Acquisitions and Divestitures (Details) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014 USD ($)	Sep. 04, 2015 a
Divestitures
Gas and Oil Area Developed and Undeveloped | a					12,000
Payments to Acquire Oil and Gas Property and Equipment			$ 114
Operating expenses
(Loss) income from discontinued operations, net of tax	$ 0	$ (1)	$ 0	$ 3
Arklatex Area, South Louisiana Wilcox Area, And Brazilian Operations
Summary of operating results of discontinued operations
Operating revenues		14		82
Operating expenses
Transportation costs		0		5
Lease operating expense		6		31
Depreciation, depletion and amortization		0		8
Impairment charges		3		18
Other expense		4		17
Total operating expenses		13		79
Loss on sale of assets		(1)		0
Other (expense) income		(1)		4
(Loss) income from discontinued operations before income taxes		(1)		7
Income tax expense		0		4
(Loss) income from discontinued operations, net of tax		(1)		3
Brazilian operations
Operating expenses
Impairment charges		$ 3		$ 18