- Definition

Amount, after tax, of expense for award under share-based payment arrangement.

+ References

No definition available.

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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.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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Amount of tax benefit for recognition of expense of award under share-based payment arrangement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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