RISK MANAGEMENT AND FINANCIAL INSTRUMENTS - Total Derivative Instruments (Details) - CAD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	$ (760)	$ (546)
Derivative liabilities, Total Net Derivative Instruments	(760)	(546)
Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	(1,193)	(1,476)
Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	416	816
Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	17	114
Other current assets
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	693	1,015
Derivative assets, Amounts Available for Offset	(181)	(223)
Derivative assets, Total Net Derivative Instruments	512	792
Other current assets | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	304	366
Other current assets | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	318	649
Other current assets | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	71	0
Deferred amounts and other assets
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	346	627
Derivative assets, Amounts Available for Offset	(126)	(163)
Derivative assets, Total Net Derivative Instruments	220	464
Deferred amounts and other assets | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	185	216
Deferred amounts and other assets | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	130	255
Deferred amounts and other assets | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	31	156
Other current liabilities
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(579)	(898)
Derivative liabilities, Amounts Available for Offset	181	223
Derivative liabilities, Total Net Derivative Instruments	(398)	(675)
Other current liabilities | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(511)	(808)
Other current liabilities | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(19)	(48)
Other current liabilities | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(49)	(42)
Other long-term liabilities
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(1,220)	(1,290)
Derivative liabilities, Amounts Available for Offset	126	163
Derivative liabilities, Total Net Derivative Instruments	(1,094)	(1,127)
Other long-term liabilities | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(1,171)	(1,250)
Other long-term liabilities | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(13)	(40)
Other long-term liabilities | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(36)	0
Foreign exchange contracts
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	(1,009)	(1,327)
Derivative liabilities, Total Net Derivative Instruments	(1,009)	(1,327)
Foreign exchange contracts | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	(1,026)	(1,441)
Foreign exchange contracts | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	0	$ 0
Derivative Liability, Statement of Financial Position [Extensible Enumeration]		Other Liabilities, Noncurrent
Foreign exchange contracts | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	17	$ 114
Foreign exchange contracts | Other current assets
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	103	46
Derivative assets, Amounts Available for Offset	(25)	(41)
Derivative assets, Total Net Derivative Instruments	78	5
Foreign exchange contracts | Other current assets | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	32	46
Foreign exchange contracts | Other current assets | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	0	0
Foreign exchange contracts | Other current assets | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	71	0
Foreign exchange contracts | Deferred amounts and other assets
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	140	309
Derivative assets, Amounts Available for Offset	(90)	(138)
Derivative assets, Total Net Derivative Instruments	50	171
Foreign exchange contracts | Deferred amounts and other assets | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	109	153
Foreign exchange contracts | Deferred amounts and other assets | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	0	0
Foreign exchange contracts | Deferred amounts and other assets | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	31	156
Foreign exchange contracts | Other current liabilities
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(212)	(566)
Derivative liabilities, Amounts Available for Offset	25	41
Derivative liabilities, Total Net Derivative Instruments	(187)	(525)
Foreign exchange contracts | Other current liabilities | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(163)	(524)
Foreign exchange contracts | Other current liabilities | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	0	0
Foreign exchange contracts | Other current liabilities | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(49)	(42)
Foreign exchange contracts | Other long-term liabilities
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(1,040)	(1,116)
Derivative liabilities, Amounts Available for Offset	90	138
Derivative liabilities, Total Net Derivative Instruments	(950)	(978)
Foreign exchange contracts | Other long-term liabilities | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(1,004)	(1,116)
Foreign exchange contracts | Other long-term liabilities | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	0	0
Foreign exchange contracts | Other long-term liabilities | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(36)	0
Interest rate contracts
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities		(4)
Total net financial asset/(liability)	528	910
Derivative assets, Total Net Derivative Instruments	528	$ 910
Derivative Liability, Statement of Financial Position [Extensible Enumeration]		Other Liabilities, Noncurrent
Interest rate contracts | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities		$ (1)
Total net financial asset/(liability)	82	$ 10
Derivative Liability, Statement of Financial Position [Extensible Enumeration]		Other Liabilities, Noncurrent
Interest rate contracts | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities		$ (3)
Total net financial asset/(liability)	446	900
Interest rate contracts | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities		0
Total net financial asset/(liability)	0	$ 0
Derivative Liability, Statement of Financial Position [Extensible Enumeration]		Other Liabilities, Noncurrent
Interest rate contracts | Other current assets
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	384	$ 660
Derivative assets, Amounts Available for Offset	(3)	0
Derivative assets, Total Net Derivative Instruments	381	660
Interest rate contracts | Other current assets | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	66	11
Interest rate contracts | Other current assets | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	318	649
Interest rate contracts | Other current assets | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	0	0
Interest rate contracts | Deferred amounts and other assets
