RISK MANAGEMENT AND FINANCIAL INSTRUMENTS - Restricted Long-Term Investments (Details) - CAD ($) $ in Millions	3 Months Ended
Mar. 31, 2026	Mar. 31, 2025
Long-Lived Assets Held-for-sale [Line Items]
Unrealized holding gains (losses)	$ (20)	$ 1

Amount of unrealized gain (loss) on investment.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 45
-Paragraph 28
-Subparagraph (b)
-SubTopic 10
-Topic 230
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482740/230-10-45-28

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration