v3.25.4
Stock-based compensation (Options Activity) (Details) - CAD ($)
$ / shares in Units, shares in Millions, $ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Stock options additional disclosures      
Proceeds from stock options exercised $ 56 $ 41 $ 49
Stock Option Plan      
Stock option awards general disclosure      
Period of time options are generally not exercisable 12 months    
Stock option award expiration term 10 years    
Remaining common stock authorized for future issuances under plan (in shares) 12.2    
Stock options granted (in shares) 0.6 0.4 0.6
Roll forward of outstanding stock options      
Options outstanding at beginning of period (in shares) 3.2    
Granted (in shares) 0.6 0.4 0.6
Forfeited/Cancelled (in shares) (0.2)    
Exercised (in shares) (0.5)    
Options outstanding at end of period (in shares) 3.1 3.2  
Options exercisable at end of period (in shares) 1.8    
Weighted-average exercise price      
Weighted average exercise price per share of options outstanding at beginning of period (in dollars per share) $ 142.55    
Weighted average exercise price of options granted (in dollars per share) 143.19    
Weighted average exercise price of options forfeited/cancelled (in dollars per share) 152.19    
Weighted average exercise price of options exercised (in dollars per share) 115.01    
Weighted average exercise price per share of options outstanding at end of period (in dollars per share) 141.35 $ 142.55  
Weighted average exercise price of options exercisable at end of period (in dollars per share) $ 134.32    
Roll forward of outstanding nonvested stock options      
Nonvested options outstanding at beginning of period (in shares) 1.4    
Granted (in shares) 0.6 0.4 0.6
Forfeited/Cancelled (in shares) (0.2)    
Vested (in shares) (0.6)    
Nonvested options outstanding at end of period (in shares) 1.2 1.4  
Weighted-average grant date fair value      
Weighted average grant date fair value per share of nonvested options outstanding at beginning of period (in dollars per share) $ 29.82    
Weighted average grant date fair value per share of nonvested options granted during the period (in dollars per share) 26.36 $ 36.53 $ 32.96
Weighted average grant date fair value per share of nonvested options forfeited/cancelled (in dollars per share) 29.44    
Weighted average grant date fair value per share of nonvested options that vested during the period (in dollars per share) 26.96    
Weighted average grant date fair value per share of options outstanding at end of period (in dollars per share) $ 29.40 $ 29.82  
Stock options additional disclosures      
Grant date fair value of option awards in period $ 15    
Grant date fair value (in dollars per share) $ 26.36    
Unrecognized compensation cost related to nonvested options outstanding $ 17    
Unrecognized compensation cost, period of recognition 2 years 3 months 18 days    
Intrinsic value of options exercised $ 14 $ 29 $ 33
Proceeds from stock options exercised 56 41 49
Grant date fair value of options vested $ 14 $ 11 $ 10
Stock Option Plan | Awards Granted After 2024      
Stock option awards general disclosure      
Period of continuance employment to be eligible to exercise stock options 4 years    
Stock Option Plan | Awards Granted Prior To 2024      
Stock option awards general disclosure      
Period of continuance employment to be eligible to exercise stock options 5 years