REGULATORY ACCOUNTING - Components of Regulatory Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 7,693,700	$ 7,070,700
Less:  Current Portion	1,975,083	2,189,660
Total Long-Term Regulatory Assets	5,718,646	4,880,974
Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	1,959,300	2,039,400
Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	1,573,800	1,781,600
Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	1,044,500	968,400
Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	992,800	967,400
Derivative Contracts
Regulatory Assets [Line Items]
Total Regulatory Assets	753,200	57,200
Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	306,100	349,300
Cost of Removal
Regulatory Assets [Line Items]
Total Regulatory Assets	262,500	198,400
Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	230,400	247,200
Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	162,800	150,200
Environmental Remediation Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	136,100	116,200
EGMA Acquisition and Integration Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	82,300	0
Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	189,900	195,400
CL&P
Regulatory Assets [Line Items]
Total Regulatory Assets	1,981,400	2,325,500
Less:  Current Portion	265,175	638,529
Total Long-Term Regulatory Assets	1,716,212	1,687,029
CL&P | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	991,300	971,100
CL&P | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	206,500	507,700
CL&P | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	546,100	521,000
CL&P | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	173,700	168,800
CL&P | Derivative Contracts
Regulatory Assets [Line Items]
Total Regulatory Assets	100	57,200
CL&P | Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
CL&P | Cost of Removal
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	44,200	41,200
CL&P | Environmental Remediation Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
CL&P | EGMA Acquisition and Integration Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
CL&P | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	19,500	58,500
NSTAR Electric
Regulatory Assets [Line Items]
Total Regulatory Assets	2,802,300	2,107,100
Less:  Current Portion	978,754	902,770
Total Long-Term Regulatory Assets	1,823,522	1,204,337
NSTAR Electric | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	499,600	609,800
NSTAR Electric | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	705,600	650,000
NSTAR Electric | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	161,500	145,400
NSTAR Electric | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	300,000	293,600
NSTAR Electric | Derivative Contracts
Regulatory Assets [Line Items]
Total Regulatory Assets	753,100	0
NSTAR Electric | Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
NSTAR Electric | Cost of Removal
Regulatory Assets [Line Items]
Total Regulatory Assets	8,100	8,500
NSTAR Electric | Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	197,800	212,300
NSTAR Electric | Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	84,600	78,300
NSTAR Electric | Environmental Remediation Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
NSTAR Electric | EGMA Acquisition and Integration Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
NSTAR Electric | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	92,000	109,200
PSNH
Regulatory Assets [Line Items]
Total Regulatory Assets	961,100	1,065,700
Less:  Current Portion	119,871	173,267
Total Long-Term Regulatory Assets	841,203	892,411
PSNH | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	468,400	458,500
PSNH | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	93,200	162,800
PSNH | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	23,300	20,700
PSNH | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	61,700	65,600
PSNH | Derivative Contracts
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
PSNH | Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	306,100	349,300
PSNH | Cost of Removal
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
PSNH | Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
PSNH | Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	5,400	5,100
PSNH | Environmental Remediation Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
PSNH | EGMA Acquisition and Integration Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
PSNH | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 3,000	$ 3,700