Goodwill (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Changes in goodwill
Balance at beginning of period	$ 2,344	$ 2,405
Acquisitions	269
Foreign currency translation adjustments	27	10
Dispositions and reclassifications to assets held for sale	(74)	(71)
Balance at end of period	2,566	2,344
Operating Segments \| Transportation
Changes in goodwill
Balance at beginning of period	806	815
Acquisitions	269
Foreign currency translation adjustments	16	6
Dispositions and reclassifications to assets held for sale	(21)	(15)
Balance at end of period	1,070	806
Operating Segments \| Facilities
Changes in goodwill
Balance at beginning of period	1,034	1,087
Foreign currency translation adjustments	7	3
Dispositions and reclassifications to assets held for sale	(53)	(56)
Balance at end of period	988	1,034
Operating Segments \| Supply and Logistics
Changes in goodwill
Balance at beginning of period	504	503
Foreign currency translation adjustments	4	1
Balance at end of period	$ 508	$ 504

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975

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Amount of increase in asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized resulting from a business combination.

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Amount of foreign currency translation gain (loss) which increases (decreases) an asset representing future economic benefits from other assets acquired in a business combination that are not individually identified and separately recognized.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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Amount of divestiture of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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