Capital and Other Regulatory Requirements - Regulatory Capital Requirements (Details) $ in Millions	Jun. 30, 2015 USD ($)
FCStone LLC [Member]
Net Capital under Commodity Exchange Act Computation	$ 115.9
Required Net Capital under Commodity Exchange Act	63.3
Cash and Securities Segregated under Commodity Exchange Act Regulation	1,688.6
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	1,641.5
Secured Funds	78.5
Secured Funds Required Under Commodity Exchange Act	59.5
INTL FCStone Ltd [Member]
Net Capital under Commodity Exchange Act Computation	98.1
Required Net Capital under Commodity Exchange Act	67.3
Cash and Securities Segregated under Commodity Exchange Act Regulation	89.2
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	89.2
INTL Trading [Member]
Net Capital	12.9
Minimum Net Capital Required for Entity	1.3
FCC Investments [Member]
Net Capital	0.3
Minimum Net Capital Required for Entity	0.3
INTL FCStone Partners LP [Member]
Net Capital	27.1
Minimum Net Capital Required for Entity	9.9
FCStone Australia [Member]
Net Capital under Commodity Exchange Act Computation	1.5
Required Net Capital under Commodity Exchange Act	0.8
Net Capital	11.5
Cash and Securities Segregated under Commodity Exchange Act Regulation	15.1
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	7.7
Capital Required for Capital Adequacy	3.4
INTL FCStone DTVM Ltda [Member]
Net Capital	2.9
Capital Required for Capital Adequacy	0.5
Gainvest S.A. Sociedad Gerente de FCI - Comision Nacional de Valores [Member]
Net Capital under Commodity Exchange Act Computation	0.2
Required Net Capital under Commodity Exchange Act	0.1
Net Capital	5.7
Capital Required for Capital Adequacy	0.2
INTL Capital S.A – Rosario Futures Exchanges [Member] [Domain]
Net Capital	9.8
Capital Required for Capital Adequacy	8.8
INTL Capital S.A. – General Inspector of Justice [Member] [Domain]
Net Capital under Commodity Exchange Act Computation	4.5
Required Net Capital under Commodity Exchange Act	1.8
INTL Capital S.A. – Superintendence of Securities Markets of Buenos Aires [Member] [Domain]
Net Capital under Commodity Exchange Act Computation	3.7
Required Net Capital under Commodity Exchange Act	$ 1.0