Need to link Idoc Number to A/P Invoice in SAP

Hey SAP Gurus -

Currently we have Idoc configured as a payment method on a vendor.  We need to find a way to show the Idoc number on the A/P invoice in SAP so the A/P department can see how the invoice was cleared.  Currently they can see the date and the clearing document on the invoice but there is nothing on the invoice to connect it to the Idoc number that was generated for the payment to the vendor.

Thanks in advance for your advice.