StoneX (SNEX) 10-K 14 Dec 17 2017 FY Annual report Financial data

DEI Document

DEI Document - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Dec. 12, 2017	Mar. 31, 2017
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-K
Document Period End Date	Sep. 30, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Common Stock, Shares Outstanding		18,766,085
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 496.2

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
ASSETS
Cash and cash equivalents	$ 314.9	$ 316.2
Cash, securities and other assets segregated under federal and other regulations (including $54.5 and $618.8 at fair value at September 30, 2017 and September 30, 2016, respectively)	518.8	1,136.3
Securities purchased under agreements to resell	406.6	609.6
Securities Borrowed	86.6	0
Deposits with and receivables from broker-dealers, clearing organizations and counterparties (including $204.7 and $853.3 at fair value at September 30, 2017 and September 30, 2016, respectively)	2,625.1	1,761.4
Receivables from customers, net	232.7	194.5
Notes receivable, net	10.6	18.9
Income taxes receivable	0.4	1.1
Financial instruments owned, at fair value (includes securities pledged as collateral that can be sold or repledged of $19.4 and $47.2 at September 30, 2017 and September 30, 2016, respectively)	1,731.8	1,606.1
Physical commodities inventory (including $73.2 and $71.2 at fair value at September 30, 2017 and September 30, 2016, respectively)	124.8	123.8
Deferred income taxes, net	42.6	34.5
Property and equipment, net	38.7	29.4
Goodwill and intangible assets, net	59.4	56.6
Other assets	50.4	61.9
Total assets	6,243.4	5,950.3
Liabilities:
Accounts payable and other accrued liabilities (including $1.0 and $0.8 at fair value at September 30, 2017 and September 30, 2016)	135.6	161.3
Payable to:
Customers	3,072.9	2,854.2
Broker-dealers, clearing organizations and counterparties (including $4.8 and $3.5 at fair value at September 30, 2017 and September 30, 2016, respectively)	125.7	260.1
Lenders under loans	230.2	182.8
Senior unsecured notes	0	44.5
Income taxes payable	7.3	7.1
Securities sold under agreements to repurchase	1,393.1	1,167.1
Securities Loaned	111.1	0
Financial instruments sold, not yet purchased, at fair value	717.6	839.4
Total liabilities	5,793.5	5,516.5
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; 20,855,243 issued and 18,733,286 outstanding at September 30, 2017 and 20,557,175 issued and 18,435,218 outstanding at September 30, 2016	0.2	0.2
Common stock in treasury, at cost - 2,121,957 shares at September 30, 2017 and 2016	(46.3)	(46.3)
Additional paid-in capital	259	249.4
Retained earnings	261.5	255.1
Accumulated other comprehensive loss, net	(24.5)	(24.6)
Total stockholders' equity	449.9	433.8
Total liabilities and stockholders' equity	$ 6,243.4	$ 5,950.3

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
ASSETS
Securities and other assets segregated, fair value	$ 54.5	$ 618.8
Deposits and receivables from bds and counterparties at fair value	204.7	853.3
Physical commodities inventory at fair value	73.2	71.2
Securities Sold under Agreements to Repurchase, Fair Value of Collateral	19.4	47.2
Accounts pay and other accrued - fair value	1	0.8
Payables to b/ds and counterparties at fair value	$ 4.8	$ 3.5
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	20,855,243	20,557,175
Common stock - outstanding	18,733,286	18,435,218
Treasury stock - shares	2,121,957	2,121,957

Consolidated Income Statements

Consolidated Income Statements - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Revenues:
Sales of physical commodities	$ 28,673.3	$ 14,112	$ 34,089.9
Trading gains, net	332.2	321.2	328.6
Commission and clearing fees	283.4	224.3	192.5
Consulting, management, and account fees	64.8	42	42.5
Interest income	69.7	55.2	39.4
Other Income	0.2	0.2	0.3
Total revenues	29,423.6	14,754.9	34,693.2
Cost of sales of physical commodities	28,639.6	14,083.9	34,068.9
Operating revenues	784	671	624.3
Transaction-based clearing expenses	136.3	129.9	122.7
Introducing broker commissions	113	68.9	52.7
Interest expense	42.1	28.3	17.1
Net operating revenues	492.6	443.9	431.8
Compensation and other expenses:
Compensation and benefits	295.7	263.9	251.1
Communication and data services	39.4	32.7	28.1
Occupancy and equipment rental	15.2	13.3	13.5
Professional fees	15.2	14	12.5
Travel and business development	13.3	11.5	10.5
Depreciation and amortization	9.8	8.2	7.2
Bad debts	4.3	4.4	7.3
Provision for bad debt on physical coal	47	0	0
Other	37.5	29.4	23.5
Total compensation and other expenses	477.4	377.4	353.7
Gain on acquisition	0	6.2	0
Income from operations, before tax	15.2	72.7	78.1
Income tax expense	8.8	18	22.4
Net Income	$ 6.4	$ 54.7	$ 55.7
Basic earnings per share:
Net income per common share	$ 0.32	$ 2.94	$ 2.94
Diluted earnings per share:
Net income per common share	$ 0.31	$ 2.90	$ 2.87
Weighted-average number of common shares outstanding:
Basic	18,395,987	18,410,561	18,525,374
Diluted	18,687,354	18,625,372	18,932,235

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income Statement - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 6.4	$ 54.7	$ 55.7
Other comprehensive income (loss), net of tax [Abstract]
Foreign currency translation adjustment	(1.4)	(7.4)	(4)
Pension liabilities adjustment	1.2	(0.2)	(1.5)
Net unrealized gain on available-for-sale securities	0	0	2.7
Reclassification of adjustment for losses (gains) included in net income:
Periodic pension costs (included in compensation and benefits)	0.4	0.5	0.3
Realized gain on available-for-sale securities (included in trading gains, net and interest income)	0	0	(5.4)
Income tax expense from reclassification adjustments (included in income tax expense)	(0.1)	0	2
Reclassification adjustment for losses (gains) included in net income	0.3	0.5	(3.1)
Other comprehensive income (loss)	0.1	(7.1)	(5.9)
Comprehensive income	$ 6.5	$ 47.6	$ 49.8

Consolidated Cash Flows Stateme

Consolidated Cash Flows Statements - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Cash flows from operating activities:
Net income	$ 6.4	$ 54.7	$ 55.7
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for bad debt on physical coal	47	0	0
Depreciation and amortization	9.8	7.8	7.2
Provision for bad debts	4.3	4.4	7.3
Deferred income taxes	(9.8)	(0.8)	4.8
Amortization and extinguishment of debt issuance costs	1.9	1.1	0.9
Actuarial gain on pension and postretirement benefits	(0.3)	0	0
Amortization of share-based compensation expense	6.3	5.1	3.6
(Gain) loss on sale of property and equipment	(0.3)	0.4	0.5
Gain on acquisition	0	(6.2)	0
Gain on sale of exchange memberships and common stock	0	0	(1.2)
Changes in operating assets and liabilities, net:
Cash, securities and other assets segregated under federal and other regulations	622.7	(379.9)	(315)
Change in securities purchased under agreements to resell	203	(285.1)	15.2
Securities borrowed	(79.7)	0	0
Deposits and receivables from broker-dealers, clearing organizations, and counterparties	(889.1)	146.6	44.9
Receivable from customers, net	(116.4)	97.8	(169)
Notes receivable, net	8.3	59.5	(14.5)
Income taxes receivable	0.5	8.2	0
Financial instruments owned, at fair value	(125.6)	(192.9)	(565)
Physical commodities inventory	(1.7)	(91)	7.1
Other assets	(16)	(17.4)	(16.2)
Accounts payable and other accrued liabilities	(19.6)	7.5	23.2
Payable to customers	290.9	172.2	332.1
Payable to broker-dealers, clearing organizations and counterparties	(124.1)	(53.8)	251.1
Income taxes payable	0.2	0.3	1.7
Securities sold under agreements to repurchase	226	159.8	186
Securities loaned	93.6	0	0
Financial instruments sold, not yet purchased, at fair value	(124.4)	273.9	177.5
Net cash provided by (used in) provided by operating activities	13.9	(27.8)	37.9
Cash flows from investing activities:
Cash paid for acquisitions, net	(6)	(20)	(7.8)
Purchase of exchange memberships and common stock	(0.2)	(0.1)	(0.7)
Sale of exchange memberships and common stock	0	0	2.1
Purchase of property and equipment	(16.1)	(15.4)	(9.1)
Net cash used in investing activities	(22.3)	(35.5)	(15.5)
Cash flows from financing activities:
Net change in payable to lenders under loans	48.2	142	15.5
Payments related to earn-outs on acquisitions	0	(2.9)	(2.2)
Repayment of senior unsecured notes	(45.5)	0	0
Proceeds from notes payable	0	0	4
Repayment of note payable	0.8	0.8	0.4
Share repurchase	0	(19.5)	(4.7)
Debt issuance costs	(0.3)	(2.1)	(0.2)
Exercise of stock options	3.4	3.5	2.5
Income tax benefit on stock options and awards	0.7	0.8	0.5
Net cash provided by financing activities	5.7	121	15
Effect of exchange rates on cash and cash equivalents	1.4	(9.6)	(0.6)
Net increase in cash and cash equivalents	(1.3)	48.1	36.8
Cash and cash equivalents at beginning of period	316.2	268.1	231.3
Cash and cash equivalents at end of period	314.9	316.2	268.1
Supplemental disclosure of cash flow information:
Cash paid for interest	38	26	15.8
Income taxes paid, net of cash refunds	17.1	8.5	15.3
Supplemental disclosure of non-cash investing and financing activities:
Identified intangible assets and goodwill on acquisitions	0	0	1.6
Additional consideration payable related to acquisitions	(0.2)	(0.4)	1.9
Acquisition of business:
Assets acquired	0	187.1	1,011.4
Liabilities acquired	0	(136)	(995.1)
Total net assets acquired	0	51.1	16.3
Deferred consideration payable related to acquisitions	0	0	5
Escrow releases and deposits related to acquisitions	$ (5)
Escrow deposits related to acquisitions		$ 3.4	$ 5

Consolidated Statements of Shar

Consolidated Statements of Shareholders’ Equity - USD ($) $ in Millions	Total	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	Treasury Stock, Common [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]
Balances at beginning of period at Sep. 30, 2014	$ 345.4	$ 0.2	$ (17.5)	$ 229.6		$ 144.7	$ (11.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	55.7					55.7
Other comprehensive loss	(5.9)						(5.9)
Excercise of stock options	3			3
Share-based compensation	3.6			3.6
Repurchase of stock	(4.7)		(4.5)
Repurchase of stock - adjustments to APIC				(0.2)
Stock held in escrow for business combination				4.8	$ (4.8)
Balances at end of period at Sep. 30, 2015	397.1	0.2	(26.8)	240.8		200.4	(17.5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	54.7					54.7
Other comprehensive loss	(7.1)						(7.1)
Excercise of stock options	3.5			3.5
Share-based compensation	5.1			5.1
Repurchase of stock	(19.5)		(19.5)
Repurchase of stock - adjustments to APIC				0
Balances at end of period at Sep. 30, 2016	433.8	0.2	(46.3)	249.4		255.1	(24.6)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	6.4					6.4
Other comprehensive loss	0.1						0.1
Excercise of stock options	3.3			3.3
Share-based compensation	6.3			6.3
Balances at end of period at Sep. 30, 2017	$ 449.9	$ 0.2	$ (46.3)	$ 259		$ 261.5	$ (24.5)

Description of Business and Sig

Description of Business and Significant Accounting Policies (Notes)	12 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Business Description and Accounting Policies [Text Block]	Description of Business and Significant Accounting Policies INTL FCStone Inc. , a Delaware corporation, and its consolidated subsidiaries (collectively “INTL” or “the Company”), is a diversified global financial services organization providing execution, risk management and advisory services, market intelligence, and clearing services across assets classes and markets around the world. The Company’s services include comprehensive risk management advisory services for commercial customers; clearing and execution of debt and equity securities, listed futures and options on futures contracts on all major securities and commodity exchanges; structured over-the-counter (“OTC”) products in a wide range of commodities; physical trading and hedging of precious and base 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 customers in 130 countries located throughout the world, including producers, processors and end-users of nearly all widely-traded physical commodities to manage their risks and enhance margins; to commercial counterparties who are end-users of the firm’s products and services; to governmental and non-governmental organizations; and to commercial banks, brokers, institutional investors and major investment banks. Basis of Presentation The accompanying 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. Unless otherwise stated herein, all references to fiscal 2017 , fiscal 2016 , and fiscal 2015 refer to the Company’s fiscal years ended September 30. In the 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 consolidated income statements is calculated by deducting physical commodities cost of sales from total revenues. The subtotal ‘net operating revenues’ in the 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 our 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. Use of Estimates The preparation of consolidated financial statements in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent liabilities as of the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. The most significant of these estimates and assumptions relate to fair value measurements for financial instruments and investments, revenue recognition, the provision for potential losses from bad debts, valuation of inventories, valuation of goodwill and intangible assets, self-insurance liabilities, incomes taxes and contingencies. These estimates are based on management’s best knowledge of current events and actions the Company may undertake in the future. The Company reviews all significant estimates affecting the financial statements on a recurring basis and records the effect of any necessary adjustments prior to their issuance. Although these and other estimates and assumptions are based on the best available information, actual results could be materially different from these estimates. Internal Subsidiaries Consolidation Effective July 1, 2017, we merged our wholly-owned regulated United States (“U.S.”) subsidiary, Sterne Agee & Leach, Inc., into our wholly owned regulated U.S. subsidiary, INTL FCStone Financial Inc. (“INTL FCStone Financial”). As such, the assets, liabilities and equity of Sterne Agee & Leach, Inc. were transferred into INTL FCStone Financial. Effective July 1, 2015, the Company merged three of its wholly-owned regulated U.S. subsidiaries into its wholly owned regulated U.S. subsidiary, INTL FCStone Securities Inc., and the surviving entity was renamed INTL FCStone Financial Inc. and is registered as both a broker-dealer and a futures commission merchant (“FCM”). As such, the assets, liabilities and equity of FCStone, LLC, INTL FCStone Partners L.P., and FCC Investments, Inc. were transferred into INTL FCStone Financial. Foreign Currency Translation Assets and liabilities recorded in foreign currencies are translated at the exchange rates prevailing on the balance sheet date. Revenue and expenses are translated at average rates of exchange prevailing during the period. Gains or losses on translation of the financial statements of a non-U.S. operation, when the functional currency is other than the U.S. dollar, are recorded in other comprehensive income (“OCI”), net of tax, a component of stockholders’ equity. Foreign currency remeasurement gains or losses on transactions denominated in nonfunctional currencies are included in ‘trading gains, net’ in the consolidated income statements. Cash and Cash Equivalents The Company considers cash held at banks and all highly liquid investments with original or acquired maturities of 90 days or less, including certificates of deposit, which may be withdrawn at any time at the discretion of the Company without penalty, to be cash and cash equivalents. Cash and cash equivalents consist of cash, foreign currency, money market funds and certificates of deposit not deposited with or pledged to exchange-clearing organizations, broker-dealers, clearing organizations or counterparties. The money market funds are valued at period-end at the net asset value provided by the fund’s administrator, which approximates fair value. Certificates of deposit are stated at cost plus accrued interest, which approximates fair value. The Company has an investment policy, which limits the maximum amount placed in any one fund and with any one institution in order to reduce credit risk. The Company does not believe that it is exposed to significant risk on cash and cash equivalents. Cash, Securities and Other Assets Segregated under Federal and other Regulations Pursuant to requirements of the Commodity Exchange Act in the U.S. and similarly in the United Kingdom (“U.K.”), pursuant to the Markets in Financial Instruments Implementing Directive 2006/73/EC underpinning the Client Asset or ‘CASS’ rules in the Financial Services Authority (“FSA”) handbook, funds deposited by customers relating to futures and options on futures contracts in regulated commodities must be carried in separate accounts which are designated as segregated customer accounts. The deposits in segregated customer accounts are not commingled with the funds of the Company. Under the FSA’s rules, certain categories of customers may choose to opt-out of segregation. As of September 30, 2017 and 2016 , cash, securities and other assets segregated under federal and other regulations consisted of cash held at banks and money market funds of approximately $464.3 million and $515.2 million , respectively, U.S. Treasury securities and U.S. government agency obligations of approximately $33.5 million and $595.5 million , respectively, and commodities warehouse receipts of approximately $21.0 million and $23.3 million , respectively (see fair value measurements discussion in Note 4 ). Securities Purchased/Sold Under Agreements to Resell/Repurchase The Company enters into securities purchased under agreements to resell (reverse repurchase agreements) and securities sold under agreements to repurchase (repurchase agreements) primarily to finance financial instruments, acquire securities to cover short positions or to acquire securities for settlement. Reverse repurchase agreements and repurchase agreements are treated as collateralized financing transactions and are recorded at their contractual amounts plus accrued interest. The related interest is recorded in the 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, or may be required by 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. Securities Borrowed and Loaned The Company enters into securities borrowed and securities loaned transactions. Securities borrowed and securities loaned are reported as collateralized financings. Securities borrowed and securities loaned transactions are recorded at the amount of cash collateral advanced or received. The Company receives collateral generally in excess of the market value of securities loaned. The Company monitors the market value of securities borrowed and loaned on a daily basis, with additional collateral obtained or refunded as necessary. Securities borrowed and securities loaned are reported on a gross basis. Interest income and interest expense are recognized over the life of the arrangements. Deposits with and Receivables from Broker-dealers, Clearing Organizations and Counterparties, and Payables to Broker-dealers, Clearing Organizations and Counterparties As required by the regulations of the U.S. Commodity Futures Trading Commission (“CFTC”) and the aforementioned FSA handbook, customer funds received to margin, guarantee, and/or secure commodity futures transactions are segregated and accounted for separately from the general assets of the Company. Deposits with exchange-clearing organizations, broker-dealers and counterparties pertain primarily to deposits made to satisfy margin requirements on customer and proprietary open futures and options on futures positions and to satisfy the requirements set by clearing exchanges for clearing membership. The Company also pledges margin deposits with various counterparties for OTC derivative contracts, and these deposits are also included in deposits and receivables from broker-dealers and counterparties. Deposits with and receivables from exchange-clearing organizations and broker-dealers and counterparties are reported gross, except where a right of offset exists. As of September 30, 2017 and 2016 , the Company had cash and cash equivalents on deposit with or pledged to exchange-clearing organizations, broker-dealers and counterparties of $2.3 billion and $0.9 billion , respectively. These balances also include securities pledged by the Company on behalf of customers and customer-owned securities that are pledged. It is the Company’s practice to include customer owned securities on its consolidated balance sheets, as the rights to those securities have been transferred to the Company under the terms of the futures trading agreement. Securities pledged include U.S. Treasury bills and instruments backed by U.S. government sponsored entities. Securities that are not customer-owned are adjusted to fair value with associated changes in unrealized gains or losses recorded through current period earnings. For customer owned securities, the change in fair value is offset against the payable to customers with no impact recognized in the consolidated income statements. The securities, primarily U.S. Treasury securities, held by INTL FCStone Financial, a subsidiary of the Company, as collateral or as margin have been deposited with exchange-clearing organizations, broker-dealers or other counterparties. The fair value of these securities was approximately $251.4 million and $471.7 million as of September 30, 2017 and 2016 , respectively. Management has considered guidance required by the Transfers and Servicing Topic of the ASC as it relates to securities pledged by customers to margin their accounts within the FCM Division of INTL FCStone Financial. Based on a review of the agreements with the customer, management believes the transferor surrenders control over those assets because: (a) the transferred assets have been isolated from the transferor—put presumptively beyond the reach of the transferor and its creditors, even in bankruptcy or other receivership, (b) each transferee has the right to pledge or exchange the assets (or beneficial interests) it received, and no condition both constrains the transferee (or holder) from taking advantage of its right to pledge or exchange and provides more than a trivial benefit to the transferor and (c) the transferor does not maintain effective control over the transferred assets through either (1) an agreement that both entitles and obligates the transferor to repurchase or redeem them before their maturity or (2) the ability to unilaterally cause the holder to return specific assets, other than through a cleanup call. Under this guidance, the Company reflects the customer collateral assets and corresponding liabilities in the Company’s consolidated balance sheets as of September 30, 2017 and 2016 . In addition to margin, deposits with exchange-clearing organizations include guaranty deposits. The guaranty deposits are held by the clearing organization for use in potential default situations by one or more members of the clearing organization. The guaranty deposits may be applied to the Company’s obligations to the clearing organization, or to the clearing organization’s obligations to other clearing members or third parties. The Company maintains customer omnibus and proprietary accounts with other counterparties, and the equity balances in those accounts along with any margin cash or securities deposited with the carrying broker are included in deposits and receivables from broker-dealers and counterparties. Receivables from and payables to exchange-clearing organizations are also comprised of amounts due from or due to exchange-clearing organizations for daily variation settlements on open futures and options on futures positions. The variation settlements due from or due to exchange-clearing organizations are paid in cash on the following business day. Deposits and receivables from broker-dealers, clearing organizations and counterparties, and payables to broker-dealers, clearing organizations and counterparties also include amounts related to the value of customers cross-currency payment transactions related to the Global Payments segment. These amounts arise due to a clearing period before the funds are received and payments are made, which usually is one to two business days. Deposits and receivables with exchange-clearing organizations also includes the unrealized gains and losses associated with the customers’ options on futures contracts. See discussion in the Financial Instruments and Derivatives section below for additional information on the treatment of derivative contracts. For customer owned derivative contracts, the fair value is offset against the payable to customers with no impact recognized on the consolidated income statements. Receivable from and Payable to Customers Receivable from customers, net of the allowance for doubtful accounts, include the total of net deficits in individual exchange-traded and OTC trading accounts carried by the Company. Customer deficits arise from realized and unrealized trading losses on futures, options on futures, swaps and forwards and amounts due on cash and margin transactions. Customer deficit accounts are reported gross of customer accounts that contain net credit or positive balances, except where a right of offset exists. Net deficits in individual exchange-traded and OTC trading accounts include both secured and unsecured deficit balances due from customers as of the balance sheet date. Secured deficit amounts are backed by U.S. Treasury bills and notes and commodity warehouse receipts. These U.S Treasury bills and notes and commodity warehouse receipts are not netted against the secured deficit amounts, as the conditions for right of setoff have not been met. Receivables from customers, net also includes the net amounts receivable from securities customers in connection with the settlement of normal cash securities, margin loans to customers, and customer cash debits. It is the Company’s policy to report margin loans and payables that arise due to positive cash flows in the same customer’s accounts on a net basis when the conditions for netting as specified in GAAP are met. Customers’ securities transactions cleared by the Company are recorded on a settlement date. Securities owned by customers including those that collateralize margin or other similar transactions, are not reflected on the statement of financial condition as the Company does not have title to those assets. In the event of uncompleted transactions on settlement date, the Company recorded corresponding receivables and payables, respectively. The carrying value of the receivables and payables approximates fair value due to their short-term nature. Payable to customers represent the total of customer accounts with credit or positive balances. Customer accounts are used primarily in connection with commodity transactions and include gains and losses on open commodity trades as well as securities and other deposits made as required by the Company, the exchange-clearing organizations or other clearing organizations. Customer accounts with credit or positive balances are reported gross of customer deficit accounts, except where a right of offset exists. Receivables from and payables to customers also include amounts related to the value of customers cross-currency payment transactions related to the Global Payments segment. These amounts arise due to a clearing period before the funds are received and payments are made, which usually is one to two business days. The future collectability of the receivable from customers can be impacted by the Company’s collection efforts, the financial stability of its customers, and the general economic climate in which it operates. The Company evaluates accounts that it believes may become uncollectible on a specific identification basis, through reviewing daily margin deficit reports, the historical daily aging of the receivables, and by monitoring the financial strength of its customers. The Company may unilaterally close customer trading positions in certain circumstances. In addition, to evaluate customer margining and collateral requirements, customer positions are stress tested regularly and monitored for excessive concentration levels relative to the overall market size. The Company generally charges off an outstanding receivable balance when all economically sensible means of recovery have been exhausted. That determination considers information such as the occurrence of significant changes in the customer’s financial position such that the customer can no longer pay the obligation, or that the proceeds from collateral will not be sufficient to pay the balance. Notes Receivable The Company originates short-term notes receivable from customers with the outstanding balances typically being insured 90% to 98% by a third party, including accrued interest, subject to applicable deductible amounts. The Company may sell the insured portion of the notes through non-recourse participation agreements with other third parties. See discussion of notes receivable related to commodity repurchase agreements below. Accrual of commodity financing income on any note is discontinued when, in the opinion of management, there is reasonable doubt as to the timely collectability of interest or principal. Nonaccrual notes are returned to an accrual status when, in the opinion of management, the financial position of the borrower indicates there is no longer any reasonable doubt as to the timely payment of principal and interest. The Company records a charge against earnings for notes receivable losses when management believes that collectability of the principal is unlikely. Physical Commodities Inventory Inventories of certain agricultural commodities are carried at net realizable value, which approximates fair value less disposal costs. The agricultural commodities inventories have reliable, readily determinable and realizable market prices, have relatively predictable and insignificant costs of disposal and are available for immediate delivery. Changes in the fair values of these agricultural commodities inventories are included as a component of ‘cost of physical commodities sold’ in the consolidated income statements. Inventories of energy, including coal, kerosene, and propane are valued at the lower of cost or market (“LCM”). Inventories of precious metals held by our subsidiaries that are not broker-dealers are valued at the LCM, using the weighted-average price and first-in first-out costing method. Precious metals inventory held by 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’ in the consolidated income statements. INTL FCStone Ltd is regulated by the Financial Conduct Authority (“FCA”), the regulator of the financial services industry in the United Kingdom. Property and Equipment Property and equipment is stated at cost, net of accumulated depreciation and amortization and depreciated using the straight-line method over the estimated useful lives of the assets. Leasehold improvements are amortized on a straight-line basis over the estimated useful life of the improvement or the term of the lease, whichever is shorter. Certain costs of software developed or obtained for internal use are capitalized and amortized over the estimated useful life of the software. Expenditures for maintenance, repairs, and minor replacements are charged against earnings, as incurred. Expenditures that increase the value or productive capacity of assets are capitalized. When property and equipment are retired, sold, or otherwise disposed of, the asset’s carrying amount and related accumulated depreciation are removed from the accounts and any gain or loss is included in earnings. Goodwill and Identifiable Intangible Assets Goodwill is the cost of acquired companies in excess of the fair value of identifiable net assets at the acquisition date. Goodwill is not subject to amortization, but rather is evaluated for impairment at least annually. The Company evaluates its goodwill for impairment at the fiscal year end (or more frequently if indicators of potential impairment exist) in accordance with the Intangibles - Goodwill and Other Topic 350 of the ASC. Goodwill impairment is determined by comparing the estimated fair value of a reporting unit with its respective carrying value. If the estimated fair value exceeds the carrying value, goodwill at the reporting unit level is not deemed to be impaired. However, if the estimated fair value is below carrying value, further analysis is required to determine the amount of the impairment. This further analysis involves assigning tangible assets and liabilities, identified intangible assets and goodwill to reporting units and comparing the fair value of each reporting unit to its carrying amount. In the course of the evaluation of the potential impairment of goodwill, the Company may perform either a qualitative or a quantitative assessment. The Company’s qualitative assessment of potential impairment may result in the determination that a quantitative impairment analysis is not necessary. Under this elective process, the Company assesses qualitative factors to determine whether the existence of events or circumstances leads us to determine that it is more likely than not that the fair value of a reporting unit is less than its carrying amount. If after assessing the totality of events or circumstances, the Company determines it is more likely than not that the fair value of a reporting unit is greater than its carrying amount, then performing a quantitative analysis is not required. However, if the Company concludes otherwise, then we perform a quantitative impairment analysis. If the Company either chooses not to perform a qualitative assessment, or the Company chooses to perform a qualitative assessment but are unable to qualitatively conclude that no impairment has occurred, then the Company performs a quantitative evaluation. In the case of a quantitative assessment, the Company estimates the fair value of the reporting unit which the goodwill that is subject to the quantitative analysis is associated (generally defined as the businesses for which financial information is available and reviewed regularly by management) and compares it to the carrying value. If the estimated fair value of a reporting unit is less than its carrying value, the Company estimates the fair value of all assets and liabilities of the reporting unit, including goodwill. If the carrying value of the reporting unit’s goodwill is greater than the estimated fair value, an impairment charge is recognized for the excess. The fair value of the Company’s reporting units exceeded their respective carrying values under the first step of the quantitative assessment and no impairment charges were recorded for any of the periods presented. Identifiable intangible assets subject to amortization are amortized using the straight-line method over their estimated period of benefit, ranging from two to twenty years. Identifiable intangible assets are tested for impairment whenever events or changes in circumstances suggest that an asset’s or asset group’s carrying value may not be fully recoverable. Residual value is presumed to be zero for all identifiable intangible assets. Financial Instruments and Derivatives Financial instruments owned and sold, not yet purchased, at fair value consist of financial instruments carried at fair value or amounts that approximate fair value, with related unrealized changes in gains or losses recognized in earnings. The fair value of a financial instrument is the amount at which the instrument could be exchanged in a current transaction between willing parties, other than in a forced or liquidation sale. The Company accounts for its securities pledged on behalf of customers and proprietary securities as trading securities in accordance with U.S. GAAP accounting requirements for broker-dealers. Investment in managed funds, at fair value represents investments in funds managed by the Company’s fund managers. The investments are valued at period-end at the net asset value provided by the fund’s administrator. Commodities warehouse receipts are valued at the cash price, or the nearby futures prices in the absence of a cash price, for the commodity based on published market quotes. For commodities warehouse receipts, the change in fair value is offset against the payable to customers with no impact on the consolidated income statements. The Company utilizes derivative instruments to manage exposures to foreign currency, commodity price and interest rate risks for the Company and its customers. The Company’s objectives for holding derivatives include reducing, eliminating, and efficiently managing the economic impact of these exposures as effectively as possible. Derivative instruments are recognized as either assets or liabilities and are measured at fair value. As the Company does not elect hedge accounting, gains and losses from the change in fair values of derivatives for which the Company acts as principal are recognized immediately in earnings. The Company’s derivative contracts consist of exchange-traded and OTC derivatives. Fair values of exchange-traded derivatives are generally determined from quoted market prices. OTC derivatives are valued using valuation models. The valuation models used to derive the fair values of OTC derivatives require inputs including contractual terms, market prices, yield curves and measurements of volatility. The Company uses similar models to value similar instruments. Where possible, the Company verifies the values produced by pricing models by comparing them to market transactions. Inputs may involve judgment where market prices are not readily available. The Company does not elect hedge accounting under the Derivatives and Hedging Topic of the ASC in accounting for derivatives used as economic hedges on its commodities. The Company’s derivative contracts also include forward purchase and sale contracts for physical delivery of the agricultural commodities in a future period. Contracts to purchase agricultural commodities generally relate to the current or future crop year. Contracts for the sale of agricultural commodities generally do not extend beyond one year. Forward purchase and sale contracts are valued at market prices when available or other market quotes adjusted for differences, primarily in transportation, between the exchange-traded market and local markets where the terms of the contracts are based. Changes in the fair value of agricultural commodity inventories held for sale, forward purchase and sale contracts and exchange-traded futures and options contracts are recognized as a component of cost of sales of physical commodities. The Company provides clearing and execution of exchange-traded futures and options on futures for middle-market intermediaries, end-users, producers of commodities and the institutional and professional trader market segments. The Company has a subsidiary that is a registered broker-dealer/FCM, clearing on various exchanges. A primary source of revenues for the Company’s broker-dealer/FCM are commissions and clearing fees derived from executing and clearing orders for commodity futures contracts and options on futures on behalf of its customers. The Company also brokers foreign exchange forwards, options and cash, or spot, transactions between customers and external counterparties. A portion of the contracts are arranged on an offsetting basis, limiting the Company’s risk to performance of the two offsetting parties. The offsetting nature of the contracts eliminates the effects of market fluctuations on the Company’s operating results. Due to the Company’s role as a principal participating in both sides of these contracts, the amounts are presented gross on the consolidated balance sheets at their respective fair values, net of offsetting assets and liabilities. The Company holds proprietary positions in its foreign exchange line of business. On a limited basis, the Company’s foreign exchange trade desk will accept a customer transaction and will offset that transaction with a similar but not identical position with a counterparty. These unmatched transactions are intended to be short-term in nature and are often conducted to facilitate the most effective transaction for the Company’s customer. These spot and forward contracts are accounted for as free-standing derivatives and reported in the consolidated balance sheets at their fair values. The Company does not seek hedge accounting treatment for these derivatives, and accordingly, the changes in fair value during the period are recorded in the consolidated income statements in ‘trading gains, net’ (see Note 5 ). In applying the guidance in the Balance Sheet-Offsetting Topic of the ASC, the Company’s accounting policy is such that open contracts with the same customer are netted at the account level, in accordance with netting arrangements in place with each party, as applicable and rights to reclaim cash collateral or obligations to return cash collateral are netted against fair value amounts recognized for derivative instruments with the same customer in accordance with the master netting arrangements in place with each customer. The Company may lease commodities to or from customers or counterparties, or advance commodities to

