COMMON SHARES - Common Shares Authorized and Issued (Details) - $ / shares	Dec. 31, 2023	May 03, 2023	May 02, 2023	Dec. 31, 2022
Class of Stock [Line Items]
Per share par value (in dollars per share)	$ 5			$ 5
Authorized (in shares)	410,000,000	410,000,000	380,000,000	380,000,000
Issued (in shares)	359,984,073			359,984,073
CL&P
Class of Stock [Line Items]
Per share par value (in dollars per share)	$ 10			$ 10
Authorized (in shares)	24,500,000			24,500,000
Issued (in shares)	6,035,205			6,035,205
NSTAR Electric
Class of Stock [Line Items]
Per share par value (in dollars per share)	$ 1			$ 1
Authorized (in shares)	100,000,000			100,000,000
Issued (in shares)	200			200
PSNH
Class of Stock [Line Items]
Per share par value (in dollars per share)	$ 1			$ 1
Authorized (in shares)	100,000,000			100,000,000
Issued (in shares)	301			301