REGULATORY ACCOUNTING - Components of Regulatory Assets (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 5,732,600	$ 5,715,800
Less:  Current Portion	1,163,411	1,129,093
Total Long-Term Regulatory Assets	4,569,236	4,586,709
Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	1,435,000	1,481,000
Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	1,250,100	1,102,700
Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	979,000	1,050,500
Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	798,000	790,700
Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	457,300	478,900
Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	289,400	297,800
Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	213,300	249,200
Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	121,000	115,000
Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	189,500	150,000
CL&P
Regulatory Assets [Line Items]
Total Regulatory Assets	2,060,200	2,084,800
Less:  Current Portion	396,447	371,609
Total Long-Term Regulatory Assets	1,663,820	1,713,161
CL&P | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	267,600	272,400
CL&P | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	733,800	695,600
CL&P | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	306,100	333,600
CL&P | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	476,600	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	213,300	249,200
CL&P | Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	34,700	33,600
CL&P | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	28,100	29,900
NSTAR Electric
Regulatory Assets [Line Items]
Total Regulatory Assets	1,680,500	1,579,200
Less:  Current Portion	419,718	443,956
Total Long-Term Regulatory Assets	1,260,785	1,135,231
NSTAR Electric | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	397,200	395,500
NSTAR Electric | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	455,000	341,300
NSTAR Electric | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	368,700	376,600
NSTAR Electric | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	113,600	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	248,400	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	64,100	59,800
NSTAR Electric | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	33,500	37,700
PSNH
Regulatory Assets [Line Items]
Total Regulatory Assets	736,900	786,400
Less:  Current Portion	93,225	107,169
Total Long-Term Regulatory Assets	643,745	679,182
PSNH | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	116,700	118,900
PSNH | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	61,300	65,800
PSNH | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	68,300	85,400
PSNH | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	13,900	17,500
PSNH | Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	457,300	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	4,200	4,100
PSNH | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 15,200	$ 15,800