LONG-TERM DEBT - Schedule of Issuances and Repayments (Details) - USD ($) $ in Thousands	1 Months Ended									12 Months Ended
	Jan. 31, 2024	Dec. 31, 2023	Nov. 30, 2023	Sep. 30, 2023	Aug. 31, 2023	Jul. 31, 2023	May 31, 2023	Mar. 31, 2023	Jan. 31, 2023	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Debt Instrument [Line Items]
Repayments of debt										$ (2,008,470)	$ (1,175,000)	$ (1,142,500)
NSTAR Electric
Debt Instrument [Line Items]
Repayments of debt										(80,000)	(400,000)	(250,000)
CL&P
Debt Instrument [Line Items]
Repayments of debt										(400,000)	0	(120,500)
PSNH
Debt Instrument [Line Items]
Repayments of debt										(325,000)	0	(282,000)
CL&P 2023 Series A First Mortgage Bonds | First Mortgage Bonds | CL&P
Debt Instrument [Line Items]
Interest rate									5.25%
Issuance									$ 500,000
CL&P 2013 Series A First Mortgage Bonds | First Mortgage Bonds | CL&P
Debt Instrument [Line Items]
Interest rate									2.50%
Repayments of debt									$ (400,000)
CL&P 2023 Series B First Mortgage Bonds | First Mortgage Bonds | CL&P
Debt Instrument [Line Items]
Interest rate						4.90%
Issuance						$ 300,000
CL&P 2024 Series A First Mortgage Bonds | First Mortgage Bonds | CL&P | Subsequent Event
Debt Instrument [Line Items]
Interest rate	4.65%
Issuance	$ 350,000
NSTAR Electric 2023 Debentures | Debentures | NSTAR Electric
Debt Instrument [Line Items]
Interest rate				5.60%
Issuance				$ 150,000
NSTAR Electric 2013 Series G Senior Notes | Senior Notes | NSTAR Electric
Debt Instrument [Line Items]
Interest rate			3.88%
Repayments of debt			$ (80,000)
PSNH Series W First Mortgage Bonds | First Mortgage Bonds | PSNH
Debt Instrument [Line Items]
Interest rate									5.15%
Issuance									$ 300,000
PSNH Series X First Mortgage Bonds | First Mortgage Bonds | PSNH
Debt Instrument [Line Items]
Interest rate				5.35%
Issuance				$ 300,000
PSNH Series S First Mortgage Bonds | First Mortgage Bonds | PSNH
Debt Instrument [Line Items]
Interest rate			3.50%
Repayments of debt			$ (325,000)
Yankee Gas Series V First Mortgage Bonds | First Mortgage Bonds | Yankee Gas Services Company
Debt Instrument [Line Items]
Interest rate					5.51%
Issuance					$ 170,000
EGMA Series D First Mortgage Bonds | First Mortgage Bonds | EGMA
Debt Instrument [Line Items]
Interest rate			5.73%
Issuance			$ 58,000
Aquarion Water Company of Connecticut Senior Notes | Senior Notes | Aquarion Water Company Of Connecticut
Debt Instrument [Line Items]
Interest rate				5.89%
Issuance				$ 50,000
Eversource
Debt Instrument [Line Items]
Repayments of debt										$ (1,200,000)	$ (750,000)	$ (450,000)
Eversource | Eversource Parent Series Z Senior Notes | Senior Notes
Debt Instrument [Line Items]
Interest rate							5.45%	5.45%
Issuance							$ 550,000	$ 750,000
Eversource | Eversource Parent Series F Senior Notes | Senior Notes
Debt Instrument [Line Items]
Interest rate							2.80%
Repayments of debt							$ (450,000)
Eversource | Eversource Parent Series AA Senior Notes | Senior Notes
Debt Instrument [Line Items]
Interest rate							4.75%
Issuance							$ 450,000
Eversource | Eversource Parent Series BB Senior Notes | Senior Notes
Debt Instrument [Line Items]
Interest rate							5.125%
Issuance							$ 800,000
Eversource | Eversource Parent Variable Rate Series T Senior Notes | Senior Notes
Debt Instrument [Line Items]
Repayments of debt					$ (350,000)
Eversource | Eversource Parent Variable Rate Series T Senior Notes | Senior Notes | Secured Overnight Financing Rate (SOFR)
Debt Instrument [Line Items]
Basis spread on compounded SOFR					0.25%
Eversource | Eversource Parent Series CC Senior Notes | Senior Notes
Debt Instrument [Line Items]
Interest rate			5.95%
Issuance			$ 800,000
Eversource | Eversource Parent Series N Senior Notes | Senior Notes
Debt Instrument [Line Items]
Interest rate		3.80%								3.80%
Repayments of debt		$ (400,000)
Eversource | Eversource Parent Series DD Senior Notes | Senior Notes | Subsequent Event
Debt Instrument [Line Items]
Interest rate	5.00%
Issuance	$ 350,000
Eversource | Eversource Parent Series EE Senior Notes | Senior Notes | Subsequent Event
Debt Instrument [Line Items]
Interest rate	5.50%
Issuance	$ 650,000