LEASES - Other Information Related to Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Weighted-Average Remaining Lease Term (Years):
Operating Leases	9 years	9 years
Finance Leases	9 years	12 years
Weighted-Average Discount Rate (Percentage):
Operating Leases	4.10%	4.10%
Finance Leases	3.50%	3.30%
Cash Paid for Amounts Included in the Measurement of Lease Liabilities:
Operating Cash Flows from Operating Leases	$ 12.8	$ 14.5	$ 10.5
Operating Cash Flows from Finance Leases	2.8	2.6	2.0
Financing Cash Flows from Finance Leases	5.7	5.2	3.9
Supplemental Non-Cash Information on Lease Liabilities:
Right-of-use-Assets Obtained in Exchange for New Operating Lease Liabilities	1.4	15.3	12.8
Right-of-use-Assets Obtained in Exchange for New Finance Lease Liabilities	$ 19.7	$ 0.3	18.5
CL&P
Weighted-Average Remaining Lease Term (Years):
Operating Leases	3 years	4 years
Finance Leases	7 years	8 years
Weighted-Average Discount Rate (Percentage):
Operating Leases	5.30%	5.20%
Finance Leases	5.30%	5.30%
Cash Paid for Amounts Included in the Measurement of Lease Liabilities:
Operating Cash Flows from Operating Leases	$ 2.8	$ 2.5	0.7
Operating Cash Flows from Finance Leases	0.9	0.7	0.0
Financing Cash Flows from Finance Leases	1.5	1.2	0.0
Supplemental Non-Cash Information on Lease Liabilities:
Right-of-use-Assets Obtained in Exchange for New Operating Lease Liabilities	0.8	7.8	0.6
Right-of-use-Assets Obtained in Exchange for New Finance Lease Liabilities	$ 0.0	$ 0.0	18.3
NSTAR Electric
Weighted-Average Remaining Lease Term (Years):
Operating Leases	12 years	12 years
Finance Leases	16 years	17 years
Weighted-Average Discount Rate (Percentage):
Operating Leases	4.20%	4.20%
Finance Leases	2.90%	2.90%
Cash Paid for Amounts Included in the Measurement of Lease Liabilities:
Operating Cash Flows from Operating Leases	$ 5.0	$ 4.9	2.5
Operating Cash Flows from Finance Leases	0.7	0.7	0.6
Financing Cash Flows from Finance Leases	0.0	0.0	0.0
Supplemental Non-Cash Information on Lease Liabilities:
Right-of-use-Assets Obtained in Exchange for New Operating Lease Liabilities	0.1	5.7	7.0
Right-of-use-Assets Obtained in Exchange for New Finance Lease Liabilities	$ 0.0	$ 0.0	0.0
PSNH
Weighted-Average Remaining Lease Term (Years):
Operating Leases	2 years	2 years
Finance Leases	4 years
Weighted-Average Discount Rate (Percentage):
Operating Leases	5.10%	5.20%
Finance Leases	4.60%	0.00%
Cash Paid for Amounts Included in the Measurement of Lease Liabilities:
Operating Cash Flows from Operating Leases	$ 1.9	$ 1.8	0.4
Operating Cash Flows from Finance Leases	0.0	0.0	0.0
Financing Cash Flows from Finance Leases	0.2	0.0	0.0
Supplemental Non-Cash Information on Lease Liabilities:
Right-of-use-Assets Obtained in Exchange for New Operating Lease Liabilities	0.1	0.3	5.0
Right-of-use-Assets Obtained in Exchange for New Finance Lease Liabilities	$ 0.7	$ 0.0	$ 0.0