Property, Plant and Equipment - Table of Property and Equipment, net (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017
Property and equipment, at cost:
Proved	$ 47,350	$ 47,295
Unproved and properties under development	2,425	2,457
Total oil and gas	49,775	49,752
Less accumulated DD&A	(36,818)	(36,434)
Oil and gas property and equipment, net	12,957	13,318
Other property and equipment	1,883	1,955
Less accumulated DD&A	(719)	(689)
Other property and equipment, net	1,164	1,266
Total property and equipment, net	$ 14,121	$ 14,584	$ 14,217