Capital and Other Regulatory Requirements - Regulatory Capital Requirements (Details) $ in Millions	Mar. 31, 2016 USD ($)
FCStone LLC [Member]
Net Capital under Commodity Exchange Act Computation	$ 126.9
Required Net Capital under Commodity Exchange Act	64.8
Cash and Securities Segregated under Commodity Exchange Act Regulation	1,884.0
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	1,831.2
Secured Funds	123.6
Secured Funds Required Under Commodity Exchange Act	106.9
INTL FCStone Ltd [Member]
Net Capital under Commodity Exchange Act Computation	136.1
Required Net Capital under Commodity Exchange Act	70.7
Cash and Securities Segregated under Commodity Exchange Act Regulation	51.1
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	44.9
INTL Netherlands BV [Member]
Net Capital under Commodity Exchange Act Computation	135.3
Required Net Capital under Commodity Exchange Act	70.8
INTL FCStone DTVM Ltda [Member]
Net Capital	2.2
Capital Required for Capital Adequacy	0.4
Gainvest S.A. Sociedad Gerente de FCI - Comision Nacional de Valores [Member]
Net Capital under Commodity Exchange Act Computation	3.9
Required Net Capital under Commodity Exchange Act	0.1
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	5.7
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	7.6
Required Net Capital under Commodity Exchange Act	$ 0.6