LEASES - Other Information Related to Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Weighted-Average Remaining Lease Term (Years):
Operating Leases	11 years	13 years
Finance Leases	15 years	16 years
Weighted-Average Discount Rate (Percentage):
Operating Leases	3.20%	4.10%
Finance Leases	2.70%	2.70%
Cash Paid for Amounts Included in the Measurement of Lease Liabilities:
Operating Cash Flows from Operating Leases	$ 11.3	$ 12.1	$ 10.9
Operating Cash Flows from Finance Leases	2.0	3.4	1.7
Financing Cash Flows from Finance Leases	3.9	4.1	2.8
Supplemental Non-Cash Information on Lease Liabilities:
Right-of-use-Assets Obtained in Exchange for New Operating Lease Liabilities	18.9	2.1	0.6
Right-of-use-Assets Obtained in Exchange for New Finance Lease Liabilities	$ 3.5	$ 2.3	0.7
CL&P
Weighted-Average Remaining Lease Term (Years):
Operating Leases	4 years	7 years
Weighted-Average Discount Rate (Percentage):
Operating Leases	3.80%	3.00%
Finance Leases	0.00%	0.00%
Cash Paid for Amounts Included in the Measurement of Lease Liabilities:
Operating Cash Flows from Operating Leases	$ 0.3	$ 0.3	0.6
Operating Cash Flows from Finance Leases	0.0	0.1	0.3
Financing Cash Flows from Finance Leases	0.0	1.4	1.6
Supplemental Non-Cash Information on Lease Liabilities:
Right-of-use-Assets Obtained in Exchange for New Operating Lease Liabilities	2.4	0.0	0.1
Right-of-use-Assets Obtained in Exchange for New Finance Lease Liabilities	$ 0.0	$ 0.0	0.0
NSTAR Electric
Weighted-Average Remaining Lease Term (Years):
Operating Leases	17 years	18 years
Finance Leases	19 years	20 years
Weighted-Average Discount Rate (Percentage):
Operating Leases	4.00%	4.00%
Finance Leases	2.90%	2.90%
Cash Paid for Amounts Included in the Measurement of Lease Liabilities:
Operating Cash Flows from Operating Leases	$ 2.1	$ 2.1	1.8
Operating Cash Flows from Finance Leases	0.6	0.6	0.6
Financing Cash Flows from Finance Leases	0.0	0.0	0.0
Supplemental Non-Cash Information on Lease Liabilities:
Right-of-use-Assets Obtained in Exchange for New Operating Lease Liabilities	0.0	1.9	0.2
Right-of-use-Assets Obtained in Exchange for New Finance Lease Liabilities	$ 0.0	$ 0.0	0.3
PSNH
Weighted-Average Remaining Lease Term (Years):
Operating Leases		7 years
Finance Leases		7 years
Weighted-Average Discount Rate (Percentage):
Operating Leases	0.00%	3.70%
Finance Leases	0.00%	3.50%
Cash Paid for Amounts Included in the Measurement of Lease Liabilities:
Operating Cash Flows from Operating Leases	$ 0.1	$ 0.1	0.1
Operating Cash Flows from Finance Leases	0.0	0.0	0.0
Financing Cash Flows from Finance Leases	0.1	0.1	0.1
Supplemental Non-Cash Information on Lease Liabilities:
Right-of-use-Assets Obtained in Exchange for New Operating Lease Liabilities	0.0	0.0	0.0
Right-of-use-Assets Obtained in Exchange for New Finance Lease Liabilities	$ 0.0	$ 0.0	$ 0.0