REGULATORY ACCOUNTING - Components of Regulatory Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 6,728,800	$ 6,389,200
Less:  Current Portion	1,889,499	1,674,196
Total Long-Term Regulatory Assets	4,839,271	4,714,970
Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	1,942,700	1,785,900
Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	1,541,200	1,319,200
Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	1,098,100	1,117,300
Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	925,700	912,400
Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	381,700	392,500
Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	259,900	264,100
Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	141,000	137,900
Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	103,700	120,900
Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	334,800	339,000
CL&P
Regulatory Assets [Line Items]
Total Regulatory Assets	2,427,700	2,143,200
Less:  Current Portion	717,608	480,369
Total Long-Term Regulatory Assets	1,710,091	1,662,778
CL&P | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	957,600	896,600
CL&P | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	593,500	354,500
CL&P | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	194,500	197,400
CL&P | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	517,500	512,600
CL&P | Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
CL&P | Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
CL&P | Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	39,100	38,500
CL&P | Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	103,700	120,900
CL&P | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	21,800	22,700
NSTAR Electric
Regulatory Assets [Line Items]
Total Regulatory Assets	2,040,900	1,957,900
Less:  Current Portion	718,726	676,083
Total Long-Term Regulatory Assets	1,322,249	1,281,836
NSTAR Electric | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	657,300	609,100
NSTAR Electric | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	522,300	482,900
NSTAR Electric | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	330,200	336,700
NSTAR Electric | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	133,600	128,600
NSTAR Electric | Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
NSTAR Electric | Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	223,100	226,700
NSTAR Electric | Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	73,800	72,300
NSTAR Electric | Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
NSTAR Electric | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	100,600	101,600
PSNH
Regulatory Assets [Line Items]
Total Regulatory Assets	999,600	963,300
Less:  Current Portion	188,057	189,450
Total Long-Term Regulatory Assets	811,457	773,783
PSNH | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	327,800	280,200
PSNH | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	184,900	182,200
PSNH | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	78,000	79,300
PSNH | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	15,500	16,400
PSNH | Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	381,700	392,500
PSNH | Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
PSNH | Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	4,900	4,700
PSNH | Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
PSNH | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 6,800	$ 8,000