Bad Debt on Physical Coal Bad D

Bad Debt on Physical Coal Bad Debt on Physical Coal (Notes)	12 Months Ended
	Sep. 30, 2017
Bad Debt on Physical Coal [Abstract]
Unusual or Infrequent Items, or Both, Disclosure [Text Block]	During the fourth quarter of fiscal 2017, the Company recorded a charge to earnings of $47.0 million , to record an allowance for doubtful accounts related to a bad debt incurred in the physical coal business, conducted solely in the Company’s Singapore subsidiary, INTL Asia Pte. Ltd., with a coal supplier. Components of the bad debt on physical coal include allowances on amounts due to the Company from the supplier related to: coal paid for but not delivered to customers; reimbursement of demurrage claims, dead freight and other charges paid by INTL Asia Pte. Ltd. to its customers; reimbursement due for deficiencies in the quality of coal delivered to customers; and losses incurred related to the cancellation of open sales contracts. The Company purchased coal delivered onto barges and paid 80% of the value against bills of lading and purchase invoices, with the remaining 20% payable following inspection upon delivery to customers’ vessels. The Company took title of the coal when it was loaded onto barges and maintained title until it was offloaded onto customers’ vessels. The logistics related to the delivery of coal to the customers’ vessels was out-sourced to the Company’s coal supplier, and the Company determined that certain purchased coal was not delivered to the customers’ vessels during the fourth quarter ended September 30, 2017. Furthermore, the Company determined that the supplier was unable to deliver such purchased coal to its customers. Demurrage claims, dead freight, and other penalty charges paid by INTL Asia Pte. Ltd. to its customers were due to be reimbursed by the supplier based on transaction agreements with the supplier. Subsequent to the end of the fourth quarter ended September 30, 2017, the Company determined the supplier was unable to make this reimbursement. The Company has received an acknowledgment of debt and a note from the supplier in its first quarter ending December 31, 2017. However, there is substantial uncertainty as to whether the supplier will be able to meet its financial obligations to the Company and as to the timing of any recovery. The bad debt on physical coal is presented separately as a component of income from operations in the consolidated income statements. As of September 30, 2017, the physical coal business is part of our Physical Commodities segment and conducted solely in INTL Asia Pte. Ltd. Subsequent to September 30, 2017, the Company ceased and exited the physical coal business. All remaining open sales contracts have been canceled. During the first quarter ending December 31, 2017, the Company expects to record additional bad debt expense of $1.0 million related to reimbursement due the Company from the supplier for demurrage and other charges related to contracts with delivery dates subsequent to September 30, 2017. The Company has considered the impact of the exit of the physical coal business on the Company’s financial position, future operating results and liquidity, and believes the exit will not have a material negative impact to the consolidated financial statements, expected cash flows or liquidity of the Company. The physical coal business had not contributed significantly to income from operations. The Company has no long-lived or intangible assets related to the physical coal business, and accordingly has recorded no impairment charges. The Company believes any additional exit costs will not be material to the consolidated financial statements.

Earnings per Share (Notes)

Earnings per Share (Notes)	12 Months Ended
	Sep. 30, 2017
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 net income per share computations for the periods presented below. Year Ended September 30, (in millions, except share amounts) 2017 2016 2015 Numerator: Net income $ 6.4 $ 54.7 $ 55.7 Less: Allocation to participating securities (0.1 ) (1.0 ) (1.3 ) Net income allocated to common stockholders $ 6.3 $ 53.7 $ 54.4 Denominator: Weighted average number of: Common shares outstanding 18,395,987 18,410,561 18,525,374 Dilutive potential common shares outstanding: Share-based awards 291,367 214,811 406,861 Diluted shares outstanding 18,687,354 18,625,372 18,932,235 The dilutive effect of share-based awards is reflected in diluted net income per share by application of the treasury stock method, which includes consideration of unamortized share-based compensation expense. Options to purchase 230,135 , 910,060 and 997,459 shares of common stock for fiscal years ended September 30, 2017, 2016, and 2015 , respectively, were excluded from the calculation of diluted earnings per share because they would have been anti-dilutive.

Assets and Liabilities, at Fair

Assets and Liabilities, at Fair Value (Notes)	12 Months Ended
	Sep. 30, 2017
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 exchange 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 securities. 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 generated from prices or valuation techniques that require inputs that are 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 makers. 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 each counterparty to deposit margin collateral for all OTC instruments and is also required to deposit margin collateral with counterparties. The Company has assessed the nature of these deposits and used its discretion to adjust each based on the underlying credit considerations for the counterparty and determined that the collateral deposits minimize the exposure to counterparty credit risk in the evaluation of the fair value of OTC instruments as determined by a market participant. Fair value of financial and nonfinancial assets and liabilities that are carried on the Consolidated Balance Sheets at fair value on a recurring basis Cash and cash equivalents reported at fair value on a recurring basis includes money market funds, which are valued at period-end at the net asset value provided by the fund’s administrator, and 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 money market funds and other 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 debt obligations, U.S. Treasury obligations, U.S. government agency obligations, foreign government obligations, agency mortgage-backed obligations, asset-backed obligations, derivative financial instruments, 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, and the fair value of exchange memberships is determined by recent sale transactions. Physical commodities inventory 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 and energy 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. Cash equivalents, securities, commodities warehouse receipts, physical commodities inventory, derivative financial instruments 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, agricultural, and energy commodities, equity investments in exchange firms, mutual funds, as well as futures and options on futures contracts traded on national exchanges. The fair value of exchange memberships is determined by recent sale transactions and is included within Level 1. 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 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, OTC firm purchase and sale commitments related to precious metals commodities, and OTC firm purchase and sale commitments related to the Company’s agricultural and energy commodities. Derivatives without a quoted price in an active market and derivatives executed OTC are valued using internal valuation techniques, including pricing models which utilize significant inputs observable to market participants. The valuation techniques and inputs depend on the type of derivative and the nature of the underlying instrument. The key inputs depend upon the type of derivative and the nature of the underlying instrument and include interest yield curves, foreign exchange rates, commodity prices, volatilities and correlation. These derivative instruments are included within Level 2 of the fair value hierarchy. 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 September 30, 2017 and 2016 . 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 financial statements since that date 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 September 30, 2017 and September 30, 2016 by level in the fair value hierarchy. There were no assets or liabilities that were measured at fair value on a nonrecurring basis as of September 30, 2017 and 2016 . September 30, 2017 (in millions) Level 1 Level 2 Level 3 Netting (1) Total Assets: Certificate of deposits 3.8 — — — 3.8 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 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 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 ) — Payables 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 are included in that level. September 30, 2016 (in millions) Level 1 Level 2 Level 3 Netting (1) Total Assets: Unrestricted cash equivalents - certificates of deposits $ 7.1 $ — $ — $ — $ 7.1 Commodities warehouse receipts 23.3 — — — 23.3 U.S. government obligations — 595.5 — — 595.5 Securities and other assets segregated under federal and other regulations 23.3 595.5 — — 618.8 Money market funds 512.7 — — — 512.7 U.S. government obligations — 472.1 — — 472.1 TBA and forward settling securities — 0.3 — — 0.3 Derivatives 2,149.9 8.0 — (2,289.7 ) (131.8 ) Deposits and receivables from broker-dealers, clearing organizations and counterparties 2,662.6 480.4 — (2,289.7 ) 853.3 Common and preferred stock, ADRs, and GDRs 34.6 1.7 0.2 — 36.5 Exchangeable foreign ordinary equities, ADRs, and GDRs 25.2 0.5 — — 25.7 Corporate and municipal bonds 36.9 0.9 3.0 — 40.8 U.S. government obligations — 514.9 — — 514.9 Foreign government obligations — 14.6 — — 14.6 Mortgage-backed securities — 747.5 — — 747.5 Derivatives 206.9 1,350.8 — (1,363.8 ) 193.9 Commodities leases — 137.2 — (129.1 ) 8.1 Commodities warehouse receipts 8.9 — — — 8.9 Exchange firm common stock 6.4 — — — 6.4 Mutual funds and other 8.8 — — — 8.8 Financial instruments owned 327.7 2,768.1 3.2 (1,492.9 ) 1,606.1 Physical commodities inventory 71.2 — — — 71.2 Total assets at fair value $ 3,091.9 $ 3,844.0 $ 3.2 $ (3,782.6 ) $ 3,156.5 Liabilities: Accounts payable and other accrued liabilities - contingent liabilities $ — $ — $ 0.8 $ — $ 0.8 TBA and forward settling securities — 2.6 — 0.9 3.5 Derivatives 1,961.7 97.5 — (2,059.2 ) — Payable to broker-dealers, clearing organizations and counterparties - derivatives 1,961.7 100.1 — (2,058.3 ) 3.5 Common and preferred stock, ADRs, and GDRs 23.5 0.4 — — 23.9 Exchangeable foreign ordinary equities, ADRs, and GDRs 25.3 0.5 — — 25.8 Corporate and municipal bonds 6.9 — — — 6.9 U.S. government obligations — 509.8 — — 509.8 Foreign government obligations — — — — — Mortgage-backed securities — — — — — Derivatives 199.4 1,319.3 — (1,307.8 ) 210.9 Commodities leases — 207.8 — (145.7 ) 62.1 Financial instruments sold, not yet purchased 255.1 2,037.8 — (1,453.5 ) 839.4 Total liabilities at fair value $ 2,216.8 $ 2,137.9 $ 0.8 $ (3,511.8 ) $ 843.7 (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 are included in that level. Realized and unrealized gains and losses are included in ‘trading gains, net’ and ‘cost of sales of physical commodities’ in the consolidated income statements. Information on Level 3 Financial Assets and Liabilities The Company’s financial assets at fair value classified within level 3 of the fair value hierarchy as of September 30, 2017 and 2016 are summarized below: (in millions) September 30, 2017 September 30, 2016 Total level 3 assets $ 0.1 $ 3.2 Level 3 assets for which the Company bears economic exposure $ 0.1 $ 3.2 Total assets $ 6,243.4 $ 5,950.3 Total financial assets at fair value $ 2,068.0 $ 3,156.5 Total level 3 assets as a percentage of total assets — % 0.1 % Level 3 assets for which the Company bears economic exposure as a percentage of total assets — % 0.1 % Total level 3 assets as a percentage of total financial assets at fair value — % 0.1 % 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 fiscal years ended September 30, 2017 and 2016 , including a summary of unrealized gains (losses) during the fiscal year ended on the Company’s Level 3 financial assets and liabilities still held as of September 30, 2017 . Level 3 Financial Assets and Financial Liabilities (in millions) Balances at Realized gains Unrealized Purchases/ Settlements Transfers in Balances at Assets: Common and preferred stock and ADRs $ 0.2 $ — $ (0.1 ) $ — $ — $ — $ 0.1 Corporate and municipal bonds 3.0 — — — (3.0 ) — — $ 3.2 $ — $ (0.1 ) $ — $ (3.0 ) $ — $ 0.1 (in millions) Balances at Realized gains Remeasurement Acquisitions Settlements Transfers in Balances at Liabilities: Contingent liabilities $ 0.8 $ — $ 0.2 $ — $ — $ — $ 1.0 Level 3 Financial Assets and Financial Liabilities (in millions) Balances at Realized gains Unrealized Purchases/ Settlements Transfers in Balances at Assets: Common and preferred stock and ADRs $ 0.5 $ — $ (0.3 ) $ — $ — $ — $ 0.2 Corporate and municipal bonds 3.2 — (0.2 ) — — — 3.0 $ 3.7 $ — $ (0.5 ) $ — $ — $ — $ 3.2 (in millions) Balances at Realized gains Remeasurement Acquisitions Settlements Transfers in Balances at Liabilities: Contingent liabilities $ 3.3 $ — $ 0.4 $ — $ (2.9 ) $ — $ 0.8 The Company had debentures issued by a single asset owning company of Suriwongse Hotel located in Chiang Mai, Thailand. As of September 30, 2016, the Company’s investment in the hotel was $3.0 million , and was included within the corporate and municipal bonds classification in the Level 3 financial assets and financial liabilities table. The Company classified its investment in the hotel within Level 3 of the fair value hierarchy because the fair value was determined using significant unobservable inputs, which included projected cash flows. These cash flows were discounted employing present value techniques. In December 2016, the Company sold the debentures and collected an amount approximating their carrying value. The Company is required to make additional future cash payments based on certain financial performance measures of its acquired businesses. The Company is required to remeasure the fair value of the cash earnout arrangements on a recurring basis The Company has classified its liabilities for the contingent earnout arrangements within Level 3 of the fair value hierarchy because the fair value is determined using significant unobservable inputs, which include projected cash flows. The estimated fair value of the contingent purchase consideration is based upon management-developed forecasts, a Level 3 input in the fair value hierarchy. These cash flows are discounted employing present value techniques in arriving at fair value. The discount rate was developed using market participant company data and there have been no significant changes in the discount rate environment. From the dates of acquisition to September 30, 2017 , certain acquisitions have had changes in the estimates of undiscounted cash flows, based on actual performances fluctuating from estimates. During the fiscal years ended September 30, 2017 and 2016 , the fair value of the contingent consideration increased $0.2 million and $0.4 million , respectively, with the corresponding expense classified as ‘other’ in the consolidated income statements. The value of an exchange-traded derivative contract is equal to the unrealized gain or loss on the contract determined by marking the contract to the current settlement price for a like contract on the valuation date of the contract. A settlement price may not be used if the market makes a limit move with respect to a particular derivative contract or if the securities underlying the contract experience significant price fluctuations after the determination of the settlement price. When a settlement price cannot be used, derivative contracts will be valued at their fair value as determined in good faith pursuant to procedures adopted by management of the Company. The Company has classified equity investments in exchange firms’ common stock not pledged for clearing purposes as trading securities. The investments are recorded at fair value, with unrealized gains and losses recorded, net of taxes, included in earnings. As of September 30, 2017 , the cost and fair value of the equity investments in exchange firms is $3.9 million and $8.3 million , respectively. As of September 30, 2016 , the cost and fair value of the equity investments in exchange firms was $3.7 million and $6.4 million , respectively. Additional disclosures about the fair value of financial instruments that are not carried on the 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 Consolidated Balance Sheets. The following represents financial instruments in which the ending balance at September 30, 2017 and 2016 was not carried at fair value in accordance with U.S. GAAP on our 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 us 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 overnight 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: R eceivables 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: P ayables 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. Senior unsecured notes : The fair value of the Company’s senior unsecured notes was estimated to be $46.2 million (carrying value of $45.5 million ) as of September 30, 2016 based on the transaction price at public exchanges for the same issue and is classified as Level 1 under the fair value hierarchy. The senior secured notes were redeemed during the year ended September 30, 2017, as discussed further in Note 11.

Financial Instruments with Off-

Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk (Notes)	12 Months Ended
	Sep. 30, 2016
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 consolidated financial statements as of 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 September 30, 2017 . The total of $717.6 million as of September 30, 2017 includes $317.0 million for derivative contracts, which represent a liability to the Company based on their fair values as of 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 Company’s derivative positions are included in the consolidating balance sheets in ‘deposits with and receivables from broker-dealers, clearing organizations, and counterparties’, ‘financial instruments owned and sold, not yet purchased, at fair value’ and ‘payables to broker-dealers, clearing organizations and counterparties’. The Company employs an interest rate risk management strategy using derivative financial instruments in the form of interest rate swaps as well as outright purchases of medium-term U.S. Treasury notes to manage a portion of the aggregate interest rate position. The Company’s objective when using interest rate swaps under the strategy, is to invest certain amounts of customer deposits in high quality, short-term investments and swap the resulting variable interest earnings into medium-term interest earnings. When used, the risk mitigation of these interest rate swaps are not within the documented hedging designation requirements of the Derivatives and Hedging Topic of the ASC, and as a result are recorded at fair value, with changes in the fair value of the interest rate swaps recorded within ‘trading gains, net’ in the consolidated income statements. At September 30, 2016, the Company had $375 million in notional principal of interest rate swaps outstanding with a weighted-average life of 15 months. During the year ended September 30, 2017, the Company settled these interest rate swaps in advance of their original maturity date. Listed below are the fair values of the Company’s derivative assets and liabilities as of September 30, 2017 and 2016 . Assets represent net unrealized gains and liabilities represent net unrealized losses. September 30, 2017 September 30, 2016 (in millions) Assets (1) Liabilities (1) Assets (1) Liabilities (1) Derivative contracts not accounted for as hedges: Exchange-traded commodity derivatives $ 2,094.2 $ 1,975.0 $ 2,022.1 $ 1,920.5 OTC commodity derivatives 1,084.0 1,110.3 1,217.0 1,188.9 Exchange-traded foreign exchange derivatives 66.0 52.0 12.2 7.5 OTC foreign exchange derivatives 618.5 609.8 346.5 290.2 Exchange-traded interest rate derivatives 228.4 203.6 78.7 120.5 Equity index derivatives 221.3 245.4 39.1 50.3 TBA and forward settling securities 8.8 4.9 0.3 2.6 Gross fair value of derivative contracts 4,321.2 4,201.0 3,715.9 3,580.5 Impact of netting and collateral (4,205.5 ) (3,879.2 ) (3,653.5 ) (3,366.1 ) Total fair value included in ‘Deposits with and receivables from broker-dealers, clearing organizations and counterparties’ $ (46.4 ) $ (131.5 ) Total fair value included in ‘Financial instruments owned, at fair value’ $ 162.1 $ 193.9 Total fair value included in ‘Payables to broker-dealers, clearing organizations and counterparties $ 4.8 $ 3.5 Fair value included in ‘Financial instruments sold, not yet purchased, at fair value’ $ 317.0 $ 210.9 (1) As of September 30, 2017 and 2016 , the Company’s derivative contract volume for open positions was approximately 6.1 million and 4.0 million contracts, respectively. The Company’s derivative contracts are principally held in its Commodities and Risk Management Services (“Commercial Hedging”) segment. 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 generally offsetting the customer’s transaction simultaneously with one of the Company’s trading counterparties or will offset that transaction with a similar but not identical position on the exchange. 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 transacts in derivative instruments, which consist of futures, mortgage-backed TBA securities and forward settling transactions, that are used to manage risk exposures. The fair value of these transactions is recorded in receivables 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’. The Company enters into TBA securities transactions for the sole purpose of managing risk associated with the purchase of mortgage pass-through securities. TBA securities are included within payables to broker-dealers, clearing organizations and counterparties. Forward settling securities represent non-regular way securities and are included in financial instruments owned and sold. As of September 30, 2017 , these transactions are summarized as follows (in millions): Gain / (Loss) Notional Amounts Unrealized gain on TBA securities purchased within payables to broker-dealers, clearing organizations and counterparties and related notional amounts (1) $ — $ 51.3 Unrealized loss on TBA securities purchased within payables to broker-dealers, clearing organizations and counterparties and related notional amounts (1) $ (2.9 ) $ 1,236.8 Unrealized gain on TBA securities sold within deposits with and receivables from broker-dealers, clearing organizations and counterparties and related notional amounts (1) $ 5.8 $ (1,881.9 ) Unrealized loss on TBA securities sold within deposits with and receivables from broker-dealers, clearing organizations and counterparties and related notional amounts (1) $ (0.1 ) $ (404.1 ) Unrealized loss on forward settling securities purchased within payables to broker-dealers, clearing organizations and counterparties and related notional amounts $ (2.0 ) $ 882.9 Unrealized gain on forward settling securities sold within receivables from broker-dealers, clearing organizations and counterparties and related notional amounts $ 3.0 $ (590.2 ) (1) The notional amounts of these instruments reflect the extent of the Company’s involvement in TBA securities and do not represent risk of loss due to counterparty non-performance. The following table sets forth the Company’s net gains (losses) related to derivative financial instruments for the fiscal years ended September 30, 2017, 2016, and 2015 , in accordance with the Derivatives and Hedging Topic of the ASC. The net gains (losses) set forth below are included in ‘trading gains, net’ and ‘cost of sales of physical commodities’ in the consolidated income statements. Year Ended September 30, (in millions) 2017 2016 2015 Commodities $ 47.3 $ 41.8 $ 78.6 Foreign exchange 8.7 9.7 7.5 Interest rate and equity (0.1 ) 0.8 3.2 TBA and forward settling securities (2.5 ) (14.4 ) (5.1 ) Net gains from derivative contracts $ 53.4 $ 37.9 $ 84.2 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 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 execution of orders for commodity futures, options on futures 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 counterparties 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 September 30, 2017 and September 30, 2016 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. 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 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 commodity pricing and 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)	12 Months Ended
	Sep. 30, 2016
Receivables from customers and notes receivable, net [Abstract]
Receivables from Customers and Notes Receivable [Text Block]	Allowance for Doubtful Accounts Deposits with and receivables from broker-dealers, clearing organizations, and counterparties, net, receivables from customers, net, and notes receivable, net include an allowance for doubtful accounts, which reflects the Company’s best estimate of probable losses inherent in the accounts. The Company provides for an allowance for doubtful accounts based on a specific-identification basis. The Company continually reviews its allowance for doubtful accounts. The allowance for doubtful accounts related to deposits with and receivables from broker-dealers, clearing organizations, and counterparties was $47.0 million and zero as of September 30, 2017 and 2016 , respectively. The allowance for doubtful accounts related to receivables from customers was $7.6 million and $9.5 million as of September 30, 2017 and 2016 , respectively. The allowance for doubtful accounts related to notes receivable was zero and $0.2 million as of September 30, 2017 and 2016 , respectively. During the year ended September 30, 2017 , the Company recorded bad debt expense related to customers, net of recoveries, of $4.3 million , including provision increases of $4.2 million , direct write-offs of $0.1 million . The increase in bad debts during fiscal 2017 primarily related to $3.8 million of customer deficits in the Commercial Hedging segment, primarily related to account deficits from South Korean and Dubai commercial LME customers, $0.2 million of uncollectible customer receivables in the Physical Commodities segment, and $0.3 million of uncollectible customer receivables in the Clearing and Execution segment, primarily related to our derivatives voice brokerage business. During the fourth quarter of fiscal 2017, the Company recorded a charge to earnings of $47.0 million , to record an allowance for doubtful accounts related to a bad debt incurred in the physical coal business conducted solely in INTL Asia Pte. Ltd., with a coal supplier, as further discussed in Note 2 . During the year ended September 30, 2016, the Company recorded bad debt expense related to customers, net of recoveries, of $4.4 million , including provision increases of $4.2 million and direct write-offs of $0.4 million , offset by recoveries of $0.2 million . The increase in bad debts during fiscal 2016 primarily related to $3.6 million of customer deficits in the Commercial Hedging segment, $0.4 million of uncollectible customer receivables in the Physical Commodities segment, and $0.4 million of uncollectible service fees and notes in the Securities segment. During the year ended September 30, 2015, the Company recorded bad debt expense related to customers, net of recoveries, of $7.3 million , including provision increases of $6.6 million and direct write-offs of $0.7 million , offset by minimal recoveries. The increase in bad debts during fiscal 2015 related to $2.8 million of receivables from a renewable fuels customer in the Physical Commodities segment, $2.3 million of OTC customer deficits and $0.6 million of LME customer deficits in the Commercial Hedging segment, $0.5 million of uncollectible service fees and notes in our Securities segment, and $1.1 million of notes receivable related to loans pertaining to a former acquisition. Activity in the allowance for doubtful accounts for the years ended September 30, 2017, 2016, and 2015 was as follows: (in millions) 2017 2016 2015 Balance, beginning of year $ 9.7 $ 11.2 $ 5.8 Provision for bad debts 51.0 4.2 6.0 Charge-offs (6.1 ) (5.7 ) (0.6 ) Balance, end of year $ 54.6 $ 9.7 $ 11.2 The Company originates short-term notes receivable from customers with the outstanding balances typically being insured 90% to 98% by a third party, including accrued interest, subject to applicable deductible amounts. The total balance outstanding under insured notes receivable was $2.1 million and $5.0 million as of September 30, 2017 and 2016 , respectively. The Company has sold $2.1 million and $4.6 million of the insured portion of the notes through non-recourse participation agreements with other third parties as of September 30, 2017 and 2016 , respectively. The Company has completed its exit of the majority of this activity during the year ended September 30, 2017. The Company believes the run-off of the remaining activity will have a minimal impact on the Company. See discussion of notes receivable related to commodity repurchase agreements in Note 14 .

Physical Commodities Inventory

Physical Commodities Inventory (Notes)	12 Months Ended
	Sep. 30, 2017
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) September 30, September 30, Physical Ag & Energy (1) $ 65.1 $ 65.9 Precious metals - held by broker-dealer subsidiary (2) 13.3 5.3 Precious metals - held by non-broker-dealer subsidiaries (3) 46.4 52.6 Physical commodities inventory $ 124.8 $ 123.8 (1) Physical Ag & Energy maintains agricultural commodity inventories, including corn, soybeans, wheat, dried distillers grain, canola, sorghum, coffee 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 consolidated income statement. 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 inventory, primarily coal, kerosene, and propane which are valued at the lower of cost or market. (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 consolidated income statement, 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 market value. The Company has recorded lower of cost or market (“LCM”) adjustments for certain precious metals inventory of $0.7 million and $0.6 million as of September 30, 2017 and 2016 , respectively. The adjustments are included in ‘cost of sales of physical commodities’ in the consolidated income statements.

Property and Equipment, net (No

Property and Equipment, net (Notes)	12 Months Ended
	Sep. 30, 2017
Property and Equipment, net [Abstract]
Property, Plant and Equipment Disclosure [Text Block]	Property and Equipment, net Property and equipment are stated at cost, and reported net of accumulated depreciation on the consolidated balance sheets. Depreciation on property and equipment is calculated using the straight-line method over the estimated useful lives of the assets. The estimated useful lives of property and equipment range from 3 to 10 years. During the fiscal years ended September 30, 2017, 2016, and 2015 , depreciation expense was $7.0 million , $6.6 million and $5.7 million , respectively. A summary of property and equipment, at cost less accumulated depreciation as of September 30, 2017 and 2016 is as follows: (in millions) September 30, 2017 September 30, 2016 Property and equipment: Furniture and fixtures $ 7.2 $ 6.8 Software 25.3 22.8 Equipment 22.6 20.6 Leasehold improvements 15.4 11.9 Total property and equipment 70.5 62.1 Less accumulated depreciation (31.8 ) (32.7 ) Property and equipment, net $ 38.7 $ 29.4

Goodwill (Notes)

Goodwill (Notes)	12 Months Ended
	Sep. 30, 2017
Goodwill [Abstract]
Goodwill Disclosure [Text Block]	Goodwill Goodwill allocated to the Company’s operating segments as of September 30, 2017 and 2016 is as follows: (in millions) September 30, September 30, Commercial Hedging $ 30.7 $ 30.7 Global Payments 6.3 6.3 Physical Commodities 2.4 2.4 Securities 7.7 8.1 Goodwill $ 47.1 $ 47.5

Intangible Assets (Notes)

Intangible Assets (Notes)	12 Months Ended
	Sep. 30, 2017
Intangible Assets [Abstract]
Intangible Assets Disclosure [Text Block]	Intangible Assets During the year ended September 30, 2017, the Company recorded additional customer base intangible assets of $6.0 million as part of the ICAP acquisition. See Note 19 - Acquisitions for additional discussion. 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): September 30, 2017 September 30, 2016 Gross Amount Accumulated Amortization Net Amount Gross Amount Accumulated Amortization Net Amount Intangible assets subject to amortization: Trade name $ — $ — $ — $ 1.1 $ (0.6 ) $ 0.5 Software programs/platforms 2.7 (2.5 ) 0.2 2.7 (2.4 ) 0.3 Customer base 20.0 (7.9 ) 12.1 14.0 (5.7 ) 8.3 Total intangible assets $ 22.7 $ (10.4 ) $ 12.3 $ 17.8 $ (8.7 ) $ 9.1 Amortization expense related to intangible assets was $2.8 million , $1.6 million , and $1.5 million for the fiscal years ended September 30, 2017, 2016, and 2015 , respectively. The estimated future amortization expense as of September 30, 2017 is as follows (in millions): Year ending September 30, 2018 $ 2.2 2019 2.2 2020 2.0 2021 1.9 2022 and thereafter 4.0 $ 12.3

Credit Facilities (Notes)

Credit Facilities (Notes)	12 Months Ended
	Sep. 30, 2017
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 $532.0 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 credit facilities are as follows: • A three-year syndicated committed loan facility under which $262.0 million is available to the Company for general working capital requirements. The line of credit is secured by a pledge of shares held in certain of the Company’s subsidiaries. Unused portions of the loan facility require a commitment fee of 0.625% on the unused commitment. Borrowings under the facility bear interest at the Eurodollar Rate, as defined, plus 3.00% or the Base Rate, as defined, plus 2.00% , and averaged 4.20% as of September 30, 2017. The agreement contains financial covenants related to consolidated tangible net worth, consolidated funded debt to net worth ratio, consolidated fixed charge coverage ratio and consolidated net unencumbered liquid assets, as defined. The agreement also contains a non-financial covenant related to the allowable annual consolidated capital expenditures permitted under the agreement. On November 30, 2017, the Company amended the loan facility to increase the allowable annual consolidated capital expenditures from $15.0 million to $17.5 million . The agreement also amended the definition of consolidated EBITDA for the purposes of the consolidated fixed charge coverage ratio. This amendment allowed the Company to add back a portion of the bad debt on physical coal discussed in Note 2 in calculating consolidated EBITDA. Under the terms of the agreement, the amendment was deemed effective as of September 30, 2017 . As a result of this amendment, the Company was in compliance with all covenants under the loan facility as of September 30, 2017 . • An unsecured syndicated committed line of credit under which $75.0 million is available to the Company’s subsidiary, INTL FCStone Financial to provide short term funding of margin to commodity exchanges as necessary. This line of credit is subject to annual review, and the continued availability of this line of credit is subject to INTL FCStone Financial’s financial condition and operating results continuing to be satisfactory as set forth in the agreement. Unused portions of the margin line require a commitment fee of 0.50% on the unused commitment. Borrowings under the margin line are on a demand basis and bear interest at the Base Rate, as defined, plus 2.00% , which was 6.25% as of September 30, 2017 . The agreement contains financial covenants related to INTL FCStone Financial’s tangible net worth, excess net capital and maximum net loss over a trailing twelve month period, as defined. INTL FCStone Financial was in compliance with these covenants as of September 30, 2017 . The facility is guaranteed by the Company. • A syndicated committed borrowing facility under which $170.0 million is available to the Company’s subsidiary, FCStone Merchant Services, LLC (“FCStone Merchants”) for financing traditional commodity financing arrangements and commodity repurchase agreements. The facility is secured by the assets of FCStone Merchants, and guaranteed by the Company. Unused portions of the borrowing facility require a commitment fee of 0.50% on the unused commitment. The borrowings outstanding under the facility bear interest at a rate per annum equal to the Eurodollar Rate plus Applicable Margin, as defined, or the Base Rate plus Applicable Margin, as defined, which averaged 4.00% as of September 30, 2017 . The agreement contains financial covenants related to tangible net worth, as defined. FCStone Merchants was in compliance with this covenant as of September 30, 2017 . FCStone Merchants paid minimal debt issuance costs in connection with this credit facility. • A syndicated committed borrowing facility under which $25.0 million is available to the Company’s subsidiary, INTL FCStone Ltd for short term funding of margin to commodity exchanges. The borrowings outstanding under the facility bear interest at a rate per annum equal to 2.50% plus the Federal Funds Rate, as defined. The agreement contains financial covenants related to consolidated tangible net worth, as defined. INTL FCStone Ltd was in compliance with this covenant as of September 30, 2017 . INTL FCStone Ltd paid minimal debt issuance costs in connection with this credit facility. The facility is guaranteed by the Company. 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 commodity warehouse receipts, to facilitate financing of commodities under repurchase agreement services to its customers, subject to certain terms and conditions of the credit agreement. The Company also has a secured, uncommitted loan facility, under which the Company’s wholly owned subsidiary, INTL FCStone Financial may borrow up to $50.0 million , collateralized by commodity warehouse receipts, to facilitate U.S. commodity exchange deliveries of its customers, subject to certain terms and conditions of the credit agreement. There were $23.0 million in borrowings outstanding under this credit facility at September 30, 2017, and no borrowings outstanding at September 30, 2016. The Company also has a secured uncommitted loan facility under which the Company’s wholly owned subsidiary, INTL FCStone Financial 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 facility bears interest at a rate per annum equal to such rate in respect of such day as determined by the bank in its sole discretion. In the event that the Company fails to pay the principal and interest on the scheduled due date, the facilities bear penalty interest at a rate equal to the Federal Funds rate plus 2% . The amounts borrowed under the facilities are payable on demand. As of September 30, 2017 and September 30, 2016, the Company had no borrowings outstanding under this credit facility. The Company also has a secured uncommitted loan facility under which the Company’s wholly owned subsidiary, INTL FCStone Financial 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 loans are payable on demand and bear interest at a rate mutually agreed to with the lender. The borrowings are secured by first liens on firm owned marketable securities or customer owned securities which have been pledged to us under a clearing arrangement. There were $11.0 million in borrowings outstanding under this credit facility at September 30, 2017, and no borrowings outstanding at September 30, 2016. Note Payable to Bank In April 2015, the Company obtained a $4.0 million 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% . Senior Unsecured Notes In July 2013, the Company completed an offering of $45.5 million aggregate principal amount of the Company’s 8.5% Senior Notes due 2020 (the “Notes”). The net proceeds of the sale of the Notes were being used for general corporate purposes. The Notes bore interest at a rate of 8.5% per year (payable quarterly on January 30, April 30, July 30 and October 30 of each year). The Notes were scheduled to mature on July 30, 2020. The Company could redeem the Notes, in whole or in part, at any time on and after July 30, 2016, at a redemption price equal to 100% of the principal amount redeemed plus accrued and unpaid interest to, but not including, the redemption date. The Company incurred debt issuance costs of $1.7 million in connection with the issuance of the Notes, which were being amortized over the term of the Notes. On September 15, 2016, the Company provided notice, through the trustee of the Notes, to the record holders of the Notes that the Company would redeem the outstanding $45.5 million aggregate principal amount of the Notes in full. On October 15, 2016, the Company redeemed the Notes at a prices equal to 100% of the principal amount redeemed plus accrued and unpaid interest to, but not including, October 15, 2016. The remaining unamortized deferred financing costs of $1.0 million were written off in connection with the redemption of the Notes and are included in ‘interest expense’ in the consolidated income statement for the year ended September 30, 2017. The following table sets forth a listing of credit facilities, the current committed amounts, as of the report date, on the facilities, and outstanding borrowings on the facilities as well as indebtedness on a promissory note and on senior notes as of September 30, 2017 and 2016 : (in millions) Credit Facilities Amounts Outstanding Borrower Security Renewal / Expiration Date Total Commitment September 30, September 30, Committed Credit Facilities INTL FCStone Inc. Pledged shares of certain subsidiaries March 18, 2019 $ 262.0 $ 150.0 $ 136.5 INTL FCStone Financial, Inc. None April 5, 2018 75.0 — — FCStone Merchants Services, LLC Certain commodities assets May 1, 2018 170.0 44.2 43.5 INTL FCStone Ltd. None November 7, 2018 25.0 — — $ 532.0 194.2 180.0 Uncommitted Credit Facilities INTL FCStone Financial, Inc. Commodity warehouse receipts and certain pledged securities n/a — 34.0 — INTL FCStone Ltd. Commodity warehouse receipts n/a — — — Note Payable to Bank Monthly installments, due March 2020 and secured by certain equipment 2.0 2.8 Senior Unsecured Notes 8.50% senior notes, redeemed October 15, 2016 — 44.5 Total indebtedness $ 230.2 $ 227.3 As reflected above, $245 million of the Company’s committed credit facilities are scheduled to expire during the fiscal year ended September 30, 2018. The Company intends to renew or replace these facilities as they expire, and based on the Company’s liquidity position and capital structure, the Company believes it will be able to do so.

Commitments and Contingencies (

Commitments and Contingencies (Notes)	12 Months Ended
	Sep. 30, 2017
Commitments and Contingencies [Abstract]
Commitments and Contingencies Disclosure [Text Block]	Commitments and Contingencies Legal Proceedings Certain conditions may exist as of the date the financial statements are issued, which may result in a loss to the Company but which will only be resolved when one or more future events occur or fail to occur. The Company assesses such contingent liabilities, and such assessment inherently involves an exercise of judgment. In assessing loss contingencies related to legal proceedings that are pending against the Company or unasserted claims that may result in such proceedings, the Company’s legal counsel evaluates the perceived merits of any legal proceedings or unasserted claims as well as the perceived merits of the amount of relief sought or expected to be sought therein. If the assessment of a contingency indicates that it is probable that a material loss had been incurred at the date of the financial statements and the amount of the liability can be estimated, then the estimated liability would be accrued in the Company’s financial statements. If the assessment indicates that a potentially material loss contingency is not probable, but is reasonably possible, or is probable but cannot be estimated, then the nature of the contingent liability, together with an estimate of the range of possible loss if determinable and material, would be disclosed. Neither accrual nor disclosure is required for loss contingencies that are deemed remote. The Company accrues legal fees related to contingent liabilities as they are incurred. In addition to the matters discussed below, 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 September 30, 2017 and 2016 , the consolidated balance sheets include loss contingency accruals, recorded during and prior to these fiscal years then ended, 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, and in addition to the possible losses discussed below, is not 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. In the complaint, the trustee sought avoidance of alleged transfers or withdrawals of funds received by FCStone, LLC and other FCMs within 90 days prior to the filing of the Sentinel bankruptcy petition, as well as avoidance of post-petition distributions and disallowance of the proof of claim filed by FCStone, LLC. 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 in January 2013. In January 2013, the trial court entered an agreed order, staying execution and enforcement, pending an appeal of the judgment. In March 2014, the appeal court ruled in favor of FCStone, LLC. In April 2014, the trustee filed a petition for rehearing of the appeal. In May 2014, the U.S. Court of Appeals for the Seventh Circuit denied the petition. The trustee did not file a writ for certiorari with the U.S. Supreme Court during the time allotted to do so. In February 2015, based on a new theory, the trustee filed a motion for judgment against FCStone, LLC in the U.S. District Court, for the Northern District of Illinois, seeking to claw back the post-petition transfer of $14.5 million and to recover the funds held in reserve in the name of FCStone, LLC. FCStone, LLC filed its opposition brief and an associated motion for judgment in March 2015. In March 2016, the U.S. District Court for the Northern District of Illinois entered an order in favor of FCStone, LLC (now INTL FCStone Financial Inc.) and against the trustee on the trustee’s post-petition claim, in light of the Seventh Circuit’s opinion. The same court previously ruled against INTL FCStone Financial and in favor of the trustee with respect to the funds held in reserve accounts. In April 2016, INTL FCStone Financial filed a notice of appeal to the U.S. Court of Appeals for the Seventh Circuit relating to the portion of the final judgment dated March 28, 2016 of the district court and INTL FCStone Financial’s claim to funds in reserve accounts. In April 2016, the trustee filed its notice of appeal from the March 28, 2016 final judgment of the district court. During April 2016, the court consolidated the two appeals and directed the trustee to file an opening brief. In June 2016, the trustee filed its appellate brief. In August 2016, the Futures Industry Association, Inc. filed a voluntary brief in support of INTL FCStone Financial’s cross-appeal. 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. The trustee petitioned the Seventh Circuit for a rehearing on September 11, 2017, seeking reconsideration of the court’s prior ruling. On October 2, 2017 that petition was denied. With the Seventh Circuit having issued a mandate requiring the U.S. District Court for the Northern District of Illinois to enter a judgment in favor of INTL FCStone Financial on all counts on the issue of liability, INTL FCStone Financial filed a motion in the District Court on October 13, 2017 for an order directing the distribution of reserve funds in the approximate amount of $2.0 million . This motion was argued in the District Court on October 19, 2017, and the District Court directed the parties to file proposed orders relating to the distribution of the reserve funds. On October 24, 2017, INTL FCStone Financial Inc. submitted a judgment order and an order directing the trustee to carry out the requirements of the judgment. On October 24, 2017, the trustee filed an objection to INTL FCStone Financial’s motion, and on November 8, 2017, INTL FCStone Financial filed its reply. The parties appeared before the District Court on November 28, 2017 to address the motions. INTL FCStone Financial requested immediate payment of funds due based on the August 14, 2017 ruling in its favor, however the trustee requested that the distribution of those reserve funds be held in abeyance pending his final appeal to the United States Supreme Court. The Company has determined that losses related to this matter are neither probable nor reasonably possible. The Company believes the case is without merit and intends to defend itself vigorously. 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 Contingent Liabilities - Acquisition Under the terms of the purchase agreement, the Company has a contingent liability related to the acquisition in fiscal year 2015 further discussed in Note 19 . The Company has an obligation to pay additional consideration if specific conditions and earnings targets are met by the acquired business. The fair value of the additional consideration was recognized as a contingent liability as of the acquisition date, and is remeasured to its fair value each reporting period with changes in fair value recorded in current earnings. The contingent liability for these estimated additional purchase price considerations of $1.0 million and $0.8 million are included in ‘accounts payable and other accrued liabilities’ in the consolidated balance sheets as of September 30, 2017 and 2016 , respectively. The change in fair value during the years ended September 30, 2017, 2016, and 2015 were increases of $0.2 million , $0.4 million and $1.8 million , respectively, and are included in ‘other’ in the consolidated income statements. The estimated total purchase price, including contingent consideration, is $27.5 million as of September 30, 2017 , of which $1.0 million remains outstanding. Operating Leases The Company is obligated under various noncancelable operating leases for the rental of office facilities, automobiles, service obligations and certain office equipment, and accounts for these lease obligations on a straight line basis. The expense associated with operating leases was $11.3 million , $9.9 million and $10.1 million , for fiscal years ended September 30, 2017, 2016, and 2015 , respectively. The expenses associated with the operating leases and service obligations are reported in the consolidated income statements in ‘occupancy and equipment rental’, ‘transaction-based clearing expenses’ and ‘other’ expenses. Future aggregate minimum lease payments under noncancelable operating leases as of September 30, 2017 are as follows: (in millions) Year ending September 30, 2018 $ 8.9 2019 8.3 2020 7.7 2021 6.7 2022 4.7 Thereafter 10.1 $ 46.4 Purchase Commitments The Company determines an estimate of contractual purchase commitments in the ordinary course of business primarily for the purchase of precious metals and agricultural and energy commodities. Unpriced contract commitments have been estimated using September 30, 2017 fair values. The purchase commitments and other obligations as of September 30, 2017 for less than one year, one to three years and three to five years were $675.7 million , $1.8 million and $2.1 million , respectively. There were $1.7 million in purchase commitments and other obligations after five years as of September 30, 2017 . The purchase commitments for less than one year will be partially offset by corresponding sales commitments of $583.5 million . Exchange Member Guarantees The Company is a member of various exchanges that trade and clear futures and option contracts. In connection with the Sterne acquisition, the Company is also a member of and provides guarantees to securities clearinghouses and exchanges in connection with customer trading activities. Associated with its memberships, the Company may be required to pay a proportionate share of the financial obligations of another member who may default on its obligations to the exchanges. While the rules governing different exchange memberships vary, in general the Company’s guarantee obligations would arise only if the exchange had previously exhausted its resources. In addition, any such guarantee obligation would be apportioned among the other non-defaulting members of the exchange. Any potential contingent liability under these arrangements is not quantifiable and could exceed the cash and securities it has posted to the clearinghouse as collateral. The Company has not recorded any contingent liability in the consolidated financial statements for these agreements and believes that any potential requirement to make payments under these agreements is remote. 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. Liabilities are recognized based on claims filed and an estimate of claims incurred but not reported. The Company has purchased stop-loss coverage to limit its exposure on a per claim basis and in aggregate in the event that aggregated actual claims would exceed 120% of actuarially estimated claims. The Company is insured for covered costs in excess of these limits. Although the ultimate outcome of these matters may exceed the amounts recorded and additional losses may be incurred, the Company does not believe that any additional potential exposure for such liabilities will have a material adverse effect on the Company’s consolidated financial position or results of operations. As of September 30, 2017 and 2016 , the Company had $0.8 million and $1.0 million , respectively, accrued for self-insured medical and dental claims included in ‘accounts payable and other liabilities’ in the consolidated balance sheets.

