Commitments and Contingencies (Notes)	6 Months Ended
Mar. 31, 2018
Commitments and Contingencies [Abstract]
Commitments and Contingencies Disclosure [Text Block]	Commitments and Contingencies 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 March 31, 2018 and September 30, 2017, 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. The following is a summary of a significant legal matter involving the Company: Sentinel Litigation Prior to the July 1, 2015 merger into INTL FCStone Financial, our subsidiary, FCStone, LLC, had a portion of its excess segregated funds invested with Sentinel Management Group Inc. (“Sentinel”), a registered futures commission merchant (“FCM”) and an Illinois-based money manager that provided cash management services to other FCMs. In August 2007, Sentinel halted redemptions to customers and sold certain of the assets it managed to an unaffiliated third party at a significant discount. On August 17, 2007, subsequent to Sentinel’s sale of certain assets, Sentinel filed for bankruptcy protection. In aggregate, $15.5 million of FCStone, LLC’s $21.9 million in invested funds were returned to it before and after Sentinel’s bankruptcy petition. In August 2008, the bankruptcy trustee of Sentinel filed adversary proceedings against FCStone, LLC, and a number of other FCMs in the Bankruptcy Court for the Northern District of Illinois. The case was subsequently reassigned to the U.S. District Court, for the Northern District of Illinois. The trustee sought recovery of pre- and post-petition transfers totaling approximately $15.5 million. The trial of this matter took place during October 2012. The trial court entered a judgment against FCStone, LLC on January 4, 2013. The case has been appealed to the Seventh Circuit several times. The latest oral argument was heard in the Seventh Circuit on June 7, 2017. On August 14, 2017, the Seventh Circuit ruled in favor of all of INTL FCStone Financial’s arguments. On April 23, 2018, the United States Supreme Court denied the trustee’s petition for writ of certiorari. Following this, INTL FCStone Financial requested immediate payment of funds due based on the August 14, 2017 ruling in its favor. On May 1, 2018, INTL FCStone Financial received funds in the amount of $1.9 million, which it will recognize as a gain during the quarter ending June 30, 2018. Our assessments are based on estimates and assumptions that have been deemed reasonable by management, but that may later prove to be incomplete or inaccurate, and unanticipated events and circumstances may occur that might cause us to change those estimates and assumptions. 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 March 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

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 March 31, 2018 and September 30, 2017, 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.

The following is a summary of a significant legal matter involving the Company:

Sentinel Litigation

Prior to the July 1, 2015 merger into INTL FCStone Financial, our subsidiary, FCStone, LLC, had a portion of its excess segregated funds invested with Sentinel Management Group Inc. (“Sentinel”), a registered futures commission merchant (“FCM”) and an Illinois-based money manager that provided cash management services to other FCMs. In August 2007, Sentinel halted redemptions to customers and sold certain of the assets it managed to an unaffiliated third party at a significant discount. On August 17, 2007, subsequent to Sentinel’s sale of certain assets, Sentinel filed for bankruptcy protection. In aggregate, $15.5 million of FCStone, LLC’s $21.9 million in invested funds were returned to it before and after Sentinel’s bankruptcy petition.

In August 2008, the bankruptcy trustee of Sentinel filed adversary proceedings against FCStone, LLC, and a number of other FCMs in the Bankruptcy Court for the Northern District of Illinois. The case was subsequently reassigned to the U.S. District Court, for the Northern District of Illinois. The trustee sought recovery of pre- and post-petition transfers totaling approximately $15.5 million.

The trial of this matter took place during October 2012. The trial court entered a judgment against FCStone, LLC on January 4, 2013. The case has been appealed to the Seventh Circuit several times. The latest oral argument was heard in the Seventh Circuit on June 7, 2017. On August 14, 2017, the Seventh Circuit ruled in favor of all of INTL FCStone Financial’s arguments.

On April 23, 2018, the United States Supreme Court denied the trustee’s petition for writ of certiorari. Following this, INTL FCStone Financial requested immediate payment of funds due based on the August 14, 2017 ruling in its favor. On May 1, 2018, INTL FCStone Financial received funds in the amount of $1.9 million, which it will recognize as a gain during the quarter ending June 30, 2018.

Our assessments are based on estimates and assumptions that have been deemed reasonable by management, but that may later prove to be incomplete or inaccurate, and unanticipated events and circumstances may occur that might cause us to change those estimates and assumptions.

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 March 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.