COMMON SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Class of Stock [Line Items]
Noncontrolling Interest - Preferred Stock of Subsidiaries	$ 155,568		$ 155,568
The Connecticut Light And Power Company [Member]
Class of Stock [Line Items]
Net income attributable to noncontrolling interests	1,900
Noncontrolling Interest - Preferred Stock of Subsidiaries	116,200		116,200
NSTAR Electric Company [Member]
Class of Stock [Line Items]
Net income attributable to noncontrolling interests		$ 1,900
Noncontrolling Interest - Preferred Stock of Subsidiaries	$ 43,000		$ 43,000