Regulatory Requirements and Subsidiary Dividend Restrictions - Regulatory Capital Requirements (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Sep. 30, 2012
Cash and Securities Segregated under Commodity Exchange Act Regulation	$ 1,693.5	$ 1,665.5
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	(1,669.6)	(1,620.5)
Secured funds	82.5	89.3
Secured Funds Required Under Commodity Exchange Act	(59.8)	(77.6)
FCStone LLC [Member]
Net Capital under Commodity Exchange Act Computation	106.3
Required Net Capital under Commodity Exchange Act	66.3
INTL FCStone Europe [Member]
Net Capital under Commodity Exchange Act Computation	60.8
Required Net Capital under Commodity Exchange Act	23.4
Cash and Securities Segregated under Commodity Exchange Act Regulation	61.2
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	61.1
INTL Global Currencies [Member]
Net Capital under Commodity Exchange Act Computation	11.4
Required Net Capital under Commodity Exchange Act	1.2
INTL Trading [Member]
Net Capital	5.0
Minimum Net Capital Required for Entity	1.0
FCC Investments [Member]
Net Capital	0.3
Minimum Net Capital Required for Entity	0.3
FCStone Australia [Member]
Net Capital under Commodity Exchange Act Computation	1.8
Required Net Capital under Commodity Exchange Act	0.9
Net Capital	11.6
Capital Required for Capital Adequacy	4.1
FCStone Europe [Member]
Net Capital under Commodity Exchange Act Computation	2.0
Required Net Capital under Commodity Exchange Act	0.6
INTL FCStone DTVM Ltda [Member]
Net Capital	0.7
Capital Required for Capital Adequacy	0.7
INTL Capital S.A – Rosario Futures Exchanges [Member] [Domain]
Net Capital	6.3
Capital Required for Capital Adequacy	0.1
INTL Capital S.A. – General Inspector of Justice [Member] [Domain]
Net Capital under Commodity Exchange Act Computation	8.5
Required Net Capital under Commodity Exchange Act	6.4
INTL Capital S.A. – Superintendence of Securities Markets of Buenos Aires [Member] [Domain]
Net Capital under Commodity Exchange Act Computation	4.0
Required Net Capital under Commodity Exchange Act	$ 0.3