Supplemental Information On Oil And Gas Operations (Proved Undeveloped Reserves) (Details)	12 Months Ended
	Dec. 31, 2016 MMBoe
Reserve Quantities [Line Items]
Proved undeveloped reserves (MMBoe) beginning balance	376	[1]
Proved undeveloped reserves, extensions and discoveries	78
Proved undeveloped reserves, revisions due to prices	2
Proved undeveloped reserves, revisions other than price	(5)
Proved undeveloped reserves, sale of reserves	(1)
Proved undeveloped reserves, conversion to proved developed reserves	(41)
Proved undeveloped reserves (MMBoe) ending balance	409	[1]
United States [Member]
Reserve Quantities [Line Items]
Proved undeveloped reserves (MMBoe) beginning balance	75	[1]
Proved undeveloped reserves, extensions and discoveries	78
Proved undeveloped reserves, revisions due to prices	(8)
Proved undeveloped reserves, revisions other than price	(1)
Proved undeveloped reserves, sale of reserves	(1)
Proved undeveloped reserves, conversion to proved developed reserves	(28)
Proved undeveloped reserves (MMBoe) ending balance	115	[1]
Canada [Member]
Reserve Quantities [Line Items]
Proved undeveloped reserves (MMBoe) beginning balance	301	[1]
Proved undeveloped reserves, revisions due to prices	10
Proved undeveloped reserves, revisions other than price	(4)
Proved undeveloped reserves, conversion to proved developed reserves	(13)
Proved undeveloped reserves (MMBoe) ending balance	294	[1]

[1] Gas reserves are converted to Boe at the rate of six Mcf per Bbl of oil, based upon the approximate relative energy content of gas and oil. This rate is not necessarily indicative of the relationship of natural gas and oil prices. Bitumen and NGL reserves are converted to Boe on a one-to-one basis with oil.