Basis of Presentation and Consolidation and Recently Issued Accounting Standards (Details)	3 Months Ended
Dec. 31, 2014
Basis of Presentation and Consolidation [Abstract]
Number of different types of foreign currencies	150
Number of accounts for customers company-wide	20,000
Number of customers company-wide	11,000intl_NumberOfCustomersCompanyWide

The number of accounts for the customers the company provides services.

No definition available.

Name:	intl_Numberofaccountsforcustomerscompanywide
Namespace Prefix:	intl_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration