RISK MANAGEMENT AND FINANCIAL INSTRUMENTS - Schedule of Significant Unobservable Inputs Used in the Fair Value Measurement of Level 3 Derivative Instruments (Details) $ in Millions	Mar. 31, 2025 CAD ($) $ / bbl $ / MillionsofBTU-MMBTU $ / MWh	Dec. 31, 2024 CAD ($)
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	$ (2,209)	$ (2,250)
Fair Value
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	(2,209)	(2,250)
Level 3
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	57
Level 3 | Fair Value
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	$ 57	$ (52)
Commodity Options | Level 3 | Market Approach Valuation Technique | Minimum Price/Volatility
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Price volatility (in $/MMBTU, $/barrel, $ / MW/H, percent)	0.11
Commodity Options | Level 3 | Market Approach Valuation Technique | Maximum Price/ Volatility
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Price volatility (in $/MMBTU, $/barrel, $ / MW/H, percent)	0.77
Commodity Options | Level 3 | Market Approach Valuation Technique | Weighted Average Price/Volatility
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Price volatility (in $/MMBTU, $/barrel, $ / MW/H, percent)	0.53
Natural gas | Commodity Contracts - Financial | Level 3 | Market Approach Valuation Technique | Minimum Price/Volatility
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Price volatility (in $/MMBTU, $/barrel, $ / MW/H, percent) | $ / MillionsofBTU-MMBTU	3.78
Natural gas | Commodity Contracts - Financial | Level 3 | Market Approach Valuation Technique | Maximum Price/ Volatility
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Price volatility (in $/MMBTU, $/barrel, $ / MW/H, percent) | $ / MillionsofBTU-MMBTU	9.85
Natural gas | Commodity Contracts - Financial | Level 3 | Market Approach Valuation Technique | Weighted Average Price/Volatility
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Price volatility (in $/MMBTU, $/barrel, $ / MW/H, percent) | $ / MillionsofBTU-MMBTU	5.91
Natural gas | Commodity Contracts - Financial | Level 3 | Fair Value | Market Approach Valuation Technique
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	$ 11
Natural gas | Commodity Contracts - Physical | Level 3 | Market Approach Valuation Technique | Minimum Price/Volatility
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Price volatility (in $/MMBTU, $/barrel, $ / MW/H, percent) | $ / MillionsofBTU-MMBTU	0.59
Natural gas | Commodity Contracts - Physical | Level 3 | Market Approach Valuation Technique | Maximum Price/ Volatility
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Price volatility (in $/MMBTU, $/barrel, $ / MW/H, percent) | $ / MillionsofBTU-MMBTU	12.21
Natural gas | Commodity Contracts - Physical | Level 3 | Market Approach Valuation Technique | Weighted Average Price/Volatility
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Price volatility (in $/MMBTU, $/barrel, $ / MW/H, percent) | $ / MillionsofBTU-MMBTU	4.61
Natural gas | Commodity Contracts - Physical | Level 3 | Fair Value | Market Approach Valuation Technique
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	$ (71)
Natural gas | Commodity Options | Level 3 | Market Approach Valuation Technique | Minimum Price/Volatility
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Price volatility (in $/MMBTU, $/barrel, $ / MW/H, percent) | $ / MillionsofBTU-MMBTU	4.66
Natural gas | Commodity Options | Level 3 | Market Approach Valuation Technique | Maximum Price/ Volatility
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Price volatility (in $/MMBTU, $/barrel, $ / MW/H, percent) | $ / MillionsofBTU-MMBTU	11.29
Natural gas | Commodity Options | Level 3 | Market Approach Valuation Technique | Weighted Average Price/Volatility
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Price volatility (in $/MMBTU, $/barrel, $ / MW/H, percent) | $ / MillionsofBTU-MMBTU	7.60
Natural gas | Commodity Options | Level 3 | Fair Value | Market Approach Valuation Technique
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	$ 134
Crude | Commodity Contracts - Financial | Level 3 | Market Approach Valuation Technique | Minimum Price/Volatility
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Price volatility (in $/MMBTU, $/barrel, $ / MW/H, percent) | $ / bbl	76.32
Crude | Commodity Contracts - Financial | Level 3 | Market Approach Valuation Technique | Maximum Price/ Volatility
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Price volatility (in $/MMBTU, $/barrel, $ / MW/H, percent) | $ / bbl	103.75
Crude | Commodity Contracts - Financial | Level 3 | Market Approach Valuation Technique | Weighted Average Price/Volatility
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Price volatility (in $/MMBTU, $/barrel, $ / MW/H, percent) | $ / bbl	97.19
Crude | Commodity Contracts - Financial | Level 3 | Fair Value | Market Approach Valuation Technique
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	$ (8)
Crude | Commodity Contracts - Physical | Level 3 | Market Approach Valuation Technique | Minimum Price/Volatility
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Price volatility (in $/MMBTU, $/barrel, $ / MW/H, percent) | $ / bbl	76.45
Crude | Commodity Contracts - Physical | Level 3 | Market Approach Valuation Technique | Maximum Price/ Volatility
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Price volatility (in $/MMBTU, $/barrel, $ / MW/H, percent) | $ / bbl	118.36
Crude | Commodity Contracts - Physical | Level 3 | Market Approach Valuation Technique | Weighted Average Price/Volatility
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Price volatility (in $/MMBTU, $/barrel, $ / MW/H, percent) | $ / bbl	99.11
Crude | Commodity Contracts - Physical | Level 3 | Fair Value | Market Approach Valuation Technique
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	$ 25
Power | Commodity Contracts - Financial | Level 3 | Market Approach Valuation Technique | Minimum Price/Volatility
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Price volatility (in $/MMBTU, $/barrel, $ / MW/H, percent) | $ / MWh	28.60
Power | Commodity Contracts - Financial | Level 3 | Market Approach Valuation Technique | Maximum Price/ Volatility
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Price volatility (in $/MMBTU, $/barrel, $ / MW/H, percent) | $ / MWh	195.45
Power | Commodity Contracts - Financial | Level 3 | Market Approach Valuation Technique | Weighted Average Price/Volatility
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Price volatility (in $/MMBTU, $/barrel, $ / MW/H, percent) | $ / MWh	74.48
Power | Commodity Contracts - Financial | Level 3 | Fair Value | Market Approach Valuation Technique
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	$ (19)
Power | Commodity Contracts - Physical | Level 3 | Market Approach Valuation Technique | Minimum Price/Volatility
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Price volatility (in $/MMBTU, $/barrel, $ / MW/H, percent) | $ / MWh	24.97
Power | Commodity Contracts - Physical | Level 3 | Market Approach Valuation Technique | Maximum Price/ Volatility
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Price volatility (in $/MMBTU, $/barrel, $ / MW/H, percent) | $ / MWh	138.58
Power | Commodity Contracts - Physical | Level 3 | Market Approach Valuation Technique | Weighted Average Price/Volatility
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Price volatility (in $/MMBTU, $/barrel, $ / MW/H, percent) | $ / MWh	76.37
Power | Commodity Contracts - Physical | Level 3 | Fair Value | Market Approach Valuation Technique
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	$ (15)