REGULATORY ACCOUNTING - Components of Regulatory Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2025	Dec. 31, 2024
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 5,538,100	$ 4,664,900
Less:  Current Portion	1,264,609	632,282
Total Long-Term Regulatory Liabilities	4,273,465	4,032,564
EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	2,423,400	2,442,700
Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,186,600	702,400
Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	867,100	684,100
Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	509,400	427,100
AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	179,400	154,800
Derivative Contract
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	91,000	0
Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	80,400	69,300
Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	200,800	184,500
CL&P
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,862,600	1,520,000
Less:  Current Portion	417,498	124,122
Total Long-Term Regulatory Liabilities	1,445,140	1,395,883
CL&P | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	933,300	956,600
CL&P | Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	457,300	180,300
CL&P | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	275,100	212,800
CL&P | Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	72,800	61,600
CL&P | AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	72,000	65,100
CL&P | Derivative Contract
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
CL&P | Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	8,800	4,500
CL&P | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	43,300	39,100
NSTAR Electric
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	2,352,900	2,079,400
Less:  Current Portion	650,813	436,312
Total Long-Term Regulatory Liabilities	1,702,059	1,643,079
NSTAR Electric | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	847,900	877,600
NSTAR Electric | Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	535,200	413,600
NSTAR Electric | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	479,400	451,300
NSTAR Electric | Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	252,500	211,600
NSTAR Electric | AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	107,400	89,700
NSTAR Electric | Derivative Contract
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	91,000	0
NSTAR Electric | Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	24,500	21,400
NSTAR Electric | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	15,000	14,200
PSNH
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	535,800	516,100
Less:  Current Portion	118,443	121,058
Total Long-Term Regulatory Liabilities	417,442	394,982
PSNH | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	319,800	330,600
PSNH | Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	111,200	114,400
PSNH | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	45,500	20,100
PSNH | Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	48,500	42,600
PSNH | AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
PSNH | Derivative Contract
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
PSNH | Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	6,800	3,900
PSNH | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 4,000	$ 4,500