Supplemental Oil and Gas Information (Narrative) (Details) Mcfe in Millions, ft³ in Billions	1 Months Ended	12 Months Ended
	Jan. 31, 2015	Dec. 31, 2016 T / bbl Mcfe $ / bbl ft³	Dec. 31, 2014
Reserve Quantities [Line Items]
Percentage of bitumen from total bulk tar sand mined		10.00%
Percentage of bitumen removed by extraction process that is contained within the tar sand		90.00%
Metric tons of oil sand used to produce one barrel of synthetic crude oil | T / bbl		2
Natural gas proved reserves expected to receive sale proceeds, per thousand cubic foot | $ / bbl		0.24
Future net cash flows annual discount factor, percentage		10.00%
Oil Reserves [Member]
Reserve Quantities [Line Items]
Oil and natural gas reserves associated with the production sharing contracts | Mcfe		66.2
Minimum [Member]
Reserve Quantities [Line Items]
Catalytic cracking process efficiency level		85.00%
Maximum [Member]
Reserve Quantities [Line Items]
Catalytic cracking process efficiency level		90.00%
Canada [Member] | Synthetic Oil [Member]
Reserve Quantities [Line Items]
Interest in synthetic oil operations at Syncrude in Western Canada, percentage		5.00%
Process of mining tar sands and converting the raw bitumen into a pipeline-quality crude		The high-density core-hole drilling, at a spacing of less than 500 meters (proved area), provides engineering and geologic data needed to estimate the volumes of tar sand in place and its associated bitumen content.
Malaysia [Member]
Reserve Quantities [Line Items]
Percentage of interest in oil and gas property sold during period	10.00%		20.00%
Malaysia [Member] | Natural Gas Reserves [Member] | Kikeh Field [Member]
Reserve Quantities [Line Items]
Oil and natural gas reserves associated with the production sharing contracts | ft³		26.5