DERIVATIVE INSTRUMENTS - Gross Fair Values and Net Amounts of Contracts (Details) - CL&P - Level 3 - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Current Derivative Assets
Derivative Assets (Liabilities), at Fair Value, Net, by Balance Sheet Classification [Abstract]
Commodity Supply and Price Risk Management	$ 14.8	$ 14.7
Netting	(0.4)	(1.0)
Net Amount Recorded as a Derivative	14.4	13.7
Other Long-Term Assets
Derivative Assets (Liabilities), at Fair Value, Net, by Balance Sheet Classification [Abstract]
Commodity Supply and Price Risk Management	41.4	46.9
Netting	(1.3)	(0.9)
Net Amount Recorded as a Derivative	40.1	46.0
Current Derivative Liabilities
Current and Long-Term Derivative Liabilities
Commodity Supply and Price Risk Management	(74.4)	(73.5)
Netting	0.0	0.0
Net Amount Recorded as a Derivative	(74.4)	(73.5)
Long-Term Derivative Liabilities
Current and Long-Term Derivative Liabilities
Commodity Supply and Price Risk Management	(209.5)	(235.4)
Netting	0.0	0.0
Net Amount Recorded as a Derivative	$ (209.5)	$ (235.4)

Fair value of liability associated with financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset.

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