SEGMENT INFORMATION - Narrative (Details)	12 Months Ended
	Dec. 31, 2016 segment
The Connecticut Light And Power Company [Member]
Segment Reporting Information [Line Items]
Number of reportable segments	1
NSTAR Electric Company [Member]
Segment Reporting Information [Line Items]
Number of reportable segments	1
Public Service Company Of New Hampshire [Member]
Segment Reporting Information [Line Items]
Number of reportable segments	1
Western Massachusetts Electric Company [Member]
Segment Reporting Information [Line Items]
Number of reportable segments	1