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	149	254
Derivative assets, Amounts Available for Offset	0	0
Derivative assets, Total Net Derivative Instruments	149	254
Interest rate contracts | Deferred amounts and other assets | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	19	0
Interest rate contracts | Deferred amounts and other assets | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	130	254
Interest rate contracts | Deferred amounts and other assets | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	0	0
Interest rate contracts | Other current liabilities
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(3)
Derivative liabilities, Amounts Available for Offset	3
Derivative liabilities, Total Net Derivative Instruments	0
Interest rate contracts | Other current liabilities | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(3)
Interest rate contracts | Other current liabilities | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	0
Interest rate contracts | Other current liabilities | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	0
Interest rate contracts | Other long-term liabilities
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(2)
Derivative liabilities, Amounts Available for Offset	0	0
Derivative liabilities, Total Net Derivative Instruments	(2)	(4)
Interest rate contracts | Other long-term liabilities | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	0
Interest rate contracts | Other long-term liabilities | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(2)
Interest rate contracts | Other long-term liabilities | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	0
Commodity contracts
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	(275)	(139)
Derivative liabilities, Total Net Derivative Instruments	(275)	(139)
Commodity contracts | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	(246)	(54)
Commodity contracts | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	(29)	(85)
Commodity contracts | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	0	0
Commodity contracts | Other current assets
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	206	302
Derivative assets, Amounts Available for Offset	(153)	(182)
Derivative assets, Total Net Derivative Instruments	53	120
Commodity contracts | Other current assets | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	206	302
Commodity contracts | Other current assets | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	0	0
Commodity contracts | Other current assets | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	0	0
Commodity contracts | Deferred amounts and other assets
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	57	61
Derivative assets, Amounts Available for Offset	(36)	(25)
Derivative assets, Total Net Derivative Instruments	21	36
Commodity contracts | Deferred amounts and other assets | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	57	61
Commodity contracts | Deferred amounts and other assets | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	0	0
Commodity contracts | Deferred amounts and other assets | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	0	0
Commodity contracts | Other current liabilities
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(362)	(332)
Derivative liabilities, Amounts Available for Offset	153	182
Derivative liabilities, Total Net Derivative Instruments	(209)	(150)
Commodity contracts | Other current liabilities | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(343)	(284)
Commodity contracts | Other current liabilities | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(19)	(48)
Commodity contracts | Other current liabilities | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	0	0
Commodity contracts | Other long-term liabilities
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(176)	(170)
Derivative liabilities, Amounts Available for Offset	36	25
Derivative liabilities, Total Net Derivative Instruments	(140)	(145)
Commodity contracts | Other long-term liabilities | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(166)	(133)
Commodity contracts | Other long-term liabilities | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(10)	(37)
Commodity contracts | Other long-term liabilities | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	0	0
Other contracts
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	(4)	10
Derivative assets, Total Net Derivative Instruments		10
Derivative liabilities, Total Net Derivative Instruments	(4)
Other contracts | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	(3)	9
Other contracts | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	(1)	1
Other contracts | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	0	0
Other contracts | Other current assets
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets		7
Derivative assets, Amounts Available for Offset		0
Derivative assets, Total Net Derivative Instruments		7
Other contracts | Other current assets | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets		7
Other contracts | Other current assets | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets		0
Other contracts | Other current assets | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets		0
Other contracts | Deferred amounts and other assets
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets		3
Derivative assets, Amounts Available for Offset		0
Derivative assets, Total Net Derivative Instruments		3
Other contracts | Deferred amounts and other assets | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets		2
Other contracts | Deferred amounts and other assets | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets		1
Other contracts | Deferred amounts and other assets | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets		$ 0
Other contracts | Other current liabilities
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(2)
Derivative liabilities, Amounts Available for Offset	0
Derivative liabilities, Total Net Derivative Instruments	(2)
Other contracts | Other current liabilities | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(2)
Other contracts | Other current liabilities | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	0
Other contracts | Other current liabilities | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	0
Other contracts | Other long-term liabilities
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(2)
Derivative liabilities, Amounts Available for Offset	0
Derivative liabilities, Total Net Derivative Instruments	(2)
Other contracts | Other long-term liabilities | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(1)
Other contracts | Other long-term liabilities | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(1)
Other contracts | Other long-term liabilities | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	$ 0