v3.25.4
Stock-based compensation (Employee Share Investment Plan) (Details)
$ / shares in Units, shares in Millions, $ in Millions
 12 Months Ended
Dec. 31, 2025
CAD ($)
participant
$ / shares
shares
Dec. 31, 2024
CAD ($)
participant
$ / shares
shares
Dec. 31, 2023
participant
shares
Employee Share Investment Plan      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Maximum percentage of gross salary eligible employees can subscribe to purchase shares of Company's common stock on the open market 10.00%    
Maximum percentage of additional contribution made by the Company of amount invested by employee 35.00%    
Maximum percentage of gross salary employer can contribute toward purchase of Company's common stock 6.00%    
Vesting period 1 year    
Roll forward of nonvested RSUs      
Units nonvested at beginning of period (in shares) 0.2    
Company contributions (in shares) 0.3    
Vested (in shares) (0.2)    
Forfeited (in shares) 0.0    
Units nonvested at end of period (in shares) 0.3 0.2  
Weighted-average share price      
Beginning of period (in dollars per share) | $ / shares $ 163.25    
Company contributions (in dollars per share) | $ / shares 138.50    
Vested (in dollars per share) | $ / shares 163.11    
Forfeited (in dollars per share) | $ / shares 143.95    
End of period (in dollars per share) | $ / shares $ 138.17 $ 163.25  
Fair value of units vested | $ $ 30 $ 28  
Unrecognized compensation costs, awards other than options | $ $ 17    
Unrecognized compensation cost, period of recognition 12 months    
Employee Share Investment Plan, Participants      
Weighted-average share price      
Number of participants holding shares | participant 22,015 21,492 21,450
Total number of ESIP shares purchased on behalf of employees (in shares) 1.6 1.2 1.2