Stock-Based Compensation (Details) - USD ($)	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Mar. 08, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Sale of Stock, Price Per Share				$ 15.25
Payments for Repurchase of Common Stock	$ 79,000,000	$ 0	$ 0
Share-based Compensation Arrangement by Share-based Payment Award Accelerated Compensation Cost	35,000,000
Stock-based compensation expense	41,000,000	36,000,000	30,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Total Intrinsic Value	11,000,000	0	1,000,000
Option exercises	0	0	1,000,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Total Fair Value	88,000,000	23,000,000	17,000,000
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Share-based Liabilities Paid	25,000,000
Share-based Compensation Arrangement by Liability Classified Share-based Payment Awards Accelerated Compensation Cost	16,000,000
Allocated Share Based Compensation Expense Liability Classified Share-Based Awards	$ 16,000,000	$ 6,000,000	$ 1,000,000

Allocated Share Based Compensation Expense Liability Classified Share-Based Awards

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- Definition

Share-based Compensation Arrangement by Liability Classified Share-based Payment Awards Accelerated Compensation Cost

+ References

No definition available.

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- Definition

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

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The cash outflow to reacquire common stock during the period.

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- Definition

Amount of cash inflow from exercise of stock options granted under share-based compensation arrangement.

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Per share amount received by subsidiary or equity investee for each share of common stock issued or sold in the stock transaction.

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Additional share-based compensation cost recognized as a result of an occurrence of an event that accelerates its recognition.

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Amount of cash paid related to share-based compensation liabilities.

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- Definition

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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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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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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