LEASES - Supplemental Balance Sheet Information Related to Leases (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Operating Leases:
Right-of-use-Assets, Net	$ 56.9	$ 47.2
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Other Long-Term Assets	Other Long-Term Assets
Current Portion	$ 9.0	$ 10.0
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Other Current Liabilities	Other Current Liabilities
Long-Term	$ 47.9	$ 37.2
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Other Long-Term Liabilities	Other Long-Term Liabilities
Total Operating Lease Liabilities	$ 56.9	$ 47.2
Finance Leases:
Right-of-use-Assets, Net	$ 54.5	$ 58.0
Finance Lease, Right-of-Use Asset, Statement of Financial Position [Extensible Enumeration]	Property, Plant and Equipment, Net	Property, Plant and Equipment, Net
Current Portion	$ 3.8	$ 3.9
Finance Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Other Current Liabilities	Other Current Liabilities
Long-Term	$ 54.2	$ 55.4
Finance Lease, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Other Long-Term Liabilities	Other Long-Term Liabilities
Total Finance Lease Liabilities	$ 58.0	$ 59.3
CL&P
Operating Leases:
Right-of-use-Assets, Net	2.2	0.1
Current Portion	0.6	0.1
Long-Term	1.6	0.0
Total Operating Lease Liabilities	2.2	0.1
Finance Leases:
Right-of-use-Assets, Net	0.0	0.0
Current Portion	0.0	0.0
Long-Term	0.0	0.0
Total Finance Lease Liabilities	0.0	0.0
NSTAR Electric
Operating Leases:
Right-of-use-Assets, Net	22.5	24.3
Current Portion	1.2	1.1
Long-Term	21.3	23.2
Total Operating Lease Liabilities	22.5	24.3
Finance Leases:
Right-of-use-Assets, Net	3.2	3.3
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	0.0	0.3
Current Portion	0.0	0.0
Long-Term	0.0	0.3
Total Operating Lease Liabilities	0.0	0.3
Finance Leases:
Right-of-use-Assets, Net	0.0	0.7
Current Portion	0.0	0.1
Long-Term	0.0	0.6
Total Finance Lease Liabilities	$ 0.0	$ 0.7