Calculating difference on Pivot Table Totals
 

I have a pivot Table as follows

Region State jan Feb ... Columm
North NY 1 5
NJ 5 1
North Total 6 6

South FL 2 6
GA 6 2
South Total 8 8

Grand Total 14 14

I would like to change the display of Grand total to show the difference
between the region as follows

Grand total difference (2) (2)

Any help on this is greatly appreciated.