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