Suspended Exploratory Well Costs - Aging by Geographic Area and the Year the Costs Were Suspended (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Capitalized Exploratory Well Costs [Line Items]
Suspended exploratory well costs	$ 2,062		$ 1,353	$ 935	$ 579
Suspended exploratory well costs capitalized for a period less than one year after completion of drilling	917	[1]
Year Costs Incurred 2011 [Member]
Capitalized Exploratory Well Costs [Line Items]
Suspended exploratory well costs capitalized for a period greater than one year after completion of drilling	394
Year Costs Incurred 2010 [Member]
Capitalized Exploratory Well Costs [Line Items]
Suspended exploratory well costs capitalized for a period greater than one year after completion of drilling	375
Year Costs Incurred 2009 and Prior [Member]
Capitalized Exploratory Well Costs [Line Items]
Suspended exploratory well costs capitalized for a period greater than one year after completion of drilling	376
United States Onshore
Capitalized Exploratory Well Costs [Line Items]
Suspended exploratory well costs	136
Suspended exploratory well costs capitalized for a period less than one year after completion of drilling	123	[1]
United States Onshore | Year Costs Incurred 2011 [Member]
Capitalized Exploratory Well Costs [Line Items]
Suspended exploratory well costs capitalized for a period greater than one year after completion of drilling	3
United States Onshore | Year Costs Incurred 2009 and Prior [Member]
Capitalized Exploratory Well Costs [Line Items]
Suspended exploratory well costs capitalized for a period greater than one year after completion of drilling	10
United States Offshore
Capitalized Exploratory Well Costs [Line Items]
Suspended exploratory well costs	392
Suspended exploratory well costs capitalized for a period less than one year after completion of drilling	158	[1]
United States Offshore | Year Costs Incurred 2011 [Member]
Capitalized Exploratory Well Costs [Line Items]
Suspended exploratory well costs capitalized for a period greater than one year after completion of drilling	(5)
United States Offshore | Year Costs Incurred 2010 [Member]
Capitalized Exploratory Well Costs [Line Items]
Suspended exploratory well costs capitalized for a period greater than one year after completion of drilling	61
United States Offshore | Year Costs Incurred 2009 and Prior [Member]
Capitalized Exploratory Well Costs [Line Items]
Suspended exploratory well costs capitalized for a period greater than one year after completion of drilling	178
International [Member]
Capitalized Exploratory Well Costs [Line Items]
Suspended exploratory well costs	1,534
Suspended exploratory well costs capitalized for a period less than one year after completion of drilling	636	[1]
International [Member] | Year Costs Incurred 2011 [Member]
Capitalized Exploratory Well Costs [Line Items]
Suspended exploratory well costs capitalized for a period greater than one year after completion of drilling	396
International [Member] | Year Costs Incurred 2010 [Member]
Capitalized Exploratory Well Costs [Line Items]
Suspended exploratory well costs capitalized for a period greater than one year after completion of drilling	314
International [Member] | Year Costs Incurred 2009 and Prior [Member]
Capitalized Exploratory Well Costs [Line Items]
Suspended exploratory well costs capitalized for a period greater than one year after completion of drilling	$ 188

[1] Excludes additions subsequently reclassified to proved properties within the same year.