REGULATORY ACCOUNTING - Components of Regulatory Assets (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 5,702,400	$ 5,715,800
Less:  Current Portion	1,143,646	1,129,093
Total Long-Term Regulatory Assets	4,558,776	4,586,709
Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	1,408,900	1,481,000
Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	1,243,900	1,102,700
Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	941,200	1,050,500
Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	808,500	790,700
Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	446,500	478,900
Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	285,200	297,800
Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	195,900	249,200
Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	124,300	115,000
Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	248,000	150,000
CL&P
Regulatory Assets [Line Items]
Total Regulatory Assets	1,938,500	2,084,800
Less:  Current Portion	305,556	371,609
Total Long-Term Regulatory Assets	1,632,875	1,713,161
CL&P | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	263,300	272,400
CL&P | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	722,500	695,600
CL&P | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	214,400	333,600
CL&P | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	480,000	470,500
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	195,900	249,200
CL&P | Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	35,300	33,600
CL&P | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	27,100	29,900
NSTAR Electric
Regulatory Assets [Line Items]
Total Regulatory Assets	1,645,200	1,579,200
Less:  Current Portion	387,333	443,956
Total Long-Term Regulatory Assets	1,257,884	1,135,231
NSTAR Electric | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	389,000	395,500
NSTAR Electric | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	459,900	341,300
NSTAR Electric | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	339,000	376,600
NSTAR Electric | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	114,500	112,600
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	244,800	255,700
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	66,000	59,800
NSTAR Electric | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	32,000	37,700
PSNH
Regulatory Assets [Line Items]
Total Regulatory Assets	728,800	786,400
Less:  Current Portion	110,111	107,169
Total Long-Term Regulatory Assets	618,720	679,182
PSNH | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	114,600	118,900
PSNH | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	61,500	65,800
PSNH | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	70,400	85,400
PSNH | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	17,400	17,500
PSNH | Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	446,500	478,900
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	4,300	4,100
PSNH | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 14,100	$ 15,800