Fair Value Measurements and Disclosures of Assets and Liabilities Measured on a Nonrecurring Basis (Details 2) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Asset Impairment Charges [Abstract]
Impaired of Oil and Gas Properties		$ 0	$ 33	$ 43	$ 164
Oil and Gas Property, Full Cost Method, Net	[1]	$ 0	$ 42	$ 43	$ 187
Discount Rate for Impairment Model		10.00%	10.00%	10.00%	10.00%
Quoted Prices in Active Markets (Level 1)
Asset Impairment Charges [Abstract]
Impaired of Oil and Gas Properties		$ 0	$ 0	$ 0	$ 0
Significant Other Observable Inputs (Level 2)
Asset Impairment Charges [Abstract]
Impaired of Oil and Gas Properties		0	0	0	0
Significant Unobservable Inputs (Level 3)
Asset Impairment Charges [Abstract]
Impaired of Oil and Gas Properties		$ 0	$ 9	$ 0	$ 23

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