SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of AFUDC and Weighted Average AFUDC (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Components of Other Operating Costs and Expense [Line Items]
Borrowed Funds	$ 21.8	$ 18.4	$ 23.7
Equity Funds	47.3	37.3	42.0
Total AFUDC	$ 69.1	$ 55.7	$ 65.7
Average AFUDC Rate (in percent)	4.70%	4.20%	5.00%
CL&P
Components of Other Operating Costs and Expense [Line Items]
Borrowed Funds	$ 4.8	$ 2.9	$ 6.6
Equity Funds	13.6	7.7	13.8
Total AFUDC	$ 18.4	$ 10.6	$ 20.4
Average AFUDC Rate (in percent)	6.60%	5.00%	5.90%
NSTAR Electric
Components of Other Operating Costs and Expense [Line Items]
Borrowed Funds	$ 10.7	$ 9.0	$ 9.1
Equity Funds	24.6	20.4	21.5
Total AFUDC	$ 35.3	$ 29.4	$ 30.6
Average AFUDC Rate (in percent)	5.40%	4.90%	5.70%
PSNH
Components of Other Operating Costs and Expense [Line Items]
Borrowed Funds	$ 1.4	$ 0.8	$ 2.1
Equity Funds	2.5	1.6	4.2
Total AFUDC	$ 3.9	$ 2.4	$ 6.3
Average AFUDC Rate (in percent)	2.60%	2.50%	4.70%