Capital and Other Regulatory Requirements - Regulatory Capital Requirements (Details) $ in Millions	Jun. 30, 2016 USD ($)
FCStone LLC [Member]
Net Capital under Commodity Exchange Act Computation	$ 128.7
Required Net Capital under Commodity Exchange Act	82.2
Cash and Securities Segregated under Commodity Exchange Act Regulation	1,991.4
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	1,939.5
Secured Funds	116.4
Secured Funds Required Under Commodity Exchange Act	98.9
INTL FCStone Ltd [Member]
Net Capital under Commodity Exchange Act Computation	136.8
Required Net Capital under Commodity Exchange Act	71.4
Cash and Securities Segregated under Commodity Exchange Act Regulation	52.3
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	46.7
INTL Netherlands BV [Member]
Net Capital under Commodity Exchange Act Computation	136.0
Required Net Capital under Commodity Exchange Act	71.5
INTL FCStone DTVM Ltda [Member]
Net Capital	2.4
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	0.1
Required Net Capital under Commodity Exchange Act	0.1
Net Capital	7.3
Capital Required for Capital Adequacy	0.1
INTL Capital S.A. – General Inspector of Justice [Member] [Domain]
Net Capital under Commodity Exchange Act Computation	6.7
Required Net Capital under Commodity Exchange Act	1.1
INTL Capital S.A. – Superintendence of Securities Markets of Buenos Aires [Member] [Domain]
Net Capital under Commodity Exchange Act Computation	8.8
Required Net Capital under Commodity Exchange Act	$ 0.6