SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES -Transfer of Energy Efficiency Loans (Details) - The Connecticut Light and Power Company - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Accounts, Notes, Loans and Financing Receivable [Line Items]
Maximum loans receivable outstanding	$ 55.0
Loans transferred receivable current	12.9	$ 16.5
Loans transferred receivable non-current	$ 9.5	$ 18.2