Hi,
have a look to the table FAGLFLEXT....
If the document splitting is active, the is here sum value, if is passive there are specific documents, such as in the table BSEG.
Here you can see the process flow. https://help.sap.com/saphelp_erp2004/helpdata/en/58/24d24047dd702ae10000000a155106/content.htm
Regards
Jan