Hi
The Electronic Bank statement is generally done as an automatic interface with the bank using a middleware. This could be SAP PI or any other middleware. The Bank would send in their statements in one of the accepted formats: BAI, BAI2 or MT940. These can be uplaoded into SAP and you do not need IDOC for EBS as such. Check with your Bank on the format they can send and work with your middleware to set up a test connection between your SAP system and the Bank.
Additionally, the automatic posting would happen based on the posting rule mapping to the external transaction type in the bank statement. So you would also need to request the bank for sample files to develop the interface. The below links would be of help to you:
http://help.sap.com/printdocu/core/Print46b/Data/EN/FIBLEBS.pdf
Browse through SAP help to get an insight into EBS.
Regards
Sanil Bhandari