StoneX (SNEX) 10-Q 8 May 18 2018 Q2 Quarterly report Financial data

DEI

DEI - shares	6 Months Ended
	Mar. 31, 2018	May 05, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	INTL FCSTONE INC.
Trading Symbol	INTL
Entity Central Index Key	913,760
Current Fiscal Year End Date	--09-30
Entity Filer Category	Accelerated Filer
Document Type	10-Q
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q2
Amendment Flag	false
Entity Common Stock, Shares Outstanding		18,879,487
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Millions	Mar. 31, 2018	Sep. 30, 2017
ASSETS
Cash and cash equivalents	$ 336	$ 314.9
Cash, securities and other assets segregated under federal and other regulations (including $615.6 and $54.5 at fair value at March 31, 2018 and September 30, 2017, respectively)	1,251.4	518.8
Collateralized transactions:
Securities purchased under agreements to resell	604.7	406.6
Securities borrowed	519.9	86.6
Deposits with and receivables from broker-dealers, clearing organizations and counterparties (including $649.5 and $204.7 at fair value at March 31, 2018 and September 30, 2017, respectively)	1,914.1	2,625.1
Receivables from customers, net	220.4	232.7
Notes receivable	12.4	10.6
Income taxes receivable	0.4	0.4
Financial instruments owned, at fair value (includes securities pledged as collateral that can be sold or repledged of $5.1 and $19.4 at March 31, 2018 and September 30, 2017, respectively)	1,889.7	1,731.8
Physical commodities inventory, net (including $187.1 and $73.2 at fair value at March 31, 2018 and September 30, 2017, respectively)	286.3	124.8
Deferred income taxes, net	23.9	42.6
Property and equipment, net	41	38.7
Goodwill and intangible assets, net	57.1	59.4
Other assets	46.4	50.4
Total assets	7,203.7	6,243.4
Liabilities:
Accounts payable and other accrued liabilities (including $1.0 at fair value at September 30, 2017)	129.6	135.6
Payables to:
Customers	3,231.6	3,072.9
Broker-dealers, clearing organizations and counterparties (including $5.7 and $4.8 at fair value at March 31, 2018 and September 30, 2017), respectively	79.7	125.7
Lenders under loans	340.5	230.2
Income taxes payable	11.2	7.3
Collateralized transactions:
Securities sold under agreements to repurchase	1,562.5	1,393.1
Securities loaned	559.1	111.1
Financial instruments sold, not yet purchased, at fair value	822.9	717.6
Total liabilities	6,737.1	5,793.5
Commitments and contingencies (Note 11)
Stockholders' Equity:
Preferred stock, $0.01 par value. Authorized 1,000,000 shares; no shares issued or outstanding	0	0
Common stock, $0.01 par value. Authorized 30,000,000 shares; 20,982,674 issued and 18,860,717 outstanding at March 31, 2018 and 20,855,243 issued and 18,733,286 outstanding at September 30, 2017	0.2	0.2
Common stock in treasury, at cost - 2,121,957 shares at March 31, 2018 and September 30, 2017	(46.3)	(46.3)
Additional paid-in capital	263.7	259
Retained earnings	277.3	261.5
Accumulated other comprehensive loss, net	(28.3)	(24.5)
Total stockholders' equity	466.6	449.9
Total liabilities and stockholders' equity	$ 7,203.7	$ 6,243.4

Condensed Consolidated Balance3

Condensed Consolidated Balance Sheets Parentheticals - USD ($) $ in Millions	Mar. 31, 2018	Sep. 30, 2017
Balance Sheet Parentheticals [Abstract]
Securities and other assets segregated, fair value	$ 615.6	$ 54.5
Dep and rec -b/d - fair value	649.5	204.7
Physical commodities inventory at fair value	187.1	73.2
Collateral that can be sold or repledged	5.1	19.4
Accounts pay and other accrued - fair value	0	1
Payables to b/d - fair value	$ 5.7	$ 4.8
Preferred stock - par value	$ 0.01	$ 0.01
Preferred stock - authorized	1,000,000	1,000,000
Preferred stock - issued	0	0
Preferred stock - outstanding	0	0
Common stock - par value	$ 0.01	$ 0.01
Common stock - authorized	30,000,000	30,000,000
Common stock - issued	20,982,674	20,855,243
Common stock - outstanding	18,860,717	18,733,286
Treasury stock - shares	2,121,957	2,121,957

Condensed Consolidated Income S

Condensed Consolidated Income Statements - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Revenues:
Sales of physical commodities	$ 6,255.8	$ 5,273.3	$ 13,970.2	$ 11,169.3
Trading gains, net	107.7	84	193.5	167
Commission and clearing fees	97.2	70.3	175	139.5
Consulting,management, and account fees	18.3	15.5	34.9	31.2
Interest income	27.9	17.7	51.9	28.1
Other income	0.1	0	0.1	0.1
Total revenues	6,507	5,460.8	14,425.6	11,535.2
Cost of sales of physical commodities	6,246.8	5,265	13,952.8	11,153.9
Operating revenues	260.2	195.8	472.8	381.3
Transaction-based clearing expenses	50.7	33.7	87.6	67.3
Introducing broker commissions	36.2	28.2	67.3	56.9
Interest expense	19	10	33.3	18.9
Net operating revenues	154.3	123.9	284.6	238.2
Compensation and other expenses:
Compensation and benefits	88.2	76.6	165.4	147.2
Trading systems and market information	8.9	8.5	17.1	17.4
Occupancy and equipment rental	4.2	3.8	8.3	7.2
Professional fees	3.9	3.4	8.6	8.2
Travel and business development	3	3	6.5	6.6
Non-trading technology and support	3.4	2.8	6.5	5.7
Depreciation and amortization	2.9	2.4	5.6	4.8
Communications	1.4	1.2	2.8	2.4
Bad debts	0.2	1.3	1.3	3.8
Other	8.7	6.6	14.4	12.2
Total compensation and other expenses	124.8	109.6	236.5	215.5
Income before tax	29.5	14.3	48.1	22.7
Income tax expense	6.8	3.3	32.3	5.4
Net income	$ 22.7	$ 11	$ 15.8	$ 17.3
Earnings per share:
Basic	$ 1.20	$ 0.58	$ 0.83	$ 0.92
Diluted	$ 1.18	$ 0.58	$ 0.81	$ 0.92
Weighted-average number of common shares outstanding:
Basic	18,559,849	18,404,236	18,502,795	18,325,383
Diluted	18,859,333	18,661,418	18,836,213	18,637,480

Condensed Consolidated Statemen

Condensed Consolidated Statement of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Condensed Consolidated Statement of Other Comprehensive Income (Loss) [Abstract]
Net income	$ 22.7	$ 11	$ 15.8	$ 17.3
Other comprehensive income (loss), net of tax:
Foreign currency translation adjustment	(1.6)	0.7	(3.8)	(0.2)
Other comprehensive income (loss)	(1.6)	0.7	(3.8)	(0.2)
Comprehensive income	$ 21.1	$ 11.7	$ 12	$ 17.1

Condensed Consolidated Cash Flo

Condensed Consolidated Cash Flows Statements - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Cash flows from operating activities:
Net income	$ 15.8	$ 17.3
Adjustments to reconcile net income to net cash used in operating activities:
Depreciation and amortization	5.6	4.8
Bad debts	1.3	3.8
Deferred income taxes	18.6	(3.6)
Amortization of debt issuance costs	0.5	1.4
Amortization of stock-based compensation	3.2	2.6
Gain on sale of property and equipment	0	(0.3)
Changes in operating assets and liabilities, net:
Cash, securities and other assets segregated under federal and other regulations	(758.1)	47.4
Securities purchased under agreements to resell	(198.1)	(129.2)
Securities borrowed	(433.3)	(66.7)
Deposits with and receivables from broker-dealers, clearing organizations, and counterparties	755	(126.3)
Receivables from customers, net	(72)	(2.5)
Notes receivable, net	(1.9)	7.9
Income taxes receivable	(0.6)	0
Financial instruments owned, at fair value	(125.2)	(304.8)
Physical commodities inventory, net	(162.5)	(58.2)
Other assets	3.1	7.8
Accounts payable and other accrued liabilities	1.5	(8.8)
Payables to customers	195.6	27.8
Payables to broker-dealers, clearing organizations and counterparties	(51)	(64.3)
Income taxes payable	4.5	0.9
Securities sold under agreements to repurchase	169.5	264.8
Securities loaned	448	89.9
Financial instruments sold, not yet purchased, at fair value	104.1	243.7
Net cash used in operating activities	(76.4)	(44.6)
Cash flows from investing activities:
Cash paid for acquisitions, net	0	(6)
Purchase of property and equipment	(6.9)	(6.1)
Net cash used in investing activities	(6.9)	(12.1)
Cash flows from financing activities:
Net change in payable to lenders under loans	110.7	81
Repayment of senior unsecured notes	0	(45.5)
Payments of note payable	(0.4)	(0.4)
Deferred payments on acquisitions	(5.5)	0
Debt issuance costs	(0.1)	(0.1)
Exercise of stock options	2.2	2.5
Withholding taxes on stock option exercises	(0.8)	0
Income tax benefit on stock options and awards	0	(0.2)
Net cash provided by financing activities	106.1	37.3
Effect of exchange rates on cash and cash equivalents	(1.7)	(0.5)
Net (decrease) increase in cash and cash equivalents	21.1	(19.9)
Cash and cash equivalents at beginning of period	314.9	316.2
Cash and cash equivalents at end of period	336	296.3
Supplemental disclosure of cash flow information:
Cash paid for interest	32.5	17.1
Income taxes paid, net of cash refunds	9.8	8.1
Supplemental disclosure of non-cash investing and financing activities:
Identified intangible assets and goodwill on acquisitions	$ 0	$ 6

Condensed Consolidated Stateme7

Condensed Consolidated Statement of Stockholders' Equity - 6 months ended Mar. 31, 2018 - USD ($) $ in Millions	Total	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]
Balances as of beginning of period at Sep. 30, 2017	$ 449.9	$ 0.2	$ (46.3)	$ 259	$ 261.5	$ (24.5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	15.8				15.8
Other comprehensive loss	(3.8)					(3.8)
Exercise of stock options	1.5			1.5
Share-based Compensation	3.2			3.2
Balances as of end of period at Mar. 31, 2018	$ 466.6	$ 0.2	$ (46.3)	$ 263.7	$ 277.3	$ (28.3)

Basis of Presentation and Conso

Basis of Presentation and Consolidation and Recently Issued Accounting Standards (Notes)	6 Months Ended
	Mar. 31, 2018
Basis of Presentation and Consolidation [Abstract]
Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block]	Basis of Presentation and Consolidation and Accounting Standards Adopted 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 asset 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 Company’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 unaudited condensed consolidated balance sheet as of September 30, 2017 , which has been derived from audited consolidated 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 consolidated 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, 2017 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 consolidated 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, 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. Reclassifications During the three and six months ended March 31, 2018, the Company separately classified non-trading technology and support costs that were previously included within ‘Other’ on the condensed consolidated income statements. Additionally, during the three and six months ended March 31, 2018, the Company separately classified communications related expenses separately from trading systems and market information related costs. In performing these reclassifications, the Company has made immaterial, retrospective adjustments to conform to our current period presentation. For the three and six months ending March 31, 2017, ‘Other’ expenses included $2.8 million and $5.7 million , respectively, of expenses that are now included within ‘Non-trading technology and support’ on the condensed consolidated income statements. For the three and six months ending March 31, 2017, ‘Trading systems and market information’ included $1.2 million and $2.4 million , respectively, of expenses that are now included within ‘Communications’ on the condensed consolidated income statements. Accounting Standards Adopted In March 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update No. 2016-09, “Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting” (“ASU 2016-09”), which simplifies several aspects of the accounting for share-based payment transactions. Under ASU 2016-09, excess tax benefits and tax deficiencies are recognized as income tax expense or benefit in the income statement instead of additional paid in capital. ASU 2016-09 also provides entities with the option to elect an accounting policy to estimate forfeitures of share-based awards over the service period (current GAAP) or account for forfeitures when they occur. Under ASU 2016-09, previously unrecognized excess tax benefits should be recognized using a modified retrospective transition. In addition, amendments requiring recognition of excess tax benefits and tax deficiencies in the income statement, as well as changes in the computation of weighted-average diluted shares outstanding, should be applied prospectively. ASU 2016-09 is effective for and was adopted by the Company in the first quarter of 2018 and the impact of the adoption resulted in the following: • During the six months ended March 31, 2018, the Company recognized excess tax benefits from share-based compensation of $0.3 million within income tax expense on the condensed consolidated income statement and within net income on the condensed consolidated cash flow statement. Prior to adoption, the tax effect of share-based awards would have been recognized in additional paid-in-capital on the condensed consolidated balance sheets and separately stated in the financing activities in the condensed consolidated cash flow statements. The Company has elected to adopt this guidance prospectively. • The Company has elected to account for forfeitures of share-based awards as they occur. The Company elected to account for forfeitures as they occur using a modified retrospective transition method. The adoption of this guidance did not have a material impact on our condensed consolidated financial statements. • The excess tax benefits from the assumed proceeds available to repurchase shares were excluded in the computation of diluted earnings per share for the three and six months ended March 31, 2018. The Company has elected to adopt this guidance prospectively. • For the six months ended March 31, 2018, the Company has classified as a financing activity in the condensed consolidated cash flow statement $0.8 million of cash paid to taxing authorities for restricted stock shares withheld to satisfy statutory income tax withholding obligations. The retrospective application of this guidance had no impact on the condensed consolidated cash flow statement for the six months ended March 31, 2017. In July 2015, the FASB issued ASU No. 2015-11, “Simplifying the Measurement of Inventory (Topic 330).” Under ASU 2015-11, inventory that is measured using the first-in, first-out (FIFO), specific identification, or average cost methods should be measured at the lower of cost or net realizable value. This ASU does not impact inventory measurement under the last-in, first-out (LIFO) or retail inventory methods. The Company adopted this ASU prospectively in the first quarter of 2018. The adoption of this ASU did not have a material impact on the condensed consolidated financial statements.

Earnings per Share (Notes)

Earnings per Share (Notes)	6 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
Earnings Per Share [Text Block]	Earnings per Share The Company presents basic and diluted earnings per share (“EPS”) using the two-class method which requires all outstanding unvested share-based payment awards that contain rights to non-forfeitable dividends and therefore participate in undistributed earnings with common stockholders be included in computing earnings per share. Under the two-class method, net earnings are reduced by the amount of dividends declared in the period for each class of common stock and participating security. The remaining undistributed earnings are then allocated to common stock and participating securities, based on their respective rights to receive dividends. Restricted stock awards granted to certain employees and directors contain non-forfeitable rights to dividends at the same rate as common stock, and are considered participating securities. Basic EPS has been computed by dividing net income by the weighted-average number of common shares outstanding. The following is a reconciliation of the numerator and denominator of the diluted earnings per share computations for the periods presented below. Three Months Ended March 31, Six Months Ended March 31, (in millions, except share amounts) 2018 2017 2018 2017 Numerator: Net income $ 22.7 $ 11.0 $ 15.8 $ 17.3 Less: Allocation to participating securities (0.3 ) (0.2 ) (0.3 ) (0.3 ) Net income allocated to common stockholders $ 22.4 $ 10.8 $ 15.5 $ 17.0 Denominator: Weighted average number of: Common shares outstanding 18,559,849 18,404,236 18,502,795 18,325,383 Dilutive potential common shares outstanding: Share-based awards 299,484 257,182 333,418 312,097 Diluted weighted-average common shares 18,859,333 18,661,418 18,836,213 18,637,480 The dilutive effect of share-based awards is reflected in diluted earnings per share by application of the treasury stock method, which includes consideration of unamortized share-based compensation expense required under the Compensation – Stock Compensation Topic of the ASC. Options to purchase 173,992 and 322,974 shares of common stock for the three months ended March 31, 2018 and 2017 , respectively, and options to purchase 136,440 and 242,448 shares of common stock for the six months ended March 31, 2018 and 2017, respectively, were excluded from the calculation of diluted earnings per share as they would have been anti-dilutive

Assets and Liabilities, at Fair

Assets and Liabilities, at Fair Value (Notes)	6 Months Ended
	Mar. 31, 2018
Assets and Liabilities, at Fair Value [Abstract]
Fair Value Disclosures [Text Block]	Assets and Liabilities, at Fair Value Fair value is defined by U.S. GAAP as the price that would be received for an asset or paid to transfer a liability (an exit price) in the principal or most advantageous market for the asset or liability in an orderly transaction between willing market participants on the measurement date. Fair value is a market-based measure considered from the perspective of a market participant rather than an entity-specific measure. Therefore, even when market assumptions are not readily available, the Company is required to develop a set of assumptions that reflect those that market participants would use in pricing the asset or liability at the measurement date. The Company uses prices and inputs that are current as of the measurement date, including periods of market dislocation. In periods of market dislocation, the observability of prices and inputs may be reduced for many assets and liabilities. This condition could cause a security to be reclassified to a lower level within the fair value hierarchy. The Company has designed independent price verification controls and periodically performs such controls to ensure the reasonableness of such values. In accordance with FASB ASC 820, Fair Value Measurement, the Company groups its assets and liabilities measured at fair value in three levels based on the markets in which the assets and liabilities are traded and the reliability of the assumptions used to determine fair value. These levels are: Level 1 - Valuation is based upon unadjusted quoted prices in active markets that are accessible at the measurement date for identical, unrestricted assets or liabilities. Level 1 consists of financial assets and liabilities whose fair values are estimated using quoted market prices. Level 2 - Valuation is based upon quoted prices for identical or similar assets or liabilities in markets that are less active, that is, markets in which there are few transactions for the asset or liability that are observable for substantially the full term. Included in Level 2 are those financial assets and liabilities for which fair values are estimated using models or other valuation methodologies. These models are primarily industry-standard models that consider various observable inputs, including time value, yield curve, volatility factors, observable current market and contractual prices for the underlying financial instruments, as well as other relevant economic measures. Level 3 - Valuation is based on prices or valuation techniques that require an input that is both significant to the fair value measurement and unobservable (i.e., supported by little or no market activity). Level 3 comprises financial assets and liabilities whose fair value is estimated based on internally developed models or methodologies utilizing significant inputs that are not readily observable from objective sources. Financial and nonfinancial assets and liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 measurements) and the lowest priority to unobservable inputs (Level 3 measurements). A market is active if there are sufficient transactions on an ongoing basis to provide current pricing information for the asset or liability, pricing information is released publicly, and price quotations do not vary substantially either over time or among market participants. Observable inputs reflect the assumptions market participants would use in pricing the asset or liability developed based on market data obtained from sources independent of the reporting entity. The guidance requires the Company to consider counterparty credit risk of all parties of outstanding derivative instruments that would be considered by a market participant in the transfer or settlement of such contracts (exit price). The Company’s exposure to credit risk on derivative financial instruments relates to the portfolio of OTC derivative contracts as all exchange-traded contracts held can be settled on an active market with a credit guarantee by the respective exchange. The Company requires most counterparties to deposit margin collateral for all OTC instruments and is also required to deposit margin collateral with counterparties, which mitigates the impact of counterparty credit risk in the evaluation of the fair value of OTC derivative contracts. Fair value of financial and nonfinancial assets and liabilities that are carried on the Condensed Consolidated Balance Sheets at fair value on a recurring basis Cash and cash equivalents reported at fair value on a recurring basis includes certificates of deposit, which are stated at cost plus accrued interest, which approximates fair value. Cash, securities and other assets segregated under federal and other regulations reported at fair value on a recurring basis include the value of pledged investments, primarily U.S. Treasury obligations and commodities warehouse receipts. Deposits with and receivables from broker-dealers, clearing organizations and counterparties and payable to customers and broker-dealers, clearing organizations and counterparties include the value of pledged investments, primarily U.S. Treasury obligations and foreign government obligations. These balances also include the fair value of exchange-traded options on futures and exchange-cleared OTC swaps and options determined by quoted prices on the applicable exchange. Financial instruments owned and sold, not yet purchased include the value of common and preferred stock, American Depository Receipts (“ADRs”), and Global Depository Receipts (“GDRs”), exchangeable foreign ordinary equities, ADRs, and GDRs, corporate and municipal bonds, U.S. Treasury obligations, U.S. government agency obligations, foreign government obligations, agency mortgage-backed obligations, asset-backed obligations, derivative financial instruments, commodities leases, commodities warehouse receipts, exchange firm common stock, and mutual funds and investments in managed funds. The fair value of exchange firm common stock is determined by quoted market prices. Physical commodities inventory recorded at fair value on a recurring basis includes precious metals that are a part of the trading activities of a regulated broker-dealer subsidiary and is recorded at fair value using spot prices. Physical commodities inventory also includes agricultural commodities that are a part of the trading activities of a non-broker dealer subsidiary and are also recorded at net realizable value using spot prices. Precious metals inventory held by subsidiaries that are not broker-dealers are valued at fair value on a non-recurring basis. Except as disclosed in Note 6 , the Company did not have any fair value adjustments for assets or liabilities measured at fair value on a non-recurring basis as of March 31, 2018 and September 30, 2017 . Cash equivalents, securities, commodities warehouse receipts, physical commodities inventory, derivative financial instruments, commodities leases, and contingent liabilities are carried at fair value, on a recurring basis, and are classified and disclosed into three levels in the fair value hierarchy. The following section describes the valuation methodologies used by the Company to measure classes of financial instruments at fair value and specifies the level within the fair value hierarchy where various financial instruments are classified. The Company uses quoted prices in active markets, where available, and classifies such instruments within Level 1 of the fair value hierarchy. Examples include U.S. Treasury obligations, commodities warehouse receipts, some common and preferred stock, ADRs, and GDRs, some exchangeable foreign ordinary equities, ADRs, and GDRs, some corporate and municipal obligations, physical precious metals, exchange firm common stock, mutual funds, as well as exchange traded options on futures contracts. When instruments are traded in secondary markets and observable prices are not available for substantially the full term, the Company generally relies on internal valuation techniques that use observable inputs or prices obtained from third-party pricing services or brokers or a combination thereof, and accordingly, classified these instruments as Level 2. Examples include U.S. government agency obligations, agency-mortgage backed obligations, asset-backed obligations, foreign government obligations, some common and preferred stock, ADRs, and GDRs, certain exchangeable foreign ordinary equities, ADRs, and GDRs, OTC commodity and foreign exchange forwards, swaps, and options, physical agricultural commodity inventory, and OTC firm purchase and sale commitments related to the Company’s agricultural and energy commodities. With the exception of certain derivative instruments, financial instruments owned and sold are primarily valued using third party pricing sources. Third party vendors compile prices from various sources and often apply matrix pricing for similar securities when no prices are observable. The Company reviews the pricing methodologies provided by the various vendors in order to determine if observable market information is being used, versus unobservable inputs. When evaluating the propriety of an internal trader price compared with vendor prices, considerations include the range and quality of vendor prices. Trader or broker prices are used to ensure the reasonableness of a vendor price; however valuing financial instruments involves judgments acquired from knowledge of a particular market. If a trader asserts that a vendor or market price is not reflective of market value, justification for using the trader price, including recent sales activity where possible, must be provided to and approved by the appropriate levels of management. Financial instruments owned and sold that are valued using third party pricing sources are included within either Level 1 or Level 2 of the fair value hierarchy based upon the observability of the inputs used and the level of activity in the market. Level 3 comprises financial assets and liabilities whose fair value is estimated based on internally developed models or methodologies utilizing significant inputs that are not readily observable from objective sources. Included in Level 3 are some common stock and ADRs, some corporate and municipal obligations, and contingent liabilities. Level 3 assets and liabilities are valued using an income approach based upon management developed discounted cash flow projections, which are an unobservable input. The fair value estimates presented herein are based on pertinent information available to management as of March 31, 2018 and September 30, 2017 . Although management is not aware of any factors that would significantly affect the estimated fair value amounts, such amounts have not been comprehensively revalued for purposes of these condensed consolidated financial statements since those respective dates and current estimates of fair value may differ significantly from the amounts presented herein. The following tables set forth the Company’s financial and nonfinancial assets and liabilities accounted for at fair value, on a recurring basis, as of March 31, 2018 by level in the fair value hierarchy. March 31, 2018 (in millions) Level 1 Level 2 Level 3 Netting and Total Assets: Unrestricted cash equivalents - certificate of deposits $ 3.7 $ — $ — $ — $ 3.7 Commodities warehouse receipts 14.7 — — — 14.7 U.S. Treasury obligations 600.9 — — — 600.9 Cash, securities and other assets segregated under federal and other regulations 615.6 — — — 615.6 U.S. Treasury obligations 648.6 — — — 648.6 "To be announced" (TBA) and forward settling securities — 4.8 — 0.2 5.0 Foreign government obligations — 6.3 — — 6.3 Derivatives 3,698.4 21.2 — (3,730.0 ) (10.4 ) Deposits with and receivables from broker-dealers, clearing organization and counterparties 4,347.0 32.3 — (3,729.8 ) 649.5 Common and preferred stock, ADRs, and GDRs 46.6 2.9 — — 49.5 Exchangeable foreign ordinary equities, ADRs, and GDRs 17.7 0.5 — — 18.2 Corporate and municipal bonds 40.9 1.9 — — 42.8 U.S. Treasury obligations 96.5 — — — 96.5 U.S. government agency obligations — 408.1 — — 408.1 Foreign government obligations — 11.3 — — 11.3 Agency mortgage-backed obligations — 1,028.9 — — 1,028.9 Asset-backed obligations — 41.3 — — 41.3 Derivatives 1.7 779.2 — (612.4 ) 168.5 Commodities leases — 47.3 — (39.3 ) 8.0 Commodities warehouse receipts 2.0 — — — 2.0 Exchange firm common stock 9.9 — — — 9.9 Mutual funds and other 4.7 — — — 4.7 Financial instruments owned 220.0 2,321.4 — (651.7 ) 1,889.7 Physical commodities inventory, net 26.9 160.2 — — 187.1 Total assets at fair value $ 5,213.2 $ 2,513.9 $ — $ (4,381.5 ) $ 3,345.6 Liabilities: TBA and forward settling securities — 5.7 — (0.1 ) 5.6 Derivatives 3,832.7 34.4 — (3,867.0 ) 0.1 Payable to broker-dealers, clearing organizations and counterparties 3,832.7 40.1 — (3,867.1 ) 5.7 Common and preferred stock, ADRs, and GDRs 52.4 0.5 — — 52.9 Exchangeable foreign ordinary equities, ADRs, and GDRs 18.3 — — — 18.3 Corporate and municipal bonds 0.1 — — — 0.1 U.S. Treasury obligations 471.7 — — — 471.7 U.S. government agency obligations — 55.7 — — 55.7 Agency mortgage-backed obligations — 0.1 — — 0.1 Derivatives — 801.6 — (625.0 ) 176.6 Commodities leases — 45.6 — 1.9 47.5 Financial instruments sold, not yet purchased 542.5 903.5 — (623.1 ) 822.9 Total liabilities at fair value $ 4,375.2 $ 943.6 $ — $ (4,490.2 ) $ 828.6 (1) Represents cash collateral and the impact of netting across the levels of the fair value hierarchy. Netting among positions classified within the same level is included in that level. The following table sets forth the Company’s financial and nonfinancial assets and liabilities accounted for at fair value, on a recurring basis, as of September 30, 2017 by level in the fair value hierarchy. September 30, 2017 (in millions) Level 1 Level 2 Level 3 Netting and Total Assets: Unrestricted cash equivalents - certificates of deposits $ 3.8 $ — $ — $ — $ 3.8 Commodities warehouse receipts 21.0 — — — 21.0 U.S. Treasury obligations 33.5 — — — 33.5 Cash, securities and other assets segregated under federal and other regulations 54.5 — — — 54.5 U.S. Treasury obligations 244.7 — — — 244.7 "To be announced" (TBA) and forward settling securities — 8.8 — — 8.8 Foreign government obligations — 6.4 — — 6.4 Derivatives 2,608.6 289.1 — (2,952.9 ) (55.2 ) Deposits with and receivables from broker-dealers, clearing organizations, and counterparties 2,853.3 304.3 — (2,952.9 ) 204.7 Common and preferred stock, ADRs, and GDRs 31.2 3.4 0.1 — 34.7 Exchangeable foreign ordinary equities, ADRs, and GDRs 9.2 1.2 — — 10.4 Corporate and municipal bonds 28.2 0.9 — — 29.1 U.S. Treasury obligations 60.0 — — — 60.0 U.S. government agency obligations — 368.9 — — 368.9 Foreign government obligations — 10.2 — — 10.2 Agency mortgage-backed obligations — 920.9 — — 920.9 Asset-backed obligations — 47.3 — — 47.3 Derivatives 1.3 1,413.4 — (1,252.6 ) 162.1 Commodities leases — 174.1 — (138.7 ) 35.4 Commodities warehouse receipts 38.5 — — — 38.5 Exchange firm common stock 8.3 — — — 8.3 Mutual funds and other 6.0 — — — 6.0 Financial instruments owned 182.7 2,940.3 0.1 (1,391.3 ) 1,731.8 Physical commodities inventory, net 73.2 — — — 73.2 Total assets at fair value $ 3,167.5 $ 3,244.6 $ 0.1 $ (4,344.2 ) $ 2,068.0 Liabilities: Accounts payable and other accrued liabilities - contingent liabilities $ — $ — $ 1.0 $ — $ 1.0 TBA and forward settling securities — 4.9 — (0.1 ) 4.8 Derivatives 2,476.2 292.8 — (2,769.0 ) — Payable to broker-dealers, clearing organizations and counterparties 2,476.2 297.7 — (2,769.1 ) 4.8 Common and preferred stock, ADRs, and GDRs 33.7 0.7 — — 34.4 Exchangeable foreign ordinary equities, ADRs, and GDRs 10.3 0.2 — — 10.5 Corporate and municipal bonds 0.3 — — — 0.3 U.S. Treasury obligations 285.9 — — — 285.9 U.S. government agency obligations — 27.9 — — 27.9 Agency mortgage-backed obligations — 0.1 — — 0.1 Derivatives — 1,427.2 — (1,110.2 ) 317.0 Commodities leases — 191.1 — (149.6 ) 41.5 Financial instruments sold, not yet purchased 330.2 1,647.2 — (1,259.8 ) 717.6 Total liabilities at fair value $ 2,806.4 $ 1,944.9 $ 1.0 $ (4,028.9 ) $ 723.4 (1) Represents cash collateral and the impact of netting across the levels of the fair value hierarchy. Netting among positions classified within the same level is included in that level. Realized and unrealized gains and losses are included in ‘trading gains, net’ and ‘interest income’ in the condensed consolidated income statements. Information on Level 3 Financial Assets and Liabilities The following tables set forth a summary of changes in the fair value of the Company’s Level 3 financial assets and liabilities during the three and six months ended March 31, 2018 and 2017, including a summary of unrealized gains (losses) during the respective periods on the Company’s Level 3 financial assets and liabilities held during the periods. Level 3 Financial Assets For the Three and Six Months Ended March 31, 2018 (in millions) Balances at Realized gains Unrealized Purchases/issuances Settlements Transfers in Balances at Assets: Common and preferred stock, ADRs, and GDRs $ 0.1 $ — $ (0.1 ) $ — $ — $ — $ — $ 0.1 $ — $ (0.1 ) $ — $ — $ — $ — Level 3 Financial Assets and Financial Liabilities For the Three Months Ended March 31, 2017 (in millions) Balances at Realized gains Unrealized Purchases/issuances Settlements Transfers in Balances at Assets: Common and preferred stock, ADRs, and GDRs $ 0.2 $ — $ — $ — $ — $ — $ 0.2 Corporate and municipal bonds — — — — — — — $ 0.2 $ — $ — $ — $ — $ — $ 0.2 (in millions) Balances at Realized (gains) Unrealized Purchases/issuances Settlements Transfers in Balances at Liabilities: Contingent liabilities $ 0.8 $ — $ 0.1 $ — $ — $ — $ 0.9 Level 3 Financial Assets and Financial Liabilities For the Six Months Ended March 31, 2017 (in millions) Balances at Realized gains Unrealized Purchases/issuances Settlements Transfers in Balances at Assets: Common and preferred stock, ADRs, and GDRs $ 0.2 $ — $ — $ — $ — $ — $ 0.2 Corporate and municipal bonds 3.0 — — — (3.0 ) — — $ 3.2 $ — $ — $ — $ (3.0 ) $ — $ 0.2 (in millions) Balances at Realized (gains) Unrealized Purchases/issuances Settlements Transfers in Balances at Liabilities: Contingent liabilities $ 0.8 $ — $ 0.1 $ — $ — $ — $ 0.9 The Company was required to make additional future cash payments based on certain financial performance measures of an acquired business. The Company was required to remeasure the fair value of contingent consideration arrangements on a recurring basis. As of September 30, 2017, the Company had classified its liability for the contingent consideration within Level 3 of the fair value hierarchy because the fair value was determined using significant unobservable inputs, which included projected cash flows. The estimated fair value of the contingent consideration arrangements was based upon management-developed earnings forecasts for the remaining contingency period, which was a Level 3 input in the fair value hierarchy. The fair value of the contingent consideration increased by $0.1 million during the three and six months ended March 31, 2017, with the corresponding amount classified as ‘other’ in the condensed consolidated income statements. The contingency period for the contingent consideration arrangements ended as of December 31, 2017 and the accrued balance of $1.0 million was paid during the three months ended March 31, 2018. The Company reports transfers in and out of Levels 1, 2 and 3, as applicable, using the fair value of the securities as of the beginning of the reporting period in which the transfer occurred. The Company did not have any transfers in and out of Levels 1, 2, and 3 during the three and six months ended March 31, 2018 and 2017. Additional disclosures about the fair value of financial instruments that are not carried on the Condensed Consolidated Balance Sheets at fair value Many, but not all, of the financial instruments that the Company holds are recorded at fair value in the Condensed Consolidated Balance Sheets. The following represents financial instruments in which the ending balance at March 31, 2018 and September 30, 2017 was not carried at fair value in accordance with U.S. GAAP on our Condensed Consolidated Balance Sheets: Short-term financial instruments: The carrying value of short-term financial instruments, including cash and cash equivalents, cash segregated under federal and other regulations, securities purchased under agreements to re-sell and securities sold under agreements to re-purchase, and securities borrowed and loaned are recorded at amounts that approximate the fair value of these instruments due to their short-term nature and level of collateralization. These financial instruments generally expose the Company to limited credit risk and have no stated maturities or have short-term maturities and carry interest rates that approximate market rates. Under the fair value hierarchy, cash and cash equivalents and cash segregated under federal and other regulations are classified as Level 1. Securities purchased under agreements to re-sell and securities sold under agreements to re-purchase, and securities borrowed and loaned are classified as Level 2 under the fair value hierarchy as they are generally short-term in nature and are collateralized by common stock, U.S. Treasury obligations, U.S. government agency obligations, agency mortgage-backed obligations, and asset-backed obligations. Receivables and other assets: Receivables from broker-dealers, clearing organizations, and counterparties, receivables from customers, net, notes receivables, net and certain other assets are recorded at amounts that approximate fair value due to their short-term nature and are classified as Level 2 under the fair value hierarchy. Payables: Payables to customers and payables to brokers-dealers, clearing organizations, and counterparties are recorded at amounts that approximate fair value due to their short-term nature and are classified as Level 2 under the fair value hierarchy. Lender under loans : Payables to lenders under loans carry variable rates of interest and thus approximate fair value and are classified as Level 2 under the fair value hierarchy.

