REGULATORY ACCOUNTING - Components of Regulatory Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 6,389,200	$ 5,578,300
Less:  Current Portion	1,674,196	1,335,491
Total Long-Term Regulatory Assets	4,714,970	4,242,794
Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	1,785,900	1,379,100
Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	1,319,200	1,075,300
Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	1,117,300	921,700
Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	912,400	853,300
Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	392,500	435,700
Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	264,100	281,000
Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	137,900	127,900
Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	120,900	181,800
Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	339,000	322,500
CL&P
Regulatory Assets [Line Items]
Total Regulatory Assets	2,143,200	1,907,800
Less:  Current Portion	480,369	314,089
Total Long-Term Regulatory Assets	1,662,778	1,593,693
CL&P | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	896,600	799,300
CL&P | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	354,500	216,800
CL&P | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	197,400	156,700
CL&P | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	512,600	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 | Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	38,500	35,900
CL&P | Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	120,900	181,800
CL&P | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	22,700	26,200
NSTAR Electric
Regulatory Assets [Line Items]
Total Regulatory Assets	1,957,900	1,714,400
Less:  Current Portion	676,083	492,759
Total Long-Term Regulatory Assets	1,281,836	1,221,619
NSTAR Electric | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	609,100	484,400
NSTAR Electric | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	482,900	391,500
NSTAR Electric | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	336,700	299,500
NSTAR Electric | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	128,600	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	226,700	241,200
NSTAR Electric | Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	72,300	68,200
NSTAR Electric | Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
NSTAR Electric | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	101,600	114,000
PSNH
Regulatory Assets [Line Items]
Total Regulatory Assets	963,300	696,200
Less:  Current Portion	189,450	102,240
Total Long-Term Regulatory Assets	773,783	593,974
PSNH | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	280,200	95,400
PSNH | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	182,200	73,700
PSNH | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	79,300	56,600
PSNH | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	16,400	16,000
PSNH | Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	392,500	435,700
PSNH | Goodwill-related
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 | Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
PSNH | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 8,000	$ 14,400