COMMITMENTS AND CONTINGENCIES - CL&P Tropical Storm Isaias Response Investigation (Details) - Unfavorable Regulatory Action - Subsequent Event $ in Millions	May 07, 2021 USD ($)
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