REGULATORY ACCOUNTING - Components of Regulatory Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2024	Dec. 31, 2023
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 7,018,000	$ 6,389,200
Less:  Current Portion	2,024,897	1,674,196
Total Long-Term Regulatory Assets	4,993,145	4,714,970
Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	2,077,200	1,785,900
Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	1,638,100	1,319,200
Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	1,096,000	1,117,300
Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	944,900	912,400
Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	360,100	392,500
Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	251,500	264,100
Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	147,000	137,900
Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	72,600	120,900
Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	430,600	339,000
CL&P
Regulatory Assets [Line Items]
Total Regulatory Assets	2,426,700	2,143,200
Less:  Current Portion	672,835	480,369
Total Long-Term Regulatory Assets	1,753,887	1,662,778
CL&P | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	998,300	896,600
CL&P | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	529,300	354,500
CL&P | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	198,200	197,400
CL&P | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	522,700	512,600
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	40,500	38,500
CL&P | Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	72,600	120,900
CL&P | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	65,100	22,700
NSTAR Electric
Regulatory Assets [Line Items]
Total Regulatory Assets	2,049,800	1,957,900
Less:  Current Portion	778,916	676,083
Total Long-Term Regulatory Assets	1,270,882	1,281,836
NSTAR Electric | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	626,300	609,100
NSTAR Electric | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	572,600	482,900
NSTAR Electric | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	313,800	336,700
NSTAR Electric | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	141,600	128,600
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	215,900	226,700
NSTAR Electric | Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	76,800	72,300
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	102,800	101,600
PSNH
Regulatory Assets [Line Items]
Total Regulatory Assets	1,075,200	963,300
Less:  Current Portion	170,501	189,450
Total Long-Term Regulatory Assets	904,717	773,783
PSNH | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	452,600	280,200
PSNH | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	153,900	182,200
PSNH | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	79,700	79,300
PSNH | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	19,100	16,400
PSNH | Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	360,100	392,500
PSNH | Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
PSNH | Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	5,000	4,700
PSNH | Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
PSNH | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 4,800	$ 8,000