RISK MANAGEMENT AND FINANCIAL INSTRUMENTS - Fair Value of Derivatives (Details) - CAD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Fair Value of Derivatives
Total net financial asset/(liability)	$ (760)	$ (546)
Fair Value
Fair Value of Derivatives
Current derivative assets	693	1,015
Long-term derivative assets	346	627
Current derivative liabilities	(579)	(898)
Long-term derivative liabilities	(1,220)	(1,290)
Total net financial asset/(liability)	(760)	(546)
Foreign exchange contracts
Fair Value of Derivatives
Total net financial asset/(liability)	(1,009)	(1,327)
Foreign exchange contracts | Fair Value
Fair Value of Derivatives
Current derivative assets	103	46
Long-term derivative assets	140	309
Current derivative liabilities	(212)	(566)
Long-term derivative liabilities	(1,040)	(1,116)
Total net financial asset/(liability)	(1,009)	(1,327)
Interest rate contracts
Fair Value of Derivatives
Total net financial asset/(liability)	528	910
Interest rate contracts | Fair Value
Fair Value of Derivatives
Current derivative assets	384	660
Long-term derivative assets	149	254
Current derivative liabilities	(3)
Long-term derivative liabilities	(2)	(4)
Total net financial asset/(liability)	528	910
Commodity contracts
Fair Value of Derivatives
Total net financial asset/(liability)	(275)	(139)
Commodity contracts | Fair Value
Fair Value of Derivatives
Current derivative assets	206	302
Long-term derivative assets	57	61
Current derivative liabilities	(362)	(332)
Long-term derivative liabilities	(176)	(170)
Total net financial asset/(liability)	(275)	(139)
Other contracts
Fair Value of Derivatives
Total net financial asset/(liability)	(4)	10
Other contracts | Fair Value
Fair Value of Derivatives
Current derivative assets		7
Long-term derivative assets		3
Current derivative liabilities	(2)
Long-term derivative liabilities	(2)
Total net financial asset/(liability)	(4)	10
Level 1 | Fair Value
Fair Value of Derivatives
Current derivative assets	58	65
Long-term derivative assets	0	0
Current derivative liabilities	(93)	(60)
Long-term derivative liabilities	0	0
Total net financial asset/(liability)	(35)	5
Level 1 | Foreign exchange contracts | Fair Value
Fair Value of Derivatives
Current derivative assets	0	0
Long-term derivative assets	0	0
Current derivative liabilities	0	0
Long-term derivative liabilities	0	0
Total net financial asset/(liability)	0	0
Level 1 | Interest rate contracts | Fair Value
Fair Value of Derivatives
Current derivative assets	0	0
Long-term derivative assets	0	0
Current derivative liabilities	0
Long-term derivative liabilities	0	0
Total net financial asset/(liability)	0	0
Level 1 | Commodity contracts | Fair Value
Fair Value of Derivatives
Current derivative assets	58	65
Long-term derivative assets	0	0
Current derivative liabilities	(93)	(60)
Long-term derivative liabilities	0	0
Total net financial asset/(liability)	(35)	5
Level 1 | Other contracts | Fair Value
Fair Value of Derivatives
Current derivative assets		0
Long-term derivative assets		0
Current derivative liabilities	0
Long-term derivative liabilities	0
Total net financial asset/(liability)	0	0
Level 2 | Fair Value
Fair Value of Derivatives
Current derivative assets	523	803
Long-term derivative assets	305	583
Current derivative liabilities	(267)	(643)
Long-term derivative liabilities	(1,064)	(1,158)
Total net financial asset/(liability)	(503)	(415)
Level 2 | Foreign exchange contracts | Fair Value
Fair Value of Derivatives
Current derivative assets	103	46
Long-term derivative assets	140	309
Current derivative liabilities	(212)	(566)
Long-term derivative liabilities	(1,040)	(1,116)
Total net financial asset/(liability)	(1,009)	(1,327)
Level 2 | Interest rate contracts | Fair Value
Fair Value of Derivatives
Current derivative assets	384	660
Long-term derivative assets	149	254
Current derivative liabilities	(3)
Long-term derivative liabilities	(2)	(4)
Total net financial asset/(liability)	528	910
Level 2 | Commodity contracts | Fair Value
Fair Value of Derivatives
Current derivative assets	36	90
Long-term derivative assets	16	17
Current derivative liabilities	(50)	(77)
Long-term derivative liabilities	(20)	(38)
Total net financial asset/(liability)	(18)	(8)
Level 2 | Other contracts | Fair Value
Fair Value of Derivatives
Current derivative assets		7
Long-term derivative assets		3
Current derivative liabilities	(2)
Long-term derivative liabilities	(2)
Total net financial asset/(liability)	(4)	10
Level 3
Fair Value of Derivatives
Total net financial asset/(liability)	(222)
Level 3 | Fair Value
Fair Value of Derivatives
Current derivative assets	112	147
Long-term derivative assets	41	44
Current derivative liabilities	(219)	(195)
Long-term derivative liabilities	(156)	(132)
Total net financial asset/(liability)	(222)	(136)
Level 3 | Foreign exchange contracts | Fair Value
Fair Value of Derivatives
Current derivative assets	0	0
Long-term derivative assets	0	0
Current derivative liabilities	0	0
Long-term derivative liabilities	0	0
Total net financial asset/(liability)	0	0
Level 3 | Interest rate contracts | Fair Value
Fair Value of Derivatives
Current derivative assets	0	0
Long-term derivative assets	0	0
Current derivative liabilities	0
Long-term derivative liabilities	0	0
Total net financial asset/(liability)	0	0
Level 3 | Commodity contracts | Fair Value
Fair Value of Derivatives
Current derivative assets	112	147
Long-term derivative assets	41	44
Current derivative liabilities	(219)	(195)
Long-term derivative liabilities	(156)	(132)
Total net financial asset/(liability)	(222)	(136)
Level 3 | Other contracts | Fair Value
Fair Value of Derivatives
Current derivative assets		0
Long-term derivative assets		0
Current derivative liabilities	0
Long-term derivative liabilities	0
Total net financial asset/(liability)	$ 0	$ 0