Totaling Sum values returned by LookupSet

I used Code.SumLookup(LookupSet(Fields!ID.Value, Fields!ID, Value, Fields!PaidAmount.Value, "DataSet2"))

When I drill down in my table I can see these values, but as I drill back up it leaves the space or puts a 0 since every id does not have a payment amount and some have multiple. How do I total all of the values returned? If I drill down that paid amount will populate the sum of the payments by each ID. Hope this makes sense.

Year            Month            IDs              PaidAmount

2012            Total             400                0