Plan cost line items for cost centers report

Hello,

I am displaying the report: Plan cost line items for cost centers and when I display the details of a line item it appears a document number, where could I display this document?

I have tried to display it in FB03 transaction but it seems not to be this kind of document.

On the other hand in the field Business transaction it appears RKP6, what is the meaning of this field?

Thank you very much