Property, Plant and Equipment (Narrative) (Details) - USD ($)			1 Months Ended	3 Months Ended	12 Months Ended
		Sep. 30, 2014	Jan. 31, 2015	Jun. 30, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property Plant And Equipment [Line Items]
Proceeds from sales of property, plant and equipment					$ 1,155,144,000	$ 423,911,000	$ 1,467,046,000
Cost of acquired assets					225,300,000	12,600,000	100,300,000
Impairment of assets					95,088,000	2,493,156,000	51,314,000
Total capitalized exploratory well costs					148,500,000	130,514,000	120,455,000	$ 393,030,000
Redetermination expense	[1]				39,100,000
Exploratory well costs capitalized more than one year					$ 128,019,000
UK Refining And Marketing Operations [Member]
Property Plant And Equipment [Line Items]
Proceeds from sales of property, plant and equipment		$ 211,965,000		$ 5,500,000
Impairment of assets							$ 269,200,000
Syncrude Canada Ltd. [Member]
Property Plant And Equipment [Line Items]
Percentage of interest in oil and gas property sold during period					5.00%
Gain (loss) on sale of assets, net of taxes					$ 71,700,000
Montney Natural Gas Fields [Member]
Property Plant And Equipment [Line Items]
Proceeds from sales of property, plant and equipment					414,100,000
Deferred gain on sale of property					$ 187,000,000
Deferred gain, period of recognition					20 years
Deferred gain, accumulated amortization					$ 5,108,000
Brunei [Member]
Property Plant And Equipment [Line Items]
Exploratory well costs capitalized more than one year					$ 64,492,000
Kaybob Duvernay Lands, Alberta [Member]
Property Plant And Equipment [Line Items]
Interest in assets acquired					70.00%
Montney Lands, Alberta [Member]
Property Plant And Equipment [Line Items]
Interest in assets acquired					30.00%
Kakap Field, Block K, Malaysia [Member]
Property Plant And Equipment [Line Items]
Working interest					8.60%
Malaysia [Member]
Property Plant And Equipment [Line Items]
Percentage of interest in oil and gas property sold during period			10.00%				20.00%
Proceeds from sales of property, plant and equipment			$ 417,200,000				$ 1,460,425,000
Gain (loss) on sale of assets, net of taxes						218,800,000	321,454,000
Impairment of assets	[1]					1,480,600,000
Redetermination expense	[1]				$ 39,100,000
Exploratory well costs capitalized more than one year					63,527,000
Gulf Of Mexico [Member]
Property Plant And Equipment [Line Items]
Impairment of assets						328,982,000	14,267,000
Parent Company [Member] | Syncrude Canada Ltd. [Member]
Property Plant And Equipment [Line Items]
Proceeds from sales of property, plant and equipment					739,100,000
Parent Company [Member] | Montney Lands, Alberta [Member]
Property Plant And Equipment [Line Items]
Cost of acquired assets, cash paid					206,700,000
Athabasca Oil Corporation [Member]
Property Plant And Equipment [Line Items]
Cost of acquired assets, carried interest					$ 168,000,000
Cost of acquired assets, interest carry period					5 years
Athabasca Oil Corporation [Member] | Subsidiary [Member]
Property Plant And Equipment [Line Items]
Cost of acquired assets					$ 375,000,000
Zero to One Year [Member]
Property Plant And Equipment [Line Items]
Total capitalized exploratory well costs					20,481,000	66,032,000
One to Two Years [Member]
Property Plant And Equipment [Line Items]
Total capitalized exploratory well costs					63,527,000		59,330,000
Two to Three Years [Member]
Property Plant And Equipment [Line Items]
Total capitalized exploratory well costs						57,876,000	6,606,000
Three Years or More [Member]
Property Plant And Equipment [Line Items]
Total capitalized exploratory well costs					$ 64,492,000	$ 6,606,000	$ 54,519,000

[1] Results exclude corporate overhead, interest and discontinued operations.