Condensed Parent Only Financial Statements - Balance Sheet (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011
Cash and cash equivalents	$ 231.3	$ 156.1	$ 236.3	$ 220.6
Income taxes receivable	10.8	15.5
Deferred Tax Assets, Net	32.0	25.5
Property and equipment, net	15.9	17.5
Total assets	3,039.7	2,848.0	2,953.0
Liabilities:
Accounts payable and other accrued liabilities	114.1	114.0
Payables to Customers	2,228.7	2,091.8
Payables to lenders under loans	22.5	61.0
Senior unsecured notes	45.5	45.5
Financial Instruments Sold, Not yet Purchased, at Fair Value	264.0	179.9
Total liabilities	2,694.3	2,512.6
INTL FCStone Inc. (Parent Company Only) stockholders’ equity:
Common stock, $0.01 par value. Authorized 30,000,000 shares; 19,826,635 issued and 18,883,662 outstanding at September 30, 2014 and 19,638,330 issued and 19,209,157 outstanding at September 30, 2013	0.2	0.2
Common stock in treasury, at cost - 942,973 shares at September 30, 2014 and 429,173 shares at September 30, 2013	(17.5)	(7.8)
Additional Paid in Capital	229.6	224.0
Retained earnings	144.7	125.4
Accumulated other comprehensive loss	(11.6)	(6.4)
Total INTL FCStone Inc. (Parent Company Only) stockholders’ equity	345.4	335.4
Total liabilities and stockholders' equity	3,039.7	2,848.0
Parent Company [Member]
Cash and cash equivalents	3.0	3.1	13.1	2.0
Receivables from subsidiaries	0	22.9
Notes receivable, net	40.0	27.3
Income taxes receivable	12.9	17.5
Investment in subsidiaries	237.7	237.3
Deferred Tax Assets, Net	16.6	7.1
Property and equipment, net	3.6	3.6
Other assets	4.9	4.3
Total assets	318.7	323.1
Adjustment to Investment in Subs for Equity Method Accounting	195.1	149.6
Liabilities:
Accounts payable and other accrued liabilities	8.8	11.1
Payables to Customers	25.8	18.7
Payables to lenders under loans	15.0	55.0
Payable to subsidiaries, net	61.7	0
Senior unsecured notes	45.5	45.5
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0.6
Total liabilities	156.8	130.9
INTL FCStone Inc. (Parent Company Only) stockholders’ equity:
Preferred stock, $.01 par value. Authorized 1,000,000 shares; no shares issued or outstanding	0	0
Common stock, $0.01 par value. Authorized 30,000,000 shares; 19,826,635 issued and 18,883,662 outstanding at September 30, 2014 and 19,638,330 issued and 19,209,157 outstanding at September 30, 2013	0.2	0.2
Common stock in treasury, at cost - 942,973 shares at September 30, 2014 and 429,173 shares at September 30, 2013	17.5	7.8
Additional Paid in Capital	229.6	224.0
Retained earnings	(50.4)	(24.2)
Total INTL FCStone Inc. (Parent Company Only) stockholders’ equity	161.9	192.2
Total liabilities and stockholders' equity	$ 318.7	$ 323.1