Investment and other income - Gains and Losses on Asset Sales (Detail) - CAD ($) $ in Millions	3 Months Ended
Mar. 31, 2024	Mar. 31, 2023
Schedule of Investments [Abstract]
Proceeds from asset sales	$ 4	$ 14
Book value of asset sales	2	5
Gain (loss) on asset sales, before tax	2	9
Gain (loss) on asset sales, after tax	$ 2	$ 8

Aggregate cash proceeds received from a combination of transactions that are classified as investing activities in which assets, which may include one or more investments, are sold to third-party buyers. This element can be used by entities to aggregate proceeds from all asset sales that are classified as investing activities.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 12
-SubTopic 10
-Topic 230
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482740/230-10-45-12

Name:	us-gaap_ProceedsFromSalesOfAssetsInvestingActivities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration