INCOME TAXES - Reconciliation of Unrecognized Tax Benefit (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning Balance	$ 65.8	$ 61.8	$ 55.0
Gross Increases - Current Year	11.5	11.3	11.9
Gross Increases - Prior Year			1.4
Gross Decreases - Prior Year	(2.4)	(0.3)
Lapse of Statute of Limitations	(7.8)	(7.0)	(6.5)
Ending Balance	67.1	65.8	61.8
CL&P
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning Balance	26.2	25.8	23.1
Gross Increases - Current Year	3.5	3.8	4.6
Gross Increases - Prior Year			0.7
Gross Decreases - Prior Year	(0.9)	(0.6)
Lapse of Statute of Limitations	(3.3)	(2.8)	(2.6)
Ending Balance	$ 25.5	$ 26.2	$ 25.8