Supplemental Information On Oil And Gas Operations (Proved Total MMBoe Reserves) (Details)		12 Months Ended
		Dec. 31, 2016 MMBoe	Dec. 31, 2015 MMBoe	Dec. 31, 2014 MMBoe	Dec. 31, 2013 MMBoe
Reserve Quantities [Line Items]
Proved developed and undeveloped reserves, beginning balance (MMBoe)	[1]	2,182	2,754	2,963
Proved developed and undeveloped reserves, revisions due to prices (MMBoe)	[1]	(27)	(302)	9
Proved developed and undeveloped reserves, revisions other than price (MMBoe)	[1]	137	(142)	(65)
Proved developed and undeveloped reserves, extension and discoveries (MMBoe)	[1]	126	118	211
Proved developed and undeveloped reserves, purchase of reserves (MMBoe)	[1]	20	9	265
Proved developed and undeveloped reserves, production (MMBoe)	[1]	(223)	(248)	(246)
Proved developed and undeveloped reserves, sale of reserves (MMBoe)	[1]	(157)	(7)	(383)
Proved developed and undeveloped reserves, ending balance (MMBoe)	[1]	2,058	2,182	2,754
Proved developed reserves (MMBoe)	[1]	1,649	1,806	2,065	2,262
Proved developed producing reserves (MMBoe)	[1]	1,593	1,749	1,977	2,154
Proved undeveloped reserves (MMBoe)	[1]	409	376	689	701
Conversion rate of gas reserves from barrels of oil to Boe		6
United States [Member]
Reserve Quantities [Line Items]
Proved developed and undeveloped reserves, beginning balance (MMBoe)	[1]	1,638	2,205	2,205
Proved developed and undeveloped reserves, revisions due to prices (MMBoe)	[1]	(48)	(408)	38
Proved developed and undeveloped reserves, revisions other than price (MMBoe)	[1]	151	(59)	(86)
Proved developed and undeveloped reserves, extension and discoveries (MMBoe)	[1]	124	104	197
Proved developed and undeveloped reserves, purchase of reserves (MMBoe)	[1]	20	9	265
Proved developed and undeveloped reserves, production (MMBoe)	[1]	(174)	(206)	(207)
Proved developed and undeveloped reserves, sale of reserves (MMBoe)	[1]	(157)	(7)	(207)
Proved developed and undeveloped reserves, ending balance (MMBoe)	[1]	1,554	1,638	2,205
Proved developed reserves (MMBoe)	[1]	1,439	1,563	1,900	1,947
Proved developed producing reserves (MMBoe)	[1]	1,386	1,509	1,815	1,857
Proved undeveloped reserves (MMBoe)	[1]	115	75	305	258
Canada [Member]
Reserve Quantities [Line Items]
Proved developed and undeveloped reserves, beginning balance (MMBoe)	[1]	544	549	758
Proved developed and undeveloped reserves, revisions due to prices (MMBoe)	[1]	21	106	(29)
Proved developed and undeveloped reserves, revisions other than price (MMBoe)	[1]	(14)	(83)	21
Proved developed and undeveloped reserves, extension and discoveries (MMBoe)	[1]	2	14	14
Proved developed and undeveloped reserves, production (MMBoe)	[1]	(49)	(42)	(39)
Proved developed and undeveloped reserves, sale of reserves (MMBoe)	[1]			(176)
Proved developed and undeveloped reserves, ending balance (MMBoe)	[1]	504	544	549
Proved developed reserves (MMBoe)	[1]	210	243	165	315
Proved developed producing reserves (MMBoe)	[1]	207	240	162	297
Proved undeveloped reserves (MMBoe)	[1]	294	301	384	443

[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.