Supplemental Oil and Gas Disclosures - Costs Incurred in Oil and Gas Property Acquisitions, Exploration and Development Activities (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]
Proved	$ 1,251	$ 2,755	$ 8,681
Unproved	2,355	688	3,216
Exploration	2,689	1,762	1,584
Development	7,536	5,587	3,727
Costs incurred	13,831	10,792	17,208
Proved properties	78,383	67,805
Unproved properties	8,754	5,530
Capitalized costs, gross	87,137	73,335
Accumulated DD&A	(38,978)	(32,254)
Capitalized costs, net	48,159	41,081
United States [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Proved	1,076	368	5,604
Unproved	2,329	116	2,497
Exploration	1,369	418	261
Development	4,465	2,832	1,724
Costs incurred	9,239	3,734	10,086
Proved properties	40,163	33,905
Unproved properties	5,641	2,690
Capitalized costs, gross	45,804	36,595
Accumulated DD&A	(17,968)	(16,013)
Capitalized costs, net	27,836	20,582
Canada [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Proved	5		2,752
Unproved		33	542
Exploration	111	209	312
Development	762	883	611
Costs incurred	878	1,125	4,217
Proved properties	13,477	12,619
Unproved properties	1,059	1,093
Capitalized costs, gross	14,536	13,712
Accumulated DD&A	(8,899)	(6,506)
Capitalized costs, net	5,637	7,206
Egypt [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Proved	28	(12)	325
Unproved		2	145
Exploration	696	570	477
Development	394	344	290
Costs incurred	1,118	904	1,237
Proved properties	7,165	6,117
Unproved properties	686	615
Capitalized costs, gross	7,851	6,732
Accumulated DD&A	(4,474)	(3,672)
Capitalized costs, net	3,377	3,060
Australia [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Proved	32
Unproved		48	32
Exploration	149	286	236
Development	915	429	496
Costs incurred	1,096	763	764
Proved properties	6,319	5,183
Unproved properties	284	270
Capitalized costs, gross	6,603	5,453
Accumulated DD&A	(2,478)	(2,061)
Capitalized costs, net	4,125	3,392
North Sea [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Proved	110	2,399
Unproved	26	476
Exploration	111	18	142
Development	837	941	475
Costs incurred	1,084	3,834	617
Proved properties	8,401	7,430
Unproved properties	626	513
Capitalized costs, gross	9,027	7,943
Accumulated DD&A	(3,445)	(2,550)
Capitalized costs, net	5,582	5,393
Argentina [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Exploration	157	202	136
Development	161	156	131
Costs incurred	318	358	267
Proved properties	2,706	2,442
Unproved properties	382	327
Capitalized costs, gross	3,088	2,769
Accumulated DD&A	(1,562)	(1,343)
Capitalized costs, net	1,526	1,426
Other International [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Unproved		13
Exploration	96	59	20
Development	2	2
Costs incurred	98	74	20
Proved properties	152	109
Unproved properties	76	22
Capitalized costs, gross	228	131
Accumulated DD&A	(152)	(109)
Capitalized costs, net	$ 76	$ 22