SCHEDULE II - VALUATION AND QUALIFYING ACCOUNTS AND RESERVES (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Increase due to CMA acquisition		$ 24,200
Allowance for uncollectible accounts for late fees and other receivable amounts	$ 417,406	358,851	$ 224,800
Restatement Adjustment
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Allowance for uncollectible accounts for late fees and other receivable amounts		23,800
The Connecticut Light and Power Company
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Period of accounts receivable recoverable under financial or medical duress	180 days
Increase due to CMA acquisition		0
Allowance for uncollectible accounts for late fees and other receivable amounts	$ 181,319	157,447	97,300
The Connecticut Light and Power Company | Restatement Adjustment
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Allowance for uncollectible accounts for late fees and other receivable amounts		22,200
NSTAR Electric Company
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Increase due to CMA acquisition		0
Allowance for uncollectible accounts for late fees and other receivable amounts	97,005	91,583	75,400
NSTAR Electric Company | Restatement Adjustment
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Allowance for uncollectible accounts for late fees and other receivable amounts		(1,300)
Public Service Company of New Hampshire
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Increase due to CMA acquisition		0
Allowance for uncollectible accounts for late fees and other receivable amounts	$ 24,331	17,157	10,500
Public Service Company of New Hampshire | Restatement Adjustment
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Allowance for uncollectible accounts for late fees and other receivable amounts		300
Yankee Gas Services Company
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Period of accounts receivable recoverable under financial or medical duress	90 days
Allowance for Doubtful Accounts
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	$ 358,851	224,821	212,723
Additions, Charged to Costs and Expense	60,886	53,461	63,446
Additions, Charged to Other Accounts	110,572	145,005	57,223
Deductions	112,903	64,436	108,571
Balance at end of period	417,406	358,851	224,821
Allowance for Doubtful Accounts | The Connecticut Light and Power Company
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	157,447	97,348	88,034
Additions, Charged to Costs and Expense	13,495	12,882	15,947
Additions, Charged to Other Accounts	57,779	71,223	38,935
Deductions	47,402	24,006	45,568
Balance at end of period	181,319	157,447	97,348
Allowance for Doubtful Accounts | NSTAR Electric Company
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	91,583	75,406	74,516
Additions, Charged to Costs and Expense	16,649	15,293	25,079
Additions, Charged to Other Accounts	20,064	23,424	12,556
Deductions	31,291	22,540	36,745
Balance at end of period	97,005	91,583	75,406
Allowance for Doubtful Accounts | Public Service Company of New Hampshire
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	17,157	10,497	11,065
Additions, Charged to Costs and Expense	13,113	5,164	6,726
Additions, Charged to Other Accounts	3,135	7,692	872
Deductions	9,074	6,196	8,166
Balance at end of period	$ 24,331	$ 17,157	$ 10,497