Income taxes - Expected Income Tax Expense at Canadian Statutory Rates Reconciled to Income Tax Expense (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Statutory federal and provincial income tax rate (Canada)	26.12%	26.12%	26.31%
Expected income tax expense at Canadian enacted statutory tax rates	$ 1,083	$ 946	$ 842
(Decrease) increase in taxes resulting from:
Gains not subject to tax	(9)	(116)	(23)
Canadian tax rate differentials	(12)	(22)	(3)
Foreign tax rate differentials	(94)	(37)	(32)
Effect of tax rate decrease	(25)	(11)	(32)
Deduction for dividends taxed on outside basis	(270)	0	0
Unrecognized tax benefits	(24)	(2)	(7)
Other	(21)	10	13
Total income taxes	$ 628	$ 768	$ 758