v3.25.4
Pensions and other postretirement benefits (Components of Net Periodic Benefit Cost Income) (Details) - CAD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]      
Total Other components of net periodic benefit cost (income) $ (502) $ (454) $ (479)
Pensions      
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]      
Current service cost 80 91 83
Interest cost 604 669 703
Expected return on plan assets (1,160) (1,182) (1,186)
Amortization of prior service cost (credit) 0 0 0
Amortization of net actuarial loss (gain) 58 62 7
Total Other components of net periodic benefit cost (income) (498) (451) (476)
Net periodic benefit cost (income) (418) (360) (393)
Other postretirement benefits      
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]      
Current service cost 1 1 1
Interest cost 6 7 7
Expected return on plan assets 0 0 0
Amortization of prior service cost (credit) (4) (4) (3)
Amortization of net actuarial loss (gain) (6) (6) (7)
Total Other components of net periodic benefit cost (income) (4) (3) (3)
Net periodic benefit cost (income) $ (3) $ (2) $ (2)