Regulatory Requirements and Subsidiary Dividend Restrictions - Regulatory Capital Requirements (Details) - USD ($)	Sep. 30, 2015	Sep. 30, 2014
Cash and Securities Segregated under Commodity Exchange Act Regulation		$ 1,805,800,000
Secured funds		73,200,000
Minimum Net Capital Required for Entity	$ 0.08
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated		(1,769,300,000)
Secured Funds Required Under Commodity Exchange Act		$ (53,300,000)
INTL FCStone Financial [Member]
Net Capital	146,300,000
Cash and Securities Segregated under Commodity Exchange Act Regulation	1,880,200,000
Secured funds	85,600,000
Minimum Net Capital Required for Entity	67,200,000
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	(1,830,900,000)
Secured Funds Required Under Commodity Exchange Act	(65,200,000)
INTL FCStone, Ltd [Member]
Cash and Securities Segregated under Commodity Exchange Act Regulation	149,900,000
Net Capital under Commodity Exchange Act Computation	110,800,000
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	149,900,000
Required Net Capital under Commodity Exchange Act	59,700,000
INTL FCStone Europe [Member]
Net Capital under Commodity Exchange Act Computation	100,900,000
Required Net Capital under Commodity Exchange Act	59,900,000
FCStone Australia [Member]
Net Capital	11,400,000
Cash and Securities Segregated under Commodity Exchange Act Regulation	23,300,000
Net Capital under Commodity Exchange Act Computation	1,700,000
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	12,500,000
Required Net Capital under Commodity Exchange Act	700,000
Capital Required for Capital Adequacy	3,200,000
INTL FCStone DTVM Ltda [Member]
Net Capital	2,600,000
Capital Required for Capital Adequacy	400,000
Gainvest S.A. Sociedad Gerente de FCI - Comision Nacional de Valores [Member]
Net Capital	6,400,000
Net Capital under Commodity Exchange Act Computation	400,000
Required Net Capital under Commodity Exchange Act	100,000
Capital Required for Capital Adequacy	200,000
INTL Capital S.A. – General Inspector of Justice [Member] [Domain]
Net Capital under Commodity Exchange Act Computation	12,100,000
Required Net Capital under Commodity Exchange Act	9,900,000
INTL CIBSA S.A. - Comision Nacional de Valores [Member]
Net Capital	5,100,000
Net Capital under Commodity Exchange Act Computation	0
Required Net Capital under Commodity Exchange Act	0
Capital Required for Capital Adequacy	$ 1,700,000