REVENUES (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021	Sep. 01, 2021	May 06, 2021
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	$ 2,561,600	$ 2,142,900	$ 6,013,700	$ 4,915,500
Alternative Revenue Programs	8,200	(21,400)	23,900	30,300
Other Revenues	2,800	1,000	6,400	2,600
Operating Revenues	$ 2,572,641	$ 2,122,538	6,043,951	4,948,378
(Customer Credits)/Reserve at CL&P related to PURA Settlement Agreement and Storm Performance Penalty			(64,909)	28,583
Operating Lease, Income, Comprehensive Income [Extensible Enumeration]	Operating Revenues	Operating Revenues
Lease revenue	$ 1,000	$ 1,000	2,000	2,700
Unfavorable Regulatory Action
Disaggregation of Revenue [Line Items]
Loss contingency, estimate of possible earnings impact, non-compliance with performance standards							$ 28,400
CL&P
Disaggregation of Revenue [Line Items]
Operating Revenues	$ 1,035,682	$ 829,597	2,321,514	1,816,871
(Customer Credits)/Reserve at CL&P related to PURA Settlement Agreement and Storm Performance Penalty			(64,909)	28,583
Operating Lease, Income, Comprehensive Income [Extensible Enumeration]	Operating Revenues	Operating Revenues
Lease revenue	$ 200	$ 200	400	400
CL&P | Unfavorable Regulatory Action
Disaggregation of Revenue [Line Items]
Loss contingency, estimate of possible earnings impact, non-compliance with performance standards						$ 28,400
CL&P | Unfavorable Regulatory Action | Sales
Disaggregation of Revenue [Line Items]
(Customer Credits)/Reserve at CL&P related to PURA Settlement Agreement and Storm Performance Penalty			65,000
NSTAR Electric
Disaggregation of Revenue [Line Items]
Operating Revenues	$ 783,650	$ 687,375	1,646,825	1,424,418
Operating Lease, Income, Comprehensive Income [Extensible Enumeration]	Operating Revenues	Operating Revenues
Lease revenue	$ 600	$ 700	1,200	1,800
PSNH
Disaggregation of Revenue [Line Items]
Operating Revenues	$ 307,055	$ 278,849	646,482	572,284
Operating Lease, Income, Comprehensive Income [Extensible Enumeration]	Operating Revenues	Operating Revenues
Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	$ 2,189,000	$ 1,904,300	5,046,800	4,381,400
Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,258,600	1,092,300	3,029,700	2,652,900
Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	802,000	698,500	1,734,400	1,478,500
Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	128,400	113,500	282,700	250,000
Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	93,200	91,300	199,200	183,800
Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	246,700	113,900	646,500	290,100
Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	25,900	33,400	56,300	60,200
(Reserve for)/Amortization of Revenues Subject to Refund
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	6,800		64,900
Operating Segments | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,091,300	958,200	2,521,500	2,060,900
Alternative Revenue Programs	92,200	(1,100)	93,400	7,800
Other Revenues	200	(200)	300	100
Operating Segments | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	908,500	824,200	1,913,100	1,662,700
Alternative Revenue Programs	14,300	(15,300)	6,100	(1,500)
Other Revenues	1,600	700	3,600	1,800
Operating Segments | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	335,300	319,600	730,400	653,300
Alternative Revenue Programs	19,300	2,300	16,000	5,300
Other Revenues	700	500	1,600	500
Operating Segments | Total Retail Tariff Sales Revenues | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	817,400	684,900	1,692,200	1,481,700
Operating Segments | Total Retail Tariff Sales Revenues | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	685,300	629,900	1,455,300	1,285,100
Operating Segments | Total Retail Tariff Sales Revenues | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	255,800	243,900	548,700	501,200
Operating Segments | Residential | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	526,100	440,800	1,125,200	986,600
Operating Segments | Residential | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	326,900	304,700	731,500	667,100
Operating Segments | Residential | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	151,800	136,600	334,300	294,400
Operating Segments | Commercial | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	255,300	215,700	497,500	429,900
Operating Segments | Commercial | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	327,800	296,100	659,100	564,400
Operating Segments | Commercial | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	81,700	82,800	170,100	160,600
Operating Segments | Industrial | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	36,000	28,400	69,500	65,200
Operating Segments | Industrial | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	30,600	29,100	64,700	53,600
Operating Segments | Industrial | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	22,300	24,500	44,300	46,200
Operating Segments | Wholesale Transmission Revenues | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	115,800	195,700	325,000	384,600
Operating Segments | Wholesale Transmission Revenues | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	163,600	160,100	328,800	307,200
Operating Segments | Wholesale Transmission Revenues | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	55,100	61,100	126,900	119,400
Operating Segments | Wholesale Market Sales Revenues | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	143,400	68,100	423,400	177,800
Operating Segments | Wholesale Market Sales Revenues | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	47,800	18,900	105,600	43,400
Operating Segments | Wholesale Market Sales Revenues | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	21,400	10,200	49,100	25,100
Operating Segments | Other Revenues from Contracts with Customers | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	7,500	9,500	15,300	16,800
Operating Segments | Other Revenues from Contracts with Customers | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	11,800	15,300	23,400	27,000
Operating Segments | Other Revenues from Contracts with Customers | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	3,000	4,400	5,700	7,600
Operating Segments | (Reserve for)/Amortization of Revenues Subject to Refund | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	7,200	0	65,600	0
Operating Segments | (Reserve for)/Amortization of Revenues Subject to Refund | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0	0
Operating Segments | (Reserve for)/Amortization of Revenues Subject to Refund | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0	0
Operating Segments | Reserves For Revenues Subject To Refund | CL&P | Unfavorable Regulatory Action
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers					$ 93,400
Other
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	335,700	330,000	719,300	673,000
Alternative Revenue Programs	0	0	0	0
Other Revenues	0	0	0	0
Operating Revenues	335,700	330,000	719,300	673,000
