Equity (Unrecognized Compensation Expense Related to Stock-Based Compensation) (Details) $ in Millions	12 Months Ended
Dec. 31, 2018 USD ($)
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expense	$ 3
Weighted Average Period	1 year 1 month 12 days
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expense	$ 21
Weighted Average Period	1 year 8 months 19 days
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expense	$ 32
Weighted Average Period	1 year 3 months 9 days

Unrecognized cost of unvested share-based compensation awards.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

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

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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