Regulatory Requirements and Subsidiary Dividend Restrictions - Regulatory Capital Requirements (Details) - USD ($)	Sep. 30, 2016	Sep. 30, 2015
Cash and Securities Segregated under Commodity Exchange Act Regulation		$ 1,880,200,000
Secured funds		85,600,000
Minimum Net Capital Required for Entity	$ 0.08
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 Financial [Member]
Net Capital	140,800,000
Cash and Securities Segregated under Commodity Exchange Act Regulation	2,177,900,000
Secured funds	107,700,000
Minimum Net Capital Required for Entity	81,700,000
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	2,126,400,000
Secured Funds Required Under Commodity Exchange Act	(91,300,000)
Sterne Agee Clearing, Inc. [Member]
Net Capital	1,000,000
Minimum Net Capital Required for Entity	100,000
Sterne Agee and Leach, Inc. [Member]
Net Capital	29,000,000
Minimum Net Capital Required for Entity	2,000,000
Sterne Agee Financial Services, Inc. [Member]
Net Capital	3,300,000
Minimum Net Capital Required for Entity	300,000
INTL FCStone, Ltd [Member]
Cash and Securities Segregated under Commodity Exchange Act Regulation	54,800,000
Net Capital under Commodity Exchange Act Computation	136,900,000
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	49,500,000
Required Net Capital under Commodity Exchange Act	84,900,000
INTL FCStone Europe [Member]
Net Capital under Commodity Exchange Act Computation	136,100,000
Required Net Capital under Commodity Exchange Act	85,000,000
INTL FCStone DTVM Ltda [Member]
Net Capital	2,500,000
Capital Required for Capital Adequacy	500,000
Gainvest S.A. Sociedad Gerente de FCI - Comision Nacional de Valores [Member]
Net Capital	7,700,000
Net Capital under Commodity Exchange Act Computation	3,600,000
Required Net Capital under Commodity Exchange Act	100,000
Capital Required for Capital Adequacy	100,000
INTL Capital S.A. – General Inspector of Justice [Member] [Domain]
Net Capital under Commodity Exchange Act Computation	15,300,000
Required Net Capital under Commodity Exchange Act	12,600,000
INTL CIBSA S.A. - Comision Nacional de Valores [Member]
Net Capital	7,100,000
Net Capital under Commodity Exchange Act Computation	0
Required Net Capital under Commodity Exchange Act	0
Capital Required for Capital Adequacy	$ 1,100,000