DERIVATIVE INSTRUMENTS - Gross Fair Values and Net Amounts of Contracts (Details) - CL&P - Level 3 - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022
Current Derivative Assets
Derivative Assets (Liabilities), at Fair Value, Net, by Balance Sheet Classification [Abstract]
Commodity Supply and Price Risk Management	$ 17.0	$ 16.3
Netting	(0.5)	(0.5)
Net Amount Recorded as a Derivative	16.5	15.8
Other Long-Term Assets
Derivative Assets (Liabilities), at Fair Value, Net, by Balance Sheet Classification [Abstract]
Commodity Supply and Price Risk Management	24.9	28.8
Netting	(0.8)	(0.9)
Net Amount Recorded as a Derivative	24.1	27.9
Current Derivative Liabilities
Current and Long-Term Derivative Liabilities
Commodity Supply and Price Risk Management	(85.1)	(81.6)
Netting	0.0	0.0
Net Amount Recorded as a Derivative	(85.1)	(81.6)
Long-Term Derivative Liabilities
Current and Long-Term Derivative Liabilities
Commodity Supply and Price Risk Management	(124.3)	(143.9)
Netting	0.0	0.0
Net Amount Recorded as a Derivative	$ (124.3)	$ (143.9)