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SHORT-TERM AND LONG-TERM DEBT - Summary of Long-Term Debt Issuance and Repayments (Details) - USD ($) $ in Thousands	1 Months Ended					6 Months Ended
	Jul. 31, 2025	Jun. 30, 2025	May 31, 2025	Feb. 28, 2025	Jan. 31, 2025	Jun. 30, 2025	Jun. 30, 2024
Debt Instrument [Line Items]
Retirement of Long-Term Debt						$ 375,122	$ 900,000
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
Short-term debt, paid				3.25%
NSTAR Electric \| Unsecured Debt \| NSTAR Electric Debentures
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)				5.20%
Issuances				$ 400,000
Short-term debt, paid				3.25%
PSNH \| First Mortgage \| PSNH Series Y First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)		4.40%				4.40%
Issuances		$ 300,000
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 Y First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)		4.86%				4.86%
Issuances		$ 205,000
NSTAR Gas Series R First Mortgage Bonds \| First Mortgage \| NSTAR Gas Series Z First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)		5.30%				5.30%
Issuances		$ 20,000
NSTAR Gas Series R First Mortgage Bonds \| First Mortgage \| NSTAR Gas Series R First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)			2.33%
Retirement of Long-Term Debt			$ 75,000
Yankee Gas \| First Mortgage \| Yankee Gas Series Y First Mortgage Bonds \| Subsequent Event
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)	5.02%
Issuances	$ 148,000
Yankee Gas \| First Mortgage \| Yankee Gas Series Z First Mortgage Bonds \| Subsequent Event
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)	5.55%
Issuances	$ 37,000