v3.26.1
REGULATORY ACCOUNTING - Components of Regulatory Liabilities (Details) - USD ($)
$ in Thousands
Jun. 30, 2026
Dec. 31, 2025
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities $ 5,927,500 $ 5,538,100
Less:  Current Portion 1,696,398 1,264,609
Total Long-Term Regulatory Liabilities 4,231,128 4,273,465
EDIT due to Tax Cuts and Jobs Act of 2017    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 2,343,900 2,423,400
Regulatory Tracking Mechanisms    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 1,560,000 1,186,600
Cost of Removal    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 877,800 867,100
Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 557,800 509,400
AFUDC - Transmission    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 196,200 179,400
Derivative Contract    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 115,100 91,000
Benefit Costs    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 74,600 80,400
Other Regulatory Liabilities    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 202,100 200,800
CL&P    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 2,133,400 1,862,600
Less:  Current Portion 653,665 417,498
Total Long-Term Regulatory Liabilities 1,479,698 1,445,140
CL&P | EDIT due to Tax Cuts and Jobs Act of 2017    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 924,000 933,300
CL&P | Regulatory Tracking Mechanisms    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 673,000 457,300
CL&P | Cost of Removal    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 310,300 275,100
CL&P | Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 79,400 72,800
CL&P | AFUDC - Transmission    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 78,000 72,000
CL&P | Derivative Contract    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 0 0
CL&P | Benefit Costs    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 10,400 8,800
CL&P | Other Regulatory Liabilities    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 58,300 43,300
NSTAR Electric    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 2,503,600 2,352,900
Less:  Current Portion 775,303 650,813
Total Long-Term Regulatory Liabilities 1,728,295 1,702,059
NSTAR Electric | EDIT due to Tax Cuts and Jobs Act of 2017    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 834,600 847,900
NSTAR Electric | Regulatory Tracking Mechanisms    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 615,700 535,200
NSTAR Electric | Cost of Removal    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 504,900 479,400
NSTAR Electric | Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 276,400 252,500
NSTAR Electric | AFUDC - Transmission    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 118,200 107,400
NSTAR Electric | Derivative Contract    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 115,100 91,000
NSTAR Electric | Benefit Costs    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 14,400 24,500
NSTAR Electric | Other Regulatory Liabilities    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 24,300 15,000
PSNH    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 583,100 535,800
Less:  Current Portion 150,745 118,443
Total Long-Term Regulatory Liabilities 432,400 417,442
PSNH | EDIT due to Tax Cuts and Jobs Act of 2017    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 314,800 319,800
PSNH | Regulatory Tracking Mechanisms    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 141,300 111,200
PSNH | Cost of Removal    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 62,600 45,500
PSNH | Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities 53,200 48,500
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 7,200 6,800
PSNH | Other Regulatory Liabilities    
Regulatory Liabilities [Line Items]    
Total Regulatory Liabilities $ 4,000 $ 4,000