Property, Plant and Equipment (Narrative) (Details) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended	6 Months Ended		12 Months Ended
	Jun. 30, 2016	Apr. 30, 2016	Jun. 30, 2016	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Property Plant And Equipment [Line Items]
Proceeds from sales of property, plant and equipment				$ 1,153,325	$ 423,106
Impairment of assets				$ 95,088
Syncrude Canada Ltd. [Member]
Property Plant And Equipment [Line Items]
Gain (loss) on sale of assets, net of taxes			$ 71,700
Percentage of interest in oil and gas property sold during period			5.00%
Montney Natural Gas Fields [Member]
Property Plant And Equipment [Line Items]
Proceeds from sales of property, plant and equipment		$ 414,100
Deferred gain on sale of property		$ 187,000
Amortization of deferred gain			$ 1,800
Deferred gain, period of recognition				20 years
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%
Canada [Member]
Property Plant And Equipment [Line Items]
Impairment of assets				$ 95,088
Malaysia [Member]
Property Plant And Equipment [Line Items]
Proceeds from sales of property, plant and equipment						$ 417,200
Gain (loss) on sale of assets, net of taxes						$ 199,500
Percentage of interest in oil and gas property sold during period						10.00%
Parent Company [Member]
Property Plant And Equipment [Line Items]
Cost of acquired assets, cash paid			$ 206,700
Parent Company [Member] | Syncrude Canada Ltd. [Member]
Property Plant And Equipment [Line Items]
Proceeds from sales of property, plant and equipment	$ 739,100
Athabasca Oil Corporation [Member]
Property Plant And Equipment [Line Items]
Cost of acquired assets, carried interest			$ 168,000
Cost of acquired assets, interest carry period				5 years
Athabasca Oil Corporation [Member] | Kaybob Duvernay Lands, Alberta [Member]
Property Plant And Equipment [Line Items]
Interest in assets acquired			70.00%
Athabasca Oil Corporation [Member] | Montney Lands, Alberta [Member]
Property Plant And Equipment [Line Items]
Interest in assets acquired			30.00%
Athabasca Oil Corporation [Member] | Subsidiary [Member]
Property Plant And Equipment [Line Items]
Cost of acquired assets			$ 375,000