LEASES - Narrative (Details)	12 Months Ended
	Dec. 31, 2019
Minimum
Lessee, Lease, Description [Line Items]
Renewal period	1 year
Maximum
Lessee, Lease, Description [Line Items]
Renewal period	20 years
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 | Minimum
Lessee, Lease, Description [Line Items]
Renewal period	1 year
NSTAR Electric | Maximum
Lessee, Lease, Description [Line Items]
Renewal period	20 years
PSNH | Minimum
Lessee, Lease, Description [Line Items]
Renewal period	1 year
PSNH | Maximum
Lessee, Lease, Description [Line Items]
Renewal period	20 years