REGULATORY ACCOUNTING - Components of Regulatory Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2026	Dec. 31, 2025
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 7,665,400	$ 7,693,700
Less:  Current Portion	1,897,191	1,975,083
Total Long-Term Regulatory Assets	5,768,159	5,718,646
Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	2,100,400	1,959,300
Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	1,540,300	1,573,800
Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	1,051,000	1,044,500
Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	984,900	992,800
Derivative Contracts
Regulatory Assets [Line Items]
Total Regulatory Assets	636,200	753,200
Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	295,300	306,100
Cost of Removal
Regulatory Assets [Line Items]
Total Regulatory Assets	267,500	262,500
Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	226,200	230,400
Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	166,000	162,800
Environmental Remediation Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	134,200	136,100
EGMA Acquisition and Integration Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	82,300	82,300
Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	181,100	189,900
CL&P
Regulatory Assets [Line Items]
Total Regulatory Assets	1,985,400	1,981,400
Less:  Current Portion	235,015	265,175
Total Long-Term Regulatory Assets	1,750,400	1,716,212
CL&P | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	1,028,900	991,300
CL&P | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	172,700	206,500
CL&P | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	547,000	546,100
CL&P | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	172,500	173,700
CL&P | Derivative Contracts
Regulatory Assets [Line Items]
Total Regulatory Assets	0	100
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	44,900	44,200
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	19,400	19,500
NSTAR Electric
Regulatory Assets [Line Items]
Total Regulatory Assets	2,824,500	2,802,300
Less:  Current Portion	1,018,886	978,754
Total Long-Term Regulatory Assets	1,805,604	1,823,522
NSTAR Electric | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	602,700	499,600
NSTAR Electric | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	749,700	705,600
NSTAR Electric | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	165,900	161,500
NSTAR Electric | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	297,100	300,000
NSTAR Electric | Derivative Contracts
Regulatory Assets [Line Items]
Total Regulatory Assets	636,200	753,100
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	8,100
NSTAR Electric | Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	194,200	197,800
NSTAR Electric | Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	86,100	84,600
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	84,500	92,000
PSNH
Regulatory Assets [Line Items]
Total Regulatory Assets	971,900	961,100
Less:  Current Portion	101,449	119,871
Total Long-Term Regulatory Assets	870,534	841,203
PSNH | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	468,800	468,400
PSNH | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	115,900	93,200
PSNH | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	22,400	23,300
PSNH | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	61,300	61,700
PSNH | Derivative Contracts
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
PSNH | Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	295,300	306,100
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	5,500	5,400
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	$ 2,700	$ 3,000