LEASES - Components of Lease Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Lease, Cost [Abstract]
Amortization of Right-of-use-Assets	$ 8.3	$ 4.6	$ 2.6
Interest on Lease Liabilities	2.0	3.9	1.4
Total Finance Lease Cost	10.3	8.5	4.0
Operating Lease Cost	11.6	12.2	11.1
Variable Lease Cost	78.1	61.0	57.8
Total Lease Cost	100.0	81.7	72.9
CL&P
Lease, Cost [Abstract]
Amortization of Right-of-use-Assets	0.0	0.5	0.7
Interest on Lease Liabilities	0.0	0.1	0.3
Total Finance Lease Cost	0.0	0.6	1.0
Operating Lease Cost	0.3	0.3	0.6
Variable Lease Cost	25.6	16.2	12.2
Total Lease Cost	25.9	17.1	13.8
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	2.3	2.3	2.1
Variable Lease Cost	0.0	0.0	0.0
Total Lease Cost	3.1	3.1	2.9
PSNH
Lease, Cost [Abstract]
Amortization of Right-of-use-Assets	0.1	0.1	0.1
Interest on Lease Liabilities	0.0	0.0	0.0
Total Finance Lease Cost	0.1	0.1	0.1
Operating Lease Cost	0.1	0.1	0.1
Variable Lease Cost	52.5	44.8	45.6
Total Lease Cost	$ 52.7	$ 45.0	$ 45.8