Financial Instruments with Off-

Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk (Notes)	6 Months Ended
	Mar. 31, 2018
Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk [Abstract]
Derivative Instruments and Hedging Activities Disclosure [Text Block]	Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk The Company is party to certain financial instruments with off-balance sheet risk in the normal course of its business. The Company has sold financial instruments that it does not currently own and will therefore be obliged to purchase such financial instruments at a future date. The Company has recorded these obligations in the condensed consolidated financial statements as of March 31, 2018 and September 30, 2017 at the fair values of the related financial instruments. The Company will incur losses if the fair value of the underlying financial instruments increases subsequent to March 31, 2018 . The total financial instruments sold, not yet purchased of $822.9 million and $717.6 million as of March 31, 2018 and September 30, 2017 , respectively, includes $176.6 million and $317.0 million for derivative contracts, respectively, which represented a liability to the Company based on their fair values as of March 31, 2018 and September 30, 2017 . Derivatives The Company utilizes derivative products in its trading capacity as a dealer in order to satisfy customer needs and mitigate risk. The Company manages risks from both derivatives and non-derivative cash instruments on a consolidated basis. The risks of derivatives should not be viewed in isolation, but in aggregate with the Company’s other trading activities. The majority of the Company’s derivative positions are included in the condensed consolidated balance sheets in ‘Deposits with and receivables from broker-dealers, clearing organizations and counterparties’, ‘Financial instruments owned, at fair value’, ‘Financial instruments sold, not yet purchased, at fair value’ and ‘Payables to broker-dealers, clearing organizations and counterparties’. Listed below are the fair values of the Company’s derivative assets and liabilities as of March 31, 2018 and September 30, 2017 . Assets represent net unrealized gains and liabilities represent net unrealized losses. March 31, 2018 September 30, 2017 (in millions) Assets (1) Liabilities (1) Assets (1) Liabilities (1) Derivative contracts not accounted for as hedges: Exchange-traded commodity derivatives $ 2,624.2 $ 2,940.3 $ 2,094.2 $ 1,975.0 OTC commodity derivatives 513.9 523.9 1,084.0 1,110.3 Exchange-traded foreign exchange derivatives 107.1 59.7 66.0 52.0 OTC foreign exchange derivatives 254.6 266.9 618.5 609.8 Exchange-traded interest rate derivatives 732.6 615.9 228.4 203.6 OTC interest rate derivatives 31.8 31.7 — — Exchange traded equity index derivatives 236.2 230.2 221.3 245.4 TBA and forward settling securities 4.9 5.8 8.8 4.9 Gross fair value of derivative contracts 4,505.3 4,674.4 4,321.2 4,201.0 Impact of netting and collateral (4,342.2 ) (4,492.1 ) (4,205.5 ) (3,879.2 ) Total fair value included in ‘Deposits with and receivables from broker-dealers, clearing organizations, and counterparties’ $ (5.4 ) $ (46.4 ) Total fair value included in ‘Financial instruments owned, at fair value’ $ 168.5 $ 162.1 Total fair value included in ‘Payables to broker-dealers, clearing organizations and counterparties $ 5.7 $ 4.8 Fair value included in ‘Financial instruments sold, not yet purchased, at fair value’ $ 176.6 $ 317.0 (1) As of March 31, 2018 and September 30, 2017 , the Company’s derivative contract volume for open positions were approximately 9.2 million and 6.1 million contracts, respectively. The Company’s derivative contracts are principally held in its Commercial Hedging and Clearing and Execution Services segments. The Company assists its Commercial Hedging segment customers in protecting the value of their future production by entering into option or forward agreements with them on an OTC basis. The Company also provides its Commercial Hedging segment customers with option products, including combinations of buying and selling puts and calls. The Company mitigates its risk by offsetting the customer’s transaction simultaneously with one of the Company’s trading counterparties or with a similar but not identical exchange-traded position. The risk mitigation of these offsetting trades is not within the documented hedging designation requirements of the Derivatives and Hedging Topic of the ASC. These derivative contracts are traded along with cash transactions because of the integrated nature of the markets for these products. The Company manages the risks associated with derivatives on an aggregate basis along with the risks associated with its proprietary trading and market-making activities in cash instruments as part of its firm-wide risk management policies. In particular, the risks related to derivative positions may be partially offset by inventory, unrealized gains in inventory or cash collateral paid or received. The Company has derivative instruments, which consist of mortgage-backed TBA securities and forward settling transactions that are used to manage risk exposures in the trading inventory of the Company’s domestic institutional fixed income business. The fair value on these transactions are recorded in deposits with and receivables from or payables to broker-dealers, clearing organizations and counterparties. Realized and unrealized gains and losses on securities and derivative transactions are reflected in ‘trading gains, net’. As of March 31, 2018 and September 30, 2017 , these transactions are summarized as follows: March 31, 2018 September 30, 2017 (in millions) Gain / (Loss) Notional Amounts Gain / (Loss) Notional Amounts Unrealized gain on TBA securities purchased within deposits with and receivables from broker-dealers, clearing organizations and counterparties and related notional amounts (1) $ 2.9 $ 832.5 $ — $ 51.3 Unrealized loss on TBA securities purchased within deposits with and receivables from broker-dealers, clearing organizations and counterparties and related notional amounts (1) $ — $ 49.9 $ (2.9 ) $ 1,236.8 Unrealized gain on TBA securities sold within payables to broker-dealers, clearing organizations and counterparties and related notional amounts (1) $ 0.1 $ (118.7 ) $ 5.8 $ (1,881.9 ) Unrealized loss on TBA securities sold within payables to broker-dealers, clearing organizations and counterparties and related notional amounts (1) $ (5.8 ) $ (1,611.1 ) $ (0.1 ) $ (404.1 ) Unrealized gain (loss) on forward settling securities purchased within deposits with and receivables from broker-dealers, clearing organizations and counterparties and related notional amounts $ 0.3 $ 410.9 $ (2.0 ) $ 882.9 Unrealized gain on forward settling securities sold within deposits with and receivables from broker-dealers, clearing organizations and counterparties and related notional amounts $ 1.8 $ (308.1 ) $ 3.0 $ (590.2 ) (1) The notional amounts of these instruments reflect the extent of the Company's involvement in TBA and forward settling securities and do not represent risk of loss due to counterparty non-performance. The following table sets forth the Company’s gains (losses) related to derivative financial instruments for the three and six months ended March 31, 2018 and 2017 in accordance with the Derivatives and Hedging Topic of the ASC. The net gains set forth below are included in ‘Cost of sales of physical commodities’ and ‘Trading gains, net’ in the condensed consolidated income statements. Three Months Ended March 31, Six Months Ended March 31, (in millions) 2018 2017 2018 2017 Commodities $ 12.3 $ 13.9 $ 33.8 $ 18.8 Foreign exchange 2.5 0.8 4.8 2.0 Interest rate 0.2 — 0.6 (1.0 ) TBA and forward settling securities 10.7 (4.9 ) 10.3 8.5 Net gains from derivative contracts $ 25.7 $ 9.8 $ 49.5 $ 28.3 Credit Risk In the normal course of business, the Company purchases and sells financial instruments, commodities and foreign currencies as either principal or agent on behalf of its customers. If either the customer or counterparty fails to perform, the Company may be required to discharge the obligations of the nonperforming party. In such circumstances, the Company may sustain a loss if the fair value of the financial instrument or foreign currency is different from the contract value of the transaction. The majority of the Company’s transactions and, consequently, the concentration of its credit exposure are with commodity exchanges, customers, broker-dealers and other financial institutions. These activities primarily involve collateralized and uncollateralized arrangements and may result in credit exposure in the event that a counterparty fails to meet its contractual obligations. The Company’s exposure to credit risk can be directly impacted by volatile financial markets, which may impair the ability of counterparties to satisfy their contractual obligations. The Company seeks to control its credit risk through a variety of reporting and control procedures, including establishing credit and/or position limits based upon a review of the counterparties’ financial condition and credit ratings. The Company monitors collateral levels on a daily basis for compliance with regulatory and internal guidelines and requests changes in collateral levels as appropriate. The Company is a party to financial instruments in the normal course of its business through customer and proprietary trading accounts in exchange-traded and OTC derivative instruments. These instruments are primarily the result of the execution of orders for commodity futures, options on futures, OTC swaps and options and spot and forward foreign currency contracts on behalf of its customers, substantially all of which are transacted on a margin basis. Such transactions may expose the Company to significant credit risk in the event margin requirements are not sufficient to fully cover losses which customers may incur. The Company controls the risks associated with these transactions by requiring customers to maintain margin deposits in compliance with individual exchange regulations and internal guidelines. The Company monitors required margin levels daily, and therefore may require customers to deposit additional collateral or reduce positions when necessary. The Company also establishes credit limits for customers, which are monitored daily. The Company evaluates each customer’s creditworthiness on a case by case basis. Clearing, financing, and settlement activities may require the Company to maintain funds with or pledge securities as collateral with other financial institutions. Generally, these exposures to both customers and exchanges are subject to master netting, or customer agreements, which reduce the exposure to the Company by permitting receivables and payables with such customers to be offset in the event of a customer default. Management believes that the margin deposits held as of March 31, 2018 and September 30, 2017 were adequate to minimize the risk of material loss that could be created by positions held at that time. Additionally, the Company monitors collateral fair value on a daily basis and adjusts collateral levels in the event of excess market exposure. Generally, these exposures to both customers and counterparties are subject to master netting or customer agreements which reduce the exposure to the Company. Derivative financial instruments involve varying degrees of off-balance sheet market risk whereby changes in the fair values of underlying financial instruments may result in changes in the fair value of the financial instruments in excess of the amounts reflected in the condensed consolidated balance sheets. Exposure to market risk is influenced by a number of factors, including the relationships between the financial instruments and the Company’s positions, as well as the volatility and liquidity in the markets in which the financial instruments are traded. The principal risk components of financial instruments include, among other things, interest rate volatility, the duration of the underlying instruments and changes in foreign exchange rates. The Company attempts to manage its exposure to market risk through various techniques. Aggregate market limits have been established and market risk measures are routinely monitored against these limits.

Receivables From Customers, Net

Receivables From Customers, Net and Notes Receivable, Net (Notes)	6 Months Ended
	Mar. 31, 2018
Receivables from customers and notes receivable, net [Abstract]
Financing Receivables [Text Block]	Allowance for Doubtful Accounts The allowance for doubtful accounts related to receivables from customers was $7.8 million and $7.6 million as of March 31, 2018 and September 30, 2017 , respectively. The allowance for doubtful accounts related to deposits with and receivables from broker-dealers, clearing organizations, and counterparties was $48.1 million and $47.0 million as of March 31, 2018 and September 30, 2017 , respectively. During the three months ended March 31, 2018 , the Company recorded bad debt expense of $0.2 million . The bad debt expense was primarily related to a precious metals customer trading account deficit in the Company’s Physical Commodities segment, partially offset by bad debt recoveries in the Physical Commodities and Commercial Hedging segments. During the three months ended March 31, 2017, the Company recorded bad debt expense of $1.3 million , primarily related to LME Metals customer deficits in the Company’s Commercial Hedging Segment. During the six months ended March 31, 2018, the Company recorded bad debt expense of $1.3 million . The provision for bad debts was primarily related an additional provision of $1.0 million related to a bad debt in the physical coal business for amounts due to the Company from a coal supplier for demurrage and other charges related to contracts with delivery dates subsequent to September 30, 2017 . During the six months ended March 31, 2017, the Company recorded bad debt expense of $3.8 million , primarily related to LME Metals customer deficits in the Company’s Commercial Hedging Segment.

Physical Commodities Inventory

Physical Commodities Inventory (Notes)	6 Months Ended
	Mar. 31, 2018
Physical Commodities Inventory [Abstract]
Inventory Disclosure [Text Block]	Physical Commodities Inventory The Company’s inventories consist of finished physical commodities. Inventories by component of the Company’s Physical Commodities segment are shown below. (in millions) March 31, September 30, Physical Ag & Energy (1) $ 160.2 $ 65.1 Precious metals - held by broker-dealer subsidiary (2) 26.9 13.3 Precious metals - held by non-broker-dealer subsidiaries (3) 99.2 46.4 Physical commodities inventory $ 286.3 $ 124.8 (1) Physical Ag & Energy maintains agricultural commodity inventories, including corn, soybeans, wheat, dried distillers grain, canola, sorghum, coffee, cocoa, cotton, and others. The agricultural commodity inventories are carried at net realizable value, which approximates fair value less disposal costs, with changes in net realizable value included as a component of ‘cost of sales of physical commodities’ on the condensed consolidated income statements. The agricultural inventories have reliable, readily determinable and realizable market prices, have relatively insignificant costs of disposal and are available for immediate delivery. Physical Ag & Energy also maintains energy related inventory, primarily kerosene, which is valued at the lower of cost or net realizable value. (2) Precious metals held by the Company’s subsidiary, INTL FCStone Ltd, a United Kingdom based broker-dealer subsidiary, is measured at fair value, with changes in fair value included as a component of ‘trading gains, net’ on the condensed consolidated income statements, in accordance with U.S. GAAP accounting requirements for broker-dealers. (3) Precious metals inventory held by subsidiaries that are not broker-dealers are valued at the lower of cost or net realizable value. The Company has recorded lower of cost or net realizable adjustments for certain precious metals inventory of $0.1 million and $0.7 million as of March 31, 2018 and September 30, 2017 , respectively. The adjustments are included in ‘cost of sales of physical commodities’ in the condensed consolidated income statements.

Goodwill (Notes)

Goodwill (Notes)	6 Months Ended
	Mar. 31, 2018
Goodwill [Abstract]
Goodwill Disclosure [Text Block]	Goodwill The carrying value of goodwill is allocated to the Company’s operating segments as follows: (in millions) March 31, September 30, Commercial Hedging $ 30.3 $ 30.7 Global Payments 6.3 6.3 Physical Commodities 2.4 2.4 Securities 6.9 7.7 Goodwill $ 45.9 $ 47.1 The Company recorded $1.2 million in foreign exchange revaluation adjustments on goodwill for the six months ended March 31, 2018 .

Intangible Assets - (Notes)

Intangible Assets - (Notes)	6 Months Ended
	Mar. 31, 2018
Intangible Assets [Abstract]
Intangible Assets Disclosure [Text Block]	Intangible Assets The gross and net carrying values of intangible assets as of the balance sheet dates, by major intangible asset class are as follows (in millions): March 31, 2018 September 30, 2017 Gross Amount Accumulated Amortization Net Amount Gross Amount Accumulated Amortization Net Amount Intangible assets subject to amortization: Software programs/platforms 2.7 (2.5 ) 0.2 2.7 (2.5 ) 0.2 Customer base 20.0 (9.0 ) 11.0 20.0 (7.9 ) 12.1 Total intangible assets $ 22.7 $ (11.5 ) $ 11.2 $ 22.7 $ (10.4 ) $ 12.3 Amortization expense related to intangible assets was $1.1 million and $1.4 million for the six months ended March 31, 2018 and 2017 , respectively. As of March 31, 2018 , the estimated future amortization expense was as follows: (in millions) Fiscal 2018 (remaining six months) $ 1.1 Fiscal 2019 2.2 Fiscal 2020 2.0 Fiscal 2021 1.9 Fiscal 2022 and thereafter 4.0 $ 11.2

Credit Facilities (Notes)

Credit Facilities (Notes)	6 Months Ended
	Mar. 31, 2018
Credit Facilities [Abstract]
Debt Disclosure [Text Block]	Credit Facilities Variable-Rate Credit Facilities The Company has four committed credit facilities under which the Company and its subsidiaries may borrow up to $594.5 million , subject to the terms and conditions for these facilities. The amounts outstanding under these credit facilities are short term borrowings and carry variable rates of interest, thus approximating fair value. The Company’s committed credit facilities consist of the following: • $262.0 million facility available to INTL FCStone Inc. for general working capital requirements. • $75.0 million facility available to the Company’s wholly owned subsidiary, INTL FCStone Financial Inc., for short-term funding of margin to commodity exchanges. The facility is subject to annual review and guaranteed by INTL FCStone Inc. • $232.5 million facility available to the Company’s wholly owned subsidiary, FCStone Merchant Services, LLC, for financing traditional commodity financing arrangements and commodity repurchase agreements. The facility is guaranteed by INTL FCStone Inc. On May 1, 2018, the facility was amended to increase the total commitment from $170.0 million to $232.5 million and extend the maturity through November 1, 2019. • $25.0 million facility available to the Company’s wholly owned subsidiary, INTL FCStone Ltd, for short-term funding of margin to commodity exchanges. The facility is subject to annual review and is guaranteed by INTL FCStone Inc. The Company also has a secured, uncommitted loan facility, under which the Company’s wholly owned subsidiary, INTL FCStone Ltd may borrow up to approximately $25.0 million , collateralized by commodities warehouse receipts, to facilitate financing of commodities under repurchase agreement services to its customers, subject to certain terms and conditions of the credit agreement. There were no borrowings outstanding under this credit facility as of March 31, 2018 and September 30, 2017. The Company also has a secured, uncommitted loan facility, under which the Company’s wholly owned subsidiary, INTL FCStone Financial Inc. may borrow up to $75.0 million , collateralized by commodities warehouse receipts, to facilitate U.S. commodity exchange deliveries of its customers, subject to certain terms and conditions of the credit agreement. There were zero and $23.0 million in borrowings outstanding under this credit facility as of March 31, 2018, and September 30, 2017, respectively. The Company also has a secured, uncommitted loan facility, under which the Company’s wholly owned subsidiary, INTL FCStone Financial Inc. may borrow for short term funding of firm and customer securities margin requirements, subject to certain terms and conditions of the agreement. The uncommitted amount available to be borrowed is not specified, and all requests for borrowing are subject to the sole discretion of the lender. The borrowings are secured by first liens on firm owned marketable securities or customer owned securities which have been pledged under a clearing arrangement. The amounts borrowed under the facilities are payable on demand. As of March 31, 2018, there were $48.0 million in borrowings outstanding under this credit facility and no borrowings outstanding as of September 30, 2017. The Company also has a secured, uncommitted loan facility, under which the Company’s wholly owned subsidiary, INTL FCStone Financial Inc. may borrow up to $100.0 million for short term funding of firm and customer securities margin requirements, subject to certain terms and conditions of the agreement. The borrowings are secured by first liens on firm owned marketable securities or customer owned securities which have been pledged under a clearing arrangement. The amounts borrowed under the facilities are payable on demand. There were zero and $11.0 million in borrowings outstanding under this credit facility as of March 31, 2018, and September 30, 2017, respectively. Note Payable to Bank The Company has a loan from a commercial bank, secured by equipment purchased with the proceeds. The note is payable in monthly installments, ending in March 2020. The note bears interest at a rate per annum equal to LIBOR plus 2.00%. The following table sets forth a listing of credit facilities, the current committed amounts as of the report date on the facilities, outstanding borrowings on the facilities, as well as indebtedness on a promissory note as of March 31, 2018 and September 30, 2017 : (in millions) Credit Facilities Amounts Outstanding Borrower Security Renewal / Expiration Date Total Commitment March 31, September 30, Committed Credit Facilities INTL FCStone Inc. Pledged shares of certain subsidiaries March 18, 2019 $ 262.0 $ 143.4 $ 150.0 INTL FCStone Financial, Inc. None April 4, 2019 75.0 9.5 — FCStone Merchants Services, LLC Certain commodities assets November 1, 2019 232.5 138.0 44.2 INTL FCStone Ltd. None November 7, 2018 25.0 — — $ 594.5 290.9 194.2 Uncommitted Credit Facilities INTL FCStone Financial, Inc. Commodities warehouse receipts and certain pledged securities n/a $ — 48.0 34.0 INTL FCStone Ltd. Commodities warehouse receipts n/a $ — — — Note Payable to Bank Monthly installments, due March 2020 and secured by certain equipment 1.6 2.0 Total indebtedness $ 340.5 $ 230.2 As reflected above, $362.0 million of the Company’s committed credit facilities are scheduled to expire within twelve months of this filing. The Company intends to renew or replace the facilities when they expire, and based on the Company’s liquidity position and capital structure, the Company believes it will be able to do so. The Company’s credit facility agreements contain financial covenants relating to financial measures on a consolidated basis, as well as on a certain stand-alone subsidiary basis, including minimum tangible net worth, minimum regulatory capital, minimum net unencumbered liquid assets, maximum net loss, minimum fixed charge coverage ratio and maximum funded debt to net worth ratio. Failure to comply with these covenants could result in the debt becoming payable on demand. As of March 31, 2018 , the Company was in compliance with all of its financial covenants under its credit facilities.

