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Financial Instruments - Carrying Amounts and Reconciliation of Derivative Financial Instruments (Details)
$ in Millions
 12 Months Ended
Dec. 31, 2025
USD ($)
MMBTU
Dec. 31, 2024
USD ($)
MMBTU
Dec. 31, 2024
CAD ($)
Dec. 31, 2023
CAD ($)
Dec. 31, 2022
CAD ($)
Disclosure of detailed information about hedging instruments [line items]          
Derivatives held for trading     $ 5 $ 9  
Current portion of other long-term assets     13 12  
Current portion of other long-term liabilities     (8) (4)  
Other long-term assets     0 1  
Derivative financial asset (liability), net     5 9 $ 6
Derivative, volume per day | MMBTU   50,000      
Derivative, AECO fixed price   $ 1.82      
Derivative Contract One          
Disclosure of detailed information about hedging instruments [line items]          
Derivative, volume per day | MMBTU 12,500        
Derivative, AECO fixed price $ 1.47        
Derivative Contract Two          
Disclosure of detailed information about hedging instruments [line items]          
Derivative, volume per day | MMBTU 25,000        
Derivative, AECO fixed price $ 1.82        
Natural Gas          
Disclosure of detailed information about hedging instruments [line items]          
Derivatives held for trading     7 (3)  
Foreign currency forward contracts          
Disclosure of detailed information about hedging instruments [line items]          
Derivatives held for trading     $ (2) $ 12