Impairments - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Property, Plant, and Equipment [Line Items]
Impairments	$ 128	$ 10	$ 147	$ 383
Impairment of unproved properties			149	1,466
Assets Impaired During Fiscal Year to Date [Member]
Property, Plant, and Equipment [Line Items]
Impairments				383
Unproved Gulf of Mexico Properties [Member]
Property, Plant, and Equipment [Line Items]
Impairment of unproved properties			$ 94	555
Unproved Shenandoah Properties [Member]
Property, Plant, and Equipment [Line Items]
Impairment of unproved properties				463
Exploration and Production [Member] | Gulf of Mexico Properties [Member] | Assets Impaired During Fiscal Year to Date [Member]
Property, Plant, and Equipment [Line Items]
Impairment of long-lived assets held for use				211
WES Midstream [Member] | Assets Impaired During Quarter [Member]
Property, Plant, and Equipment [Line Items]
Impairments	$ 128
WES Midstream [Member] | Onshore Domestic [Member] | Assets Impaired During Fiscal Year to Date [Member]
Property, Plant, and Equipment [Line Items]
Impairment of long-lived assets held for use				168
Income Approach Valuation Technique [Member] | Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member] | Exploration and Production [Member] | Gulf of Mexico Properties [Member] | Assets Impaired During Fiscal Year to Date [Member]
Property, Plant, and Equipment [Line Items]
Fair value of long-lived assets held for use		231		231
Income Approach Valuation Technique [Member] | Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member] | WES Midstream [Member] | Onshore Domestic [Member] | Assets Impaired During Fiscal Year to Date [Member]
Property, Plant, and Equipment [Line Items]
Fair value of long-lived assets held for use		$ 58		$ 58