Pensions and other benefits - Changes in Fund Assets (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Change in plan assets:
Fair value of plan assets as at January 1	$ 13,478	$ 12,867
Actual return on plan assets	1,702	1,208
Employer contributions	48	52
Employee contributions	50	48
Benefits paid	(695)	(693)
Foreign currency changes	15	(4)
Fair value of plan assets as at December 31	14,598	13,478
Funded status - plan surplus (deficit)	3,993	2,709
Pensions
Change in plan assets:
Fair value of plan assets as at January 1	13,472	12,862
Actual return on plan assets	1,701	1,207
Employer contributions	13	15
Employee contributions	50	48
Benefits paid	(659)	(656)
Foreign currency changes	15	(4)
Fair value of plan assets as at December 31	14,592	13,472
Funded status - plan surplus (deficit)	4,426	3,166
Other benefits
Change in plan assets:
Fair value of plan assets as at January 1	6	5
Actual return on plan assets	1	1
Employer contributions	35	37
Employee contributions	0	0
Benefits paid	(36)	(37)
Foreign currency changes	0	0
Fair value of plan assets as at December 31	6	6
Funded status - plan surplus (deficit)	$ (433)	$ (457)