DERIVATIVE INSTRUMENTS - Gross Fair Values and Net Amounts of Contracts (Details) - CL&P - Level 3 - USD ($) $ in Millions	Sep. 30, 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	$ 15.7	$ 14.7
Netting	(0.5)	(1.0)
Net Amount Recorded as a Derivative	15.2	13.7
Other Long-Term Assets
Derivative Assets (Liabilities), at Fair Value, Net, by Balance Sheet Classification [Abstract]
Commodity Supply and Price Risk Management	32.8	46.9
Netting	(1.0)	(0.9)
Net Amount Recorded as a Derivative	31.8	46.0
Current Derivative Liabilities
Current and Long-Term Derivative Liabilities
Commodity Supply and Price Risk Management	(78.6)	(73.5)
Netting	0.0	0.0
Net Amount Recorded as a Derivative	(78.6)	(73.5)
Long-Term Derivative Liabilities
Current and Long-Term Derivative Liabilities
Commodity Supply and Price Risk Management	(164.3)	(235.4)
Netting	0.0	0.0
Net Amount Recorded as a Derivative	$ (164.3)	$ (235.4)