Receivables from customers and notes receivable, net Level 4 - Notes Receivable (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Sep. 30, 2011
Receivables from customers and notes receivable, net [Abstract]
Financing Receivable, Net	$ 10.3	$ 24.3

Financing Receivables, net - Sales/Repurchase Agreements

No definition available.

Name:	intl_FinancingReceivablesNetSalesrepurchaseAgreements
Namespace Prefix:	intl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant