RISK MANAGEMENT AND FINANCIAL INSTRUMENTS - Fair Value of Derivatives (Details) - CAD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Fair Value of Derivatives
Total net financial asset/(liability)	$ (1,020)	$ (404)
Fair Value
Fair Value of Derivatives
Current derivative assets	467	623
Long-term derivative assets	304	463
Current derivative liabilities	(653)	(738)
Long-term derivative liabilities	(1,138)	(752)
Total net financial asset/(liability)	(1,020)	(404)
Foreign exchange contracts
Fair Value of Derivatives
Total net financial asset/(liability)	(940)	(152)
Foreign exchange contracts | Fair Value
Fair Value of Derivatives
Current derivative assets	124	139
Long-term derivative assets	124	335
Current derivative liabilities	(238)	(128)
Long-term derivative liabilities	(950)	(498)
Total net financial asset/(liability)	(940)	(152)
Interest rate contracts
Fair Value of Derivatives
Total net financial asset/(liability)	74	(156)
Interest rate contracts | Fair Value
Fair Value of Derivatives
Current derivative assets	102	65
Long-term derivative assets	93	53
Current derivative liabilities	(99)	(186)
Long-term derivative liabilities	(22)	(88)
Total net financial asset/(liability)	74	(156)
Commodity contracts
Fair Value of Derivatives
Total net financial asset/(liability)	(153)	(96)
Commodity contracts | Fair Value
Fair Value of Derivatives
Current derivative assets	241	418
Long-term derivative assets	87	75
Current derivative liabilities	(315)	(423)
Long-term derivative liabilities	(166)	(166)
Total net financial asset/(liability)	(153)	(96)
Other contracts
Fair Value of Derivatives
Total net financial asset/(liability)	(1)	0
Other contracts | Fair Value
Fair Value of Derivatives
Current derivative assets		1
Current derivative liabilities	(1)	(1)
Total net financial asset/(liability)	(1)	0
Level 1 | Fair Value
Fair Value of Derivatives
Current derivative assets	35	142
Long-term derivative assets	0	0
Current derivative liabilities	(63)	(136)
Long-term derivative liabilities	0	0
Total net financial asset/(liability)	(28)	6
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	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	35	142
Long-term derivative assets	0	0
Current derivative liabilities	(63)	(136)
Long-term derivative liabilities	0	0
Total net financial asset/(liability)	(28)	6
Level 1 | Other contracts | Fair Value
Fair Value of Derivatives
Current derivative assets		0
Current derivative liabilities	0	0
Total net financial asset/(liability)	0	0
Level 2 | Fair Value
Fair Value of Derivatives
Current derivative assets	308	308
Long-term derivative assets	231	412
Current derivative liabilities	(416)	(391)
Long-term derivative liabilities	(988)	(608)
Total net financial asset/(liability)	(865)	(279)
Level 2 | Foreign exchange contracts | Fair Value
Fair Value of Derivatives
Current derivative assets	124	139
Long-term derivative assets	124	335
Current derivative liabilities	(238)	(128)
Long-term derivative liabilities	(950)	(498)
Total net financial asset/(liability)	(940)	(152)
Level 2 | Interest rate contracts | Fair Value
Fair Value of Derivatives
Current derivative assets	102	65
Long-term derivative assets	93	53
Current derivative liabilities	(99)	(186)
Long-term derivative liabilities	(22)	(88)
Total net financial asset/(liability)	74	(156)
Level 2 | Commodity contracts | Fair Value
Fair Value of Derivatives
Current derivative assets	82	103
Long-term derivative assets	14	24
Current derivative liabilities	(78)	(76)
Long-term derivative liabilities	(16)	(22)
Total net financial asset/(liability)	2	29
Level 2 | Other contracts | Fair Value
Fair Value of Derivatives
Current derivative assets		1
Current derivative liabilities	(1)	(1)
Total net financial asset/(liability)	(1)	0
Level 3
Fair Value of Derivatives
Total net financial asset/(liability)	(127)
Level 3 | Fair Value
Fair Value of Derivatives
Current derivative assets	124	173
Long-term derivative assets	73	51
Current derivative liabilities	(174)	(211)
Long-term derivative liabilities	(150)	(144)
Total net financial asset/(liability)	(127)	(131)
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	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	124	173
Long-term derivative assets	73	51
Current derivative liabilities	(174)	(211)
Long-term derivative liabilities	(150)	(144)
Total net financial asset/(liability)	(127)	(131)
Level 3 | Other contracts | Fair Value
Fair Value of Derivatives
Current derivative assets		0
Current derivative liabilities	0	0
Total net financial asset/(liability)	$ 0	$ 0