v3.25.4
Post-employment benefit plans - Post-Employment Benefit Plan Assets (Details) - CAD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Disclosure of fair value of plan assets [line items]    
Equity securities, total plan assets fair value percent 14.00% 13.00%
Debt securities, total plan assets fair value percent 52.00% 53.00%
Alternative investments, total plan asset fair value percent 34.00% 34.00%
Total plan assets fair value percent 100.00% 100.00%
Defined benefit obligation hedged $ 3,000.0  
DB pension    
Disclosure of fair value of plan assets [line items]    
Plan assets, at fair value 24,413.0 $ 24,188.0
Equity securities included in total plan assets $ 0.1 $ 0.1
Equity securities percent included in total plan assets 0.10% 0.10%
Debt securities included in total plan assets $ 36.0 $ 41.0
Debt securities percent included in total plan assets 0.10% 0.20%
DB pension | Money market    
Disclosure of fair value of plan assets [line items]    
Debt securities $ 357.0 $ 257.0
DB pension | Private equities    
Disclosure of fair value of plan assets [line items]    
Alternative investments 1,077.0 1,066.0
DB pension | Hedge funds    
Disclosure of fair value of plan assets [line items]    
Alternative investments 1,543.0 1,301.0
DB pension | Real estate and infrastructure    
Disclosure of fair value of plan assets [line items]    
Alternative investments 4,452.0 4,341.0
DB pension | Private debt    
Disclosure of fair value of plan assets [line items]    
Alternative investments 1,325.0 1,451.0
DB pension | Other    
Disclosure of fair value of plan assets [line items]    
Alternative investments 24.0 23.0
DB pension | Canadian    
Disclosure of fair value of plan assets [line items]    
Equity securities 759.0 862.0
DB pension | Canadian | Debt securities, excluding money market    
Disclosure of fair value of plan assets [line items]    
Debt securities 10,075.0 11,117.0
DB pension | Foreign    
Disclosure of fair value of plan assets [line items]    
Equity securities 2,577.0 2,344.0
DB pension | Foreign | Debt securities, excluding money market    
Disclosure of fair value of plan assets [line items]    
Debt securities $ 2,224.0 $ 1,426.0
Bottom of range    
Disclosure of fair value of plan assets [line items]    
Equity securities, weighted average target allocation 0.00%  
Debt securities, weighted average target allocation 40.00%  
Alternative investments, weighted average target allocation 0.00%  
Top of range    
Disclosure of fair value of plan assets [line items]    
Equity securities, weighted average target allocation 40.00%  
Debt securities, weighted average target allocation 100.00%  
Alternative investments, weighted average target allocation 60.00%