LEASES - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Lessee, Lease, Description [Line Items]
Right-of-use assets in exchange for the assumption of new operating lease liabilities	$ 18.9	$ 2.1	$ 0.6
Right-of-use assets in exchange for the assumption of new finance lease liabilities	$ 3.5	2.3	0.7
CMA
Lessee, Lease, Description [Line Items]
Right-of-use assets in exchange for the assumption of new operating lease liabilities			14.7
Right-of-use assets in exchange for the assumption of new finance lease liabilities			54.2
Minimum
Lessee, Lease, Description [Line Items]
Renewal period	1 year
Maximum
Lessee, Lease, Description [Line Items]
Renewal period	20 years
CL&P
Lessee, Lease, Description [Line Items]
Right-of-use assets in exchange for the assumption of new operating lease liabilities	$ 2.4	0.0	0.1
Right-of-use assets in exchange for the assumption of new finance lease liabilities	$ 0.0	0.0	0.0
CL&P | Minimum
Lessee, Lease, Description [Line Items]
Renewal period	1 year
CL&P | Maximum
Lessee, Lease, Description [Line Items]
Renewal period	20 years
NSTAR Electric
Lessee, Lease, Description [Line Items]
Right-of-use assets in exchange for the assumption of new operating lease liabilities	$ 0.0	1.9	0.2
Right-of-use assets in exchange for the assumption of new finance lease liabilities	$ 0.0	0.0	0.3
NSTAR Electric | Minimum
Lessee, Lease, Description [Line Items]
Renewal period	1 year
NSTAR Electric | Maximum
Lessee, Lease, Description [Line Items]
Renewal period	20 years
PSNH
Lessee, Lease, Description [Line Items]
Right-of-use assets in exchange for the assumption of new operating lease liabilities	$ 0.0	0.0	0.0
Right-of-use assets in exchange for the assumption of new finance lease liabilities	$ 0.0	$ 0.0	$ 0.0
PSNH | Minimum
Lessee, Lease, Description [Line Items]
Renewal period	1 year
PSNH | Maximum
Lessee, Lease, Description [Line Items]
Renewal period	20 years