RISK MANAGEMENT AND FINANCIAL INSTRUMENTS - Level 3 Inputs (Details) $ in Millions	Dec. 31, 2023 CAD ($) $ / MWh $ / bbl $ / MillionsofBTU-MMBTU	Dec. 31, 2022 CAD ($)
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	$ (404)	$ (546)
Fair Value
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	(404)	(546)
Level 3
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	(131)
Level 3 | Fair Value
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	$ (131)	$ (136)
Market approach valuation technique | Level 3 | Commodity Contracts - Financial | Natural gas | Minimum Price
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price | $ / MillionsofBTU-MMBTU	2.66
Market approach valuation technique | Level 3 | Commodity Contracts - Financial | Natural gas | Maximum Price
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price | $ / MillionsofBTU-MMBTU	8.29
Market approach valuation technique | Level 3 | Commodity Contracts - Financial | Natural gas | Weighted Average Price
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price | $ / MillionsofBTU-MMBTU	3.78
Market approach valuation technique | Level 3 | Commodity Contracts - Financial | Crude | Minimum Price
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price | $ / bbl	69.01
Market approach valuation technique | Level 3 | Commodity Contracts - Financial | Crude | Maximum Price
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price | $ / bbl	92.76
Market approach valuation technique | Level 3 | Commodity Contracts - Financial | Crude | Weighted Average Price
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price | $ / bbl	80.35
Market approach valuation technique | Level 3 | Commodity Contracts - Financial | Power | Minimum Price
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price | $ / MWh	29.75
Market approach valuation technique | Level 3 | Commodity Contracts - Financial | Power | Maximum Price
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price | $ / MWh	145.24
Market approach valuation technique | Level 3 | Commodity Contracts - Financial | Power | Weighted Average Price
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price | $ / MWh	59.21
Market approach valuation technique | Level 3 | Commodity Contracts - Physical | Natural gas | Minimum Price
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price | $ / MillionsofBTU-MMBTU	0.86
Market approach valuation technique | Level 3 | Commodity Contracts - Physical | Natural gas | Maximum Price
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price | $ / MillionsofBTU-MMBTU	11.85
Market approach valuation technique | Level 3 | Commodity Contracts - Physical | Natural gas | Weighted Average Price
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price | $ / MillionsofBTU-MMBTU	3.42
Market approach valuation technique | Level 3 | Commodity Contracts - Physical | Crude | Minimum Price
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price | $ / bbl	64.51
Market approach valuation technique | Level 3 | Commodity Contracts - Physical | Crude | Maximum Price
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price | $ / bbl	98.11
Market approach valuation technique | Level 3 | Commodity Contracts - Physical | Crude | Weighted Average Price
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price | $ / bbl	82.85
Market approach valuation technique | Level 3 | Commodity Contracts - Physical | Power | Minimum Price
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price | $ / MWh	18.20
Market approach valuation technique | Level 3 | Commodity Contracts - Physical | Power | Maximum Price
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price | $ / MWh	164.84
Market approach valuation technique | Level 3 | Commodity Contracts - Physical | Power | Weighted Average Price
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Forward price | $ / MWh	58.46
Market approach valuation technique | Level 3 | Fair Value | Commodity Contracts - Financial | Natural gas
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	$ (6)
Market approach valuation technique | Level 3 | Fair Value | Commodity Contracts - Financial | Crude
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	(7)
Market approach valuation technique | Level 3 | Fair Value | Commodity Contracts - Financial | Power
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	(87)
Market approach valuation technique | Level 3 | Fair Value | Commodity Contracts - Physical | Natural gas
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	14
Market approach valuation technique | Level 3 | Fair Value | Commodity Contracts - Physical | Crude
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	(7)
Market approach valuation technique | Level 3 | Fair Value | Commodity Contracts - Physical | Power
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	$ (38)