Capital and Other Regulatory Requirements - Regulatory Capital Requirements (Details) $ in Millions	Dec. 31, 2019 USD ($)
FCStone LLC [Member]
Cash Reserve Deposit Required and Made	$ 9.7
Cash Reserve Deposit Required	9.1
Net Capital under Commodity Exchange Act Computation	163.4
Required Net Capital under Commodity Exchange Act	96.2
Cash and Securities Segregated under Commodity Exchange Act Regulation	2,272.5
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	2,215.7
Secured Funds	166.6
Secured Funds Required Under Commodity Exchange Act	154.0
INTL FCStone Ltd [Member]
Net Capital under Commodity Exchange Act Computation	270.6
Required Net Capital under Commodity Exchange Act	130.4
Cash and Securities Segregated under Commodity Exchange Act Regulation	381.9
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	376.6
INTL FCStone Pte Ltd [Member]
Cash and Securities Segregated under Commodity Exchange Act Regulation	271.4
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	$ 238.3