Property, Plant and Equipment, Net - Summary of PP&E Under Construction and Not Subject to DD&A (Detail) - CAD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Disclosure Of Property Plant And Equipment [Line Items]
Property Plant and Equipment Temporarily Idle	$ 2,033	$ 2,008
Development & Production Upstream Assets [Member]
Disclosure Of Property Plant And Equipment [Line Items]
Property Plant and Equipment Temporarily Idle	1,807	1,836
Refining Equipment [Member]
Disclosure Of Property Plant And Equipment [Line Items]
Property Plant and Equipment Temporarily Idle	$ 226	$ 172

The amount of expenditures recognised in the carrying amount of an item of property, plant and equipment in the course of its construction. [Refer: Carrying amount [member]; Property, plant and equipment]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 16
-IssueDate 2020-01-01
-Paragraph 74
-Subparagraph b
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=16&code=ifrs-tx-2020-en-r&anchor=para_74_b&doctype=Standard
-URIDate 2020-01-01

Name:	ifrs-full_PropertyPlantAndEquipmentExpendituresRecognisedForConstructions
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant