RISK MANAGEMENT AND FINANCIAL INSTRUMENTS - Total Derivative Instruments (Details) - CAD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	$ (1,020)	$ (404)
Derivative liabilities, Total Net Derivative Instruments	$ (1,020)	(404)
Derivative Asset, Statement of Financial Position [Extensible Enumeration]	Other current assets
Non- Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	$ (973)	(278)
Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	15	(122)
Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	(62)	(4)
Other current assets
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	467	623
Derivative assets, Amounts Available for Offset	(233)	(335)
Derivative assets, Total Net Derivative Instruments	234	$ 288
Derivative Asset, Statement of Financial Position [Extensible Enumeration]		Other current assets
Other current assets | Non- Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	384	$ 551
Other current assets | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	51	31
Other current assets | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	32	41
Deferred amounts and other assets
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	304	463
Derivative assets, Amounts Available for Offset	(145)	(184)
Derivative assets, Total Net Derivative Instruments	$ 159	$ 279
Derivative Asset, Statement of Financial Position [Extensible Enumeration]	Deferred Costs and Other Assets	Deferred Costs and Other Assets
Deferred amounts and other assets | Non- Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	$ 237	$ 396
Deferred amounts and other assets | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	67	51
Deferred amounts and other assets | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	0	16
Other current liabilities
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(653)	(738)
Derivative liabilities, Amounts Available for Offset	233	335
Derivative liabilities, Total Net Derivative Instruments	$ (420)	$ (403)
Derivative Liability, Statement of Financial Position [Extensible Enumeration]	Other current liabilities	Other current liabilities
Other current liabilities | Non- Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	$ (509)	$ (500)
Other current liabilities | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(101)	(194)
Other current liabilities | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(43)	(44)
Other long-term liabilities
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(1,138)	(752)
Derivative liabilities, Amounts Available for Offset	145	184
Derivative liabilities, Total Net Derivative Instruments	$ (993)	$ (568)
Derivative Liability, Statement of Financial Position [Extensible Enumeration]	Other Liabilities, Noncurrent	Other Liabilities, Noncurrent
Other long-term liabilities | Non- Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	$ (1,085)	$ (725)
Other long-term liabilities | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(2)	(10)
Other long-term liabilities | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(51)	(17)
Foreign exchange contracts
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	(940)	(152)
Derivative liabilities, Total Net Derivative Instruments	(940)	(152)
Foreign exchange contracts | Non- Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	(878)	(148)
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)	(62)	$ (4)
Foreign exchange contracts | Other current assets
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	124	139
Derivative assets, Amounts Available for Offset	(26)	(32)
Derivative assets, Total Net Derivative Instruments	98	107
Foreign exchange contracts | Other current assets | Non- Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	92	98
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	32	41
Foreign exchange contracts | Deferred amounts and other assets
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	124	335
Derivative assets, Amounts Available for Offset	(98)	(122)
Derivative assets, Total Net Derivative Instruments	26	213
Foreign exchange contracts | Deferred amounts and other assets | Non- Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	124	319
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	0	16
Foreign exchange contracts | Other current liabilities
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(238)	(128)
Derivative liabilities, Amounts Available for Offset	26	32
Derivative liabilities, Total Net Derivative Instruments	(212)	(96)
Foreign exchange contracts | Other current liabilities | Non- Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(195)	(84)
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	(43)	(44)
Foreign exchange contracts | Other long-term liabilities
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(950)	(498)
Derivative liabilities, Amounts Available for Offset	98	122
Derivative liabilities, Total Net Derivative Instruments	(852)	(376)
Foreign exchange contracts | Other long-term liabilities | Non- Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(899)	(481)
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	(51)	(17)
Interest rate contracts
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	74	(156)
Derivative assets, Total Net Derivative Instruments	74
Derivative liabilities, Total Net Derivative Instruments		$ (156)
Derivative Liability, Statement of Financial Position [Extensible Enumeration]		Other Liabilities, Noncurrent
Interest rate contracts | Non- Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	53	$ (52)
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
Total net financial asset/(liability)	21	$ (104)
Interest rate contracts | Derivative Instruments Used as Fair Value 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
Interest rate contracts | Other current assets
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	102	$ 65
Derivative assets, Amounts Available for Offset	(50)	(32)
Derivative assets, Total Net Derivative Instruments	52	33
Interest rate contracts | Other current assets | Non- Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	51	34
Interest rate contracts | Other current assets | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	51	31
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	93	53
Derivative assets, Amounts Available for Offset	(7)	(21)
Derivative assets, Total Net Derivative Instruments	86	32
Interest rate contracts | Deferred amounts and other assets | Non- Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	26	2
Interest rate contracts | Deferred amounts and other assets | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	67	51
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	(99)	(186)
Derivative liabilities, Amounts Available for Offset	50	32
Derivative liabilities, Total Net Derivative Instruments	(49)	(154)
Interest rate contracts | Other current liabilities | Non- Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(2)	(3)
Interest rate contracts | Other current liabilities | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(97)	(183)
Interest rate contracts | Other current liabilities | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	0	0
Interest rate contracts | Other long-term liabilities
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(22)	(88)
Derivative liabilities, Amounts Available for Offset	7	21
Derivative liabilities, Total Net Derivative Instruments	(15)	(67)
Interest rate contracts | Other long-term liabilities | Non- Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(22)	(85)
Interest rate contracts | Other long-term liabilities | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	0	(3)
Interest rate contracts | Other long-term liabilities | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	0	0
Commodity contracts
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	(153)	(96)
Derivative liabilities, Total Net Derivative Instruments	(153)	(96)
Commodity contracts | Non- Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	(147)	(78)
Commodity contracts | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	(6)	(18)
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	241	418
Derivative assets, Amounts Available for Offset	(157)	(270)
Derivative assets, Total Net Derivative Instruments	84	148
Commodity contracts | Other current assets | Non- Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	241	418
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	87	75
Derivative assets, Amounts Available for Offset	(40)	(41)
Derivative assets, Total Net Derivative Instruments	47	34
Commodity contracts | Deferred amounts and other assets | Non- Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	87	75
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	(315)	(423)
Derivative liabilities, Amounts Available for Offset	157	270
Derivative liabilities, Total Net Derivative Instruments	(158)	(153)
Commodity contracts | Other current liabilities | Non- Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(311)	(412)
Commodity contracts | Other current liabilities | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(4)	(11)
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	(166)	(166)
Derivative liabilities, Amounts Available for Offset	40	41
Derivative liabilities, Total Net Derivative Instruments	(126)	(125)
Commodity contracts | Other long-term liabilities | Non- Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(164)	(159)
Commodity contracts | Other long-term liabilities | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(2)	(7)
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
Derivative assets		1
Derivative liabilities	(1)	(1)
Total net financial asset/(liability)	(1)	0
Derivative assets, Amounts Available for Offset		(1)
Derivative liabilities, Amounts Available for Offset	0	1
Derivative assets, Total Net Derivative Instruments		0
Derivative liabilities, Total Net Derivative Instruments	(1)	0
Other contracts | Non- Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets		1
Derivative liabilities	(1)	(1)
Total net financial asset/(liability)	(1)	0
Other contracts | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets		0
Derivative liabilities	0	0
Total net financial asset/(liability)	0	0
Other contracts | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets		0
Derivative liabilities	0	0
Total net financial asset/(liability)	$ 0	$ 0