SHORT-TERM AND LONG-TERM DEBT - Narrative (Details) - USD ($)	9 Months Ended
	Sep. 30, 2023	Jun. 07, 2023	Dec. 31, 2022
CL&P
Line of Credit Facility [Line Items]
Notes payable to Eversource parent	$ 213,400,000		$ 0
CL&P | Related Party
Line of Credit Facility [Line Items]
Notes payable to Eversource parent	213,400,000
PSNH
Line of Credit Facility [Line Items]
Notes payable to Eversource parent	100,000		173,300,000
PSNH | Related Party
Line of Credit Facility [Line Items]
Notes payable to Eversource parent	100,000		173,300,000
Line of Credit | CL&P
Line of Credit Facility [Line Items]
Maximum borrowing capacity	375,000,000
Amount outstanding under line of credit	0
Line of Credit | PSNH
Line of Credit Facility [Line Items]
Maximum borrowing capacity	250,000,000
Amount outstanding under line of credit	0
Line of Credit | Yankee Gas
Line of Credit Facility [Line Items]
Maximum borrowing capacity		$ 350,000,000
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 (in years)	5 years
NSTAR Electric | Line of Credit | NSTAR Electric
Line of Credit Facility [Line Items]
Debt instrument term (in years)	5 years