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. 15, 2022	Oct. 31, 2022	Sep. 30, 2022	Aug. 31, 2022	Jul. 31, 2022	Jun. 30, 2022	May 31, 2022	Mar. 31, 2022	Feb. 28, 2022	Sep. 30, 2022	Sep. 30, 2021
Debt Instrument [Line Items]
Retirement of Long-Term Debt										$ (775,000)	$ (1,142,500)
NSTAR Electric
Debt Instrument [Line Items]
Retirement of Long-Term Debt										$ 0	$ (250,000)
NSTAR Electric | Subsequent Event
Debt Instrument [Line Items]
Retirement of Long-Term Debt	$ (400,000)
NSTAR Electric | Debentures | NSTAR Electric 4.55% 2022 Debentures
Debt Instrument [Line Items]
Interest rate, stated percentage							4.55%
Issuances							$ 450,000
NSTAR Electric | Debentures | NSTAR Electric 4.95% 2022 Debentures
Debt Instrument [Line Items]
Interest rate, stated percentage			4.95%							4.95%
Issuances			$ 400,000
NSTAR Electric | Debentures | NSTAR Electric 2.375% 2012 Debentures | Subsequent Event
Debt Instrument [Line Items]
Interest rate, stated percentage		2.375%
Retirement of Long-Term Debt		$ (400,000)
Yankee Gas | First Mortgage | Yankee Gas 8.48% Series B First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage								8.48%
Retirement of Long-Term Debt								$ (20,000)
Yankee Gas | First Mortgage | Yankee Gas 4.31% Series U First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage			4.31%							4.31%
Issuances			$ 100,000
EGMA | First Mortgage | EGMA 4.70% Series C First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage						4.70%
Issuances						$ 100,000
NSTAR Gas | First Mortgage | NSTAR Gas 4.40% Series V First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage					4.40%
Issuances					$ 125,000
Aquarian Water Company | Senior Notes | Aquarion Water Company of Connecticut 4.69% Senior Notes
Debt Instrument [Line Items]
Interest rate, stated percentage				4.69%
Issuances				$ 70,000
Aquarian Water Company | General Mortgage Bonds | Aquarion Water Company of New Hampshire 4.45% General Mortgage Bonds
Debt Instrument [Line Items]
Interest rate, stated percentage					4.45%
Retirement of Long-Term Debt					$ (5,000)
Eversource Parent | Senior Notes | Eversource Parent 2.90% Series V Senior Notes
Debt Instrument [Line Items]
Interest rate, stated percentage									2.90%
Issuances									$ 650,000
Eversource Parent | Senior Notes | Eversource Parent 3.375% Series W Senior Notes
Debt Instrument [Line Items]
Interest rate, stated percentage									3.375%
Issuances									$ 650,000
Eversource Parent | Senior Notes | Eversource Parent 4.20% Series X Senior Notes
Debt Instrument [Line Items]
Interest rate, stated percentage						4.20%
Issuances						$ 900,000
Eversource Parent | Senior Notes | Eversource Parent 4.60% Series Y Senior Notes
Debt Instrument [Line Items]
Interest rate, stated percentage						4.60%
Issuances						$ 600,000
Eversource Parent | Senior Notes | Eversource Parent 2.75% Series K Senior Notes
Debt Instrument [Line Items]
Interest rate, stated percentage								2.75%
Retirement of Long-Term Debt								$ (750,000)