Financial Instruments - Counterparty Credit Risk Management (Details) - CAD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disclosure of detailed information about financial instruments [line items]
Expected credit loss rate	1.00%	1.00%
Derivative financial asset (liability), net	$ (24)	$ 178	$ 356
Credit risk
Disclosure of detailed information about financial instruments [line items]
Derivative financial asset (liability), net	$ 129	$ 265

The rate of expected credit losses, calculated as percentage of the gross carrying amount. Expected credit losses are the weighted average of credit losses with the respective risks of a default occurring as the weights.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Name IFRS
-Number 7
-IssueDate 2020-01-01
-Paragraph IG20D
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2020-en-r&anchor=para_IG20D&doctype=Implementation%20Guidance
-URIDate 2020-01-01

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Name IFRS
-Number 7
-IssueDate 2020-01-01
-Paragraph 35N
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2020-en-r&anchor=para_35N&doctype=Standard
-URIDate 2020-01-01

Name:	ifrs-full_ExpectedCreditLossRate
Namespace Prefix:	ifrs-full_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant