LEASES - Components of Lease Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Lease, Cost [Abstract]
Amortization of Right-of-use-Assets	$ 9.5	$ 6.4	$ 4.8
Interest on Lease Liabilities	2.9	2.7	2.0
Total Finance Lease Cost	12.4	9.1	6.8
Operating Lease Cost	13.0	15.2	11.4
Variable Lease Cost	18.6	18.3	69.2
Total Lease Cost	44.0	42.6	87.4
CL&P
Lease, Cost [Abstract]
Amortization of Right-of-use-Assets	2.0	1.7	0.0
Interest on Lease Liabilities	0.9	0.8	0.0
Total Finance Lease Cost	2.9	2.5	0.0
Operating Lease Cost	2.8	2.6	0.7
Variable Lease Cost	18.6	18.9	21.9
Total Lease Cost	24.3	24.0	22.6
NSTAR Electric
Lease, Cost [Abstract]
Amortization of Right-of-use-Assets	0.2	0.2	0.2
Interest on Lease Liabilities	0.6	0.6	0.6
Total Finance Lease Cost	0.8	0.8	0.8
Operating Lease Cost	5.1	5.3	3.0
Variable Lease Cost	0.0	0.0	0.0
Total Lease Cost	5.9	6.1	3.8
PSNH
Lease, Cost [Abstract]
Amortization of Right-of-use-Assets	0.1	0.0	0.0
Interest on Lease Liabilities	0.0	0.0	0.0
Total Finance Lease Cost	0.1	0.0	0.0
Operating Lease Cost	1.9	1.8	0.4
Variable Lease Cost	0.0		47.3
Variable Lease Cost		(0.6)
Total Lease Cost	$ 2.0	$ 1.2	$ 47.7