RISK MANAGEMENT AND FINANCIAL INSTRUMENTS - Other Financial Instruments (Details) - CAD ($)	3 Months Ended
Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021
Fair Value of Other Financial Instruments
FMVA investments	$ 52,000,000		$ 52,000,000
Restricted long-term investments	594,000,000		630,000,000
Long-term debt, carrying value	75,200,000,000		74,400,000,000
Long-term debt	75,500,000,000		82,000,000,000
Level 1
Fair Value of Other Financial Instruments
Restricted long-term investments	213,000,000		217,000,000
Level 2
Fair Value of Other Financial Instruments
Restricted long-term investments	381,000,000		413,000,000
Net investment hedges
Fair Value of Other Financial Instruments
Unrealized foreign exchange gain (loss) on translation of United States dollar denominated debt	133,000,000	$ 105,000,000
Unrealized gain (loss) on change in fair value of outstanding forward exchange forward contracts	0	0
Fair Value
Fair Value of Other Financial Instruments
Unrealized holding losses	60,000,000	$ 45,000,000
Carrying value
Fair Value of Other Financial Instruments
Noncurrent notes receivable	$ 900,000,000		$ 1,000,000,000

Fair value of investment other than investment in equity security, investment in debt security and equity method investment. Includes, but is not limited to, investment in certain entities that calculate net asset value per share. Example includes, but is not limited to, investment in hedge fund, venture capital fund, private equity fund, and real estate partnership or fund.

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Amount of gain (loss) recognized in other comprehensive income (OCI) from asset measured at fair value on recurring basis using unobservable input (level 3).

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The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

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Fair value portion of an agreement for an unconditional promise by the maker to pay the holder a definite sum of money at a future date.

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Amount before tax and reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature.

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Amount, before tax and adjustments, of gain (loss) from increase (decrease) in value of excluded component of derivative designated and qualifying as hedge. Adjustments include, but are not limited to, reclassifications for sale and settlement, and amounts recognized under systematic and rational method.

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The aggregate value of all restricted investments.

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