Accounting for Suspended Exploratory Wells (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 Project	Dec. 31, 2010 Project	Dec. 31, 2009 Project
Changes in company's suspended exploratory well costs
Beginning balance at January 1	$ 2,718	$ 2,435	$ 2,118
Additions to capitalized exploratory well costs pending the determination of proved reserves	652	482	663
Reclassifications to wells, facilities and equipment based on the determination of proved reserves	(828)	(129)	(174)
Capitalized exploratory well costs charged to expense	(45)	(70)	(172)
Other reductions	(63)
Ending balance at December 31	2,434	2,718	2,435
Aging of capitalized well costs and number of project
Exploratory well costs capitalized for a period of one year or less	557	419	564
Exploratory well costs capitalized for a period greater than one year	1,877	2,299	1,871
Balance at December 31	$ 2,434	$ 2,718	$ 2,435
Number of projects with exploratory well costs that have been capitalized for a period greater than one year	47	53	46