SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES (Details) - Allowance for Doubtful Accounts - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	$ 486,297	$ 417,406	$ 358,851
Additions, Charged to Costs and Expense	72,468	61,876	60,886
Additions, Charged to Other Accounts	158,205	112,533	110,572
Deductions	162,515	105,518	112,903
Balance at end of period	554,455	486,297	417,406
CL&P
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	225,320	181,319	157,447
Additions, Charged to Costs and Expense	11,675	15,578	13,495
Additions, Charged to Other Accounts	126,360	59,485	57,779
Deductions	67,325	31,062	47,402
Balance at end of period	296,030	225,320	181,319
NSTAR Electric
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	94,958	97,005	91,583
Additions, Charged to Costs and Expense	22,791	21,550	16,649
Additions, Charged to Other Accounts	17,488	12,412	20,064
Deductions	38,211	36,009	31,291
Balance at end of period	97,026	94,958	97,005
PSNH
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	29,236	24,331	17,157
Additions, Charged to Costs and Expense	3,989	9,211	13,113
Additions, Charged to Other Accounts	(8,735)	2,539	3,135
Deductions	10,168	6,845	9,074
Balance at end of period	$ 14,322	$ 29,236	$ 24,331