Supplemental Oil and Gas Disclosures - Costs Incurred in Oil and Gas Property Acquisitions, Exploration and Development Activities (Parenthetical) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Capitalized interest	$ 236	$ 310	$ 340
Asset retirement costs	65	307	537
United States [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Capitalized interest	169	209	239
Asset retirement costs	123	43	480
Canada [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Capitalized interest	25	38	35
Asset retirement costs	8	175	17
Egypt [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Capitalized interest	17	15	15
Australia [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Capitalized interest	9	20	16
Asset retirement costs		55	(30)
North Sea [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Capitalized interest	16	25	25
Asset retirement costs	$ (66)	34	67
Argentina [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Capitalized interest		$ 3	10
Asset retirement costs			$ 3