SHORT-TERM AND LONG-TERM DEBT - Narrative (Details) - USD ($)	6 Months Ended
	Jun. 30, 2024	Jul. 24, 2024	May 01, 2024	Feb. 08, 2024	Dec. 31, 2023
Line of Credit Facility [Line Items]
Long-Term Debt	$ 25,836,078,000				$ 23,588,616,000
Long-term debt, current maturities classified as noncurrent	100,000,000
NSTAR Electric
Line of Credit Facility [Line Items]
Long-Term Debt	5,092,959,000				4,496,947,000
CL&P
Line of Credit Facility [Line Items]
Long-Term Debt	4,814,280,000				4,814,429,000
Notes payable to Eversource parent	407,800,000				249,670,000
CL&P | Related Party
Line of Credit Facility [Line Items]
Long-Term Debt					207,300,000
Notes payable to Eversource parent	407,800,000				457,000,000.0
PSNH
Line of Credit Facility [Line Items]
Long-Term Debt	1,731,461,000				1,431,591,000
Notes payable to Eversource parent	132,000,000				233,000,000
PSNH | Related Party
Line of Credit Facility [Line Items]
Notes payable to Eversource parent	132,000,000.0				233,000,000.0
Line of Credit | NSTAR Electric
Line of Credit Facility [Line Items]
Maximum borrowing capacity			$ 2,400,000,000
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 | CL&P | Subsequent Event
Line of Credit Facility [Line Items]
Maximum borrowing capacity		$ 1,000,000,000
Line of Credit | PSNH
Line of Credit Facility [Line Items]
Maximum borrowing capacity	250,000,000			$ 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
Commercial Paper | CL&P
Line of Credit Facility [Line Items]
Long-Term Debt					207,300,000
Commercial Paper | Yankee Gas
Line of Credit Facility [Line Items]
Long-Term Debt	37,900,000
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	2,000,000,000.00
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