REGULATORY ACCOUNTING - Components of Regulatory Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2025	Dec. 31, 2024
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 6,691,300	$ 7,070,700
Less:  Current Portion	1,793,285	2,189,660
Total Long-Term Regulatory Assets	4,898,037	4,880,974
Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	2,034,100	2,039,400
Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	1,416,000	1,781,600
Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	979,100	968,400
Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	957,900	967,400
Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	338,500	349,300
Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	243,000	247,200
Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	153,200	150,200
Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	41,800	57,200
Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	527,700	510,000
CL&P
Regulatory Assets [Line Items]
Total Regulatory Assets	2,125,500	2,325,500
Less:  Current Portion	417,267	638,529
Total Long-Term Regulatory Assets	1,708,150	1,687,029
CL&P | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	986,500	971,100
CL&P | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	311,300	507,700
CL&P | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	525,000	521,000
CL&P | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	167,500	168,800
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	42,000	41,200
CL&P | Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	41,800	57,200
CL&P | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	51,400	58,500
NSTAR Electric
Regulatory Assets [Line Items]
Total Regulatory Assets	2,042,900	2,107,100
Less:  Current Portion	874,087	902,770
Total Long-Term Regulatory Assets	1,168,754	1,204,337
NSTAR Electric | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	579,900	609,800
NSTAR Electric | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	622,800	650,000
NSTAR Electric | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	149,500	145,400
NSTAR Electric | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	290,400	293,600
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	208,600	212,300
NSTAR Electric | Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	79,800	78,300
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	111,900	117,700
PSNH
Regulatory Assets [Line Items]
Total Regulatory Assets	1,048,000	1,065,700
Less:  Current Portion	153,635	173,267
Total Long-Term Regulatory Assets	894,369	892,411
PSNH | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	467,700	458,500
PSNH | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	147,600	162,800
PSNH | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	20,500	20,700
PSNH | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	65,000	65,600
PSNH | Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	338,500	349,300
PSNH | Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
PSNH | Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	5,200	5,100
PSNH | Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
PSNH | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 3,500	$ 3,700