SHORT-TERM AND LONG-TERM DEBT - Narrative (Details) - USD ($)	9 Months Ended
	Sep. 30, 2024	Aug. 12, 2024	Jul. 24, 2024	May 01, 2024	Feb. 08, 2024	Dec. 31, 2023
Line of Credit Facility [Line Items]
Long-Term Debt	$ 25,971,408,000					$ 23,588,616,000
NSTAR Electric
Line of Credit Facility [Line Items]
Long-Term Debt	5,093,701,000					4,496,947,000
CL&P
Line of Credit Facility [Line Items]
Long-Term Debt	5,110,791,000					4,814,429,000
Notes payable to Eversource parent	135,000,000					249,670,000
CL&P | Related Party
Line of Credit Facility [Line Items]
Long-Term Debt						207,300,000
Notes payable to Eversource parent	135,000,000.0					457,000,000.0
PSNH
Line of Credit Facility [Line Items]
Long-Term Debt	1,731,764,000					1,431,591,000
Notes payable to Eversource parent	89,300,000					233,000,000
PSNH | Related Party
Line of Credit Facility [Line Items]
Notes payable to Eversource parent	89,300,000					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		$ 1,000,000,000
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
Line of Credit | Eversource Gas Company of Massachusetts
Line of Credit Facility [Line Items]
Maximum borrowing capacity		$ 325,000,000
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 | Eversource Gas Company of Massachusetts
Line of Credit Facility [Line Items]
Long-Term Debt	100,000,000
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	2,000,000,000.00
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