SHORT-TERM DEBT - Schedule of Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024
Line of Credit Facility [Line Items]
Borrowings Outstanding as of December 31,	$ 1,525,445	$ 2,042,793
Eversource Parent Commercial Paper Program
Line of Credit Facility [Line Items]
Borrowings Outstanding as of December 31,	1,280,000	1,538,011
Commercial Paper | Eversource Parent Commercial Paper Program
Line of Credit Facility [Line Items]
Borrowings Outstanding as of December 31,	1,280,000	1,538,000
Available Borrowing Capacity as of December 31,	$ 720,000	$ 462,000
Weighted-Average Interest Rate as of December 31,	3.98%	4.76%
Commercial Paper | NSTAR Electric
Line of Credit Facility [Line Items]
Borrowings Outstanding as of December 31,	$ 245,400	$ 504,800
Available Borrowing Capacity as of December 31,	$ 404,600	$ 145,200
Weighted-Average Interest Rate as of December 31,	3.87%	4.55%