Pensions and other benefits - Additional Information (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Period of average market values for calculating net periodic benefit cost	5 years
Benefit obligation, discount rate	5.01%	3.01%	2.58%
Defined benefit plan with accumulated benefit obligation in excess of plan assets, accumulated benefit obligation	$ 332	$ 410
Defined benefit plan with accumulated benefit obligation in excess of plan assets, plan assets	$ 186	$ 201
Maximum value of underlying assets represented by financial derivatives, excluding currency forwards	30.00%
Solvency funded position hedged against interest rate risk	45.00%	47.00%
Company's common shares in fund assets (in shares)	570,074	426,304
Net cost of defined contribution plan	$ 12	$ 13	$ 12
Multi-employer benefit plan, Employer contributions	$ 2	$ 3	$ 3
US Dollar
Defined Benefit Plan Disclosure [Line Items]
Plans exposure to foreign currency risk percentage	50.00%	43.00%
Euro
Defined Benefit Plan Disclosure [Line Items]
Plans exposure to foreign currency risk percentage	6.00%	5.00%
Other Currencies
Defined Benefit Plan Disclosure [Line Items]
Plans exposure to foreign currency risk percentage	10.00%	10.00%
Public equity
Defined Benefit Plan Disclosure [Line Items]
Company's securities in fund assets	$ 58	$ 39
Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Company's securities in fund assets	$ 5	$ 5
Pensions
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation, discount rate	5.01%	3.01%	2.58%
Defined benefit pension plans accumulated benefit obligation	$ 9,747	$ 12,591