REVENUES (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	$ 3,067,400	$ 2,833,500	$ 8,859,500	$ 9,211,000
Alternative Revenue Programs	(10,100)	(48,200)	52,500	(14,000)
Other Revenues	5,900	6,200	17,300	19,500
Total Operating Revenues	3,063,224	2,791,482	8,929,321	9,216,467
CL&P
Disaggregation of Revenue [Line Items]
Total Operating Revenues	1,345,253	1,190,096	3,431,167	3,563,150
NSTAR Electric
Disaggregation of Revenue [Line Items]
Total Operating Revenues	1,077,523	953,531	2,870,206	2,728,782
PSNH
Disaggregation of Revenue [Line Items]
Total Operating Revenues	342,027	353,074	955,453	1,123,300
Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	2,679,800	2,441,000	7,790,600	8,129,800
Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,595,900	1,503,600	4,657,200	4,952,700
Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	945,000	816,300	2,730,400	2,778,100
Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	138,900	121,100	403,000	399,000
Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	152,500	133,600	381,800	342,600
Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	204,000	227,600	596,400	647,800
Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	31,100	31,300	90,700	90,800
Operating Segments | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,563,600	1,396,200	3,926,400	3,972,200
Alternative Revenue Programs	(46,500)	(49,300)	4,900	28,000
Other Revenues	2,400	2,400	6,700	7,100
Operating Segments | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,236,800	1,129,200	3,339,900	3,194,500
Alternative Revenue Programs	8,100	(29,000)	20,100	(43,500)
Other Revenues	2,000	1,900	5,600	6,300
Operating Segments | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	418,500	411,000	1,140,500	1,247,700
Alternative Revenue Programs	(9,700)	900	1,300	32,400
Other Revenues	500	700	2,000	2,300
Operating Segments | Total Retail Tariff Sales Revenues | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,158,200	1,029,300	2,864,900	3,000,700
Operating Segments | Total Retail Tariff Sales Revenues | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	980,600	901,800	2,611,100	2,535,400
Operating Segments | Total Retail Tariff Sales Revenues | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	296,300	303,800	809,700	959,700
Operating Segments | Residential | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	757,100	703,900	1,897,700	2,059,900
Operating Segments | Residential | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	530,800	480,500	1,373,200	1,318,700
Operating Segments | Residential | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	177,600	191,500	476,200	603,500
Operating Segments | Commercial | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	349,900	286,400	850,200	836,700
Operating Segments | Commercial | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	416,900	389,400	1,144,800	1,121,000
Operating Segments | Commercial | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	91,400	88,700	254,600	287,500
Operating Segments | Industrial | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	51,200	39,000	117,000	104,100
Operating Segments | Industrial | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	32,900	31,900	93,100	95,700
Operating Segments | Industrial | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	27,300	23,600	78,900	68,700
Operating Segments | Wholesale Transmission Revenues | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	262,200	245,100	681,700	613,300
Operating Segments | Wholesale Transmission Revenues | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	212,300	186,400	602,000	521,000
Operating Segments | Wholesale Transmission Revenues | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	109,100	88,700	286,900	223,900
Operating Segments | Wholesale Market Sales Revenues | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	134,100	112,800	352,800	330,400
Operating Segments | Wholesale Market Sales Revenues | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	31,800	28,600	90,300	102,100
Operating Segments | Wholesale Market Sales Revenues | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	7,900	13,500	28,000	51,900
Operating Segments | Other Revenues from Contracts with Customers | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	9,100	9,000	27,000	27,800
Operating Segments | Other Revenues from Contracts with Customers | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	12,100	12,400	36,500	36,000
Operating Segments | Other Revenues from Contracts with Customers | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	5,200	5,000	15,900	12,200
Other
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	414,700	394,700	1,253,600	1,217,300
Alternative Revenue Programs	0	0	0	0
