Stock-based Compensation Expense (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Payment Arrangement [Abstract]
Share-based Payment Arrangement, Noncash Expense	$ 11	$ 9	$ 5
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	4,687,500
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	2,737,180
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Share-based Liabilities Paid	$ 1	1	1
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Total Fair Value	9	7	4
Share-based Payment Arrangement, Decrease for Tax Withholding Obligation	2	$ 2	$ 2
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	$ 13
Stock-based Compensation, Attainment of Performance Goals That Allows Vesting	157.30%	129.00%	69.00%
Stock-based Compensation, Forfeiture Rate	5.00%
Share-based Payment Arrangement, Amount Capitalized	$ 0	$ 0	$ 0
Performance based stock award percentage - minimum	0.00%
Performance based stock award percentage - maximum	175.00%

Performance based stock award percentage - maximum

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Performance based stock award percentage - minimum

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Rate used in the determination of stock-based compensation expense for performance stock units. Assumed level of attainment of performance goals that allows the vesting of this percent.

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Forfeiture rate used in determining the period stock-based compensation expense.

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Amount of decrease to equity for grantee's tax withholding obligation for award under share-based payment arrangement.

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Amount of cost capitalized for award under share-based payment arrangement.

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

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Amount of noncash expense for share-based payment arrangement.

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Amount of cash paid to settle liability for award under share-based payment arrangement.

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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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

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The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable.

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