SHORT-TERM AND LONG-TERM DEBT - Narrative (Details) - USD ($)			9 Months Ended
	Oct. 15, 2022	Sep. 15, 2022	Sep. 30, 2022	Sep. 30, 2021	Jun. 14, 2022	Dec. 31, 2021
Line of Credit Facility [Line Items]
Proceeds from long-term debt issuance			$ 4,045,000,000	$ 3,150,000,000
Payment of long-term debt			775,000,000	1,142,500,000
NSTAR Electric
Line of Credit Facility [Line Items]
Notes payable to Eversource parent			2,800,000
Proceeds from long-term debt issuance		$ 400,000,000	850,000,000	600,000,000
Payment of long-term debt			0	250,000,000
NSTAR Electric | Subsequent Event
Line of Credit Facility [Line Items]
Payment of long-term debt	$ 400,000,000
CL&P
Line of Credit Facility [Line Items]
Notes payable to Eversource parent			26,000,000
Proceeds from long-term debt issuance			0	425,000,000
Payment of long-term debt			0	120,500,000
PSNH
Line of Credit Facility [Line Items]
Notes payable to Eversource parent			139,700,000			$ 110,600,000
Proceeds from long-term debt issuance			0	350,000,000
Payment of long-term debt			0	$ 282,000,000
Line of Credit | CL&P
Line of Credit Facility [Line Items]
Maximum borrowing capacity			450,000,000
Amount outstanding under line of credit			0
Line of Credit | PSNH
Line of Credit Facility [Line Items]
Maximum borrowing capacity			300,000,000
Amount outstanding under line of credit			0
Line of Credit | NSTAR Gas
Line of Credit Facility [Line Items]
Maximum borrowing capacity					$ 325,000,000
Commercial Paper | NSTAR Electric
Line of Credit Facility [Line Items]
Maximum borrowing capacity			650,000,000
Line of Credit
Line of Credit Facility [Line Items]
Amount outstanding under line of credit			0			$ 0
Line of Credit | NSTAR Electric
Line of Credit Facility [Line Items]
Maximum borrowing capacity			650,000,000
Eversource Parent | Commercial Paper
Line of Credit Facility [Line Items]
Maximum borrowing capacity			2,000,000,000
Eversource Parent | Line of Credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity			$ 2,000,000,000
Debt instrument term			5 years
NSTAR Electric | Line of Credit | NSTAR Electric
Line of Credit Facility [Line Items]
Debt instrument term			5 years