Impairments - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Property, Plant, and Equipment [Line Items]
Impairments	$ 172	$ 0	$ 319	$ 383
Impairment of unproved properties			212	2,144
Assets Impaired During Fiscal Year to Date [Member]
Property, Plant, and Equipment [Line Items]
Impairments			319	383
Hard-minerals Properties [Member] | Assets Impaired During Fiscal Year to Date [Member]
Property, Plant, and Equipment [Line Items]
Impairment of long-lived assets held for use			145
Unproved Gulf of Mexico Properties [Member]
Property, Plant, and Equipment [Line Items]
Impairment of unproved properties			158	586
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] | DJ Basin Complex [Member] | Assets Impaired During Fiscal Year to Date [Member]
Property, Plant, and Equipment [Line Items]
Impairment of long-lived assets held for use			126
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
Valuation, Income Approach [Member] | Fair Value, Measurements, Nonrecurring [Member] | Fair Value, Inputs, Level 3 [Member] | Hard-minerals 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	$ 15		$ 15
Valuation, Income Approach [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
Valuation, Income Approach [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