Condensed Parent Only Financial Statements [Schedule] Balance Sheet (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2010
Cash and cash equivalents	$ 156.1	$ 236.3	$ 220.6	$ 81.9
Income taxes receivable	15.5	15.5
Financial instruments, owned, at fair value	158.5	171.7
Deferred Tax Assets, Net	25.5	19.9
Property and equipment, net	17.5	18.9
Goodwill and intangible assets, net	59.1	55.8
Total assets	2,848.0	2,953.0	2,632.0
Liabilities:
Accounts payable and other accrued liabilities	114.0	127.0
Payables to Customers	2,091.8	2,072.3
Payables to lenders under loans	61.0	218.2
Senior unsecured notes	45.5	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	179.9	175.4
Total liabilities	2,512.6	2,639.8
INTL FCStone Inc. (Parent Company Only) stockholders’ equity:
Common stock, $.01 par value. Authorized 30,000,000 shares; 19,638,330 issued and 19,209,157 outstanding at September 30, 2013 and 19,214,219 issued and 18,984,951 outstanding at September 30, 2012	0.2	0.2
Common stock in treasury, at cost - 429,173 shares at September 30, 2013 and 229,064 shares at September 30, 2012	(7.8)	(4.1)
Additional Paid in Capital	224.0	213.2
Retained earnings	125.4	106.1
Accumulated other comprehensive loss	(6.4)	(2.2)
Total INTL FCStone Inc. (Parent Company Only) stockholders’ equity	335.4	313.2
Total liabilities and equity	2,848.0	2,953.0
Parent Company [Member]
Cash and cash equivalents	3.1	13.1	2.0	0.4
Receivables from subsidiaries	22.9	20.1
Notes receivable, net	27.3	10.2
Income taxes receivable	17.5	14.3
Financial instruments, owned, at fair value	0	1.5
Investment in subsidiaries	237.3	220.1
Deferred Tax Assets, Net	7.1	0.9
Property and equipment, net	3.6	4.3
Goodwill and intangible assets, net	0	0
Other assets	4.3	3.4
Total assets	323.1	287.9
Adjustment to Investment in Subs for Equity Method Accounting	149.6	105.7
Adjustment to Retained Earnings for Equity Method	155.2	111.6
Liabilities:
Accounts payable and other accrued liabilities	11.1	4.2
Payables to Customers	18.7	0.7
Payables to lenders under loans	55.0	48.0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0.6	25.3
Total liabilities	130.9	78.2
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, $.01 par value. Authorized 30,000,000 shares; 19,638,330 issued and 19,209,157 outstanding at September 30, 2013 and 19,214,219 issued and 18,984,951 outstanding at September 30, 2012	0.2	0.2
Common stock in treasury, at cost - 429,173 shares at September 30, 2013 and 229,064 shares at September 30, 2012	7.8	4.1
Additional Paid in Capital	224.0	213.2
Retained earnings	(24.2)	0.4
Total INTL FCStone Inc. (Parent Company Only) stockholders’ equity	192.2	209.7
Total liabilities and equity	$ 323.1	$ 287.9