SHORT-TERM DEBT - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 18, 2023	Nov. 30, 2023
Short-term Debt [Line Items]
Long-Term Debt	$ 23,588,616,000	$ 19,723,994,000
Eversource
Short-term Debt [Line Items]
Long-Term Debt	9,952,351,000	6,972,804,000
Commercial Paper
Short-term Debt [Line Items]
Long-Term Debt	990,900,000
Commercial Paper | Eversource
Short-term Debt [Line Items]
Maximum borrowing capacity	2,000,000,000
Line of Credit
Short-term Debt [Line Items]
Amount outstanding during period	0	0
Line of Credit | Eversource
Short-term Debt [Line Items]
Maximum borrowing capacity	$ 2,000,000,000
Debt instrument term (in years)	5 years
CL&P
Short-term Debt [Line Items]
Short-term borrowing limit approved by regulatory agency				$ 600,000,000
Long-Term Debt	$ 4,814,429,000	4,216,488,000
Notes payable	249,670,000	0
CL&P | Related Party
Short-term Debt [Line Items]
Long-Term Debt	207,300,000
Notes payable	$ 457,000,000
CL&P | Unsecured Debt
Short-term Debt [Line Items]
Period of maturity restricting provisions of debt	10 years
Total capitalization (as a percentage)	10.00%
Capacity available under preferred stock provisions	$ 625,700,000
CL&P | Commercial Paper
Short-term Debt [Line Items]
Long-Term Debt	139,800,000	400,000,000
CL&P | Commercial Paper
Short-term Debt [Line Items]
Long-Term Debt	207,300,000
CL&P | Line of Credit
Short-term Debt [Line Items]
Maximum borrowing capacity	375,000,000
Borrowings outstanding	0
NSTAR Electric
Short-term Debt [Line Items]
Short-term borrowing limit approved by regulatory agency			$ 655,000,000
Long-Term Debt	4,496,947,000	4,345,085,000
Notes payable	365,847,000	0
NSTAR Electric | Unsecured Debt
Short-term Debt [Line Items]
Long-Term Debt	4,400,000,000	4,250,000,000
NSTAR Electric | Commercial Paper
Short-term Debt [Line Items]
Maximum borrowing capacity	650,000,000
NSTAR Electric | Line of Credit
Short-term Debt [Line Items]
Maximum borrowing capacity	$ 650,000,000
Debt instrument term (in years)	5 years
PSNH
Short-term Debt [Line Items]
Short-term borrowing limit approved by regulatory agency	$ 483,200,000
Long-Term Debt	1,431,591,000	1,134,914,000
Notes payable	233,000,000	173,300,000
PSNH | Related Party
Short-term Debt [Line Items]
Notes payable	$ 233,000,000	173,300,000
PSNH | Commercial Paper
Short-term Debt [Line Items]
Long-Term Debt		$ 295,300,000
PSNH | Short Term Debt Authorization Calculation
Short-term Debt [Line Items]
Interest rate	10.00%
Short-term debt borrowing calculation approved by regulatory agency	$ 60,000,000
PSNH | Line of Credit
Short-term Debt [Line Items]
Maximum borrowing capacity	$ 250,000,000