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DERIVATIVE INSTRUMENTS - Changes in the Level 3 Category of Derivative Assets Measured at Fair Value on a Recurring Basis (Details) - CL&P - Level 2 - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
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Jun. 30, 2023 | Jun. 30, 2023
Derivatives, Net [Rollforward] |  |
Fair Value as of Beginning of Period | $ (168.8) | $ (181.8)
Net Realized/Unrealized Gains/(Losses) Included in Regulatory Assets | 1.8 | (0.1)
Settlements | 14.9 | 29.8
Fair Value as of End of Period | $ (152.1) | $ (152.1)

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