Capital and Other Regulatory Requirements - Regulatory Capital Requirements (Details) $ in Millions	Dec. 31, 2015 USD ($)
FCStone LLC [Member]
Net Capital under Commodity Exchange Act Computation	$ 121.2
Required Net Capital under Commodity Exchange Act	67.6
Cash and Securities Segregated under Commodity Exchange Act Regulation	1,962.2
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	1,913.1
Secured Funds	107.5
Secured Funds Required Under Commodity Exchange Act	89.0
INTL FCStone Ltd [Member]
Net Capital under Commodity Exchange Act Computation	134.1
Required Net Capital under Commodity Exchange Act	64.9
Cash and Securities Segregated under Commodity Exchange Act Regulation	149.9
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	149.9
INTL Netherlands BV [Member]
Net Capital under Commodity Exchange Act Computation	133.3
Required Net Capital under Commodity Exchange Act	65.0
FCStone Australia [Member]
Net Capital	11.8
Capital Required for Capital Adequacy	3.4
INTL FCStone DTVM Ltda [Member]
Net Capital	2.0
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	1.8
Required Net Capital under Commodity Exchange Act	0.1
Net Capital	6.0
Capital Required for Capital Adequacy	0.1
INTL Capital S.A. – General Inspector of Justice [Member] [Domain]
Net Capital under Commodity Exchange Act Computation	5.2
Required Net Capital under Commodity Exchange Act	1.3
INTL Capital S.A. – Superintendence of Securities Markets of Buenos Aires [Member] [Domain]
Net Capital under Commodity Exchange Act Computation	10.6
Required Net Capital under Commodity Exchange Act	$ 0.7