v3.25.4
FINANCIAL RISK MANAGEMENT AND FINANCIAL INSTRUMENTS - Financial Instruments at Fair Value (Details) - CAD ($)
$ in Millions
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Disclosure of detailed information about financial instruments [line items]      
Investments in private companies $ 212 $ 128  
Total financial assets 1,057 1,461  
Long-term debt (including current portion) 37,058 41,896 $ 40,855
MLSE put liability 3,316 0  
Total financial liabilities 41,122 42,804  
Fair value (Level 2) | Fair value      
Disclosure of detailed information about financial instruments [line items]      
Investments in private companies 0 0  
Total financial assets 845 1,333  
Long-term debt (including current portion) 36,523 39,765  
MLSE put liability 0 0  
Total financial liabilities 37,271 40,673  
Fair value (Level 2) | Fair value | Debt derivatives      
Disclosure of detailed information about financial instruments [line items]      
Derivative financial assets 0 7  
Derivative financial liabilities 0 2  
Fair value (Level 2) | Fair value | Expenditure derivative instruments:      
Disclosure of detailed information about financial instruments [line items]      
Derivative financial liabilities 17 0  
Fair value (Level 2) | Fair value | Equity derivative instruments      
Disclosure of detailed information about financial instruments [line items]      
Derivative financial assets 37 0  
Derivative financial liabilities 9 54  
Fair value (Level 2) | Fair value | Subsidiary equity derivative instruments      
Disclosure of detailed information about financial instruments [line items]      
Derivative financial assets 1 0  
Derivative financial liabilities 36 0  
Fair value (Level 2) | Fair value | Virtual power purchase agreement      
Disclosure of detailed information about financial instruments [line items]      
Derivative financial liabilities 6 10  
Fair value (Level 2) | Fair value | Cash flow hedges | Debt derivatives      
Disclosure of detailed information about financial instruments [line items]      
Derivative financial assets 787 1,194  
Derivative financial liabilities 645 842  
Fair value (Level 2) | Fair value | Cash flow hedges | MLSE interest rate swap      
Disclosure of detailed information about financial instruments [line items]      
Derivative financial liabilities 7 0  
Fair value (Level 2) | Fair value | Cash flow hedges | Expenditure derivative instruments:      
Disclosure of detailed information about financial instruments [line items]      
Derivative financial assets 20 132  
Derivative financial liabilities 28 0  
Fair value (Level 3) | Fair value      
Disclosure of detailed information about financial instruments [line items]      
Investments in private companies 212 128  
Total financial assets 212 128  
Long-term debt (including current portion) 0 0  
MLSE put liability 3,316 0  
Total financial liabilities 3,316 0  
Fair value (Level 3) | Fair value | Debt derivatives      
Disclosure of detailed information about financial instruments [line items]      
Derivative financial assets 0 0  
Derivative financial liabilities 0 0  
Fair value (Level 3) | Fair value | Expenditure derivative instruments:      
Disclosure of detailed information about financial instruments [line items]      
Derivative financial liabilities 0 0  
Fair value (Level 3) | Fair value | Equity derivative instruments      
Disclosure of detailed information about financial instruments [line items]      
Derivative financial assets 0 0  
Derivative financial liabilities 0 0  
Fair value (Level 3) | Fair value | Subsidiary equity derivative instruments      
Disclosure of detailed information about financial instruments [line items]      
Derivative financial assets 0 0  
Derivative financial liabilities 0 0  
Fair value (Level 3) | Fair value | Virtual power purchase agreement      
Disclosure of detailed information about financial instruments [line items]      
Derivative financial liabilities 0 0  
Fair value (Level 3) | Fair value | Cash flow hedges | Debt derivatives      
Disclosure of detailed information about financial instruments [line items]      
Derivative financial assets 0 0  
Derivative financial liabilities 0 0  
Fair value (Level 3) | Fair value | Cash flow hedges | MLSE interest rate swap      
Disclosure of detailed information about financial instruments [line items]      
Derivative financial liabilities 0 0  
Fair value (Level 3) | Fair value | Cash flow hedges | Expenditure derivative instruments:      
Disclosure of detailed information about financial instruments [line items]      
Derivative financial assets 0 0  
Derivative financial liabilities 0 0  
Before Offset Amount      
Disclosure of detailed information about financial instruments [line items]      
Derivative financial assets 845 1,333  
Before Offset Amount | Debt derivatives      
Disclosure of detailed information about financial instruments [line items]      
Derivative financial assets 0    
Derivative financial liabilities 0 2  
Before Offset Amount | Expenditure derivative instruments:      
Disclosure of detailed information about financial instruments [line items]      
Derivative financial assets 0    
Derivative financial liabilities 17 0  
Before Offset Amount | Equity derivative instruments      
Disclosure of detailed information about financial instruments [line items]      
Derivative financial assets   0  
Derivative financial liabilities 9 54  
Before Offset Amount | Subsidiary equity derivative instruments      
Disclosure of detailed information about financial instruments [line items]      
Derivative financial assets   0  
Derivative financial liabilities 36 0  
Before Offset Amount | Virtual power purchase agreement      
Disclosure of detailed information about financial instruments [line items]      
Derivative financial assets 0 0  
Derivative financial liabilities 6 10  
Before Offset Amount | Cash flow hedges | Debt derivatives      
Disclosure of detailed information about financial instruments [line items]      
Derivative financial liabilities 645 842  
Before Offset Amount | Cash flow hedges | MLSE interest rate swap      
Disclosure of detailed information about financial instruments [line items]      
Derivative financial liabilities 7 0  
Before Offset Amount | Cash flow hedges | Expenditure derivative instruments:      
Disclosure of detailed information about financial instruments [line items]      
Derivative financial liabilities $ 28 $ 0