COMMITMENTS AND CONTINGENCIES - Spent Nuclear Fuel Obligations - Yankee Companies (Details) - USD ($) $ in Millions				1 Months Ended
	Jun. 12, 2019	Feb. 21, 2019	May 22, 2017	Dec. 31, 2019	Jul. 31, 2019
Loss Contingencies [Line Items]
Damages awarded	$ 0.5
Remaining damages sought		$ 1.0
Damages paid					$ 0.5
DOE settlement payment				$ 29.0
YAEC
Loss Contingencies [Line Items]
Damages awarded				2.8
Total amount of damages awarded				5.4
MYAPC
Loss Contingencies [Line Items]
Damages awarded				5.0
Total amount of damages awarded				$ 21.0
CYAPC, YAEC, and MYAPC
Loss Contingencies [Line Items]
Damages sought			$ 104.4
Damages awarded		103.2
CYAPC
Loss Contingencies [Line Items]
Damages awarded		40.7
YAEC
Loss Contingencies [Line Items]
Damages awarded		28.1
MYAPC
Loss Contingencies [Line Items]
Damages awarded		$ 34.4