income taxes - Other (Details) - Investment Tax Credits - CAD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Other
Tax benefits recognized	$ 8	$ 10
Property, plant, and equipment and/or intangible assets
Other
Tax benefits recognized	$ 4	$ 6

The amount of benefit arising from a previously unrecognised tax loss, tax credit or temporary difference of a prior period that is used to reduce current tax expense. [Refer: Temporary differences [member]; Unused tax losses [member]; Unused tax credits [member]]

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Name IAS
-Number 12
-IssueDate 2019-01-01
-Paragraph 80
-Subparagraph e
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=12&code=ifrs-tx-2019-en-r&anchor=para_80_e&doctype=Standard
-URIDate 2019-03-27

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