SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Allowance for Uncollectible Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	$ 417,406	$ 358,900	$ 224,800
Increase due to CMA acquisition			24,200
Uncollectible Expense	61,876	60,886	53,461
Uncollectible Costs Deferred	112,500	110,600	97,000
Write-Offs	(124,000)	(129,700)	(78,000)
Recoveries Collected	18,500	16,700	13,600
Ending Balance	486,297	417,406	358,900
Restatement Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance		23,800	23,800
Ending Balance			23,800
Hardship Accounts
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	226,100	194,800	143,300
Increase due to CMA acquisition			0
Uncollectible Expense	0	0	0
Uncollectible Costs Deferred	77,800	51,900	43,100
Write-Offs	(21,300)	(22,000)	(14,700)
Recoveries Collected	1,800	1,400	1,500
Ending Balance	284,400	226,100	194,800
Hardship Accounts | Restatement Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance			21,600
Retail (Non-Hardship), Wholesale, and Other
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	191,300	164,100	81,500
Increase due to CMA acquisition			24,200
Uncollectible Expense	61,900	60,900	53,500
Uncollectible Costs Deferred	34,700	58,700	53,900
Write-Offs	(102,700)	(107,700)	(63,300)
Recoveries Collected	16,700	15,300	12,100
Ending Balance	201,900	191,300	164,100
Retail (Non-Hardship), Wholesale, and Other | Restatement Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance			2,200
CL&P
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	181,319	157,400	97,300
Increase due to CMA acquisition			0
Uncollectible Expense	15,578	13,495	12,882
Uncollectible Costs Deferred	59,500	57,800	49,000
Write-Offs	(38,300)	(54,200)	(29,700)
Recoveries Collected	7,200	6,800	5,700
Ending Balance	225,320	181,319	157,400
CL&P | Restatement Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance		22,200	22,200
Ending Balance			22,200
CL&P | Hardship Accounts
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	144,600	129,100	80,100
Increase due to CMA acquisition			0
Uncollectible Expense	0	0	0
Uncollectible Costs Deferred	58,300	32,300	38,200
Write-Offs	(15,300)	(18,000)	(11,900)
Recoveries Collected	1,300	1,200	1,400
Ending Balance	188,900	144,600	129,100
CL&P | Hardship Accounts | Restatement Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance			21,300
CL&P | Retail (Non-Hardship), Wholesale, and Other
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	36,700	28,300	17,200
Increase due to CMA acquisition			0
Uncollectible Expense	15,600	13,500	12,900
Uncollectible Costs Deferred	1,200	25,500	10,800
Write-Offs	(23,000)	(36,200)	(17,800)
Recoveries Collected	5,900	5,600	4,300
Ending Balance	36,400	36,700	28,300
CL&P | Retail (Non-Hardship), Wholesale, and Other | Restatement Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance			900
NSTAR Electric
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	97,005	91,600	75,400
Increase due to CMA acquisition			0
Uncollectible Expense	21,550	16,649	15,293
Uncollectible Costs Deferred	12,400	20,100	24,700
Write-Offs	(42,300)	(37,000)	(27,200)
Recoveries Collected	6,300	5,700	4,700
Ending Balance	94,958	97,005	91,600
NSTAR Electric | Restatement Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance		(1,300)	(1,300)
Ending Balance			(1,300)
NSTAR Electric | Hardship Accounts
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	43,300	39,700	43,900
Increase due to CMA acquisition			0
Uncollectible Expense	0	0	0
Uncollectible Costs Deferred	1,500	4,300	(1,700)
Write-Offs	(1,100)	(700)	(900)
Recoveries Collected	0	0	0
Ending Balance	43,700	43,300	39,700
NSTAR Electric | Hardship Accounts | Restatement Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance			(1,600)
NSTAR Electric | Retail (Non-Hardship), Wholesale, and Other
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	53,700	51,900	31,500
Increase due to CMA acquisition			0
Uncollectible Expense	21,600	16,600	15,300
Uncollectible Costs Deferred	10,900	15,800	26,400
Write-Offs	(41,200)	(36,300)	(26,300)
Recoveries Collected	6,300	5,700	4,700
Ending Balance	51,300	53,700	51,900
NSTAR Electric | Retail (Non-Hardship), Wholesale, and Other | Restatement Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance			300
PSNH
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance	24,331	17,200	10,500
Increase due to CMA acquisition			0
Uncollectible Expense	9,211	13,113	5,164
Uncollectible Costs Deferred	2,500	3,100	7,400
Write-Offs	(7,700)	(10,000)	(6,900)
Recoveries Collected	900	900	700
Ending Balance	$ 29,236	24,331	17,200
PSNH | Restatement Adjustment
Financing Receivable, Allowance for Credit Loss [Roll Forward]
Beginning Balance		$ 300	300
Ending Balance			$ 300