Regulatory Requirements and Subsidiary Dividend Restrictions - Regulatory Capital Requirements (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Sep. 30, 2011
Cash and Securities Segregated under Commodity Exchange Act Regulation	$ 1,665.5	$ 1,457.5
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	1,620.5	1,406.6
Secured funds	89.3	38.8
Secured Funds Required Under Commodity Exchange Act	77.6	27.2
FCStone LLC [Member]
Net Capital under Commodity Exchange Act Computation	124.3
Required Net Capital under Commodity Exchange Act	86.3
INTL FCStone Europe [Member]
Net Capital under Commodity Exchange Act Computation	35.0
Required Net Capital under Commodity Exchange Act	18.8
Net Capital	26.4
Cash and Securities Segregated under Commodity Exchange Act Regulation	26.4
INTL Global Currencies [Member]
Net Capital under Commodity Exchange Act Computation	7.6
Required Net Capital under Commodity Exchange Act	1.2
TRX Futures [Member]
Net Capital	8.5
Capital Required for Capital Adequacy	4.3
INTL Trading [Member]
Net Capital	2.0
Minimum Net Capital Required for Entity	1.0
FCC Investments [Member]
Net Capital	0.4
Minimum Net Capital Required for Entity	0.3
FCStone Australia [Member]
Net Capital under Commodity Exchange Act Computation	1.9
Required Net Capital under Commodity Exchange Act	1.0
Net Capital	11.5
Capital Required for Capital Adequacy	1.3
FCStone Europe [Member]
Net Capital under Commodity Exchange Act Computation	1.8
Required Net Capital under Commodity Exchange Act	$ 0.4