Is your "Details" field set up in your Target Application? If this is not already set up, you can take a look at the FDMEE admin guide about setting up a Lookup dimension. Then map the Details field in the import format to this lookup dimension (UDx). Then, in the multi dimension mapping, you can specify when Account is 1010101, Entity is 100, and UDx is "UAE", then account is 1010104.
An alternative to the multi dimension map would be a SQL mapping script using Case When statements to define the mapping. That is in the admin guide under mapping script (or search for #SQL).