Income Taxes - Narrative (Details) - USD ($) $ in Billions	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Income Tax Contingency [Line Items]
Effective income tax rate	33.00%	21.00%	29.00%	27.00%
Undistributed earnings of foreign subsidiaries	$ 4.3		$ 4.3

Amount of undistributed earnings of foreign subsidiaries intended to be permanently reinvested outside the country of domicile.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 740
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6487024&loc=d3e29054-158556

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 740
-Section 50
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-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6479915&loc=d3e66715-112838

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 995
-SubTopic 740
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6503627&loc=d3e59836-110443

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
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-Section 25
-Paragraph 3
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-URI http://asc.fasb.org/extlink&oid=96869850&loc=d3e28200-109314

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 30
-Section 50
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-URI http://asc.fasb.org/extlink&oid=6424122&loc=d3e41874-109331

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant