Supplemental Information On Oil And Gas Operations (Proved Natural Gas Liquids 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
Natural Gas Liquids [Member]
Reserve Quantities [Line Items]
Proved developed and undeveloped reserves, beginning balance	428	578	575
Proved developed and undeveloped reserves, revisions due to prices	(13)	(119)	8
Proved developed and undeveloped reserves, revisions other than price	48	(6)	2
Proved developed and undeveloped reserves, extensions and discoveries	42	24	47
Proved developed and undeveloped reserves, purchase of reserves	7	1	57
Proved developed and undeveloped reserves, production	(42)	(50)	(51)
Proved developed and undeveloped reserves, sale of reserves	(45)		(60)
Proved developed and undeveloped reserves, ending balance	425	428	578
Proved developed reserves	387	411	486	491
Proved developed producing reserves	370	393	467	463
Proved undeveloped reserves	38	17	92	84
Natural Gas Liquids [Member] | United States [Member]
Reserve Quantities [Line Items]
Proved developed and undeveloped reserves, beginning balance	428	578	552
Proved developed and undeveloped reserves, revisions due to prices	(13)	(119)	7
Proved developed and undeveloped reserves, revisions other than price	48	(6)	2
Proved developed and undeveloped reserves, extensions and discoveries	42	24	47
Proved developed and undeveloped reserves, purchase of reserves	7	1	57
Proved developed and undeveloped reserves, production	(42)	(50)	(50)
Proved developed and undeveloped reserves, sale of reserves	(45)		(37)
Proved developed and undeveloped reserves, ending balance	425	428	578
Proved developed reserves	387	411	486	468
Proved developed producing reserves	370	393	467	442
Proved undeveloped reserves	38	17	92	84
Natural Gas Liquids [Member] | Canada [Member]
Reserve Quantities [Line Items]
Proved developed and undeveloped reserves, beginning balance			23
Proved developed and undeveloped reserves, revisions due to prices			1
Proved developed and undeveloped reserves, production			(1)
Proved developed and undeveloped reserves, sale of reserves			(23)
Proved developed reserves				23
Proved developed producing reserves				21