Regulatory Requirements and Sub

Regulatory Requirements and Subsidiary Dividend Restrictions (Notes)	12 Months Ended
	Sep. 30, 2016
Capital and Other Regulatory Requirements [Abstract]
Regulatory Capital Requirements under Banking Regulations [Text Block]	Regulatory Requirements and Subsidiary Dividend Restrictions The Company’s subsidiary INTL FCStone Financial is registered as a broker dealer and member of the Financial Industry Regulatory Authority (“FINRA”) subject to the SEC Uniform Net Capital Rule 15c3-1, which requires the maintenance of minimum net capital. INTL FCStone Financial is also a commodity futures commission merchant registered with the CFTC and subject to the net capital requirements of the CFTC Regulation 1.17. Under the more restrictive of these rules, INTL FCStone Financial is required to maintain “adjusted net capital”, equivalent to the greater of $1,000,000 or 8 percent of customer and noncustomer risk maintenance margin requirements on all positions, as defined in such rules, regulations, and requirements. Net capital and the related net capital requirement may fluctuate on a daily basis. INTL FCStone Financial also has restriction on dividends, which restricts the withdrawal of equity capital if the planned withdrawal would reduce net capital, subsequent to haircuts and charges, to an amount less than 120% of the greatest minimum requirement. INTL FCStone Financial as a registered securities carrying broker dealer is also subject to Rule 15c3-3 of the Securities Exchange Act of 1934, which requires the Company to maintain separate accounts for the benefit of securities customers and proprietary accounts of broker dealers (“PABs”). These customer protection rules requires the Company to maintain special reserve bank accounts (“SRBAs”) for the exclusive benefit of securities customers and PABs. Pursuant to the requirements of the Commodity Exchange Act, funds deposited by customers of INTL FCStone Financial relating to their trading of futures and options on futures on a U.S. commodities exchange must be carried in separate accounts which are designated as segregated customers’ accounts. Pursuant to the requirements of the CFTC, funds deposited by customers of INTL FCStone Financial relating to their trading of futures and options on futures traded on, or subject to the rules of, a foreign board of trade must be carried in separate accounts in an amount sufficient to satisfy all of INTL FCStone Financial’s current obligations to customers trading foreign futures and foreign options on foreign commodity exchanges or boards of trade, which are designated as secured customers’ accounts. See below for additional information regarding INTL FCStone Financial’s calculation of segregated and secured customer funds. The Company’s subsidiaries INTL Custody & Clearing Solutions Inc. (formerly Sterne Agee Clearing, Inc.) and SA Stone Wealth Management Inc. (formerly Sterne Agee Financial Services, Inc.) are subject to the SEC Uniform Net Capital Rule 15c3-1 under the Securities Exchange Act of 1934. The Company’s subsidiary INTL FCStone Ltd is regulated by the Financial Conduct Authority (“FCA”), the regulator of the financial services industry in the United Kingdom, as a Financial Services Firm under part IV of the Financial Services and Markets Act 2000. The regulations impose regulatory capital, as well as conduct of business, governance, and other requirements. The conduct of business rules include those that govern the treatment of customer money and other assets which under certain circumstances for certain classes of customer must be segregated from the firm’s own assets. The Company’s subsidiary INTL FCStone Pty Ltd is regulated by the Australian Securities and Investment Commission and is subject to a net tangible asset capital requirement. FCStone Commodity Services (Europe), Ltd. is domiciled in Ireland and subject to regulation by the Central Bank of Ireland, and is subject to a net capital requirement. INTL FCStone DTVM Ltda. (“INTL FCStone DTVM”) is a registered broker-dealer and regulated by the Brazilian Central Bank and Securities and Exchange Commission of Brazil, and is subject to a capital adequacy requirement. All subsidiaries of the Company are in compliance with all of their regulatory requirements as of September 30, 2017 , as follows: (in millions) As of September 30, 2017 Subsidiary Regulatory Authority Requirement Type Actual Minimum Requirement INTL FCStone Financial Inc. SEC and CFTC Net capital $ 157.1 $ 74.0 INTL FCStone Financial Inc. CFTC Segregated funds $ 2,248.0 $ 2,195.7 INTL FCStone Financial Inc. CFTC Secured funds $ 165.1 $ 148.7 INTL FCStone Financial Inc. SEC Customer reserve $ 7.2 $ — INTL FCStone Financial Inc. SEC PAB reserve $ 13.5 $ 0.2 INTL Custody & Clearing Solutions Inc. SEC Net capital $ 1.5 $ 0.1 SA Stone Wealth Management Inc. SEC Net capital $ 4.9 $ 0.3 INTL FCStone Ltd FCA (United Kingdom) Net capital $ 158.7 $ 88.3 INTL FCStone Ltd FCA (United Kingdom) Segregated funds $ 107.1 $ 106.6 INTL Netherlands BV FCA (United Kingdom) Net capital $ 158.0 $ 88.3 INTL FCStone DTVM Ltda. Brazilian Central Bank and Securities and Exchange Commission of Brazil Capital adequacy $ 13.0 $ 0.5 INTL Gainvest S.A. National Securities Commission ("CNV") Capital adequacy $ 5.1 $ 0.2 INTL Gainvest S.A. CNV Net capital $ 0.4 $ 0.1 INTL CIBSA S.A. CNV Capital adequacy $ 7.6 $ 0.9 INTL CIBSA S.A. CNV Net capital $ 1.4 $ 0.5 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 September 30, 2017 , these subsidiaries were in compliance with their local capital adequacy requirements.

Commodity and Other Repurchase

Commodity and Other Repurchase Agreements (Notes)	12 Months Ended
	Sep. 30, 2017
Commodity and Other Repurchase Agreements [Abstract]
Repurchase Agreements, Resale Agreements, Securities Borrowed, and Securities Loaned Disclosure [Text Block]	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 $0.8 million and $1.5 million as of September 30, 2017 and 2016, 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 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 September 30, 2017 , financial instruments owned, at fair value of $19.4 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 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 $108.4 million . In addition, as of September 30, 2017 , the Company pledged financial instruments owned, at fair value of $1,406.6 million as collateral for tri-party repurchase agreements. For these securities, the counterparties do not have the right to sell or repledge the collateral. At September 30, 2017 , 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 September 30, 2017 , was $631.7 million of which $306.9 million was used to cover securities sold short which are recorded in financial instruments sold, not yet purchased on the 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 September 30, 2017 , 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 table provides the contractual maturities of gross obligations under repurchase and securities lending agreements as of September 30, 2017 (in millions): 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 September 30, 2017 (in millions): Securities sold under agreements to repurchase: U.S. Treasury obligations $ 7.0 U.S. government agency obligations 332.6 Asset-backed obligations 36.4 Agency mortgage-backed obligations 1,017.1 Total securities sold under agreements to repurchase $ 1,393.1 Securities loaned: Common stock 111.1 Total securities loaned 111.1 Gross amount of secured financing $ 1,504.2

Share-Based Compensation (Notes

Share-Based Compensation (Notes)	12 Months Ended
	Sep. 30, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Disclosure of Compensation Related Costs, Share-based Payments [Text Block]	Share-Based Compensation Share-based compensation expense is included in ‘compensation and benefits’ in the consolidated income statements and totaled $6.3 million , $5.1 million and $3.6 million for the fiscal years ended September 30, 2017, 2016, and 2015 , respectively. Stock Option Plans The Company sponsors a stock option plan for its directors, officers, employees and consultants. The 2013 Stock Option Plan, which was approved by the Company’s Board of Directors and shareholders, authorizes the Company to issue stock options covering up to 1.0 million shares of the Company’s common stock. As of September 30, 2017 , there were 0.7 million shares authorized for future grant under this plan. Awards that expire or are canceled generally become available for issuance again under the plan. The Company settles stock option exercises with newly issued shares of common stock. Fair value is estimated at the grant date based on a Black-Scholes-Merton option-pricing model using the following weighted-average assumptions: Year Ended September 30, 2017 2016 2015 Expected stock price volatility 31 % 28 % 28 % Expected dividend yield — % — % — % Risk free interest rate 0.99 % 0.83 % 0.66 % Average expected life (in years) 3.08 3.06 3.22 Expected stock price volatility rates are primarily based on the historical volatility. The Company has not paid dividends in the past and does not currently expect to do so in the future. Risk free interest rates are based on the U.S. Treasury yield curve in effect at the time of grant for periods corresponding with the expected life of the option or award. The average expected life represents the estimated period of time that options or awards granted are expected to be outstanding, based on the Company’s historical share option exercise experience for similar option grants. The weighted average fair value of options issued during fiscal years ended September 30, 2017, 2016, and 2015 was $8.67 , $6.40 and $4.31 , respectively. The following is a summary of stock option activity for the year ended September 30, 2017 : Shares Available for Grant Number of Options Outstanding Weighted Average Exercise Price Weighted Average Grant Date Fair Value Weighted Average Remaining Term (in years) Aggregate Intrinsic Value ($ millions) Balances at September 30, 2016 754,163 1,215,821 $ 29.55 $ 12.88 3.80 $ 14.1 Granted (110,000 ) 110,000 $ 38.77 $ 8.67 Exercised (155,588 ) $ 22.54 $ 9.05 Forfeited 8,331 (106,996 ) $ 26.15 $ 13.20 Expired (181,834 ) $ 54.02 $ 19.93 Balances at September 30, 2017 652,494 881,403 $ 27.31 $ 11.55 3.57 $ 9.8 Exercisable at September 30, 2017 222,116 $ 24.42 $ 10.43 2.52 $ 3.1 The total compensation cost not yet recognized for non-vested awards of $3.9 million as of September 30, 2017 has a weighted-average period of 3.92 years over which the compensation expense is expected to be recognized. The total intrinsic value of options exercised during fiscal years 2017, 2016 and 2015 was $2.6 million , $1.9 million and $3.6 million , respectively. The options outstanding as of September 30, 2017 broken down by exercise price are as follows: Exercise Price Number of Options Outstanding Weighted Average Exercise Price Weighted Average Remaining Term $ — - $ 5.00 — n/a n/a $ 5.00 - $ 10.00 — n/a n/a $ 10.00 - $ 15.00 — n/a n/a $ 15.00 - $ 20.00 22,414 $ 19.24 0.30 $ 20.00 - $ 25.00 97,911 $ 21.77 0.84 $ 25.00 - $ 30.00 580,000 $ 25.91 4.37 $ 30.00 - $ 35.00 73,578 $ 31.37 2.28 $ 35.00 - $ 40.00 107,500 $ 38.77 3.27 $ 40.00 - $ 45.00 — n/a n/a $ 45.00 - $ 50.00 — n/a n/a $ 50.00 - $ 55.00 — n/a n/a 881,403 $ 27.31 3.57 Restricted Stock Plan The Company sponsors a restricted stock plan for its directors, officers and employees. The Company’s 2017 restricted stock plan, which was approved by the Company’s Board of Directors and shareholders, authorizes up to 1.5 million shares to be issued. As of September 30, 2017 , 1.5 million shares were authorized for future grant under the restricted stock plan. Awards that expire or are canceled generally become available for issuance again under the plan. The Company utilizes newly issued shares of common stock to make restricted stock grants. The following is a summary of restricted stock activity through September 30, 2017 : Shares Available for Grant Number of Shares Outstanding Weighted Average Grant Date Fair Value Weighted Average Remaining Term (in years) Aggregate Intrinsic Value ($ millions) Balances at September 30, 2016 747,782 357,752 $ 27.39 1.39 $ 13.9 Additional shares authorized by shareholders 1,500,000 Termination of 2012 plan (640,539 ) Granted (147,726 ) 147,726 $ 40.98 Vested (150,545 ) $ 26.69 Forfeited 459 (459 ) $ 37.31 Balances at September 30, 2017 1,459,976 354,474 $ 33.34 1.26 $ 13.6 The total compensation cost not yet recognized of $8.2 million as of September 30, 2017 has a weighted-average period of 1.26 years over which the compensation expense is expected to be recognized. Compensation expense is amortized on a straight-line basis over the vesting period. Restricted stock grants are included in the Company’s total issued and outstanding common shares.

Retirement Plans (Notes)

Retirement Plans (Notes)	12 Months Ended
	Sep. 30, 2017
Retirement Benefits [Abstract]
Pension and Other Postretirement Benefits Disclosure [Text Block]	Retirement Plans Defined Benefit Retirement Plans The Company has a frozen defined benefit pension plan (the “Plan”) and recognizes its funded status, measured as the difference between the fair value of the plan assets and the projected benefit obligation, in “accounts payable and other accrued liabilities” in the consolidated balance sheets. Plan assets, which are managed in a third-party trust, primarily consist of a diversified blend of approximately 80% debt securities and 20% equity investments and had a total fair value of $36.4 million and $33.7 million as of September 30, 2017 and 2016, respectively. All plan assets fall within Level 2 of the fair value hierarchy. The benefit obligation associated with the Plan will vary over time only as a result of changes in market interest rates, the life expectancy of the plan participants, and benefit payments, since the accrual of benefits was suspended when the Plan was frozen in 2006. The benefit obligation was $36.5 million and $38.5 million and the discount rate assumption used in the measurement of this obligation was 3.75% and 3.60% as of September 30, 2017 and 2016, respectively. The Company’s unfunded pension obligation was $0.1 million and $4.8 million as of September 30, 2017 and 2016, respectively. The Company recognized a net periodic benefit $0.3 million for the year ended September 30, 2017. The net periodic benefit cost associated with the Plan was $0.2 million for the year ended September 30, 2016 and less than $0.1 million for the year ended September 30, 2015. The expected long-term return on plan assets assumption is 6.00% for 2017. The Company made contributions of $2.0 million and $1.8 million to the Plan in the years ended September 30, 2017 and 2016, respectively. The Company complies with minimum funding requirements. The estimated undiscounted future benefit payments are expected to be $2.1 million in 2018, $2.1 million in 2019, $2.0 million in 2020, $2.0 million in 2021, $1.9 million in 2022 and $9.5 million in 2023 through 2027. Defined Contribution Retirement Plans The Company offers participation in the INTL FCStone Inc. 401(k) Plan (“401(k) Plan”), a defined contribution plan providing retirement benefits, to all domestic employees who have reached 21 years of age, and provided four months of service to the Company. Employees may contribute from 1% to 80% of their annual compensation to the 401(k) Plan, limited to a maximum annual amount as set periodically by the Internal Revenue Service. The Company makes matching contributions to the 401(k) Plan in an amount equal to 62.5% of each participant’s eligible elective deferral contribution to the 401(k) Plan, up to 8% of employee compensation. Matching contributions vest, by participant, based on the following years of service schedule: less than two years – none, after two years – 33% , after three years – 66% , and after four years – 100% . U.K. based employees of INTL FCStone are eligible to participate in a defined contribution pension plan. The Company contributes double the employee’s contribution up to 10% of total base salary for this plan. For this plan, employees are 100% vested in both the employee and employer contributions at all times. For fiscal years ended September 30, 2017, 2016, and 2015 , the Company’s contribution to these defined contribution plans were $6.1 million , $5.3 million and $5.1 million , respectively.

Other Expenses (Notes)

Other Expenses (Notes)	12 Months Ended
	Sep. 30, 2017
Other Expenses [Abstract]
Other Expenses [Text Block]	Other Expenses Other expenses for the years ended September 30, 2017, 2016, and 2015 are comprised of the following: Year Ended September 30, (in millions) 2017 2016 2015 Contingent consideration, net (1) 0.1 0.4 1.8 Insurance 2.7 2.1 1.7 Advertising, meetings and conferences 4.0 5.1 2.7 Non-trading hardware and software maintenance and software licensing 11.6 7.1 4.7 Office supplies and printing 2.1 1.1 1.2 Other clearing related expenses 2.6 1.3 1.1 Other non-income taxes 4.6 4.3 3.7 Other 9.8 8.0 6.6 Total other expenses $ 37.5 $ 29.4 $ 23.5 (1) Contingent consideration includes remeasurement of contingent liabilities related to business combinations accounted for in accordance with the provisions of the Business Combinations Topic of the ASC (see Note 4 ).

Income Taxes (Notes)

Income Taxes (Notes)	12 Months Ended
	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Income Tax Disclosure [Text Block]	Income Taxes Income tax expense (benefit) for the years ended September 30, 2017, 2016, and 2015 was allocated as follows: Year Ended September 30, (in millions) 2017 2016 2015 Income tax expense attributable to income from operations $ 8.8 $ 18.0 $ 22.4 Taxes allocated to stockholders’ equity, related to unrealized losses on available-for-sale securities — — (0.4 ) Taxes allocated to stockholders’ equity, related to pension liabilities 1.0 0.2 (0.8 ) Taxes allocated to additional paid-in capital, related to share-based compensation 0.1 (0.8 ) (0.5 ) Total income tax expense $ 9.9 $ 17.4 $ 20.7 The components of income tax expense (benefit) attributable to income from operations were as follows: Year Ended September 30, (in millions) 2017 2016 2015 Current taxes: U.S. federal $ 0.7 $ 1.3 $ 0.8 U.S. State and local 1.2 0.8 1.2 International 16.7 16.8 15.4 Total current taxes 18.6 18.9 17.4 Deferred taxes (9.8 ) (0.8 ) 5.0 Income tax benefit attributable to interest income $ — $ (0.1 ) $ — Income tax expense $ 8.8 $ 18.0 $ 22.4 U.S. and international components of (loss) income from operations, before tax, was as follows: Year Ended September 30, (in millions) 2017 2016 2015 U.S. $ (13.9 ) $ 4.9 $ 14.5 International 29.1 67.9 63.7 Income from operations, before tax $ 15.2 $ 72.8 $ 78.2 Items accounting for the difference between income taxes computed at the federal statutory rate and income tax expense were as follows: Year Ended September 30, 2017 2016 2015 Federal statutory rate effect of: 35.0 % 35.0 % 35.0 % U.S. State and local income taxes (2.6 )% 1.3 % 1.8 % Foreign earnings and losses taxed at lower rates 11.5 % (11.0 )% (11.1 )% Change in foreign valuation allowance (1.4 )% (0.3 )% (0.1 )% Change in state valuation allowance 4.1 % — % 0.6 % U.S. permanent items 3.6 % 0.8 % 0.5 % Foreign permanent items 8.1 % 1.9 % 2.1 % U.S. bargain purchase gain — % (3.0 )% — % Other reconciling items (0.6 )% 0.3 % (0.1 )% Effective rate 57.7 % 25.0 % 28.7 % The components of deferred income tax assets and liabilities were as follows: (in millions) September 30, 2017 September 30, 2016 Deferred tax assets: Share-based compensation $ 3.7 $ 4.3 Pension liability 0.1 1.9 Deferred compensation 2.0 2.0 Foreign net operating loss carryforwards 5.6 2.0 U.S. State and local net operating loss carryforwards 6.6 4.9 U.S. federal net operating loss carryforwards 21.9 12.4 Intangible assets 6.1 8.3 Bad debt reserve 1.4 1.6 Tax credit carryforwards 1.6 1.4 Other compensation 3.6 3.3 Other 1.9 1.8 Total gross deferred tax assets 54.5 43.9 Less valuation allowance (4.0 ) (3.6 ) Deferred tax assets 50.5 40.3 Deferred income tax liabilities: Unrealized gain on securities 3.2 1.3 Prepaid expenses 2.5 1.9 Property and equipment 2.2 2.6 Deferred income tax liabilities 7.9 5.8 Deferred income taxes, net $ 42.6 $ 34.5 Deferred income tax balances reflect the effects of temporary differences between the carrying amounts of assets and liabilities and their tax bases and are stated at enacted tax rates expected to be in effect when taxes are actually paid or recovered. As of September 30, 2017 and 2016 , the Company has net operating loss carryforwards for U.S. federal, state, local, and foreign income tax purposes of $30.1 million and $15.7 million , net of valuation allowances, respectively, which are available to offset future taxable income in these jurisdictions. The U.S. federal net operating loss carryforward of $21.9 million begins to expire after September 2033. The state and local net operating loss carryforwards of $4.4 million , net of valuation allowance, begin to expire after September 2020. The Company has an Alternative Minimum Tax credit carryforward of $1.3 million , which has an indefinite life, and an R&D credit carryforward of $0.4 million that begins to expire after September 2031. INTL Asia Pte. Ltd. has a net operating loss carryforward of $3.8 million . This Singapore net operating loss has an indefinite carryforward and, in the judgment of management, is more likely than not to be realized. The valuation allowance for deferred tax assets as of September 30, 2017 was $4.0 million . The net change in the total valuation allowance for the year ended September 30, 2017 was an increase of $0.4 million . The valuation allowances as of September 30, 2017 and 2016 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 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 taxes are realizable, the Company considered deferred tax liabilities of $4.9 million that are scheduled to reverse from 2018 to 2020 and $3.1 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 11 years. Based on the tax planning strategies that can be implemented, 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. The total amount of undistributed earnings in the Company’s foreign subsidiaries, for income tax purposes, was $321.3 million and $294.3 million as of September 30, 2017 and 2016 , respectively. It is the Company’s current intention to reinvest undistributed earnings of its foreign subsidiaries in the foreign jurisdictions, resulting in the indefinite postponement of the remittance of those earnings. Accordingly, no provision has been made for foreign withholding taxes or U.S. federal income taxes which may become payable if undistributed earnings of foreign subsidiaries were paid as dividends to the Company. The Company recognizes the tax benefit from an uncertain tax position only if it is more likely than not that the tax position will be sustained on examination by the taxing authority, based upon the technical merits of the position. The tax benefit recognized in the consolidated financial statements from such a position is measured based on the largest benefit that has a greater than 50% likelihood of being realized upon ultimate settlement. A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows: Year Ended September 30, (in millions) 2017 2016 2015 Balance, beginning of year $ 0.1 $ — $ — Gross increases for tax positions related to current year — — — Gross increases for tax positions related to prior years — 0.1 — Gross decreases for tax positions of prior years — — — Settlements — — — Lapse of statute of limitations — — — Balance, end of year $ 0.1 $ 0.1 $ — The Company has a minimal balance of unrecognized tax benefits as of September 30, 2017 , that, if recognized, would affect the effective tax rate. While it is expected that the amount of unrecognized tax benefits will change in the next twelve months, the Company does not expect this change to have a material impact on the results of operations or the financial position of the Company. Accrued interest and penalties are included in the related tax liability line in the consolidated balance sheets. The Company had no accrued interest and penalties included in the consolidated balance sheets as of September 30, 2017 and 2016 . The Company recognizes accrued interest and penalties related to income taxes as a component of income tax expense. The Company had no amount of interest, net of federal benefit, and penalties recognized as a component of income tax expense during the years ended September 30, 2017, 2016, and 2015 . The Company and its subsidiaries file income tax returns with the U.S. federal jurisdiction and various U.S. state and 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, 2016. 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.

Acquisitions and Disposals (Not

Acquisitions and Disposals (Notes)	12 Months Ended
	Sep. 30, 2017
Business Combinations [Abstract]
Business Combination Disclosure [Text Block]	Acquisitions The Company’s consolidated financial statements include the operating results of the acquired businesses from the dates of acquisition. Acquisition in Fiscal 2017 ICAP’s EMEA Oils Broking Business Effective October 1, 2016, the Company’s subsidiary, INTL FCStone Ltd acquired the London-based EMEA oils business of ICAP Plc. The business included more than 30 front office employees across the fuel, crude, middle distillates, futures and options desks that have relationships with more than 200 commercial and institutional customers throughout Europe, the Middle East and Africa. The terms of the agreement included cash consideration of $6.0 million paid directly to ICAP as well as incentive amounts payable to employees acquired based upon their continued employment. The cash consideration paid to ICAP was dependent upon the number of brokers who accepted INTL FCStone Ltd’s employment offer. The transaction was accounted for as an asset acquisition in accordance with FASB ASC 805-50 and FASB ASC 350. The cash consideration paid was allocated entirely to the intangible asset recognized related to the customer base acquired. The intangible asset was assigned to the Clearing and Execution Services segment and will be amortized over a useful life of 5 years. Acquisition in Fiscal 2016 Sterne Agee Effective July 1, 2016 , the Company acquired all of the equity interests of Sterne Agee, LLC’s (a wholly-owned subsidiary of Stifel Financial Corp.) legacy independent brokerage and clearing businesses, Sterne Agee & Leach, Inc.; Sterne Agee Clearing, Inc.; Sterne Agee Financial Services, Inc. Effective August 1, 2016 , the Company acquired all of the equity interests of Sterne Agee, LLC’s legacy Registered Investment Advisor (“RIA”) business, Sterne Agee Asset Management, Inc. and Sterne Agee Investment Advisor Services, Inc. - collectively (“Sterne Agee”) for cash consideration. Effective July 1, 2017, Sterne Agee & Leach, Inc. was merged into the Company’s wholly-owned regulated U.S. subsidiary, INTL FCStone Financial. Additionally, during 2017, Sterne Agee Clearing, Inc., Sterne Agee Financial Services, Inc., Sterne Agee Asset Management, Inc., and Sterne Agee Investment Advisor Services, Inc. were renamed INTL Custody & Clearing Solutions, Inc., SA Stone Wealth Management, Inc., INTL Advisory Consultants, Inc., and SA Stone Investment Advisors, Inc., respectively. The acquisition-date fair value of the consideration transferred totaled $45.0 million . The purchase price allocation resulted in $24.9 million in cash, $151.6 million in receivables, $5.7 million in deferred tax assets, $4.8 million in other assets and $136.0 million in liabilities assumed. The fair value of identifiable assets acquired and liabilities assumed exceeded the fair value of the consideration transferred. Consequently, the Company reassessed the recognition and measurement of identifiable assets acquired and liabilities assumed and concluded that all acquired assets and assumed liabilities were recognized and that the valuation procedures and resulting measures were appropriate. As a result, the Company recognized a gain of $6.2 million for the year ended September 30, 2016, which is included in the line item ‘gain on acquisition’ in the consolidated income statement. The Company believes the transaction resulted in a gain primarily due to the Company’s ability to incorporate these business activities into its existing business structure, and its ability to utilize certain deferred tax assets and other assets while operating the business that may not have been likely to be realized by the seller. There were no purchase price adjustments recorded during the measurement period and the purchase price allocation is now considered final. The businesses have been included within the Company’s Clearing and Execution Services Segment. The Company’s consolidated income statement for the year ended September 30, 2016 includes the post-acquisition results of the Sterne Agee businesses, which were immaterial. The acquired businesses contributed net operating revenues of $8.6 million and net loss of $0.1 million to the Company for the period from July 1, 2016 to September 30, 2016. Acquisition in Fiscal 2015 G.X. Clarke & Co. Effective January 1, 2015, the Company acquired all of the partnership interests of G.X. Clarke & Co., an SEC registered institutional dealer in fixed income securities. G.X. Clarke was based in New Jersey, transacted in U.S. Treasury, U.S. government agency and agency mortgage-backed securities, and was a FINRA member with an institutional customer base consisting of asset managers, commercial bank trust and investment departments, broker-dealers, and insurance companies. The purchase price payable by the Company was equal to G.X. Clarke’s net tangible book value at closing of approximately $25.9 million plus a premium of $1.5 million , and up to an additional $1.5 million over the next three years, subject to the achievement of certain profitability thresholds. In conjunction with the acquisition, the name of G.X. Clarke was changed to INTL FCStone Partners L.P. INTL FCStone Partners L.P. was subsequently merged into the Company’s wholly-owned regulated U.S. subsidiary, INTL FCStone Financial. The acquisition agreement included the purchase of certain tangible assets and assumption of certain liabilities. For the acquisition, management made an initial fair value estimate of the assets acquired and liabilities assumed as of January 1, 2015. The Company believed that due to the short-term nature of many of the tangible assets acquired and liabilities assumed, that their carrying values, as included in the historical financial statements of G.X. Clarke, approximated their fair values. The Company finalized its purchase accounting estimates with the assistance of a third-party valuation expert. The portion of the purchase price representing the initial premium of $1.5 million and the contingent consideration of $0.1 million has been assigned to the customer base and software programs/platforms intangible assets (see Note 10 ). The Company assigned useful lives of 5 years for the customer base and software programs/platforms intangible assets. As part of the net cash paid, the Company and G.X. Clarke established two escrow accounts totaling $10.0 million , related to an Adjustment Escrow and Indemnity Escrow. The Adjustment Escrow, of $5.0 million , related to potential purchase price adjustment obligations was released, during year ended September 30, 2015, upon determination of the final tangible book value of net assets of G.X. Clarke. The Indemnity Escrow, of $5.0 million , related to potential claims made by the Company for indemnification in accordance with the terms of the acquisition agreement and was to be released immediately following the twenty-four month anniversary of the closing date of the acquisition. The Indemnity Escrow was released during the year ended September 30, 2017. In addition, as part of the net cash paid for the acquisition, the Company deferred payment of $5.0 million , in accordance with the terms of the acquisition agreement. The deferred payment is equal to $5.0 million less the aggregate net loss, if any, incurred for the twelve full fiscal quarters commencing after the closing date. The deferred payment amount shall be due upon and payable shortly after the twelfth full fiscal quarter commencing after the closing date. A pro rata share of the deferred payment amount is due to partners who are terminated prior to the maturity date assuming certain conditions of the agreement are met. The unpaid deferred payment amount of $4.5 million is included in ‘accounts payable and other accrued liabilities’ in the consolidated balance sheet. As discussed above, the terms of the acquisition agreement include a contingent payment of an additional purchase price of up to $1.5 million , based on the performance of the acquired business. The contingent consideration, which in no event shall exceed $1.5 million , is expected to be paid in two payments. The first payment was made after the first four full fiscal quarters commencing after the closing date, and totaled $0.5 million , as the acquired business generated more than $5.0 million in after-tax net income over the first four full fiscal quarters after the closing date. The second and final payment is expected to occur in February 2018. This payment is estimated to be $1.0 million , if the acquired business has generated accumulated after-tax net income of greater than $30.0 million over the twelve full fiscal quarters commencing after the closing date.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss) (Notes)	12 Months Ended
	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Abstract]
Comprehensive Income (Loss) Note [Text Block]	Accumulated Other Comprehensive Income (Loss) 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 income (loss) includes net actuarial gains from defined benefit pension plans and losses on foreign currency translations. The following table summarizes the changes in accumulated other comprehensive income (loss) for the year ended September 30, 2017 . (in millions) Foreign Currency Translation Adjustment Pension Benefits Adjustment Accumulated Other Comprehensive Loss Balances as of September 30, 2016 $ (20.1 ) $ (4.5 ) $ (24.6 ) Other comprehensive income (loss), net of tax before reclassifications (1.4 ) 1.2 (0.2 ) Amounts reclassified from AOCI, net of tax — 0.3 0.3 Other comprehensive income (loss), net of tax (1.4 ) 1.5 0.1 Balances as of September 30, 2017 $ (21.5 ) $ (3.0 ) $ (24.5 )

Quarterly Financial Information

Quarterly Financial Information (Unaudited) (Notes)	12 Months Ended
	Sep. 30, 2017
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information [Text Block]	Quarterly Financial Information (Unaudited) The Company has set forth certain quarterly unaudited financial data for the past two years in the tables below: For the 2017 Fiscal Quarter Ended (in millions, except per share amounts) September 30 (1) June 30 March 31 December 31 Total revenues $ 12,382.5 $ 5,505.9 $ 5,460.8 $ 6,074.4 Cost of sales of physical commodities 12,177.4 5,308.3 5,265.0 5,888.9 Operating revenues 205.1 197.6 195.8 185.5 Transaction-based clearing expenses 35.1 33.9 33.7 33.6 Introducing broker commissions 26.9 29.2 28.2 28.7 Interest expense 12.0 11.2 10.0 8.9 Net operating revenues 131.1 123.3 123.9 114.3 Compensation and benefits 73.0 75.5 76.6 70.6 Bad debts 0.4 0.1 1.3 2.5 Bad debt on physical coal 47.0 — — — Other expenses 33.2 32.7 31.7 32.8 Total compensation and other expenses 153.6 108.3 109.6 105.9 (Loss) income from operations, before tax (22.5 ) 15.0 14.3 8.4 Income tax expense 1.1 2.3 3.3 2.1 Net (loss) income $ (23.6 ) $ 12.7 $ 11.0 $ 6.3 Net basic (loss) earnings per share $ (1.27 ) $ 0.67 $ 0.58 $ 0.34 Net diluted (loss) earnings per share $ (1.27 ) $ 0.66 $ 0.58 $ 0.34 (1) During the fourth quarter of fiscal 2017, the Company recorded a charge to earnings of $47.0 million , to record an allowance for doubtful accounts related to a bad debt incurred in the physical coal business conducted solely in INTL Asia Pte. Ltd., with a coal supplier, as further discussed in Note 2 . For the 2016 Fiscal Quarter Ended (in millions, except per share amounts) September 30 June 30 March 31 December 31 Total revenues $ 2,777.6 $ 4,868.5 $ 3,708.9 $ 3,399.9 Cost of sales of physical commodities 2,599.0 4,693.5 3,542.8 3,248.6 Operating revenues 178.6 175.0 166.1 151.3 Transaction-based clearing expenses 32.0 35.2 32.9 29.8 Introducing broker commissions 28.1 14.8 13.2 12.8 Interest expense 7.5 7.7 7.1 6.0 Net operating revenues 111.0 117.3 112.9 102.7 Compensation and benefits 66.2 69.4 65.2 63.1 Bad debts (0.2 ) — 2.6 2.0 Other expenses 32.0 26.5 25.1 25.5 Total compensation and other expenses 98.0 95.9 92.9 90.6 Gain on acquisition 6.2 — — — Income from operations, before tax 19.2 21.4 20.0 12.1 Income tax expense 2.4 6.8 5.5 3.3 Net income $ 16.8 $ 14.6 $ 14.5 $ 8.8 Net basic earnings per share $ 0.91 $ 0.79 $ 0.77 $ 0.47 Net diluted earnings per share $ 0.90 $ 0.78 $ 0.76 $ 0.46

Segment and Geographic Informat

Segment and Geographic Information (Notes)	12 Months Ended
	Sep. 30, 2017
Segment Analysis [Abstract]
Segment Reporting Disclosure [Text Block]	Segment and Geographic Information 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 and Options, FX Prime Brokerage, Correspondent Clearing, Independent Wealth Management, and Derivative Voice Brokerage) Commercial Hedging The Company serves its commercial customers through its team of risk management consultants, providing a high-value-added service that it believes differentiates the Company from its competitors and maximizes the opportunity to retain customers. The Company’s risk management consulting services are designed to quantify and monitor commercial entities’ exposure to commodity and financial risk. Upon assessing this exposure, the Company develops a plan to control and hedge these risks with post-trade reporting against specific customer objectives. Customers are assisted in the execution of their hedging strategies through a wide range of products from listed exchange-traded futures and options, to basic OTC instruments that offer greater flexibility, to structured OTC products designed for customized solutions. The Company’s services span virtually all traded commodity markets, with the largest concentrations in agricultural and energy commodities (consisting primarily of grains, energy and renewable fuels, coffee, sugar, cotton, and food service) and base metals products listed on the LME. The Company’s base metals business includes a position as a Category One ring dealing member of the LME, providing execution, clearing and advisory services in exchange-traded futures and OTC products. The Company also provides execution of foreign currency forwards and options and interest rate swaps as well as a wide range of structured product solutions to commercial customers who are seeking cost-effective hedging strategies. Generally, customers direct their own trading activity and the Company’s risk management consultants do not have discretionary authority to transact trades on behalf of customers. Global Payments The Company provides global payment solutions to banks and commercial businesses as well as charities and non-governmental organizations and government organizations. The Company offers payments services in more than 175 countries and 140 currencies, which it believes is more than any other payments solution provider, and provides competitive and transparent pricing. Its proprietary FXecute global payments platform is integrated with a financial information exchange (“FIX”) protocol. This FIX protocol is an electronic communication method for the real-time exchange of information, and the Company believes it represents one of the first FIX offerings for cross-border payments in exotic currencies. FIX functionality allows customers to view real time market rates for various currencies, execute and manage orders in real-time, and view the status of their payments through the easy-to-use portal. Additionally, as a member of the Society for Worldwide Interbank Financial Telecommunication (“SWIFT”), the Company is able to offer its services to large money center and global banks seeking more competitive international payments services. Through this single comprehensive platform and our commitment to customer service, the Company believes it is able to provide simple and fast execution, ensuring delivery of funds in any of these countries quickly through its global network of approximately 300 correspondent banks. In this business, the Company primarily acts as a principal in buying and selling foreign currencies on a spot basis. The Company derives revenue from the difference between the purchase and sale prices. The Company believes its customers value its ability to provide exchange rates that are significantly more competitive than those offered by large international banks, a competitive advantage that stems from its years of foreign exchange expertise focused on smaller, less liquid currencies. Securities The Company provides value-added solutions that facilitate cross-border trading and believes its customers value the Company’s ability to manage complex transactions, including foreign exchange, utilizing its local understanding of market convention, liquidity and settlement protocols around the world. The Company’s customers include U.S.-based regional and national broker-dealers and institutions investing or executing customer transactions in international markets and foreign institutions seeking access to the U.S. securities markets. The Company is one of the leading market makers in foreign securities, including unlisted ADRs, GDRs and foreign ordinary shares. The Company makes markets in over 3,600 ADRs, GDRs and foreign ordinary shares, of which over 2,000 trade in the OTC market. In addition, it will, on request, make prices in more than 10,000 unlisted foreign securities. The Company is also a broker-dealer in Argentina where we are active in providing institutional executions in the local capital markets. The Company acts as an institutional dealer in fixed income securities, including U.S. Treasury, U.S. government agency, agency mortgage-backed and asset-backed securities to a customer base including asset managers, commercial bank trust and investment departments, broker-dealers and insurance companies. The Company also originates, structures and places debt instruments in the international and domestic capital markets. These instruments include complex asset-backed securities (primarily in Argentina) and domestic municipal securities. On occasion, the Company may invest its own capital in debt instruments before selling them. The Company also actively trades in a variety of international debt instruments and operates an asset management business in which it earns fees, commissions and other revenues for management of third party assets and investment gains or losses on its investments in funds and proprietary accounts managed either by its investment managers or by independent investment managers. Physical Commodities This segment consists of the Company’s physical Precious Metals trading and Physical Agricultural and Energy commodity businesses. In Precious Metals, the Company provides a full range of trading and hedging capabilities, including OTC products, to select producers, consumers, and investors. In the Company’s trading activities, it acts as a principal, committing its own capital to buy and sell precious metals on a spot and forward basis. In the Company’s Physical Ag & Energy commodity business, it acts as a principal to facilitate financing, structured pricing and logistics services to clients across the commodity complex, including energy commodities, grains, oil seeds, cotton, coffee, cocoa, edible oils and feed products. The Company provides financing to commercial commodity-related companies against physical inventories. The Company uses sale and repurchase agreements to purchase commodities evidenced by warehouse receipts, subject to a simultaneous agreement to sell such commodities back to the original seller at a later date. Transactions where the sale and repurchase price are fixed upon execution, and meet additional required conditions, are accounted for as product financing arrangements, and accordingly no commodity inventory, purchases or sales are recorded. Transactions where the repurchase price is not fixed at execution do not meet all the criteria to be accounted for as product financing arrangements, and therefore are recorded as commodity inventory, purchases and sales. INTL FCStone Ltd precious metals sales and cost of sales are presented on a net basis and included as a component of ‘trading gains, net’ in the consolidated income statements, in accordance with U.S GAAP accounting requirements for broker-dealers. Precious metals sales and cost of sales for subsidiaries that are not broker-dealers continue to be recorded on a gross basis. Precious metals inventory held by subsidiaries that are not broker-dealers continues to be valued at the lower of cost or market value. Precious metals sales and cost of sales for subsidiaries that are not broker-dealers continue to be recorded on a gross basis. The agricultural commodity inventories are carried at net realizable value, which approximates fair value less disposal costs. The agricultural inventories have reliable, readily determinable and realizable market prices, have relatively insignificant costs of disposal and are available for immediate delivery. The Company records its Physical Ag & Energy commodities revenues on a gross basis. Operating revenues and losses from its precious metals commodities derivatives activities are included in ‘trading gains, net’ in the consolidated income statements. Operating revenues and losses from our Physical Ag and Energy commodity business are included in ‘cost of sales of physical commodities’ in the consolidated income statements The Company generally mitigates the price risk associated with commodities held in inventory through the use of derivatives. The Company does not elect hedge accounting under U.S. GAAP in accounting for this price risk mitigation. The Company’s management continues to evaluate performance and allocated resources on an operating revenue basis. Clearing and Execution Services (CES) The Company provides competitive and efficient clearing and execution in all major futures and securities exchanges globally as well as prime brokerage in all major foreign currency pairs and swap transactions. Through its platform, customer orders are accepted and directed to the appropriate exchange for execution. The Company then facilitates the clearing of customers’ transactions. Clearing involves the matching of customers’ trades with the exchange, the collection and management of customer margin deposits to support the transactions, and the accounting and reporting of the transactions to customers. As of September 30, 2017 , the Company held $2.2 billion in required customer segregated assets, which it believes makes it the third largest independent futures commission merchant (“FCM”) in the United States not affiliated with a major financial institution or commodity intermediary, end-user or producer, as measured by required customer segregated assets. The Company seeks to leverage its capabilities and capacity by offering facilities management or outsourcing solutions to other FCM’s. Following the Company’s acquisition of the Sterne Agee correspondent clearing business, it is an independent full-service provider to introducing broker-dealers (“IBD’s”) of clearing, custody, research, syndicated and security-based lending products and services, including a proprietary technology platform which offers seamless connectivity to ensure a positive customer experience through the clearing and settlement process. Also as part of this transaction, the Company acquired Sterne Agee’s independent wealth management business which offers a comprehensive product suite to retail customers nationwide. As a result it is one of the leading mid-market clearer’s in the securities industry, with approximately 50 correspondent clearing relationships with over $15 billion in assets under management or administration as of September 30, 2017 . In addition, the Company believes it is one of the largest non-bank prime brokers and swap dealers in the world. Through this offering, it provides prime brokerage foreign exchange services to financial institutions and professional traders. The Company provides its customers with the full range of OTC products, including 24-hour a day execution of spot, forwards and options as well as non-deliverable forwards in both liquid and exotic currencies. The Company also operates a proprietary foreign exchange desk that arbitrages the exchange-traded foreign exchange markets with the cash markets. Following the October 1, 2016 acquisition of ICAP plc’s London-based EMEA oil voice brokerage business, the Company employs over 30 employees providing brokerage services across the fuel, crude and middle distillates markets with over 200 well known commercial and institutional customers throughout Europe, the Middle East and Africa. ******** The total revenues reported combine gross revenues for the physical commodities business and net revenues for all other businesses. In order to reflect the way that the Company’s management views the results, the tables below also reflect the segment contribution to ‘operating revenues’, which is shown on the face of the 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 debts 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 for 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 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 concerning operations in these segments of business is shown in accordance with the Segment Reporting Topic of the ASC as follows: Year Ended September 30, (in millions) 2017 2016 2015 Total revenues: Commercial Hedging $ 244.6 $ 236.1 $ 262.4 Global Payments 89.2 73.2 77.1 Securities 151.7 175.2 129.8 Physical Commodities 28,684.4 14,120.5 34,092.0 Clearing and Execution Services 259.8 151.1 123.4 Corporate unallocated (6.1 ) (1.2 ) 8.5 Total $ 29,423.6 $ 14,754.9 $ 34,693.2 Operating revenues (loss): Commercial Hedging $ 244.6 $ 236.1 $ 262.4 Global Payments 89.2 73.2 77.1 Securities 151.7 175.2 129.8 Physical Commodities 44.8 36.6 23.1 Clearing and Execution Services 259.8 151.1 123.4 Corporate unallocated (6.1 ) (1.2 ) 8.5 Total $ 784.0 $ 671.0 $ 624.3 Net operating revenues (loss): Commercial Hedging $ 194.3 $ 188.2 $ 214.7 Global Payments 80.6 65.3 68.5 Securities 94.6 121.9 88.6 Physical Commodities 37.3 31.5 21.2 Clearing and Execution Services 102.2 48.8 38.3 Corporate unallocated (16.4 ) (11.8 ) 0.5 Total $ 492.6 $ 443.9 $ 431.8 Net contribution: (Revenues less cost of sales, transaction-based clearing expenses, variable bonus compensation, introducing broker commissions and interest expense): Commercial Hedging $ 141.8 $ 134.4 $ 151.7 Global Payments 64.4 52.2 54.5 Securities 75.6 97.5 67.4 Physical Commodities 27.2 23.4 16.9 Clearing and Execution Services 78.0 39.5 30.1 Total $ 387.0 $ 347.0 $ 320.6 Segment income: (Net contribution less non-variable direct segment costs): Commercial Hedging $ 72.8 $ 68.7 $ 85.6 Global Payments 50.6 39.8 43.3 Securities 46.6 69.4 40.5 Physical Commodities (1) (31.4 ) 13.3 5.8 Clearing and Execution Services 30.4 14.8 12.9 Total $ 169.0 $ 206.0 $ 188.1 Reconciliation of segment income to income from operations, before tax: Segment income $ 169.0 $ 206.0 $ 188.1 Costs not allocated to operating segments 153.8 133.3 110.0 Income from operations, before tax $ 15.2 $ 72.7 $ 78.1 (1) During the fourth quarter of fiscal 2017, the Company recorded a charge to earnings of $47.0 million, to record an allowance for doubtful accounts related to a bad debt incurred in the physical coal business conducted solely in INTL Asia Pte. Ltd., with a coal supplier, as further discussed in Note 2 . (in millions) As of September 30, 2017 As of September 30, 2016 As of September 30, 2015 Total assets: Commercial Hedging $ 1,650.3 $ 1,637.5 $ 1,548.1 Global Payments 199.5 191.4 207.3 Securities 2,101.7 2,130.7 1,861.0 Physical Commodities 339.5 258.0 190.9 Clearing and Execution Services 1,818.9 1,617.4 1,163.8 Corporate unallocated 133.5 115.3 98.9 Total $ 6,243.4 $ 5,950.3 $ 5,070.0 Information regarding revenues and operating revenues for the years ended September 30, 2017, 2016, and 2015 , and information regarding long-lived assets (defined as property, equipment, leasehold improvements and software) as of September 30, 2017, 2016, and 2015 in geographic areas were as follows: Year Ended September 30, (in millions) 2017 2016 2015 Total revenues: United States $ 1,168.0 $ 817.1 $ 25,959.0 Europe 166.9 463.5 121.2 South America 53.9 64.8 49.0 Asia 28,030.3 13,405.1 8,560.0 Other 4.5 4.4 4.0 Total $ 29,423.6 $ 14,754.9 $ 34,693.2 Operating revenues: United States $ 529.4 $ 457.0 $ 424.3 Europe 166.9 120.2 125.0 South America 54.0 64.8 49.0 Asia 29.2 24.6 21.9 Other 4.5 4.4 4.1 Total $ 784.0 $ 671.0 $ 624.3 (in millions) As of September 30, 2017 As of September 30, 2016 As of September 30, 2015 Long-lived assets, as defined: United States $ 29.7 $ 23.3 $ 13.8 Europe 7.3 4.8 4.0 South America 1.5 1.2 1.7 Asia 0.2 0.1 0.2 Total $ 38.7 $ 29.4 $ 19.7

