General and Administrative - Summary of General and Administrative Expenses (Detail) - CAD ($) $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
General And Administrative Expenses [Abstract]
Salaries and Benefits	$ 145	$ 143	$ 205
Administrative and Other	84	95	177
Onerous Contract Provisions (Recovery)	18	(5)	629
Stock-Based Compensation Expense (Note 32)	49	67	9
Other Long-Term Incentive Expense (Recovery)	(4)	31
General and Administrative Expense	$ 292	$ 331	$ 1,020

The amount of expense relating to general and administrative activities of the entity.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 1
-IssueDate 2020-01-01
-Paragraph 112
-Subparagraph c
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=1&code=ifrs-tx-2020-en-r&anchor=para_112_c&doctype=Standard
-URIDate 2020-01-01

Name:	ifrs-full_GeneralAndAdministrativeExpense
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration