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Regulatory Requirements and Subsidiary Dividend Restrictions - Regulatory Capital Requirements (Details) - USD ($) | Sep. 30, 2018 | Sep. 30, 2017 | Sep. 30, 2016
--- | --- | --- | ---
Minimum Net Capital Required for Entity |  | $ 0.08 |
Cash Held at Banks and Money Market Funds - Segregated | $ 765,400,000 | $ 464,300,000 |
INTL FCStone Financial [Member] |  |  |
Net Capital | 167,700,000 |  |
Cash and Securities Segregated under Commodity Exchange Act Regulation | 2,637,000,000 |  |
Secured funds | 148,900,000 |  |
Minimum Net Capital Required for Entity | 101,400,000 |  |
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated | 2,579,700,000 |  |
Secured Funds Required Under Commodity Exchange Act | 132,800,000 |  |
Cash Reserve Deposit Required and Made |  |  | $ 6,400,000
Cash Held at Banks and Money Market Funds - Segregated | 300,000 |  |
Sterne Agee Clearing, Inc. [Member] |  |  |
Net Capital | 0 |  |
Minimum Net Capital Required for Entity | 0 |  |
Sterne Agee Financial Services, Inc. [Member] |  |  |
Net Capital | 4,600,000 |  |
Minimum Net Capital Required for Entity | 400,000 |  |
INTL FCStone, Ltd [Member] |  |  |
Cash and Securities Segregated under Commodity Exchange Act Regulation | 187,300,000 |  |
Net Capital under Commodity Exchange Act Computation | 193,100,000 |  |
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated | 182,100,000 |  |
Required Net Capital under Commodity Exchange Act | 95,900,000 |  |
INTL FCStone Europe [Member] |  |  |
Net Capital under Commodity Exchange Act Computation | 193,000,000 |  |
Required Net Capital under Commodity Exchange Act | 95,900,000 |  |
INTL FCStone DTVM Ltda [Member] |  |  |
Net Capital | 11,200,000 |  |
Capital Required for Capital Adequacy | 2,100,000 |  |
Gainvest S.A. Sociedad Gerente de FCI - Comision Nacional de Valores [Member] |  |  |
Net Capital | 4,200,000 |  |
Net Capital under Commodity Exchange Act Computation | 1,200,000 |  |
Required Net Capital under Commodity Exchange Act | 100,000 |  |
Capital Required for Capital Adequacy | 100,000 |  |
INTL CIBSA S.A. - Comision Nacional de Valores [Member] |  |  |
Net Capital | 4,400,000 |  |
Net Capital under Commodity Exchange Act Computation | 0 |  |
Required Net Capital under Commodity Exchange Act | 0 |  |
Capital Required for Capital Adequacy | $ 500,000 |  |

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- Definition Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated + References No definition available. + Details
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- Definition Cash Held at Banks and Money Market Funds - Segregated + References No definition available. + Details
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- Definition The minimum amount of Total Capital required for capital adequacy purposes under the regulatory framework for prompt corrective action. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1H -Subparagraph (c)(2) -URI http://asc.fasb.org/extlink&oid=84167132&loc=d3e65071-112826 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 505 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=84167132&loc=SL5958568-112826 + Details
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- Definition Cash deposited in a special reserve account for the exclusive benefit of customers pursuant to SEC Regulations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 305 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6478312&loc=d3e61473-112792 + Details
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- Definition Minimum amount of net capital required to be maintained by the entity to engage in securities transactions. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Rule 15c3-1 -Number 240 -Section 15c3-1 + Details
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- Definition Net capital is equal to the net worth of the broker dealer, less certain items such as exchange memberships, carrying value of securities not readily marketable, haircuts on marketable securities in proprietary accounts, furniture and equipment and other illiquid assets as defined. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Rule 15c3-1 -Number 240 -Section 15c3-1 + Details
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