Goodwill - Changes in Carrying Amount of Goodwill (Detail) $ in Millions	9 Months Ended
Sep. 30, 2017 USD ($)
Goodwill [Line Items]
Balance at January 1, 2017	$ 375
Disposition	(15)
Balance at September 30, 2017	360
Exploration and Production
Goodwill [Line Items]
Balance at January 1, 2017	0
Disposition	0
Balance at September 30, 2017	0
Midstream
Goodwill [Line Items]
Balance at January 1, 2017	375
Disposition	(15)
Balance at September 30, 2017	$ 360

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

Name:	us-gaap_Goodwill
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant