Segment Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Segment Reporting Information [Line Items]
Revenues from Third Parties	$ 1,112	$ 851
Income from Equity Method Investees	53	48
Total Revenues	1,165	899
DD&A	312	221
(Gain) Loss on Commodity Derivative Instruments	96	286
Income (Loss) Before Income Taxes	374	37
Goodwill	696		696
Total Assets	17,064		16,444
United States [Member]
Segment Reporting Information [Line Items]
Revenues from Third Parties	554	505
Income from Equity Method Investees	2	0
Total Revenues	556	505
DD&A	198	167
(Gain) Loss on Commodity Derivative Instruments	(9)	192
Income (Loss) Before Income Taxes	193	(37)
Goodwill	696		696
Total Assets	11,220		11,201
West Africa [Member]
Segment Reporting Information [Line Items]
Revenues from Third Parties	383	130
Income from Equity Method Investees	51	48
Total Revenues	434	178
DD&A	73	10
(Gain) Loss on Commodity Derivative Instruments	105	94
Income (Loss) Before Income Taxes	227	74
Goodwill	0		0
Total Assets	2,948		2,728
Eastern Mediterranean [Member]
Segment Reporting Information [Line Items]
Revenues from Third Parties	44	52
Income from Equity Method Investees	0	0
Total Revenues	44	52
DD&A	5	4
(Gain) Loss on Commodity Derivative Instruments	0	0
Income (Loss) Before Income Taxes	32	39
Goodwill	0		0
Total Assets	2,107		1,751
North Sea [Member]
Segment Reporting Information [Line Items]
Revenues from Third Parties	75	114
Income from Equity Method Investees	0	0
Total Revenues	75	114
DD&A	18	28
(Gain) Loss on Commodity Derivative Instruments	0	0
Income (Loss) Before Income Taxes	40	68
Goodwill	0		0
Total Assets	458		544
Other International And Corporate [Member]
Segment Reporting Information [Line Items]
Revenues from Third Parties	56	50
Income from Equity Method Investees	0	0
Total Revenues	56	50
DD&A	18	12
(Gain) Loss on Commodity Derivative Instruments	0	0
Income (Loss) Before Income Taxes	(118)	(107)
Goodwill	0		0
Total Assets	$ 331		$ 220