v3.25.4
Post-employment benefit plans - Healthcare Cost Trend Rates and Sensitivity Analysis (Details)
$ in Millions
 12 Months Ended
Dec. 31, 2025
CAD ($)
Actuarial assumption of medical cost trend rates  
Disclosure of sensitivity analysis for actuarial assumptions [line items]  
Percentage of reasonably possible decrease in actuarial assumption 1.00%
Percentage of reasonably possible increase in actuarial assumption 1.00%
Impact on net post-employment benefit plans cost, increase in assumption $ 2
Impact on net post-employment benefit plans cost, decrease in assumption (2)
Impact on post-employment benefit obligation, increase in assumption 55
Impact on post-employment benefit obligation, decrease in assumption $ (47)
Actuarial assumption of discount rates  
Disclosure of sensitivity analysis for actuarial assumptions [line items]  
Percentage of reasonably possible increase in actuarial assumption 0.50%
Impact on net post-employment benefit plans cost, increase in assumption $ (79)
Impact on net post-employment benefit plans cost, decrease in assumption 76
Impact on post-employment benefit obligation, increase in assumption (1,026)
Impact on post-employment benefit obligation, decrease in assumption $ 1,102
Actuarial assumption of expected rates of inflation  
Disclosure of sensitivity analysis for actuarial assumptions [line items]  
Percentage of reasonably possible increase in actuarial assumption 0.50%
Impact on net post-employment benefit plans cost, increase in assumption $ 54
Impact on net post-employment benefit plans cost, decrease in assumption (42)
Impact on post-employment benefit obligation, increase in assumption 997
Impact on post-employment benefit obligation, decrease in assumption (800)
Actuarial assumption of life expectancy  
Disclosure of sensitivity analysis for actuarial assumptions [line items]  
Impact on net post-employment benefit plans cost, increase in assumption 41
Impact on net post-employment benefit plans cost, decrease in assumption (40)
Impact on post-employment benefit obligation, increase in assumption 782
Impact on post-employment benefit obligation, decrease in assumption $ (782)
Duration of reasonably possible decrease in actuarial assumptions 1 year
Duration of reasonably possible increase in actuarial assumption 1 year