REGULATORY ACCOUNTING - Components of Regulatory Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 5,773,000	$ 5,578,300
Less:  Current Portion	1,382,150	1,335,491
Total Long-Term Regulatory Assets	4,390,816	4,242,794
Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	1,680,700	1,379,100
Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	1,075,700	1,075,300
Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	873,900	921,700
Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	864,700	853,300
Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	414,100	435,700
Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	272,500	281,000
Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	152,100	181,800
Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	132,100	127,900
Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	307,200	322,500
CL&P
Regulatory Assets [Line Items]
Total Regulatory Assets	2,019,300	1,907,800
Less:  Current Portion	417,824	314,089
Total Long-Term Regulatory Assets	1,601,540	1,593,693
CL&P | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	875,200	799,300
CL&P | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	286,600	216,800
CL&P | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	144,100	156,700
CL&P | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	499,800	491,100
CL&P | Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
CL&P | Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
CL&P | Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	152,100	181,800
CL&P | Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	37,100	35,900
CL&P | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	24,400	26,200
NSTAR Electric
Regulatory Assets [Line Items]
Total Regulatory Assets	1,800,200	1,714,400
Less:  Current Portion	569,697	492,759
Total Long-Term Regulatory Assets	1,230,486	1,221,619
NSTAR Electric | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	552,900	484,400
NSTAR Electric | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	438,300	391,500
NSTAR Electric | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	282,200	299,500
NSTAR Electric | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	121,700	115,600
NSTAR Electric | Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
NSTAR Electric | Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	234,000	241,200
NSTAR Electric | Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
NSTAR Electric | Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	69,400	68,200
NSTAR Electric | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	101,700	114,000
PSNH
Regulatory Assets [Line Items]
Total Regulatory Assets	883,600	696,200
Less:  Current Portion	152,019	102,240
Total Long-Term Regulatory Assets	731,621	593,974
PSNH | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	252,600	95,400
PSNH | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	136,900	73,700
PSNH | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	52,300	56,600
PSNH | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	12,700	16,000
PSNH | Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	414,100	435,700
PSNH | Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
PSNH | Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
PSNH | Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	4,500	4,400
PSNH | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 10,500	$ 14,400