COMMON SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Class of Stock [Line Items]
Net income attributable to noncontrolling interests	$ 1,880	$ 1,879	$ 5,639	$ 5,639
Noncontrolling Interest - Preferred Stock of Subsidiaries	155,568		155,568		$ 155,568
The Connecticut Light And Power Company [Member]
Class of Stock [Line Items]
Noncontrolling Interest - Preferred Stock of Subsidiaries	116,200		116,200		116,200
NSTAR Electric Company [Member]
Class of Stock [Line Items]
Noncontrolling Interest - Preferred Stock of Subsidiaries	$ 43,000		$ 43,000		$ 43,000