Revenue from Contracts with Customers - Disaggregation of Revenue (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Revenues from Customers	$ 3,338	$ 3,236
Revenue from Other than Customers	(120)	(191)
Total	3,218	3,045
Oil sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	2,096	2,127
Natural gas sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	320	247
Natural-gas liquids sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	240	292
Gathering, processing, and marketing sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	648	548
Revenue from Other than Customers	(178)	(188)
Gains (losses) on divestitures, net [Member]
Disaggregation of Revenue [Line Items]
Revenue from Other than Customers	(5)	(24)
Other, net [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	34	22
Revenue from Other than Customers	63	21
Operating Segments [Member] | Exploration and Production [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	2,666	2,669
Revenue from Other than Customers	(1)	(45)
Total	2,665	2,624
Operating Segments [Member] | Exploration and Production [Member] | Oil sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	2,096	2,127
Operating Segments [Member] | Exploration and Production [Member] | Natural gas sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	320	247
Operating Segments [Member] | Exploration and Production [Member] | Natural-gas liquids sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	240	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	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	0	(33)
Operating Segments [Member] | Exploration and Production [Member] | Other, net [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	9	3
Revenue from Other than Customers	(1)	(12)
Operating Segments [Member] | WES Midstream [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	672	502
Revenue from Other than Customers	57	43
Total	729	545
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	672	502
Revenue from Other than Customers	0	(1)
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	57	44
Other and Intersegment Eliminations [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	0	65
Revenue from Other than Customers	(176)	(189)
Total	(176)	(124)
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	(25)	46
Revenue from Other than Customers	(178)	(187)
Third-party marketing revenue	209	224
Intercompany eliminations	(223)	(163)
Other and Intersegment Eliminations [Member] | Gains (losses) on divestitures, net [Member]
Disaggregation of Revenue [Line Items]
Revenue from Other than Customers	(5)	9
Other and Intersegment Eliminations [Member] | Other, net [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	25	19
Revenue from Other than Customers	$ 7	$ (11)