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, 2024	Aug. 31, 2024	Jul. 31, 2024	Jun. 30, 2024	May 31, 2024	Apr. 30, 2024	Jan. 31, 2024	Sep. 30, 2024	Sep. 30, 2023
Debt Instrument [Line Items]
Retirement of Long-Term Debt								$ (1,260,148)	$ (1,203,000)
Senior Notes | Eversource Parent Series DD Senior Notes | Eversource Parent
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)							5.00%
Issuances							$ 350,000
Senior Notes | Eversource Parent Series EE Senior Notes | Eversource Parent
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)							5.50%
Issuances							$ 650,000
Senior Notes | Eversource Parent Series FF Senior Notes | Eversource Parent
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)						5.85%
Issuances						$ 700,000
Senior Notes | Eversource Parent Series GG Senior Notes | Eversource Parent
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)						5.95%
Issuances						$ 700,000
Senior Notes | Eversource Parent Series X Senior Notes | Eversource Parent
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)				4.20%
Retirement of Long-Term Debt				$ (900,000)
Senior Notes | Eversource Parent Series L Senior Notes | Eversource Parent | Subsequent Event
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)	2.90%
Retirement of Long-Term Debt	$ (450,000)
CL&P
Debt Instrument [Line Items]
Retirement of Long-Term Debt								$ 0	$ (400,000)
CL&P | First Mortgage | CL&P Series A First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)							4.65%
Issuances							$ 350,000
CL&P | First Mortgage | CL&P Series B First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)		4.95%
Issuances		$ 300,000
CL&P | First Mortgage | CL&P Series D First Mortgage Bonds | Subsequent Event
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)	7.875%
Retirement of Long-Term Debt	$ (139,800)
PSNH | First Mortgage | PSNH Series X First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)						5.35%
Issuances						$ 300,000
NSTAR Electric | Unsecured Debt | NSTAR Electric Debentures
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)					5.40%
Issuances					$ 600,000
NSTAR Gas | First Mortgage | NSTAR Gas Series W First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)				5.29%
Issuances				$ 160,000
NSTAR Gas | First Mortgage | NSTAR Gas Series X First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)				5.48%
Issuances				$ 40,000
Yankee Gas | First Mortgage | Yankee Gas Series W First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)			5.50%
Issuances			$ 90,000
Yankee Gas | First Mortgage | Yankee Gas Series X First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)			5.74%
Issuances			$ 90,000
Yankee Gas | First Mortgage | Yankee Gas Series P First Mortgage Bonds | Subsequent Event
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)	2.23%
Retirement of Long-Term Debt	$ (100,000)
Eversource Gas Company of Massachusetts | First Mortgage | EGMA Series E First Mortgage Bonds | Subsequent Event
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)	5.17%
Issuances	$ 100,000
Aquarion Company and its Subsidiaries | Senior Notes | Aquarion Senior Notes
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)		4.00%
Retirement of Long-Term Debt		$ (360,000)
Aquarion Company and its Subsidiaries | Senior Notes | Aquarion Water Company of Connecticut Senior Notes
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)		5.57%
Issuances		$ 70,000