Supplemental Information On Oil And Gas Operations (Proved Bitumen Reserves) (Details) MBbls in Thousands	12 Months Ended
	Dec. 31, 2016 MBbls	Dec. 31, 2015 MBbls	Dec. 31, 2014 MBbls	Dec. 31, 2013 MBbls
Reserve Quantities [Line Items]
Conversion rate of gas reserves from barrels of oil to Boe	6
Bitumen [Member]
Reserve Quantities [Line Items]
Proved developed and undeveloped reserves, beginning balance	520	521	552
Proved developed and undeveloped reserves, revisions due to prices	23	103	(37)
Proved developed and undeveloped reserves, revisions other than price	(19)	(84)	18
Proved developed and undeveloped reserves, extensions and discoveries		11	8
Proved developed and undeveloped reserves, production	(40)	(31)	(20)
Proved developed and undeveloped reserves, ending balance	484	520	521
Proved developed reserves	190	219	137	111
Proved developed producing reserves	190	219	137	111
Proved undeveloped reserves	294	301	384	441
Bitumen [Member] | Canada [Member]
Reserve Quantities [Line Items]
Proved developed and undeveloped reserves, beginning balance	520	521	552
Proved developed and undeveloped reserves, revisions due to prices	23	103	(37)
Proved developed and undeveloped reserves, revisions other than price	(19)	(84)	18
Proved developed and undeveloped reserves, extensions and discoveries		11	8
Proved developed and undeveloped reserves, production	(40)	(31)	(20)
Proved developed and undeveloped reserves, ending balance	484	520	521
Proved developed reserves	190	219	137	111
Proved developed producing reserves	190	219	137	111
Proved undeveloped reserves	294	301	384	441