
Your base currency determines the currency of translation for your statements and the currency used for determining margin requirements. Base currency is determined when you open an account. Customers who hold a margin account may change their base currency at any time through Account Management.
Cash accounts can have multi-currency (MULT) capability and can trade non-base currency products. 1
Base currencies are available in AUD, CAD, CZK, CHF, EUR, GBP, HKD, HUF, INR, JPY, MXN, NZD, SEK, or USD. You are not restricted from making deposits and withdrawals in any one of the aforementioned non-base currencies. 2
http://www.interactivebrokers.com/en/index.php?f=accountConfig&p=baseCurrency