Difference between two values

I am trying to show the difference between two values (£200 and -£100.00), I am using the formula ‘ABS(AB15-Z15)’ which is doing the trick but I need the cell showing the difference as a negative figure as this is for a profit/loss sheet.

I appreciate the difference between 200 and -100 is 300 but I need it to show -£300 as this is the true loss.

Thanks guys.