REGULATORY ACCOUNTING - Components of Regulatory Assets (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 5,739,900	$ 5,578,300
Less:  Current Portion	1,332,028	1,335,491
Total Long-Term Regulatory Assets	4,407,875	4,242,794
Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	1,658,700	1,379,100
Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	1,028,700	1,075,300
Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	910,300	921,700
Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	856,100	853,300
Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	424,900	435,700
Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	276,700	281,000
Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	168,800	181,800
Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	129,200	127,900
Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	286,500	322,500
CL&P
Regulatory Assets [Line Items]
Total Regulatory Assets	1,996,500	1,907,800
Less:  Current Portion	356,468	314,089
Total Long-Term Regulatory Assets	1,639,960	1,593,693
CL&P | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	889,200	799,300
CL&P | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	228,200	216,800
CL&P | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	155,600	156,700
CL&P | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	492,900	491,100
CL&P | Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
CL&P | Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
CL&P | Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	168,800	181,800
CL&P | Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	36,500	35,900
CL&P | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	25,300	26,200
NSTAR Electric
Regulatory Assets [Line Items]
Total Regulatory Assets	1,823,300	1,714,400
Less:  Current Portion	559,758	492,759
Total Long-Term Regulatory Assets	1,263,534	1,221,619
NSTAR Electric | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	564,900	484,400
NSTAR Electric | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	432,400	391,500
NSTAR Electric | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	294,400	299,500
NSTAR Electric | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	118,100	115,600
NSTAR Electric | Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
NSTAR Electric | Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	237,600	241,200
NSTAR Electric | Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
NSTAR Electric | Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	68,000	68,200
NSTAR Electric | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	107,900	114,000
PSNH
Regulatory Assets [Line Items]
Total Regulatory Assets	838,500	696,200
Less:  Current Portion	140,912	102,240
Total Long-Term Regulatory Assets	697,568	593,974
PSNH | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	204,600	95,400
PSNH | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	122,800	73,700
PSNH | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	56,100	56,600
PSNH | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	13,100	16,000
PSNH | Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	424,900	435,700
PSNH | Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
PSNH | Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	0	0
PSNH | Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	4,500	4,400
PSNH | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 12,500	$ 14,400