SHORT-TERM AND LONG-TERM DEBT - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2026	Mar. 03, 2026	Dec. 31, 2025
CL&P
Line of Credit Facility [Line Items]
Notes payable to Eversource parent	$ 39,000,000		$ 0
CL&P | Related Party
Line of Credit Facility [Line Items]
Notes payable to Eversource parent	39,000,000.0
CL&P | Line of Credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity	375,000,000
Amount outstanding under line of credit	0		0
PSNH
Line of Credit Facility [Line Items]
Notes payable to Eversource parent	79,400,000		49,300,000
PSNH | Related Party
Line of Credit Facility [Line Items]
Notes payable to Eversource parent	79,400,000		49,300,000
PSNH | Line of Credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity	250,000,000	$ 200,000,000.0
Amount outstanding under line of credit	0		0
Commercial Paper | NSTAR Electric
Line of Credit Facility [Line Items]
Maximum borrowing capacity	650,000,000
Line of Credit | NSTAR Electric
Line of Credit Facility [Line Items]
Maximum borrowing capacity	650,000,000
Eversource Parent Commercial Paper Program | Commercial Paper
Line of Credit Facility [Line Items]
Maximum borrowing capacity	2,000,000,000.00
Eversource Parent Commercial Paper Program | Line of Credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 2,000,000,000.00
Debt instrument term (in years)	5 years
Debt instrument, extension term	1 year
NSTAR Electric | Line of Credit | NSTAR Electric
Line of Credit Facility [Line Items]
Debt instrument term (in years)	5 years
NSTAR Electric and Eversource | Line of Credit
Line of Credit Facility [Line Items]
Amount outstanding under line of credit	$ 0		$ 0