SSRS

I created an SSRS report that has 2 row groups and 2 column groups. I need to divide each Child Column Group total by the Parent Column Group total, see below. I tried the following expression within the child column group =count(fields!id.value) / count(fields!id.value,"ParentRowGroup"), but this gives me the percent of each Child Column Group total by the Parent Row Group  total.  I also tried =count(fields!id.value) / count(fields!id.value,"ParentRowGroup","ParentColumnGroup"), but I got an error that basically says "text box has an expression with an invalid recursive/simple flag".  What I need to do is something like the following.

How do I get the below percentages?

Parent Row Group Total    Parent Column Group Total

                                                                         Child Column    % of Parent Column    Child Column     % of Parent Column

                                                                         Group 1 Total   Group Total                Group 2 Total     Group Total

4,756                              2,798                           956                 34.17%                      1,842                65.83%