Fair Value Measurements and Disclosures of Assets and Liabilities Measured on a Nonrecurring Basis (Details 2) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Asset Impairment Charges [Abstract]
Impaired of Oil and Gas Properties	$ 15	$ 34	$ 43	$ 131
Oil and Gas Property, Full Cost Method, Net	$ 15	$ 42	$ 43	$ 145
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	$ 8	$ 0	$ 14