Pensions and other benefits - Changes in Projected Benefit Obligation (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Pensions
Change in projected benefit obligation:
Benefit obligation at January 1	$ 13,799	$ 12,610
Current service cost	171	140	$ 107
Interest cost	351	406	450
Employee contributions	42	42
Benefits paid	(667)	(653)
Foreign currency changes	0	(5)
Plan amendments and other	0	3
Actuarial loss (gain)	(812)	1,256
Projected benefit obligation at December 31	12,884	13,799	12,610
Other benefits
Change in projected benefit obligation:
Benefit obligation at January 1	553	541
Current service cost	13	12	11
Interest cost	16	17	20
Employee contributions	0	0
Benefits paid	(31)	(34)
Foreign currency changes	0	0
Plan amendments and other	0	0
Actuarial loss (gain)	(48)	17
Projected benefit obligation at December 31	$ 503	$ 553	$ 541