Supplemental Oil and Gas Disclosures - Summary of Oil and Gas Property Costs Not Being Amortized (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Property acquisition costs	$ 1,960
Exploration and development	586
Capitalized interest	65
Costs incurred	2,611
2015 [Member]
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Property acquisition costs	316
Exploration and development	569
Capitalized interest	16
Costs incurred	$ 901
2014 [Member]
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Property acquisition costs		$ 1,311
Exploration and development		15
Capitalized interest		13
Costs incurred		$ 1,339
2013 [Member]
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Property acquisition costs			$ 210
Exploration and development			1
Capitalized interest			4
Costs incurred			$ 215
2012 and Prior [Member]
Capitalized Costs of Unproved Properties Excluded from Amortization [Line Items]
Property acquisition costs				$ 123
Exploration and development				1
Capitalized interest				32
Costs incurred				$ 156