COMMITMENTS AND CONTINGENCIES - Spent Nuclear Fuel Obligations Narrative (Details) - USD ($) $ in Millions	Mar. 22, 2017	Mar. 25, 2016
Guarantor Obligations [Line Items]
Damages awarded		$ 26.1
Yankee Companies
Guarantor Obligations [Line Items]
Damages sought	$ 100.0	78.0
CYAPC
Guarantor Obligations [Line Items]
Damages awarded		32.6
YAEC
Guarantor Obligations [Line Items]
Damages awarded		19.6
Amount refunded		56.5
MYAPC
Guarantor Obligations [Line Items]
Damages awarded		24.6
The Connecticut Light And Power Company
Guarantor Obligations [Line Items]
Damages awarded		13.6
NSTAR Electric Company
Guarantor Obligations [Line Items]
Damages awarded		8.6
Public Service Company Of New Hampshire
Guarantor Obligations [Line Items]
Damages awarded		3.9
Yankee Companies
Guarantor Obligations [Line Items]
Damages awarded		$ 76.8