REGULATORY ACCOUNTING - Components of Regulatory Liabilities (Details) - USD ($) $ in Thousands	Jun. 30, 2024	Dec. 31, 2023
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 4,745,100	$ 4,614,700
Less:  Current Portion	652,291	591,750
Total Long-Term Regulatory Liabilities	4,092,811	4,022,923
EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	2,526,700	2,548,600
Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	722,700	668,300
Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	717,400	666,600
Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	391,500	354,000
AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	142,400	124,300
Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	40,400	51,000
Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	204,000	201,900
CL&P
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,485,200	1,418,100
Less:  Current Portion	133,305	102,239
Total Long-Term Regulatory Liabilities	1,351,877	1,315,928
CL&P | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	963,900	969,200
CL&P | Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	183,200	154,000
CL&P | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	182,100	157,900
CL&P | Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	56,000	49,900
CL&P | AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	61,000	56,100
CL&P | Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	500	600
CL&P | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	38,500	30,400
NSTAR Electric
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	2,033,100	1,953,400
Less:  Current Portion	413,492	368,070
Total Long-Term Regulatory Liabilities	1,619,614	1,585,311
NSTAR Electric | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	894,000	905,100
NSTAR Electric | Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	393,300	347,200
NSTAR Electric | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	442,200	420,900
NSTAR Electric | Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	194,000	175,900
NSTAR Electric | AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	81,400	68,200
NSTAR Electric | Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	14,700	22,200
NSTAR Electric | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	13,500	13,900
PSNH
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	471,300	511,100
Less:  Current Portion	79,112	117,515
Total Long-Term Regulatory Liabilities	392,184	393,574
PSNH | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	335,700	339,300
PSNH | Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	72,600	114,400
PSNH | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	18,400	16,200
PSNH | Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	39,700	36,600
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	$ 4,600