Accrued Liabilities (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Accrued Liabilities [Line Items]
Accrued liabilities	$ 880	$ 978
Revenue payable [Member]
Accrued Liabilities [Line Items]
Accrued liabilities	197	175
Accrued capital costs [Member]
Accrued Liabilities [Line Items]
Accrued liabilities	441	458
Accrued lease operating expenses [Member]
Accrued Liabilities [Line Items]
Accrued liabilities	47	71
Employee incentive expense [Member]
Accrued Liabilities [Line Items]
Accrued liabilities	62	64
Accrued interest on debt [Member]
Accrued Liabilities [Line Items]
Accrued liabilities	67	72
Taxes payable [Member]
Accrued Liabilities [Line Items]
Accrued liabilities	32	93
Other accrued liabilities [Member]
Accrued Liabilities [Line Items]
Accrued liabilities	$ 34	$ 45