v3.25.2
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Provision for Uncollectible Accounts (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Jun. 30, 2025
Jun. 30, 2024
Jun. 30, 2025
Jun. 30, 2024
Financing Receivable, Allowance for Credit Loss [Roll Forward]        
Beginning Balance $ 565,600 $ 570,100 $ 556,200 $ 554,500
Uncollectible Expense 18,600 9,900 41,519 26,279
Uncollectible Costs Deferred 26,700 36,000 59,900 74,900
Write-Offs (39,200) (39,800) (89,600) (83,500)
Recoveries Collected 3,900 3,400 7,600 7,400
Ending Balance 575,600 579,600 575,600 579,600
CL&P        
Financing Receivable, Allowance for Credit Loss [Roll Forward]        
Beginning Balance 276,200 307,800 279,100 296,000
Uncollectible Expense 5,400 2,800 10,118 6,326
Uncollectible Costs Deferred 6,100 17,900 16,800 43,400
Write-Offs (15,400) (21,200) (34,800) (39,800)
Recoveries Collected 1,300 1,300 2,400 2,700
Ending Balance 273,600 308,600 273,600 308,600
NSTAR Electric        
Financing Receivable, Allowance for Credit Loss [Roll Forward]        
Beginning Balance 116,000 97,700 114,900 97,000
Uncollectible Expense 6,500 5,900 14,002 12,007
Uncollectible Costs Deferred 9,000 9,000 18,000 12,600
Write-Offs (12,800) (7,300) (29,600) (17,500)
Recoveries Collected 1,500 900 2,900 2,100
Ending Balance 120,200 106,200 120,200 106,200
PSNH        
Financing Receivable, Allowance for Credit Loss [Roll Forward]        
Beginning Balance 14,300 13,800 14,100 14,300
Uncollectible Expense 1,100 1,000 2,447 2,178
Uncollectible Costs Deferred 1,200 1,100 2,600 2,400
Write-Offs (1,800) (2,000) (4,500) (5,200)
Recoveries Collected 200 200 400 400
Ending Balance 15,000 14,100 15,000 14,100
Hardship Accounts        
Financing Receivable, Allowance for Credit Loss [Roll Forward]        
Beginning Balance 371,500 379,400 364,600 366,800
Uncollectible Expense 0 0 0 0
Uncollectible Costs Deferred 14,900 26,000 34,300 53,500
Write-Offs (9,600) (16,500) (22,200) (31,700)
Recoveries Collected 200 200 300 500
Ending Balance 377,000 389,100 377,000 389,100
Hardship Accounts | CL&P        
Financing Receivable, Allowance for Credit Loss [Roll Forward]        
Beginning Balance 240,300 271,800 240,700 259,700
Uncollectible Expense 0 0 0 0
Uncollectible Costs Deferred 3,200 15,300 12,000 38,100
Write-Offs (7,300) (12,900) (16,600) (23,800)
Recoveries Collected 100 200 200 400
Ending Balance 236,300 274,400 236,300 274,400
Hardship Accounts | NSTAR Electric        
Financing Receivable, Allowance for Credit Loss [Roll Forward]        
Beginning Balance 57,800 41,800 55,200 43,600
Uncollectible Expense 0 0 0 0
Uncollectible Costs Deferred 3,200 4,300 6,700 3,500
Write-Offs (700) (200) (1,600) (1,200)
Recoveries Collected 0 0 0 0
Ending Balance 60,300 45,900 60,300 45,900
Retail (Non-Hardship), Wholesale, and Other        
Financing Receivable, Allowance for Credit Loss [Roll Forward]        
Beginning Balance 194,100 190,700 191,600 187,700
Uncollectible Expense 18,600 9,900 41,500 26,300
Uncollectible Costs Deferred 11,800 10,000 25,600 21,400
Write-Offs (29,600) (23,300) (67,400) (51,800)
Recoveries Collected 3,700 3,200 7,300 6,900
Ending Balance 198,600 190,500 198,600 190,500
Retail (Non-Hardship), Wholesale, and Other | CL&P        
Financing Receivable, Allowance for Credit Loss [Roll Forward]        
Beginning Balance 35,900 36,000 38,400 36,300
Uncollectible Expense 5,400 2,800 10,100 6,300
Uncollectible Costs Deferred 2,900 2,600 4,800 5,300
Write-Offs (8,100) (8,300) (18,200) (16,000)
Recoveries Collected 1,200 1,100 2,200 2,300
Ending Balance 37,300 34,200 37,300 34,200
Retail (Non-Hardship), Wholesale, and Other | NSTAR Electric        
Financing Receivable, Allowance for Credit Loss [Roll Forward]        
Beginning Balance 58,200 55,900 59,700 53,400
Uncollectible Expense 6,500 5,900 14,000 12,000
Uncollectible Costs Deferred 5,800 4,700 11,300 9,100
Write-Offs (12,100) (7,100) (28,000) (16,300)
Recoveries Collected 1,500 900 2,900 2,100
Ending Balance $ 59,900 $ 60,300 $ 59,900 $ 60,300