REGULATORY ACCOUNTING - Components of Regulatory Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Dec. 31, 2021
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 5,578,300	$ 5,715,800
Less:  Current Portion	1,335,491	1,129,093
Total Long-Term Regulatory Assets	4,242,794	4,586,709
Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	921,700	1,481,000
Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	1,379,100	1,102,700
Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	1,075,300	1,050,500
Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	853,300	790,700
Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	435,700	478,900
Goodwill-related
Regulatory Assets [Line Items]
Total Regulatory Assets	281,000	297,800
Derivative Liabilities
Regulatory Assets [Line Items]
Total Regulatory Assets	181,800	249,200
Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	127,900	115,000
Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	322,500	150,000
CL&P
Regulatory Assets [Line Items]
Total Regulatory Assets	1,907,800	2,084,800
Less:  Current Portion	314,089	371,609
Total Long-Term Regulatory Assets	1,593,693	1,713,161
CL&P | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	156,700	272,400
CL&P | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	799,300	695,600
CL&P | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	216,800	333,600
CL&P | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	491,100	470,500
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	181,800	249,200
CL&P | Asset Retirement Obligations
Regulatory Assets [Line Items]
Total Regulatory Assets	35,900	33,600
CL&P | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	26,200	29,900
NSTAR Electric
Regulatory Assets [Line Items]
Total Regulatory Assets	1,714,400	1,579,200
Less:  Current Portion	492,759	443,956
Total Long-Term Regulatory Assets	1,221,619	1,135,231
NSTAR Electric | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	299,500	395,500
NSTAR Electric | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	484,400	341,300
NSTAR Electric | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	391,500	376,600
NSTAR Electric | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	115,600	112,600
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	241,200	255,700
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	68,200	59,800
NSTAR Electric | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	114,000	37,700
PSNH
Regulatory Assets [Line Items]
Total Regulatory Assets	696,200	786,400
Less:  Current Portion	102,240	107,169
Total Long-Term Regulatory Assets	593,974	679,182
PSNH | Benefit Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	56,600	118,900
PSNH | Storm Costs, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	95,400	65,800
PSNH | Regulatory Tracking Mechanisms
Regulatory Assets [Line Items]
Total Regulatory Assets	73,700	85,400
PSNH | Income Taxes, Net
Regulatory Assets [Line Items]
Total Regulatory Assets	16,000	17,500
PSNH | Securitized Stranded Costs
Regulatory Assets [Line Items]
Total Regulatory Assets	435,700	478,900
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	4,400	4,100
PSNH | Other Regulatory Assets
Regulatory Assets [Line Items]
Total Regulatory Assets	$ 14,400	$ 15,800