REGULATORY ACCOUNTING - Components of Regulatory Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2022	Dec. 31, 2021
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 4,889,800	$ 4,468,700
Less:  Current Portion	988,714	602,432
Total Long-Term Regulatory Liabilities	3,901,106	3,866,251
EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	2,629,000	2,685,200
Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	654,500	649,600
Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	957,400	448,400
Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	240,300	148,300
Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	110,900	133,500
AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	93,100	81,000
CL&P Settlement Agreement and Storm Performance Penalty
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	81,300
Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	204,600	241,400
CL&P
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,678,100	1,459,800
Less:  Current Portion	434,465	266,489
Total Long-Term Regulatory Liabilities	1,243,581	1,193,259
CL&P | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	986,100	996,100
CL&P | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	122,400	100,100
CL&P | Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	455,700	182,000
CL&P | Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	28,900	12,000
CL&P | Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
CL&P | AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	46,400	43,200
CL&P | CL&P Settlement Agreement and Storm Performance Penalty
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	81,300
CL&P | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	38,600	45,100
NSTAR Electric
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,963,800	1,787,300
Less:  Current Portion	368,044	228,248
Total Long-Term Regulatory Liabilities	1,595,754	1,559,072
NSTAR Electric | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	952,600	984,500
NSTAR Electric | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	418,300	381,000
NSTAR Electric | Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	326,200	185,100
NSTAR Electric | Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	127,500	90,700
NSTAR Electric | Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	88,100	107,400
NSTAR Electric | AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	46,700	37,800
NSTAR Electric | CL&P Settlement Agreement and Storm Performance Penalty
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
NSTAR Electric | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	4,400	800
PSNH
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	566,400	501,600
Less:  Current Portion	185,092	120,176
Total Long-Term Regulatory Liabilities	381,294	381,366
PSNH | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	350,000	359,200
PSNH | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	19,300	17,200
PSNH | Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	165,100	107,000
PSNH | Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	25,300	14,900
PSNH | Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
PSNH | AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
PSNH | CL&P Settlement Agreement and Storm Performance Penalty
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
PSNH | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 6,700	$ 3,300