Property, Plant and Equipment (Details 2) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2017 USD ($) project	Dec. 31, 2016 USD ($) project	Dec. 31, 2015 USD ($) project
Property, Plant and Equipment [Abstract]
Amounts capitalized less than one year after completion of drilling				$ 263	$ 131	$ 352
Amounts capitalized greater than one year after completion of drilling				32	118	85
Total deferred exploratory well costs	$ 249	$ 437	$ 573	$ 295	$ 249	$ 437
Projects that have Exploratory Well Costs that have been Capitalized for Period Greater than One Year, Number of Projects | project				1	3	2
Increase (Decrease) in Capitalized Exploratory Well Costs that are Pending Determination of Proved Reserves [Roll Forward]
Beginning balance	249	437	573
Additions	212	299	610
Charges to expense	(64)	(23)	(111)
Transfers to development	(102)	(388)	(635)
Dispositions	0	(76)	0
Ending balance	$ 295	$ 249	$ 437