COMMITMENTS AND CONTINGENCIES - CL&P Tropical Storm Isaias Response Investigation (Details) - USD ($) $ / shares in Units, $ in Millions	May 07, 2021	Jul. 14, 2021	May 06, 2021	Apr. 28, 2021
Loss Contingencies [Line Items]
Loss contingency, allowed rate of ROE				9.25%
Unfavorable Regulatory Action
Loss Contingencies [Line Items]
Loss contingency, estimate of possible earnings impact			$ 30.0
Loss contingency, estimate of possible earnings impact, non-compliance with performance standards			28.4
Loss contingency, estimate of possible earnings impact, accident reporting violation fines			$ 1.6
Loss contingency, penalty rate as a percent of distribution revenues	2.50%
Decrease in future annual revenues as a result of a 90 basis point ROE reduction	$ 31.0
Increase in future earnings as a result of a 90 basis point ROE reduction	$ 21.0
Unfavorable Regulatory Action | Subsequent Event
Loss Contingencies [Line Items]
Non-compliance fine		$ 28.6
Loss contingency, accident reporting violation fines		$ 0.2
Loss contingency, after-tax earnings impact per share		$ 0.07