Commodity and Other Repurchase

Commodity and Other Repurchase Agreements and Collateralized Transactions (Notes)	6 Months Ended
	Mar. 31, 2018
Commodity and Other Repurchase Agreements [Abstract]
Commodity and Other Repurchase Agreements and Collateralized Transactions	Securities and Commodity Financing Transactions The Company’s outstanding notes receivable in connection with repurchase agreements for agricultural and energy commodities, whereby the customers sell to the Company certain commodity inventory and agree to repurchase the commodity inventory at a future date at a fixed price were $2.2 million and $0.8 million as of March 31, 2018 and September 30 2017, respectively. The Company enters into securities purchased under agreements to resell, securities sold under agreements to repurchase, securities borrowed and securities loaned transactions to, among other things, finance financial instruments, acquire securities to cover short positions, acquire securities for settlement, and to accommodate counterparties’ needs. These agreements are recorded as collateralized financings at their contractual amounts plus accrued interest. The related interest is recorded in the condensed consolidated income statements as interest income or interest expense, as applicable. In connection with these agreements and transactions, it is the policy of the Company to receive or pledge cash or securities to adequately collateralize such agreements and transactions in accordance with general industry guidelines and practices. The value of the collateral is valued daily and the Company may require counterparties to deposit additional collateral or return collateral pledged, when appropriate. The carrying amounts of these agreements and transactions approximate fair value due to their short-term nature and the level of collateralization. The Company pledges financial instruments owned to collateralize repurchase agreements. At March 31, 2018 , financial instruments owned, at fair value of $5.1 million were pledged as collateral under repurchase agreements. The counterparty has the right to repledge the collateral in connection with these transactions. These financial instruments owned have been pledged as collateral and have been parenthetically disclosed on the condensed consolidated balance sheet. The Company also has repledged securities borrowed and securities held on behalf of correspondent brokers to collateralize securities loaned agreements with a fair value of $547.9 million as of March 31, 2018 . In addition, as of March 31, 2018 , the Company pledged financial instruments owned, at fair value of $1,485.1 million and securities received under reverse repurchase agreements of $111.4 million to cover collateral requirements for tri-party repurchase agreements. For these securities, the counterparties do not have the right to sell or repledge the collateral and, therefore, they have not been parenthetically disclosed on the condensed consolidated balance sheet. At March 31, 2018 , the Company has accepted collateral that it is permitted by contract to sell or repledge. This collateral consists primarily of securities received in reverse repurchase agreements, securities borrowed agreements, and margin securities held on behalf of correspondent brokers. The fair value of such collateral at March 31, 2018 , was $1,320.2 million of which $496.3 million was used to cover securities sold short which are recorded in financial instruments sold, not yet purchased on the condensed consolidated balance sheet. In the normal course of business, this collateral is used by the Company to cover financial instruments sold, not yet purchased, to obtain financing in the form of repurchase agreements, and to meet counterparties’ needs under lending arrangements. At March 31, 2018 , substantially all of the above collateral had been delivered against financial instruments sold, not yet purchased or repledged by the Company to obtain financing. The following tables provide the contractual maturities of gross obligations under repurchase and securities lending agreements as of March 31, 2018 and September 30, 2017 (in millions): March 31, 2018 Overnight and Open Less than 30 Days 30-90 Days Over 90 Days Total Securities sold under agreements to repurchase $ 797.7 $ 464.3 $ 280.5 $ 20.0 $ 1,562.5 Securities loaned 559.1 — — — 559.1 Gross amount of secured financing $ 1,356.8 $ 464.3 $ 280.5 $ 20.0 $ 2,121.6 September 30, 2017 Overnight and Open Less than 30 Days 30-90 Days Over 90 Days Total Securities sold under agreements to repurchase $ 640.2 $ 432.9 $ 320.0 $ — $ 1,393.1 Securities loaned 111.1 — — — 111.1 Gross amount of secured financing $ 751.3 $ 432.9 $ 320.0 $ — $ 1,504.2 The following table provides the underlying collateral types of the gross obligations under repurchase and securities lending agreements as of March 31, 2018 and September 30, 2017 (in millions): Securities sold under agreements to repurchase: March 31, 2018 September 30, 2017 U.S. Treasury obligations $ 5.1 $ 7.0 U.S. government agency obligations 358.1 332.6 Asset-backed obligations 75.0 36.4 Agency mortgage-backed obligations 1,124.3 1,017.1 Total securities sold under agreements to repurchase 1,562.5 1,393.1 Securities loaned: Common stock 559.1 111.1 Total securities loaned 559.1 111.1 Gross amount of secured financing $ 2,121.6 $ 1,504.2

Commitments and Contingencies (

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.

Capital and Other Regulatory Re

Capital and Other Regulatory Requirements (Notes)	6 Months Ended
	Mar. 31, 2018
Capital and Other Regulatory Requirements [Abstract]
Regulatory Capital Requirements under Banking Regulations [Text Block]	Capital and Other Regulatory Requirements The Company’s activities are subject to significant governmental regulation, both in the United States and in the international jurisdictions in which it operates. The subsidiaries of the Company were in compliance with all of their regulatory requirements as of March 31, 2018 , as follows: (in millions) As of March 31, 2018 Subsidiary Regulatory Authority Jurisdiction Requirement Type Actual Minimum Requirement INTL FCStone Financial Inc. SEC and Commodity Futures Trading Commission ("CFTC") United States Net capital $ 152.3 $ 83.6 INTL FCStone Financial Inc. CFTC United States Segregated funds $ 2,357.1 $ 2,303.2 INTL FCStone Financial Inc. CFTC United States Secured funds $ 144.0 $ 128.3 INTL FCStone Financial Inc. SEC United States Customer reserve $ 0.7 $ — INTL FCStone Financial Inc. SEC United States PAB reserve $ 5.5 $ 2.7 INTL Custody & Clearing Solutions Inc. SEC United States Net capital $ 1.9 $ 0.1 SA Stone Wealth Management Inc. SEC United States Net capital $ 3.9 $ 0.4 INTL FCStone Ltd (1) Financial Conduct Authority ("FCA") United Kingdom Net capital $ 193.6 $ 90.3 INTL FCStone Ltd FCA United Kingdom Segregated funds $ 183.4 $ 183.4 INTL Netherlands BV (1) FCA United Kingdom Net capital $ 192.9 $ 90.3 INTL FCStone DTVM Ltda. Brazilian Central Bank and Securities and Exchange Commission of Brazil Brazil Capital adequacy $ 12.9 $ 2.3 INTL Gainvest S.A. National Securities Commission ("CNV") Argentina Capital adequacy $ 4.8 $ 0.1 INTL Gainvest S.A. CNV Argentina Net capital $ 2.8 $ 0.1 INTL CIBSA S.A. CNV Argentina Capital adequacy $ 5.2 $ 0.8 INTL CIBSA S.A. CNV Argentina Net capital $ 1.1 $ 0.4 (1) INTL Netherlands BV is a holding company that includes the ownership equity of INTL FCStone Ltd. The associated net capital amounts and minimum requirements should not be considered in aggregate. Certain other non-U.S. subsidiaries of the Company are also subject to capital adequacy requirements promulgated by authorities of the countries in which they operate. As of March 31, 2018 , these subsidiaries were in compliance with their local capital adequacy requirements.

Other Expenses (Notes)

Other Expenses (Notes)	6 Months Ended
	Mar. 31, 2018
Other Expenses [Abstract]
Other Expenses [Text Block]	Other Expenses Other expenses for the three and six months ended March 31, 2018 and 2017 consisted of the following: Three Months Ended March 31, Six Months Ended March 31, (in millions) 2018 2017 2018 2017 Contingent consideration, net $ — $ 0.1 $ — $ 0.1 Insurance 0.6 0.8 1.2 1.3 Advertising, meetings and conferences 3.4 1.2 4.3 2.1 Office supplies and printing 0.4 0.5 0.8 1.1 Other clearing related expenses 0.5 0.3 1.0 0.7 Other non-income taxes 1.3 1.2 2.5 2.3 Other 2.5 2.5 4.6 4.6 Total other expenses $ 8.7 $ 6.6 $ 14.4 $ 12.2

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss) (Notes)	6 Months Ended
	Mar. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Abstract]
Comprehensive Income (Loss) Note [Text Block]	Accumulated Other Comprehensive Loss, Net Comprehensive income consists of net income and other gains and losses affecting stockholders’ equity that, under U.S. GAAP, are excluded from net income. Other comprehensive loss includes net actuarial losses from defined benefit pension plans and foreign currency translation adjustments. The following table summarizes the changes in accumulated other comprehensive loss, net for the six months ended March 31, 2018 . (in millions) Foreign Currency Translation Adjustment Pension Benefits Adjustment Accumulated Other Comprehensive Loss Balances as of September 30, 2017 $ (21.5 ) $ (3.0 ) $ (24.5 ) Other comprehensive loss, net of tax (3.8 ) — (3.8 ) Balances as of March 31, 2018 $ (25.3 ) $ (3.0 ) $ (28.3 )

Income Taxes (Notes)

Income Taxes (Notes)	6 Months Ended
	Mar. 31, 2018
Income Taxes [Abstract]
Income Tax Disclosure [Text Block]	Income Taxes The income tax provision for interim periods is comprised of tax on ordinary income (loss) provided at the most recent estimated annual effective tax rate, adjusted for the tax effect of discrete items. Management uses an estimated annual effective tax rate based on the forecasted pretax income (loss) and statutory tax rates in the various jurisdictions in which it operates. The Company’s effective tax rate differs from the U.S. statutory rate primarily due to state and local taxes, and differing statutory tax rates applied to the income of non-U.S. subsidiaries. The Company records the tax effect of certain discrete items, including the effects of changes in tax laws, tax rates and adjustments with respect to valuation allowances or other unusual or nonrecurring tax adjustments, in the interim period in which they occur, as an addition to, or reduction from, the income tax provision, rather than being included in the estimated effective annual income tax rate. In addition, jurisdictions with a projected loss for the year or a year-to-date loss where no tax benefit can be recognized are excluded from the estimated annual effective income tax rate. The Company is required to assess its deferred tax assets and the need for a valuation allowance at each reporting period. This assessment requires judgment on the part of management with respect to benefits that may be realized. The Company will record a valuation allowance against deferred tax assets when it is considered more likely than not that all or a portion of the deferred tax assets will not be realized. Effects of the Tax Cuts and Jobs Act On December 22, 2017, the President of the United States signed and enacted into law H.R. 1, the Tax Cuts and Jobs Act (“the Tax Reform”). Among the significant changes to the U.S. Internal Revenue Code, the Tax Reform lowers the U.S. federal corporate income tax rate from 35% to 21%, effective January 1, 2018. The Company will compute its income tax expense (benefit) for the September 30, 2018 tax year using a U.S. statutory tax rate of 24.5% . The 21% U.S. statutory tax rate will apply to fiscal years ending September 30, 2019 and thereafter. For the six months ended March 31, 2018, the Company recorded tax expense of $8.8 million related to the remeasurement of deferred tax assets and liabilities. For the three months ended December 31, 2017, the Company recorded tax expense of $8.9 million related to the remeasurement of deferred tax assets and liabilities. Due to additional information becoming available in the three months ending March 31, 2018, the Company recorded a benefit of $0.1 million related to the remeasurement of deferred tax assets and liabilities. This amount remains provisional. The Tax Reform also includes a one-time mandatory repatriation transition tax on previously untaxed accumulated and current earnings and profits (E&P) of certain of the Company’s foreign subsidiaries. To determine the amount of the transition tax, the Company must determine, in addition to other factors, the amount of post 1986 E&P of the relevant subsidiaries, as well as the amount of non-US income taxes paid on such earnings. The Company made a reasonable estimate of the transition tax and recorded a provisional transition tax obligation of $12.0 million in the three months ended December 31, 2017. In the three months ending March 31, 2018, the Company recorded a benefit of $0.7 million due to revised E&P computations, net operating loss carryforward available, and revised non-US income taxes paid. The total provisional transition tax obligation to date is $11.3 million . The Company continues to gather additional information to more precisely compute the amount of the transition tax. The SEC staff issued Staff Accounting Bulletin No. 118 (SAB 118), which provides guidance on accounting for the tax effects of the Tax Reform. SAB 118 provides a measurement period that should not extend beyond one year from the Tax Reform enactment date for companies to complete the accounting under ASC 740. In accordance with SAB 118, a company must reflect the income tax effects of those aspects of the Tax Reform for which the accounting under ASC 740 is complete. To the extent that a company’s accounting for certain income tax effects of the Tax Reform is incomplete but it can determine a reasonable estimate, it must record a provisional estimate in the financial statements. If a company cannot determine a provisional estimate to be included in the financial statements, it should continue to apply ASC 740 based on the tax laws that were in effect immediately before the enactment of the Tax Reform. While the Company can make reasonable estimates of the impact of the reduction in corporate rate and the deemed repatriation transition tax, the final impact of the Tax Reform may differ from these estimates, due to, among other things, changes in interpretations and assumptions, additional guidance that may be issued by taxing authorities, and actions the Company may take. The Tax Reform also establishes new tax laws that will affect the fiscal year ending September 30, 2019, including, but not limited to, (1) elimination of the corporate alternative minimum tax, (2) a new provision designed to tax global intangible low-taxed income (GILTI), (3) limitations on the utilization of net operating losses generated after December 31, 2017 to 80 percent of taxable income per tax year, (4) the creation of the base erosion anti-abuse tax (BEAT), (5) a general elimination of U.S. federal income taxes on dividends from foreign subsidiaries, and (6) limitations on the deductibility of certain executive compensation. Effects of tax law changes where a reasonable estimate of the accounting effects has not yet been made include additional limitations on certain meals and entertainment expenses and the unlimited carryforward of net operating losses. The Company has also not yet determined the potential tax impact of provisions that are not yet effective, such as GILTI, BEAT, elimination of U.S. tax on dividends of future foreign earnings, and a limitation of the utilization of net operating losses generated after fiscal 2018 to 80 percent of taxable income per tax year. The Company expects to make the policy election to treat GILTI as a period expense in the fiscal year ending September 30, 2018. Current and Prior Period Tax Expense Income tax expense of $6.8 million and $3.3 million for the three months ended March 31, 2018 and 2017 , respectively, and income tax expense of $32.3 million and $5.4 million for the six months ended March 31, 2018 and 2017 , respectively, reflect estimated federal, foreign, state and local taxes. Due to Tax Reform, the Company recorded discrete expense of $20.1 million . This consists of expense of $20.9 million in the three months ended December 31, 2017, and benefit of $0.8 million in the three months ended March 31, 2018. Tax expense, excluding the discrete expense related to the Tax Reform, was $7.6 million for the three months ended March 31, 2018, and $12.2 million for the six months ended March 31, 2018. For the three months ended March 31, 2018 and 2017, the Company’s effective tax rate was 23% . The discrete benefit of $0.8 million related to Tax Reform decreased the effective rate by 2.8% . For the three months ended March 31, 2018, the Company’s effective tax rate was 25.8% , excluding the impacts of Tax Reform. For the six months ended March 31, 2018 and 2017, the Company’s effective tax rate was 67% and 24% , respectively. For the six months ended March 31, 2018, the discrete expense of $20.1 million related to Tax Reform, increased the effective tax rate by 42% . The effective rate for the six months ended March 31, 2018 was 25.3% , excluding the impacts of Tax Reform. The Company’s effective tax rate decreased 0.6% due to excess tax benefits on share-based compensation recognized through the first six months of 2018 related to the adoption of ASU 2016-09. See Note 1 for more information regarding the adoption of ASU 2016-09. The effective rate, excluding the impacts of Tax Reform, was higher than the U.S. federal statutory rate due to U.S. state and local taxes and foreign permanent differences. The valuation allowance for deferred tax assets as of March 31, 2018 and September 30, 2017 was $4.5 million and $4.0 million , respectively. The valuation allowances as of March 31, 2018 and September 30, 2017 were primarily related to U.S., state and local and foreign net operating loss carryforwards that, in the judgment of management, are not more likely than not to be realized. In assessing the realizability of deferred tax assets, management considers whether it is more likely than not that some or all of the deferred tax assets will not be realized. The Company incurred U.S. federal, state, and local taxable income (losses) for the fiscal years ended September 30, 2017, 2016, and 2015 of $(24.7) million , $(9.7) million and $16.5 million , respectively. The differences between actual levels of past taxable income (losses) and pre-tax book income (losses) are primarily attributable to temporary differences in these jurisdictions. When evaluating if U.S. federal, state, and local deferred tax assets are realizable, the Company considered deferred tax liabilities of $3.3 million that are scheduled to reverse from 2018 to 2020 and $2.2 million of deferred tax liabilities associated with unrealized gains in securities which the Company could sell, if necessary. Furthermore, the Company considered its ability to implement business and tax planning strategies that would allow the remaining U.S. federal, state, and local deferred tax assets, net of valuation allowances, to be realized within approximately 5 years . Based on the tax planning strategies that are prudent and feasible, management believes that it is more likely than not that the Company will realize the tax benefit of the deferred tax assets, net of the existing valuation allowance, in the future. However, the realization of deferred income taxes is dependent on future events, and changes in estimates in future periods could result in adjustments to the valuation allowance. The Company and its subsidiaries file income tax returns with the U.S. federal jurisdiction and various state, local and foreign jurisdictions. The Company has open tax years ranging from September 30, 2010 through September 30, 2017 with U.S. federal and state and local taxing authorities. In the U.K., the Company has open tax years ending September 30, 2016 to September 30, 2017. In Brazil, the Company has open tax years ranging from December 31, 2012 through December 31, 2017. In Argentina, the Company has open tax years ranging from September 30, 2010 to September 30, 2017. In Singapore, the Company has open tax years ranging from September 30, 2012 to September 30, 2017.

Segment Analysis (Notes)

Segment Analysis (Notes)	6 Months Ended
	Mar. 31, 2018
Segment Analysis [Abstract]
Segment Reporting Disclosure [Text Block]	Segment Analysis The Company reports its operating segments based on services provided to customers. The Company’s business activities are managed as operating segments and organized into reportable segments as follows: • Commercial Hedging (includes components Financial Agricultural (Ag) & Energy and LME Metals) • Global Payments • Securities (includes components Equity Market-Making, Debt Trading, Investment Banking, and Asset Management) • Physical Commodities (includes components Precious Metals and Physical Ag & Energy) • Clearing and Execution Services (includes components Exchange-traded Futures & Options, FX Prime Brokerage, Correspondent Clearing, Independent Wealth Management, and Derivative Voice Brokerage) The total revenues reported combine gross revenues for the physical commodities business for subsidiaries that are not broker-dealers and net revenues for all other businesses. In order to reflect the way that the Company’s management views the results, the table below also reflects the segment contribution to ‘operating revenues’, which is shown on the face of the condensed consolidated income statements and which is calculated by deducting physical commodities cost of sales from total revenues. Segment data includes the profitability measure of net contribution by segment. Net contribution is one of the key measures used by management to assess the performance of each segment and for decisions regarding the allocation of the Company’s resources. Net contribution is calculated as revenue less direct cost of sales, transaction-based clearing expenses, variable compensation, introducing broker commissions, and interest expense. Variable compensation paid to risk management consultants/traders generally represents a fixed percentage of an amount equal to revenues generated, and in some cases, revenues produced less transaction-based clearing charges, base salaries and an overhead allocation. Segment data also includes segment income which is calculated as net contribution less non-variable direct expenses of the segment. These non-variable direct expenses include trader base compensation and benefits, operational employee compensation and benefits, communication and data services, business development, professional fees, bad debt expense and other direct expenses. Inter-segment revenues, charges, receivables and payables are eliminated upon consolidation, except revenues and costs related to foreign currency transactions undertaken on an arm’s length basis by the foreign exchange trading business for the securities business. The foreign exchange trading business competes for this business as it does any other business. If its rates are not competitive, the securities businesses buy or sell their foreign currency through other market counterparties. On a recurring basis, the Company sweeps excess cash from certain U.S. operating segments to a centralized corporate treasury function in exchange for an intercompany receivable asset. The intercompany receivable asset is eliminated during consolidation, and therefore this practice may impact reported total assets between segments. Information for the reportable segments is shown in accordance with the Segment Reporting Topic of the ASC as follows Three Months Ended March 31, Six Months Ended March 31, (in millions) 2018 2017 2018 2017 Total revenues: Commercial Hedging $ 78.3 $ 62.7 $ 139.8 $ 120.2 Global Payments 23.4 21.5 48.0 44.6 Securities 55.5 37.9 98.5 75.3 Physical Commodities 6,262.3 5,276.2 13,978.9 11,174.9 Clearing and Execution Services 88.0 64.2 160.2 127.8 Corporate unallocated (0.5 ) (1.7 ) 0.2 (7.6 ) Total $ 6,507.0 $ 5,460.8 $ 14,425.6 $ 11,535.2 Operating revenues (loss): Commercial Hedging $ 78.3 $ 62.7 $ 139.8 $ 120.2 Global Payments 23.4 21.5 48.0 44.6 Securities 55.5 37.9 98.5 75.3 Physical Commodities 15.5 11.2 26.1 21.0 Clearing and Execution Services 88.0 64.2 160.2 127.8 Corporate unallocated (0.5 ) (1.7 ) 0.2 (7.6 ) Total $ 260.2 $ 195.8 $ 472.8 $ 381.3 Net operating revenues (loss): Commercial Hedging $ 61.9 $ 50.5 $ 111.0 $ 96.1 Global Payments 21.9 19.1 44.9 39.7 Securities 27.6 24.1 51.1 49.2 Physical Commodities 12.5 9.0 20.9 17.1 Clearing and Execution Services 31.8 25.4 59.2 49.5 Corporate unallocated (1.4 ) (4.2 ) (2.5 ) (13.4 ) Total $ 154.3 $ 123.9 $ 284.6 $ 238.2 Net contribution: (Revenues less cost of sales of physical commodities, transaction-based clearing expenses, variable bonus compensation, introducing broker commissions and interest expense) Commercial Hedging $ 44.7 $ 36.9 $ 81.2 $ 70.3 Global Payments 17.6 15.3 36.0 31.7 Securities 20.3 18.9 38.1 38.7 Physical Commodities 9.4 6.5 15.0 12.3 Clearing and Execution Services 23.9 19.6 44.4 37.6 Total $ 115.9 $ 97.2 $ 214.7 $ 190.6 Segment income: (Net contribution less non-variable direct segment costs) Commercial Hedging $ 27.6 $ 18.7 $ 48.7 $ 34.1 Global Payments 13.5 11.7 28.1 24.9 Securities 12.8 11.7 23.8 24.6 Physical Commodities 5.6 3.9 6.7 6.9 Clearing and Execution Services 12.7 7.9 23.2 13.6 Total $ 72.2 $ 53.9 $ 130.5 $ 104.1 Reconciliation of segment income to income before tax: Segment income $ 72.2 $ 53.9 $ 130.5 $ 104.1 Net costs not allocated to operating segments 42.7 39.6 82.4 81.4 Income before tax $ 29.5 $ 14.3 $ 48.1 $ 22.7 (in millions) As of March 31, 2018 As of September 30, 2017 Total assets: Commercial Hedging $ 1,636.1 $ 1,650.3 Global Payments 208.8 199.5 Securities 2,901.3 2,101.7 Physical Commodities 378.0 339.5 Clearing and Execution Services 1,996.5 1,818.9 Corporate unallocated 83.0 133.5 Total $ 7,203.7 $ 6,243.4

Basis of Presentation and Con24

Basis of Presentation and Consolidation and Recently Issued Accounting Standards (Policies)	6 Months Ended
	Mar. 31, 2018
Basis of Presentation and Consolidation [Abstract]
Basis of Accounting, Policy [Policy Text Block]	The accompanying unaudited condensed consolidated balance sheet as of September 30, 2017 , which has been derived from audited consolidated 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 consolidated 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, 2017 filed with the SEC.
Consolidation, Policy [Policy Text Block]	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.
Fiscal Period, Policy [Policy Text Block]	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.
Use of Estimates, Policy [Policy Text Block]	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 consolidated 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, 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.
Reclassification, Policy [Policy Text Block]	Reclassifications During the three and six months ended March 31, 2018, the Company separately classified non-trading technology and support costs that were previously included within ‘Other’ on the condensed consolidated income statements. Additionally, during the three and six months ended March 31, 2018, the Company separately classified communications related expenses separately from trading systems and market information related costs. In performing these reclassifications, the Company has made immaterial, retrospective adjustments to conform to our current period presentation. For the three and six months ending March 31, 2017, ‘Other’ expenses included $2.8 million and $5.7 million , respectively, of expenses that are now included within ‘Non-trading technology and support’ on the condensed consolidated income statements. For the three and six months ending March 31, 2017, ‘Trading systems and market information’ included $1.2 million and $2.4 million , respectively, of expenses that are now included within ‘Communications’ on the condensed consolidated income statements.
New Accounting Pronouncement or Change in Accounting Principle, Description	Accounting Standards Adopted In March 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update No. 2016-09, “Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting” (“ASU 2016-09”), which simplifies several aspects of the accounting for share-based payment transactions. Under ASU 2016-09, excess tax benefits and tax deficiencies are recognized as income tax expense or benefit in the income statement instead of additional paid in capital. ASU 2016-09 also provides entities with the option to elect an accounting policy to estimate forfeitures of share-based awards over the service period (current GAAP) or account for forfeitures when they occur. Under ASU 2016-09, previously unrecognized excess tax benefits should be recognized using a modified retrospective transition. In addition, amendments requiring recognition of excess tax benefits and tax deficiencies in the income statement, as well as changes in the computation of weighted-average diluted shares outstanding, should be applied prospectively. ASU 2016-09 is effective for and was adopted by the Company in the first quarter of 2018 and the impact of the adoption resulted in the following: • During the six months ended March 31, 2018, the Company recognized excess tax benefits from share-based compensation of $0.3 million within income tax expense on the condensed consolidated income statement and within net income on the condensed consolidated cash flow statement. Prior to adoption, the tax effect of share-based awards would have been recognized in additional paid-in-capital on the condensed consolidated balance sheets and separately stated in the financing activities in the condensed consolidated cash flow statements. The Company has elected to adopt this guidance prospectively. • The Company has elected to account for forfeitures of share-based awards as they occur. The Company elected to account for forfeitures as they occur using a modified retrospective transition method. The adoption of this guidance did not have a material impact on our condensed consolidated financial statements. • The excess tax benefits from the assumed proceeds available to repurchase shares were excluded in the computation of diluted earnings per share for the three and six months ended March 31, 2018. The Company has elected to adopt this guidance prospectively. • For the six months ended March 31, 2018, the Company has classified as a financing activity in the condensed consolidated cash flow statement $0.8 million of cash paid to taxing authorities for restricted stock shares withheld to satisfy statutory income tax withholding obligations. The retrospective application of this guidance had no impact on the condensed consolidated cash flow statement for the six months ended March 31, 2017. In July 2015, the FASB issued ASU No. 2015-11, “Simplifying the Measurement of Inventory (Topic 330).” Under ASU 2015-11, inventory that is measured using the first-in, first-out (FIFO), specific identification, or average cost methods should be measured at the lower of cost or net realizable value. This ASU does not impact inventory measurement under the last-in, first-out (LIFO) or retail inventory methods. The Company adopted this ASU prospectively in the first quarter of 2018. The adoption of this ASU did not have a material impact on the condensed consolidated financial statements.

Earnings per Share (Policies)

Earnings per Share (Policies)	6 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
Earnings Per Share, Potentially Dilutive Securities	The Company presents basic and diluted earnings per share (“EPS”) using the two-class method which requires all outstanding unvested share-based payment awards that contain rights to non-forfeitable dividends and therefore participate in undistributed earnings with common stockholders be included in computing earnings per share. Under the two-class method, net earnings are reduced by the amount of dividends declared in the period for each class of common stock and participating security. The remaining undistributed earnings are then allocated to common stock and participating securities, based on their respective rights to receive dividends. Restricted stock awards granted to certain employees and directors contain non-forfeitable rights to dividends at the same rate as common stock, and are considered participating securities. Basic EPS has been computed by dividing net income by the weighted-average number of common shares outstanding.

Income Taxes (Policies)

Income Taxes (Policies)	6 Months Ended
	Mar. 31, 2018
Income Taxes [Abstract]
Income Tax, Policy [Policy Text Block]	Note 15 – Income Taxes The income tax provision for interim periods is comprised of tax on ordinary income (loss) provided at the most recent estimated annual effective tax rate, adjusted for the tax effect of discrete items. Management uses an estimated annual effective tax rate based on the forecasted pretax income (loss) and statutory tax rates in the various jurisdictions in which it operates. The Company’s effective tax rate differs from the U.S. statutory rate primarily due to state and local taxes, and differing statutory tax rates applied to the income of non-U.S. subsidiaries. The Company records the tax effect of certain discrete items, including the effects of changes in tax laws, tax rates and adjustments with respect to valuation allowances or other unusual or nonrecurring tax adjustments, in the interim period in which they occur, as an addition to, or reduction from, the income tax provision, rather than being included in the estimated effective annual income tax rate. In addition, jurisdictions with a projected loss for the year or a year-to-date loss where no tax benefit can be recognized are excluded from the estimated annual effective income tax rate. The Company is required to assess its deferred tax assets and the need for a valuation allowance at each reporting period. This assessment requires judgment on the part of management with respect to benefits that may be realized. The Company will record a valuation allowance against deferred tax assets when it is considered more likely than not that all or a portion of the deferred tax assets will not be realized. Effects of the Tax Cuts and Jobs Act On December 22, 2017, the President of the United States signed and enacted into law H.R. 1, the Tax Cuts and Jobs Act (“the Tax Reform”). Among the significant changes to the U.S. Internal Revenue Code, the Tax Reform lowers the U.S. federal corporate income tax rate from 35% to 21%, effective January 1, 2018. The Company will compute its income tax expense (benefit) for the September 30, 2018 tax year using a U.S. statutory tax rate of 24.5% . The 21% U.S. statutory tax rate will apply to fiscal years ending September 30, 2019 and thereafter. For the six months ended March 31, 2018, the Company recorded tax expense of $8.8 million related to the remeasurement of deferred tax assets and liabilities. For the three months ended December 31, 2017, the Company recorded tax expense of $8.9 million related to the remeasurement of deferred tax assets and liabilities. Due to additional information becoming available in the three months ending March 31, 2018, the Company recorded a benefit of $0.1 million related to the remeasurement of deferred tax assets and liabilities. This amount remains provisional. The Tax Reform also includes a one-time mandatory repatriation transition tax on previously untaxed accumulated and current earnings and profits (E&P) of certain of the Company’s foreign subsidiaries. To determine the amount of the transition tax, the Company must determine, in addition to other factors, the amount of post 1986 E&P of the relevant subsidiaries, as well as the amount of non-US income taxes paid on such earnings. The Company made a reasonable estimate of the transition tax and recorded a provisional transition tax obligation of $12.0 million in the three months ended December 31, 2017. In the three months ending March 31, 2018, the Company recorded a benefit of $0.7 million due to revised E&P computations, net operating loss carryforward available, and revised non-US income taxes paid. The total provisional transition tax obligation to date is $11.3 million . The Company continues to gather additional information to more precisely compute the amount of the transition tax. The SEC staff issued Staff Accounting Bulletin No. 118 (SAB 118), which provides guidance on accounting for the tax effects of the Tax Reform. SAB 118 provides a measurement period that should not extend beyond one year from the Tax Reform enactment date for companies to complete the accounting under ASC 740. In accordance with SAB 118, a company must reflect the income tax effects of those aspects of the Tax Reform for which the accounting under ASC 740 is complete. To the extent that a company’s accounting for certain income tax effects of the Tax Reform is incomplete but it can determine a reasonable estimate, it must record a provisional estimate in the financial statements. If a company cannot determine a provisional estimate to be included in the financial statements, it should continue to apply ASC 740 based on the tax laws that were in effect immediately before the enactment of the Tax Reform. While the Company can make reasonable estimates of the impact of the reduction in corporate rate and the deemed repatriation transition tax, the final impact of the Tax Reform may differ from these estimates, due to, among other things, changes in interpretations and assumptions, additional guidance that may be issued by taxing authorities, and actions the Company may take. The Tax Reform also establishes new tax laws that will affect the fiscal year ending September 30, 2019, including, but not limited to, (1) elimination of the corporate alternative minimum tax, (2) a new provision designed to tax global intangible low-taxed income (GILTI), (3) limitations on the utilization of net operating losses generated after December 31, 2017 to 80 percent of taxable income per tax year, (4) the creation of the base erosion anti-abuse tax (BEAT), (5) a general elimination of U.S. federal income taxes on dividends from foreign subsidiaries, and (6) limitations on the deductibility of certain executive compensation. Effects of tax law changes where a reasonable estimate of the accounting effects has not yet been made include additional limitations on certain meals and entertainment expenses and the unlimited carryforward of net operating losses. The Company has also not yet determined the potential tax impact of provisions that are not yet effective, such as GILTI, BEAT, elimination of U.S. tax on dividends of future foreign earnings, and a limitation of the utilization of net operating losses generated after fiscal 2018 to 80 percent of taxable income per tax year. The Company expects to make the policy election to treat GILTI as a period expense in the fiscal year ending September 30, 2018. Current and Prior Period Tax Expense Income tax expense of $6.8 million and $3.3 million for the three months ended March 31, 2018 and 2017 , respectively, and income tax expense of $32.3 million and $5.4 million for the six months ended March 31, 2018 and 2017 , respectively, reflect estimated federal, foreign, state and local taxes. Due to Tax Reform, the Company recorded discrete expense of $20.1 million . This consists of expense of $20.9 million in the three months ended December 31, 2017, and benefit of $0.8 million in the three months ended March 31, 2018. Tax expense, excluding the discrete expense related to the Tax Reform, was $7.6 million for the three months ended March 31, 2018, and $12.2 million for the six months ended March 31, 2018. For the three months ended March 31, 2018 and 2017, the Company’s effective tax rate was 23% . The discrete benefit of $0.8 million related to Tax Reform decreased the effective rate by 2.8% . For the three months ended March 31, 2018, the Company’s effective tax rate was 25.8% , excluding the impacts of Tax Reform. For the six months ended March 31, 2018 and 2017, the Company’s effective tax rate was 67% and 24% , respectively. For the six months ended March 31, 2018, the discrete expense of $20.1 million related to Tax Reform, increased the effective tax rate by 42% . The effective rate for the six months ended March 31, 2018 was 25.3% , excluding the impacts of Tax Reform. The Company’s effective tax rate decreased 0.6% due to excess tax benefits on share-based compensation recognized through the first six months of 2018 related to the adoption of ASU 2016-09. See Note 1 for more information regarding the adoption of ASU 2016-09. The effective rate, excluding the impacts of Tax Reform, was higher than the U.S. federal statutory rate due to U.S. state and local taxes and foreign permanent differences. The valuation allowance for deferred tax assets as of March 31, 2018 and September 30, 2017 was $4.5 million and $4.0 million , respectively. The valuation allowances as of March 31, 2018 and September 30, 2017 were primarily related to U.S., state and local and foreign net operating loss carryforwards that, in the judgment of management, are not more likely than not to be realized. In assessing the realizability of deferred tax assets, management considers whether it is more likely than not that some or all of the deferred tax assets will not be realized. The Company incurred U.S. federal, state, and local taxable income (losses) for the fiscal years ended September 30, 2017, 2016, and 2015 of $(24.7) million , $(9.7) million and $16.5 million , respectively. The differences between actual levels of past taxable income (losses) and pre-tax book income (losses) are primarily attributable to temporary differences in these jurisdictions. When evaluating if U.S. federal, state, and local deferred tax assets are realizable, the Company considered deferred tax liabilities of $3.3 million that are scheduled to reverse from 2018 to 2020 and $2.2 million of deferred tax liabilities associated with unrealized gains in securities which the Company could sell, if necessary. Furthermore, the Company considered its ability to implement business and tax planning strategies that would allow the remaining U.S. federal, state, and local deferred tax assets, net of valuation allowances, to be realized within approximately 5 years . Based on the tax planning strategies that are prudent and feasible, management believes that it is more likely than not that the Company will realize the tax benefit of the deferred tax assets, net of the existing valuation allowance, in the future. However, the realization of deferred income taxes is dependent on future events, and changes in estimates in future periods could result in adjustments to the valuation allowance. The Company and its subsidiaries file income tax returns with the U.S. federal jurisdiction and various state, local and foreign jurisdictions. The Company has open tax years ranging from September 30, 2010 through September 30, 2017 with U.S. federal and state and local taxing authorities. In the U.K., the Company has open tax years ending September 30, 2016 to September 30, 2017. In Brazil, the Company has open tax years ranging from December 31, 2012 through December 31, 2017. In Argentina, the Company has open tax years ranging from September 30, 2010 to September 30, 2017. In Singapore, the Company has open tax years ranging from September 30, 2012 to September 30, 2017.

Earnings per Share (Tables)

Earnings per Share (Tables)	6 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
Schedule of Calculation of Numerator and Denominator in Earnings Per Share [Table Text Block]	Basic EPS has been computed by dividing net income by the weighted-average number of common shares outstanding. The following is a reconciliation of the numerator and denominator of the diluted earnings per share computations for the periods presented below. Three Months Ended March 31, Six Months Ended March 31, (in millions, except share amounts) 2018 2017 2018 2017 Numerator: Net income $ 22.7 $ 11.0 $ 15.8 $ 17.3 Less: Allocation to participating securities (0.3 ) (0.2 ) (0.3 ) (0.3 ) Net income allocated to common stockholders $ 22.4 $ 10.8 $ 15.5 $ 17.0 Denominator: Weighted average number of: Common shares outstanding 18,559,849 18,404,236 18,502,795 18,325,383 Dilutive potential common shares outstanding: Share-based awards 299,484 257,182 333,418 312,097 Diluted weighted-average common shares 18,859,333 18,661,418 18,836,213 18,637,480

