Property, Plant and Equipment - Schedule of Aggregate Capitalized Costs Related to Oil and Gas and Non-oil and Gas Activities (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Capitalized Costs Relating To Oil And Gas Producing Activities By Geographic Area [Line Items]
Proved	$ 47,295	$ 45,005
Unproved and properties under development	2,457	3,392
Total oil and gas	49,752	48,397
Accumulated DD&A	(36,434)	(35,399)
Oil and gas property and equipment, net	13,318	12,998
US [Member]
Capitalized Costs Relating To Oil And Gas Producing Activities By Geographic Area [Line Items]
Proved	40,491	38,842
Unproved and properties under development	984	2,115
Total oil and gas	41,475	40,957
Accumulated DD&A	(32,379)	(31,979)
Oil and gas property and equipment, net	9,096	8,978
Canada
Capitalized Costs Relating To Oil And Gas Producing Activities By Geographic Area [Line Items]
Proved	6,804	6,163
Unproved and properties under development	1,473	1,277
Total oil and gas	8,277	7,440
Accumulated DD&A	(4,055)	(3,420)
Oil and gas property and equipment, net	$ 4,222	$ 4,020