Other Revenues	0	0	0	0
Total Operating Revenues	414,700	394,700	1,253,600	1,217,300
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	0	0	0	0
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	414,700	394,700	1,253,600	1,217,300
Eliminations
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(851,600)	(784,900)	(2,458,700)	(2,244,300)
Alternative Revenue Programs	41,000	31,900	(1,700)	(50,800)
Other Revenues	0	0	0	0
Total Operating Revenues	(810,600)	(753,000)	(2,460,400)	(2,295,100)
Eliminations | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(7,900)	(5,900)	(22,200)	(18,000)
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	(2,500)	(1,100)	(5,700)	(3,400)
Eliminations | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(5,400)	(4,800)	(16,500)	(14,600)
Eliminations | Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(431,100)	(386,600)	(1,188,800)	(1,015,600)
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	(412,600)	(392,400)	(1,247,700)	(1,210,700)
Consolidations Eliminations | CL&P
Disaggregation of Revenue [Line Items]
Total Operating Revenues	(174,200)	(159,200)	(506,800)	(444,100)
Consolidations Eliminations | NSTAR Electric
Disaggregation of Revenue [Line Items]
Total Operating Revenues	(169,400)	(148,600)	(495,400)	(428,500)
Consolidations Eliminations | PSNH
Disaggregation of Revenue [Line Items]
Total Operating Revenues	(67,300)	(59,500)	(188,300)	(159,100)
Electric Distribution | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	2,630,900	2,410,300	6,822,500	7,039,800
Alternative Revenue Programs	(2,900)	(43,800)	24,400	(40,700)
Other Revenues	4,800	4,800	13,900	15,200
Total Operating Revenues	2,632,800	2,371,300	6,860,800	7,014,300
Electric Distribution | Operating Segments | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	2,434,700	2,234,500	6,284,600	6,495,300
Electric Distribution | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,465,500	1,375,900	3,747,100	3,982,100
Electric Distribution | Operating Segments | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	857,800	764,100	2,248,500	2,244,700
Electric Distribution | Operating Segments | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	111,400	94,500	289,000	268,500
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	173,800	154,900	471,100	484,400
Electric Distribution | Operating Segments | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	22,400	20,900	66,800	60,100
Natural Gas Distribution | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	220,200	219,800	1,486,500	1,647,700
Alternative Revenue Programs	(3,600)	(2,400)	28,100	21,900
Other Revenues	600	900	2,100	3,000
Total Operating Revenues	217,200	218,300	1,516,700	1,672,600
Natural Gas Distribution | Operating Segments | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	189,300	146,900	1,359,800	1,483,300
Natural Gas Distribution | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	86,700	83,000	798,300	858,000
Natural Gas Distribution | Operating Segments | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	71,000	33,700	434,500	483,600
Natural Gas Distribution | Operating Segments | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	31,600	30,200	127,000	141,700
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	29,000	71,600	122,200	160,500
Natural Gas Distribution | Operating Segments | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,900	1,300	4,500	3,900
Electric Transmission | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	587,100	525,000	1,581,600	1,372,300
Alternative Revenue Programs	(45,200)	(33,600)	1,900	57,600
Other Revenues	100	200	400	500
Total Operating Revenues	542,000	491,600	1,583,900	1,430,400
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	583,600	520,200	1,570,600	1,358,200
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	3,500	4,800	11,000	14,100
Water Distribution | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	66,100	68,600	174,000	178,200
Alternative Revenue Programs	600	(300)	(200)	(2,000)
Other Revenues	400	300	900	800
Total Operating Revenues	67,100	68,600	174,700	177,000
Water Distribution | Operating Segments | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	63,700	65,500	168,400	169,200
Water Distribution | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	43,700	44,700	111,800	112,600
Water Distribution | Operating Segments | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	18,700	19,600	53,100	53,200
Water Distribution | Operating Segments | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,300	1,200	3,500	3,400
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	1,200	1,100	3,100	2,900
Water Distribution | Operating Segments | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	$ 1,200	$ 2,000	$ 2,500	$ 6,100