Fair Value Measurements and Disclosures of Assets and Liabilities Measured on a Nonrecurring Basis (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended			6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012		Jun. 30, 2013	Jun. 30, 2012
Asset Impairment Charges [Abstract]
Impairment of Oil and Gas Properties	$ 0	$ 73	[1]	$ 0	$ 73	[1]
Discount Rate for Impairment Model	10.00%	10.00%		10.00%	10.00%
Quoted Prices in Active Markets (Level 1)
Asset Impairment Charges [Abstract]
Impairment of Oil and Gas Properties	0	0		0	0
Significant Other Observable Inputs (Level 2)
Asset Impairment Charges [Abstract]
Impairment of Oil and Gas Properties	0	0		0	0
Significant Unobservable Inputs (Level 3)
Asset Impairment Charges [Abstract]
Impairment of Oil and Gas Properties	0	172		0	172
Net Book Value
Asset Impairment Charges [Abstract]
Impairment of Oil and Gas Properties	$ 0	$ 245		$ 0	$ 245

[1] Amounts for 2012 related primarily to our South Raton development in the deepwater Gulf of Mexico and our Piceance development, onshore US. The assets were written down to their estimated fair values, which were determined using discounted cash flow models.