Regulatory Requirements and Subsidiary Dividend Restrictions - Regulatory Capital Requirements (Details)	Sep. 30, 2019 USD ($)
Minimum Net Capital Required for Entity	$ 0.08
INTL FCStone Financial [Member]
Cash and Securities Segregated under Commodity Exchange Act Regulation	2,288,700,000
Secured funds	173,500,000
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	2,232,100,000
Secured Funds Required Under Commodity Exchange Act	(161,000,000)
INTL FCStone, Ltd [Member]
Cash and Securities Segregated under Commodity Exchange Act Regulation	207,600,000
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	$ 196,900,000