FAIR VALUE OF FINANCIAL INSTRUMENTS AND RISK MANAGEMENT - Summary of Fair Value Hierarchy of Financial Assets and Liabilities (Details) - CAD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Liabilities:
Long-term debt, including current portion	$ 18,721	$ 17,364
Carrying Value
Liabilities:
Long-term debt, including current portion	19,017	17,479
Total liabilities	19,021	17,486
Carrying Value \| Cash flow hedges, including current portion
Liabilities:
Cash flow hedges, including current portion	4	7
Fair Value
Liabilities:
Long-term debt, including current portion	18,721	17,364
Total liabilities	18,725	17,371
Fair Value \| Cash flow hedges, including current portion
Liabilities:
Cash flow hedges, including current portion	4	7
Fair Value \| Level 1
Liabilities:
Long-term debt, including current portion	0	0
Total liabilities	0	0
Fair Value \| Level 1 \| Cash flow hedges, including current portion
Liabilities:
Cash flow hedges, including current portion	0	0
Fair Value \| Level 2
Liabilities:
Long-term debt, including current portion	18,721	17,364
Total liabilities	18,725	17,371
Fair Value \| Level 2 \| Cash flow hedges, including current portion
Liabilities:
Cash flow hedges, including current portion	4	7
Fair Value \| Level 3
Liabilities:
Long-term debt, including current portion	0	0
Total liabilities	0	0
Fair Value \| Level 3 \| Cash flow hedges, including current portion
Liabilities:
Cash flow hedges, including current portion	$ 0	$ 0

Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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