INCOME TAXES - Tax Credits and Loss Carryforwards (Details) - State and Local Jurisdiction - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Operating Loss Carryforwards [Line Items]
Federal and State Tax Credit	$ 197.7	$ 186.6
Operating Loss Carryforwards	138.3	183.4
Federal and State Charitable Contribution	23.7	10.2
The Connecticut Light and Power Company
Operating Loss Carryforwards [Line Items]
Federal and State Tax Credit	137.0	133.4
Operating Loss Carryforwards	0.0	0.0
Federal and State Charitable Contribution	0.0	0.0
NSTAR Electric Company
Operating Loss Carryforwards [Line Items]
Federal and State Tax Credit	0.0	0.0
Operating Loss Carryforwards	0.0	0.0
Federal and State Charitable Contribution	0.0	0.0
Public Service Company of New Hampshire
Operating Loss Carryforwards [Line Items]
Federal and State Tax Credit	0.0	0.0
Operating Loss Carryforwards	0.0	0.0
Federal and State Charitable Contribution	$ 0.0	$ 0.0