In an IBKR Universal account a security like a Stock, Bond or Treasury resting in the account's Securities segment can not be moved into the account's Commodities segment to help meet a margin requirement for an open Future contract. If there is positive unpledged cash your IBKR Universal account's Securities segment then that cash could be moved over to the Commodities segment. In addition, if the Securities segment is holding marginable stock and there is positive Excess Equity then a cash loan can be created in the Securities segment and that cash from the loan can be transferred to the Commodities segment to meet a future contracts margin requirement. Note that a cash loan created from the Available Funds in the Securities segment can not exceed the amount of the Available Funds at that time. In addition if an account's Excess Equity goes negative then the account is not meeting the minimum Maintenance Margin requirements and IBKR can start Liquidating positions to ensure the account remains margin compliant.
For more information, please visit the Account Window page of the TWS User's Guide.