Assets and Liabilities, at Fa28

Assets and Liabilities, at Fair Value (Tables)	6 Months Ended
	Mar. 31, 2018
Assets and Liabilities, at Fair Value [Abstract]
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block]	The following tables set forth the Company’s financial and nonfinancial assets and liabilities accounted for at fair value, on a recurring basis, as of March 31, 2018 by level in the fair value hierarchy. March 31, 2018 (in millions) Level 1 Level 2 Level 3 Netting and Total Assets: Unrestricted cash equivalents - certificate of deposits $ 3.7 $ — $ — $ — $ 3.7 Commodities warehouse receipts 14.7 — — — 14.7 U.S. Treasury obligations 600.9 — — — 600.9 Cash, securities and other assets segregated under federal and other regulations 615.6 — — — 615.6 U.S. Treasury obligations 648.6 — — — 648.6 "To be announced" (TBA) and forward settling securities — 4.8 — 0.2 5.0 Foreign government obligations — 6.3 — — 6.3 Derivatives 3,698.4 21.2 — (3,730.0 ) (10.4 ) Deposits with and receivables from broker-dealers, clearing organization and counterparties 4,347.0 32.3 — (3,729.8 ) 649.5 Common and preferred stock, ADRs, and GDRs 46.6 2.9 — — 49.5 Exchangeable foreign ordinary equities, ADRs, and GDRs 17.7 0.5 — — 18.2 Corporate and municipal bonds 40.9 1.9 — — 42.8 U.S. Treasury obligations 96.5 — — — 96.5 U.S. government agency obligations — 408.1 — — 408.1 Foreign government obligations — 11.3 — — 11.3 Agency mortgage-backed obligations — 1,028.9 — — 1,028.9 Asset-backed obligations — 41.3 — — 41.3 Derivatives 1.7 779.2 — (612.4 ) 168.5 Commodities leases — 47.3 — (39.3 ) 8.0 Commodities warehouse receipts 2.0 — — — 2.0 Exchange firm common stock 9.9 — — — 9.9 Mutual funds and other 4.7 — — — 4.7 Financial instruments owned 220.0 2,321.4 — (651.7 ) 1,889.7 Physical commodities inventory, net 26.9 160.2 — — 187.1 Total assets at fair value $ 5,213.2 $ 2,513.9 $ — $ (4,381.5 ) $ 3,345.6 Liabilities: TBA and forward settling securities — 5.7 — (0.1 ) 5.6 Derivatives 3,832.7 34.4 — (3,867.0 ) 0.1 Payable to broker-dealers, clearing organizations and counterparties 3,832.7 40.1 — (3,867.1 ) 5.7 Common and preferred stock, ADRs, and GDRs 52.4 0.5 — — 52.9 Exchangeable foreign ordinary equities, ADRs, and GDRs 18.3 — — — 18.3 Corporate and municipal bonds 0.1 — — — 0.1 U.S. Treasury obligations 471.7 — — — 471.7 U.S. government agency obligations — 55.7 — — 55.7 Agency mortgage-backed obligations — 0.1 — — 0.1 Derivatives — 801.6 — (625.0 ) 176.6 Commodities leases — 45.6 — 1.9 47.5 Financial instruments sold, not yet purchased 542.5 903.5 — (623.1 ) 822.9 Total liabilities at fair value $ 4,375.2 $ 943.6 $ — $ (4,490.2 ) $ 828.6 (1) Represents cash collateral and the impact of netting across the levels of the fair value hierarchy. Netting among positions classified within the same level is included in that level. The following table sets forth the Company’s financial and nonfinancial assets and liabilities accounted for at fair value, on a recurring basis, as of September 30, 2017 by level in the fair value hierarchy. September 30, 2017 (in millions) Level 1 Level 2 Level 3 Netting and Total Assets: Unrestricted cash equivalents - certificates of deposits $ 3.8 $ — $ — $ — $ 3.8 Commodities warehouse receipts 21.0 — — — 21.0 U.S. Treasury obligations 33.5 — — — 33.5 Cash, securities and other assets segregated under federal and other regulations 54.5 — — — 54.5 U.S. Treasury obligations 244.7 — — — 244.7 "To be announced" (TBA) and forward settling securities — 8.8 — — 8.8 Foreign government obligations — 6.4 — — 6.4 Derivatives 2,608.6 289.1 — (2,952.9 ) (55.2 ) Deposits with and receivables from broker-dealers, clearing organizations, and counterparties 2,853.3 304.3 — (2,952.9 ) 204.7 Common and preferred stock, ADRs, and GDRs 31.2 3.4 0.1 — 34.7 Exchangeable foreign ordinary equities, ADRs, and GDRs 9.2 1.2 — — 10.4 Corporate and municipal bonds 28.2 0.9 — — 29.1 U.S. Treasury obligations 60.0 — — — 60.0 U.S. government agency obligations — 368.9 — — 368.9 Foreign government obligations — 10.2 — — 10.2 Agency mortgage-backed obligations — 920.9 — — 920.9 Asset-backed obligations — 47.3 — — 47.3 Derivatives 1.3 1,413.4 — (1,252.6 ) 162.1 Commodities leases — 174.1 — (138.7 ) 35.4 Commodities warehouse receipts 38.5 — — — 38.5 Exchange firm common stock 8.3 — — — 8.3 Mutual funds and other 6.0 — — — 6.0 Financial instruments owned 182.7 2,940.3 0.1 (1,391.3 ) 1,731.8 Physical commodities inventory, net 73.2 — — — 73.2 Total assets at fair value $ 3,167.5 $ 3,244.6 $ 0.1 $ (4,344.2 ) $ 2,068.0 Liabilities: Accounts payable and other accrued liabilities - contingent liabilities $ — $ — $ 1.0 $ — $ 1.0 TBA and forward settling securities — 4.9 — (0.1 ) 4.8 Derivatives 2,476.2 292.8 — (2,769.0 ) — Payable to broker-dealers, clearing organizations and counterparties 2,476.2 297.7 — (2,769.1 ) 4.8 Common and preferred stock, ADRs, and GDRs 33.7 0.7 — — 34.4 Exchangeable foreign ordinary equities, ADRs, and GDRs 10.3 0.2 — — 10.5 Corporate and municipal bonds 0.3 — — — 0.3 U.S. Treasury obligations 285.9 — — — 285.9 U.S. government agency obligations — 27.9 — — 27.9 Agency mortgage-backed obligations — 0.1 — — 0.1 Derivatives — 1,427.2 — (1,110.2 ) 317.0 Commodities leases — 191.1 — (149.6 ) 41.5 Financial instruments sold, not yet purchased 330.2 1,647.2 — (1,259.8 ) 717.6 Total liabilities at fair value $ 2,806.4 $ 1,944.9 $ 1.0 $ (4,028.9 ) $ 723.4 (1) Represents cash collateral and the impact of netting across the levels of the fair value hierarchy. Netting among positions classified within the same level is included in that level.
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block]	Information on Level 3 Financial Assets and Liabilities The following tables set forth a summary of changes in the fair value of the Company’s Level 3 financial assets and liabilities during the three and six months ended March 31, 2018 and 2017, including a summary of unrealized gains (losses) during the respective periods on the Company’s Level 3 financial assets and liabilities held during the periods. Level 3 Financial Assets For the Three and Six Months Ended March 31, 2018 (in millions) Balances at Realized gains Unrealized Purchases/issuances Settlements Transfers in Balances at Assets: Common and preferred stock, ADRs, and GDRs $ 0.1 $ — $ (0.1 ) $ — $ — $ — $ — $ 0.1 $ — $ (0.1 ) $ — $ — $ — $ — Level 3 Financial Assets and Financial Liabilities For the Three Months Ended March 31, 2017 (in millions) Balances at Realized gains Unrealized Purchases/issuances Settlements Transfers in Balances at Assets: Common and preferred stock, ADRs, and GDRs $ 0.2 $ — $ — $ — $ — $ — $ 0.2 Corporate and municipal bonds — — — — — — — $ 0.2 $ — $ — $ — $ — $ — $ 0.2 (in millions) Balances at Realized (gains) Unrealized Purchases/issuances Settlements Transfers in Balances at Liabilities: Contingent liabilities $ 0.8 $ — $ 0.1 $ — $ — $ — $ 0.9 Level 3 Financial Assets and Financial Liabilities For the Six Months Ended March 31, 2017 (in millions) Balances at Realized gains Unrealized Purchases/issuances Settlements Transfers in Balances at Assets: Common and preferred stock, ADRs, and GDRs $ 0.2 $ — $ — $ — $ — $ — $ 0.2 Corporate and municipal bonds 3.0 — — — (3.0 ) — — $ 3.2 $ — $ — $ — $ (3.0 ) $ — $ 0.2 (in millions) Balances at Realized (gains) Unrealized Purchases/issuances Settlements Transfers in Balances at Liabilities: Contingent liabilities $ 0.8 $ — $ 0.1 $ — $ — $ — $ 0.9

Financial Instruments with Of29

Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk (Tables)	6 Months Ended
	Mar. 31, 2018
Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk [Abstract]
Schedule of Derivative Instruments [Table Text Block]	Listed below are the fair values of the Company’s derivative assets and liabilities as of March 31, 2018 and September 30, 2017 . Assets represent net unrealized gains and liabilities represent net unrealized losses. March 31, 2018 September 30, 2017 (in millions) Assets (1) Liabilities (1) Assets (1) Liabilities (1) Derivative contracts not accounted for as hedges: Exchange-traded commodity derivatives $ 2,624.2 $ 2,940.3 $ 2,094.2 $ 1,975.0 OTC commodity derivatives 513.9 523.9 1,084.0 1,110.3 Exchange-traded foreign exchange derivatives 107.1 59.7 66.0 52.0 OTC foreign exchange derivatives 254.6 266.9 618.5 609.8 Exchange-traded interest rate derivatives 732.6 615.9 228.4 203.6 OTC interest rate derivatives 31.8 31.7 — — Exchange traded equity index derivatives 236.2 230.2 221.3 245.4 TBA and forward settling securities 4.9 5.8 8.8 4.9 Gross fair value of derivative contracts 4,505.3 4,674.4 4,321.2 4,201.0 Impact of netting and collateral (4,342.2 ) (4,492.1 ) (4,205.5 ) (3,879.2 ) Total fair value included in ‘Deposits with and receivables from broker-dealers, clearing organizations, and counterparties’ $ (5.4 ) $ (46.4 ) Total fair value included in ‘Financial instruments owned, at fair value’ $ 168.5 $ 162.1 Total fair value included in ‘Payables to broker-dealers, clearing organizations and counterparties $ 5.7 $ 4.8 Fair value included in ‘Financial instruments sold, not yet purchased, at fair value’ $ 176.6 $ 317.0 (1) As of March 31, 2018 and September 30, 2017 , the Company’s derivative contract volume for open positions were approximately 9.2 million and 6.1 million contracts, respectively. The Company’s derivative contracts are principally held in its Commercial Hedging and Clearing and Execution Services segments. The Company assists its Commercial Hedging segment customers in protecting the value of their future production by entering into option or forward agreements with them on an OTC basis. The Company also provides its Commercial Hedging segment customers with option products, including combinations of buying and selling puts and calls. The Company mitigates its risk by offsetting the customer’s transaction simultaneously with one of the Company’s trading counterparties or with a similar but not identical exchange-traded position. The risk mitigation of these offsetting trades is not within the documented hedging designation requirements of the Derivatives and Hedging Topic of the ASC. These derivative contracts are traded along with cash transactions because of the integrated nature of the markets for these products. The Company manages the risks associated with derivatives on an aggregate basis along with the risks associated with its proprietary trading and market-making activities in cash instruments as part of its firm-wide risk management policies. In particular, the risks related to derivative positions may be partially offset by inventory, unrealized gains in inventory or cash collateral paid or received. The Company has derivative instruments, which consist of mortgage-backed TBA securities and forward settling transactions that are used to manage risk exposures in the trading inventory of the Company’s domestic institutional fixed income business. The fair value on these transactions are recorded in deposits with and receivables from or payables to broker-dealers, clearing organizations and counterparties. Realized and unrealized gains and losses on securities and derivative transactions are reflected in ‘trading gains, net’. As of March 31, 2018 and September 30, 2017 , these transactions are summarized as follows: March 31, 2018 September 30, 2017 (in millions) Gain / (Loss) Notional Amounts Gain / (Loss) Notional Amounts Unrealized gain on TBA securities purchased within deposits with and receivables from broker-dealers, clearing organizations and counterparties and related notional amounts (1) $ 2.9 $ 832.5 $ — $ 51.3 Unrealized loss on TBA securities purchased within deposits with and receivables from broker-dealers, clearing organizations and counterparties and related notional amounts (1) $ — $ 49.9 $ (2.9 ) $ 1,236.8 Unrealized gain on TBA securities sold within payables to broker-dealers, clearing organizations and counterparties and related notional amounts (1) $ 0.1 $ (118.7 ) $ 5.8 $ (1,881.9 ) Unrealized loss on TBA securities sold within payables to broker-dealers, clearing organizations and counterparties and related notional amounts (1) $ (5.8 ) $ (1,611.1 ) $ (0.1 ) $ (404.1 ) Unrealized gain (loss) on forward settling securities purchased within deposits with and receivables from broker-dealers, clearing organizations and counterparties and related notional amounts $ 0.3 $ 410.9 $ (2.0 ) $ 882.9 Unrealized gain on forward settling securities sold within deposits with and receivables from broker-dealers, clearing organizations and counterparties and related notional amounts $ 1.8 $ (308.1 ) $ 3.0 $ (590.2 ) (1) The notional amounts of these instruments reflect the extent of the Company's involvement in TBA and forward settling securities and do not represent risk of loss due to counterparty non-performance.
Schedule of Derivative Instruments, Gain (Loss) in Statement of Financial Performance [Table Text Block]	The following table sets forth the Company’s gains (losses) related to derivative financial instruments for the three and six months ended March 31, 2018 and 2017 in accordance with the Derivatives and Hedging Topic of the ASC. The net gains set forth below are included in ‘Cost of sales of physical commodities’ and ‘Trading gains, net’ in the condensed consolidated income statements. Three Months Ended March 31, Six Months Ended March 31, (in millions) 2018 2017 2018 2017 Commodities $ 12.3 $ 13.9 $ 33.8 $ 18.8 Foreign exchange 2.5 0.8 4.8 2.0 Interest rate 0.2 — 0.6 (1.0 ) TBA and forward settling securities 10.7 (4.9 ) 10.3 8.5 Net gains from derivative contracts $ 25.7 $ 9.8 $ 49.5 $ 28.3

Physical Commodities Inventor30

Physical Commodities Inventory Physical Commodities Table (Tables)	6 Months Ended
	Mar. 31, 2018
Inventory Disclosure [Abstract]
Schedule of Inventory, Current [Table Text Block]	(in millions) March 31, September 30, Physical Ag & Energy (1) $ 160.2 $ 65.1 Precious metals - held by broker-dealer subsidiary (2) 26.9 13.3 Precious metals - held by non-broker-dealer subsidiaries (3) 99.2 46.4 Physical commodities inventory $ 286.3 $ 124.8

Goodwill (Tables)

Goodwill (Tables)	6 Months Ended
	Mar. 31, 2018
Goodwill [Abstract]
Schedule of Goodwill [Table Text Block]	The carrying value of goodwill is allocated to the Company’s operating segments as follows: (in millions) March 31, September 30, Commercial Hedging $ 30.3 $ 30.7 Global Payments 6.3 6.3 Physical Commodities 2.4 2.4 Securities 6.9 7.7 Goodwill $ 45.9 $ 47.1

Intangible Assets - (Tables)

Intangible Assets - (Tables)	6 Months Ended
	Mar. 31, 2018
Intangible Assets [Abstract]
Schedule of Finite and Indefinite-Lived Intangible Assets [Table Text Block]	The gross and net carrying values of intangible assets as of the balance sheet dates, by major intangible asset class are as follows (in millions): March 31, 2018 September 30, 2017 Gross Amount Accumulated Amortization Net Amount Gross Amount Accumulated Amortization Net Amount Intangible assets subject to amortization: Software programs/platforms 2.7 (2.5 ) 0.2 2.7 (2.5 ) 0.2 Customer base 20.0 (9.0 ) 11.0 20.0 (7.9 ) 12.1 Total intangible assets $ 22.7 $ (11.5 ) $ 11.2 $ 22.7 $ (10.4 ) $ 12.3
Schedule of Expected Amortization Expense [Table Text Block]	Amortization expense related to intangible assets was $1.1 million and $1.4 million for the six months ended March 31, 2018 and 2017 , respectively. As of March 31, 2018 , the estimated future amortization expense was as follows: (in millions) Fiscal 2018 (remaining six months) $ 1.1 Fiscal 2019 2.2 Fiscal 2020 2.0 Fiscal 2021 1.9 Fiscal 2022 and thereafter 4.0 $ 11.2

Credit Facilities (Tables)

Credit Facilities (Tables)	6 Months Ended
	Mar. 31, 2018
Credit Facilities [Abstract]
Schedule of Debt [Table Text Block]	The following table sets forth a listing of credit facilities, the current committed amounts as of the report date on the facilities, outstanding borrowings on the facilities, as well as indebtedness on a promissory note as of March 31, 2018 and September 30, 2017 : (in millions) Credit Facilities Amounts Outstanding Borrower Security Renewal / Expiration Date Total Commitment March 31, September 30, Committed Credit Facilities INTL FCStone Inc. Pledged shares of certain subsidiaries March 18, 2019 $ 262.0 $ 143.4 $ 150.0 INTL FCStone Financial, Inc. None April 4, 2019 75.0 9.5 — FCStone Merchants Services, LLC Certain commodities assets November 1, 2019 232.5 138.0 44.2 INTL FCStone Ltd. None November 7, 2018 25.0 — — $ 594.5 290.9 194.2 Uncommitted Credit Facilities INTL FCStone Financial, Inc. Commodities warehouse receipts and certain pledged securities n/a $ — 48.0 34.0 INTL FCStone Ltd. Commodities warehouse receipts n/a $ — — — Note Payable to Bank Monthly installments, due March 2020 and secured by certain equipment 1.6 2.0 Total indebtedness $ 340.5 $ 230.2

Commodity and Other Repurchas34

Commodity and Other Repurchase Agreements and Collateralized Transactions Schedule of Gross Collateralized Financings by Maturity (Tables)	6 Months Ended
	Mar. 31, 2018
Assets Sold under Agreements to Repurchase [Line Items]
Schedule of Repurchase Agreement Counterparties with Whom Repurchase Agreements Exceed 10 Percent of Stockholders' Equity [Table Text Block]	March 31, 2018 Overnight and Open Less than 30 Days 30-90 Days Over 90 Days Total Securities sold under agreements to repurchase $ 797.7 $ 464.3 $ 280.5 $ 20.0 $ 1,562.5 Securities loaned 559.1 — — — 559.1 Gross amount of secured financing $ 1,356.8 $ 464.3 $ 280.5 $ 20.0 $ 2,121.6 September 30, 2017 Overnight and Open Less than 30 Days 30-90 Days Over 90 Days Total Securities sold under agreements to repurchase $ 640.2 $ 432.9 $ 320.0 $ — $ 1,393.1 Securities loaned 111.1 — — — 111.1 Gross amount of secured financing $ 751.3 $ 432.9 $ 320.0 $ — $ 1,504.2

Commodity and Other Repurchas35

Commodity and Other Repurchase Agreements and Collateralized Transactions Schedule of Collateralized Financings by Collateral Type (Tables)	6 Months Ended
	Mar. 31, 2018
Financial Instruments Owned and Pledged as Collateral [Line Items]
Schedule of Financial Instruments Owned and Pledged as Collateral [Table Text Block]	Securities sold under agreements to repurchase: March 31, 2018 September 30, 2017 U.S. Treasury obligations $ 5.1 $ 7.0 U.S. government agency obligations 358.1 332.6 Asset-backed obligations 75.0 36.4 Agency mortgage-backed obligations 1,124.3 1,017.1 Total securities sold under agreements to repurchase 1,562.5 1,393.1 Securities loaned: Common stock 559.1 111.1 Total securities loaned 559.1 111.1 Gross amount of secured financing $ 2,121.6 $ 1,504.2

Capital and Other Regulatory 36

Capital and Other Regulatory Requirements (Tables)	6 Months Ended
	Mar. 31, 2018
Capital and Other Regulatory Requirements [Abstract]
Regulatory Capital Requirements under Banking Regulations [Text Block]	Capital and Other Regulatory Requirements The Company’s activities are subject to significant governmental regulation, both in the United States and in the international jurisdictions in which it operates. The subsidiaries of the Company were in compliance with all of their regulatory requirements as of March 31, 2018 , as follows: (in millions) As of March 31, 2018 Subsidiary Regulatory Authority Jurisdiction Requirement Type Actual Minimum Requirement INTL FCStone Financial Inc. SEC and Commodity Futures Trading Commission ("CFTC") United States Net capital $ 152.3 $ 83.6 INTL FCStone Financial Inc. CFTC United States Segregated funds $ 2,357.1 $ 2,303.2 INTL FCStone Financial Inc. CFTC United States Secured funds $ 144.0 $ 128.3 INTL FCStone Financial Inc. SEC United States Customer reserve $ 0.7 $ — INTL FCStone Financial Inc. SEC United States PAB reserve $ 5.5 $ 2.7 INTL Custody & Clearing Solutions Inc. SEC United States Net capital $ 1.9 $ 0.1 SA Stone Wealth Management Inc. SEC United States Net capital $ 3.9 $ 0.4 INTL FCStone Ltd (1) Financial Conduct Authority ("FCA") United Kingdom Net capital $ 193.6 $ 90.3 INTL FCStone Ltd FCA United Kingdom Segregated funds $ 183.4 $ 183.4 INTL Netherlands BV (1) FCA United Kingdom Net capital $ 192.9 $ 90.3 INTL FCStone DTVM Ltda. Brazilian Central Bank and Securities and Exchange Commission of Brazil Brazil Capital adequacy $ 12.9 $ 2.3 INTL Gainvest S.A. National Securities Commission ("CNV") Argentina Capital adequacy $ 4.8 $ 0.1 INTL Gainvest S.A. CNV Argentina Net capital $ 2.8 $ 0.1 INTL CIBSA S.A. CNV Argentina Capital adequacy $ 5.2 $ 0.8 INTL CIBSA S.A. CNV Argentina Net capital $ 1.1 $ 0.4 (1) INTL Netherlands BV is a holding company that includes the ownership equity of INTL FCStone Ltd. The associated net capital amounts and minimum requirements should not be considered in aggregate. Certain other non-U.S. subsidiaries of the Company are also subject to capital adequacy requirements promulgated by authorities of the countries in which they operate. As of March 31, 2018 , these subsidiaries were in compliance with their local capital adequacy requirements.

