Revenue from Contracts with Customers - Disaggregation of Revenue (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Disaggregation of Revenue [Line Items]
Revenues from Customers		$ 3,236
Revenue from Other than Customers		(191)
Total		3,045	$ 3,767
Oil sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		2,127
Natural gas sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		247
Natural-gas liquids sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		292
Gathering, processing, and marketing sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	[1]	548
Revenue from Other than Customers	[2]	(188)
Gains (losses) on divestitures, net [Member]
Disaggregation of Revenue [Line Items]
Revenue from Other than Customers		(24)
Other, net [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		22
Revenue from Other than Customers		21
Operating Segments [Member] | Exploration and Production [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		2,669
Revenue from Other than Customers		(45)
Total		2,624
Operating Segments [Member] | Exploration and Production [Member] | Oil sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		2,127
Operating Segments [Member] | Exploration and Production [Member] | Natural gas sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		247
Operating Segments [Member] | Exploration and Production [Member] | Natural-gas liquids sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		292
Operating Segments [Member] | Exploration and Production [Member] | Gathering, processing, and marketing sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	[1]	0
Revenue from Other than Customers	[2]	0
Operating Segments [Member] | Exploration and Production [Member] | Gains (losses) on divestitures, net [Member]
Disaggregation of Revenue [Line Items]
Revenue from Other than Customers		(33)
Operating Segments [Member] | Exploration and Production [Member] | Other, net [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		3
Revenue from Other than Customers		(12)
Operating Segments [Member] | WES Midstream [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		438
Revenue from Other than Customers		28
Total		466
Operating Segments [Member] | WES Midstream [Member] | Oil sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		0
Operating Segments [Member] | WES Midstream [Member] | Natural gas sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		0
Operating Segments [Member] | WES Midstream [Member] | Natural-gas liquids sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		0
Operating Segments [Member] | WES Midstream [Member] | Gathering, processing, and marketing sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	[1]	438
Revenue from Other than Customers	[2]	(1)
Operating Segments [Member] | WES Midstream [Member] | Gains (losses) on divestitures, net [Member]
Disaggregation of Revenue [Line Items]
Revenue from Other than Customers		0
Operating Segments [Member] | WES Midstream [Member] | Other, net [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		0
Revenue from Other than Customers		29
Operating Segments [Member] | Other Midstream [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		86
Revenue from Other than Customers		21
Total		107
Operating Segments [Member] | Other Midstream [Member] | Oil sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		0
Operating Segments [Member] | Other Midstream [Member] | Natural gas sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		0
Operating Segments [Member] | Other Midstream [Member] | Natural-gas liquids sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		0
Operating Segments [Member] | Other Midstream [Member] | Gathering, processing, and marketing sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	[1]	86
Revenue from Other than Customers	[2]	2
Operating Segments [Member] | Other Midstream [Member] | Gains (losses) on divestitures, net [Member]
Disaggregation of Revenue [Line Items]
Revenue from Other than Customers		9
Operating Segments [Member] | Other Midstream [Member] | Other, net [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		0
Revenue from Other than Customers		10
Other and Intersegment Eliminations [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		43
Revenue from Other than Customers		(195)
Total		(152)
Other and Intersegment Eliminations [Member] | Oil sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		0
Other and Intersegment Eliminations [Member] | Natural gas sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		0
Other and Intersegment Eliminations [Member] | Natural-gas liquids sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		0
Other and Intersegment Eliminations [Member] | Gathering, processing, and marketing sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	[1]	24
Revenue from Other than Customers	[2]	(189)
Third-party marketing revenue		224
Intercompany eliminations		(196)
Other and Intersegment Eliminations [Member] | Gains (losses) on divestitures, net [Member]
Disaggregation of Revenue [Line Items]
Revenue from Other than Customers		0
Other and Intersegment Eliminations [Member] | Other, net [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers		19
Revenue from Other than Customers		$ (6)

[1] The amount in Other and Intersegment Eliminations primarily represents sales of third-party natural gas and NGLs of $224 million and intercompany eliminations of $(196) million.

[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.