LEASES - Supplemental Balance Sheet Information Related to Leases (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Operating Leases:
Right-of-use-Assets, Net	$ 47.4	$ 56.1
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Other Long-Term Assets	Other Long-Term Assets
Current Portion	$ 10.0	$ 10.4
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Other Current Liabilities	Other Current Liabilities
Long-Term	$ 37.4	$ 45.7
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Other Long-Term Liabilities	Other Long-Term Liabilities
Total Operating Lease Liabilities	$ 47.4	$ 56.1
Finance Leases:
Right-of-use-Assets, Net	$ 76.6	$ 61.9
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Property, Plant and Equipment, Net	Property, Plant and Equipment, Net
Current Portion	$ 24.5	$ 5.6
Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Other Current Liabilities	Other Current Liabilities
Long-Term	$ 57.2	$ 62.1
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Other Long-Term Liabilities	Other Long-Term Liabilities
Total Finance Lease Liabilities	$ 81.7	$ 67.7
CL&P
Operating Leases:
Right-of-use-Assets, Net	6.1	7.7
Current Portion	2.3	2.2
Long-Term	3.8	5.5
Total Operating Lease Liabilities	6.1	7.7
Finance Leases:
Right-of-use-Assets, Net	14.6	16.6
Current Portion	1.6	1.5
Long-Term	14.0	15.6
Total Finance Lease Liabilities	15.6	17.1
NSTAR Electric
Operating Leases:
Right-of-use-Assets, Net	27.2	29.4
Current Portion	3.9	3.7
Long-Term	23.3	25.7
Total Operating Lease Liabilities	27.2	29.4
Finance Leases:
Right-of-use-Assets, Net	2.6	2.8
Current Portion	0.0	0.0
Long-Term	4.9	4.9
Total Finance Lease Liabilities	4.9	4.9
PSNH
Operating Leases:
Right-of-use-Assets, Net	1.5	3.3
Current Portion	1.5	1.7
Long-Term	0.0	1.6
Total Operating Lease Liabilities	1.5	3.3
Finance Leases:
Right-of-use-Assets, Net	0.6	0.0
Current Portion	0.1	0.0
Long-Term	0.4	0.0
Total Finance Lease Liabilities	$ 0.5	$ 0.0