Accounting Ideas

My bank combines interest and service fees into a single transaction at the end of each month. I've tried to split the downloaded transaction to appropriately allocate to interest income and bank fee expenses but can't find a way since the split won't accept a negative value. Using a positive number for the bank fee just increases the transaction value, so it needs to accept a negative value for it to balance. For example: $75 interest, $2.50 service fees, deposit of $72.50.