SHORT-TERM AND LONG-TERM DEBT - Summary of Long-Term Debt Issuance and Repayments (Details) - USD ($) $ in Thousands	1 Months Ended			3 Months Ended
	May 31, 2025	Feb. 28, 2025	Jan. 31, 2025	Mar. 31, 2025	Mar. 31, 2024
Debt Instrument [Line Items]
Retirement of Long-Term Debt				$ (300,051)	$ 0
CL&P | First Mortgage | CL&P Series A First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)			4.95%
Issuances			$ 400,000
NSTAR Electric | Unsecured Debt | NSTAR Electric Debentures
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)		4.85%
Issuances		$ 400,000
NSTAR Electric | Unsecured Debt | NSTAR Electric Debentures
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)		5.20%
Issuances		$ 400,000
Eversource Parent Series H Senior Notes | Senior Notes | Eversource Parent Series H Senior Notes | Eversource Parent
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)			3.15%
Retirement of Long-Term Debt			$ (300,000)
NSTAR Gas Series R First Mortgage Bonds | First Mortgage | NSTAR Gas Series R First Mortgage Bonds | Forecast
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)	2.33%
Retirement of Long-Term Debt	$ (75,000)