SHORT-TERM AND LONG-TERM DEBT - Narrative (Details) - USD ($)	6 Months Ended
	Jun. 30, 2022	Jun. 14, 2022	Dec. 31, 2021
Commercial Paper
Line of Credit Facility [Line Items]
Long-term debt	$ 88,700,000
NSTAR Electric
Line of Credit Facility [Line Items]
Notes payable to Eversource parent	3,200,000
CL&P
Line of Credit Facility [Line Items]
Notes payable to Eversource parent	67,500,000
PSNH
Line of Credit Facility [Line Items]
Notes payable to Eversource parent	89,300,000		$ 110,600,000
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