Segment Information - Foreign and U.S. Revenues (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues from external customers	$ 9,959	$ 9,599	$ 19,995	$ 19,243

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.

No definition available.

Name:	us-gaap_RevenuesFromExternalCustomersAndLongLivedAssetsLineItems
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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration