Basis of Presentation and Consolidation and Recently Issued Accounting Standards (Notes)	6 Months Ended
Mar. 31, 2017
Basis of Presentation and Consolidation [Abstract]
Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block]	Basis of Presentation and Consolidation and Recently Issued Accounting Standards INTL FCStone Inc., a Delaware corporation, and its consolidated subsidiaries (collectively “INTL” or “the Company”), is a diversified global financial services organization providing execution, risk management and advisory services, market intelligence, and clearing services across assets classes and markets around the world. The Company’s services include comprehensive risk management advisory services for commercial customers; execution of listed futures and options on futures contracts on all major commodity exchanges; structured over-the-counter (“OTC”) products in a wide range of commodities; physical trading and hedging of precious metals and select other commodities; trading of more than 140 foreign currencies; market-making in international equities; fixed income; debt origination and asset management. The Company provides these services to a diverse group of more than 20,000 predominantly wholesale organizations located throughout the world, including producers, processors and end-users of nearly all widely-traded physical commodities to manage their risks and enhance margins; to commercial counterparties who are end-users of the firm’s products and services; to governmental and non-governmental organizations; and to commercial banks, brokers, institutional investors and major investment banks. Basis of Presentation and Consolidation The accompanying condensed consolidated balance sheet as of September 30, 2016, which has been derived from audited financial statements, and the unaudited interim condensed consolidated financial statements have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”). Certain information and note disclosures normally included in annual financial statements prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) have been condensed or omitted pursuant to those rules and regulations. The Company believes that the disclosures made are adequate to make the information presented not misleading. In the opinion of management, all adjustments (consisting of normal recurring accruals) considered necessary for a fair presentation of the condensed consolidated financial statements for the interim periods presented have been reflected as required by Rule 10-01 of Regulation S-X. Operating results for interim periods are not necessarily indicative of the results that may be expected for the full year. These interim condensed consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and related notes contained in the Company’s Form 10-K for the fiscal year ended September 30, 2016 filed with the SEC. These condensed consolidated financial statements include the accounts of INTL FCStone Inc. and all other entities in which the Company has a controlling financial interest. All material intercompany transactions and balances have been eliminated in consolidation. The Company’s fiscal year end is September 30, and the fiscal quarters end on December 31, March 31, June 30 and September 30. Unless otherwise stated, all dates refer to fiscal years and fiscal interim periods. The preparation of condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent liabilities as of the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. The most significant of these estimates and assumptions relate to fair value measurement for financial instruments and investments, revenue recognition, the provision for potential losses from bad debts, valuation of inventories, valuation of goodwill and intangible assets, self-insurance liabilities, incomes taxes and contingencies. Although these and other estimates and assumptions are based on the best available information, actual results could be materially different from these estimates. In the condensed consolidated income statements, the total revenues reported combine gross revenues for the physical commodities business and net revenues for all other businesses. The subtotal ‘operating revenues’ in the condensed consolidated income statements is calculated by deducting physical commodities cost of sales from total revenues. The subtotal ‘net operating revenues’ in the condensed consolidated income statements is calculated as operating revenues less transaction-based clearing expenses, introducing broker commissions and interest expense. Transaction-based clearing expenses represent variable expenses paid to executing brokers, exchanges, clearing organizations and banks in relation to transactional volumes. Introducing broker commissions include commission paid to non-employee third parties that have introduced customers to the Company. Net operating revenues represent revenues available to pay variable compensation to risk management consultants and traders and direct non-variable expenses, as well as variable and non-variable expenses of operational and administrative employees. During the quarter ended March 31, 2017, the Company’s Securities reportable segment established a stock lending business. Stock borrowed and stock loaned are accounted for as collateralized financings. Securities borrowed and securities loaned are recorded at the amount of cash collateral advanced or received. Stock borrowed and stock loaned is reported on a gross basis as the Company has determined that the right of offset does not exist. Interest income and interest expense are recognized over the life of the arrangements. Accounting Standards Adopted In April 2015, the FASB issued Accounting Standards Update (“ASU”) No. 2015-03, Interest – Imputation of Interest (Subtopic 835-30). ASU 2015-03 requires that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability. In June 2015, the FASB issued ASU 2015-15 as an amendment to this guidance to address the absence of authoritative guidance for debt issuance costs related to line-of-credit arrangements. The SEC staff stated that they would not object to an entity deferring and presenting debt issuance costs as an asset and subsequently amortizing the deferred debt issuance costs ratably over the term of the line-of-credit arrangement, regardless of whether there are any outstanding borrowings on the line-of-credit arrangement. ASU 2015-03 required retrospective application to all prior periods presented in the financial statements. This new guidance was effective for the Company in the first quarter of 2017. As a result of adopting this standard on October 1, 2016, deferred financing costs of $1.0 million as of September 30, 2016, previously reported within other assets, were reclassified to senior unsecured notes in the consolidated balance sheets. As of December 31, 2016, there were no deferred financing costs as the senior unsecured notes were redeemed during the three months ended December 31, 2016, as discussed in Note 9. In January 2017, the FASB issued ASU 2017-01, Business Combinations - Clarifying the Definition of a Business, which clarifies the definition of a business for determining whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. This ASU is effective for public business entities for annual and interim periods in fiscal years beginning after December 15, 2017. The adoption of this standard should be applied prospectively on or after the effective date. Early adoption is permitted for transactions for which the acquisition date occurs before the issuance date or effective date of the amendments and only when the transaction has not been reported in financial statements that have been issued or made available for issuance. The Company has early adopted this guidance effective October 1, 2016, and applied the guidance in determining whether the acquisition discussed in Note 16 is the acquisition of an asset or of a business.

