REGULATORY ACCOUNTING - Components of Regulatory Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	$ 4,624,900	$ 4,821,100
Less:  Current Portion	650,538	890,786
Total Long-Term Regulatory Liabilities	3,974,374	3,930,305
EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	2,601,800	2,619,300
Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	705,400	670,600
Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	653,600	890,800
Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	291,400	270,900
AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	103,800	98,200
Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	49,200	55,400
Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	219,700	215,900
CL&P
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,401,900	1,599,400
Less:  Current Portion	124,640	336,048
Total Long-Term Regulatory Liabilities	1,277,281	1,263,396
CL&P | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	980,000	983,600
CL&P | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	144,200	130,800
CL&P | Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	145,000	361,000
CL&P | Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	38,300	34,500
CL&P | AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	49,800	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	44,000	40,600
NSTAR Electric
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	1,932,600	1,921,300
Less:  Current Portion	375,047	373,221
Total Long-Term Regulatory Liabilities	1,557,614	1,548,081
NSTAR Electric | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	933,900	944,300
NSTAR Electric | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	412,900	405,300
NSTAR Electric | Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	341,600	336,100
NSTAR Electric | Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	148,500	139,700
NSTAR Electric | AFUDC - Transmission
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	54,000	50,000
NSTAR Electric | Benefit Costs
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	27,100	31,400
NSTAR Electric | Other Regulatory Liabilities
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	14,600	14,500
PSNH
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	476,900	553,600
Less:  Current Portion	86,569	161,963
Total Long-Term Regulatory Liabilities	390,290	391,628
PSNH | EDIT due to Tax Cuts and Jobs Act of 2017
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	346,100	348,600
PSNH | Cost of Removal
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	20,200	14,700
PSNH | Regulatory Tracking Mechanisms
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	73,200	155,000
PSNH | Deferred Portion of Non-Service Income Components of Pension, SERP and PBOP
Regulatory Liabilities [Line Items]
Total Regulatory Liabilities	30,800	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	$ 6,600	$ 6,500