Supplemental Information On Oil And Gas Operations (Proved Oil 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
Oil [Member]
Reserve Quantities [Line Items]
Proved developed and undeveloped reserves, beginning balance	264	374	285
Proved developed and undeveloped reserves, revisions due to prices	(20)	(49)	(1)
Proved developed and undeveloped reserves, revisions other than price	1	(50)	(37)
Proved developed and undeveloped reserves, extensions and discoveries	38	54	99
Proved developed and undeveloped reserves, purchase of reserves	8	5	132
Proved developed and undeveloped reserves, production	(55)	(70)	(58)
Proved developed and undeveloped reserves, sale of reserves	(25)		(46)
Proved developed and undeveloped reserves, ending balance	211	264	374
Proved developed reserves	177	225	278	250
Proved developed producing reserves	156	211	243	229
Proved undeveloped reserves	34	39	96	35
Oil [Member] | United States [Member]
Reserve Quantities [Line Items]
Proved developed and undeveloped reserves, beginning balance	242	351	229
Proved developed and undeveloped reserves, revisions due to prices	(18)	(53)	(1)
Proved developed and undeveloped reserves, revisions other than price	(2)	(52)	(38)
Proved developed and undeveloped reserves, extensions and discoveries	36	51	94
Proved developed and undeveloped reserves, purchase of reserves	8	5	132
Proved developed and undeveloped reserves, production	(47)	(60)	(48)
Proved developed and undeveloped reserves, sale of reserves	(25)		(17)
Proved developed and undeveloped reserves, ending balance	194	242	351
Proved developed reserves	160	203	255	194
Proved developed producing reserves	143	192	224	178
Proved undeveloped reserves	34	39	96	35
Oil [Member] | Canada [Member]
Reserve Quantities [Line Items]
Proved developed and undeveloped reserves, beginning balance	22	23	56
Proved developed and undeveloped reserves, revisions due to prices	(2)	4
Proved developed and undeveloped reserves, revisions other than price	3	2	1
Proved developed and undeveloped reserves, extensions and discoveries	2	3	5
Proved developed and undeveloped reserves, production	(8)	(10)	(10)
Proved developed and undeveloped reserves, sale of reserves			(29)
Proved developed and undeveloped reserves, ending balance	17	22	23
Proved developed reserves	17	22	23	56
Proved developed producing reserves	13	19	19	51