Retainage Accounts PayableTrial Balance By Supplier

Hi, How can I produce an Accounts Payable Trial Balance to display the Retainage balance by Supplier?  Is there an standard report?

Can I modify the standard Accounts Payable Trial Balance report to display to running Retainage supplier balance using XML Publisher Administrator or Report eXchange Designer?

We are implementing Rel 12.2.4.  This is a Construction company , construction scenario.

So far I've been able to successfully :

• Create a Complex PO document Style
• Add Retainage Liability Account to AP Financial Options
• Add PO categories, assign "Pay Items", i.e. retainage %, maximum retainage amount, etc.
• Submit Complex PO for approval and get it approved (self approval for now, it's development instance)