Commitments and Contingencies (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011	Dec. 31, 2010
Significant Purchase And Supply Commitments [Line Items]
Rental Expense for office buildings and oil and gas operations equipment	$ 37		$ 31	$ 27
2013	939
2014	383
2015	383
2016	286
2017	180
2018 and Thereafter	722
Total	2,893
Drilling, Equipment, and Purchase Obligations [Member]
Significant Purchase And Supply Commitments [Line Items]
2013	739
2014	191
2015	175
2016	101
2017	0
2018 and Thereafter	0
Total	1,206
Transportation and Gathering [Member]
Significant Purchase And Supply Commitments [Line Items]
2013	81
2014	78
2015	86
2016	88
2017	87
2018 and Thereafter	311
Total	731
Operating Lease Obligations [Member]
Significant Purchase And Supply Commitments [Line Items]
2013	47
2014	42
2015	52
2016	52
2017	48
2018 and Thereafter	302
Total	543
FPSO Lease Obligation [Member]
Significant Purchase And Supply Commitments [Line Items]
2013	72	[1]
2014	72	[1]
2015	70	[1]
2016	45	[1]
2017	45	[1]
2018 and Thereafter	109	[1]
Total	$ 413	[1]

[1] Annual lease payments, net to our interest, exclude regular maintenance and operational costs. See Note 12. Long-Term Debt.