v3.25.4
Pensions and other postretirement benefits (Obligations and Funded Status) (Details) - CAD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Change in plan assets      
Increase in discount rate   0.23%  
Pensions      
Change in benefit obligation      
Projected benefit obligation at beginning of year $ 14,244 $ 14,755  
Interest cost 604 669 $ 703
Actuarial loss (gain) on projected benefit obligation (382) (319)  
Current service cost 80 91 83
Plan participants' contributions 59 63  
Foreign currency changes (12) 20  
Benefit payments, settlements and transfers (1,037) (1,035)  
Projected benefit obligation at the end of the year 13,556 14,244 14,755
Component representing future salary increases (47) (71)  
Accumulated benefit obligation at end of year 13,509 14,173  
Change in plan assets      
Fair value of plan assets at beginning of year 18,435 17,533  
Net employer contributions (withdrawals) (8) 25  
Plan participants' contributions 59 63  
Foreign currency changes (10) 15  
Actual return on plan assets 1,150 1,834  
Benefit payments, settlements and transfers (1,037) (1,035)  
Fair value of plan assets at end of year 18,589 18,435 17,533
Funded status - Excess (deficiency) of fair value of plan assets over projected benefit obligation at end of year 5,033 4,191  
Pensions | CN Pension Plan      
Change in benefit obligation      
Projected benefit obligation at beginning of year 13,241    
Projected benefit obligation at the end of the year 12,603 13,241  
Change in plan assets      
Fair value of plan assets at beginning of year 17,642    
Fair value of plan assets at end of year 17,815 17,642  
Other postretirement benefits      
Change in benefit obligation      
Projected benefit obligation at beginning of year 143 145  
Interest cost 6 7 7
Actuarial loss (gain) on projected benefit obligation (4) (2)  
Current service cost 1 1 1
Plan participants' contributions 0 0  
Foreign currency changes (2) 3  
Benefit payments, settlements and transfers (10) (11)  
Projected benefit obligation at the end of the year 134 143 145
Component representing future salary increases 0 0  
Accumulated benefit obligation at end of year 134 143  
Change in plan assets      
Fair value of plan assets at beginning of year 0 0  
Net employer contributions (withdrawals) 0 0  
Plan participants' contributions 0 0  
Foreign currency changes 0 0  
Actual return on plan assets 0 0  
Benefit payments, settlements and transfers 0 0  
Fair value of plan assets at end of year 0 0 $ 0
Funded status - Excess (deficiency) of fair value of plan assets over projected benefit obligation at end of year $ (134) $ (143)