Goodwill (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Jun. 30, 2017
Goodwill [Line Items]
Goodwill, gross		$ 115	$ 115
Less: accumulated impairment		0	0
Goodwill [Roll Forward]
Beginning balance, net	$ 115	115
Dispositions	0	0
Impairment	0	0
Ending balance, net	115	115	115
United States Exploration and Production [Member]
Goodwill [Line Items]
Goodwill, gross		0	0
Less: accumulated impairment		0	0
Goodwill [Roll Forward]
Beginning balance, net	0	0
Dispositions	0	0
Impairment	0	0	340
Ending balance, net	0	0	0
International Exploration and Production [Member]
Goodwill [Line Items]
Reporting Unit, Percentage of Fair Value in Excess of Carrying Amount				40.00%
Goodwill, gross		115	115
Less: accumulated impairment		0	0
Goodwill [Roll Forward]
Beginning balance, net	115	115
Dispositions	0	0
Impairment	0	0
Ending balance, net	$ 115	$ 115	$ 115

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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- Definition

Amount before 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.

+ References

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- Definition

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

+ References

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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13854-109267

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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-URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13777-109266

Reference 3: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

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-Section 50
-Paragraph 1
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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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- Definition

Percentage of fair value of reporting unit in excess of carrying amount.

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No definition available.

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