v3.26.1
RISK MANAGEMENT AND FINANCIAL INSTRUMENTS - Other Financial Instruments (Details) - CAD ($)
3 Months Ended 6 Months Ended 12 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Dec. 31, 2025
Fair Value of Other Financial Instruments          
Transfer into or out of level 3     $ 0   $ 0
FMVA investments $ 190,000,000   190,000,000   185,000,000
Fair value of investments 1,483,000,000   1,483,000,000   $ 1,293,000,000
Unrealized gain (loss) on investment $ 2,000,000 $ 1,000,000 $ (18,000,000) $ 1,000,000  
Investment, Type [Extensible Enumeration] Debt Securities   Debt Securities   Debt Securities
Long-term debt $ 110,400,000,000   $ 110,400,000,000   $ 102,700,000,000
Level 2          
Fair Value of Other Financial Instruments          
Fair value of investments 453,000,000   453,000,000   416,000,000
Restricted long-term investments, cost basis 1,300,000,000   1,300,000,000   1,200,000,000
Level 2 | Debt Securities          
Fair Value of Other Financial Instruments          
Fair value of investments 1,300,000,000   1,300,000,000   1,200,000,000
Carrying Value          
Fair Value of Other Financial Instruments          
Long-term debt $ 111,000,000,000   111,000,000,000   $ 104,400,000,000
Net investment hedges          
Fair Value of Other Financial Instruments          
Unrealized foreign exchange (loss) gain on translation of United States dollar denominated debt     (495,000,000) 494,000,000  
Realized loss associated with the settlement of foreign exchange forward contracts     $ 0 $ (81,000,000)