v3.26.3
RISK MANAGEMENT FINANCIAL INSTRUMENTS - Schedule of Restricted Long-Term Investments And Cash Held In Trust (Details) - CAD ($)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Dec. 31, 2025
Fair Value, Option, Quantitative Disclosures [Line Items]          
Fair value of investments $ 1,534   $ 1,534   $ 1,293
Cost value of investments 1,330   1,330   1,170
Restricted Long Term Investment          
Fair Value, Option, Quantitative Disclosures [Line Items]          
Unrealized holding gains/(losses) (4) $ 50 81 $ 96  
Fair Value, Inputs, Level 1 [Member]          
Fair Value, Option, Quantitative Disclosures [Line Items]          
Fair value of investments 1,085   1,085   877
Cost value of investments 861   861   744
Fair Value, Inputs, Level 2 [Member]          
Fair Value, Option, Quantitative Disclosures [Line Items]          
Fair value of investments 449   449   416
Cost value of investments $ 469   $ 469   $ 426