REVENUES - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021	Apr. 28, 2021
Loss Contingencies [Line Items]
Revenue	$ 11,890,600	$ 12,270,200	$ 9,815,000
Loss related to litigation settlement	0	(72,041)	81,274
Lease revenue	$ 4,600	$ 4,000	$ 4,800
Operating Lease, Lease Income, Statement of Income or Comprehensive Income [Extensible Enumeration]	Other Income, Net	Other Income, Net	Other Income, Net
CL&P
Loss Contingencies [Line Items]
Loss related to litigation settlement	$ 0	$ (72,041)	$ 81,274
Lease revenue	700	800	800
NSTAR Electric
Loss Contingencies [Line Items]
Lease revenue	2,500	2,500	3,100
Amortization of Revenues Subject to Refund
Loss Contingencies [Line Items]
Revenue	4,300	72,000	(78,700)
Operating Segments | CL&P
Loss Contingencies [Line Items]
Revenue	5,077,600	5,343,200	4,238,900
Operating Segments | NSTAR Electric
Loss Contingencies [Line Items]
Revenue	4,129,400	4,127,300	3,541,600
Operating Segments | Amortization of Revenues Subject to Refund | CL&P
Loss Contingencies [Line Items]
Revenue	4,300	72,700	(76,100)
Operating Segments | Amortization of Revenues Subject to Refund | NSTAR Electric
Loss Contingencies [Line Items]
Revenue	$ 0	$ 0	0
Unfavorable Regulatory Action
Loss Contingencies [Line Items]
Loss related to litigation settlement			103,600
Unfavorable Regulatory Action | CL&P
Loss Contingencies [Line Items]
Loss contingency, estimate of possible earnings impact, non-compliance with performance standards				$ 28,400
Unfavorable Regulatory Action | Operating Segments | Amortization of Revenues Subject to Refund | CL&P
Loss Contingencies [Line Items]
Revenue			93,400
Sales | Unfavorable Regulatory Action
Loss Contingencies [Line Items]
Loss related to litigation settlement			65,000
Sales | Unfavorable Regulatory Action | CL&P
Loss Contingencies [Line Items]
Loss related to litigation settlement			$ 65,000