Commitments and Contingencies (Notes)	3 Months Ended
Dec. 31, 2018
Commitments and Contingencies [Abstract]
Commitments and Contingencies Disclosure [Text Block]	Commitments and Contingencies Contingencies 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 Inc., declined below required maintenance margin levels, primarily as a result of significant and unexpected 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 Inc.’s client agreements and obligations under market regulation standards. A CTA is registered with the U.S. Commodity Futures Trading Commission (“CFTC”) and a member of, and subject to audit by, the National Futures Association (“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 clients full discretionary authority to manage the trading in the client accounts, while INTL FCStone Financial Inc. acted solely as the clearing firm in its role as the FCM. INTL FCStone Financial Inc.’s client agreements 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. As of February 5, 2019 and December 31, 2018, the aggregate receivable from these client accounts, net of collections and other allowable deductions, was $29.4 million and $30.0 million, respectively, with no individual account receivable exceeding $1.4 million. INTL FCStone Financial Inc. continues to pursue collection of these receivables and intends both to enforce and to defend its rights aggressively, and to claim interest and costs of collection where applicable. The Company has done an assessment of the collectability of these accounts and has concluded that it does not have a sufficient basis to determine an allowance against these uncollected balances. As the Company moves through the collection process and additional information becomes available, the Company will continue to evaluate the likelihood of collection and consider the need for an allowance against the carrying value of these uncollected balances. Depending on future collections and its ongoing assessments, any provisions for bad debts and actual losses ultimately may or may not be material to the Company’s financial results. Currently, the Company does not believe that any potential losses from amounts not collected would impact its ability to comply with its ongoing liquidity, capital, and regulatory requirements. INTL FCStone Financial Inc. has been named in arbitrations brought by clients seeking damages relating to the trading losses in these accounts. The Company believes that such cases are without merit and intend to defend them vigorously. However, the arbitrations are in the very early stages of the process and no prediction can be made regarding the ultimate outcome of the arbitrators’ decisions. Legal Proceedings From time to time and in the ordinary course of business, the Company is involved in various legal actions and proceedings, including tort claims, contractual disputes, employment matters, workers’ compensation claims and collections. The Company carries insurance that provides protection against certain types of claims, up to the policy limits of the insurance. As of December 31, 2018 and September 30, 2018, the condensed consolidated balance sheets include loss contingency accruals, which are not material, individually or in the aggregate, to the Company’s financial position or liquidity. In the opinion of management, possible exposure from loss contingencies in excess of the amounts accrued, is not likely to be material to the Company’s earnings, financial position or liquidity. There have been no material changes to the legal actions and proceedings compared to September 30, 2018. Contractual Commitments Self-Insurance The Company self-insures its costs related to medical and dental claims. The Company is self-insured, up to a stop loss amount, for eligible participating employees and retirees, and for qualified dependent medical and dental claims, subject to deductibles and limitations. As of December 31, 2018, the Company had $0.8 million accrued for self-insured medical and dental claims included in ‘accounts payable and other liabilities’ in the condensed consolidated balance sheet.

Commitments and Contingencies

Contingencies

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 Inc., declined below required maintenance margin levels, primarily as a result of significant and unexpected 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 Inc.’s client agreements and obligations under market regulation standards.

A CTA is registered with the U.S. Commodity Futures Trading Commission (“CFTC”) and a member of, and subject to audit by, the National Futures Association (“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 clients full discretionary authority to manage the trading in the client accounts, while INTL FCStone Financial Inc. acted solely as the clearing firm in its role as the FCM.

INTL FCStone Financial Inc.’s client agreements 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. As of February 5, 2019 and December 31, 2018, the aggregate receivable from these client accounts, net of collections and other allowable deductions, was $29.4 million and $30.0 million, respectively, with no individual account receivable exceeding $1.4 million. INTL FCStone Financial Inc. continues to pursue collection of these receivables and intends both to enforce and to defend its rights aggressively, and to claim interest and costs of collection where applicable.

The Company has done an assessment of the collectability of these accounts and has concluded that it does not have a sufficient basis to determine an allowance against these uncollected balances. As the Company moves through the collection process and additional information becomes available, the Company will continue to evaluate the likelihood of collection and consider the need for an allowance against the carrying value of these uncollected balances. Depending on future collections and its ongoing assessments, any provisions for bad debts and actual losses ultimately may or may not be material to the Company’s financial results. Currently, the Company does not believe that any potential losses from amounts not collected would impact its ability to comply with its ongoing liquidity, capital, and regulatory requirements.

INTL FCStone Financial Inc. has been named in arbitrations brought by clients seeking damages relating to the trading losses in these accounts. The Company believes that such cases are without merit and intend to defend them vigorously. However, the arbitrations are in the very early stages of the process and no prediction can be made regarding the ultimate outcome of the arbitrators’ decisions.

Legal Proceedings

From time to time and in the ordinary course of business, the Company is involved in various legal actions and proceedings, including tort claims, contractual disputes, employment matters, workers’ compensation claims and collections. The Company carries insurance that provides protection against certain types of claims, up to the policy limits of the insurance.

As of December 31, 2018 and September 30, 2018, the condensed consolidated balance sheets include loss contingency accruals, which are not material, individually or in the aggregate, to the Company’s financial position or liquidity. In the opinion of management, possible exposure from loss contingencies in excess of the amounts accrued, is not likely to be material to the Company’s earnings, financial position or liquidity.

There have been no material changes to the legal actions and proceedings compared to September 30, 2018.

Contractual Commitments

Self-Insurance

The Company self-insures its costs related to medical and dental claims. The Company is self-insured, up to a stop loss amount, for eligible participating employees and retirees, and for qualified dependent medical and dental claims, subject to deductibles and limitations. As of December 31, 2018, the Company had $0.8 million accrued for self-insured medical and dental claims included in ‘accounts payable and other liabilities’ in the condensed consolidated balance sheet.