Capital and Other Regulatory Requirements - Regulatory Capital Requirements (Details) $ in Millions	Jun. 30, 2020 USD ($)
FCStone LLC [Member]
Cash Reserve Deposit Required and Made	$ 43.7
Cash Reserve Deposit Required	46.8
Futures Commission Merchant, Commodity Exchange Act, Adjusted Net Capital	198.6
Futures Commission Merchant, Commodity Exchange Act, Required Net Capital	126.0
Cash and Securities Segregated under Commodity Exchange Act Regulation	2,705.6
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	2,650.1
Secured Funds	160.6
Secured Funds Required Under Commodity Exchange Act	148.8
INTL FCStone Ltd [Member]
Futures Commission Merchant, Commodity Exchange Act, Adjusted Net Capital	264.9
Futures Commission Merchant, Commodity Exchange Act, Required Net Capital	110.8
Cash and Securities Segregated under Commodity Exchange Act Regulation	471.8
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	467.4
INTL FCStone Pte Ltd [Member]
Cash and Securities Segregated under Commodity Exchange Act Regulation	313.8
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	$ 307.0