SHORT-TERM AND LONG-TERM DEBT - Borrowings Outstanding and Available under the Commercial Paper Programs (Details) - Commercial Paper - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Borrowings outstanding	$ 529.0	$ 1,442.2
Available borrowing capacity	$ 1,471.0	$ 557.8
Weighted-average interest rate (in percent)	5.31%	4.63%
NSTAR Electric
Debt Instrument [Line Items]
Borrowings outstanding	$ 324.0	$ 0.0
Available borrowing capacity	$ 326.0	$ 650.0
Weighted-average interest rate (in percent)	5.17%	0.00%