Capitalized Exploratory Well Costs (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Increase (Decrease) in Capitalized Exploratory Well Costs that are Pending Determination of Proved Reserves [Roll Forward]
Capitalized Exploratory Well Costs, Beginning of Period	$ 1,337	$ 1,301	$ 900
Additions to Capitalized Exploratory Well Costs Pending Determination of Proved Reserves	123	316	581
Reclassified to Proved Oil and Gas Properties Based on Determination of Proved Reserves or to Assets Held for Sale(1)	(19)	(196)	(177)
Capitalized Exploratory Well Costs Charged to Expense	(88)	(84)	(3)
Capitalized Exploratory Well Costs, End of Period	1,353	1,337	1,301
Exploratory Well Costs Capitalized for a Period of One Year or Less				$ 95	$ 247	$ 568
Exploratory Well Costs Capitalized for a Period Greater Than One Year Since Commencement of Drilling				1,258	1,090	733
Capitalized Exploratory Well Costs,	$ 1,337	$ 1,301	$ 900	$ 1,353	$ 1,337	$ 1,301
Number of Projects with Exploratory Well Costs That Have Been Capitalized for a Period Greater Than One Year Since Commencement of Drilling				14	13	13