REVENUES (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	$ 3,225,500	$ 3,067,400	$ 10,159,900	$ 8,859,500
Alternative Revenue Programs	(10,500)	(10,100)	300	52,500
Other Revenues	5,600	5,900	16,800	17,300
Total Operating Revenues	3,220,625	3,063,224	10,177,048	8,929,321
CL&P
Disaggregation of Revenue [Line Items]
Total Operating Revenues	1,362,524	1,345,253	4,035,882	3,431,167
NSTAR Electric
Disaggregation of Revenue [Line Items]
Total Operating Revenues	1,129,537	1,077,523	3,012,688	2,870,206
PSNH
Disaggregation of Revenue [Line Items]
Total Operating Revenues	351,219	342,027	1,002,332	955,453
Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	2,757,700	2,679,800	8,705,600	7,790,600
Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,618,900	1,595,900	5,215,100	4,657,200
Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	997,000	945,000	3,036,900	2,730,400
Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	141,800	138,900	453,600	403,000
Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	191,700	152,500	503,200	381,800
Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	251,400	204,000	867,800	596,400
Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	24,700	31,100	83,300	90,700
Operating Segments | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,624,500	1,563,600	4,665,400	3,926,400
Alternative Revenue Programs	(73,300)	(46,500)	(89,000)	4,900
Other Revenues	2,200	2,400	5,000	6,700
Operating Segments | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,314,100	1,236,800	3,576,100	3,339,900
Alternative Revenue Programs	(1,000)	8,100	(18,000)	20,100
Other Revenues	1,900	2,000	6,500	5,600
Operating Segments | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	467,700	418,500	1,289,900	1,140,500
Alternative Revenue Programs	(39,600)	(9,700)	(78,000)	1,300
Other Revenues	700	500	2,100	2,000
Operating Segments | Total Retail Tariff Sales Revenues | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,131,800	1,158,200	3,262,500	2,864,900
Operating Segments | Total Retail Tariff Sales Revenues | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,030,700	980,600	2,734,000	2,611,100
Operating Segments | Total Retail Tariff Sales Revenues | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	307,700	296,300	854,600	809,700
Operating Segments | Residential | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	752,900	757,100	2,137,700	1,897,700
Operating Segments | Residential | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	514,400	530,800	1,400,100	1,373,200
Operating Segments | Residential | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	185,100	177,600	508,200	476,200
Operating Segments | Commercial | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	333,700	349,900	987,200	850,200
Operating Segments | Commercial | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	476,000	416,900	1,229,500	1,144,800
Operating Segments | Commercial | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	95,900	91,400	269,300	254,600
Operating Segments | Industrial | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	45,200	51,200	137,600	117,000
Operating Segments | Industrial | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	40,300	32,900	104,400	93,100
Operating Segments | Industrial | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	26,700	27,300	77,100	78,900
Operating Segments | Wholesale Transmission Revenues | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	305,200	262,200	803,500	681,700
Operating Segments | Wholesale Transmission Revenues | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	236,200	212,300	681,200	602,000
Operating Segments | Wholesale Transmission Revenues | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	150,300	109,100	397,400	286,900
Operating Segments | Wholesale Market Sales Revenues | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	177,700	134,100	572,300	352,800
Operating Segments | Wholesale Market Sales Revenues | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	35,600	31,800	125,100	90,300
Operating Segments | Wholesale Market Sales Revenues | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	7,300	7,900	26,100	28,000
Operating Segments | Other Revenues from Contracts with Customers | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	9,800	9,100	27,100	27,000
Operating Segments | Other Revenues from Contracts with Customers | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	11,600	12,100	35,800	36,500
Operating Segments | Other Revenues from Contracts with Customers | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	2,400	5,200	11,800	15,900
Other
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	428,300	414,700	1,273,200	1,253,600
