Supplemental Oil and Gas Disclosures - Costs Incurred in Oil and Gas Property Acquisitions, Exploration and Development Activities (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Capitalized interest	$ 316	$ 243	$ 111
Asset retirement costs	1,032	1,411	1,306
United States [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Capitalized interest	215	152	52
Asset retirement costs	473	380	1,099
Canada [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Capitalized interest	38	47	23
Asset retirement costs	245	228	98
Egypt [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Capitalized interest	16	18	10
Australia [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Capitalized interest	12	14	15
Asset retirement costs	207	125	93
North Sea [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Capitalized interest	24
Asset retirement costs	89	678
Argentina [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Capitalized interest	11	12	11
Asset retirement costs	$ 18		$ 16