SHORT-TERM AND LONG-TERM DEBT - Narrative (Details)	1 Months Ended	3 Months Ended
	Jun. 30, 2024 USD ($)	Mar. 31, 2024 USD ($) bond	May 01, 2024 USD ($)	Feb. 08, 2024 USD ($)	Dec. 31, 2023 USD ($)
Line of Credit Facility [Line Items]
Long-Term Debt		$ 24,929,813,000			$ 23,588,616,000
Long-term debt, current maturities classified as noncurrent		1,390,000,000
NSTAR Electric
Line of Credit Facility [Line Items]
Long-Term Debt		4,497,954,000			4,496,947,000
CL&P
Line of Credit Facility [Line Items]
Long-Term Debt		4,814,040,000			4,814,429,000
Notes payable to Eversource parent		426,100,000			249,670,000
CL&P | Related Party
Line of Credit Facility [Line Items]
Long-Term Debt					207,300,000
Notes payable to Eversource parent		426,100,000			457,000,000
PSNH
Line of Credit Facility [Line Items]
Long-Term Debt		1,682,679,000			1,431,591,000
Notes payable to Eversource parent		0			233,000,000
PSNH | Related Party
Line of Credit Facility [Line Items]
Long-Term Debt		251,000,000
Notes payable to Eversource parent		$ 251,000,000			233,000,000
NSTAR Gas | First Mortgage
Line of Credit Facility [Line Items]
Number of first mortgage bonds closed | bond		2
NSTAR Gas | First Mortgage | NSTAR Gas, First Mortgage Bonds, Series W | Forecast
Line of Credit Facility [Line Items]
Issuances	$ 160,000,000
NSTAR Gas | First Mortgage | NSTAR Gas, First Mortgage Bonds, Series X | Forecast
Line of Credit Facility [Line Items]
Issuances	$ 40,000,000
Line of Credit | NSTAR Electric | Subsequent Event
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 | 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 | PSNH
Line of Credit Facility [Line Items]
Long-Term Debt		251,000,000
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