Revenue from Contracts with Customers - Disaggregation of Revenue (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Disaggregation of Revenue [Line Items]
Revenues from Customers	$ 3,528	$ 3,414	$ 6,866	$ 6,650
Revenue from Other than Customers	(86)	(123)	(206)	(314)
Total	3,442	3,291	6,660	6,336
Oil sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	2,470	2,265	4,566	4,392
Natural-gas sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	205	203	525	450
Natural-gas liquids sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	216	318	456	610
Gathering, processing, and marketing sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	604	603	1,252	1,151
Revenue from Other than Customers	(139)	(221)	(317)	(409)
Gains (losses) on divestitures, net [Member]
Disaggregation of Revenue [Line Items]
Revenue from Other than Customers	6	52	1	28
Other, net [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	33	25	67	47
Revenue from Other than Customers	47	46	110	67
Operating Segments [Member] | Exploration & Production [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	2,904	2,790	5,570	5,459
Revenue from Other than Customers	(10)	51	(11)	6
Total	2,894	2,841	5,559	5,465
Operating Segments [Member] | Exploration & Production [Member] | Oil sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	2,470	2,265	4,566	4,392
Operating Segments [Member] | Exploration & Production [Member] | Natural-gas sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	205	203	525	450
Operating Segments [Member] | Exploration & Production [Member] | Natural-gas liquids sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	216	318	456	610
Operating Segments [Member] | Exploration & Production [Member] | Gathering, processing, and marketing sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	1	0	2	0
Revenue from Other than Customers	0	0	0	0
Operating Segments [Member] | Exploration & Production [Member] | Gains (losses) on divestitures, net [Member]
Disaggregation of Revenue [Line Items]
Revenue from Other than Customers	6	52	6	19
Operating Segments [Member] | Exploration & Production [Member] | Other, net [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	12	4	21	7
Revenue from Other than Customers	(16)	(1)	(17)	(13)
Operating Segments [Member] | WES Midstream [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	685	519	1,357	1,021
Revenue from Other than Customers	70	39	132	79
Total	755	558	1,489	1,100
Operating Segments [Member] | WES Midstream [Member] | Oil sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	0	0	0	0
Operating Segments [Member] | WES Midstream [Member] | Natural-gas sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	0	0	0	0
Operating Segments [Member] | WES Midstream [Member] | Natural-gas liquids sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	0	0	0	0
Operating Segments [Member] | WES Midstream [Member] | Gathering, processing, and marketing sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	685	519	1,357	1,021
Revenue from Other than Customers	0	(1)	0	(2)
Operating Segments [Member] | WES Midstream [Member] | Gains (losses) on divestitures, net [Member]
Disaggregation of Revenue [Line Items]
Revenue from Other than Customers	0	1	0	1
Operating Segments [Member] | WES Midstream [Member] | Other, net [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	0	0	0	0
Revenue from Other than Customers	70	39	132	80
Other and Intersegment Eliminations [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	(61)	105	(61)	170
Revenue from Other than Customers	(146)	(213)	(327)	(399)
Total	(207)	(108)	(388)	(229)
Other and Intersegment Eliminations [Member] | Oil sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	0	0	0	0
Other and Intersegment Eliminations [Member] | Natural-gas sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	0	0	0	0
Other and Intersegment Eliminations [Member] | Natural-gas liquids sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	0	0	0	0
Other and Intersegment Eliminations [Member] | Gathering, processing, and marketing sales [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	(82)	84	(107)	130
Revenue from Other than Customers	(139)	(220)	(317)	(407)
Third-party marketing revenue	176	261	381	485
Intercompany eliminations	(233)	(174)	(456)	(337)
Other and Intersegment Eliminations [Member] | Gains (losses) on divestitures, net [Member]
Disaggregation of Revenue [Line Items]
Revenue from Other than Customers	0	(1)	(5)	8
Other and Intersegment Eliminations [Member] | Other, net [Member]
Disaggregation of Revenue [Line Items]
Revenues from Customers	21	21	46	40
Revenue from Other than Customers	$ (7)	$ 8	$ (5)	$ 0