v3.26.1
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Provision for Uncollectible Accounts (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Financing Receivable, Allowance for Credit Loss [Roll Forward]        
Beginning balance $ 611,700 $ 565,600 $ 580,500 $ 556,200
Uncollectible Expense 19,800 18,600 50,585 41,519
Uncollectible Costs Deferred 51,200 26,700 97,800 59,900
Write-Offs (38,900) (39,200) (89,600) (89,600)
Recoveries Collected 3,300 3,900 7,800 7,600
Sale of Aquarion (2,200)   (2,200)  
Ending balance 644,900 575,600 644,900 575,600
CL&P        
Financing Receivable, Allowance for Credit Loss [Roll Forward]        
Beginning balance 274,000 276,200 258,500 279,100
Uncollectible Expense 4,300 5,400 9,842 10,118
Uncollectible Costs Deferred 12,100 6,100 37,000 16,800
Write-Offs (16,700) (15,400) (33,100) (34,800)
Recoveries Collected 1,300 1,300 2,800 2,400
Sale of Aquarion 0   0  
Ending balance 275,000 273,600 275,000 273,600
NSTAR Electric        
Financing Receivable, Allowance for Credit Loss [Roll Forward]        
Beginning balance 127,100 116,000 132,600 114,900
Uncollectible Expense 7,300 6,500 15,604 14,002
Uncollectible Costs Deferred 15,400 9,000 19,300 18,000
Write-Offs (9,800) (12,800) (29,000) (29,600)
Recoveries Collected 1,100 1,500 2,600 2,900
Sale of Aquarion 0   0  
Ending balance 141,100 120,200 141,100 120,200
PSNH        
Financing Receivable, Allowance for Credit Loss [Roll Forward]        
Beginning balance 24,300 14,300 23,500 14,100
Uncollectible Expense 1,200 1,100 2,627 2,447
Uncollectible Costs Deferred 2,000 1,200 4,200 2,600
Write-Offs (2,800) (1,800) (5,900) (4,500)
Recoveries Collected 200 200 500 400
Sale of Aquarion 0   0  
Ending balance 24,900 15,000 24,900 15,000
Hardship Accounts        
Financing Receivable, Allowance for Credit Loss [Roll Forward]        
Beginning balance 383,200 371,500 367,200 364,600
Uncollectible Expense 0 0 0 0
Uncollectible Costs Deferred 36,700 14,900 64,500 34,300
Write-Offs (10,200) (9,600) (22,400) (22,200)
Recoveries Collected 300 200 700 300
Sale of Aquarion 0   0  
Ending balance 410,000 377,000 410,000 377,000
Hardship Accounts | CL&P        
Financing Receivable, Allowance for Credit Loss [Roll Forward]        
Beginning balance 238,600 240,300 225,700 240,700
Uncollectible Expense 0 0 0 0
Uncollectible Costs Deferred 9,000 3,200 31,100 12,000
Write-Offs (8,000) (7,300) (17,500) (16,600)
Recoveries Collected 300 100 600 200
Sale of Aquarion 0   0  
Ending balance 239,900 236,300 239,900 236,300
Hardship Accounts | NSTAR Electric        
Financing Receivable, Allowance for Credit Loss [Roll Forward]        
Beginning balance 56,600 57,800 60,700 55,200
Uncollectible Expense 0 0 0 0
Uncollectible Costs Deferred 8,800 3,200 5,300 6,700
Write-Offs (400) (700) (1,000) (1,600)
Recoveries Collected 0 0 0 0
Sale of Aquarion 0   0  
Ending balance 65,000 60,300 65,000 60,300
Retail (Non-Hardship), Wholesale, and Other        
Financing Receivable, Allowance for Credit Loss [Roll Forward]        
Beginning balance 228,500 194,100 213,300 191,600
Uncollectible Expense 19,800 18,600 50,600 41,500
Uncollectible Costs Deferred 14,500 11,800 33,300 25,600
Write-Offs (28,700) (29,600) (67,200) (67,400)
Recoveries Collected 3,000 3,700 7,100 7,300
Sale of Aquarion (2,200)   (2,200)  
Ending balance 234,900 198,600 234,900 198,600
Retail (Non-Hardship), Wholesale, and Other | CL&P        
Financing Receivable, Allowance for Credit Loss [Roll Forward]        
Beginning balance 35,400 35,900 32,800 38,400
Uncollectible Expense 4,300 5,400 9,800 10,100
Uncollectible Costs Deferred 3,100 2,900 5,900 4,800
Write-Offs (8,700) (8,100) (15,600) (18,200)
Recoveries Collected 1,000 1,200 2,200 2,200
Sale of Aquarion 0   0  
Ending balance 35,100 37,300 35,100 37,300
Retail (Non-Hardship), Wholesale, and Other | NSTAR Electric        
Financing Receivable, Allowance for Credit Loss [Roll Forward]        
Beginning balance 70,500 58,200 71,900 59,700
Uncollectible Expense 7,300 6,500 15,600 14,000
Uncollectible Costs Deferred 6,600 5,800 14,000 11,300
Write-Offs (9,400) (12,100) (28,000) (28,000)
Recoveries Collected 1,100 1,500 2,600 2,900
Sale of Aquarion 0   0  
Ending balance $ 76,100 $ 59,900 $ 76,100 $ 59,900