Supplemental Oil and Gas Disclosures - Unaudited Information of Future Net Cash Flows for Oil and Gas Reserves, Net of Income Tax Expense (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Schedule Of Changes In Standardized Measure Of Discounted Future Net Cash Flows [Line Items]
Cash inflows	$ 161,347	$ 172,533
Production costs	(52,408)	(54,576)
Development costs	(17,225)	(18,035)
Income tax expense	(24,216)	(28,980)
Net cash flows	67,498	70,942
10 percent discount rate	(32,945)	(34,995)
Discounted future net cash flows	34,553	35,947
United States [Member]
Schedule Of Changes In Standardized Measure Of Discounted Future Net Cash Flows [Line Items]
Cash inflows	84,060	85,041
Production costs	(27,230)	(25,379)
Development costs	(6,768)	(6,493)
Income tax expense	(12,740)	(15,351)
Net cash flows	37,322	37,818
10 percent discount rate	(19,464)	(20,311)
Discounted future net cash flows	17,858	17,507
Canada [Member]
Schedule Of Changes In Standardized Measure Of Discounted Future Net Cash Flows [Line Items]
Cash inflows	20,512	27,727
Production costs	(8,543)	(13,142)
Development costs	(2,916)	(3,274)
Income tax expense	(754)	(972)
Net cash flows	8,299	10,339
10 percent discount rate	(4,472)	(4,956)
Discounted future net cash flows	3,827	5,383
Egypt [Member]
Schedule Of Changes In Standardized Measure Of Discounted Future Net Cash Flows [Line Items]
Cash inflows	16,210	17,092
Production costs	(2,126)	(2,467)
Development costs	(1,756)	(1,909)
Income tax expense	(4,246)	(4,565)
Net cash flows	8,082	8,151
10 percent discount rate	(2,107)	(2,168)
Discounted future net cash flows	5,975	5,983
Australia [Member]
Schedule Of Changes In Standardized Measure Of Discounted Future Net Cash Flows [Line Items]
Cash inflows	20,823	20,579
Production costs	(4,896)	(3,588)
Development costs	(2,484)	(3,124)
Income tax expense	(3,172)	(3,455)
Net cash flows	10,271	10,412
10 percent discount rate	(6,361)	(6,624)
Discounted future net cash flows	3,910	3,788
North Sea [Member]
Schedule Of Changes In Standardized Measure Of Discounted Future Net Cash Flows [Line Items]
Cash inflows	16,732	19,012
Production costs	(8,451)	(8,810)
Development costs	(3,053)	(3,003)
Income tax expense	(3,163)	(4,453)
Net cash flows	2,065	2,746
10 percent discount rate	(98)	(493)
Discounted future net cash flows	1,967	2,253
Argentina [Member]
Schedule Of Changes In Standardized Measure Of Discounted Future Net Cash Flows [Line Items]
Cash inflows	3,010	3,082
Production costs	(1,162)	(1,190)
Development costs	(248)	(232)
Income tax expense	(141)	(184)
Net cash flows	1,459	1,476
10 percent discount rate	(443)	(443)
Discounted future net cash flows	$ 1,016	$ 1,033