Stock Compensation Plans - Narrative (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
Mar. 31, 2019	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 3	$ 2
Unearned compensation cost related to the unvested portion of all stock-based awards	$ 56
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity instruments granted (shares)	1.5
Weighted average fair value per share granted (dollars per share)	$ 20.08
Performance Share Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity instruments granted (shares)	0.4
Weighted average fair value per share granted (dollars per share)	$ 18.00

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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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
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- Definition

Unrecognized cost of unvested share-based compensation awards.

+ References

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- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

+ References

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-Publisher FASB
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- Definition

The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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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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