Futures contracts can be traded in a "Cash" type account. Note that futures are mark to market contracts and are not assets like stocks. While a "Margin" type account is required if you want to borrow funds to purchase a stock, futures contracts require no financing. Futures accounts do, however, require a cash deposit referred to as a "Performance Bond" (or sometimes "Margin Deposit"), which is intended to ensure your performance on the contract. As these contracts are routinely marked to the market by the clearinghouse performance each day prior to expiration, any unrealized losses must be met by cash.
The amount of cash Performance Bond varies by product, and sometimes by contract delivery month, and is typically set at a level intended to cover a one day adverse price change. IBKR marks to market, or revalues, futures contracts continuously throughout the day to ensure your account is margin compliant and to meet the ensuing cash settlement obligation with the clearinghouse.