PENSION AND POST-RETIREMENT AND POST-EMPLOYMENT BENEFITS - Summary of Components of Regulatory Assets That Have Not Been Recognized as Components of Net Periodic Benefit Costs (Details) - CAD ($) $ in Millions |
Dec. 31, 2025 |
Dec. 31, 2024 |
|---|---|---|
| Pension Benefits | ||
| Pension Plans, Postretirement and Other Employee Benefits [Line Items] | ||
| Actuarial gain | $ (610) | $ (647) |
| Post-Retirement and Post-Employment Benefits | ||
| Pension Plans, Postretirement and Other Employee Benefits [Line Items] | ||
| Actuarial gain | $ (336) | $ (376) |