RISK MANAGEMENT AND FINANCIAL INSTRUMENTS - Total Derivative Instruments (Details) - CAD ($) $ in Millions	Jun. 30, 2022	Dec. 31, 2021
TOTAL DERIVATIVE INSTRUMENTS
Total net financial assets/(liabilities)	$ 217	$ (359)
Derivative liabilities, Total Net Derivative Instruments	217	(359)
Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Total net financial assets/(liabilities)	(620)	(202)
Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Total net financial assets/(liabilities)	856	(45)
Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Total net financial assets/(liabilities)	(19)	(112)
Accounts receivable and other
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	848	529
Derivative assets, Amounts Available for Offset	(316)	(170)
Derivative assets, Total Net Derivative Instruments	532	359
Accounts receivable and other | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	505	465
Accounts receivable and other | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	343	64
Accounts receivable and other | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	0	0
Deferred amounts and other assets
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	833	360
Derivative assets, Amounts Available for Offset	(145)	(75)
Derivative assets, Total Net Derivative Instruments	688	285
Deferred amounts and other assets | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	245	272
Deferred amounts and other assets | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	568	88
Deferred amounts and other assets | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	20	0
Accounts payable and other
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(741)	(717)
Derivative liabilities, Amounts Available for Offset	316	170
Derivative liabilities, Total Net Derivative Instruments	(425)	(547)
Accounts payable and other | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(677)	(426)
Accounts payable and other | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(33)	(179)
Accounts payable and other | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(31)	(112)
Other long-term liabilities
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(723)	(531)
Derivative liabilities, Amounts Available for Offset	145	75
Derivative liabilities, Total Net Derivative Instruments	(578)	(456)
Other long-term liabilities | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(693)	(513)
Other long-term liabilities | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(22)	(18)
Other long-term liabilities | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(8)	0
Accounts receivable from affiliates
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	84
Accounts payable to affiliates
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(128)
Foreign exchange contracts
TOTAL DERIVATIVE INSTRUMENTS
Total net financial assets/(liabilities)	(491)	(227)
Derivative liabilities, Total Net Derivative Instruments	(491)	(227)
Foreign exchange contracts | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Total net financial assets/(liabilities)	(472)	(100)
Foreign exchange contracts | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Total net financial assets/(liabilities)	0	(15)
Foreign exchange contracts | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Total net financial assets/(liabilities)	(19)	(112)
Foreign exchange contracts | Accounts receivable and other
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	140	259
Derivative assets, Amounts Available for Offset	(41)	(41)
Derivative assets, Total Net Derivative Instruments	99	218
Foreign exchange contracts | Accounts receivable and other | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	140	259
Foreign exchange contracts | Accounts receivable and other | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	0	0
Foreign exchange contracts | Accounts receivable and other | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	0	0
Foreign exchange contracts | Deferred amounts and other assets
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	203	240
Derivative assets, Amounts Available for Offset	(123)	(61)
Derivative assets, Total Net Derivative Instruments	80	179
Foreign exchange contracts | Deferred amounts and other assets | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	183
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	20	0
Foreign exchange contracts | Accounts payable and other
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(252)	(303)
Derivative liabilities, Amounts Available for Offset	41	41
Derivative liabilities, Total Net Derivative Instruments	(211)	(262)
Foreign exchange contracts | Accounts payable and other | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(221)	(176)
Foreign exchange contracts | Accounts payable and other | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	0	(15)
Foreign exchange contracts | Accounts payable and other | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(31)	(112)
Foreign exchange contracts | Other long-term liabilities
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(582)	(423)
Derivative liabilities, Amounts Available for Offset	123	61
Derivative liabilities, Total Net Derivative Instruments	(459)	(362)
Foreign exchange contracts | Other long-term liabilities | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(574)	(423)
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	(8)	0
Interest rate contracts
TOTAL DERIVATIVE INSTRUMENTS
Total net financial assets/(liabilities)	854	(22)
Derivative liabilities, Total Net Derivative Instruments	854	(22)
Interest rate contracts | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Total net financial assets/(liabilities)	(40)	(23)
Interest rate contracts | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Total net financial assets/(liabilities)	894	1
