Asset Acquisitions, Dispositions and Other (Details) $ in Millions	1 Months Ended	3 Months Ended
Apr. 30, 2017 USD ($)	Sep. 30, 2017 USD ($) item
Non-strategic acreage in Midland Basin Counties \| Disposed of by sale
Asset Acquisitions, Dispositions and Other
Number of divestitures of non-strategic acreage \| item		2
Sale consideration		$ 600
Pre-tax gain on disposal		81
South Texas operations \| Disposed of by sale
Asset Acquisitions, Dispositions and Other
Sale consideration	$ 500
Pre-tax gain on disposal	$ 500
Seminole-San Andres EOR
Asset Acquisitions, Dispositions and Other
Cost of acquired business assets		$ 600

Amount before tax of gain (loss) not previously recognized resulting from the disposal of a discontinued operation.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 45
-Paragraph 3B
-URI http://asc.fasb.org/extlink&oid=65878427&loc=SL51721525-107759

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=64827811&loc=d3e1361-107760

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 45
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=65878427&loc=d3e957-107759

Name:	us-gaap_DiscontinuedOperationGainLossFromDisposalOfDiscontinuedOperationBeforeIncomeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration