Receivables from customers, net and notes receivable, net - Notes Receivable (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for Doubtful Accounts Receivable, Charge-offs	$ 0	$ (11.2)	$ (113.3)
Allowance for Doubtful Accounts Receivable, Recoveries	0	(0.1)	(3.7)
FCStone LLC [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Remaining Acquired Notes Receivable	0.7
Notes receivable charge-off during the year			$ 111.5