Regulatory Requirements and Subsidiary Dividend Restrictions - Regulatory Capital Requirements (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Sep. 30, 2013
Cash and Securities Segregated under Commodity Exchange Act Regulation	$ 1,805.8	$ 1,693.5
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	(1,769.3)	(1,669.6)
Secured funds	73.2	82.5
Secured Funds Required Under Commodity Exchange Act	(53.3)	(59.8)
FCStone LLC [Member]
Net Capital under Commodity Exchange Act Computation	119.6
Required Net Capital under Commodity Exchange Act	67.5
INTL FCStone Europe [Member]
Net Capital under Commodity Exchange Act Computation	83.9
Required Net Capital under Commodity Exchange Act	53.6
Cash and Securities Segregated under Commodity Exchange Act Regulation	127.7
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	127.7
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	1.5
Required Net Capital under Commodity Exchange Act	0.9
Net Capital	11.4
Cash and Securities Segregated under Commodity Exchange Act Regulation	38.4
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	31.5
Capital Required for Capital Adequacy	3.9
INTL FCStone DTVM Ltda [Member]
Net Capital	3.2
Capital Required for Capital Adequacy	0.6
Gainvest S.A. Sociedad Gerente de FCI - Comision Nacional de Valores [Member]
Net Capital under Commodity Exchange Act Computation	1.8
Required Net Capital under Commodity Exchange Act	0.1
Net Capital	4.0
Capital Required for Capital Adequacy	0.2
INTL Capital S.A. – General Inspector of Justice [Member] [Domain]
Net Capital under Commodity Exchange Act Computation	10.5
Required Net Capital under Commodity Exchange Act	8.2
INTL CIBSA S.A. - Comision Nacional de Valores [Member]
Net Capital under Commodity Exchange Act Computation	0
Required Net Capital under Commodity Exchange Act	0
Net Capital	5.9
Capital Required for Capital Adequacy	$ 1.8