v3.26.1
Stock-based compensation - Narrative (Details) - CAD ($)
$ / shares in Units, $ in Millions
3 Months Ended 6 Months Ended 12 Months Ended
Dec. 31, 2025
Jun. 30, 2026
Mar. 31, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Dec. 31, 2023
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Stock-based compensation expense   $ 94   $ 59 $ 143 $ 92  
Stock Options              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Number of options issued (in shares)         1,189,411    
Options issued, weighted average price per share (In cad per share)         $ 104.69    
Expiration period (in years)         7 years    
Stock options grant date fair value         $ 30    
Stock Options | Minimum              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Vesting period (in years or months)         12 months    
Stock Options | Maximum              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Vesting period (in years or months)         48 months    
Performance Share Units (PSUs)              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Units issued (in shares)         629,722   544,175
Grant date fair value         $ 66    
Number of trading days         30 days    
Cash payout of associated shares (in shares)     461,766        
Performance Share Units (PSUs) | Share-based Payment Arrangement, Tranche One              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
PSU payout percentage         91.00%    
Cash payout     $ 42        
Performance Deferred Share Units (PDSUs)              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Units issued (in shares)         20,386   26,333
Grant date fair value         $ 3    
Number of units that can be granted as percentage of shares acquired   25.00%     25.00%    
Vested in period (in shares) 26,555            
Payout in future periods $ 3            
PSUs and PDSUs | Minimum              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Vesting period (in years or months)         3 years    
PSUs and PDSUs | Maximum              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Vesting period (in years or months)         4 years