LONG-TERM DEBT - Narrative (Details) - USD ($) $ in Thousands	Feb. 08, 2024	Dec. 31, 2023	Nov. 21, 2023	Jun. 07, 2023	Dec. 31, 2022	Nov. 30, 2022	Jun. 14, 2022
Debt Instrument [Line Items]
Long-term debt		$ 23,588,616			$ 19,723,994
Interest included in payment to settle spent nuclear fuel obligation		9,500			8,800
CL&P
Debt Instrument [Line Items]
Long-term debt		4,814,429			4,216,488
PSNH
Debt Instrument [Line Items]
Long-term debt		1,431,591			1,134,914
NSTAR Electric
Debt Instrument [Line Items]
Long-term debt		4,496,947			4,345,085
Line of Credit | NSTAR Gas
Debt Instrument [Line Items]
Amount of long-term debt requested for issuance							$ 325,000
Line of Credit | CL&P
Debt Instrument [Line Items]
Amount of long-term debt requested for issuance						$ 1,150,000
Line of Credit | PSNH | Subsequent Event
Debt Instrument [Line Items]
Amount of long-term debt requested for issuance	$ 300,000
Line of Credit | Yankee Gas Services Company
Debt Instrument [Line Items]
Amount of long-term debt requested for issuance				$ 350,000
Line of Credit | NSTAR Electric
Debt Instrument [Line Items]
Amount of long-term debt requested for issuance			$ 2,400,000
Pre-1983 Spent Nuclear Fuel Obligation (CYAPC)
Debt Instrument [Line Items]
Long-term debt		$ 12,500			$ 11,900