Segment Analysis - Reportable Segments (Details)	6 Months Ended
Mar. 31, 2015
Segment Analysis [Abstract]
Number of different types of foreign currencies	150

Number of different types of foreign currencies the company trades

No definition available.

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