Accounting for Suspended Exploratory Wells (Details Textual) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 Project Well		Dec. 31, 2011 Project		Dec. 31, 2010 Project
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Capitalized exploratory well costs that have been capitalized for period greater than one year	$ 2,180		$ 1,877		$ 2,299
Number of projects with exploratory well costs that have been capitalized for a period greater than one year	46	[1]	47	[1]	53	[1]
Expected period for decision on the recognition of proved reserves	3 years
Exploratory well costs capitalized for a period greater than one year	2,180		1,877		2,299
Capitalized exploratory well costs that are approved and construction in progress	42
Total number of exploratory wells that have been capitalized for period greater than one year	166
Project [Member]
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Number of projects with exploratory well costs that have been capitalized for a period greater than one year	8
Drilling Activity [Member]
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Capitalized exploratory well costs that have been capitalized for period greater than one year	1,359
Exploratory well costs capitalized for a period greater than one year	1,359
Drilling Activity [Member] | Project [Member]
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Number of projects with exploratory well costs that have been capitalized for a period greater than one year	23
No Drilling Activity [Member]
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Capitalized exploratory well costs that have been capitalized for period greater than one year	821
Exploratory well costs capitalized for a period greater than one year	821
No Drilling Activity [Member] | Project [Member]
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Number of projects with exploratory well costs that have been capitalized for a period greater than one year	23
Development Concept Under Review by Government [Member]
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Capitalized exploratory well costs that have been capitalized for period greater than one year	218
Exploratory well costs capitalized for a period greater than one year	218
Development Concept Under Review by Government [Member] | Project [Member]
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Number of projects with exploratory well costs that have been capitalized for a period greater than one year	4
Reviewing Development Alternatives [Member]
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Capitalized exploratory well costs that have been capitalized for period greater than one year	359
Exploratory well costs capitalized for a period greater than one year	359
Reviewing Development Alternatives [Member] | Project [Member]
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Number of projects with exploratory well costs that have been capitalized for a period greater than one year	6
Undergoing Front End Engineering and Design with Final Investment Decision Expected [Member]
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Capitalized exploratory well costs that have been capitalized for period greater than one year	202
Exploratory well costs capitalized for a period greater than one year	$ 202
Undergoing Front End Engineering and Design with Final Investment Decision Expected [Member] | Project [Member]
Projects with Exploratory Well Costs Capitalized for More than One Year [Line Items]
Number of projects with exploratory well costs that have been capitalized for a period greater than one year	5
Undergoing front-end engineering and design with final investment decision expected in three years	3 years

[1] Certain projects have multiple wells or fields or both.