SHORT-TERM DEBT - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 03, 2021	Dec. 18, 2019
Commercial Paper | Eversource
Short-term Debt [Line Items]
Amount of commercial paper program	$ 2,000,000,000
Line of Credit
Short-term Debt [Line Items]
Amount outstanding during period	0	$ 0
Line of Credit | Eversource
Short-term Debt [Line Items]
Amount of commercial paper program	$ 2,000,000,000
Debt instrument term	5 years
The Connecticut Light and Power Company
Short-term Debt [Line Items]
Short-term borrowing limit approved by regulatory agency			$ 600,000,000
The Connecticut Light and Power Company | Unsecured Debt
Short-term Debt [Line Items]
Period of maturity restricting provisions of debt	10 years
Total capitalization (as a percentage)	10.00%
Capacity available under preferred stock provisions	$ 963,600,000
The Connecticut Light and Power Company | Line of Credit
Short-term Debt [Line Items]
Amount of commercial paper program	450,000,000
Borrowings outstanding	0
NSTAR Electric Company
Short-term Debt [Line Items]
Short-term borrowing limit approved by regulatory agency				$ 655,000,000
Notes payable to related parties	0	21,300,000
NSTAR Electric Company | Commercial Paper
Short-term Debt [Line Items]
Amount of commercial paper program	650,000,000
NSTAR Electric Company | Line of Credit
Short-term Debt [Line Items]
Amount of commercial paper program	$ 650,000,000
Debt instrument term	5 years
Public Service Company of New Hampshire
Short-term Debt [Line Items]
Short-term borrowing limit approved by regulatory agency	$ 408,000,000
Notes payable to related parties	$ 110,600,000	$ 46,300,000
Public Service Company of New Hampshire | Short Term Debt Authorization Calculation
Short-term Debt [Line Items]
Interest rate	10.00%
Short-term debt borrowing calculation approved by regulatory agency	$ 60,000,000
Public Service Company of New Hampshire | Line of Credit
Short-term Debt [Line Items]
Amount of commercial paper program	$ 300,000,000