Property Plant And Equipment (Details) - CAD CAD in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Reconciliation of changes in property, plant and equipment [abstract]
Balance at the beginning	CAD 71,259.0
Balance at the end	73,493.0	CAD 71,259.0
Cost
Reconciliation of changes in property, plant and equipment [abstract]
Balance at the beginning	107,678.0	93,712.0
Additions	7,110.0	6,570.0
Transfers from exploration and evaluation		65.0
Acquisitions	335.0	10,806.0
Changes in decommissioning and restoration	843.0	(47.0)
Disposals and derecognition	(884.0)	(969.0)
Foreign exchange adjustments	(269.0)	(1,552.0)
Reclassified to assets held for sale		(907.0)
Reclassified from assets held for sale	(35.0)
Balance at the end	114,848.0	107,678.0
Accumulated provision
Reconciliation of changes in property, plant and equipment [abstract]
Balance at the beginning	(36,419.0)	(32,561.0)
Disposals and derecognition	368.0	645.0
Foreign exchange adjustments	129.0	1,033.0
Reclassified to assets held for sale	(3.0)
Reclassified from assets held for sale		(195.0)
Depreciation and depletion	(5,430.0)	(5,731.0)
Balance at the end	(41,355.0)	(36,419.0)
Oil and Gas properties
Reconciliation of changes in property, plant and equipment [abstract]
Balance at the beginning	18,079.0
Balance at the end	18,234.0	18,079.0
Oil and Gas properties \| Cost
Reconciliation of changes in property, plant and equipment [abstract]
Balance at the beginning	34,141.0	32,635.0
Additions	1,235.0	1,428.0
Transfers from exploration and evaluation		65.0
Acquisitions	25.0	1,678.0
Changes in decommissioning and restoration	821.0	(68.0)
Disposals and derecognition		(166.0)
Foreign exchange adjustments	(13.0)	(1,431.0)
Balance at the end	36,209.0	34,141.0
Oil and Gas properties \| Accumulated provision
Reconciliation of changes in property, plant and equipment [abstract]
Balance at the beginning	(16,062.0)	(14,442.0)
Foreign exchange adjustments	3.0	978.0
Depreciation and depletion	(1,916.0)	(2,598.0)
Balance at the end	(17,975.0)	(16,062.0)
Plant and Equipment
Reconciliation of changes in property, plant and equipment [abstract]
Balance at the beginning	53,180.0
Balance at the end	55,259.0	53,180.0
Plant and Equipment \| Cost
Reconciliation of changes in property, plant and equipment [abstract]
Balance at the beginning	73,537.0	61,077.0
Additions	5,875.0	5,142.0
Acquisitions	310.0	9,128.0
Changes in decommissioning and restoration	22.0	21.0
Disposals and derecognition	(884.0)	(803.0)
Foreign exchange adjustments	(256.0)	(121.0)
Reclassified to assets held for sale		(907.0)
Reclassified from assets held for sale	(35.0)
Balance at the end	78,639.0	73,537.0
Plant and Equipment \| Accumulated provision
Reconciliation of changes in property, plant and equipment [abstract]
Balance at the beginning	(20,357.0)	(18,119.0)
Disposals and derecognition	368.0	645.0
Foreign exchange adjustments	126.0	55.0
Reclassified to assets held for sale	(3.0)
Reclassified from assets held for sale		(195.0)
Depreciation and depletion	(3,514.0)	(3,133.0)
Balance at the end	CAD (23,380.0)	CAD (20,357.0)

The increase in property, plant and equipment resulting from acquisitions through business combinations. [Refer: Business combinations [member]; Property, plant and equipment]

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- Definition

The amount of additions to property, plant and equipment other than those acquired through business combinations. [Refer: Business combinations [member]; Property, plant and equipment]

+ References

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-Name IAS
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The decrease in property, plant and equipment through classification as held for sale or inclusion in a disposal group classified as held for sale. [Refer: Disposal groups classified as held for sale [member]; Property, plant and equipment; Disposal groups classified as held for sale [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

The amount of depreciation of property, plant and equipment. [Refer: Depreciation and amortisation expense; Property, plant and equipment]

+ References

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The decrease in property, plant and equipment resulting from disposals and retirements. [Refer: Property, plant and equipment]

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-Name IAS
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The increase (decrease) in property, plant and equipment resulting from net exchange differences arising on the translation of the financial statements from the functional currency into a different presentation currency, including the translation of a foreign operation into the presentation currency of the reporting entity. [Refer: Property, plant and equipment]

+ References

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The amount of tangible assets that: (a) are held for use in the production or supply of goods or services, for rental to others, or for administrative purposes; and (b) are expected to be used during more than one period.

+ References

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The increase (decrease) in property, plant and equipment due to decommissioning or restoration.

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The increase in property, plant and equipment in a reclassification from held for sale or inclusion in a disposal group classified as held for sale.

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The additions to oil and gas equipment from exploration and evaluation.

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