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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The total amount of cash and securities held by third party trustees pursuant to terms of debt instruments or other agreements as of the date of each statement of financial position presented, which can be used by the trustee only to pay the noncurrent portion of specified obligations.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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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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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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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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Fair value of investment in debt security measured at amortized cost (held-to-maturity).

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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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Amount, before tax and adjustment, of unrealized gain (loss) on investment in debt security measured at amortized cost (held-to-maturity) from transfer to investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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RISK MANAGEMENT AND FINANCIAL INSTRUMENTS - Other Financial Instruments (Details) - CAD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Fair Value of Other Financial Instruments
FMVA investments	$ 51	$ 51		$ 52
Long-term debt, carrying value	67,100	67,100		66,100
Long-term debt	$ 74,000	$ 74,000		75,100
Noverco
Fair Value of Other Financial Instruments
Ownership interest (percent)	38.90%	38.90%
Net Investment Hedges
Fair Value of Other Financial Instruments
Unrealized foreign exchange gain (loss) on translation of United States dollar denominated debt		$ 251	$ (371)
Unrealized gain (loss) on change in fair value of outstanding forward exchange forward contracts		0	$ (4)
Preferred share investment
Fair Value of Other Financial Instruments
Available-for-sale investment, fair value	$ 580	580
Held to maturity investment, fair value				567
Gains (losses) recognized in OCI upon reclassification	0
Fair Value
Fair Value of Other Financial Instruments
Restricted long-term investments held in trust	573	573		553
Carrying value
Fair Value of Other Financial Instruments
Noncurrent notes receivable	$ 1,000	$ 1,000		$ 1,100