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, 2014	Dec. 31, 2013	Dec. 31, 2012
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Proved	$ 104	$ 177	$ 1,251
Unproved	1,388	379	3,407
Exploration	973	1,678	1,637
Development	9,180	8,548	7,536
Costs incurred	11,645	10,782	13,831
Proved properties	89,852	83,390
Unproved properties	7,014	8,363
Capitalized costs, gross	96,866	91,753
Accumulated DD&A	(53,001)	(45,253)
Capitalized costs, net	43,865	46,500
United States [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Proved	102	17	1,076
Unproved	1,221	195	3,334
Exploration	467	562	364
Development	5,301	5,435	4,465
Costs incurred	7,091	6,209	9,239
Proved properties	47,001	41,904
Unproved properties	4,151	5,042
Capitalized costs, gross	51,152	46,946
Accumulated DD&A	(27,205)	(20,745)
Capitalized costs, net	23,947	26,201
Canada [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Proved			5
Unproved	141	151	17
Exploration	82	36	94
Development	846	722	762
Costs incurred	1,069	909	878
Proved properties	14,003	13,231
Unproved properties	1,090	1,116
Capitalized costs, gross	15,093	14,347
Accumulated DD&A	(9,653)	(9,310)
Capitalized costs, net	5,440	5,037
Egypt [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Proved	1	35	28
Unproved	10	15	6
Exploration	193	559	690
Development	1,142	618	394
Costs incurred	1,346	1,227	1,118
Proved properties	9,895	8,418
Unproved properties	529	660
Capitalized costs, gross	10,424	9,078
Accumulated DD&A	(6,369)	(5,356)
Capitalized costs, net	4,055	3,722
Australia [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Proved	1		32
Unproved	16	(10)	7
Exploration	137	179	142
Development	914	996	915
Costs incurred	1,068	1,165	1,096
Proved properties	8,289	7,298
Unproved properties	549	471
Capitalized costs, gross	8,838	7,769
Accumulated DD&A	(3,198)	(2,839)
Capitalized costs, net	5,640	4,930
North Sea [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Proved		125	110
Unproved		17	26
Exploration	84	278	111
Development	971	635	837
Costs incurred	1,055	1,055	1,084
Proved properties	10,463	9,378
Unproved properties	672	702
Capitalized costs, gross	11,135	10,080
Accumulated DD&A	(6,375)	(4,811)
Capitalized costs, net	4,760	5,269
Argentina [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Unproved		11	2
Exploration	9	42	155
Development	6	142	161
Costs incurred	15	195	318
Proved properties		2,933
Unproved properties		349
Capitalized costs, gross		3,282
Accumulated DD&A		(1,964)
Capitalized costs, net		1,318
Other International [Member]
Results of Operations for Oil and Gas Producing Activities, by Geographic Area [Line Items]
Unproved			15
Exploration	1	22	81
Development			2
Costs incurred	1	22	98
Proved properties	201	228
Unproved properties	23	23
Capitalized costs, gross	224	251
Accumulated DD&A	(201)	(228)
Capitalized costs, net	$ 23	$ 23