COMMITMENTS AND CONTINGENCIES - Schedule of Total Costs Incurred (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Long-term Purchase Commitment [Line Items]
Renewable Energy Purchase Contracts	$ 678.1	$ 609.2	$ 584.2
Natural Gas Procurement	1,042.8	712.7	453.4
Purchased Power and Capacity	61.6	56.4	62.7
Peaker CfDs	13.4	24.3	22.7
Transmission Support Commitments	12.7	15.4	22.1
CL&P
Long-term Purchase Commitment [Line Items]
Renewable Energy Purchase Contracts	513.2	457.1	426.3
Purchased Power and Capacity	57.7	53.1	59.3
Peaker CfDs	13.4	24.3	22.7
Transmission Support Commitments	5.0	6.1	8.7
NSTAR Electric
Long-term Purchase Commitment [Line Items]
Renewable Energy Purchase Contracts	90.8	84.7	88.8
Purchased Power and Capacity	3.0	3.0	3.1
Peaker CfDs	0.0	0.0	0.0
Transmission Support Commitments	5.0	6.0	8.7
PSNH
Long-term Purchase Commitment [Line Items]
Renewable Energy Purchase Contracts	74.1	67.4	69.1
Purchased Power and Capacity	0.9	0.3	0.3
Peaker CfDs	0.0	0.0	0.0
Transmission Support Commitments	$ 2.7	$ 3.3	$ 4.7