Customer money is segregated in special bank or custody accounts, which are designated for the exclusive benefit of customers of IBKR. This protection (the SEC term is "reserve" and the CFTC term is "segregation") is a core principle of securities and commodities brokerage. By properly segregating the customer's assets, if no money or stock is borrowed and no futures positions are held by the customer, then the customer's assets are available to be returned to the customer in the event of a default by or bankruptcy of the broker.