RISK MANAGEMENT AND FINANCIAL INSTRUMENTS - Total Derivative Instruments (Details) - CAD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	$ (561)	$ (546)
Derivative liabilities, Total Net Derivative Instruments	(561)	(546)
Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	(944)	(1,476)
Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	274	816
Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	109	114
Other current assets
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	532	1,015
Derivative assets, Amounts Available for Offset	(142)	(223)
Derivative assets, Total Net Derivative Instruments	390	792
Other current assets | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	270	366
Other current assets | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	194	649
Other current assets | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	68	0
Deferred amounts and other assets
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	479	627
Derivative assets, Amounts Available for Offset	(181)	(163)
Derivative assets, Total Net Derivative Instruments	298	464
Deferred amounts and other assets | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	242	216
Deferred amounts and other assets | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	154	255
Deferred amounts and other assets | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	83	156
Other current liabilities
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(399)	(898)
Derivative liabilities, Amounts Available for Offset	142	223
Derivative liabilities, Total Net Derivative Instruments	(257)	(675)
Other current liabilities | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(308)	(808)
Other current liabilities | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(49)	(48)
Other current liabilities | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(42)	(42)
Other long-term liabilities
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(1,173)	(1,290)
Derivative liabilities, Amounts Available for Offset	181	163
Derivative liabilities, Total Net Derivative Instruments	(992)	(1,127)
Other long-term liabilities | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(1,148)	(1,250)
Other long-term liabilities | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(25)	(40)
Other long-term liabilities | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	0	0
Foreign exchange contracts
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	(775)	(1,327)
Derivative liabilities, Total Net Derivative Instruments	(775)	(1,327)
Foreign exchange contracts | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	(884)	(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)	109	$ 114
Foreign exchange contracts | Other current assets
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	122	46
Derivative assets, Amounts Available for Offset	(13)	(41)
Derivative assets, Total Net Derivative Instruments	109	5
Foreign exchange contracts | Other current assets | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	54	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	68	0
Foreign exchange contracts | Deferred amounts and other assets
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	214	309
Derivative assets, Amounts Available for Offset	(108)	(138)
Derivative assets, Total Net Derivative Instruments	106	171
Foreign exchange contracts | Deferred amounts and other assets | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	131	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	83	156
Foreign exchange contracts | Other current liabilities
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(131)	(566)
Derivative liabilities, Amounts Available for Offset	13	41
Derivative liabilities, Total Net Derivative Instruments	(118)	(525)
Foreign exchange contracts | Other current liabilities | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(89)	(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	(42)	(42)
Foreign exchange contracts | Other long-term liabilities
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(980)	(1,116)
Derivative liabilities, Amounts Available for Offset	108	138
Derivative liabilities, Total Net Derivative Instruments	(872)	(978)
Foreign exchange contracts | Other long-term liabilities | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(980)	(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	0	0
Interest rate contracts
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities		(4)
Total net financial asset/(liability)	344	910
Derivative liabilities, Total Net Derivative Instruments	344	$ 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)	19	$ 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)	325	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	215	$ 660
Derivative assets, Amounts Available for Offset	(11)	0
Derivative assets, Total Net Derivative Instruments	204	660
Interest rate contracts | Other current assets | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	21	11
Interest rate contracts | Other current assets | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	194	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	198	254
Derivative assets, Amounts Available for Offset	(43)	0
Derivative assets, Total Net Derivative Instruments	155	254
Interest rate contracts | Deferred amounts and other assets | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	44	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	154	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	(20)
Derivative liabilities, Amounts Available for Offset	11
Derivative liabilities, Total Net Derivative Instruments	(9)
Interest rate contracts | Other current liabilities | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(1)
Interest rate contracts | Other current liabilities | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(19)
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	(49)
Derivative liabilities, Amounts Available for Offset	43	0
Derivative liabilities, Total Net Derivative Instruments	(6)	(4)
Interest rate contracts | Other long-term liabilities | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(45)
Interest rate contracts | Other long-term liabilities | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(4)
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)	(132)	(139)
Derivative liabilities, Total Net Derivative Instruments	(132)	(139)
Commodity contracts | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	(81)	(54)
Commodity contracts | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Total net financial asset/(liability)	(51)	(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	193	302
Derivative assets, Amounts Available for Offset	(118)	(182)
Derivative assets, Total Net Derivative Instruments	75	120
Commodity contracts | Other current assets | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	193	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	67	61
Derivative assets, Amounts Available for Offset	(30)	(25)
Derivative assets, Total Net Derivative Instruments	37	36
Commodity contracts | Deferred amounts and other assets | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	67	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	(248)	(332)
Derivative liabilities, Amounts Available for Offset	118	182
Derivative liabilities, Total Net Derivative Instruments	(130)	(150)
Commodity contracts | Other current liabilities | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(218)	(284)
Commodity contracts | Other current liabilities | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(30)	(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	(144)	(170)
Derivative liabilities, Amounts Available for Offset	30	25
Derivative liabilities, Total Net Derivative Instruments	(114)	(145)
Commodity contracts | Other long-term liabilities | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(123)	(133)
Commodity contracts | Other long-term liabilities | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(21)	(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
Derivative assets	2
Total net financial asset/(liability)	2	10
Derivative assets, Amounts Available for Offset	0
Derivative assets, Total Net Derivative Instruments	2
Derivative liabilities, Total Net Derivative Instruments	2	10
Other contracts | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	2
Total net financial asset/(liability)	2	9
Other contracts | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	0
Total net financial asset/(liability)	0	1
Other contracts | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	0
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