SHORT-TERM AND LONG-TERM DEBT - Summary of Long-Term Debt Issuance and Repayments (Details) - USD ($) $ in Thousands	1 Months Ended							9 Months Ended
	Nov. 30, 2023	Sep. 30, 2023	Aug. 31, 2023	Jul. 31, 2023	May 31, 2023	Mar. 31, 2023	Jan. 31, 2023	Sep. 30, 2023	Sep. 30, 2022
Debt Instrument [Line Items]
Retirement of Long-Term Debt								$ (1,203,000)	$ (775,000)
CL&P
Debt Instrument [Line Items]
Retirement of Long-Term Debt								$ (400,000)	$ 0
CL&P | First Mortgage | CL&P 2023 Series A First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)							5.25%
Issuances							$ 500,000
CL&P | First Mortgage | CL&P 2013 Series A First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)							2.50%
Retirement of Long-Term Debt							$ (400,000)
CL&P | First Mortgage | CL&P 2023 Series B First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)				4.90%
Issuances				$ 300,000
PSNH | First Mortgage | PSNH Series W First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)							5.15%
Issuances							$ 300,000
PSNH | First Mortgage | PSNH Series X First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)		5.35%						5.35%
Issuances		$ 300,000
PSNH | First Mortgage | PSNH Series S First Mortgage Bonds | Subsequent Event | Forecast
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)	3.50%
Retirement of Long-Term Debt	$ (325,000)
Yankee Gas | First Mortgage | Yankee Gas Series V First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)			5.51%
Issuances			$ 170,000
Aquarion Water Company Of Connecticut | Senior Notes | Aquarion Water Company of Connecticut Senior Notes
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)		5.89%						5.89%
Issuances		$ 50,000
NSTAR Electric | Debentures | NSTAR Electric 2023 Debentures
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)		5.60%						5.60%
Issuances		$ 150,000
Eversource Parent | Senior Notes | Eversource Parent Series Z Senior Notes
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)					5.45%	5.45%
Issuances					$ 550,000	$ 750,000
Eversource Parent | Senior Notes | Eversource Parent Series F Senior Notes
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)					2.80%
Retirement of Long-Term Debt					$ (450,000)
Eversource Parent | Senior Notes | Eversource Parent Series AA Senior Notes
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)					4.75%
Issuances					$ 450,000
Eversource Parent | Senior Notes | Eversource Parent Series BB Senior Notes
Debt Instrument [Line Items]
Interest rate, stated percentage (in percent)					5.125%
Issuances					$ 800,000
Eversource Parent | Senior Notes | Eversource Parent Variable Rate Series T Senior Notes
Debt Instrument [Line Items]
Retirement of Long-Term Debt			$ (350,000)
Eversource Parent | Senior Notes | Eversource Parent Variable Rate Series T Senior Notes | Secured Overnight Financing Rate (SOFR)
Debt Instrument [Line Items]
Basis spread on variable rate (in percent)			0.25%