Other | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0	0
Other | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0	0
Other | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0	0
Other | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0	0
Other | Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	25,100	20,300	49,600	39,500
Other | Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0	0
Other | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	310,600	309,700	669,700	633,500
Other | (Reserve for)/Amortization of Revenues Subject to Refund
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0		0
Eliminations
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(582,700)	(658,600)	(1,306,100)	(1,305,900)
Alternative Revenue Programs	(113,200)	(1,200)	(99,600)	1,000
Other Revenues	0	0	0	0
Operating Revenues	(695,900)	(659,800)	(1,405,700)	(1,304,900)
Eliminations | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(6,500)	(5,700)	(12,100)	(10,700)
Eliminations | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0	0
Eliminations | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(1,400)	(1,300)	(2,500)	(2,700)
Eliminations | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(5,100)	(4,400)	(9,600)	(8,000)
Eliminations | Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(266,400)	(345,900)	(631,100)	(666,900)
Eliminations | Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0	0
Eliminations | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(309,800)	(307,000)	(662,900)	(628,300)
Eliminations | (Reserve for)/Amortization of Revenues Subject to Refund
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0		0
Eliminations | CL&P
Disaggregation of Revenue [Line Items]
Operating Revenues	(148,000)	(127,300)	(293,700)	(251,900)
Eliminations | NSTAR Electric
Disaggregation of Revenue [Line Items]
Operating Revenues	(140,700)	(122,200)	(276,000)	(238,600)
Eliminations | PSNH
Disaggregation of Revenue [Line Items]
Operating Revenues	(48,200)	(43,600)	(101,500)	(86,800)
Electric Distribution | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,995,300	1,680,500	4,374,100	3,556,800
Alternative Revenue Programs	6,800	(4,800)	11,500	18,200
Other Revenues	2,300	800	5,100	1,900
Operating Revenues	2,004,400	1,676,500	4,390,700	3,576,900
Electric Distribution | Operating Segments | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,757,800	1,558,200	3,695,000	3,267,100
Electric Distribution | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,004,800	882,100	2,191,000	1,948,100
Electric Distribution | Operating Segments | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	664,100	594,100	1,325,500	1,154,000
Electric Distribution | Operating Segments | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	88,900	82,000	178,500	165,000
Electric Distribution | Operating Segments | Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0	0
Electric Distribution | Operating Segments | Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	212,600	97,200	578,100	246,300
Electric Distribution | Operating Segments | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	18,400	25,100	36,100	43,400
Electric Distribution | Operating Segments | (Reserve for)/Amortization of Revenues Subject to Refund
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	6,500		64,900
Natural Gas Distribution | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	419,000	315,300	1,335,900	1,073,700
Alternative Revenue Programs	(3,000)	(3,400)	7,200	18,600
Other Revenues	200	(100)	700	0
Operating Revenues	416,200	311,800	1,343,800	1,092,300
Natural Gas Distribution | Operating Segments | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	384,600	298,600	1,267,000	1,029,300
Natural Gas Distribution | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	218,500	174,200	775,300	641,100
Natural Gas Distribution | Operating Segments | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	122,600	89,600	380,100	297,400
Natural Gas Distribution | Operating Segments | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	43,500	34,800	111,600	90,800
Natural Gas Distribution | Operating Segments | Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0	0
Natural Gas Distribution | Operating Segments | Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	33,200	15,700	66,700	42,000
Natural Gas Distribution | Operating Segments | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,200	1,000	2,200	2,400
Natural Gas Distribution | Operating Segments | (Reserve for)/Amortization of Revenues Subject to Refund
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0		0
Electric Transmission | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	338,400	420,300	788,400	818,000
Alternative Revenue Programs	119,000	(9,300)	104,000	(6,600)
Other Revenues	200	200	400	500
Operating Revenues	457,600	411,200	892,800	811,900
Electric Transmission | Operating Segments | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0	0
Electric Transmission | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0	0
Electric Transmission | Operating Segments | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0	0
Electric Transmission | Operating Segments | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0	0
Electric Transmission | Operating Segments | Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	334,500	416,900	780,700	811,200
Electric Transmission | Operating Segments | Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0	0
Electric Transmission | Operating Segments | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	3,200	3,400	7,000	6,800
Electric Transmission | Operating Segments | (Reserve for)/Amortization of Revenues Subject to Refund
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	700		700
Water Distribution | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	55,900	55,400	102,100	99,900
Alternative Revenue Programs	(1,400)	(2,700)	800	(900)
Other Revenues	100	100	200	200
Operating Revenues	54,600	52,800	103,100	99,200
Water Distribution | Operating Segments | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	53,100	53,200	96,900	95,700
Water Distribution | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	35,300	36,000	63,400	63,700
Water Distribution | Operating Segments | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	16,700	16,100	31,300	29,800
Water Distribution | Operating Segments | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,100	1,100	2,200	2,200
Water Distribution | Operating Segments | Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0	0	0
Water Distribution | Operating Segments | Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	900	1,000	1,700	1,800
Water Distribution | Operating Segments | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	2,300	$ 1,200	4,200	$ 2,400
Water Distribution | Operating Segments | (Reserve for)/Amortization of Revenues Subject to Refund
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	$ (400)		$ (700)