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.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
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- Definition

Unrecognized cost of unvested share-based compensation awards.

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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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- 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).

+ References

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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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No definition available.

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- Definition

Net number of share options (or share units) granted during the period.

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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

Weighted average per share amount at which grantees can acquire shares of common stock by exercise of options.

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No definition available.

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Stock Compensation Plans - Narrative (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 5	$ 7	$ 17	$ 18
Unearned compensation cost related to the unvested portion of all stock-based awards	$ 29		$ 29
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options granted (shares)			0.7
Weighted average exercise price (dollars per share)			$ 35.26
Weighted average fair value, stock option grants (dollars per share)			$ 12.08
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity instruments granted (shares)			0.1
Weighted average fair value per share granted (dollars per share)			$ 35.05
Performance Share Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity instruments granted (shares)			0.2
Weighted average fair value per share granted (dollars per share)			$ 36.78