Pensions and other benefits - Changes in Fund Assets (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Change in plan assets:
Fair value of fund assets at January 1	$ 14,938
Fair value of fund assets at December 31	12,862	$ 14,938
Pensions
Change in plan assets:
Fair value of fund assets at January 1	14,938	14,365
Actual return on plan assets	(1,464)	1,180
Employer contributions	14	18
Employee contributions	42	42
Benefits paid	(680)	(667)
Foreign currency changes	12	0
Fair value of fund assets at December 31	12,862	14,938
Funded status – plan surplus (deficit)	2,926	2,054
Other benefits
Change in plan assets:
Fair value of fund assets at January 1	5	5
Actual return on plan assets	0	0
Employer contributions	22	31
Employee contributions	0	0
Benefits paid	(22)	(31)
Foreign currency changes	0	0
Fair value of fund assets at December 31	5	5
Funded status – plan surplus (deficit)	$ (406)	$ (498)