DERIVATIVE INSTRUMENTS - Unobservable Inputs Utilized (Details) - The Connecticut Light and Power Company - Level 3 - $ / KWmo	Dec. 31, 2021	Dec. 31, 2020
Capacity Prices | Minimum
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative measurement input	2.61	4.30
Capacity Prices | Maximum
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative measurement input		5.30
Capacity Prices | Weighted Average
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative measurement input	2.61	4.63
Forward Reserve | Minimum
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative measurement input	0.50	0.54
Forward Reserve | Maximum
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative measurement input	1.15	0.90
Forward Reserve | Weighted Average
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Derivative measurement input	0.82	0.72