Pensions and other benefits - Net Periodic Benefit Cost (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Total other components of net periodic benefit (recovery) cost	$ (411)	$ (387)	$ (342)
Pensions
Defined Benefit Plan Disclosure [Line Items]
Current service cost (benefits earned by employees)	148	171	140
Interest cost on benefit obligation	383	351	406
Expected return on plan assets	(959)	(959)	(945)
Recognized net actuarial loss (gain)	153	206	177
Amortization of prior service costs (recoveries)	1	0	(1)
Total other components of net periodic benefit (recovery) cost	(422)	(402)	(363)
Net periodic benefit (recovery) cost	(274)	(231)	(223)
Other benefits
Defined Benefit Plan Disclosure [Line Items]
Current service cost (benefits earned by employees)	11	13	12
Interest cost on benefit obligation	16	16	17
Expected return on plan assets	0	0	0
Recognized net actuarial loss (gain)	(5)	(1)	4
Amortization of prior service costs (recoveries)	0	0	0
Total other components of net periodic benefit (recovery) cost	11	15	21
Net periodic benefit (recovery) cost	$ 22	$ 28	$ 33