SHORT-TERM AND LONG-TERM DEBT - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2022	Dec. 31, 2021
NSTAR Electric
Line of Credit Facility [Line Items]
Notes payable to Eversource parent	$ 4,000,000
PSNH
Line of Credit Facility [Line Items]
Notes payable to Eversource parent	196,400,000	$ 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
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