REGULATORY ACCOUNTING - Components of Regulatory Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 4,821,100	$ 4,468,700
Less:  Current Portion	890,786	602,432
Total Long-Term Regulatory Liabilities	3,930,305	3,866,251
EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	2,619,300	2,685,200
Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	670,600	649,600
Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	890,800	448,400
Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	270,900	148,300
Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	55,400	133,500
AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	98,200	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	215,900	241,400
CL&P
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,599,400	1,459,800
Less:  Current Portion	336,048	266,489
Total Long-Term Regulatory Liabilities	1,263,396	1,193,259
CL&P | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	983,600	996,100
CL&P | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	130,800	100,100
CL&P | Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	361,000	182,000
CL&P | Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	34,500	12,000
CL&P | Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	700	0
CL&P | AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	48,200	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	40,600	45,100
NSTAR Electric
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,921,300	1,787,300
Less:  Current Portion	373,221	228,248
Total Long-Term Regulatory Liabilities	1,548,081	1,559,072
NSTAR Electric | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	944,300	984,500
NSTAR Electric | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	405,300	381,000
NSTAR Electric | Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	336,100	185,100
NSTAR Electric | Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	139,700	90,700
NSTAR Electric | Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	31,400	107,400
NSTAR Electric | AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	50,000	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	14,500	800
PSNH
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	553,600	501,600
Less:  Current Portion	161,963	120,176
Total Long-Term Regulatory Liabilities	391,628	381,366
PSNH | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	348,600	359,200
PSNH | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	14,700	17,200
PSNH | Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	155,000	107,000
PSNH | Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	28,800	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	$ 6,500	$ 3,300