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