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Supplementary Oil And Gas Information (Unaudited) - Proved and Proved Developed Oil and Natural Gas Liquids, Net of Royalties (Details) - MMBbls	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Crude Oil, Synthetic Crude Oil, Bitumen, Natural Gas, Natural Gas Liquids
Proved Developed And Undeveloped Reserves [Roll Forward]
Proved reserves, net, beginning balance	8,544	7,919	7,091
Extensions and discoveries (in MMbbl)	726	364	912
Improved recovery (in MMbbl)	58	181	64
Purchases of reserves in place (in MMbbl)	28	668	16
Sales of reserves in place (in MMbbl)	0	0	(4)
Production (in MMbbl)	(320)	(285)	(274)
Economic revisions due to prices (in MMbbl)	805	(285)	(51)
Revisions of prior estimates (in MMbbl)	103	(19)	165
Proved reserves, net, ending balance	9,943	8,544	7,919
Net proved developed reserves (in MMbbl)	7,751	6,543	6,571	5,825
North America | Synthetic Crude Oil
Proved Developed And Undeveloped Reserves [Roll Forward]
Proved reserves, net, beginning balance	5,554	5,661	4,956
Extensions and discoveries (in MMbbl)	708	334	744
Improved recovery (in MMbbl)	0	0	0
Purchases of reserves in place (in MMbbl)	0	0	0
Sales of reserves in place (in MMbbl)	0	0	0
Production (in MMbbl)	(151)	(137)	(148)
Economic revisions due to prices (in MMbbl)	701	(288)	0
Revisions of prior estimates (in MMbbl)	36	(17)	109
Proved reserves, net, ending balance	6,847	5,554	5,661
Net proved developed reserves (in MMbbl)	6,770	5,452	5,661	4,967
North America | Bitumen
Proved Developed And Undeveloped Reserves [Roll Forward]
Proved reserves, net, beginning balance	2,216	1,469	1,365
Extensions and discoveries (in MMbbl)	8	18	151
Improved recovery (in MMbbl)	49	169	10
Purchases of reserves in place (in MMbbl)	0	666	2
Sales of reserves in place (in MMbbl)	0	0	(4)
Production (in MMbbl)	(109)	(81)	(64)
Economic revisions due to prices (in MMbbl)	207	3	(45)
Revisions of prior estimates (in MMbbl)	41	(27)	54
Proved reserves, net, ending balance	2,413	2,216	1,469
Net proved developed reserves (in MMbbl)	628	661	461	410
North America | Crude Oil and NGLs
Proved Developed And Undeveloped Reserves [Roll Forward]
Proved reserves, net, beginning balance	598	604	594
Extensions and discoveries (in MMbbl)	10	12	17
Improved recovery (in MMbbl)	9	12	50
Purchases of reserves in place (in MMbbl)	28	2	7
Sales of reserves in place (in MMbbl)	0	0	0
Production (in MMbbl)	(45)	(49)	(47)
Economic revisions due to prices (in MMbbl)	(94)	0	(18)
Revisions of prior estimates (in MMbbl)	20	17	1
Proved reserves, net, ending balance	525	598	604
Net proved developed reserves (in MMbbl)	285	354	378	399
North America | Crude Oil, Synthetic Crude Oil, Bitumen, Natural Gas, Natural Gas Liquids
Proved Developed And Undeveloped Reserves [Roll Forward]
Proved reserves, net, beginning balance	8,368	7,734	6,915
Extensions and discoveries (in MMbbl)	726	364	912
Improved recovery (in MMbbl)	58	181	60
Purchases of reserves in place (in MMbbl)	28	668	9
Sales of reserves in place (in MMbbl)	0	0	(4)
Production (in MMbbl)	(305)	(267)	(259)
Economic revisions due to prices (in MMbbl)	814	(285)	(63)
Revisions of prior estimates (in MMbbl)	97	(28)	164
Proved reserves, net, ending balance	9,785	8,368	7,734
Net proved developed reserves (in MMbbl)	7,682	6,466	6,500	5,776
North Sea | Crude Oil and NGLs
Proved Developed And Undeveloped Reserves [Roll Forward]
Proved reserves, net, beginning balance	105	114	107
Extensions and discoveries (in MMbbl)	0	0	0
Improved recovery (in MMbbl)	0	0	1
Purchases of reserves in place (in MMbbl)	0	0	7
Sales of reserves in place (in MMbbl)	0	0	0
Production (in MMbbl)	(8)	(10)	(9)
Economic revisions due to prices (in MMbbl)	(12)	(1)	11
Revisions of prior estimates (in MMbbl)	3	3	(3)
Proved reserves, net, ending balance	87	105	114
Net proved developed reserves (in MMbbl)	32	38	37	28
Offshore Africa | Crude Oil and NGLs
Proved Developed And Undeveloped Reserves [Roll Forward]
Proved reserves, net, beginning balance	70	71	69
Extensions and discoveries (in MMbbl)	0	0	0
Improved recovery (in MMbbl)	0	0	3
Purchases of reserves in place (in MMbbl)	0	0	0
Sales of reserves in place (in MMbbl)	0	0	0
Production (in MMbbl)	(6)	(7)	(6)
Economic revisions due to prices (in MMbbl)	3	1	1
Revisions of prior estimates (in MMbbl)	4	6	4
Proved reserves, net, ending balance	71	70	71
Net proved developed reserves (in MMbbl)	37	39	34	21

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Proved Developed And Undeveloped Reserves1 [Roll Forward]

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Additions to proved reserves that result from (1) extension of the proved acreage of previously discovered (old) reservoirs through additional drilling in periods after discovery and (2) discovery of new fields with proved reserves or of new reservoirs of proved reserves in old fields.

+ References

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Changes in proved reserve estimates resulting from application of improved recovery techniques.

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The net quantity of proved reserves as of the balance sheet date. Proved oil reserves are the estimated quantities of crude oil and natural gas liquids which geological and engineering data demonstrate with reasonable certainty to be recoverable.

+ References

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Production of proved reserves.

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Revisions represent changes in previous estimates of proved reserves, either upward or downward, resulting from new information (except for an increase in proved acreage) normally obtained from development drilling and production history or resulting from change in economic factors.

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Sales of minerals in place.

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Net quantities of an enterprise's interests in proved developed reserves of either crude oil (including condensate and natural gas liquids), natural gas, synthetic oil and gas, or other nonrenewable natural resource that is intended to be upgraded into synthetic oil and gas as of the beginning and the end of the year. "Net" quantities of reserves include those relating to the enterprise's operating and nonoperating interests in properties. Quantities of reserves relating to royalty interests owned are included in "net" quantities if the necessary information is available to the enterprise. "Net" quantities does not include reserves relating to interests of others in properties owned by the enterprise. The unit of measure for reserve quantities is defined as "barrels" for oil and synthetic oil reserves or "cubic feet" or "cubic meters" for natural gas and synthetic gas reserves.

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