REGULATORY ACCOUNTING - Components of Regulatory Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 4,646,600	$ 4,468,700
Less:  Current Portion	759,733	602,432
Total Long-Term Regulatory Liabilities	3,886,914	3,866,251
EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	2,646,100	2,685,200
Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	653,900	649,600
Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	701,900	448,400
Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	209,700	148,300
Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	116,000	133,500
AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	88,900	81,000
CL&P Settlement Agreement and Storm Performance Penalty
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	6,400	81,300
Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	223,700	241,400
CL&P
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,554,900	1,459,800
Less:  Current Portion	337,240	266,489
Total Long-Term Regulatory Liabilities	1,217,711	1,193,259
CL&P | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	989,400	996,100
CL&P | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	113,600	100,100
CL&P | Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	319,400	182,000
CL&P | Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	23,300	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	44,900	43,200
CL&P | CL&P Settlement Agreement and Storm Performance Penalty
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	6,400	81,300
CL&P | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	57,900	45,100
NSTAR Electric
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,845,800	1,787,300
Less:  Current Portion	274,139	228,248
Total Long-Term Regulatory Liabilities	1,571,705	1,559,072
NSTAR Electric | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	962,100	984,500
NSTAR Electric | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	395,000	381,000
NSTAR Electric | Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	232,700	185,100
NSTAR Electric | Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	115,200	90,700
NSTAR Electric | Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	92,400	107,400
NSTAR Electric | AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	44,000	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	500,300	501,600
Less:  Current Portion	106,554	120,176
Total Long-Term Regulatory Liabilities	393,673	381,366
PSNH | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	353,000	359,200
PSNH | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	19,000	17,200
PSNH | Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	99,800	107,000
PSNH | Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	21,800	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