Subsequent Events Subsequent Events (Notes)	12 Months Ended
Sep. 30, 2018
Subsequent Events [Abstract]
Subsequent Events [Text Block]	Note 23 – Subsequent Events During the week ended November 16, 2018, balances in approximately 300 accounts of the FCM division of the Company’s wholly owned subsidiary, INTL FCStone Financial, declined below required maintenance margin levels, primarily as a result of significant price fluctuations in the natural gas markets. All positions in these accounts, which were managed by OptionSellers.com Inc. (“OptionSellers”), an independent Commodity Trading Advisor (“CTA”), were liquidated in accordance with the INTL FCStone Financial’s customer agreements and obligations under market regulation standards. A CTA is by definition registered with the CFTC and a member of, and subject to audit by, the NFA. OptionSellers is registered under a CFTC Rule 4.7 exemption for “qualified eligible persons”, which requires the account holders authorizing OptionSellers to act as their CTA to meet or exceed certain minimum financial requirements. OptionSellers, in its role as a CTA, had been granted by each of its customers full discretionary authority to manage the trading in the customer accounts, while INTL FCStone Financial acted solely as the clearing firm in its role as the FCM, at all times meeting its obligations as the FCM to these accounts. INTL FCStone Financial’s customer agreements conform to NFA guidance, disclose the risks to which account-holders are exposed, hold account-holders liable for all losses in their accounts, and obligate the account holders to reimburse INTL FCStone Financial for any account deficits in their accounts. INTL FCStone Financial continues to pursue collection of these receivables in the ordinary course of business. INTL FCStone Financial intends both to enforce and to defend its rights aggressively, and to claim interest and costs of collection where applicable. INTL FCStone Financial’s standard customer agreements provide for arbitration of disputes between parties. As of December 10, 2018, the aggregate receivable from these customer accounts, net of collections and other allowable deductions thus far, is $31.3 million, with no individual account receivable exceeding $1.4 million. The exposure to losses from these customer accounts is not yet determinable, as collection efforts are in early stages, given the timing of events that lead to the receivable balances disclosed above. Depending on future collections and an assessment to be made under U.S. GAAP, any provisions for bad debts and actual losses ultimately may or may not be material to the Company’s financial results. The Company believes that these accounts receivable balances, along with possible exposure to losses from these customer accounts, will not impact the Company’s ability to comply with its ongoing liquidity, capital, and regulatory requirements.

Note 23 – Subsequent Events

During the week ended November 16, 2018, balances in approximately 300 accounts of the FCM division of the Company’s wholly owned subsidiary, INTL FCStone Financial, declined below required maintenance margin levels, primarily as a result of significant price fluctuations in the natural gas markets. All positions in these accounts, which were managed by OptionSellers.com Inc. (“OptionSellers”), an independent Commodity Trading Advisor (“CTA”), were liquidated in accordance with the INTL FCStone Financial’s customer agreements and obligations under market regulation standards.

A CTA is by definition registered with the CFTC and a member of, and subject to audit by, the NFA. OptionSellers is registered under a CFTC Rule 4.7 exemption for “qualified eligible persons”, which requires the account holders authorizing OptionSellers to act as their CTA to meet or exceed certain minimum financial requirements. OptionSellers, in its role as a CTA, had been granted by each of its customers full discretionary authority to manage the trading in the customer accounts, while INTL FCStone Financial acted solely as the clearing firm in its role as the FCM, at all times meeting its obligations as the FCM to these accounts.

INTL FCStone Financial’s customer agreements conform to NFA guidance, disclose the risks to which account-holders are exposed, hold account-holders liable for all losses in their accounts, and obligate the account holders to reimburse INTL FCStone Financial for any account deficits in their accounts. INTL FCStone Financial continues to pursue collection of these receivables in the ordinary course of business. INTL FCStone Financial intends both to enforce and to defend its rights aggressively, and to claim interest and costs of collection where applicable. INTL FCStone Financial’s standard customer agreements provide for arbitration of disputes between parties.

As of December 10, 2018, the aggregate receivable from these customer accounts, net of collections and other allowable deductions thus far, is $31.3 million, with no individual account receivable exceeding $1.4 million. The exposure to losses from these customer accounts is not yet determinable, as collection efforts are in early stages, given the timing of events that lead to the receivable balances disclosed above. Depending on future collections and an assessment to be made under U.S. GAAP, any provisions for bad debts and actual losses ultimately may or may not be material to the Company’s financial results. The Company believes that these accounts receivable balances, along with possible exposure to losses from these customer accounts, will not impact the Company’s ability to comply with its ongoing liquidity, capital, and regulatory requirements.