Accounting Policies - Revenue Adoption Retained Earnings Adjustment (Details) - ASU 2014-09 $ in Millions	Jan. 01, 2018 USD ($)
Retained earnings adjustment
Retained earnings adjustment net of tax	$ (13)
Retained earnings adjustment before of tax	$ (17)

Amount of the cumulative effect on retained earnings before related income tax effect.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=64853466&loc=d3e22663-107794

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Amount of the cumulative effect on retained earnings net of related income tax effect.

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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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