Fair Value Measurements and Disclosures of Assets and Liabilities Measured on a Nonrecurring Basis (Details 2) - USD ($)		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Inventory Write-down		$ 14,000,000	$ 0	$ 14,000,000	$ 0
Asset Impairment Charges				0
Asset Impairment Charges [Abstract]
Impaired of Oil and Gas Properties		0	0	0	43,000,000
Impairment Of Materials And Supply Inventory				14,000,000
Assets Held For Sale, Net Book Value		65,000,000		65,000,000
Impairments On Assets Held For Sale				23,000,000
Material and Supply Inventory, Net Book Value				105,000,000
Oil and Gas Property, Full Cost Method, Net	[1]			0	43,000,000
Gain (Loss) on Disposition of Oil and Gas Property		0	$ 0	(23,000,000)	0
Quoted Prices in Active Markets (Level 1)
Asset Impairment Charges [Abstract]
Impaired of Oil and Gas Properties				0	0
Impairment Of Materials And Supply Inventory				0
Loss On Assets Held For Sale		0		0
Significant Other Observable Inputs (Level 2)
Asset Impairment Charges [Abstract]
Impaired of Oil and Gas Properties				0	0
Impairment Of Materials And Supply Inventory				0
Loss On Assets Held For Sale		0		0
Significant Unobservable Inputs (Level 3)
Asset Impairment Charges [Abstract]
Impaired of Oil and Gas Properties				0	$ 0
Impairment Of Materials And Supply Inventory				91,000,000
Loss On Assets Held For Sale		$ 42,000,000		$ 42,000,000

[1] Amount represents net book value at the date of assessment.