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

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Number of shares authorized for issuance under share-based payment arrangement.

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Stock-Based Compensation (Narrative) (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]
Number of shares authorized (in shares)	8,000,000
Maximum shares available for grants (in shares)	2,300,000
Settled performance share units and restricted stock units	$ 58	$ 83	$ 54
Compensation cost not yet recognized	$ 34
Expected weighted average recognition period for share-based compensation expense, in months	22 months
Performance Share Units \| Market Condition PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	38 months
Award Requisite Service Period	5 years
Percentage of shares issued per share unit, minimum	0.00%
Percentage of shares issued per share unit, maximum	200.00%
Performance Share Units \| Performance Condition PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	38 months
Award Requisite Service Period	5 years
Percentage of shares issued per share unit, minimum	0.00%
Percentage of shares issued per share unit, maximum	200.00%
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period	38 months
Award Requisite Service Period	5 years
Income taxes
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Service Share-based Compensation, Tax Benefit from Exercise of Stock Options	$ 8	$ 15	$ 6