Capital and Other Regulatory Requirements - Regulatory Capital Requirements (Details) $ in Millions	Mar. 31, 2020 USD ($)
FCStone LLC [Member]
Cash Reserve Deposit Required and Made	$ 33.1
Cash Reserve Deposit Required	66.1
Net Capital under Commodity Exchange Act Computation	175.7
Required Net Capital under Commodity Exchange Act	108.3
Cash and Securities Segregated under Commodity Exchange Act Regulation	2,543.6
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	2,485.9
Secured Funds	162.5
Secured Funds Required Under Commodity Exchange Act	150.0
INTL FCStone Ltd [Member]
Net Capital under Commodity Exchange Act Computation	270.3
Required Net Capital under Commodity Exchange Act	140.0
Cash and Securities Segregated under Commodity Exchange Act Regulation	437.8
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	430.1
INTL FCStone Pte Ltd [Member]
Cash and Securities Segregated under Commodity Exchange Act Regulation	208.2
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	$ 202.6