Income taxes - Summary of Major Components of Company's Income Tax Expense (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Current income tax expense	$ 526	$ 537	$ 525
Origination and reversal of temporary differences	259	277	316
Effect of tax rate decrease	(11)	(32)	(95)
Effect of hedge of net investment in foreign subsidiaries	(3)	(18)	(38)
Other	(3)	(6)	(2)
Total deferred income tax expense	242	221	181
Total income taxes	768	758	706
Income before income tax expense
Canada	2,899	2,518	2,392
Foreign	721	684	754
Income before income tax expense	3,620	3,202	3,146
Current
Canada	404	412	410
Foreign	122	125	115
Total current income tax expense	526	537	525
Deferred
Canada	(179)	231	141
Foreign	421	(10)	40
Total deferred income tax expense	242	221	181
Total income taxes	$ 768	$ 758	$ 706