Excel - filtering + or - in columns

I have set out a spreadsheet so credits are just displayed in each cell as, e.g. £200.50, and expenses are displayed with a minus sign, e.g. -£25.40.  Therefore, what I want to do is to create a filter, or find out how to filter, so that I can see the expenses or credits separately (for the totals) if I want to.  How can I do this?  

Thanks! 

FP