Hello Andrew,
The "Appendix B" (section 6 and 6.1) of IDM SAP provisioning framework configuration guide( SAP NetWeaver Identity Management for SAP System Landscapes: Configuration Guide), explains the attributes mapping between IDM and ABAP system. Please you can find it from following SCN IDM documentation list page:
http://scn.sap.com/docs/DOC-8397
Hope this should be the doc you are searching for?
BR, Keith