Property, Plant and Equipment Property, Plant and Equipment (Details 3) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013
Total Deferred Exploratory Well Costs [Abstract]
Amounts capitalized greater than one year after completion of drilling	$ 220
Capitalized exploratory well cost period increase decrease for sold assets	9
Angola Blk 31 [Member]
Total Deferred Exploratory Well Costs [Abstract]
Amounts capitalized greater than one year after completion of drilling	127
EQUATORIAL GUINEA
Total Deferred Exploratory Well Costs [Abstract]
Amounts capitalized greater than one year after completion of drilling	$ 22