RISK MANAGEMENT AND FINANCIAL INSTRUMENTS - Schedule of Derivative Assets and Liabilities Measured at Fair Value (Details) - CAD ($) $ in Millions	Jun. 30, 2025	Dec. 31, 2024
Fair Value of Derivatives
Total net derivative asset/(liability)	$ (926)	$ (2,250)
Fair Value
Fair Value of Derivatives
Current derivative assets	456	557
Long-term derivative assets	308	426
Current derivative liabilities	(768)	(1,335)
Long-term derivative liabilities	(922)	(1,898)
Total net derivative asset/(liability)	(926)	(2,250)
Level 1 | Fair Value
Fair Value of Derivatives
Current derivative assets	65	34
Long-term derivative assets	2	1
Current derivative liabilities	(79)	(52)
Long-term derivative liabilities	(8)	(1)
Total net derivative asset/(liability)	(20)	(18)
Level 2 | Fair Value
Fair Value of Derivatives
Current derivative assets	137	267
Long-term derivative assets	206	243
Current derivative liabilities	(443)	(1,000)
Long-term derivative liabilities	(823)	(1,690)
Total net derivative asset/(liability)	(923)	(2,180)
Level 3
Fair Value of Derivatives
Total net derivative asset/(liability)	17
Level 3 | Fair Value
Fair Value of Derivatives
Current derivative assets	254	256
Long-term derivative assets	100	182
Current derivative liabilities	(246)	(283)
Long-term derivative liabilities	(91)	(207)
Total net derivative asset/(liability)	17	(52)
Foreign exchange contracts
Fair Value of Derivatives
Total net derivative asset/(liability)	(947)	(2,175)
Foreign exchange contracts | Fair Value
Fair Value of Derivatives
Current derivative assets	33	125
Long-term derivative assets	75	83
Current derivative liabilities	(721)	(804)
Long-term derivative liabilities	(334)	(1,579)
Total net derivative asset/(liability)	(947)	(2,175)
Foreign exchange contracts | Level 1 | 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 derivative asset/(liability)	0	0
Foreign exchange contracts | Level 2 | Fair Value
Fair Value of Derivatives
Current derivative assets	33	125
Long-term derivative assets	75	83
Current derivative liabilities	(721)	(804)
Long-term derivative liabilities	(334)	(1,579)
Total net derivative asset/(liability)	(947)	(2,175)
Foreign exchange contracts | Level 3 | 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 derivative asset/(liability)	0	0
Interest rate contracts
Fair Value of Derivatives
Total net derivative asset/(liability)	32	53
Interest rate contracts | Fair Value
Fair Value of Derivatives
Current derivative assets	32	67
Long-term derivative assets	117	146
Current derivative liabilities	(38)	(80)
Long-term derivative liabilities	(79)	(80)
Total net derivative asset/(liability)	32	53
Interest rate contracts | Level 1 | 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 derivative asset/(liability)		0
Interest rate contracts | Level 2 | Fair Value
Fair Value of Derivatives
Current derivative assets	32	67
Long-term derivative assets	117	146
Current derivative liabilities	(38)	(80)
Long-term derivative liabilities	(79)	(80)
Total net derivative asset/(liability)	32	53
Interest rate contracts | Level 3 | 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 derivative asset/(liability)		0
Commodity contracts
Fair Value of Derivatives
Total net derivative asset/(liability)	(11)	(131)
Commodity contracts | Fair Value
Fair Value of Derivatives
Current derivative assets	391	362
Long-term derivative assets	116	197
Current derivative liabilities	(396)	(451)
Long-term derivative liabilities	(122)	(239)
Total net derivative asset/(liability)	(11)	(131)
Commodity contracts | Level 1 | Fair Value
Fair Value of Derivatives
Current derivative assets	65	34
Long-term derivative assets	2	1
Current derivative liabilities	(79)	(52)
Long-term derivative liabilities	(8)	(1)
Total net derivative asset/(liability)	(20)	(18)
Commodity contracts | Level 2 | Fair Value
Fair Value of Derivatives
Current derivative assets	72	72
Long-term derivative assets	14	14
Current derivative liabilities	(71)	(116)
Long-term derivative liabilities	(23)	(31)
Total net derivative asset/(liability)	(8)	(61)
Commodity contracts | Level 3 | Fair Value
Fair Value of Derivatives
Current derivative assets	254	256
Long-term derivative assets	100	182
Current derivative liabilities	(246)	(283)
Long-term derivative liabilities	(91)	(207)
Total net derivative asset/(liability)	$ 17	(52)
Other contracts
Fair Value of Derivatives
Total net derivative asset/(liability)		3
Other contracts | Fair Value
Fair Value of Derivatives
Current derivative assets		3
Total net derivative asset/(liability)		3
Other contracts | Level 1 | Fair Value
Fair Value of Derivatives
Current derivative assets		0
Total net derivative asset/(liability)		0
Other contracts | Level 2 | Fair Value
Fair Value of Derivatives
Current derivative assets		3
Total net derivative asset/(liability)		3
Other contracts | Level 3 | Fair Value
Fair Value of Derivatives
Current derivative assets		0
Total net derivative asset/(liability)		$ 0