REVENUES (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	$ 3,276,800	$ 3,751,800
Alternative Revenue Programs	49,100	36,900
Other Revenues	6,700	6,900
Operating Revenues	3,332,575	3,795,643
CL&P
Disaggregation of Revenue [Line Items]
Operating Revenues	1,121,291	1,338,905
NSTAR Electric
Disaggregation of Revenue [Line Items]
Operating Revenues	947,615	956,283
PSNH
Disaggregation of Revenue [Line Items]
Operating Revenues	326,116	420,155
Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	2,904,500	3,347,100
Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,792,000	2,069,500
Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	969,100	1,122,900
Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	143,400	154,700
Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	112,500	109,700
Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	224,400	267,200
Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	35,400	27,800
Operating Segments | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,250,800	1,451,800
Alternative Revenue Programs	27,400	24,600
Other Revenues	2,900	2,200
Operating Segments | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,097,100	1,104,400
Alternative Revenue Programs	7,800	(9,500)
Other Revenues	2,000	2,500
Operating Segments | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	373,900	461,100
Alternative Revenue Programs	7,600	9,600
Other Revenues	800	1,000
Operating Segments | Total Retail Tariff Sales Revenues | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	912,500	1,091,400
Operating Segments | Total Retail Tariff Sales Revenues | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	865,600	884,700
Operating Segments | Total Retail Tariff Sales Revenues | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	271,600	365,200
Operating Segments | Residential | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	626,800	762,200
Operating Segments | Residential | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	462,200	467,800
Operating Segments | Residential | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	165,100	234,000
Operating Segments | Commercial | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	252,400	295,300
Operating Segments | Commercial | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	373,500	384,300
Operating Segments | Commercial | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	82,000	108,600
Operating Segments | Industrial | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	33,300	33,900
Operating Segments | Industrial | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	29,900	32,600
Operating Segments | Industrial | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	24,500	22,600
Operating Segments | Wholesale Transmission Revenues | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	200,700	195,800
Operating Segments | Wholesale Transmission Revenues | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	188,800	167,800
Operating Segments | Wholesale Transmission Revenues | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	84,600	71,400
Operating Segments | Wholesale Market Sales Revenues | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	121,200	154,600
Operating Segments | Wholesale Market Sales Revenues | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	31,600	41,100
Operating Segments | Wholesale Market Sales Revenues | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	12,500	21,600
Operating Segments | Other Revenues from Contracts with Customers | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	16,400	10,000
Operating Segments | Other Revenues from Contracts with Customers | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	11,100	10,800
Operating Segments | Other Revenues from Contracts with Customers | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	5,200	2,900
Other
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	443,600	413,800
Alternative Revenue Programs	0	0
Other Revenues	0	0
Operating Revenues	443,600	413,800
Other | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0
Other | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0
Other | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0
Other | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0
Other | Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0
Other | Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0
Other | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	443,600	413,800
Eliminations
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(809,800)	(744,000)
Alternative Revenue Programs	(26,800)	(16,900)
Other Revenues	0	0
Operating Revenues	(836,600)	(760,900)
Eliminations | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(6,800)	(6,100)
Eliminations | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0
Eliminations | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(1,700)	(1,000)
Eliminations | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(5,100)	(5,100)
Eliminations | Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(361,600)	(325,300)
Eliminations | Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0
Eliminations | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(441,400)	(412,600)
Consolidations Eliminations | CL&P
Disaggregation of Revenue [Line Items]
Operating Revenues	(159,800)	(139,700)
Consolidations Eliminations | NSTAR Electric
Disaggregation of Revenue [Line Items]
Operating Revenues	(159,300)	(141,100)
Consolidations Eliminations | PSNH
Disaggregation of Revenue [Line Items]
Operating Revenues	(56,200)	(51,500)
Electric Distribution | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	2,243,000	2,577,100
Alternative Revenue Programs	13,200	6,000
Other Revenues	5,500	5,500
Operating Revenues	2,261,700	2,588,600
Electric Distribution | Operating Segments | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	2,049,300	2,341,500
Electric Distribution | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,254,100	1,464,000
Electric Distribution | Operating Segments | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	707,500	788,400
Electric Distribution | Operating Segments | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	87,700	89,100
Electric Distribution | Operating Segments | Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0
Electric Distribution | Operating Segments | Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	165,300	217,300
Electric Distribution | Operating Segments | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	28,400	18,300
Natural Gas Distribution | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	873,800	1,016,800
Alternative Revenue Programs	31,500	27,400
Other Revenues	700	1,000
Operating Revenues	906,000	1,045,200
Natural Gas Distribution | Operating Segments | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	814,500	966,200
Natural Gas Distribution | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	507,600	576,600
Natural Gas Distribution | Operating Segments | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	247,100	320,000
Natural Gas Distribution | Operating Segments | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	59,800	69,600
Natural Gas Distribution | Operating Segments | Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0
Natural Gas Distribution | Operating Segments | Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	58,200	49,100
Natural Gas Distribution | Operating Segments | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,100	1,500
Electric Transmission | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	478,000	439,700
Alternative Revenue Programs	29,600	18,700
Other Revenues	200	200
Operating Revenues	507,800	458,600
Electric Transmission | Operating Segments | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0
Electric Transmission | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0
Electric Transmission | Operating Segments | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0
Electric Transmission | Operating Segments | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0
Electric Transmission | Operating Segments | Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	474,100	435,000
Electric Transmission | Operating Segments | Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0
Electric Transmission | Operating Segments | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	3,900	4,700
Water Distribution | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	48,200	48,400
Alternative Revenue Programs	1,600	1,700
Other Revenues	300	200
Operating Revenues	50,100	50,300
Water Distribution | Operating Segments | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	47,500	45,500
Water Distribution | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	30,300	28,900
Water Distribution | Operating Segments | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	16,200	15,500
Water Distribution | Operating Segments | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,000	1,100
Water Distribution | Operating Segments | Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	0	0
Water Distribution | Operating Segments | Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	900	800
Water Distribution | Operating Segments | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	$ (200)	$ 2,100