Equity (Unrecognized Compensation Expense Related to Stock-Based Compensation) (Details) $ in Millions	12 Months Ended
Dec. 31, 2017 USD ($)
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expense	$ 4
Weighted Average Period	1 year 9 months 7 days
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expense	$ 30
Weighted Average Period	1 year 7 months 1 day
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expense	$ 40
Weighted Average Period	1 year 10 months 4 days

Unrecognized cost of unvested share-based compensation awards.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=96867065&loc=d3e5070-113901

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

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- Definition

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