RISK MANAGEMENT AND FINANCIAL INSTRUMENTS - Level 3 Inputs (Details) $ in Millions	Dec. 31, 2024 CAD ($) $ / MWh $ / MillionsofBTU-MMBTU $ / bbl	Dec. 31, 2023 CAD ($)
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	$ (2,250)	$ (404)
Fair Value
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	(2,250)	(404)
Level 3
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	(52)
Level 3 | Fair Value
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	$ (52)	$ (131)
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)	0.03
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)	0.50
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	3.73
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	4.12
Natural gas | Commodity Contracts - Financial | Level 3 | Market approach valuation technique | Fair Value
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	$ (5)
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	1.40
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	22.57
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	4.12
Natural gas | Commodity Contracts - Physical | Level 3 | Market approach valuation technique | Fair Value
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	$ (80)
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	2.44
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	7.09
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	4.44
Natural gas | Commodity Options | Level 3 | Market approach valuation technique | Fair Value
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	$ 166
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	73.54
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	104.42
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	97.44
Crude | Commodity Contracts - Financial | Level 3 | Market approach valuation technique | Fair Value
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	$ (13)
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	77.31
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	118.28
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	99.76
Crude | Commodity Contracts - Physical | Level 3 | Market approach valuation technique | Fair Value
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	$ 22
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	31.17
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	229.29
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	68.51
Power | Commodity Contracts - Financial | Level 3 | Market approach valuation technique | Fair Value
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	$ (44)
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	12.94
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	211.42
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	70.30
Power | Commodity Contracts - Physical | Level 3 | Market approach valuation technique | Fair Value
Significant unobservable inputs used in the fair value measurement of Level 3 derivative instruments
Fair Value	$ (98)