MMDAs are deposits and, as mentioned, are covered by FDIC insurance. The FDIC says federal insurance would cover only your principal, not any interest, because there is no specific, guaranteed interest earned under terms of the contract. The Federal Reserve is the country's Central Bank. It controls the flow of money in and out of banks and maintains the stability of the financial system. All national banks must be members of the Federal Reserve.
Membership is optional for state banks.
State banks are chartered, regulated and supervised by their state's banking division. The FDIC is the federal regulator of state-chartered banks that don't belong to the Federal Reserve System. The Office of Thrift Supervision is the primary regulator of all federal and many state-chartered thrift institutions, which include savings banks and savings and loan associations. Credit Unions are non-profit, cooperative financial institutions owned and controlled by their members, the people who use its services. Generally, there's a common bond, such as where people work or worship, that qualifies someone for membership.