Basis of Presentation and Consolidation and Recently Issued Accounting Standards

INTL FCStone Inc., a Delaware corporation, and its consolidated subsidiaries (collectively “INTL” or “the Company”), is a diversified global financial services organization providing execution, risk management and advisory services, market intelligence, and clearing services across assets classes and markets around the world. The Company’s services include comprehensive risk management advisory services for commercial customers; execution of listed futures and options on futures contracts on all major commodity exchanges; structured over-the-counter (“OTC”) products in a wide range of commodities; physical trading and hedging of precious metals and select other commodities; trading of more than 140 foreign currencies; market-making in international equities; fixed income; debt origination and asset management.

The Company provides these services to a diverse group of more than 20,000 predominantly wholesale organizations located throughout the world, including producers, processors and end-users of nearly all widely-traded physical commodities to manage their risks and enhance margins; to commercial counterparties who are end-users of the firm’s products and services; to governmental and non-governmental organizations; and to commercial banks, brokers, institutional investors and major investment banks.

Basis of Presentation and Consolidation

The accompanying condensed consolidated balance sheet as of September 30, 2016, which has been derived from audited financial statements, and the unaudited interim condensed consolidated financial statements have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”). Certain information and note disclosures normally included in annual financial statements prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) have been condensed or omitted pursuant to those rules and regulations. The Company believes that the disclosures made are adequate to make the information presented not misleading. In the opinion of management, all adjustments (consisting of normal recurring accruals) considered necessary for a fair presentation of the condensed consolidated financial statements for the interim periods presented have been reflected as required by Rule 10-01 of Regulation S-X.

Operating results for interim periods are not necessarily indicative of the results that may be expected for the full year. These interim condensed consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and related notes contained in the Company’s Form 10-K for the fiscal year ended September 30, 2016 filed with the SEC.

These condensed consolidated financial statements include the accounts of INTL FCStone Inc. and all other entities in which the Company has a controlling financial interest. All material intercompany transactions and balances have been eliminated in consolidation.

The Company’s fiscal year end is September 30, and the fiscal quarters end on December 31, March 31, June 30 and September 30. Unless otherwise stated, all dates refer to fiscal years and fiscal interim periods.

The preparation of condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent liabilities as of the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. The most significant of these estimates and assumptions relate to fair value measurement for financial instruments and investments, revenue recognition, the provision for potential losses from bad debts, valuation of inventories, valuation of goodwill and intangible assets, self-insurance liabilities, incomes taxes and contingencies. Although these and other estimates and assumptions are based on the best available information, actual results could be materially different from these estimates.

In the condensed consolidated income statements, the total revenues reported combine gross revenues for the physical commodities business and net revenues for all other businesses. The subtotal ‘operating revenues’ in the condensed consolidated income statements is calculated by deducting physical commodities cost of sales from total revenues. The subtotal ‘net operating revenues’ in the condensed consolidated income statements is calculated as operating revenues less transaction-based clearing expenses, introducing broker commissions and interest expense. Transaction-based clearing expenses represent variable expenses paid to executing brokers, exchanges, clearing organizations and banks in relation to transactional volumes. Introducing broker commissions include commission paid to non-employee third parties that have introduced customers to the Company. Net operating revenues represent revenues available to pay variable compensation to risk management consultants and traders and direct non-variable expenses, as well as variable and non-variable expenses of operational and administrative employees.

During the quarter ended March 31, 2017, the Company’s Securities reportable segment established a stock lending business. Stock borrowed and stock loaned are accounted for as collateralized financings. Securities borrowed and securities loaned are recorded at the amount of cash collateral advanced or received. Stock borrowed and stock loaned is reported on a gross basis as the Company has determined that the right of offset does not exist. Interest income and interest expense are recognized over the life of the arrangements.

Accounting Standards Adopted

In April 2015, the FASB issued Accounting Standards Update (“ASU”) No. 2015-03, Interest – Imputation of Interest (Subtopic 835-30). ASU 2015-03 requires that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability. In June 2015, the FASB issued ASU 2015-15 as an amendment to this guidance to address the absence of authoritative guidance for debt issuance costs related to line-of-credit arrangements. The SEC staff stated that they would not object to an entity deferring and presenting debt issuance costs as an asset and subsequently amortizing the deferred debt issuance costs ratably over the term of the line-of-credit arrangement, regardless of whether there are any outstanding borrowings on the line-of-credit arrangement. ASU 2015-03 required retrospective application to all prior periods presented in the financial statements. This new guidance was effective for the Company in the first quarter of 2017. As a result of adopting this standard on October 1, 2016, deferred financing costs of $1.0 million as of September 30, 2016, previously reported within other assets, were reclassified to senior unsecured notes in the consolidated balance sheets. As of December 31, 2016, there were no deferred financing costs as the senior unsecured notes were redeemed during the three months ended December 31, 2016, as discussed in Note 9.

In January 2017, the FASB issued ASU 2017-01, Business Combinations - Clarifying the Definition of a Business, which clarifies the definition of a business for determining whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. This ASU is effective for public business entities for annual and interim periods in fiscal years beginning after December 15, 2017. The adoption of this standard should be applied prospectively on or after the effective date. Early adoption is permitted for transactions for which the acquisition date occurs before the issuance date or effective date of the amendments and only when the transaction has not been reported in financial statements that have been issued or made available for issuance. The Company has early adopted this guidance effective October 1, 2016, and applied the guidance in determining whether the acquisition discussed in Note 16 is the acquisition of an asset or of a business.