Other Expenses (Tables)

Other Expenses (Tables)	6 Months Ended
	Mar. 31, 2018
Other Expenses [Abstract]
Schedule of Other Operating Cost and Expense, by Component [Table Text Block]	Other expenses for the three and six months ended March 31, 2018 and 2017 consisted of the following: Three Months Ended March 31, Six Months Ended March 31, (in millions) 2018 2017 2018 2017 Contingent consideration, net $ — $ 0.1 $ — $ 0.1 Insurance 0.6 0.8 1.2 1.3 Advertising, meetings and conferences 3.4 1.2 4.3 2.1 Office supplies and printing 0.4 0.5 0.8 1.1 Other clearing related expenses 0.5 0.3 1.0 0.7 Other non-income taxes 1.3 1.2 2.5 2.3 Other 2.5 2.5 4.6 4.6 Total other expenses $ 8.7 $ 6.6 $ 14.4 $ 12.2

Accumulated Other Comprehensi38

Accumulated Other Comprehensive Income (Loss) (Tables)	6 Months Ended
	Mar. 31, 2018
Accumulated Other Comprehensive Income (Loss) [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]	The following table summarizes the changes in accumulated other comprehensive loss, net for the six months ended March 31, 2018 . (in millions) Foreign Currency Translation Adjustment Pension Benefits Adjustment Accumulated Other Comprehensive Loss Balances as of September 30, 2017 $ (21.5 ) $ (3.0 ) $ (24.5 ) Other comprehensive loss, net of tax (3.8 ) — (3.8 ) Balances as of March 31, 2018 $ (25.3 ) $ (3.0 ) $ (28.3 )

Segment Analysis (Tables)

Segment Analysis (Tables)	6 Months Ended
	Mar. 31, 2018
Segment Analysis [Abstract]
Schedule of Segment Reporting Information, by Segment [Table Text Block]	Information for the reportable segments is shown in accordance with the Segment Reporting Topic of the ASC as follows Three Months Ended March 31, Six Months Ended March 31, (in millions) 2018 2017 2018 2017 Total revenues: Commercial Hedging $ 78.3 $ 62.7 $ 139.8 $ 120.2 Global Payments 23.4 21.5 48.0 44.6 Securities 55.5 37.9 98.5 75.3 Physical Commodities 6,262.3 5,276.2 13,978.9 11,174.9 Clearing and Execution Services 88.0 64.2 160.2 127.8 Corporate unallocated (0.5 ) (1.7 ) 0.2 (7.6 ) Total $ 6,507.0 $ 5,460.8 $ 14,425.6 $ 11,535.2 Operating revenues (loss): Commercial Hedging $ 78.3 $ 62.7 $ 139.8 $ 120.2 Global Payments 23.4 21.5 48.0 44.6 Securities 55.5 37.9 98.5 75.3 Physical Commodities 15.5 11.2 26.1 21.0 Clearing and Execution Services 88.0 64.2 160.2 127.8 Corporate unallocated (0.5 ) (1.7 ) 0.2 (7.6 ) Total $ 260.2 $ 195.8 $ 472.8 $ 381.3 Net operating revenues (loss): Commercial Hedging $ 61.9 $ 50.5 $ 111.0 $ 96.1 Global Payments 21.9 19.1 44.9 39.7 Securities 27.6 24.1 51.1 49.2 Physical Commodities 12.5 9.0 20.9 17.1 Clearing and Execution Services 31.8 25.4 59.2 49.5 Corporate unallocated (1.4 ) (4.2 ) (2.5 ) (13.4 ) Total $ 154.3 $ 123.9 $ 284.6 $ 238.2 Net contribution: (Revenues less cost of sales of physical commodities, transaction-based clearing expenses, variable bonus compensation, introducing broker commissions and interest expense) Commercial Hedging $ 44.7 $ 36.9 $ 81.2 $ 70.3 Global Payments 17.6 15.3 36.0 31.7 Securities 20.3 18.9 38.1 38.7 Physical Commodities 9.4 6.5 15.0 12.3 Clearing and Execution Services 23.9 19.6 44.4 37.6 Total $ 115.9 $ 97.2 $ 214.7 $ 190.6 Segment income: (Net contribution less non-variable direct segment costs) Commercial Hedging $ 27.6 $ 18.7 $ 48.7 $ 34.1 Global Payments 13.5 11.7 28.1 24.9 Securities 12.8 11.7 23.8 24.6 Physical Commodities 5.6 3.9 6.7 6.9 Clearing and Execution Services 12.7 7.9 23.2 13.6 Total $ 72.2 $ 53.9 $ 130.5 $ 104.1 Reconciliation of segment income to income before tax: Segment income $ 72.2 $ 53.9 $ 130.5 $ 104.1 Net costs not allocated to operating segments 42.7 39.6 82.4 81.4 Income before tax $ 29.5 $ 14.3 $ 48.1 $ 22.7 (in millions) As of March 31, 2018 As of September 30, 2017 Total assets: Commercial Hedging $ 1,636.1 $ 1,650.3 Global Payments 208.8 199.5 Securities 2,901.3 2,101.7 Physical Commodities 378.0 339.5 Clearing and Execution Services 1,996.5 1,818.9 Corporate unallocated 83.0 133.5 Total $ 7,203.7 $ 6,243.4

Basis of Presentation and Con40

Basis of Presentation and Consolidation and Recently Issued Accounting Standards (Details) $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2017USD ($)	Mar. 31, 2018USD ($)	Mar. 31, 2017USD ($)
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Net Income		$ 0.3
Payments Related to Tax Withholding for Share-based Compensation		$ 0.8	$ 0
Number of different types of foreign currencies		140
Number of accounts for customers company-wide		20,000
Non-Trading Technology and Support [Member]
Prior Period Reclassification Adjustment	$ 2.8		5.7
Communications
Prior Period Reclassification Adjustment	$ 1.2		$ 2.4

Earnings per Share - EPS Reconc

Earnings per Share - EPS Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Net income	$ 22.7	$ 11	$ 15.8	$ 17.3
Less: Net income allocated to participating securities	(0.3)	(0.2)	(0.3)	(0.3)
Net income allocated to common shareholders	$ 22.4	$ 10.8	$ 15.5	$ 17
Weighted average number of common shares outstanding	18,559,849	18,404,236	18,502,795	18,325,383
Dilutive potential common shares outstanding:
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	299,484	257,182	333,418	312,097
Diluted weighted-average shares	18,859,333	18,661,418	18,836,213	18,637,480

Earnings per Share - Antiduliti

Earnings per Share - Antidulitive Securities (Details) - shares	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Earnings Per Share [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	173,992	322,974	136,440	242,448

Assets and Liabilities, at Fa43

Assets and Liabilities, at Fair Value - Financial Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2018	Sep. 30, 2017	Sep. 30, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	$ 1,251.4	$ 518.8
Receivables from Brokers-Dealers and Clearing Organizations	1,914.1	2,625.1
Financial Instruments, Owned, at Fair Value	1,889.7	1,731.8
Physical commodities inventory	286.3	124.8
Accounts Payable and Other Accrued Liabilities	129.6	135.6
Payables to Broker-Dealers and Clearing Organizations	(79.7)	(125.7)
Financial Instruments Sold, Not yet Purchased, at Fair Value	822.9	717.6
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	615.6	54.5
Receivables from Clearing Organizations	649.5	204.7
Financial Instruments, Owned, at Fair Value	1,889.7	1,731.8
Assets, Fair Value Disclosure	3,345.6	2,068
Financial Instruments Sold, Not yet Purchased, at Fair Value	822.9
Liabilities, Fair Value Disclosure	828.6	723.4
Fair Value, Measurements, Recurring [Member] | TBA and forward settling securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations	(5.6)	(4.8)
Fair Value, Measurements, Recurring [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Brokers-Dealers and Clearing Organizations	0.1
Payables to Broker-Dealers and Clearing Organizations		0
Fair Value, Measurements, Recurring [Member] | Payable to broker-dealers, clearing organizations and counterparties [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations	(5.7)	(4.8)
Fair Value, Measurements, Recurring [Member] | Contingent Consideration [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accounts Payable and Other Accrued Liabilities		1
Fair Value, Measurements, Recurring [Member] | Physical commodities inventory [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Physical commodities inventory	187.1	73.2
Fair Value, Measurements, Recurring [Member] | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	41.3	47.3
Fair Value, Measurements, Recurring [Member] | US Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	408.1	368.9
Financial Instruments Sold, Not yet Purchased, at Fair Value	55.7	27.9
Fair Value, Measurements, Recurring [Member] | Common and preferred stock, ADRs, and GDRS [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	49.5	34.7
Financial Instruments Sold, Not yet Purchased, at Fair Value	52.9	34.4
Fair Value, Measurements, Recurring [Member] | Exchangeable foreign ordinary equities, ADRs, and GDRs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	18.2	10.4
Financial Instruments Sold, Not yet Purchased, at Fair Value	18.3	10.5
Fair Value, Measurements, Recurring [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	42.8	29.1
Financial Instruments Sold, Not yet Purchased, at Fair Value	0.1	0.3
Fair Value, Measurements, Recurring [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	96.5	60
Financial Instruments Sold, Not yet Purchased, at Fair Value	471.7	285.9
Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	11.3	10.2
Financial Instruments Sold, Not yet Purchased, at Fair Value	0.1		$ 0.1
Fair Value, Measurements, Recurring [Member] | Collateralized Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	1,028.9	920.9
Fair Value, Measurements, Recurring [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	168.5	162.1
Financial Instruments Sold, Not yet Purchased, at Fair Value	176.6
Fair Value, Measurements, Recurring [Member] | Commodities leases [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	8	35.4
Financial Instruments Sold, Not yet Purchased, at Fair Value	47.5	41.5
Fair Value, Measurements, Recurring [Member] | Commodities warehouse receipts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	2	38.5
Fair Value, Measurements, Recurring [Member] | Exchange firm common stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	9.9	8.3
Fair Value, Measurements, Recurring [Member] | Mutual funds and other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	4.7	6
Fair Value, Measurements, Recurring [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	648.6
Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	6.3	6.4
Fair Value, Measurements, Recurring [Member] | Collateralized Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	5	8.8
Fair Value, Measurements, Recurring [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations	(10.4)
Fair Value, Measurements, Recurring [Member] | Commodities warehouse receipts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	14.7	21
Fair Value, Measurements, Recurring [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	600.9	33.5
Fair Value, Measurements, Recurring [Member] | Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	3.7	3.8
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	0	0
Receivables from Clearing Organizations	(3,729.8)	(2,952.9)
Financial Instruments, Owned, at Fair Value	(651.7)	(1,391.3)
Assets, Fair Value Disclosure	(4,381.5)	(4,344.2)
Financial Instruments Sold, Not yet Purchased, at Fair Value	(623.1)	(1,259.8)
Liabilities, Fair Value Disclosure	(4,490.2)	(4,028.9)
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | TBA and forward settling securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations	0.1	0.1
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations	3,867	2,769
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Payable to broker-dealers, clearing organizations and counterparties [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations	3,867.1	2,769.1
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Contingent Consideration [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accounts Payable and Other Accrued Liabilities		0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Physical commodities inventory [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Physical commodities inventory	0	0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | US Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Common and preferred stock, ADRs, and GDRS [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Exchangeable foreign ordinary equities, ADRs, and GDRs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0		0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Collateralized Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	(612.4)	(1,252.6)
Financial Instruments Sold, Not yet Purchased, at Fair Value	(625)	(1,110.2)
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Commodities leases [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	(39.3)	(138.7)
Financial Instruments Sold, Not yet Purchased, at Fair Value	1.9	(149.6)
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Commodities warehouse receipts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Exchange firm common stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Mutual funds and other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Collateralized Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	0.2
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	(3,730)
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Commodities warehouse receipts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	0	0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	0	0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	615.6	54.5
Receivables from Clearing Organizations	4,347	2,853.3
Financial Instruments, Owned, at Fair Value	220	182.7
Assets, Fair Value Disclosure	5,213.2	3,167.5
Financial Instruments Sold, Not yet Purchased, at Fair Value	542.5	330.2
Liabilities, Fair Value Disclosure	4,375.2	2,806.4
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | TBA and forward settling securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations	(3,832.7)	(2,476.2)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Payable to broker-dealers, clearing organizations and counterparties [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations	(3,832.7)	(2,476.2)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Contingent Consideration [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accounts Payable and Other Accrued Liabilities		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Physical commodities inventory [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Physical commodities inventory	26.9	73.2
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Common and preferred stock, ADRs, and GDRS [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	46.6	31.2
Financial Instruments Sold, Not yet Purchased, at Fair Value	52.4	33.7
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Exchangeable foreign ordinary equities, ADRs, and GDRs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	17.7	9.2
Financial Instruments Sold, Not yet Purchased, at Fair Value	18.3	10.3
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	40.9	28.2
Financial Instruments Sold, Not yet Purchased, at Fair Value	0.1	0.3
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	96.5	60
Financial Instruments Sold, Not yet Purchased, at Fair Value	471.7	285.9
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Collateralized Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	1.7	1.3
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Commodities leases [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Commodities warehouse receipts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	2	38.5
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Exchange firm common stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	9.9	8.3
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Mutual funds and other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	4.7	6
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	648.6
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Collateralized Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	3,698.4
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Commodities warehouse receipts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	14.7	21
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	600.9	33.5
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	3.7	3.8
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	0	0
Receivables from Clearing Organizations	32.3	304.3
Financial Instruments, Owned, at Fair Value	2,321.4	2,940.3
Assets, Fair Value Disclosure	2,513.9	3,244.6
Financial Instruments Sold, Not yet Purchased, at Fair Value	903.5	1,647.2
Liabilities, Fair Value Disclosure	943.6	1,944.9
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | TBA and forward settling securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations	(5.7)	(4.9)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations	(34.4)	(292.8)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Payable to broker-dealers, clearing organizations and counterparties [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations	(40.1)	(297.7)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Contingent Consideration [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accounts Payable and Other Accrued Liabilities		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Physical commodities inventory [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Physical commodities inventory	160.2	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	41.3	47.3
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	408.1	368.9
Financial Instruments Sold, Not yet Purchased, at Fair Value	55.7	27.9
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Common and preferred stock, ADRs, and GDRS [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	2.9	3.4
Financial Instruments Sold, Not yet Purchased, at Fair Value	0.5	0.7
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Exchangeable foreign ordinary equities, ADRs, and GDRs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0.5	1.2
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0.2
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	1.9	0.9
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	11.3	10.2
Financial Instruments Sold, Not yet Purchased, at Fair Value	0.1		0.1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Collateralized Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	1,028.9	920.9
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	779.2	1,413.4
Financial Instruments Sold, Not yet Purchased, at Fair Value	801.6	1,427.2
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commodities leases [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	47.3	174.1
Financial Instruments Sold, Not yet Purchased, at Fair Value	45.6	191.1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commodities warehouse receipts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Exchange firm common stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Mutual funds and other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	6.3	6.4
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Collateralized Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	4.8	8.8
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	21.2
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commodities warehouse receipts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	0	0
Receivables from Clearing Organizations	0	0
Financial Instruments, Owned, at Fair Value	0	0.1
Assets, Fair Value Disclosure	0	0.1
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Liabilities, Fair Value Disclosure	0	1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | TBA and forward settling securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Payable to broker-dealers, clearing organizations and counterparties [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Contingent Consideration [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accounts Payable and Other Accrued Liabilities		1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Physical commodities inventory [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Physical commodities inventory	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Common and preferred stock, ADRs, and GDRS [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0.1
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Exchangeable foreign ordinary equities, ADRs, and GDRs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Corporate Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0		$ 0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Collateralized Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Commodities leases [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Commodities warehouse receipts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Exchange firm common stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Mutual funds and other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Collateralized Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Commodities warehouse receipts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	$ 0	0
Derivative [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations		(55.2)
Derivative [Member] | Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		(2,952.9)
Derivative [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		2,608.6
Derivative [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		289.1
Derivative [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		0
US Government Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		244.7
US Government Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		0
US Government Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		244.7
US Government Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		0
US Government Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		$ 0

Assets and Liabilities, at Fa44

Assets and Liabilities, at Fair Value - Details of Level 3 Assets and Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2018	Sep. 30, 2017
Payables to Broker-Dealers and Clearing Organizations	$ 79.7	$ 125.7
Assets	7,203.7	6,243.4
Fair Value, Measurements, Recurring [Member]
Receivables from Clearing Organizations	649.5	204.7
Assets, Fair Value Disclosure	3,345.6	2,068
Fair Value, Measurements, Recurring [Member] | US Government Debt Securities [Member]
Receivables from Clearing Organizations		244.7
Fair Value, Measurements, Recurring [Member] | Derivative [Member]
Payables to Broker-Dealers and Clearing Organizations		55.2
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member]
Receivables from Clearing Organizations	(3,729.8)	(2,952.9)
Assets, Fair Value Disclosure	$ (4,381.5)	(4,344.2)
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | US Government Debt Securities [Member]
Receivables from Clearing Organizations		0
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | Collateralized Mortgage Backed Securities [Member]
Receivables from Clearing Organizations		0
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | Foreign Government Debt Securities [Member]
Receivables from Clearing Organizations		0
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | Derivative [Member]
Receivables from Clearing Organizations		$ (2,952.9)

Assets and Liabilities, at Fa45

Assets and Liabilities, at Fair Value - Rollforward of Level 3 (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Rollforward of Level 3 Securities [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		$ 0.1
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Period Increase (Decrease)		(0.1)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		0
Contingent Consideration [Member]
Rollforward of Level 3 Liabilities [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value	$ 0.8		$ 0.8
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings	0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Period Increase (Decrease)	0.1		0.1
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Purchases	0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Settlements	0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Transfers, Net	0		0
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value	0.9		0.9
Common stock and American Depositary Receipts (ADRs) [Member]
Rollforward of Level 3 Securities [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	0.2	0.1	0.2
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Period Increase (Decrease)	0	(0.1)	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net	0	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	0.2	$ 0	0.2
Corporate Debt Securities [Member]
Rollforward of Level 3 Securities [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	0		3
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Gain (Loss) Included in Earnings	0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Period Increase (Decrease)	0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	0		(3)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers, Net	0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	$ 0		$ 0

Assets and Liabilities, at Fa46

Assets and Liabilities, at Fair Value - Contingent Consideration (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2015	Mar. 31, 2018
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Change in fair value of contingent consideration for acquisitions	$ 0.1
Business Combination, Contingent Consideration, Liability			$ 1
Contingent Consideration [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Change in fair value of contingent consideration for acquisitions		$ 0.2

Financial Instruments with Of47

Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - Obligations to Purchase Financial Instruments at a Future Date (Details) - USD ($) $ in Millions	Mar. 31, 2018	Sep. 30, 2017
Financial Instruments Sold, Not yet Purchased, at Fair Value	$ 822.9	$ 717.6
Financial instrument sold, not yet purchased [Member]
Derivative, Fair Value, Net	$ 176.6	$ 317

