REGULATORY ACCOUNTING - Components of Regulatory Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2023	Dec. 31, 2022
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 4,621,200	$ 4,821,100
Less:  Current Portion	653,808	890,786
Total Long-Term Regulatory Liabilities	3,967,426	3,930,305
EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	2,584,100	2,619,300
Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	660,900	670,600
Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	683,700	890,800
Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	312,700	270,900
AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	110,200	98,200
Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	50,100	55,400
Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	219,500	215,900
CL&P
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,477,600	1,599,400
Less:  Current Portion	185,323	336,048
Total Long-Term Regulatory Liabilities	1,292,290	1,263,396
CL&P | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	976,500	983,600
CL&P | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	147,100	130,800
CL&P | Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	215,400	361,000
CL&P | Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	42,300	34,500
CL&P | AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	51,500	48,200
CL&P | Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	600	700
CL&P | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	44,200	40,600
NSTAR Electric
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,883,800	1,921,300
Less:  Current Portion	321,153	373,221
Total Long-Term Regulatory Liabilities	1,562,581	1,548,081
NSTAR Electric | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	923,600	944,300
NSTAR Electric | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	412,800	405,300
NSTAR Electric | Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	290,700	336,100
NSTAR Electric | Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	157,800	139,700
NSTAR Electric | AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	58,700	50,000
NSTAR Electric | Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	25,700	31,400
NSTAR Electric | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	14,500	14,500
PSNH
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	478,900	553,600
Less:  Current Portion	83,215	161,963
Total Long-Term Regulatory Liabilities	395,652	391,628
PSNH | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	343,700	348,600
PSNH | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	19,300	14,700
PSNH | Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	77,400	155,000
PSNH | Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	32,700	28,800
PSNH | AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
PSNH | Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	0	0
PSNH | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 5,800	$ 6,500