v3.26.1
RISK MANAGEMENT FINANCIAL INSTRUMENTS - Schedule of Restricted Long-Term Investments And Cash Held In Trust (Details) - CAD ($)
$ in Millions
3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Dec. 31, 2025
Fair Value, Option, Quantitative Disclosures [Line Items]      
Fair value of investments $ 1,329   $ 1,293
Cost value of investments 1,220   1,170
Unrealized holding gains/(losses) (11) $ 16  
Net purchases of investments classified as available for sale (41) (26)  
Purchases [Member]      
Fair Value, Option, Quantitative Disclosures [Line Items]      
Net purchases of investments classified as available for sale (73) (103)  
Sales [Member]      
Fair Value, Option, Quantitative Disclosures [Line Items]      
Net purchases of investments classified as available for sale 32 $ 77  
Fair Value, Inputs, Level 1 [Member]      
Fair Value, Option, Quantitative Disclosures [Line Items]      
Fair value of investments 903   877
Cost value of investments 783   744
Fair Value, Inputs, Level 2 [Member]      
Fair Value, Option, Quantitative Disclosures [Line Items]      
Fair value of investments 426   416
Cost value of investments $ 437   $ 426