REGULATORY ACCOUNTING - Components of Regulatory Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 5,856,600	$ 5,578,300
Less:  Current Portion	1,507,888	1,335,491
Total Long-Term Regulatory Assets	4,348,700	4,242,794
Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	1,700,600	1,379,100
Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	1,173,300	1,075,300
Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	863,400	921,700
Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	879,600	853,300
Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	403,300	435,700
Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	268,300	281,000
Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	136,600	181,800
Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	135,000	127,900
Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	296,500	322,500
CL&P
Regulatory Assets [Line Items]
Total Regulatory Assets	1,982,600	1,907,800
Less:  Current Portion	383,672	314,089
Total Long-Term Regulatory Assets	1,598,934	1,593,693
CL&P | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	882,700	799,300
CL&P | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	254,300	216,800
CL&P | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	143,200	156,700
CL&P | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	504,500	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	136,600	181,800
CL&P | Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	37,800	35,900
CL&P | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	23,500	26,200
NSTAR Electric
Regulatory Assets [Line Items]
Total Regulatory Assets	1,828,600	1,714,400
Less:  Current Portion	638,464	492,759
Total Long-Term Regulatory Assets	1,190,138	1,221,619
NSTAR Electric | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	553,900	484,400
NSTAR Electric | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	473,400	391,500
NSTAR Electric | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	278,000	299,500
NSTAR Electric | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	125,700	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	230,400	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	70,900	68,200
NSTAR Electric | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	96,300	114,000
PSNH
Regulatory Assets [Line Items]
Total Regulatory Assets	916,500	696,200
Less:  Current Portion	177,120	102,240
Total Long-Term Regulatory Assets	739,372	593,974
PSNH | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	264,000	95,400
PSNH | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	166,100	73,700
PSNH | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	51,800	56,600
PSNH | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	17,600	16,000
PSNH | Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	403,300	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	4,700	4,400
PSNH | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 9,000	$ 14,400