REGULATORY ACCOUNTING - Narrative (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved	$ 267.0	$ 241.7
Regulatory costs	87.5	82.1
CL&P
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved	180.4	166.7
Regulatory costs	64.7	64.0
NSTAR Electric
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved	27.8	21.9
Regulatory costs	10.9	7.3
PSNH
Regulatory Assets [Line Items]
Amount of regulatory costs not yet approved	$ 2.1	$ 1.2