Capital and Other Regulatory Requirements - Regulatory Capital Requirements (Details) $ in Millions	Jun. 30, 2017 USD ($)
FCStone LLC [Member]
Net Capital under Commodity Exchange Act Computation	$ 148.3
Required Net Capital under Commodity Exchange Act	77.7
Cash and Securities Segregated under Commodity Exchange Act Regulation	2,075.0
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	2,024.9
Secured Funds	137.8
Secured Funds Required Under Commodity Exchange Act	121.9
Sterne Agee Clearing, Inc. [Member]
Net Capital under Commodity Exchange Act Computation	1.3
Required Net Capital under Commodity Exchange Act	0.1
Sterne Agee, and Leach, Inc [Member]
Net Capital under Commodity Exchange Act Computation	25.3
Required Net Capital under Commodity Exchange Act	2.0
Sterne Agee Financial Services, Inc. [Member]
Net Capital under Commodity Exchange Act Computation	4.8
Required Net Capital under Commodity Exchange Act	0.3
INTL FCStone Ltd [Member]
Net Capital under Commodity Exchange Act Computation	159.5
Required Net Capital under Commodity Exchange Act	98.6
Cash and Securities Segregated under Commodity Exchange Act Regulation	93.1
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	90.1
INTL Netherlands BV [Member]
Net Capital under Commodity Exchange Act Computation	158.8
Required Net Capital under Commodity Exchange Act	98.7
INTL FCStone DTVM Ltda [Member]
Net Capital	9.4
Capital Required for Capital Adequacy	0.5
Gainvest S.A. Sociedad Gerente de FCI - Comision Nacional de Valores [Member]
Net Capital under Commodity Exchange Act Computation	0.5
Required Net Capital under Commodity Exchange Act	0.1
Net Capital	5.3
Capital Required for Capital Adequacy	0.2
INTL Capital S.A. – General Inspector of Justice [Member] [Domain]
Net Capital under Commodity Exchange Act Computation	7.4
Required Net Capital under Commodity Exchange Act	1.0
INTL Capital S.A. – Superintendence of Securities Markets of Buenos Aires [Member] [Domain]
Net Capital under Commodity Exchange Act Computation	4.3
Required Net Capital under Commodity Exchange Act	0.5
Customer Reserve Requirement [Member] [Member]
Cash Reserve Deposit Required and Made	0.0
PAB Reserve Requirement [Member]
Cash Reserve Deposit Required and Made	$ 1.8

Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated

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- Definition

Secured funds

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- Definition

Secured Funds Required Under Commodity Exchange Act

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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=35709795&loc=d3e65071-112826

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-SubTopic 505
-Section 50
-Paragraph 1
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- Definition

Cash and securities deposited in a special reserve account for the exclusive benefit of customers pursuant to the Commodity Exchange Act.

+ References

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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

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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

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- Definition

The amount of net capital calculated under the Commodity Futures Trading Commission's minimum financial requirements, pursuant to the Commodity Exchange Act, less the market value of certain commodity options.

+ References

No definition available.

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Amount of net capital required to be maintained under the Commodity Futures Trading Commission's (CFTC) minimum financial requirements, pursuant to the Commodity Exchange Act, less the market value of certain commodity options.

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