Interest rate contracts | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Total net financial assets/(liabilities)	0	0
Interest rate contracts | Accounts receivable and other
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	342	64
Derivative assets, Amounts Available for Offset	(21)	0
Derivative assets, Total Net Derivative Instruments	321	64
Interest rate contracts | Accounts receivable and other | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	1	0
Interest rate contracts | Accounts receivable and other | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	341	64
Interest rate contracts | Accounts receivable and other | 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	566	88
Derivative assets, Amounts Available for Offset	0	(1)
Derivative assets, Total Net Derivative Instruments	566	87
Interest rate contracts | Deferred amounts and other assets | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	0	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	566	88
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 | Accounts payable and other
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(51)	(150)
Derivative liabilities, Amounts Available for Offset	21	0
Derivative liabilities, Total Net Derivative Instruments	(30)	(150)
Interest rate contracts | Accounts payable and other | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(41)	0
Interest rate contracts | Accounts payable and other | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(10)	(150)
Interest rate contracts | Accounts payable and other | 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	(3)	(24)
Derivative liabilities, Amounts Available for Offset	0	1
Derivative liabilities, Total Net Derivative Instruments	(3)	(23)
Interest rate contracts | Other long-term liabilities | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	0	(23)
Interest rate contracts | Other long-term liabilities | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(3)	(1)
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 assets/(liabilities)	(158)	(115)
Derivative liabilities, Total Net Derivative Instruments	(158)	(115)
Commodity contracts | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Total net financial assets/(liabilities)	(116)	(84)
Commodity contracts | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Total net financial assets/(liabilities)	(42)	(31)
Commodity contracts | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Total net financial assets/(liabilities)	0	0
Commodity contracts | Accounts receivable and other
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	358	204
Derivative assets, Amounts Available for Offset	(254)	(129)
Derivative assets, Total Net Derivative Instruments	104	75
Commodity contracts | Accounts receivable and other | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	358	204
Commodity contracts | Accounts receivable and other | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	0	0
Commodity contracts | Accounts receivable and other | 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	60	29
Derivative assets, Amounts Available for Offset	(22)	(13)
Derivative assets, Total Net Derivative Instruments	38	16
Commodity contracts | Deferred amounts and other assets | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	60
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 | Accounts payable and other
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(438)	(264)
Derivative liabilities, Amounts Available for Offset	254	129
Derivative liabilities, Total Net Derivative Instruments	(184)	(135)
Commodity contracts | Accounts payable and other | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(415)	(250)
Commodity contracts | Accounts payable and other | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(23)	(14)
Commodity contracts | Accounts payable and other | 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	(138)	(84)
Derivative liabilities, Amounts Available for Offset	22	13
Derivative liabilities, Total Net Derivative Instruments	(116)	(71)
Commodity contracts | Other long-term liabilities | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(119)	(67)
Commodity contracts | Other long-term liabilities | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative liabilities	(19)	(17)
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 assets/(liabilities)	12	5
Derivative liabilities, Total Net Derivative Instruments	12	5
Other contracts | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Total net financial assets/(liabilities)	8	5
Other contracts | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Total net financial assets/(liabilities)	4	0
Other contracts | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Total net financial assets/(liabilities)	0	0
Other contracts | Accounts receivable and other
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	8	2
Derivative assets, Amounts Available for Offset	0	0
Derivative assets, Total Net Derivative Instruments	8	2
Other contracts | Accounts receivable and other | Non-Qualifying Derivative Instruments
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	6	2
Other contracts | Accounts receivable and other | Derivative Instruments Used as Cash Flow Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	2	0
Other contracts | Accounts receivable and other | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	0	0
Other contracts | Deferred amounts and other assets
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	4	3
Derivative assets, Amounts Available for Offset	0	0
Derivative assets, Total Net Derivative Instruments	4	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	2	0
Other contracts | Deferred amounts and other assets | Derivative Instruments Used as Fair Value Hedges | Designated as hedging instrument
TOTAL DERIVATIVE INSTRUMENTS
Derivative assets	$ 0	$ 0