PENSION PLANS AND POSTRETIREMENT BENEFITS - Components of re-measurements (Details) - Pension and postretirement benefits - CAD ($) $ in Millions	12 Months Ended
Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Disclosure of net defined benefit liability (asset)
Actuarial gain (loss) on benefit obligations	$ 26.4	$ 4.0	$ (43.0)
Actual return on plan assets, less interest income anticipated in the interest on the net defined benefit liability calculation	(1.4)	28.0	27.1
Asset limit and minimum funding adjustment	(1.1)	(9.2)	22.3
Re-measurement gain recorded in other comprehensive income	$ 23.9	$ 22.8	$ 6.4

The amount of other comprehensive income, net of tax, related to gains (losses) on remeasurements of defined benefit plans, which comprise actuarial gains and losses; the return on plan assets, excluding amounts included in net interest on the net defined benefit liability (asset); and any change in the effect of the asset ceiling, excluding amounts included in net interest on the net defined benefit liability (asset). [Refer: Other comprehensive income; Defined benefit plans [domain]; Plan assets [member]; Net defined benefit liability (asset)] [Contrast: Decrease (increase) in net defined benefit liability (asset) resulting from gain (loss) on remeasurement in other comprehensive income]

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