COMMON SHAREHOLDERS' EQUITY AND NONCONTROLLING INTERESTS (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Class of Stock [Line Items]
Dividends on preferred stock	$ 1,880	$ 1,880
Noncontrolling interest attributed to preferred stock of subsidiaries	155,570		$ 155,570
CL&P
Class of Stock [Line Items]
Dividends on preferred stock	1,390	1,390
Noncontrolling interest attributed to preferred stock of subsidiaries	116,200		116,200
NSTAR Electric
Class of Stock [Line Items]
Dividends on preferred stock	490	$ 490
Noncontrolling interest attributed to preferred stock of subsidiaries	$ 43,000		$ 43,000