Fair Value Measurements (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2018	Sep. 30, 2018	Dec. 31, 2017
Liabilities:
Carrying value of debt, net of unamortized discount	$ 10,400	$ 10,400	$ 9,900
Non-core Permian acreage
Liabilities:
Pre-tax impairment charges		42
Total Fair Value
Liabilities:
Debt estimated fair value	10,400	10,400	10,400
Recurring | Accrued liabilities
Liabilities:
Netting and Collateral	0	0	0
Recurring | Deferred credits and other liabilities - other
Liabilities:
Netting and Collateral	0	0	0
Recurring | Level 1 | Accrued liabilities
Liabilities:
Embedded derivatives	0	0	0
Recurring | Level 1 | Deferred credits and other liabilities - other
Liabilities:
Embedded derivatives	0	0	0
Recurring | Level 2 | Accrued liabilities
Liabilities:
Embedded derivatives	11	11	39
Recurring | Level 2 | Deferred credits and other liabilities - other
Liabilities:
Embedded derivatives	53	53	147
Recurring | Level 3 | Accrued liabilities
Liabilities:
Embedded derivatives	0	0	0
Recurring | Level 3 | Deferred credits and other liabilities - other
Liabilities:
Embedded derivatives	0	0	0
Recurring | Total Fair Value | Accrued liabilities
Liabilities:
Embedded derivatives	11	11	39
Recurring | Total Fair Value | Deferred credits and other liabilities - other
Liabilities:
Embedded derivatives	53	$ 53	147
Non recurring | Proved gas and oil properties
Liabilities:
Pre-tax impairment charges			$ 397
Qatar
Liabilities:
Pre-tax impairment charges	$ 196