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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								9 Months Ended
	Oct. 31, 2025	Sep. 30, 2025	Aug. 31, 2025	Jul. 31, 2025	Jun. 30, 2025	May 31, 2025	Feb. 28, 2025	Jan. 31, 2025	Sep. 30, 2025	Sep. 30, 2024
Debt Instrument [Line Items]
Payment of long-term debt									$ 750,225	$ 1,260,148
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%
NSTAR Electric | Unsecured Debt | NSTAR Electric Debentures | Subsequent Event
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)	5.20%
Issuances	$ 300,000
PSNH | First Mortgage | PSNH Series Y First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)					4.40%
Issuances					$ 300,000
Eversource Parent | Senior Notes | Eversource Parent Series HH Senior Notes | Eversource Parent | Subsequent Event
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)	4.45%
Issuances	$ (600,000)
Eversource Parent | Senior Notes | Eversource Parent Series H Senior Notes | Eversource Parent
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)								3.15%
Payment of long-term debt								$ 300,000
Eversource Parent | Senior Notes | Eversource Parent Series Q Senior Notes | Eversource Parent
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)			0.80%
Payment of long-term debt			$ 300,000
NSTAR Gas | First Mortgage | NSTAR Gas Series Y First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)					4.86%
Issuances					$ 205,000
NSTAR Gas | First Mortgage | NSTAR Gas Series Z First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)					5.30%
Issuances					$ 20,000
NSTAR Gas | First Mortgage | NSTAR Gas Series R First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)						2.33%
Payment of long-term debt						$ 75,000
Yankee Gas | First Mortgage | Yankee Gas Series Y First Mortgage Bonds
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
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)				5.55%
Issuances				$ 37,000
Yankee Gas | First Mortgage | Yankee Gas Series M First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)		3.35%							3.35%
Payment of long-term debt		$ 75,000
EGMA Series | First Mortgage | EGMA Series F First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)		4.77%							4.77%
Issuances		$ 125,000

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