Financial Instruments with Of48

Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - Gross Derivative Assets and Liabilities by Type and Balance Sheet Location (Details) - USD ($) $ in Millions	Mar. 31, 2018	Sep. 30, 2017
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 4,505.3	$ 4,321.2
Derivative Liability, Fair Value, Gross Liability	4,674.4	4,201
Impact of netting and collateral	(4,342.2)	(4,205.5)
Impact of netting and collateral	(4,492.1)	(3,879.2)
Deposits and Receivables from Exchange Clearing Organizations [Member]
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	(5.4)	(46.4)
Financial instruments owned [Member]
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	168.5	162.1
Payable to broker-dealers, clearing organizations and counterparties [Member]
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	5.7	4.8
Financial instrument sold, not yet purchased [Member]
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	176.6	317
Exchange-traded Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	2,624.2	2,094.2
Derivative Liability, Fair Value, Gross Liability	2,940.3	1,975
Over the Counter (OTC) Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	513.9	1,084
Derivative Liability, Fair Value, Gross Liability	523.9	1,110.3
Foreign Exchange Forward [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	107.1	66
Derivative Liability, Fair Value, Gross Liability	59.7	52
Over the Counter (OTC) Foreign Exchange Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	254.6	618.5
Derivative Liability, Fair Value, Gross Liability	266.9	609.8
Exchange-traded interest rate contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	732.6	228.4
Derivative Liability, Fair Value, Gross Liability	615.9	203.6
Interest Rate Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	31.8	0
Derivative Liability, Fair Value, Gross Liability	31.7	0
Equity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	236.2	221.3
Derivative Liability, Fair Value, Gross Liability	230.2	245.4
TBA and forward settling securities [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	4.9	8.8
Derivative Liability, Fair Value, Gross Liability	$ 5.8	$ 4.9

Financial Instruments with Of49

Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - Derivatives Volume (Details) number in Millions	Mar. 31, 2018	Sep. 30, 2017
Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk [Abstract]
Derivative, Number of Instruments Held	9.2	6.1

Financial Instruments with Of50

Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - TBAs and Forward Settling Securities (Details) - USD ($) $ in Millions	Mar. 31, 2018	Sep. 30, 2017
Derivative Asset, Fair Value, Gross Asset	$ 4,505.3	$ 4,321.2
Derivative Liability, Fair Value, Gross Liability	4,674.4	4,201
TBA securities purchased [Member]
Derivative Asset, Fair Value, Gross Asset	2.9	0
Derivative Liability, Notional Amount	(49.9)	(1,236.8)
Derivative Liability, Fair Value, Gross Liability	0	(2.9)
Derivative Asset, Notional Amount	832.5	51.3
TBA securities sold [Member]
Derivative Asset, Fair Value, Gross Asset	0.1	5.8
Derivative Liability, Notional Amount	(1,611.1)	(404.1)
Derivative Liability, Fair Value, Gross Liability	(5.8)	(0.1)
Derivative Asset, Notional Amount	118.7	1,881.9
Forward settling securities purchased [Member]
Derivative Asset, Fair Value, Gross Asset	0.3	(2)
Derivative Asset, Notional Amount	410.9	882.9
Over the Counter (OTC) Commodity Contracts [Member]
Derivative Liability, Notional Amount	(308.1)	(590.2)
Derivative Liability, Fair Value, Gross Liability	$ 1.8	$ 3

Financial Instruments with Of51

Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - Realized Gains/Losses on Derivative Contracts (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Commodity Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	$ 12.3	$ 13.9	$ 33.8	$ 18.8
Foreign Exchange Forward [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	2.5	0.8	4.8	2
Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	0.2	0	0.6	(1)
TBA and forward settling securities [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	10.7	(4.9)	10.3	8.5
Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	$ 25.7	$ 9.8	$ 49.5	$ 28.3

Receivables From Customers, N52

Receivables From Customers, Net and Notes Receivable, Net - Allowance for Customer Receivables (Details) - USD ($) $ in Millions	Mar. 31, 2018	Sep. 30, 2017
Receivables from customers and notes receivable, net [Abstract]
Allowance for Doubtful Accounts Receivable	$ 7.8	$ 7.6
Allowance for Doubtful Accounts, Premiums and Other Receivables	$ 48.1	$ 47

Receivables From Customers, N53

Receivables From Customers, Net and Notes Receivable, Net - Allowance for Notes Receivable (Details) $ in Millions	Sep. 30, 2016USD ($)
Receivables from customers and notes receivable, net [Abstract]
Allowance Notes Receivable	$ 0.2

Receivables From Customers, N54

Receivables From Customers, Net and Notes Receivable, Net Receivables from Customers, Net and Notes Receivables, Net - Bad Debt Expense and Recoveries (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Provision for Doubtful Accounts	$ 0.2	$ 1.3	$ 1.3	$ 3.8
Other Segments [Member]
Provision for Doubtful Accounts			$ 1

Physical Commodities Inventor55

Physical Commodities Inventory - Physical Commodities Inventory by CIP and Finished (Details) - USD ($) $ in Millions	Mar. 31, 2018	Sep. 30, 2017
Inventory [Line Items]
Physical Ag & Energy(1)	$ 160.2	$ 65.1
Precious metals - held by non-broker-dealer subsidiaries(3)	187.1	73.2
Physical commodities inventory	286.3	124.8
Physical commodities inventory - precious metals [Member]
Inventory [Line Items]
Precious metals - held by non-broker-dealer subsidiaries(3)	26.9	13.3
Finished commodities	$ 99.2	$ 46.4

Physical Commodities Inventor56

Physical Commodities Inventory - LCM Adjustments (Details) - USD ($) $ in Millions	Mar. 31, 2018	Sep. 30, 2017	Sep. 30, 2016
Physical Commodities Inventory [Abstract]
Inventory Adjustments	$ 0.1	$ 0.7	$ 0.6

Goodwill - Goodwill by Segment

Goodwill - Goodwill by Segment (Details) - USD ($) $ in Millions	Mar. 31, 2018	Sep. 30, 2017
Goodwill [Line Items]
Goodwill	$ 45.9	$ 47.1
Commercial Hedging [Member]
Goodwill [Line Items]
Goodwill	30.3	30.7
Global Payments [Member]
Goodwill [Line Items]
Goodwill	6.3	6.3
Physical Commodities [Member]
Goodwill [Line Items]
Goodwill	2.4	2.4
Securities [Member]
Goodwill [Line Items]
Goodwill	$ 6.9	$ 7.7

Goodwill Goodwill Adjustments (

Goodwill Goodwill Adjustments (Details) $ in Millions	6 Months Ended
	Mar. 31, 2018USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill, Translation and Purchase Accounting Adjustments	$ 1.2

Intangible Assets - Gross and N

Intangible Assets - Gross and Net Intangible Assets by Major Class (Details) - USD ($) $ in Millions	Mar. 31, 2018	Sep. 30, 2017
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Net	$ 11.2
Computer Software, Intangible Asset [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Computer Software, Gross	2.7	$ 2.7
Finite-Lived Intangible Assets, Accumulated Amortization	(2.5)	(2.5)
Finite-Lived Intangible Assets, Net	0.2	0.2
Customer Relationships [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Customer Lists, Gross	20	20
Finite-Lived Intangible Assets, Accumulated Amortization	(9)	(7.9)
Finite-Lived Intangible Assets, Net	$ 11	$ 12.1

Intangible Assets - Indefinite-

Intangible Assets - Indefinite-Lived Intangible Assets (Details) - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Sep. 30, 2017
Indefinite-lived Intangible Assets [Line Items]
Amortization of Intangible Assets	$ 1.1	$ 1.4
Gross Finite and Indefinite-Lived Intangible Assets	22.7		$ 22.7
Finite and Indefinited-Lived Accumulated Amortization and Impairment Charges	(11.5)		(10.4)
Intangible Assets, Net (Excluding Goodwill)	$ 11.2		$ 12.3

Intangible Assets - Finite-Live

Intangible Assets - Finite-Lived Intangible Assets Future Amortization Expense (Details) - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Amortization of Intangible Assets	$ 1.1	$ 1.4
Finite-Lived Intangible Assets, Amortization Expense, Maturity Schedule [Abstract]
Fiscal 2016 (remaining nine months)	1.1
Fiscal 2,017	2.2
Fiscal 2,018	2
Fiscal 2,019	1.9
Fiscal 2020 and thereafter	4
Finite-Lived Intangible Assets, Net	$ 11.2

Credit Facilities - Number of C

Credit Facilities - Number of Credit Facilities (Details)	Mar. 31, 2018
Number of credit facilities	4

Credit Facilities - Credit Faci

Credit Facilities - Credit Facilities (Details) - USD ($) $ in Millions	Mar. 31, 2018	Sep. 30, 2017
Line of Credit Facility [Line Items]
Short-term Debt	$ 290.9	$ 194.2
Lenders under loans	340.5	230.2
Notes Payable to Bank	1.6	2
Debt and Capital Lease Obligations	340.5	230.2
Main line of credit facilities [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	362
Line of Credit Facility, Maximum Borrowing Capacity	594.5
IFFI Uncommitted Lines of Credit [Member] [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	0
Lenders under loans	48	34
HCO Syndicated line of credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	262
Lenders under loans	143.4	150
FCS Margin line of credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	75
Line of Credit Facility, Maximum Borrowing Capacity	75
Lenders under loans	9.5	0
Sterne, Agee, and Leach [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	100
Lenders under loans	0	11
FMS Sub-note commodity line of credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	232.5
Lenders under loans	138	44.2
INTL FCStone Ltd [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	25
Line of Credit Facility, Maximum Borrowing Capacity	25
Lenders under loans	0	0
IFL Uncommitted Line of Credit [Member] [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	0
Lenders under loans	$ 0	$ 0

Commodity and Other Repurchas64

Commodity and Other Repurchase Agreements Commodity and Other Repurchase Agreements (Details) - USD ($) $ in Millions	Mar. 31, 2018	Sep. 30, 2017
Financing Receivable, Gross	$ 2.2	$ 0.8
Fair Value of Securities Received as Collateral that Can be Resold or Repledged	1,320.2
Fair Value of Securities Received as Collateral that Have Been Resold or Repledged	496.3
Financial Instruments Owned and Pledged as Collateral, Amount Eligible to be Repledged by Counterparty	5.1
Securities Loaned, Fair Value of Collateral	547.9
Securities Sold under Agreements to Repurchase, Fair Value of Collateral	5.1	$ 19.4
Trading Securities Pledged as Collateral	1,485.1
Pledged Financial Instruments, Not Separately Reported, Securities for Repurchase Agreements	$ 111.4

Commodity and Other Repurchas65

Commodity and Other Repurchase Agreements and Collateralized Transactions Gross Financings Collateral Maturities Table (Details) - USD ($) $ in Millions	Mar. 31, 2018	Sep. 30, 2017
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	$ 1,562.5	$ 1,393.1
Securities Loaned	559.1	111.1
Collateralized transactions:	2,121.6	1,504.2
Maturity Overnight and on Demand [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	797.7	640.2
Securities Loaned	559.1	111.1
Collateralized transactions:	1,356.8	751.3
Maturity Less than 30 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	464.3	432.9
Securities Loaned	0	0
Collateralized transactions:	464.3	432.9
Maturity 30 to 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	280.5	320
Securities Loaned	0	0
Collateralized transactions:	280.5	320
Maturity Greater than 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	20	0
Securities Loaned	0	0
Collateralized transactions:	$ 20	$ 0

Commodity and Other Repurchas66

Commodity and Other Repurchase Agreements and Collateralized Transactions Gross Collateralized Financings by Collateral Type Table (Details) - USD ($) $ in Millions	Mar. 31, 2018	Sep. 30, 2017
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	$ 1,562.5	$ 1,393.1
Securities Loaned	559.1	111.1
Collateralized transactions:	2,121.6	1,504.2
US Government Debt Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	5.1	7
US Government Agencies Debt Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	358.1	332.6
Asset-backed Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	75	36.4
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	1,124.3	1,017.1
Equity Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned	$ 559.1	$ 111.1

Commitments and Contingencies C

Commitments and Contingencies Commitments and Contingencies - Contingencies and Litigation (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Mar. 31, 2018
Excess segregated funds invested		$ 15.5
Pre and Post Transfers of Funds - Sentinel		$ 21.9
Litigation Settlement, Amount Awarded from Other Party	$ 1.9

Commitments and Contingencies68

Commitments and Contingencies Commitments and Contingencies - Self Insurance (Details) $ in Millions	Mar. 31, 2018USD ($)
Commitments and Contingencies [Abstract]
Self Insurance Reserve	$ 0.8

Capital and Other Regulatory 69

Capital and Other Regulatory Requirements - Regulatory Capital Requirements (Details) $ in Millions	Mar. 31, 2018USD ($)
FCStone LLC [Member]
Net Capital under Commodity Exchange Act Computation	$ 152.3
Required Net Capital under Commodity Exchange Act	83.6
Cash and Securities Segregated under Commodity Exchange Act Regulation	2,357.1
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	2,303.2
Secured Funds	144
Secured Funds Required Under Commodity Exchange Act	128.3
Sterne Agee Clearing, Inc. [Member]
Net Capital under Commodity Exchange Act Computation	1.9
Required Net Capital under Commodity Exchange Act	0.1
Sterne Agee, and Leach, Inc [Member]
Net Capital under Commodity Exchange Act Computation	3.9
Required Net Capital under Commodity Exchange Act	0.4
INTL FCStone Ltd [Member]
Net Capital under Commodity Exchange Act Computation	193.6
Required Net Capital under Commodity Exchange Act	90.3
Cash and Securities Segregated under Commodity Exchange Act Regulation	183.4
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	183.4
INTL Netherlands BV [Member]
Net Capital under Commodity Exchange Act Computation	192.9
Required Net Capital under Commodity Exchange Act	90.3
INTL FCStone DTVM Ltda [Member]
Net Capital	12.9
Capital Required for Capital Adequacy	2.3
Gainvest S.A. Sociedad Gerente de FCI - Comision Nacional de Valores [Member]
Net Capital under Commodity Exchange Act Computation	2.8
Required Net Capital under Commodity Exchange Act	0.1
Net Capital	4.8
Capital Required for Capital Adequacy	0.1
INTL Capital S.A. – General Inspector of Justice [Member] [Domain]
Net Capital under Commodity Exchange Act Computation	5.2
Required Net Capital under Commodity Exchange Act	0.8
INTL Capital S.A. – Superintendence of Securities Markets of Buenos Aires [Member] [Domain]
Net Capital under Commodity Exchange Act Computation	1.1
Required Net Capital under Commodity Exchange Act	0.4
Customer Reserve Requirement [Member] [Member]
Cash Reserve Deposit Required and Made	0.7
Cash Reserve Deposit Required	0
PAB Reserve Requirement [Member]
Cash Reserve Deposit Required and Made	5.5
Cash Reserve Deposit Required	$ 2.7

Other Expenses - Other Expenses

Other Expenses - Other Expenses Breakout (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017
Other Expenses [Abstract]
Accretion Expense	$ 0	$ 0.1	$ 0	$ 0.1
General Insurance Expense	0.6	0.8	1.2	1.3
Advertising Expense	3.4	1.2	4.3	2.1
Supplies and Postage Expense	0.4	0.5	0.8	1.1
Clearance Fees	0.5	0.3	1	0.7
Taxes, Miscellaneous	1.3	1.2	2.5	2.3
Other Expenses	2.5	2.5	4.6	4.6
Other Cost and Expense, Operating	$ 8.7	$ 6.6	$ 14.4	$ 12.2

Accumulated Other Comprehensi71

Accumulated Other Comprehensive Income (Loss) Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	$ (28.3)		$ (28.3)		$ (24.5)
Other comprehensive loss	(1.6)	$ 0.7	(3.8)	$ (0.2)
Accumulated Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	(25.3)		(25.3)		(21.5)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			(3.8)
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	(3)		(3)		(3)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			0
Accumulated Other Comprehensive Loss [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	$ (28.3)		(28.3)		$ (24.5)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			(3.8)
Other comprehensive loss			$ (3.8)

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended		12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent				0.60%
Deferred Tax Assets, Valuation Allowance	$ 4.5			$ 4.5			$ 4	$ 3.6
Income (Loss) from Continuing Operations before Income Taxes, Domestic							$ (24.7)	$ (9.7)	$ 16.5
Deferred Tax Liabilities, Net	3.3			3.3
Deferred Tax Liabilities, Unrealized Gains on Trading Securities	2.2			2.2
Income Tax Expense (Benefit)	$ 6.8		$ 3.3	$ 32.3	$ 5.4
Effective Income Tax Rate Reconciliation, Percent	23.00%			67.00%	24.00%
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount	$ 0.8			$ 20.1
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Percent	2.80%			42.00%
Deferred Income Tax Expense (Benefit)	$ 0.1	$ 8.9		$ 8.8
Effective Income Tax Rate Reconciliation, Repatriation of Foreign Earnings, Amount	$ 0.7	$ 12		$ 11.3
Scenario, Plan [Member]
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate						24.50%

Segment Analysis (Details)

Segment Analysis (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Sep. 30, 2017
Segment Reporting Information [Line Items]
Revenues	$ 6,507	$ 5,460.8	$ 14,425.6	$ 11,535.2
Operating revenues	260.2	195.8	472.8	381.3
Net operating revenues	154.3	123.9	284.6	238.2
Net Segment Contribution	115.9	97.2	214.7	190.6
Segment Income	72.2	53.9	130.5	104.1
Costs not allocated to operating segments	42.7	39.6	82.4	81.4
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Extraordinary Items, Noncontrolling Interest	29.5	14.3	48.1	22.7
Assets	7,203.7		7,203.7		$ 6,243.4
Commercial Hedging [Member]
Segment Reporting Information [Line Items]
Revenues	78.3	62.7	139.8	120.2
Operating revenues	78.3	62.7	139.8	120.2
Net operating revenues	61.9	50.5	111	96.1
Net Segment Contribution	44.7	36.9	81.2	70.3
Segment Income	27.6	18.7	48.7	34.1
Assets	1,636.1		1,636.1		1,650.3
Global Payments [Member]
Segment Reporting Information [Line Items]
Revenues	23.4	21.5	48	44.6
Operating revenues	23.4	21.5	48	44.6
Net operating revenues	21.9	19.1	44.9	39.7
Net Segment Contribution	17.6	15.3	36	31.7
Segment Income	13.5	11.7	28.1	24.9
Assets	208.8		208.8		199.5
Securities Segment [Member]
Segment Reporting Information [Line Items]
Revenues	55.5	37.9	98.5	75.3
Operating revenues	55.5	37.9	98.5	75.3
Net operating revenues	27.6	24.1	51.1	49.2
Net Segment Contribution	20.3	18.9	38.1	38.7
Segment Income	12.8	11.7	23.8	24.6
Assets	2,901.3		2,901.3		2,101.7
Physical Commodities [Member]
Segment Reporting Information [Line Items]
Revenues	6,262.3	5,276.2	13,978.9	11,174.9
Operating revenues	15.5	11.2	26.1	21
Net operating revenues	12.5	9	20.9	17.1
Net Segment Contribution	9.4	6.5	15	12.3
Segment Income	5.6	3.9	6.7	6.9
Assets	378		378		339.5
Clearing and Execution Services Segment [Member]
Segment Reporting Information [Line Items]
Revenues	88	64.2	160.2	127.8
Operating revenues	88	64.2	160.2	127.8
Net operating revenues	31.8	25.4	59.2	49.5
Net Segment Contribution	23.9	19.6	44.4	37.6
Segment Income	12.7	7.9	23.2	13.6
Assets	1,996.5		1,996.5		1,818.9
Corporate [Member]
Segment Reporting Information [Line Items]
Revenues	(0.5)	(1.7)	0.2	(7.6)
Operating revenues	(0.5)	(1.7)	0.2	(7.6)
Net operating revenues	(1.4)	$ (4.2)	(2.5)	$ (13.4)
Assets	$ 83		$ 83		$ 133.5