Net Employee Defined Benefit Liability - Additional Information (Detail) CAD in Millions	12 Months Ended
Dec. 31, 2017 CAD yr Trustee
Disclosure of defined benefit plans [abstract]
Number of employer-appointed trustee	4
Number of professional trustee	1
Number of member nominated trustee	2
Amount expected to contribute to pension plan by company \| CAD	CAD 14.9
Percentage of plans' assets invested in mutual funds and exchange-traded funds or held in cash	40.00%
Percentage of plans' assets held in annuity policies	30.00%
Weighted average duration of defined benefit obligation \| yr	15

The estimate of the expected contributions to be made to a defined benefit plan for the next annual reporting period. [Refer: Defined benefit plans [member]]

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2017-01-01
-Paragraph 147
-Subparagraph b
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2017-03-01&anchor=para_147_b&doctype=Standard
-URIDate 2017-03-09

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2017-01-01
-Paragraph 148
-Subparagraph d
-Clause iii
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2017-03-01&anchor=para_148_d_iii&doctype=Standard
-URIDate 2017-03-09

Name:	ifrs-full_EstimateOfContributionsExpectedToBePaidToPlan
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration