SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES (Details) - Allowance for Doubtful Accounts - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	$ 556,164	$ 554,455	$ 486,297
Additions, Charged to Costs and Expense	101,141	74,069	72,468
Additions, Charged to Other Accounts	120,006	119,659	158,205
Deductions	196,772	192,019	162,515
Balance at end of period	580,539	556,164	554,455
CL&P
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	279,108	296,030	225,320
Additions, Charged to Costs and Expense	17,949	17,190	11,675
Additions, Charged to Other Accounts	43,110	46,840	126,360
Deductions	81,653	80,952	67,325
Balance at end of period	258,514	279,108	296,030
NSTAR Electric
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	114,910	97,026	94,958
Additions, Charged to Costs and Expense	41,430	33,607	22,791
Additions, Charged to Other Accounts	37,050	37,653	17,488
Deductions	60,829	53,376	38,211
Balance at end of period	132,561	114,910	97,026
PSNH
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	14,090	14,322	29,236
Additions, Charged to Costs and Expense	11,973	4,688	3,989
Additions, Charged to Other Accounts	7,193	5,131	(8,735)
Deductions	9,709	10,051	10,168
Balance at end of period	$ 23,547	$ 14,090	$ 14,322