Condensed Parent Only Financial

Condensed Parent Only Financial Statements (Notes)	12 Months Ended
	Sep. 30, 2017
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed Financial Information of Parent Company Only Disclosure [Text Block]	Schedule I INTL FCStone Inc. Condensed Balance Sheets Parent Company Only (in millions) September 30, September 30, ASSETS Cash and cash equivalents $ 2.0 $ 1.3 Deposits and receivables from broker-dealers, clearing organizations and counterparties — 2.9 Receivable from subsidiaries, net 3.8 3.6 Notes receivable, net 4.8 6.9 Income taxes receivable 8.6 14.0 Investment in subsidiaries (1) 312.3 316.3 Financial instruments owned, at fair value — 1.3 Deferred income taxes, net 26.5 15.7 Property and equipment, net 24.8 12.7 Other assets 7.6 16.2 Total assets $ 390.4 $ 390.9 LIABILITIES AND EQUITY Liabilities: Accounts payable and other accrued liabilities $ 19.8 $ 27.7 Payable to customers 2.1 4.6 Payable to lenders under loans 152.0 139.3 Payable to subsidiaries, net 49.4 17.1 Senior unsecured notes — 44.5 Financial instruments sold, not yet purchased, at fair value 25.3 35.9 Total liabilities 248.6 269.1 Equity: INTL FCStone Inc. (Parent Company Only) stockholders’ equity: Preferred stock, $0.01 par value. Authorized 1,000,000 shares; no shares issued or outstanding — — Common stock, $0.01 par value. Authorized 30,000,000 shares; 20,855,243 issued and 18,733,286 outstanding at September 30, 2017 and 20,557,175 issued and 18,435,218 outstanding at September 30, 2016 0.2 0.2 Common stock in treasury, at cost - 2,121,957 shares at September 30, 2017 and 2016 (46.3 ) (46.3 ) Additional paid-in capital 259.0 249.4 Retained earnings (1) (71.1 ) (81.5 ) Total INTL FCStone Inc. (Parent Company Only) stockholders’ equity 141.8 121.8 Total liabilities and equity $ 390.4 $ 390.9 (1) Within the Condensed Balance Sheets and Condensed Statements of Operations of INTL FCStone Inc. - Parent Company Only, the Company has accounted for its investment in wholly owned subsidiaries using the cost method of accounting. Under this method, the Company’s share of the earnings or losses of such subsidiaries are not included in the Condensed Balance Sheet or Condensed Statements of Operations. If the accounting for its investment in wholly owned subsidiaries were presented under the equity method of accounting, investment in subsidiaries and retained earnings would each increase by $332.6 million as of September 30, 2017, respectively, and $336.6 million , as of September 30, 2016, respectively. Schedule I INTL FCStone Inc. Condensed Statements of Operations Parent Company Only Year Ended September 30, (in millions) 2017 2016 2015 Revenues: Management fees from affiliates $ 39.1 $ 30.1 $ 26.6 Trading (losses) gains, net (1.0 ) 0.7 3.2 Consulting fees — 2.2 2.1 Interest income 1.2 1.8 4.6 Dividend income from subsidiaries (2) 52.7 31.0 6.0 92.0 65.8 42.5 Interest expense 14.4 13.4 12.7 Net revenues 77.6 52.4 29.8 Non-interest expenses: Compensation and benefits 60.3 52.8 43.5 Clearing and related expenses 1.2 1.7 1.2 Introducing broker commissions — 0.6 0.5 Communication and data services 7.3 6.7 5.7 Occupancy and equipment rental 2.5 2.8 2.1 Professional fees 3.7 4.8 4.6 Travel and business development 2.7 1.7 1.4 Depreciation and amortization 3.3 2.5 1.8 Bad debts and impairments — 0.2 1.6 Management services fees to affiliates — 1.2 4.3 Other 13.0 11.7 10.2 Total non-interest expenses 94.0 86.7 76.9 Gain on acquisition — 6.2 — Loss from operations, before tax (16.4 ) (28.1 ) (47.1 ) Income tax benefit 26.8 24.7 19.4 Net income (loss) $ 10.4 $ (3.4 ) $ (27.7 ) (2) W ithin the Condensed Balance Sheets and Condensed Statements of Operations of INTL FCStone Inc. - Parent Company Only, the Company has accounted for its investment in wholly owned subsidiaries using the cost method of accounting. Under this method, the Company’s share of the earnings or losses of such subsidiaries are not included in the Condensed Balance Sheet or Condensed Statements of Operations. If the accounting for its investment in wholly owned subsidiaries were presented under the equity method of accounting, revenues would include a loss from investment in subsidiaries of $4.0 million for the year ended September 30, 2017, and income from investment in subsidiaries of $58.1 million and $83.4 million for the years ended September 30, 2016 and 2015, respectively. Schedule I INTL FCStone Inc. Condensed Statements of Cash Flows Parent Company Only Year Ended September 30, (in millions) 2017 2016 2015 Cash flows from operating activities: Net income (loss) $ 10.4 $ (3.4 ) $ (27.7 ) Adjustments to reconcile net loss to net cash (used in) provided by operating activities: Depreciation and amortization 3.3 2.5 1.8 Provision for impairments — 0.2 1.6 Deferred income taxes (10.7 ) (3.3 ) 4.6 Amortization and extinguishment of debt issuance costs 1.7 1.0 0.8 Amortization of share-based compensation expense 5.5 5.1 3.6 Gain on acquisition — (6.2 ) — Changes in operating assets and liabilities: Deposits and receivables from broker-dealers, clearing organizations, and counterparties 2.9 (2.8 ) — Receivables from subsidiaries, net (0.3 ) (3.1 ) — Due to/from subsidiaries 27.0 (86.6 ) 33.2 Notes receivable, net 2.1 39.1 (7.8 ) Income taxes receivable 5.4 10.3 (11.4 ) Financial instruments owned, at fair value 1.3 1.7 (3.0 ) Other assets 7.8 0.3 (3.9 ) Accounts payable and other accrued liabilities (7.8 ) 0.4 12.6 Payable to customers (2.5 ) (26.1 ) 4.9 Financial instruments sold, not yet purchased, at fair value (10.6 ) 35.9 — Net cash provided by (used in) operating activities 35.5 (35.0 ) 9.3 Cash flows from investing activities: Capital contribution in affiliates — (48.4 ) (22.4 ) Capital withdrawals from affiliates — — 7.8 Purchase of property and equipment (6.1 ) (5.5 ) (7.8 ) Net cash used in investing activities (6.1 ) (53.9 ) (22.4 ) Cash flows from financing activities: Net change in lenders under loans 13.5 108.5 13.0 Proceeds from note payable — — 4.0 Payments of notes payable (0.8 ) (0.8 ) (0.4 ) Repayment of senior unsecured notes (45.5 ) — — Payments related to earn-outs on acquisitions — (2.9 ) (2.2 ) Share repurchase — (19.5 ) (4.7 ) Debt issuance costs — (1.9 ) (0.1 ) Exercise of stock options 3.4 3.5 2.5 Income tax benefit on stock options and awards 0.7 0.8 0.5 Net cash (used in) provided by financing activities (28.7 ) 87.7 12.6 Net increase (decrease) in cash and cash equivalents 0.7 (1.2 ) (0.5 ) Cash and cash equivalents at beginning of period 1.3 2.5 3.0 Cash and cash equivalents at end of period $ 2.0 $ 1.3 $ 2.5 Supplemental disclosure of cash flow information: Cash paid for interest $ 8.2 $ 9.0 $ 11.9 Income taxes (received) paid, net of cash refunds $ (22.3 ) $ (33.8 ) $ (12.9 ) Supplemental disclosure of non-cash investing and financing activities: Additional consideration payable related to acquisitions $ (0.2 ) $ (0.4 ) $ 1.9

Subsequent Events Subsequent Ev

Subsequent Events Subsequent Events (Notes)	12 Months Ended
	Sep. 30, 2016
Subsequent Events [Abstract]
Subsequent Events [Text Block]

Description of Business and S32

Description of Business and Significant Accounting Policies (Policies)	12 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Basis of Presentation, Policy [Policy Text Block]	Basis of Presentation The accompanying 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. Unless otherwise stated herein, all references to fiscal 2017 , fiscal 2016 , and fiscal 2015 refer to the Company’s fiscal years ended September 30. In the 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 consolidated income statements is calculated by deducting physical commodities cost of sales from total revenues. The subtotal ‘net operating revenues’ in the 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 our 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.
Consolidation, Policy [Policy Text Block]	The accompanying 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]	Unless otherwise stated herein, all references to fiscal 2017 , fiscal 2016 , and fiscal 2015 refer to the Company’s fiscal years ended September 30.
Use of Estimates, Policy [Policy Text Block]	Use of Estimates The preparation of consolidated financial statements in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”) requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent liabilities as of the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. The most significant of these estimates and assumptions relate to fair value measurements for financial instruments and investments, revenue recognition, the provision for potential losses from bad debts, valuation of inventories, valuation of goodwill and intangible assets, self-insurance liabilities, incomes taxes and contingencies. These estimates are based on management’s best knowledge of current events and actions the Company may undertake in the future. The Company reviews all significant estimates affecting the financial statements on a recurring basis and records the effect of any necessary adjustments prior to their issuance. Although these and other estimates and assumptions are based on the best available information, actual results could be materially different from these estimates.
Foreign Currency Translations Policy [Policy Text Block]	Foreign Currency Translation Assets and liabilities recorded in foreign currencies are translated at the exchange rates prevailing on the balance sheet date. Revenue and expenses are translated at average rates of exchange prevailing during the period. Gains or losses on translation of the financial statements of a non-U.S. operation, when the functional currency is other than the U.S. dollar, are recorded in other comprehensive income (“OCI”), net of tax, a component of stockholders’ equity. Foreign currency remeasurement gains or losses on transactions denominated in nonfunctional currencies are included in ‘trading gains, net’ in the consolidated income statements.
Cash and Cash Equivalents, Unrestricted Cash and Cash Equivalents, Policy [Policy Text Block]	Cash and Cash Equivalents The Company considers cash held at banks and all highly liquid investments with original or acquired maturities of 90 days or less, including certificates of deposit, which may be withdrawn at any time at the discretion of the Company without penalty, to be cash and cash equivalents. Cash and cash equivalents consist of cash, foreign currency, money market funds and certificates of deposit not deposited with or pledged to exchange-clearing organizations, broker-dealers, clearing organizations or counterparties. The money market funds are valued at period-end at the net asset value provided by the fund’s administrator, which approximates fair value. Certificates of deposit are stated at cost plus accrued interest, which approximates fair value. The Company has an investment policy, which limits the maximum amount placed in any one fund and with any one institution in order to reduce credit risk. The Company does not believe that it is exposed to significant risk on cash and cash equivalents.
Cash, Securities and Other Assets Segregated, Restricted Cash and Cash Equivalents, Policy [Policy Text Block]	Cash, Securities and Other Assets Segregated under Federal and other Regulations Pursuant to requirements of the Commodity Exchange Act in the U.S. and similarly in the United Kingdom (“U.K.”), pursuant to the Markets in Financial Instruments Implementing Directive 2006/73/EC underpinning the Client Asset or ‘CASS’ rules in the Financial Services Authority (“FSA”) handbook, funds deposited by customers relating to futures and options on futures contracts in regulated commodities must be carried in separate accounts which are designated as segregated customer accounts. The deposits in segregated customer accounts are not commingled with the funds of the Company. Under the FSA’s rules, certain categories of customers may choose to opt-out of segregation. As of September 30, 2017 and 2016 , cash, securities and other assets segregated under federal and other regulations consisted of cash held at banks and money market funds of approximately $464.3 million and $515.2 million , respectively, U.S. Treasury securities and U.S. government agency obligations of approximately $33.5 million and $595.5 million , respectively, and commodities warehouse receipts of approximately $21.0 million and $23.3 million , respectively (see fair value measurements discussion in Note 4 ).
Commodity Repurchase and Other Repurchase Agreements Policy [Policy Text Block]	Securities Purchased/Sold Under Agreements to Resell/Repurchase The Company enters into securities purchased under agreements to resell (reverse repurchase agreements) and securities sold under agreements to repurchase (repurchase agreements) primarily to finance financial instruments, acquire securities to cover short positions or to acquire securities for settlement. Reverse repurchase agreements and repurchase agreements are treated as collateralized financing transactions and are recorded at their contractual amounts plus accrued interest. The related interest is recorded in the 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, or may be required by 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.
Securities Borrowed and Loaned Policy [Policy Text Block]	Securities Borrowed and Loaned The Company enters into securities borrowed and securities loaned transactions. Securities borrowed and securities loaned are reported as collateralized financings. Securities borrowed and securities loaned transactions are recorded at the amount of cash collateral advanced or received. The Company receives collateral generally in excess of the market value of securities loaned. The Company monitors the market value of securities borrowed and loaned on a daily basis, with additional collateral obtained or refunded as necessary. Securities borrowed and securities loaned are reported on a gross basis. Interest income and interest expense are recognized over the life of the arrangements.
Deposits and Receivables from Exchange-Clearing Organizations, Broker-dealers, Clearing Organizations and Counterparties, and Payables to Broker-dealers, Clearing Organizations and Counterparties Disclosure [Text Block]	Deposits with and Receivables from Broker-dealers, Clearing Organizations and Counterparties, and Payables to Broker-dealers, Clearing Organizations and Counterparties As required by the regulations of the U.S. Commodity Futures Trading Commission (“CFTC”) and the aforementioned FSA handbook, customer funds received to margin, guarantee, and/or secure commodity futures transactions are segregated and accounted for separately from the general assets of the Company. Deposits with exchange-clearing organizations, broker-dealers and counterparties pertain primarily to deposits made to satisfy margin requirements on customer and proprietary open futures and options on futures positions and to satisfy the requirements set by clearing exchanges for clearing membership. The Company also pledges margin deposits with various counterparties for OTC derivative contracts, and these deposits are also included in deposits and receivables from broker-dealers and counterparties. Deposits with and receivables from exchange-clearing organizations and broker-dealers and counterparties are reported gross, except where a right of offset exists. As of September 30, 2017 and 2016 , the Company had cash and cash equivalents on deposit with or pledged to exchange-clearing organizations, broker-dealers and counterparties of $2.3 billion and $0.9 billion , respectively. These balances also include securities pledged by the Company on behalf of customers and customer-owned securities that are pledged. It is the Company’s practice to include customer owned securities on its consolidated balance sheets, as the rights to those securities have been transferred to the Company under the terms of the futures trading agreement. Securities pledged include U.S. Treasury bills and instruments backed by U.S. government sponsored entities. Securities that are not customer-owned are adjusted to fair value with associated changes in unrealized gains or losses recorded through current period earnings. For customer owned securities, the change in fair value is offset against the payable to customers with no impact recognized in the consolidated income statements. The securities, primarily U.S. Treasury securities, held by INTL FCStone Financial, a subsidiary of the Company, as collateral or as margin have been deposited with exchange-clearing organizations, broker-dealers or other counterparties. The fair value of these securities was approximately $251.4 million and $471.7 million as of September 30, 2017 and 2016 , respectively. Management has considered guidance required by the Transfers and Servicing Topic of the ASC as it relates to securities pledged by customers to margin their accounts within the FCM Division of INTL FCStone Financial. Based on a review of the agreements with the customer, management believes the transferor surrenders control over those assets because: (a) the transferred assets have been isolated from the transferor—put presumptively beyond the reach of the transferor and its creditors, even in bankruptcy or other receivership, (b) each transferee has the right to pledge or exchange the assets (or beneficial interests) it received, and no condition both constrains the transferee (or holder) from taking advantage of its right to pledge or exchange and provides more than a trivial benefit to the transferor and (c) the transferor does not maintain effective control over the transferred assets through either (1) an agreement that both entitles and obligates the transferor to repurchase or redeem them before their maturity or (2) the ability to unilaterally cause the holder to return specific assets, other than through a cleanup call. Under this guidance, the Company reflects the customer collateral assets and corresponding liabilities in the Company’s consolidated balance sheets as of September 30, 2017 and 2016 . In addition to margin, deposits with exchange-clearing organizations include guaranty deposits. The guaranty deposits are held by the clearing organization for use in potential default situations by one or more members of the clearing organization. The guaranty deposits may be applied to the Company’s obligations to the clearing organization, or to the clearing organization’s obligations to other clearing members or third parties. The Company maintains customer omnibus and proprietary accounts with other counterparties, and the equity balances in those accounts along with any margin cash or securities deposited with the carrying broker are included in deposits and receivables from broker-dealers and counterparties. Receivables from and payables to exchange-clearing organizations are also comprised of amounts due from or due to exchange-clearing organizations for daily variation settlements on open futures and options on futures positions. The variation settlements due from or due to exchange-clearing organizations are paid in cash on the following business day. Deposits and receivables from broker-dealers, clearing organizations and counterparties, and payables to broker-dealers, clearing organizations and counterparties also include amounts related to the value of customers cross-currency payment transactions related to the Global Payments segment. These amounts arise due to a clearing period before the funds are received and payments are made, which usually is one to two business days. Deposits and receivables with exchange-clearing organizations also includes the unrealized gains and losses associated with the customers’ options on futures contracts. See discussion in the Financial Instruments and Derivatives section below for additional information on the treatment of derivative contracts. For customer owned derivative contracts, the fair value is offset against the payable to customers with no impact recognized on the consolidated income statements.
Receivable from and Payable to Customers, Policy [Policy Text Block]	Receivable from and Payable to Customers Receivable from customers, net of the allowance for doubtful accounts, include the total of net deficits in individual exchange-traded and OTC trading accounts carried by the Company. Customer deficits arise from realized and unrealized trading losses on futures, options on futures, swaps and forwards and amounts due on cash and margin transactions. Customer deficit accounts are reported gross of customer accounts that contain net credit or positive balances, except where a right of offset exists. Net deficits in individual exchange-traded and OTC trading accounts include both secured and unsecured deficit balances due from customers as of the balance sheet date. Secured deficit amounts are backed by U.S. Treasury bills and notes and commodity warehouse receipts. These U.S Treasury bills and notes and commodity warehouse receipts are not netted against the secured deficit amounts, as the conditions for right of setoff have not been met. Receivables from customers, net also includes the net amounts receivable from securities customers in connection with the settlement of normal cash securities, margin loans to customers, and customer cash debits. It is the Company’s policy to report margin loans and payables that arise due to positive cash flows in the same customer’s accounts on a net basis when the conditions for netting as specified in GAAP are met. Customers’ securities transactions cleared by the Company are recorded on a settlement date. Securities owned by customers including those that collateralize margin or other similar transactions, are not reflected on the statement of financial condition as the Company does not have title to those assets. In the event of uncompleted transactions on settlement date, the Company recorded corresponding receivables and payables, respectively. The carrying value of the receivables and payables approximates fair value due to their short-term nature. Payable to customers represent the total of customer accounts with credit or positive balances. Customer accounts are used primarily in connection with commodity transactions and include gains and losses on open commodity trades as well as securities and other deposits made as required by the Company, the exchange-clearing organizations or other clearing organizations. Customer accounts with credit or positive balances are reported gross of customer deficit accounts, except where a right of offset exists. Receivables from and payables to customers also include amounts related to the value of customers cross-currency payment transactions related to the Global Payments segment. These amounts arise due to a clearing period before the funds are received and payments are made, which usually is one to two business days. The future collectability of the receivable from customers can be impacted by the Company’s collection efforts, the financial stability of its customers, and the general economic climate in which it operates. The Company evaluates accounts that it believes may become uncollectible on a specific identification basis, through reviewing daily margin deficit reports, the historical daily aging of the receivables, and by monitoring the financial strength of its customers. The Company may unilaterally close customer trading positions in certain circumstances. In addition, to evaluate customer margining and collateral requirements, customer positions are stress tested regularly and monitored for excessive concentration levels relative to the overall market size. The Company generally charges off an outstanding receivable balance when all economically sensible means of recovery have been exhausted. That determination considers information such as the occurrence of significant changes in the customer’s financial position such that the customer can no longer pay the obligation, or that the proceeds from collateral will not be sufficient to pay the balance.
Notes Receivable, Policy [Policy Text Block]	Notes Receivable The Company originates short-term notes receivable from customers with the outstanding balances typically being insured 90% to 98% by a third party, including accrued interest, subject to applicable deductible amounts. The Company may sell the insured portion of the notes through non-recourse participation agreements with other third parties. See discussion of notes receivable related to commodity repurchase agreements below. Accrual of commodity financing income on any note is discontinued when, in the opinion of management, there is reasonable doubt as to the timely collectability of interest or principal. Nonaccrual notes are returned to an accrual status when, in the opinion of management, the financial position of the borrower indicates there is no longer any reasonable doubt as to the timely payment of principal and interest. The Company records a charge against earnings for notes receivable losses when management believes that collectability of the principal is unlikely.
Physcial Commodities Inventory, Policy [Policy Text Block]	Physical Commodities Inventory Inventories of certain agricultural commodities are carried at net realizable value, which approximates fair value less disposal costs. The agricultural commodities inventories have reliable, readily determinable and realizable market prices, have relatively predictable and insignificant costs of disposal and are available for immediate delivery. Changes in the fair values of these agricultural commodities inventories are included as a component of ‘cost of physical commodities sold’ in the consolidated income statements. Inventories of energy, including coal, kerosene, and propane are valued at the lower of cost or market (“LCM”). Inventories of precious metals held by our subsidiaries that are not broker-dealers are valued at the LCM, using the weighted-average price and first-in first-out costing method. Precious metals inventory held by 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’ in the consolidated income statements. INTL FCStone Ltd is regulated by the Financial Conduct Authority (“FCA”), the regulator of the financial services industry in the United Kingdom.
Property and Equipment, Policy [Policy Text Block]	Property and Equipment Property and equipment is stated at cost, net of accumulated depreciation and amortization and depreciated using the straight-line method over the estimated useful lives of the assets. Leasehold improvements are amortized on a straight-line basis over the estimated useful life of the improvement or the term of the lease, whichever is shorter. Certain costs of software developed or obtained for internal use are capitalized and amortized over the estimated useful life of the software. Expenditures for maintenance, repairs, and minor replacements are charged against earnings, as incurred. Expenditures that increase the value or productive capacity of assets are capitalized. When property and equipment are retired, sold, or otherwise disposed of, the asset’s carrying amount and related accumulated depreciation are removed from the accounts and any gain or loss is included in earnings.
Goodwill and Intangible Assets, Policy [Policy Text Block]	Goodwill and Identifiable Intangible Assets Goodwill is the cost of acquired companies in excess of the fair value of identifiable net assets at the acquisition date. Goodwill is not subject to amortization, but rather is evaluated for impairment at least annually. The Company evaluates its goodwill for impairment at the fiscal year end (or more frequently if indicators of potential impairment exist) in accordance with the Intangibles - Goodwill and Other Topic 350 of the ASC. Goodwill impairment is determined by comparing the estimated fair value of a reporting unit with its respective carrying value. If the estimated fair value exceeds the carrying value, goodwill at the reporting unit level is not deemed to be impaired. However, if the estimated fair value is below carrying value, further analysis is required to determine the amount of the impairment. This further analysis involves assigning tangible assets and liabilities, identified intangible assets and goodwill to reporting units and comparing the fair value of each reporting unit to its carrying amount. In the course of the evaluation of the potential impairment of goodwill, the Company may perform either a qualitative or a quantitative assessment. The Company’s qualitative assessment of potential impairment may result in the determination that a quantitative impairment analysis is not necessary. Under this elective process, the Company assesses qualitative factors to determine whether the existence of events or circumstances leads us to determine that it is more likely than not that the fair value of a reporting unit is less than its carrying amount. If after assessing the totality of events or circumstances, the Company determines it is more likely than not that the fair value of a reporting unit is greater than its carrying amount, then performing a quantitative analysis is not required. However, if the Company concludes otherwise, then we perform a quantitative impairment analysis. If the Company either chooses not to perform a qualitative assessment, or the Company chooses to perform a qualitative assessment but are unable to qualitatively conclude that no impairment has occurred, then the Company performs a quantitative evaluation. In the case of a quantitative assessment, the Company estimates the fair value of the reporting unit which the goodwill that is subject to the quantitative analysis is associated (generally defined as the businesses for which financial information is available and reviewed regularly by management) and compares it to the carrying value. If the estimated fair value of a reporting unit is less than its carrying value, the Company estimates the fair value of all assets and liabilities of the reporting unit, including goodwill. If the carrying value of the reporting unit’s goodwill is greater than the estimated fair value, an impairment charge is recognized for the excess. The fair value of the Company’s reporting units exceeded their respective carrying values under the first step of the quantitative assessment and no impairment charges were recorded for any of the periods presented. Identifiable intangible assets subject to amortization are amortized using the straight-line method over their estimated period of benefit, ranging from two to twenty years. Identifiable intangible assets are tested for impairment whenever events or changes in circumstances suggest that an asset’s or asset group’s carrying value may not be fully recoverable. Residual value is presumed to be zero for all identifiable intangible assets.
Financial Instruments and Derivatives, Policy [Policy Text Block]	Financial Instruments and Derivatives Financial instruments owned and sold, not yet purchased, at fair value consist of financial instruments carried at fair value or amounts that approximate fair value, with related unrealized changes in gains or losses recognized in earnings. The fair value of a financial instrument is the amount at which the instrument could be exchanged in a current transaction between willing parties, other than in a forced or liquidation sale. The Company accounts for its securities pledged on behalf of customers and proprietary securities as trading securities in accordance with U.S. GAAP accounting requirements for broker-dealers. Investment in managed funds, at fair value represents investments in funds managed by the Company’s fund managers. The investments are valued at period-end at the net asset value provided by the fund’s administrator. Commodities warehouse receipts are valued at the cash price, or the nearby futures prices in the absence of a cash price, for the commodity based on published market quotes. For commodities warehouse receipts, the change in fair value is offset against the payable to customers with no impact on the consolidated income statements. The Company utilizes derivative instruments to manage exposures to foreign currency, commodity price and interest rate risks for the Company and its customers. The Company’s objectives for holding derivatives include reducing, eliminating, and efficiently managing the economic impact of these exposures as effectively as possible. Derivative instruments are recognized as either assets or liabilities and are measured at fair value. As the Company does not elect hedge accounting, gains and losses from the change in fair values of derivatives for which the Company acts as principal are recognized immediately in earnings. The Company’s derivative contracts consist of exchange-traded and OTC derivatives. Fair values of exchange-traded derivatives are generally determined from quoted market prices. OTC derivatives are valued using valuation models. The valuation models used to derive the fair values of OTC derivatives require inputs including contractual terms, market prices, yield curves and measurements of volatility. The Company uses similar models to value similar instruments. Where possible, the Company verifies the values produced by pricing models by comparing them to market transactions. Inputs may involve judgment where market prices are not readily available. The Company does not elect hedge accounting under the Derivatives and Hedging Topic of the ASC in accounting for derivatives used as economic hedges on its commodities. The Company’s derivative contracts also include forward purchase and sale contracts for physical delivery of the agricultural commodities in a future period. Contracts to purchase agricultural commodities generally relate to the current or future crop year. Contracts for the sale of agricultural commodities generally do not extend beyond one year. Forward purchase and sale contracts are valued at market prices when available or other market quotes adjusted for differences, primarily in transportation, between the exchange-traded market and local markets where the terms of the contracts are based. Changes in the fair value of agricultural commodity inventories held for sale, forward purchase and sale contracts and exchange-traded futures and options contracts are recognized as a component of cost of sales of physical commodities. The Company provides clearing and execution of exchange-traded futures and options on futures for middle-market intermediaries, end-users, producers of commodities and the institutional and professional trader market segments. The Company has a subsidiary that is a registered broker-dealer/FCM, clearing on various exchanges. A primary source of revenues for the Company’s broker-dealer/FCM are commissions and clearing fees derived from executing and clearing orders for commodity futures contracts and options on futures on behalf of its customers. The Company also brokers foreign exchange forwards, options and cash, or spot, transactions between customers and external counterparties. A portion of the contracts are arranged on an offsetting basis, limiting the Company’s risk to performance of the two offsetting parties. The offsetting nature of the contracts eliminates the effects of market fluctuations on the Company’s operating results. Due to the Company’s role as a principal participating in both sides of these contracts, the amounts are presented gross on the consolidated balance sheets at their respective fair values, net of offsetting assets and liabilities. The Company holds proprietary positions in its foreign exchange line of business. On a limited basis, the Company’s foreign exchange trade desk will accept a customer transaction and will offset that transaction with a similar but not identical position with a counterparty. These unmatched transactions are intended to be short-term in nature and are often conducted to facilitate the most effective transaction for the Company’s customer. These spot and forward contracts are accounted for as free-standing derivatives and reported in the consolidated balance sheets at their fair values. The Company does not seek hedge accounting treatment for these derivatives, and accordingly, the changes in fair value during the period are recorded in the consolidated income statements in ‘trading gains, net’ (see Note 5 ). In applying the guidance in the Balance Sheet-Offsetting Topic of the ASC, the Company’s accounting policy is such that open contracts with the same customer are netted at the account level, in accordance with netting arrangements in place with each party, as applicable and rights to reclaim cash collateral or obligations to return cash collateral are netted against fair value amounts recognized for derivative instruments with the same customer in accordance with the master netting arrangements in place with each customer. The Company may lease commodities to or from customers or counterparties, or advance commodities to customers on an unpriced basis, receiving payment when they become priced. These are valued at fair value utilizing the fair value option based on guidance in the Financial Instruments Topic of the ASC. As permitted by the fair value option election, the entire instrument is recorded at fair value in the consolidated balance sheets as a component of ‘financial instruments owned and sold, not yet purchased’. Due to the short term nature of the instruments, the balance of the agreements is not materially different than the recorded fair value. The corresponding change in fair value of the instrument is recognized in the consolidated income statements as a component of ‘trading gains, net’ for the fiscal years ended September 30, 2017, 2016, and 2015 . The Company does elect to value all of their commodities lease agreements at fair value using the fair value option. See fair value measurements in Note 4 .
Exchange Memberships and Stock, Policy [Policy Text Block]	Exchange and Clearing Organization Memberships and Stock The Company is required to hold certain exchange membership seats and exchange firm and clearing organization common stock and pledges them for clearing purposes, in order to provide the Company the right to process trades directly with the various exchanges and clearing organization. Exchange memberships include seats on the Chicago Board of Trade (“CBOT”), the Minneapolis Grain Exchange, the New York Mercantile Exchange (“NYMEX”), the Commodity Exchange, Inc. (“COMEX”) Division of the New York Mercantile Exchange, Mercado de Valores de Buenos Aires S.A. (“MERVAL”), the Chicago Mercantile Exchange (“CME”) Growth and Emerging Markets, InterContinental Exchange, Inc. (“ICE”) Futures US, ICE Europe Ltd and London Metal Exchange (“LME”). Exchange firm and clearing organization common stock include shares of CME Group, Inc., ICE, LME, and the Deposit Trust and Clearing Corporation (“DTCC”). Exchange and clearing organization memberships and firm common stocks required in order to conduct business on the exchange are recorded at cost and are included in ‘other assets’ on the consolidated balance sheets. Equity investments in exchange firm common stock not required in order to conduct business on the exchange are classified as trading securities and recorded at fair value, with unrealized gains and losses recorded as a component of ‘trading gains, net’ on the consolidated income statements. Equity investments in exchange firm common stock not required in order to conduct business on the exchange are included in ‘financial instruments owned’ on the consolidated balance sheets. The cost basis for exchange and clearing organization memberships and firm common stock pledged for clearing purposes was $12.0 million and $12.1 million as of September 30, 2017 and 2016 , respectively. The fair value of exchange and clearing organization memberships and firm common stock pledged for clearing purposes was $10.2 million and $9.1 million as of September 30, 2017 and 2016 , respectively. The fair value of exchange and clearing organization firm common stock is determined by quoted market prices, and the fair value of exchange memberships is determined by recent sale transactions. The Company monitors the fair value of exchange and clearing organization membership seats and firm common stock on a quarterly basis, and does not consider any current unrealized losses on individual exchange and clearing organization memberships and firm common stock to be anything other than a temporary impairment.
Debt, Policy [Policy Text Block]	Lenders Under Loans and Senior Unsecured Notes Lenders under loans and senior unsecured notes are accounted for at amortized cost.
Business Combinations and Contingent Consideration Policy [Policy Text Block]	Business Combinations Acquisitions are accounted for as business combinations in accordance with the provisions of the Business Combinations Topic of the ASC. Under this accounting guidance most of the assets and liabilities acquired and assumed are measured at fair value as of the acquisition date. Certain contingent liabilities acquired require remeasurement at fair value in each subsequent reporting period. Noncontrolling interests are initially measured at fair value and classified as a separate component of equity. Acquisition related costs, such as fees for attorneys, accountants, and investment bankers, are expensed as incurred and are not capitalized as part of the purchase price. For all acquisitions, regardless of the consummation date, deferred tax assets, valuation allowances, and uncertain tax position adjustments occurring after the measurement period are recorded as a component of income, rather than adjusted through goodwill. Determining the fair value of certain assets and liabilities acquired is subjective in nature and often involves the use of significant estimates and assumptions. Estimating the fair value of the assets and liabilities acquired requires significant judgment. Contingent Consideration The Company estimates and records the acquisition date estimated fair value of contingent consideration as part of purchase price consideration for acquisitions. Additionally, each reporting period, the Company estimates changes in the fair value of contingent consideration, and any change in fair value is recognized in the consolidated income statement. An increase in the earn-out expected to be paid will result in a charge to operations in the period that the anticipated fair value of contingent consideration increases, while a decrease in the earn-out expected to be paid will result in a credit to operations in the period that the anticipated fair value of contingent consideration decreases. The estimate of the fair value of contingent consideration requires subjective assumptions to be made of future operating results, discount rates, and probabilities assigned to various potential operating result scenarios. Future revisions to these assumptions could materially change the estimate of the fair value of contingent consideration and, therefore, materially affect the Company’s future financial results.
Additional Paid-In Capital, Policy [Policy Text Block]	Additional Paid-In Capital The Company’s additional paid-in capital (“APIC”) consists of stockholder contributions that are in excess of par value of common stock. Included in APIC are amounts related to the exercise of stock options, share-based compensation and shares held in escrow. In September 2010, the Company acquired certain assets of Provident Group (“Provident”). The purchase price for the assets and services of the sellers was $5.0 million . Subsequent to closing, the individual sellers placed the entire purchase price into an escrow account and the funds were used to purchase outstanding shares of the Company on the open market. There were 214,325 shares purchased and placed into escrow as a result of this agreement. The entire purchase price was recorded as a reduction in additional paid in capital as shares held in escrow for business combinations. The shares held in escrow for business combinations were to be released to the individual sellers, over a five year period from the date of closing based on net profits, in accordance with the provisions of the acquisition agreement. At September 30, 2015, the end of the five year period, the terms of the agreement were not met and 204,271 shares were forfeited to the Company and recorded as treasury stock. In accordance with the acquisition agreement, there were no shares earned or released during the year ended September 30, 2015, while 10,054 shares were earned and subsequently released to the sellers prior to fiscal 2015.
Revenue Recognition, Policy [Policy Text Block]	Revenue Recognition Sales of physical commodities revenue are recognized when persuasive evidence of an arrangement exists, delivery has occurred, the fee is fixed or determinable, and collectability is reasonably assured. The Company reports its physical commodities revenues, except as described below, on a gross basis, with the corresponding cost of sales shown separately, in accordance with the guidelines provided in the Revenue Recognition Topic of the ASC. Management has historically assessed the performance of the physical commodities businesses on an operating revenue basis, and continues to do so. INTL FCStone Ltd precious metals sales and cost of sales are presented on a net basis and included as a component of ‘trading gains, net’ in the consolidated income statements, in accordance with U.S GAAP accounting requirements for broker-dealers. Precious metals sales and cost of sales for subsidiaries that are not broker-dealers continue to be recorded on a gross basis. Trading gains, net include brokerage fees and margins generated from OTC derivative trades executed with customers and other counterparties and are recognized when trades are executed. Trading gains, net also include activities where the Company acts as principal in the purchase and sale of individual securities, currencies, commodities or derivative instruments with customers. These transactions may be offset simultaneously with another customer or counterparty, offset with similar but not identical positions on an exchange, made from inventory, or may be aggregated with other purchases to provide liquidity intraday, for a number of days, or in some cases, particularly the base metals business, even longer periods (during which fair value may fluctuate). In addition, trading gains, net includes activities from the Company’s operations of a proprietary foreign exchange desk which arbitrages the futures and cash markets (see additional discussion in the Financial Instruments and Derivatives policy note for revenue recognition on proprietary trading activities). Net dealer inventory and investment gains are recognized on a trade-date basis and include realized gains or losses and changes in unrealized gains or losses on investments at fair value. Dividend income and dividend expense, on short equity positions, are recognized net, in ‘trading gain, net’ on the ex-dividend date. Commissions on various securities transactions and futures and options on futures contracts are recorded on a trade-date basis. Commissions on futures contracts are recognized on a half-turn basis in two equal parts. The first half is recognized when the contract is opened and the second half is recognized when the transaction is closed. Commissions on options on futures contracts are generally recognized on a half-turn basis, except that full commissions are recognized on options expected to expire without being exercised or offset. Commissions and fees are charged at various rates based on the type of account, the products traded, and the method of trade. Clearing and transaction fees are charged to customers on a per exchange contract basis based on the trade date. Such fees are for clearing customers’ exchange trades and include fees charged to the Company by the various futures exchanges. See discussion of transaction-based clearing expenses below. Under clearing agreements, we clear trades for unaffiliated correspondent brokers and retain a portion of commissions as a fee for our services. Correspondent clearing revenues are recorded net of commissions remitted. Commissions are also reported net of soft dollar rebates. Consulting, management, and account fees include risk management consulting fees which are billed and recognized as revenue on a monthly basis when risk management services are provided. Such agreements are generally for one year periods, but are cancelable by either party upon providing thirty days written notice to the other party and the amounts are not variable based on customer trading activities. Asset management fees are recognized as they are earned based on fees due at each period-end date. These include performance fees based on the amount that is due under the formula for exceeding performance targets as of the period-end date. Fee income for structuring and arrangement of debt transactions and management and investment advisory income is recorded when the services related to the underlying transactions are provided and success fees are recorded when complete, as determined under the terms of the assignment or engagement. Consulting, management, and account fees also includes various charges related to clearing agreements with unaffiliated introducing broker dealers such as transaction fees, annual account fees, service charges, servicing fees, platform fees, fees generated in lieu of interest income from a multi-bank sweep program with unaffiliated banks, money market processing and distribution fees, and other correspondent clearing fees. The annual account fees such as IRA fees and distribution fees are recognized as earned over the term of the contract. The transaction fees are earned and collected from clients as trades are executed. Servicing fees such as omnibus fees are paid to us for marketing and administrative services and are recognized as earned. Interest income, generated primarily from investments and customer inventory financing, is recognized on an accrual basis. Interest from investments is generated from securities purchased using customer funds deposited with the Company to satisfy margin requirements, net of interest returned to customers, and from securities acquired through internally-generated company funds. Interest also includes unrealized gains and losses on securities owned and those deposited with other parties. Revenue generally is recognized net of any taxes collected from customers and subsequently remitted to governmental authorities.
Cost of of Sales Physical Commodities, Policy [Policy Text Block]	Cost of Sales of Physical Commodities Cost of sales of physical commodities include finished commodity or raw material and processing costs along with operating costs relating to the receipt, storage and delivery of the physical commodities. Cost of sales of physical commodities also includes changes in the fair value of agricultural commodity inventories held for sale, and related forward purchase and sale contracts and exchange-traded futures and options contracts.
Interest Expense, Policy [Policy Text Block]	Interest Income and Expense Interest income and interest expense, generated primarily through investments, is recognized on an accrual basis. Interest from investments is generated from securities purchased using customer funds deposited with the Company to satisfy margin requirements and from proprietary securities acquired through internally generated funds.
Compensation and Benefits, Policy [Policy Text Block]	Compensation and Benefits Compensation and benefits consists primarily of salaries, incentive compensation, variable compensation, including commissions, related payroll taxes and employee benefits. The Company classifies employees as either risk management consultants / traders, operational or administrative personnel, which includes the executive officers. Variable compensation paid to risk management consultants and traders generally represents a fixed percentage of revenues generated, and in some cases, revenues produced less direct costs and an overhead allocation. The Company accrues commission expense on a trade date basis.
Share-based Compensation Policy [Policy Text Block]	Share-Based Compensation The Company accounts for share-based compensation in accordance with the guidance of the Compensation-Stock Compensation Topic of the ASC. The cost of employee services received in exchange for a share-based award is generally measured based on the grant-date fair value of the award. Share-based employee awards that require future service are amortized over the relevant service period. Expected forfeitures are included in determining share-based employee compensation expense. For option awards granted, compensation cost is recognized on a straight-line basis over the vesting period for the entire award.
Transaction-Based Clearing Expenses, Policy [Policy Text Block]	Transaction-Based Clearing Expenses Clearing fees and related expenses include primarily variable expenses for clearing and settlement services, including fees the Company pays to executing brokers, exchanges, clearing organizations and banks. These fees are based on transaction volume, and recorded as expense on the trade date. Clearing fees are passed on to customers and are presented gross in the consolidated statements of income under the Revenue Recognition Topic of the ASC, as the Company acts as a principal for these transactions.
Introducing Broker Commissions, Policy [Policy Text Block]	Introducing Broker Commissions Introducing broker commissions include commissions paid to non-employee third parties that have introduced customers to the Company. Introducing brokers are individuals or organizations that maintain relationships with customers and accept futures and options orders from those customers. The Company directly provides all account, transaction and margining services to introducing brokers, including accepting money, securities and property from the customers. The commissions are determined and settled monthly.
Income Tax, Policy [Policy Text Block]	Income Taxes Income tax expense includes U.S. federal, state and local and foreign income taxes. Certain items of income and expense are not reported in tax returns and financial statements in the same year. The objectives of accounting for income taxes are to recognize the amount of taxes payable or refundable for the current year. The Company utilizes the asset and liability method to provide income taxes on all transactions recorded in the consolidated financial statements. This method requires that income taxes reflect the expected future tax consequences of temporary differences between the carrying amounts of assets or liabilities for book and tax purposes. Accordingly, a deferred tax asset or liability for each temporary difference is determined based on the tax rates that the Company expects to be in effect when the underlying items of income and expense are realized. Judgment is required in assessing the future tax consequences of events that have been recognized in the Company’s financial statements or tax returns, including the repatriation of undistributed earnings of foreign subsidiaries. See Note 18 for further information on the Company’s income taxes.
Comprehensive Income, Policy [Policy Text Block]	Comprehensive Income 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 income (loss) includes net actuarial losses from defined benefit pension plans and gains and losses on foreign currency translations.
Preferred Stock [Text Block]	Preferred Stock The Company is authorized to issue one million shares of preferred stock, par value of $0.01 per share, in one or more classes or series to be established by the Company’s board of directors. As of September 30, 2017 and 2016 , no preferred shares were outstanding and the Company’s board of directors had not yet established any class or series of shares.
Recent Accounting Pronouncements, Policy [Policy Text Block]	Accounting Standards Adopted In April 2015, the FASB issued Accounting Standards Update (“ASU”) No. 2015-03, Interest – Imputation of Interest (Subtopic 835-30). ASU 2015-03 requires that debt issuance costs related to a recognized debt liability be presented in the balance sheet as a direct deduction from the carrying amount of that debt liability. In June 2015, the FASB issued ASU 2015-15 as an amendment to this guidance to address the absence of authoritative guidance for debt issuance costs related to line-of-credit arrangements. The SEC staff stated that they would not object to an entity deferring and presenting debt issuance costs as an asset and subsequently amortizing the deferred debt issuance costs ratably over the term of the line-of-credit arrangement, regardless of whether there are any outstanding borrowings on the line-of-credit arrangement. ASU 2015-03 required retrospective application to all prior periods presented in the consolidated financial statements. This new guidance was effective for the Company in the first quarter of 2017. As a result of adopting this standard on October 1, 2016, deferred financing costs of $1.0 million as of September 30, 2016, previously reported within other assets, were reclassified to senior unsecured notes in the consolidated balance sheet. As of September 30, 2017, there were no deferred financing costs as the senior unsecured notes were redeemed during the year ended September 30, 2017, as discussed in Note 10. In January 2017, the FASB issued ASU 2017-01, Business Combinations - Clarifying the Definition of a Business, which clarifies the definition of a business for determining whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. The Company early adopted this guidance effective October 1, 2016, and applied the guidance in determining whether the acquisition discussed in Note 18 is the acquisition of an asset or of a business.

