Accounting for Suspended Exploratory Wells (Details 1) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011 Well Project	Dec. 31, 2010 Project	Dec. 31, 2009 Project
Aging costs on well and project basis
Capitalized Exploratory Well Costs that Have Been Capitalized for Period Greater than One Year, Total	$ 1,877	$ 2,299	$ 1,871
Total number of exploratory wells that have been capitalized for period greater Than one year	161
Projects that have Exploratory Well Costs that have been Capitalized for Period Greater than One Year, Number of Projects, Total	47	53	46
1997-2000 [Member]
Aging costs on well and project basis
Capitalized Exploratory Well Costs that Have Been Capitalized for Period Greater than One Year, Total	49
Aging of exploratory well costs capitalized for more than one year based on drilling completion date of individual wells 1997 to 2000 number of wells	16
2001-2005 [Member]
Aging costs on well and project basis
Capitalized Exploratory Well Costs that Have Been Capitalized for Period Greater than One Year, Total	396
Aging of exploratory well costs capitalized for more than one year based on drilling completion date of individual wells 2001 to 2005 number of wells	47
2006-2010 [Member]
Aging costs on well and project basis
Capitalized Exploratory Well Costs that Have Been Capitalized for Period Greater than One Year, Total	1,432
Aging of exploratory well costs capitalized for more than one year based on drilling completion date of individual wells 2006 to 2010 number of wells	98
1999 [Member]
Aging costs on well and project basis
Capitalized Exploratory Well Costs that Have Been Capitalized for Period Greater than One Year, Total	8
Projects that have Exploratory Well Costs that have been Capitalized for Period Greater than One Year, Number of Projects, Total	1
2003-2006 [Member]
Aging costs on well and project basis
Capitalized Exploratory Well Costs that Have Been Capitalized for Period Greater than One Year, Total	345
Projects that have Exploratory Well Costs that have been Capitalized for Period Greater than One Year, Number of Projects, Total	10
2007-2011 [Member]
Aging costs on well and project basis
Capitalized Exploratory Well Costs that Have Been Capitalized for Period Greater than One Year, Total	$ 1,524
Projects that have Exploratory Well Costs that have been Capitalized for Period Greater than One Year, Number of Projects, Total	36