Condensed Parent Only Financial Statements [Schedule] Balance Sheet (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2009
Cash and cash equivalents	$ 236.3	$ 220.6	$ 81.9	$ 60.5
Income taxes receivable	11.9	8.8
Financial instruments, owned, at fair value	171.7	223.1
Deferred income taxes	19.9	20.7
Property and equipment, net	18.9	15.0
Goodwill and intangible assets, net	54.7	56.1
Total assets	2,958.9	2,635.7
Liabilities:
Accounts payable and other accrued liabilities	127.0	122.0
Payables to Customers	2,072.3	1,739.8
Payables to lenders under loans	218.2	77.4
Financial Instruments Sold, Not yet Purchased, at Fair Value	175.4	390.9
Total liabilities	2,639.8	2,338.1
INTL FCStone Inc. (Parent Company Only) stockholders’ equity:
Common stock, $.01 par value. Authorized 30,000,000 shares; 19,214,219 issued and 18,984,951 outstanding at September 30, 2012 and 18,653,964 issued and 18,642,407 outstanding at September 30, 2011	0.2	0.2
Common stock in treasury, at cost - 229,064 shares at September 30, 2012 and 11,557 shares at September 30, 2011	4.1	0.1
Additional Paid in Capital	213.2	205.2
Retained earnings	112.0	97.0
Accumulated other comprehensive loss	(2.2)	(6.0)
Total INTL FCStone Inc. (Parent Company Only) stockholders’ equity	319.1	296.3
Total liabilities and equity	2,958.9	2,635.7
Parent Company [Member]
Cash and cash equivalents	13.1	2.0	0.4	0
Receivables from subsidiaries	20.1	43.9
Notes receivable, net	10.2	0
Income taxes receivable	14.3	21.4
Financial instruments, owned, at fair value	1.5	3.2
Investment in subsidiaries	220.1	207.9
Deferred income taxes	0.9	0.8
Property and equipment, net	4.3	2.6
Goodwill and intangible assets, net	0	0.3
Other assets	3.4	3.5
Total assets	287.9	285.6
Adjustment to Investment in Subs for Equity Method Accounting	111.6	81.8
Adjustment to Retained Earnings for Equity Method	111.6	81.8
Liabilities:
Accounts payable and other accrued liabilities	4.2	6.4
Payables to Customers	0.7	0
Payables to lenders under loans	48.0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	25.3	58.7
Total liabilities	78.2	65.1
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; 19,214,219 issued and 18,984,951 outstanding at September 30, 2012 and 18,653,964 issued and 18,642,407 outstanding at September 30, 2011	0.2	0.2
Common stock in treasury, at cost - 229,064 shares at September 30, 2012 and 11,557 shares at September 30, 2011	(4.1)	(0.1)
Additional Paid in Capital	213.2	205.0
Retained earnings	0.4	15.4
Total INTL FCStone Inc. (Parent Company Only) stockholders’ equity	209.7	220.5
Total liabilities and equity	$ 287.9	$ 285.6