REGULATORY ACCOUNTING - Components of Regulatory Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2023	Dec. 31, 2022
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 4,614,700	$ 4,821,100
Less:  Current Portion	591,750	890,786
Total Long-Term Regulatory Liabilities	4,022,923	3,930,305
EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	2,548,600	2,619,300
Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	666,600	670,600
Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	668,300	890,800
Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	354,000	270,900
AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	124,300	98,200
Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	51,000	55,400
Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	201,900	215,900
CL&P
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,418,100	1,599,400
Less:  Current Portion	102,239	336,048
Total Long-Term Regulatory Liabilities	1,315,928	1,263,396
CL&P | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	969,200	983,600
CL&P | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	157,900	130,800
CL&P | Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	154,000	361,000
CL&P | Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	49,900	34,500
CL&P | AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	56,100	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	30,400	40,600
NSTAR Electric
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,953,400	1,921,300
Less:  Current Portion	368,070	373,221
Total Long-Term Regulatory Liabilities	1,585,311	1,548,081
NSTAR Electric | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	905,100	944,300
NSTAR Electric | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	420,900	405,300
NSTAR Electric | Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	347,200	336,100
NSTAR Electric | Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	175,900	139,700
NSTAR Electric | AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	68,200	50,000
NSTAR Electric | Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	22,200	31,400
NSTAR Electric | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	13,900	14,500
PSNH
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	511,100	553,600
Less:  Current Portion	117,515	161,963
Total Long-Term Regulatory Liabilities	393,574	391,628
PSNH | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	339,300	348,600
PSNH | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	16,200	14,700
PSNH | Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	114,400	155,000
PSNH | Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	36,600	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	$ 4,600	$ 6,500