Earnings per Share (Tables)

Earnings per Share (Tables)	12 Months Ended
	Sep. 30, 2017
Earnings Per Share [Abstract]
Schedule of Calculation of Numerator and Denominator in Earnings Per Share [Table Text Block]	The following is a reconciliation of the numerator and denominator of the diluted net income per share computations for the periods presented below. Year Ended September 30, (in millions, except share amounts) 2017 2016 2015 Numerator: Net income $ 6.4 $ 54.7 $ 55.7 Less: Allocation to participating securities (0.1 ) (1.0 ) (1.3 ) Net income allocated to common stockholders $ 6.3 $ 53.7 $ 54.4 Denominator: Weighted average number of: Common shares outstanding 18,395,987 18,410,561 18,525,374 Dilutive potential common shares outstanding: Share-based awards 291,367 214,811 406,861 Diluted shares outstanding 18,687,354 18,625,372 18,932,235

Assets and Liabilities, at Fa34

Assets and Liabilities, at Fair Value (Tables)	12 Months Ended
	Sep. 30, 2017
Assets and Liabilities, at Fair Value [Abstract]
Fair Value, Assets 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 September 30, 2017 and September 30, 2016 by level in the fair value hierarchy. There were no assets or liabilities that were measured at fair value on a nonrecurring basis as of September 30, 2017 and 2016 . September 30, 2017 (in millions) Level 1 Level 2 Level 3 Netting (1) Total Assets: Certificate of deposits 3.8 — — — 3.8 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 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 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 ) — Payables 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 are included in that level. September 30, 2016 (in millions) Level 1 Level 2 Level 3 Netting (1) Total Assets: Unrestricted cash equivalents - certificates of deposits $ 7.1 $ — $ — $ — $ 7.1 Commodities warehouse receipts 23.3 — — — 23.3 U.S. government obligations — 595.5 — — 595.5 Securities and other assets segregated under federal and other regulations 23.3 595.5 — — 618.8 Money market funds 512.7 — — — 512.7 U.S. government obligations — 472.1 — — 472.1 TBA and forward settling securities — 0.3 — — 0.3 Derivatives 2,149.9 8.0 — (2,289.7 ) (131.8 ) Deposits and receivables from broker-dealers, clearing organizations and counterparties 2,662.6 480.4 — (2,289.7 ) 853.3 Common and preferred stock, ADRs, and GDRs 34.6 1.7 0.2 — 36.5 Exchangeable foreign ordinary equities, ADRs, and GDRs 25.2 0.5 — — 25.7 Corporate and municipal bonds 36.9 0.9 3.0 — 40.8 U.S. government obligations — 514.9 — — 514.9 Foreign government obligations — 14.6 — — 14.6 Mortgage-backed securities — 747.5 — — 747.5 Derivatives 206.9 1,350.8 — (1,363.8 ) 193.9 Commodities leases — 137.2 — (129.1 ) 8.1 Commodities warehouse receipts 8.9 — — — 8.9 Exchange firm common stock 6.4 — — — 6.4 Mutual funds and other 8.8 — — — 8.8 Financial instruments owned 327.7 2,768.1 3.2 (1,492.9 ) 1,606.1 Physical commodities inventory 71.2 — — — 71.2 Total assets at fair value $ 3,091.9 $ 3,844.0 $ 3.2 $ (3,782.6 ) $ 3,156.5 Liabilities: Accounts payable and other accrued liabilities - contingent liabilities $ — $ — $ 0.8 $ — $ 0.8 TBA and forward settling securities — 2.6 — 0.9 3.5 Derivatives 1,961.7 97.5 — (2,059.2 ) — Payable to broker-dealers, clearing organizations and counterparties - derivatives 1,961.7 100.1 — (2,058.3 ) 3.5 Common and preferred stock, ADRs, and GDRs 23.5 0.4 — — 23.9 Exchangeable foreign ordinary equities, ADRs, and GDRs 25.3 0.5 — — 25.8 Corporate and municipal bonds 6.9 — — — 6.9 U.S. government obligations — 509.8 — — 509.8 Foreign government obligations — — — — — Mortgage-backed securities — — — — — Derivatives 199.4 1,319.3 — (1,307.8 ) 210.9 Commodities leases — 207.8 — (145.7 ) 62.1 Financial instruments sold, not yet purchased 255.1 2,037.8 — (1,453.5 ) 839.4 Total liabilities at fair value $ 2,216.8 $ 2,137.9 $ 0.8 $ (3,511.8 ) $ 843.7 (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 are included in that level.
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Table Text Block]	The Company’s financial assets at fair value classified within level 3 of the fair value hierarchy as of September 30, 2017 and 2016 are summarized below: (in millions) September 30, 2017 September 30, 2016 Total level 3 assets $ 0.1 $ 3.2 Level 3 assets for which the Company bears economic exposure $ 0.1 $ 3.2 Total assets $ 6,243.4 $ 5,950.3 Total financial assets at fair value $ 2,068.0 $ 3,156.5 Total level 3 assets as a percentage of total assets — % 0.1 % Level 3 assets for which the Company bears economic exposure as a percentage of total assets — % 0.1 % Total level 3 assets as a percentage of total financial assets at fair value — % 0.1 % 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 fiscal years ended September 30, 2017 and 2016 , including a summary of unrealized gains (losses) during the fiscal year ended on the Company’s Level 3 financial assets and liabilities still held as of September 30, 2017 . Level 3 Financial Assets and Financial Liabilities (in millions) Balances at Realized gains Unrealized Purchases/ Settlements Transfers in Balances at Assets: Common and preferred stock and ADRs $ 0.2 $ — $ (0.1 ) $ — $ — $ — $ 0.1 Corporate and municipal bonds 3.0 — — — (3.0 ) — — $ 3.2 $ — $ (0.1 ) $ — $ (3.0 ) $ — $ 0.1 (in millions) Balances at Realized gains Remeasurement Acquisitions Settlements Transfers in Balances at Liabilities: Contingent liabilities $ 0.8 $ — $ 0.2 $ — $ — $ — $ 1.0 Level 3 Financial Assets and Financial Liabilities (in millions) Balances at Realized gains Unrealized Purchases/ Settlements Transfers in Balances at Assets: Common and preferred stock and ADRs $ 0.5 $ — $ (0.3 ) $ — $ — $ — $ 0.2 Corporate and municipal bonds 3.2 — (0.2 ) — — — 3.0 $ 3.7 $ — $ (0.5 ) $ — $ — $ — $ 3.2 (in millions) Balances at Realized gains Remeasurement Acquisitions Settlements Transfers in Balances at Liabilities: Contingent liabilities $ 3.3 $ — $ 0.4 $ — $ (2.9 ) $ — $ 0.8

