ASSET RETIREMENT OBLIGATIONS - Schedule of Reconciliation of Beginning and Ending Balance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance as of Beginning of Year	$ 500.1	$ 499.7
Liabilities Settled During the Year	(22.3)	(23.9)
Accretion	28.9	29.4
Revisions in Estimated Cash Flows	(4.0)	(5.1)
Balance as of End of Year	502.7	500.1
CL&P
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance as of Beginning of Year	35.0	33.4
Liabilities Settled During the Year	0.0	(0.6)
Accretion	2.4	2.2
Revisions in Estimated Cash Flows	0.0	0.0
Balance as of End of Year	37.4	35.0
NSTAR Electric
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance as of Beginning of Year	97.5	91.8
Liabilities Settled During the Year	0.0	0.0
Accretion	4.1	4.0
Revisions in Estimated Cash Flows	(0.3)	1.7
Balance as of End of Year	101.3	97.5
PSNH
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance as of Beginning of Year	4.7	4.4
Liabilities Settled During the Year	0.0	0.0
Accretion	0.2	0.3
Revisions in Estimated Cash Flows	0.0	0.0
Balance as of End of Year	$ 4.9	$ 4.7