ASSET RETIREMENT OBLIGATIONS - Schedule of Reconciliation of Beginning and Ending Balance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance as of Beginning of Year	$ 590.9	$ 505.8
Liabilities Settled During the Year	(24.2)	(24.6)
Accretion	34.0	29.5
Revisions in Estimated Cash Flows	(5.3)	80.2
Balance as of End of Year	595.4	590.9
CL&P
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance as of Beginning of Year	42.5	39.9
Liabilities Settled During the Year	0.0	0.0
Accretion	2.9	2.6
Revisions in Estimated Cash Flows	0.0	0.0
Balance as of End of Year	45.4	42.5
NSTAR Electric
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance as of Beginning of Year	109.3	104.8
Liabilities Settled During the Year	0.0	0.0
Accretion	4.7	4.5
Revisions in Estimated Cash Flows	0.0	0.0
Balance as of End of Year	114.0	109.3
PSNH
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance as of Beginning of Year	5.6	5.2
Liabilities Settled During the Year	0.0	0.0
Accretion	0.3	0.4
Revisions in Estimated Cash Flows	0.0	0.0
Balance as of End of Year	$ 5.9	$ 5.6