RISK MANAGEMENT AND FINANCIAL INSTRUMENTS - Level 3 Inputs (Details) $ in Millions	Sep. 30, 2022 CAD ($) $ / bbl $ / MWh $ / MillionsofBTU-MMBTU	Dec. 31, 2021 CAD ($)
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	$ (934)	$ (359)
Fair Value
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	(934)	(359)
Level 3
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	(97)
Level 3 | Fair Value
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	(97)	$ (108)
Market approach valuation technique | Level 3 | Commodity contracts - financial | Natural gas | Fair Value
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	$ 9
Market approach valuation technique | Level 3 | Commodity contracts - financial | Natural gas | Minimum
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price ($ / mmbtu, barrel, gallon, MW/H) | $ / MillionsofBTU-MMBTU	5.41
Market approach valuation technique | Level 3 | Commodity contracts - financial | Natural gas | Maximum
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price ($ / mmbtu, barrel, gallon, MW/H) | $ / MillionsofBTU-MMBTU	12.51
Market approach valuation technique | Level 3 | Commodity contracts - financial | Natural gas | Weighted Average
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price ($ / mmbtu, barrel, gallon, MW/H) | $ / MillionsofBTU-MMBTU	7.75
Market approach valuation technique | Level 3 | Commodity contracts - financial | Crude | Fair Value
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	$ 5
Market approach valuation technique | Level 3 | Commodity contracts - financial | Crude | Minimum
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price ($ / mmbtu, barrel, gallon, MW/H) | $ / bbl	64.09
Market approach valuation technique | Level 3 | Commodity contracts - financial | Crude | Maximum
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price ($ / mmbtu, barrel, gallon, MW/H) | $ / bbl	108.87
Market approach valuation technique | Level 3 | Commodity contracts - financial | Crude | Weighted Average
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price ($ / mmbtu, barrel, gallon, MW/H) | $ / bbl	77.06
Market approach valuation technique | Level 3 | Commodity contracts - financial | Power | Fair Value
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	$ (80)
Market approach valuation technique | Level 3 | Commodity contracts - financial | Power | Minimum
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price ($ / mmbtu, barrel, gallon, MW/H) | $ / MWh	35.56
Market approach valuation technique | Level 3 | Commodity contracts - financial | Power | Maximum
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price ($ / mmbtu, barrel, gallon, MW/H) | $ / MWh	207.09
Market approach valuation technique | Level 3 | Commodity contracts - financial | Power | Weighted Average
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price ($ / mmbtu, barrel, gallon, MW/H) | $ / MWh	93.98
Market approach valuation technique | Level 3 | Commodity contracts - physical | Natural gas | Fair Value
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	$ (66)
Market approach valuation technique | Level 3 | Commodity contracts - physical | Natural gas | Minimum
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price ($ / mmbtu, barrel, gallon, MW/H) | $ / MillionsofBTU-MMBTU	3.43
Market approach valuation technique | Level 3 | Commodity contracts - physical | Natural gas | Maximum
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price ($ / mmbtu, barrel, gallon, MW/H) | $ / MillionsofBTU-MMBTU	22.01
Market approach valuation technique | Level 3 | Commodity contracts - physical | Natural gas | Weighted Average
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price ($ / mmbtu, barrel, gallon, MW/H) | $ / MillionsofBTU-MMBTU	7.11
Market approach valuation technique | Level 3 | Commodity contracts - physical | Crude | Fair Value
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	$ 24
Market approach valuation technique | Level 3 | Commodity contracts - physical | Crude | Minimum
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price ($ / mmbtu, barrel, gallon, MW/H) | $ / bbl	72.52
Market approach valuation technique | Level 3 | Commodity contracts - physical | Crude | Maximum
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price ($ / mmbtu, barrel, gallon, MW/H) | $ / bbl	125.74
Market approach valuation technique | Level 3 | Commodity contracts - physical | Crude | Weighted Average
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price ($ / mmbtu, barrel, gallon, MW/H) | $ / bbl	90.39
Market approach valuation technique | Level 3 | Commodity contracts - physical | Power | Fair Value
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	$ 11
Market approach valuation technique | Level 3 | Commodity contracts - physical | Power | Minimum
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price ($ / mmbtu, barrel, gallon, MW/H) | $ / MWh	37.08
Market approach valuation technique | Level 3 | Commodity contracts - physical | Power | Maximum
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price ($ / mmbtu, barrel, gallon, MW/H) | $ / MWh	175.52
Market approach valuation technique | Level 3 | Commodity contracts - physical | Power | Weighted Average
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price ($ / mmbtu, barrel, gallon, MW/H) | $ / MWh	81.95