REVENUES (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	$ 4,538,000	$ 4,106,500
Alternative Revenue Programs	(40,700)	4,500
Other Revenues	7,100	7,400
Total Operating Revenues	4,504,363	4,118,355
CL&P
Disaggregation of Revenue [Line Items]
Total Operating Revenues	1,568,126	1,541,189
NSTAR Electric
Disaggregation of Revenue [Line Items]
Total Operating Revenues	1,131,088	1,014,227
PSNH
Disaggregation of Revenue [Line Items]
Total Operating Revenues	383,517	347,981
Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	3,757,300	3,511,000
Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	2,345,200	2,217,200
Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,236,200	1,126,800
Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	175,900	167,000
Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	166,000	154,700
Wholesale Market Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	581,700	411,200
Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	33,000	29,600
Operating Segments | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,784,000	1,733,500
Alternative Revenue Programs	(32,500)	(18,900)
Other Revenues	2,200	2,700
Operating Segments | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,333,500	1,200,600
Alternative Revenue Programs	(16,300)	(9,100)
Other Revenues	2,400	2,400
Operating Segments | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	467,200	434,100
Alternative Revenue Programs	(15,600)	(19,700)
Other Revenues	1,200	900
Operating Segments | Total Retail Tariff Sales Revenues | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,131,100	1,193,700
Operating Segments | Total Retail Tariff Sales Revenues | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	940,400	912,700
Operating Segments | Total Retail Tariff Sales Revenues | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	327,600	295,100
Operating Segments | Residential | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	787,700	801,200
Operating Segments | Residential | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	471,200	506,200
Operating Segments | Residential | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	208,900	181,900
Operating Segments | Commercial | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	304,400	344,100
Operating Segments | Commercial | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	434,500	375,700
Operating Segments | Commercial | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	94,700	88,300
Operating Segments | Industrial | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	39,000	48,400
Operating Segments | Industrial | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	34,700	30,800
Operating Segments | Industrial | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	24,000	24,900
Operating Segments | Wholesale Transmission Revenues | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	269,200	251,100
Operating Segments | Wholesale Transmission Revenues | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	236,400	218,700
Operating Segments | Wholesale Transmission Revenues | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	126,700	124,200
Operating Segments | Wholesale Market Sales Revenues | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	368,700	280,000
Operating Segments | Wholesale Market Sales Revenues | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	143,300	57,300
Operating Segments | Wholesale Market Sales Revenues | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	9,200	10,500
Operating Segments | Other Revenues from Contracts with Customers | CL&P
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	15,000	8,700
Operating Segments | Other Revenues from Contracts with Customers | NSTAR Electric
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	13,400	11,900
Operating Segments | Other Revenues from Contracts with Customers | PSNH
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	3,700	4,300
Other
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	484,400	439,000
Alternative Revenue Programs	0	0
Other Revenues	0	0
Total Operating Revenues	484,400	439,000
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	484,400	439,000
Eliminations
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(961,600)	(883,000)
Alternative Revenue Programs	29,700	45,200
Other Revenues	0	0
Total Operating Revenues	(931,900)	(837,800)
Eliminations | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(10,000)	(7,900)
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	(3,500)	(2,000)
Eliminations | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(6,500)	(5,900)
Eliminations | Wholesale Transmission Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	(466,300)	(439,300)
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	(485,300)	(435,800)
Consolidations Eliminations | CL&P
Disaggregation of Revenue [Line Items]
Total Operating Revenues	(185,600)	(176,100)
Consolidations Eliminations | NSTAR Electric
Disaggregation of Revenue [Line Items]
Total Operating Revenues	(188,500)	(179,700)
Consolidations Eliminations | PSNH
Disaggregation of Revenue [Line Items]
Total Operating Revenues	(69,300)	(67,300)
Electric Distribution | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	2,940,300	2,769,600
Alternative Revenue Programs	(5,500)	2,200
Other Revenues	5,700	5,900
Total Operating Revenues	2,940,500	2,777,700
Electric Distribution | Operating Segments | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	2,398,600	2,401,000
Electric Distribution | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,467,800	1,489,300
Electric Distribution | Operating Segments | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	833,100	807,600
Electric Distribution | Operating Segments | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	97,700	104,100
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	521,200	347,800
Electric Distribution | Operating Segments | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	20,500	20,800
Natural Gas Distribution | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,379,700	1,133,900
Alternative Revenue Programs	(7,600)	6,400
Other Revenues	1,100	1,100
Total Operating Revenues	1,373,200	1,141,400
Natural Gas Distribution | Operating Segments | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,318,700	1,070,200
Natural Gas Distribution | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	844,700	696,500
Natural Gas Distribution | Operating Segments | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	390,400	305,900
Natural Gas Distribution | Operating Segments | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	83,600	67,800
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	59,400	62,300
Natural Gas Distribution | Operating Segments | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,600	1,400
Electric Transmission | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	643,400	597,600
Alternative Revenue Programs	(58,900)	(49,900)
Other Revenues	100	100
Total Operating Revenues	584,600	547,800
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	632,300	594,000
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	11,100	3,600
Water Distribution | Operating Segments
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	51,800	49,400
Alternative Revenue Programs	1,600	600
Other Revenues	200	300
Total Operating Revenues	53,600	50,300
Water Distribution | Operating Segments | Total Retail Tariff Sales Revenues
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	50,000	47,700
Water Distribution | Operating Segments | Residential
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	32,700	31,400
Water Distribution | Operating Segments | Commercial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	16,200	15,300
Water Distribution | Operating Segments | Industrial
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	1,100	1,000
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	1,100	1,100
Water Distribution | Operating Segments | Other Revenues from Contracts with Customers
Disaggregation of Revenue [Line Items]
Revenues from Contracts with Customers	$ 700	$ 600