REGULATORY ACCOUNTING - Components of Regulatory Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 4,746,200	$ 4,821,100
Less:  Current Portion	724,413	890,786
Total Long-Term Regulatory Liabilities	4,021,830	3,930,305
EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	2,568,600	2,619,300
Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	680,800	670,600
Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	740,500	890,800
Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	333,400	270,900
AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	117,600	98,200
Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	43,900	55,400
Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	261,400	215,900
CL&P
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,464,200	1,599,400
Less:  Current Portion	155,901	336,048
Total Long-Term Regulatory Liabilities	1,308,284	1,263,396
CL&P | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	973,400	983,600
CL&P | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	154,900	130,800
CL&P | Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	205,400	361,000
CL&P | Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	46,100	34,500
CL&P | AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	53,500	48,200
CL&P | Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	500	700
CL&P | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	30,400	40,600
NSTAR Electric
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	2,003,600	1,921,300
Less:  Current Portion	416,046	373,221
Total Long-Term Regulatory Liabilities	1,587,567	1,548,081
NSTAR Electric | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	915,200	944,300
NSTAR Electric | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	418,300	405,300
NSTAR Electric | Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	345,200	336,100
NSTAR Electric | Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	166,800	139,700
NSTAR Electric | AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	64,100	50,000
NSTAR Electric | Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	21,400	31,400
NSTAR Electric | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	72,600	14,500
PSNH
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	505,600	553,600
Less:  Current Portion	114,561	161,963
Total Long-Term Regulatory Liabilities	391,013	391,628
PSNH | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	341,600	348,600
PSNH | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	16,000	14,700
PSNH | Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	108,400	155,000
PSNH | Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	34,700	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	$ 4,900	$ 6,500