Acquisitions, Divestitures, and Assets Held for Sale - Subsequent Events (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended			1 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Feb. 28, 2014 Subsequent Event [Member] Rovuma Offshore Area 1 in Mozambique [Member]	Feb. 28, 2014 Subsequent Event [Member] China Oil and Gas Properties [Member]	Jan. 31, 2014 Subsequent Event [Member] Pinedale/Jonah Assets [Member]
Subsequent Event [Line Items]
Working interest sold				10.00%
Proceeds from divestitures	$ 567	$ 657	$ 555	$ 2,640		$ 581
Expected proceeds from divestiture					$ 1,075