Impairments - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Property, Plant, and Equipment [Line Items]
Impairment of unproved properties	$ 35	$ 1,009
Net book value	33,526		$ 33,751
Unproved Greater Natural Buttes Properties [Member]
Property, Plant, and Equipment [Line Items]
Impairment of unproved properties		$ 935
Depletion Group At Risk For Impairment [Member]
Property, Plant, and Equipment [Line Items]
Net book value	2,100
Potential non-cash impairments that could be recognized in the future, in excess of	$ 1,000