RISK MANAGEMENT AND FINANCIAL INSTRUMENTS - Schedule of Derivative Assets and Liabilities Measured at Fair Value (Details) - CAD ($) $ in Millions	Sep. 30, 2026	Dec. 31, 2025
Fair Value of Derivatives
Total net derivative asset/(liability)	$ (1,678)	$ (823)
Fair Value
Fair Value of Derivatives
Current derivative assets	1,407	591
Long-term derivative assets	860	293
Current derivative liabilities	(1,813)	(712)
Long-term derivative liabilities	(2,132)	(995)
Total net derivative asset/(liability)	(1,678)	(823)
Level 1 \| Fair Value
Fair Value of Derivatives
Current derivative assets	444	70
Long-term derivative assets	33	0
Current derivative liabilities	(575)	(55)
Long-term derivative liabilities	(43)	0
Total net derivative asset/(liability)	(141)	15
Level 2 \| Fair Value
Fair Value of Derivatives
Current derivative assets	335	192
Long-term derivative assets	724	176
Current derivative liabilities	(763)	(480)
Long-term derivative liabilities	(2,018)	(914)
Total net derivative asset/(liability)	(1,722)	(1,026)
Level 3
Fair Value of Derivatives
Total net derivative asset/(liability)	185
Level 3 \| Fair Value
Fair Value of Derivatives
Current derivative assets	628	329
Long-term derivative assets	103	117
Current derivative liabilities	(475)	(177)
Long-term derivative liabilities	(71)	(81)
Total net derivative asset/(liability)	185	188
Foreign exchange contracts
Fair Value of Derivatives
Total net derivative asset/(liability)	(1,616)	(1,104)
Foreign exchange contracts \| Fair Value
Fair Value of Derivatives
Current derivative assets	81	27
Long-term derivative assets	28	52
Current derivative liabilities	(664)	(364)
Long-term derivative liabilities	(1,061)	(819)
Total net derivative asset/(liability)	(1,616)	(1,104)
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	81	27
Long-term derivative assets	28	52
Current derivative liabilities	(664)	(364)
Long-term derivative liabilities	(1,061)	(819)
Total net derivative asset/(liability)	(1,616)	(1,104)
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)	(97)	91
Interest rate contracts \| Fair Value
Fair Value of Derivatives
Current derivative assets	187	106
Long-term derivative assets	691	117
Current derivative liabilities	(30)	(48)
Long-term derivative liabilities	(945)	(84)
Total net derivative asset/(liability)	(97)	91
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	0
Interest rate contracts \| Level 2 \| Fair Value
Fair Value of Derivatives
Current derivative assets	187	106
Long-term derivative assets	691	117
Current derivative liabilities	(30)	(48)
Long-term derivative liabilities	(945)	(84)
Total net derivative asset/(liability)	(97)	91
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	0
Commodity contracts
Fair Value of Derivatives
Total net derivative asset/(liability)	35	190
Commodity contracts \| Fair Value
Fair Value of Derivatives
Current derivative assets	1,139	458
Long-term derivative assets	141	124
Current derivative liabilities	(1,119)	(300)
Long-term derivative liabilities	(126)	(92)
Total net derivative asset/(liability)	35	190
Commodity contracts \| Level 1 \| Fair Value
Fair Value of Derivatives
Current derivative assets	444	70
Long-term derivative assets	33	0
Current derivative liabilities	(575)	(55)
Long-term derivative liabilities	(43)	0
Total net derivative asset/(liability)	(141)	15
Commodity contracts \| Level 2 \| Fair Value
Fair Value of Derivatives
Current derivative assets	67	59
Long-term derivative assets	5	7
Current derivative liabilities	(69)	(68)
Long-term derivative liabilities	(12)	(11)
Total net derivative asset/(liability)	(9)	(13)
Commodity contracts \| Level 3 \| Fair Value
Fair Value of Derivatives
Current derivative assets	628	329
Long-term derivative assets	103	117
Current derivative liabilities	(475)	(177)
Long-term derivative liabilities	(71)	(81)
Total net derivative asset/(liability)	$ 185	$ 188

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