DERIVATIVE INSTRUMENTS - Unobservable Inputs Utilized (Details) - Fair Value, Inputs, Level 3 [Member] - $ / KWmo	Mar. 31, 2017	Dec. 31, 2016
Eversource and The Connecticut Light And Power Company [Member] | Minimum [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Capacity Prices (in USDPerKiloWattMonth)	5.00	5.50
Forward Reserve (in USDPerKiloWattMonth)	1.40	1.40
Eversource and The Connecticut Light And Power Company [Member] | Maximum [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Capacity Prices (in USDPerKiloWattMonth)	8.70	8.70
Forward Reserve (in USDPerKiloWattMonth)	2.00	2.00
Eversource and NSTAR Electric Company [Member] | Minimum [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
REC Prices (in USDPerKiloWattMonth)	27.00	24.00
Eversource and NSTAR Electric Company [Member] | Maximum [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
REC Prices (in USDPerKiloWattMonth)	30.00	29.00