Commitments and Contingencies - Summary of Future Payments of Commitments (Parenthetical) (Detail) - CAD ($) $ in Billions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Disclosure of commitments [Line Items]
Transportation Commitment	$ 14	$ 9
WRB [Member]
Disclosure of commitments [Line Items]
Percent of ownership in joint operations	50.00%	50.00%

The proportion of ownership interest in a joint operation attributable to the entity. [Refer: Joint operations [member]]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 12
-IssueDate 2017-01-01
-Paragraph 21
-Subparagraph a
-Clause iv
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=12&date=2017-03-01&anchor=para_21_a_iv&doctype=Standard
-URIDate 2017-03-09

Name:	ifrs-full_ProportionOfOwnershipInterestInJointOperation
Namespace Prefix:	ifrs-full_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration