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SHORT-TERM AND LONG-TERM DEBT - Summary of Long-Term Debt Issuance and Repayments (Details) - USD ($) $ in Millions		1 Months Ended
	Feb. 26, 2026	Jul. 31, 2026	Jun. 30, 2026	May 31, 2026	Mar. 31, 2026	Feb. 28, 2026
NSTAR Electric Debentures \| Unsecured Debt \| NSTAR Electric
Debt Instrument [Line Items]
Interest Rate (in percent)				4.65%
Issuance				$ 350.0
Short-term debt, paid				2.70%
NSTAR Electric Debentures \| Unsecured Debt \| NSTAR Electric
Debt Instrument [Line Items]
Interest Rate (in percent)				5.20%
Issuance				$ 350.0
Short-term debt, paid				2.70%
NSTAR Electric Debentures \| Unsecured Debt \| NSTAR Electric
Debt Instrument [Line Items]
Interest Rate (in percent)			2.70%
Repayments			$ (250.0)
NSTAR Electric Series H Senior Notes \| Senior Notes \| NSTAR Electric
Debt Instrument [Line Items]
Interest Rate (in percent)			2.75%
Repayments			$ (50.0)
PSNH Series X First Mortgage Bonds \| First Mortgage \| PSNH
Debt Instrument [Line Items]
Interest Rate (in percent)			5.35%
Issuance			$ 200.0
Eversource Parent Series A Junior Notes
Debt Instrument [Line Items]
Interest Rate (in percent)	6.10%
Debt instrument term (in years)	5 years
Spread rate (in percent)	2.521%
Eversource Parent Series A Junior Notes \| Junior Notes \| Eversource Parent \| Eversource Parent Commercial Paper Program
Debt Instrument [Line Items]
Interest Rate (in percent)						6.10%
Issuance						$ 750.0
Eversource Parent Series B Junior Notes
Debt Instrument [Line Items]
Interest Rate (in percent)	6.35%
Debt instrument term (in years)	5 years
Spread rate (in percent)	2.325%
Eversource Parent Series B Junior Notes \| Junior Notes \| Eversource Parent \| Eversource Parent Commercial Paper Program
Debt Instrument [Line Items]
Interest Rate (in percent)						6.35%
Issuance						$ 750.0
Eversource Parent Series J Senior Notes \| Senior Notes \| Eversource Parent \| Eversource Parent Commercial Paper Program
Debt Instrument [Line Items]
Interest Rate (in percent)					3.35%
Repayments					$ (250.0)
Eversource Parent Series AA Senior Notes \| Senior Notes \| Eversource Parent \| Eversource Parent Commercial Paper Program
Debt Instrument [Line Items]
Interest Rate (in percent)				4.75%
Repayments				$ (450.0)
Yankee Gas Series AA First Mortgage Bonds \| First Mortgage \| Yankee Gas \| Subsequent Event
Debt Instrument [Line Items]
Interest Rate (in percent)		5.22%
Issuance		$ 75.0
Yankee Gas Series BB First Mortgage Bonds \| First Mortgage \| Yankee Gas \| Subsequent Event
Debt Instrument [Line Items]
Interest Rate (in percent)		5.61%
Issuance		$ 100.0
EGMA Series G First Mortgage Bonds \| First Mortgage \| EGMA Series \| Subsequent Event
Debt Instrument [Line Items]
Interest Rate (in percent)		5.12%
Issuance		$ 100.0