Alternative Revenue Programs	0	0	0	0
Other Revenues	0	0	0	0
Total Operating Revenues	428,300	414,700	1,273,200	1,253,600
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	428,300	414,700	1,273,200	1,253,600
Eliminations
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(937,800)	(851,600)	(2,673,800)	(2,458,700)
Alternative Revenue Programs	107,800	41,000	181,200	(1,700)
Other Revenues	0	0	0	0
Total Operating Revenues	(830,000)	(810,600)	(2,492,600)	(2,460,400)
Eliminations | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(8,900)	(7,900)	(25,700)	(22,200)
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	(2,300)	(2,500)	(6,300)	(5,700)
Eliminations | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(6,600)	(5,400)	(19,400)	(16,500)
Eliminations | Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(500,000)	(431,100)	(1,378,900)	(1,188,800)
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	(428,900)	(412,600)	(1,269,200)	(1,247,700)
Consolidations Eliminations | CL&P
Disaggregation of Revenue [Line Items]
Total Operating Revenues	(190,900)	(174,200)	(545,500)	(506,800)
Consolidations Eliminations | NSTAR Electric
Disaggregation of Revenue [Line Items]
Total Operating Revenues	(185,500)	(169,400)	(551,900)	(495,400)
Consolidations Eliminations | PSNH
Disaggregation of Revenue [Line Items]
Total Operating Revenues	(77,600)	(67,300)	(211,700)	(188,300)
Electric Distribution | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	2,709,700	2,630,900	7,635,300	6,822,500
Alternative Revenue Programs	3,500	(2,900)	13,300	24,400
Other Revenues	4,700	4,800	13,400	13,900
Total Operating Revenues	2,717,900	2,632,800	7,662,000	6,860,800
Electric Distribution | Operating Segments | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	2,469,700	2,434,700	6,849,500	6,284,600
Electric Distribution | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,452,400	1,465,500	4,046,000	3,747,100
Electric Distribution | Operating Segments | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	905,100	857,800	2,484,400	2,248,500
Electric Distribution | Operating Segments | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	112,200	111,400	319,100	289,000
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	220,600	173,800	723,500	471,100
Electric Distribution | Operating Segments | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	19,400	22,400	62,300	66,800
Natural Gas Distribution | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	248,400	220,200	1,840,300	1,486,500
Alternative Revenue Programs	8,200	(3,600)	16,700	28,100
Other Revenues	500	600	2,300	2,100
Total Operating Revenues	257,100	217,200	1,859,300	1,516,700
Natural Gas Distribution | Operating Segments | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	217,200	189,300	1,694,900	1,359,800
Natural Gas Distribution | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	109,100	86,700	1,039,800	798,300
Natural Gas Distribution | Operating Segments | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	73,400	71,000	504,900	434,500
Natural Gas Distribution | Operating Segments | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	34,700	31,600	150,200	127,000
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	29,600	29,000	140,900	122,200
Natural Gas Distribution | Operating Segments | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,600	1,900	4,500	4,500
Electric Transmission | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	695,400	587,100	1,892,700	1,581,600
Alternative Revenue Programs	(117,400)	(45,200)	(198,300)	1,900
Other Revenues	100	100	200	400
Total Operating Revenues	578,100	542,000	1,694,600	1,583,900
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	691,700	583,600	1,882,100	1,570,600
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	3,700	3,500	10,600	11,000
Water Distribution | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	81,500	66,100	192,200	174,000
Alternative Revenue Programs	(12,600)	600	(12,600)	(200)
Other Revenues	300	400	900	900
Total Operating Revenues	69,200	67,100	180,500	174,700
Water Distribution | Operating Segments | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	79,700	63,700	186,900	168,400
Water Distribution | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	57,400	43,700	129,300	111,800
Water Distribution | Operating Segments | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	20,800	18,700	53,900	53,100
Water Distribution | Operating Segments | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,500	1,300	3,700	3,500
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	1,200	3,400	3,100
Water Distribution | Operating Segments | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	$ 600	$ 1,200	$ 1,900	$ 2,500