v3.22.4
Pensions and Other Postretirement Benefits (Obligations and Funded Status) (Details) - CAD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2022
Dec. 31, 2021
Dec. 31, 2020
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Increase (decrease) in discount rate 2.11% 0.60%  
Pension Plan [Member]      
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]      
Projected benefit obligation at beginning of year $ 17,813 $ 19,499  
Amendments 0 0  
Curtailments 0 (52)  
Interest cost 468 392 $ 532
Actuarial gain on projected benefit obligation (3,548) (1,206)  
Current service cost 157 197 175
Plan participants' contributions 60 61  
Foreign currency changes 19 (3)  
Benefit payments, settlements and transfers (1,060) (1,075)  
Projected benefit obligation at end of year 13,909 17,813 19,499
Component representing future salary increases (85) (179)  
Accumulated benefit obligation at end of year 13,824 17,634  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair value of plan assets at beginning of year 20,416 19,723  
Employer contributions 47 104  
Plan participants' contributions 60 61  
Foreign currency changes 14 (2)  
Actual return on plan assets (2,888) 1,605  
Benefit payments, settlements and transfers (1,060) (1,075)  
Fair value of plan assets at end of year 16,589 20,416 19,723
Funded status - Excess (deficiency) of fair value of plan assets over projected benefit obligation at end of year 2,680 2,603  
Other postretirement benefits [Member]      
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]      
Projected benefit obligation at beginning of year 212 228  
Amendments (21) 0  
Curtailments 0 0  
Interest cost 5 5 6
Actuarial gain on projected benefit obligation (40) (7)  
Current service cost 2 2 2
Plan participants' contributions 0 0  
Foreign currency changes 3 (2)  
Benefit payments, settlements and transfers (14) (14)  
Projected benefit obligation at end of year 147 212 228
Component representing future salary increases 0 0  
Accumulated benefit obligation at end of year 147 212  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair value of plan assets at beginning of year 0 0  
Employer contributions 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 (147) (212)  
CN Pension Plan [Member] | Pension Plan [Member]      
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]      
Projected benefit obligation at beginning of year 16,557    
Projected benefit obligation at end of year 12,887 16,557  
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]      
Fair value of plan assets at beginning of year 19,485    
Fair value of plan assets at end of year $ 15,838 $ 19,485