Stock-Based Compensation (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options, exercised, number of options (in shares)	0	0	0
Weighted-average grant-date fair value of options granted (in dollars per share)			$ 3.47
2013 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum shares	88,700,000
Period of service for immediate vesting upon death, disability or retirement	3 years
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period for stock awards from grant date	3 years
Expiration period from date of grant	7 years
Increase (decrease) in deferred tax asset	$ (1)	$ 1	$ 1
Equity-classified awards, unrecognized compensation cost	$ 1
Equity-classified awards, weighted average period over which unrecognized cost is recognized, years	1 year
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period for stock awards from grant date	4 years
Increase (decrease) in deferred tax asset	$ (1)	2	9
Equity-classified awards, unrecognized compensation cost	$ 6
Equity-classified awards, weighted average period over which unrecognized cost is recognized, years	1 year
Total fair value of restricted stock grants	$ 2	2	42
Total fair value of shares vested	$ 11	19	18
Performance units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period for stock awards from grant date	3 years
Increase (decrease) in deferred tax asset	$ 1	1	$ 3
Equity-classified awards, unrecognized compensation cost	$ 1
Equity-classified awards, weighted average period over which unrecognized cost is recognized, years	1 year
Performance units \| Cliff Vesting
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period for stock awards from grant date	3 years
Liability-Classified RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increase (decrease) in deferred tax asset	$ 1	2
Liability-classified restricted stock, vesting period	4 years
Liability-classified restricted stock, unrecognized compensation cost	$ 24
Liability-classified restricted stock, weighted average period over which unrecognized cost is recognized, years	3 years
Liability-Classified Performance Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increase (decrease) in deferred tax asset	$ (1)	$ 1
Liability-classified performance units, vesting period	3 years
Liability-classified performance units, unrecognized compensation cost	$ 6
Liability-classified performance units, weighted average period over which unrecognized cost is recognized, years	2 years

Unrecognized cost of unvested liability-based performance units share-based compensation awards.

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Weighted average period over which unrecognized compensation is expected to be recognized for liability-based performance units compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Unrecognized cost of unvested liability-based restricted stock share-based compensation awards.

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Period which an employee's right to exercise liability-based performance units are no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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- Definition

Share Based Compensation Arrangement, Increase (Decrease) In Deferred Tax Asset

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Total fair value of restricted stock grants

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- Definition

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

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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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Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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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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- Definition

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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- Definition

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

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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- Definition

Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Number of share options (or share units) exercised during the current period.

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