REGULATORY ACCOUNTING - Components of Regulatory Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 7,067,700	$ 6,389,200
Less:  Current Portion	2,071,652	1,674,196
Total Long-Term Regulatory Assets	4,995,989	4,714,970
Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	2,074,800	1,785,900
Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	1,722,000	1,319,200
Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	1,116,500	1,117,300
Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	936,100	912,400
Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	370,900	392,500
Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	255,700	264,100
Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	144,000	137,900
Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	87,400	120,900
Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	360,300	339,000
CL&P
Regulatory Assets [Line Items]
Total Regulatory Assets	2,592,700	2,143,200
Less:  Current Portion	860,776	480,369
Total Long-Term Regulatory Assets	1,731,870	1,662,778
CL&P | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	976,800	896,600
CL&P | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	743,700	354,500
CL&P | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	201,600	197,400
CL&P | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	522,400	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	39,800	38,500
CL&P | Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	87,400	120,900
CL&P | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	21,000	22,700
NSTAR Electric
Regulatory Assets [Line Items]
Total Regulatory Assets	2,062,900	1,957,900
Less:  Current Portion	757,447	676,083
Total Long-Term Regulatory Assets	1,305,490	1,281,836
NSTAR Electric | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	652,100	609,100
NSTAR Electric | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	549,600	482,900
NSTAR Electric | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	320,300	336,700
NSTAR Electric | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	138,200	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	219,500	226,700
NSTAR Electric | Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	75,300	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	107,900	101,600
PSNH
Regulatory Assets [Line Items]
Total Regulatory Assets	1,097,600	963,300
Less:  Current Portion	175,003	189,450
Total Long-Term Regulatory Assets	922,613	773,783
PSNH | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	445,900	280,200
PSNH | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	174,300	182,200
PSNH | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	81,000	79,300
PSNH | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	14,800	16,400
PSNH | Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	370,900	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	4,900	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	$ 5,800	$ 8,000