Pensions and other benefits - Additional Information (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Period of average market values for calculating net periodic benefit cost	5 years
Benefit obligation, discount rate	3.01%	2.58%	3.25%
Defined benefit plan with accumulated benefit obligation in excess of plan assets, accumulated benefit obligation	$ 410	$ 443
Defined benefit plan with accumulated benefit obligation in excess of plan assets, plan assets	$ 201	$ 187
Maximum value of underlying assets represented by financial derivatives, excluding currency forwards	30.00%
Solvency funded position hedged against interest rate risk	47.00%	47.00%
Company's common shares in fund assets (in shares)	426,304	545,040
Net cost of defined contribution plan	$ 13	$ 12	$ 11
Multi-employer benefit plan, Employer contributions	$ 3	$ 3	$ 3
US Dollar
Defined Benefit Plan Disclosure [Line Items]
Plans exposure to foreign currency risk percentage	43.00%	33.00%
Percentage of plan exposed to foreign currency risk, excluding currency forwards		40.00%
Euro
Defined Benefit Plan Disclosure [Line Items]
Plans exposure to foreign currency risk percentage	5.00%	6.00%
Other Currencies
Defined Benefit Plan Disclosure [Line Items]
Plans exposure to foreign currency risk percentage	10.00%	14.00%
Public equity
Defined Benefit Plan Disclosure [Line Items]
Company's securities in fund assets	$ 39	$ 48
Fixed income securities
Defined Benefit Plan Disclosure [Line Items]
Company's securities in fund assets	$ 5	$ 0
Pensions
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation, discount rate	3.01%	2.58%	3.25%
Defined benefit pension plans accumulated benefit obligation	$ 12,591	$ 13,528