COMMITMENTS AND CONTINGENCIES - Environmental Sites and Related Reserves (Details) $ in Millions	3 Months Ended	9 Months Ended
	Mar. 31, 2022 site	Sep. 30, 2022 USD ($) site	Dec. 31, 2021 USD ($)
Site Contingency [Line Items]
Number of Sites | site	61	62
Reserve | $		$ 121.1	$ 115.4
CL&P
Site Contingency [Line Items]
Number of Sites | site	14	14
Reserve | $		$ 14.1	13.9
NSTAR Electric
Site Contingency [Line Items]
Number of Sites | site	11	11
Reserve | $		$ 3.5	3.3
PSNH
Site Contingency [Line Items]
Number of Sites | site	9	9
Reserve | $		$ 6.2	$ 6.3