LONG-TERM DEBT - Schedule of Issuances and Repayments (Details) - USD ($) $ in Thousands		1 Months Ended								12 Months Ended
	Aug. 13, 2021	Oct. 31, 2021	Sep. 30, 2021	Aug. 31, 2021	Jun. 30, 2021	Apr. 30, 2021	Mar. 31, 2021	Feb. 28, 2021	May 31, 2020	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	May 31, 2021
Debt Instrument [Line Items]
Repayments of debt										$ (1,142,500)	$ (327,236)	$ (801,078)
Senior Notes
Debt Instrument [Line Items]
Long-term debt										17,023,600	15,125,900
The Connecticut Light and Power Company
Debt Instrument [Line Items]
Repayments of debt										$ (120,500)	0	(250,000)
The Connecticut Light and Power Company | Senior Notes | 4.38% Series A PCRB
Debt Instrument [Line Items]
Interest rate			4.38%							4.375%
Repayments of debt			$ (120,500)
The Connecticut Light and Power Company | PSNH 4.050% Series Q First Mortgage Bond
Debt Instrument [Line Items]
Long-term debt										$ 4,215,400	3,914,800
The Connecticut Light and Power Company | PSNH 4.050% Series Q First Mortgage Bond | 2.050% 2021 Series A due 2031
Debt Instrument [Line Items]
Interest rate										2.05%
Issuance					$ 425,000
NSTAR Electric Company
Debt Instrument [Line Items]
Repayments of debt										$ (250,000)	(95,000)	0
NSTAR Electric Company | Senior Notes | 3.500% Senior Notes Series F due 2021
Debt Instrument [Line Items]
Interest rate					3.50%
Repayments of debt					$ (250,000)
NSTAR Electric Company | Unsecured Debt [Member]
Debt Instrument [Line Items]
Long-term debt										3,585,400	3,393,200
NSTAR Electric Company | Unsecured Debt [Member] | 3.100% due 2051
Debt Instrument [Line Items]
Interest rate													3.10%
Issuance									$ 300,000
NSTAR Electric Company | Unsecured Debt [Member] | 1.950% due 2031
Debt Instrument [Line Items]
Interest rate				1.95%
Issuance				$ 300,000
Public Service Company of New Hampshire
Debt Instrument [Line Items]
Repayments of debt										(282,000)	0	(150,000)
Public Service Company of New Hampshire | PSNH 4.050% Series Q First Mortgage Bond
Debt Instrument [Line Items]
Long-term debt										$ 1,163,800	817,100
Public Service Company of New Hampshire | PSNH 4.050% Series Q First Mortgage Bond | 4.050% Series Q due 2021
Debt Instrument [Line Items]
Interest rate							4.05%
Repayments of debt							$ (122,000)
Public Service Company of New Hampshire | PSNH 4.050% Series Q First Mortgage Bond | 3.200% Series R due 2021
Debt Instrument [Line Items]
Interest rate					3.20%
Repayments of debt					$ (160,000)
Public Service Company of New Hampshire | PSNH 4.050% Series Q First Mortgage Bond | 2.200% Series V due 2031
Debt Instrument [Line Items]
Interest rate					2.20%
Issuance					$ 350,000
Aquarion | Senior Notes | Aquarion Water Company of Connecticut 3.31% Senior Notes
Debt Instrument [Line Items]
Interest rate						3.31%
Issuance						$ 100,000
Aquarion | Senior Notes | Aquarion Water Company of Connecticut 5.50% Notes
Debt Instrument [Line Items]
Interest rate						5.50%
Repayments of debt						$ (40,000)
Yankee Gas | Senior Notes | Yankee Gas 2.88% Series T First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate				2.88%
Issuance				$ 35,000
Yankee Gas | PSNH 4.050% Series Q First Mortgage Bond | Yankee Gas - First Mortgage Bonds: 1.380% - 8.480% due 2022 - 2051
Debt Instrument [Line Items]
Issuance				$ 90,000
Yankee Gas | PSNH 4.050% Series Q First Mortgage Bond | Yankee Gas - First Mortgage Bonds: 1.380% - 8.480% due 2022 - 2051 | Minimum
Debt Instrument [Line Items]
Interest rate										1.38%
EGMA | Senior Notes
Debt Instrument [Line Items]
Refinanced amount										$ 309,400
EGMA | Senior Notes | EGMA 2.11% Series A First Mortgage Bonds
Debt Instrument [Line Items]
Issuance			310,000
EGMA | Senior Notes | EGMA 2.92% Series B First Mortgage Bonds
Debt Instrument [Line Items]
Issuance			$ 240,000
NSTAR Gas | Senior Notes | NSTAR Gas 3.03% Series U First Mortgage Bonds
Debt Instrument [Line Items]
Interest rate		3.03%
Issuance		$ 40,000
NSTAR Gas | PSNH 4.050% Series Q First Mortgage Bond | NSTAR Gas - First Mortgage Bonds: 2.250% - 7.110% due 2025 - 2051
Debt Instrument [Line Items]
Issuance		$ 40,000
NSTAR Gas | PSNH 4.050% Series Q First Mortgage Bond | NSTAR Gas - First Mortgage Bonds: 2.250% - 7.110% due 2025 - 2051 | Minimum
Debt Instrument [Line Items]
Interest rate		2.25%
Eversource
Debt Instrument [Line Items]
Repayments of debt										$ (450,000)	$ 0	$ (350,000)
Eversource | Senior Notes | Eversource Parent 2.50% Series I Senior Notes
Debt Instrument [Line Items]
Interest rate								2.50%
Repayments of debt								$ (450,000)
Eversource | Senior Notes | Eversource Parent 2.55% Series S Senior Notes
Debt Instrument [Line Items]
Interest rate							2.55%
Issuance							$ 350,000
Eversource | Senior Notes | Eversource Parent 1.40% Series U Senior Notes
Debt Instrument [Line Items]
Interest rate				1.40%
Issuance				$ 300,000
Eversource | Senior Notes | Eversource Parent Variable Rate Series T Senior Notes
Debt Instrument [Line Items]
Interest rate										0.30%
Issuance	$ 350,000			$ 350,000
Eversource | Senior Notes | Eversource Parent Variable Rate Series T Senior Notes | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate
Debt Instrument [Line Items]
Basis spread on compounded SOFR	0.25%