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REGULATORY ACCOUNTING - Narrative (Details) - USD ($) $ in Millions | Mar. 31, 2023 | Dec. 31, 2022
--- | --- | ---
Regulatory Assets [Line Items] |  |
Amount of regulatory costs not yet approved | $ 223.6 | $ 210.8
COVID-19 |  |
Regulatory Assets [Line Items] |  |
Net incremental deferred costs | 29.8 | 29.8
CL&P |  |
Regulatory Assets [Line Items] |  |
Amount of regulatory costs not yet approved | 146.5 | 135.9
CL&P | COVID-19 |  |
Regulatory Assets [Line Items] |  |
Net incremental deferred costs | 11.8 | 11.8
NSTAR Electric |  |
Regulatory Assets [Line Items] |  |
Amount of regulatory costs not yet approved | 19.7 | 19.8
NSTAR Electric | COVID-19 |  |
Regulatory Assets [Line Items] |  |
Net incremental deferred costs | 2.2 | 2.2
PSNH |  |
Regulatory Assets [Line Items] |  |
Amount of regulatory costs not yet approved | $ 1.1 | $ 1.0

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