Revenue from Contracts with Customers - Disaggregation of Revenue (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Disaggregation of Revenue [Line Items]
Revenues from Customers		$ 3,414		$ 6,650
Revenue from Other than Customers		(123)		(314)
Total		3,291	$ 2,716	6,336	$ 6,483
Oil sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		2,265		4,392
Natural gas sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		203		450
Natural-gas liquids sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		318		610
Gathering, processing, and marketing sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	[1]	603		1,151
Revenue from Other than Customers	[2]	(221)		(409)
Gains (losses) on divestitures, net [Member]
Disaggregation of Revenue [Line Items]
Revenue from Other than Customers		52		28
Other, net [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		25		47
Revenue from Other than Customers		46		67
Operating Segments [Member] | Exploration and Production [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		2,790		5,459
Revenue from Other than Customers		51		6
Total		2,841		5,465
Operating Segments [Member] | Exploration and Production [Member] | Oil sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		2,265		4,392
Operating Segments [Member] | Exploration and Production [Member] | Natural gas sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		203		450
Operating Segments [Member] | Exploration and Production [Member] | Natural-gas liquids sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		318		610
Operating Segments [Member] | Exploration and Production [Member] | Gathering, processing, and marketing sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	[1]	0		0
Revenue from Other than Customers	[2]	0		0
Operating Segments [Member] | Exploration and Production [Member] | Gains (losses) on divestitures, net [Member]
Disaggregation of Revenue [Line Items]
Revenue from Other than Customers		52		19
Operating Segments [Member] | Exploration and Production [Member] | Other, net [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		4		7
Revenue from Other than Customers		(1)		(13)
Operating Segments [Member] | WES Midstream [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		438		876
Revenue from Other than Customers		30		58
Total		468		934
Operating Segments [Member] | WES Midstream [Member] | Oil sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		0		0
Operating Segments [Member] | WES Midstream [Member] | Natural gas sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		0		0
Operating Segments [Member] | WES Midstream [Member] | Natural-gas liquids sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		0		0
Operating Segments [Member] | WES Midstream [Member] | Gathering, processing, and marketing sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	[1]	438		876
Revenue from Other than Customers	[2]	(2)		(3)
Operating Segments [Member] | WES Midstream [Member] | Gains (losses) on divestitures, net [Member]
Disaggregation of Revenue [Line Items]
Revenue from Other than Customers		0		0
Operating Segments [Member] | WES Midstream [Member] | Other, net [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		0		0
Revenue from Other than Customers		32		61
Operating Segments [Member] | Other Midstream [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		107		193
Revenue from Other than Customers		9		30
Total		116		223
Operating Segments [Member] | Other Midstream [Member] | Oil sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		0		0
Operating Segments [Member] | Other Midstream [Member] | Natural gas sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		0		0
Operating Segments [Member] | Other Midstream [Member] | Natural-gas liquids sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		0		0
Operating Segments [Member] | Other Midstream [Member] | Gathering, processing, and marketing sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	[1]	107		193
Revenue from Other than Customers	[2]	1		3
Operating Segments [Member] | Other Midstream [Member] | Gains (losses) on divestitures, net [Member]
Disaggregation of Revenue [Line Items]
Revenue from Other than Customers		0		9
Operating Segments [Member] | Other Midstream [Member] | Other, net [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		0		0
Revenue from Other than Customers		8		18
Other and Intersegment Eliminations [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		79		122
Revenue from Other than Customers		(213)		(408)
Total		(134)		(286)
Other and Intersegment Eliminations [Member] | Oil sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		0		0
Other and Intersegment Eliminations [Member] | Natural gas sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		0		0
Other and Intersegment Eliminations [Member] | Natural-gas liquids sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		0		0
Other and Intersegment Eliminations [Member] | Gathering, processing, and marketing sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	[1]	58		82
Revenue from Other than Customers	[2]	(220)		(409)
Intercompany eliminations		(207)		(403)
Third-party marketing revenue		261		485
Other and Intersegment Eliminations [Member] | Gains (losses) on divestitures, net [Member]
Disaggregation of Revenue [Line Items]
Revenue from Other than Customers		0		0
Other and Intersegment Eliminations [Member] | Other, net [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		21		40
Revenue from Other than Customers		$ 7		$ 1

[1] The amount in Other and Intersegment Eliminations primarily represents sales of third-party natural gas and NGLs of $261 million and intercompany eliminations of $(207) million for the three months ended June 30, 2018, and sales of third-party natural gas and NGLs of $485 million and intercompany eliminations of $(403) million for the six months ended June 30, 2018.

[2] The amount in Other and Intersegment Eliminations represents purchases of third-party natural gas and NGLs. Although these purchases are reported net in gathering, processing, and marketing sales in the Company’s Consolidated Statements of Income, they are shown separately on this table, as the purchases are not considered revenue from customers.