Financial Instruments with Of35

Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk (Tables)	12 Months Ended
	Sep. 30, 2016
Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk [Abstract]
Schedule of Derivative Instruments Included in Trading Activities [Table Text Block]	As of September 30, 2017 , these transactions are summarized as follows (in millions): Gain / (Loss) Notional Amounts Unrealized gain on TBA securities purchased within payables to broker-dealers, clearing organizations and counterparties and related notional amounts (1) $ — $ 51.3 Unrealized loss on TBA securities purchased within payables to broker-dealers, clearing organizations and counterparties and related notional amounts (1) $ (2.9 ) $ 1,236.8 Unrealized gain on TBA securities sold within deposits with and receivables from broker-dealers, clearing organizations and counterparties and related notional amounts (1) $ 5.8 $ (1,881.9 ) Unrealized loss on TBA securities sold within deposits with and receivables from broker-dealers, clearing organizations and counterparties and related notional amounts (1) $ (0.1 ) $ (404.1 ) Unrealized loss on forward settling securities purchased within payables to broker-dealers, clearing organizations and counterparties and related notional amounts $ (2.0 ) $ 882.9 Unrealized gain on forward settling securities sold within receivables from broker-dealers, clearing organizations and counterparties and related notional amounts $ 3.0 $ (590.2 ) (1) The notional amounts of these instruments reflect the extent of the Company’s involvement in TBA securities and do not represent risk of loss due to counterparty non-performance.
Schedule of Derivative Instruments [Table Text Block]	Listed below are the fair values of the Company’s derivative assets and liabilities as of September 30, 2017 and 2016 . Assets represent net unrealized gains and liabilities represent net unrealized losses. September 30, 2017 September 30, 2016 (in millions) Assets (1) Liabilities (1) Assets (1) Liabilities (1) Derivative contracts not accounted for as hedges: Exchange-traded commodity derivatives $ 2,094.2 $ 1,975.0 $ 2,022.1 $ 1,920.5 OTC commodity derivatives 1,084.0 1,110.3 1,217.0 1,188.9 Exchange-traded foreign exchange derivatives 66.0 52.0 12.2 7.5 OTC foreign exchange derivatives 618.5 609.8 346.5 290.2 Exchange-traded interest rate derivatives 228.4 203.6 78.7 120.5 Equity index derivatives 221.3 245.4 39.1 50.3 TBA and forward settling securities 8.8 4.9 0.3 2.6 Gross fair value of derivative contracts 4,321.2 4,201.0 3,715.9 3,580.5 Impact of netting and collateral (4,205.5 ) (3,879.2 ) (3,653.5 ) (3,366.1 ) Total fair value included in ‘Deposits with and receivables from broker-dealers, clearing organizations and counterparties’ $ (46.4 ) $ (131.5 ) Total fair value included in ‘Financial instruments owned, at fair value’ $ 162.1 $ 193.9 Total fair value included in ‘Payables to broker-dealers, clearing organizations and counterparties $ 4.8 $ 3.5 Fair value included in ‘Financial instruments sold, not yet purchased, at fair value’ $ 317.0 $ 210.9 (1) As of September 30, 2017 and 2016 , the Company’s derivative contract volume for open positions was approximately 6.1 million and 4.0 million contracts, respectively.
Schedule of Derivative Instruments, Gain (Loss) in Statement of Financial Performance [Table Text Block]	The following table sets forth the Company’s net gains (losses) related to derivative financial instruments for the fiscal years ended September 30, 2017, 2016, and 2015 , in accordance with the Derivatives and Hedging Topic of the ASC. The net gains (losses) set forth below are included in ‘trading gains, net’ and ‘cost of sales of physical commodities’ in the consolidated income statements. Year Ended September 30, (in millions) 2017 2016 2015 Commodities $ 47.3 $ 41.8 $ 78.6 Foreign exchange 8.7 9.7 7.5 Interest rate and equity (0.1 ) 0.8 3.2 TBA and forward settling securities (2.5 ) (14.4 ) (5.1 ) Net gains from derivative contracts $ 53.4 $ 37.9 $ 84.2

Receivables from customers, n36

Receivables from customers, net and notes receivable, net (Tables)	12 Months Ended
	Sep. 30, 2016
Receivables from customers and notes receivable, net [Abstract]
Allowance for Doubtful Accounts and Notes Receivables [Table Text Block]	Activity in the allowance for doubtful accounts for the years ended September 30, 2017, 2016, and 2015 was as follows: (in millions) 2017 2016 2015 Balance, beginning of year $ 9.7 $ 11.2 $ 5.8 Provision for bad debts 51.0 4.2 6.0 Charge-offs (6.1 ) (5.7 ) (0.6 ) Balance, end of year $ 54.6 $ 9.7 $ 11.2

Physical Commodities Inventor37

Physical Commodities Inventory Physical Commodities Inventory (Tables)	12 Months Ended
	Sep. 30, 2017
Inventory [Line Items]
Schedule of Inventory, Current [Table Text Block]	(in millions) September 30, September 30, Physical Ag & Energy (1) $ 65.1 $ 65.9 Precious metals - held by broker-dealer subsidiary (2) 13.3 5.3 Precious metals - held by non-broker-dealer subsidiaries (3) 46.4 52.6 Physical commodities inventory $ 124.8 $ 123.8

Property and Equipment, net (Ta

Property and Equipment, net (Tables)	12 Months Ended
	Sep. 30, 2017
Property and Equipment, net [Abstract]
Property, Plant and Equipment [Table Text Block]	A summary of property and equipment, at cost less accumulated depreciation as of September 30, 2017 and 2016 is as follows: (in millions) September 30, 2017 September 30, 2016 Property and equipment: Furniture and fixtures $ 7.2 $ 6.8 Software 25.3 22.8 Equipment 22.6 20.6 Leasehold improvements 15.4 11.9 Total property and equipment 70.5 62.1 Less accumulated depreciation (31.8 ) (32.7 ) Property and equipment, net $ 38.7 $ 29.4

Goodwill (Tables)

Goodwill (Tables)	12 Months Ended
	Sep. 30, 2017
Goodwill [Abstract]
Schedule of Goodwill [Table Text Block]	Goodwill allocated to the Company’s operating segments as of September 30, 2017 and 2016 is as follows: (in millions) September 30, September 30, Commercial Hedging $ 30.7 $ 30.7 Global Payments 6.3 6.3 Physical Commodities 2.4 2.4 Securities 7.7 8.1 Goodwill $ 47.1 $ 47.5

Intangible Assets (Tables)

Intangible Assets (Tables)	12 Months Ended
	Sep. 30, 2017
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): September 30, 2017 September 30, 2016 Gross Amount Accumulated Amortization Net Amount Gross Amount Accumulated Amortization Net Amount Intangible assets subject to amortization: Trade name $ — $ — $ — $ 1.1 $ (0.6 ) $ 0.5 Software programs/platforms 2.7 (2.5 ) 0.2 2.7 (2.4 ) 0.3 Customer base 20.0 (7.9 ) 12.1 14.0 (5.7 ) 8.3 Total intangible assets $ 22.7 $ (10.4 ) $ 12.3 $ 17.8 $ (8.7 ) $ 9.1
Schedule of Expected Amortization Expense [Table Text Block]	Amortization expense related to intangible assets was $2.8 million , $1.6 million , and $1.5 million for the fiscal years ended September 30, 2017, 2016, and 2015 , respectively. The estimated future amortization expense as of September 30, 2017 is as follows (in millions): Year ending September 30, 2018 $ 2.2 2019 2.2 2020 2.0 2021 1.9 2022 and thereafter 4.0 $ 12.3

Credit Facilities (Tables)

Credit Facilities (Tables)	12 Months Ended
	Sep. 30, 2017
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, and outstanding borrowings on the facilities as well as indebtedness on a promissory note and on senior notes as of September 30, 2017 and 2016 : (in millions) Credit Facilities Amounts Outstanding Borrower Security Renewal / Expiration Date Total Commitment September 30, September 30, Committed Credit Facilities INTL FCStone Inc. Pledged shares of certain subsidiaries March 18, 2019 $ 262.0 $ 150.0 $ 136.5 INTL FCStone Financial, Inc. None April 5, 2018 75.0 — — FCStone Merchants Services, LLC Certain commodities assets May 1, 2018 170.0 44.2 43.5 INTL FCStone Ltd. None November 7, 2018 25.0 — — $ 532.0 194.2 180.0 Uncommitted Credit Facilities INTL FCStone Financial, Inc. Commodity warehouse receipts and certain pledged securities n/a — 34.0 — INTL FCStone Ltd. Commodity warehouse receipts n/a — — — Note Payable to Bank Monthly installments, due March 2020 and secured by certain equipment 2.0 2.8 Senior Unsecured Notes 8.50% senior notes, redeemed October 15, 2016 — 44.5 Total indebtedness $ 230.2 $ 227.3

Commitments and Contingencies F

Commitments and Contingencies Future Minimum Lease Commitments (Tables)	12 Months Ended
	Sep. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block]	Future aggregate minimum lease payments under noncancelable operating leases as of September 30, 2017 are as follows: (in millions) Year ending September 30, 2018 $ 8.9 2019 8.3 2020 7.7 2021 6.7 2022 4.7 Thereafter 10.1 $ 46.4

Regulatory Requirements and S43

Regulatory Requirements and Subsidiary Dividend Restrictions (Tables)	12 Months Ended
	Sep. 30, 2016
Capital and Other Regulatory Requirements [Abstract]
Schedule of Compliance with Regulatory Capital Requirements under Banking Regulations [Table Text Block]	All subsidiaries of the Company are in compliance with all of their regulatory requirements as of September 30, 2017 , as follows: (in millions) As of September 30, 2017 Subsidiary Regulatory Authority Requirement Type Actual Minimum Requirement INTL FCStone Financial Inc. SEC and CFTC Net capital $ 157.1 $ 74.0 INTL FCStone Financial Inc. CFTC Segregated funds $ 2,248.0 $ 2,195.7 INTL FCStone Financial Inc. CFTC Secured funds $ 165.1 $ 148.7 INTL FCStone Financial Inc. SEC Customer reserve $ 7.2 $ — INTL FCStone Financial Inc. SEC PAB reserve $ 13.5 $ 0.2 INTL Custody & Clearing Solutions Inc. SEC Net capital $ 1.5 $ 0.1 SA Stone Wealth Management Inc. SEC Net capital $ 4.9 $ 0.3 INTL FCStone Ltd FCA (United Kingdom) Net capital $ 158.7 $ 88.3 INTL FCStone Ltd FCA (United Kingdom) Segregated funds $ 107.1 $ 106.6 INTL Netherlands BV FCA (United Kingdom) Net capital $ 158.0 $ 88.3 INTL FCStone DTVM Ltda. Brazilian Central Bank and Securities and Exchange Commission of Brazil Capital adequacy $ 13.0 $ 0.5 INTL Gainvest S.A. National Securities Commission ("CNV") Capital adequacy $ 5.1 $ 0.2 INTL Gainvest S.A. CNV Net capital $ 0.4 $ 0.1 INTL CIBSA S.A. CNV Capital adequacy $ 7.6 $ 0.9 INTL CIBSA S.A. CNV Net capital $ 1.4 $ 0.5
Schedule of Regulatory Assets [Table Text Block]	.

Commodity and Other Repurchas44

Commodity and Other Repurchase Agreements Gross Obligations Contractual Maturities (Tables)	12 Months Ended
	Sep. 30, 2017
Assets Sold under Agreements to Repurchase [Line Items]
Schedule of Underlying Assets of Repurchase Agreements when Amount of Repurchase Agreements Exceeds 10 Percent of Assets [Table Text Block]	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 Repurchas45

Commodity and Other Repurchase Agreements Gross Obligations Collateral Types (Tables)	12 Months Ended
	Sep. 30, 2017
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: U.S. Treasury obligations $ 7.0 U.S. government agency obligations 332.6 Asset-backed obligations 36.4 Agency mortgage-backed obligations 1,017.1 Total securities sold under agreements to repurchase $ 1,393.1 Securities loaned: Common stock 111.1 Total securities loaned 111.1 Gross amount of secured financing $ 1,504.2

Share-Based Compensation (Table

Share-Based Compensation (Tables)	12 Months Ended
	Sep. 30, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]	Fair value is estimated at the grant date based on a Black-Scholes-Merton option-pricing model using the following weighted-average assumptions: Year Ended September 30, 2017 2016 2015 Expected stock price volatility 31 % 28 % 28 % Expected dividend yield — % — % — % Risk free interest rate 0.99 % 0.83 % 0.66 % Average expected life (in years) 3.08 3.06 3.22
Share-based Compensation, Stock Options, Activity [Table Text Block]	The following is a summary of stock option activity for the year ended September 30, 2017 : Shares Available for Grant Number of Options Outstanding Weighted Average Exercise Price Weighted Average Grant Date Fair Value Weighted Average Remaining Term (in years) Aggregate Intrinsic Value ($ millions) Balances at September 30, 2016 754,163 1,215,821 $ 29.55 $ 12.88 3.80 $ 14.1 Granted (110,000 ) 110,000 $ 38.77 $ 8.67 Exercised (155,588 ) $ 22.54 $ 9.05 Forfeited 8,331 (106,996 ) $ 26.15 $ 13.20 Expired (181,834 ) $ 54.02 $ 19.93 Balances at September 30, 2017 652,494 881,403 $ 27.31 $ 11.55 3.57 $ 9.8 Exercisable at September 30, 2017 222,116 $ 24.42 $ 10.43 2.52 $ 3.1
Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range [Table Text Block]	The options outstanding as of September 30, 2017 broken down by exercise price are as follows: Exercise Price Number of Options Outstanding Weighted Average Exercise Price Weighted Average Remaining Term $ — - $ 5.00 — n/a n/a $ 5.00 - $ 10.00 — n/a n/a $ 10.00 - $ 15.00 — n/a n/a $ 15.00 - $ 20.00 22,414 $ 19.24 0.30 $ 20.00 - $ 25.00 97,911 $ 21.77 0.84 $ 25.00 - $ 30.00 580,000 $ 25.91 4.37 $ 30.00 - $ 35.00 73,578 $ 31.37 2.28 $ 35.00 - $ 40.00 107,500 $ 38.77 3.27 $ 40.00 - $ 45.00 — n/a n/a $ 45.00 - $ 50.00 — n/a n/a $ 50.00 - $ 55.00 — n/a n/a 881,403 $ 27.31 3.57
Schedule of Share-based Compensation, Restricted Stock Units Award Activity [Table Text Block]	The following is a summary of restricted stock activity through September 30, 2017 : Shares Available for Grant Number of Shares Outstanding Weighted Average Grant Date Fair Value Weighted Average Remaining Term (in years) Aggregate Intrinsic Value ($ millions) Balances at September 30, 2016 747,782 357,752 $ 27.39 1.39 $ 13.9 Additional shares authorized by shareholders 1,500,000 Termination of 2012 plan (640,539 ) Granted (147,726 ) 147,726 $ 40.98 Vested (150,545 ) $ 26.69 Forfeited 459 (459 ) $ 37.31 Balances at September 30, 2017 1,459,976 354,474 $ 33.34 1.26 $ 13.6

Other Expenses (Tables)

Other Expenses (Tables)	12 Months Ended
	Sep. 30, 2017
Other Expenses [Abstract]
Schedule of Other Operating Cost and Expense, by Component [Table Text Block]	Other expenses for the years ended September 30, 2017, 2016, and 2015 are comprised of the following: Year Ended September 30, (in millions) 2017 2016 2015 Contingent consideration, net (1) 0.1 0.4 1.8 Insurance 2.7 2.1 1.7 Advertising, meetings and conferences 4.0 5.1 2.7 Non-trading hardware and software maintenance and software licensing 11.6 7.1 4.7 Office supplies and printing 2.1 1.1 1.2 Other clearing related expenses 2.6 1.3 1.1 Other non-income taxes 4.6 4.3 3.7 Other 9.8 8.0 6.6 Total other expenses $ 37.5 $ 29.4 $ 23.5 (1) Contingent consideration includes remeasurement of contingent liabilities related to business combinations accounted for in accordance with the provisions of the Business Combinations Topic of the ASC (see Note 4 ).

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]	Income tax expense (benefit) for the years ended September 30, 2017, 2016, and 2015 was allocated as follows: Year Ended September 30, (in millions) 2017 2016 2015 Income tax expense attributable to income from operations $ 8.8 $ 18.0 $ 22.4 Taxes allocated to stockholders’ equity, related to unrealized losses on available-for-sale securities — — (0.4 ) Taxes allocated to stockholders’ equity, related to pension liabilities 1.0 0.2 (0.8 ) Taxes allocated to additional paid-in capital, related to share-based compensation 0.1 (0.8 ) (0.5 ) Total income tax expense $ 9.9 $ 17.4 $ 20.7 The components of income tax expense (benefit) attributable to income from operations were as follows: Year Ended September 30, (in millions) 2017 2016 2015 Current taxes: U.S. federal $ 0.7 $ 1.3 $ 0.8 U.S. State and local 1.2 0.8 1.2 International 16.7 16.8 15.4 Total current taxes 18.6 18.9 17.4 Deferred taxes (9.8 ) (0.8 ) 5.0 Income tax benefit attributable to interest income $ — $ (0.1 ) $ — Income tax expense $ 8.8 $ 18.0 $ 22.4
Schedule of Income before Income Tax, Domestic and Foreign [Table Text Block]	U.S. and international components of (loss) income from operations, before tax, was as follows: Year Ended September 30, (in millions) 2017 2016 2015 U.S. $ (13.9 ) $ 4.9 $ 14.5 International 29.1 67.9 63.7 Income from operations, before tax $ 15.2 $ 72.8 $ 78.2
Schedule of Effective Income Tax Rate Reconciliation [Table Text Block]	Items accounting for the difference between income taxes computed at the federal statutory rate and income tax expense were as follows: Year Ended September 30, 2017 2016 2015 Federal statutory rate effect of: 35.0 % 35.0 % 35.0 % U.S. State and local income taxes (2.6 )% 1.3 % 1.8 % Foreign earnings and losses taxed at lower rates 11.5 % (11.0 )% (11.1 )% Change in foreign valuation allowance (1.4 )% (0.3 )% (0.1 )% Change in state valuation allowance 4.1 % — % 0.6 % U.S. permanent items 3.6 % 0.8 % 0.5 % Foreign permanent items 8.1 % 1.9 % 2.1 % U.S. bargain purchase gain — % (3.0 )% — % Other reconciling items (0.6 )% 0.3 % (0.1 )% Effective rate 57.7 % 25.0 % 28.7 %
Schedule of Deferred Tax Assets and Liabilities [Table Text Block]	The components of deferred income tax assets and liabilities were as follows: (in millions) September 30, 2017 September 30, 2016 Deferred tax assets: Share-based compensation $ 3.7 $ 4.3 Pension liability 0.1 1.9 Deferred compensation 2.0 2.0 Foreign net operating loss carryforwards 5.6 2.0 U.S. State and local net operating loss carryforwards 6.6 4.9 U.S. federal net operating loss carryforwards 21.9 12.4 Intangible assets 6.1 8.3 Bad debt reserve 1.4 1.6 Tax credit carryforwards 1.6 1.4 Other compensation 3.6 3.3 Other 1.9 1.8 Total gross deferred tax assets 54.5 43.9 Less valuation allowance (4.0 ) (3.6 ) Deferred tax assets 50.5 40.3 Deferred income tax liabilities: Unrealized gain on securities 3.2 1.3 Prepaid expenses 2.5 1.9 Property and equipment 2.2 2.6 Deferred income tax liabilities 7.9 5.8 Deferred income taxes, net $ 42.6 $ 34.5
Summary of Income Tax Contingencies [Table Text Block]	A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows: Year Ended September 30, (in millions) 2017 2016 2015 Balance, beginning of year $ 0.1 $ — $ — Gross increases for tax positions related to current year — — — Gross increases for tax positions related to prior years — 0.1 — Gross decreases for tax positions of prior years — — — Settlements — — — Lapse of statute of limitations — — — Balance, end of year $ 0.1 $ 0.1 $ —

Accumulated Other Comprehensi49

Accumulated Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Sep. 30, 2017
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 income (loss) for the year ended September 30, 2017 . (in millions) Foreign Currency Translation Adjustment Pension Benefits Adjustment Accumulated Other Comprehensive Loss Balances as of September 30, 2016 $ (20.1 ) $ (4.5 ) $ (24.6 ) Other comprehensive income (loss), net of tax before reclassifications (1.4 ) 1.2 (0.2 ) Amounts reclassified from AOCI, net of tax — 0.3 0.3 Other comprehensive income (loss), net of tax (1.4 ) 1.5 0.1 Balances as of September 30, 2017 $ (21.5 ) $ (3.0 ) $ (24.5 )

Quarterly Financial Informati50

Quarterly Financial Information (Unaudited) (Tables)	12 Months Ended
	Sep. 30, 2017
Quarterly Financial Information Disclosure [Abstract]
Quarterly Financial Information [Table Text Block]	The Company has set forth certain quarterly unaudited financial data for the past two years in the tables below: For the 2017 Fiscal Quarter Ended (in millions, except per share amounts) September 30 (1) June 30 March 31 December 31 Total revenues $ 12,382.5 $ 5,505.9 $ 5,460.8 $ 6,074.4 Cost of sales of physical commodities 12,177.4 5,308.3 5,265.0 5,888.9 Operating revenues 205.1 197.6 195.8 185.5 Transaction-based clearing expenses 35.1 33.9 33.7 33.6 Introducing broker commissions 26.9 29.2 28.2 28.7 Interest expense 12.0 11.2 10.0 8.9 Net operating revenues 131.1 123.3 123.9 114.3 Compensation and benefits 73.0 75.5 76.6 70.6 Bad debts 0.4 0.1 1.3 2.5 Bad debt on physical coal 47.0 — — — Other expenses 33.2 32.7 31.7 32.8 Total compensation and other expenses 153.6 108.3 109.6 105.9 (Loss) income from operations, before tax (22.5 ) 15.0 14.3 8.4 Income tax expense 1.1 2.3 3.3 2.1 Net (loss) income $ (23.6 ) $ 12.7 $ 11.0 $ 6.3 Net basic (loss) earnings per share $ (1.27 ) $ 0.67 $ 0.58 $ 0.34 Net diluted (loss) earnings per share $ (1.27 ) $ 0.66 $ 0.58 $ 0.34 (1) During the fourth quarter of fiscal 2017, the Company recorded a charge to earnings of $47.0 million , to record an allowance for doubtful accounts related to a bad debt incurred in the physical coal business conducted solely in INTL Asia Pte. Ltd., with a coal supplier, as further discussed in Note 2 . For the 2016 Fiscal Quarter Ended (in millions, except per share amounts) September 30 June 30 March 31 December 31 Total revenues $ 2,777.6 $ 4,868.5 $ 3,708.9 $ 3,399.9 Cost of sales of physical commodities 2,599.0 4,693.5 3,542.8 3,248.6 Operating revenues 178.6 175.0 166.1 151.3 Transaction-based clearing expenses 32.0 35.2 32.9 29.8 Introducing broker commissions 28.1 14.8 13.2 12.8 Interest expense 7.5 7.7 7.1 6.0 Net operating revenues 111.0 117.3 112.9 102.7 Compensation and benefits 66.2 69.4 65.2 63.1 Bad debts (0.2 ) — 2.6 2.0 Other expenses 32.0 26.5 25.1 25.5 Total compensation and other expenses 98.0 95.9 92.9 90.6 Gain on acquisition 6.2 — — — Income from operations, before tax 19.2 21.4 20.0 12.1 Income tax expense 2.4 6.8 5.5 3.3 Net income $ 16.8 $ 14.6 $ 14.5 $ 8.8 Net basic earnings per share $ 0.91 $ 0.79 $ 0.77 $ 0.47 Net diluted earnings per share $ 0.90 $ 0.78 $ 0.76 $ 0.46

Segment and Geographic Inform51

Segment and Geographic Information (Tables)	12 Months Ended
	Sep. 30, 2017
Segment Analysis [Abstract]
Schedule of Segment Reporting Information, by Segment [Table Text Block]	Information concerning operations in these segments of business is shown in accordance with the Segment Reporting Topic of the ASC as follows: Year Ended September 30, (in millions) 2017 2016 2015 Total revenues: Commercial Hedging $ 244.6 $ 236.1 $ 262.4 Global Payments 89.2 73.2 77.1 Securities 151.7 175.2 129.8 Physical Commodities 28,684.4 14,120.5 34,092.0 Clearing and Execution Services 259.8 151.1 123.4 Corporate unallocated (6.1 ) (1.2 ) 8.5 Total $ 29,423.6 $ 14,754.9 $ 34,693.2 Operating revenues (loss): Commercial Hedging $ 244.6 $ 236.1 $ 262.4 Global Payments 89.2 73.2 77.1 Securities 151.7 175.2 129.8 Physical Commodities 44.8 36.6 23.1 Clearing and Execution Services 259.8 151.1 123.4 Corporate unallocated (6.1 ) (1.2 ) 8.5 Total $ 784.0 $ 671.0 $ 624.3 Net operating revenues (loss): Commercial Hedging $ 194.3 $ 188.2 $ 214.7 Global Payments 80.6 65.3 68.5 Securities 94.6 121.9 88.6 Physical Commodities 37.3 31.5 21.2 Clearing and Execution Services 102.2 48.8 38.3 Corporate unallocated (16.4 ) (11.8 ) 0.5 Total $ 492.6 $ 443.9 $ 431.8 Net contribution: (Revenues less cost of sales, transaction-based clearing expenses, variable bonus compensation, introducing broker commissions and interest expense): Commercial Hedging $ 141.8 $ 134.4 $ 151.7 Global Payments 64.4 52.2 54.5 Securities 75.6 97.5 67.4 Physical Commodities 27.2 23.4 16.9 Clearing and Execution Services 78.0 39.5 30.1 Total $ 387.0 $ 347.0 $ 320.6 Segment income: (Net contribution less non-variable direct segment costs): Commercial Hedging $ 72.8 $ 68.7 $ 85.6 Global Payments 50.6 39.8 43.3 Securities 46.6 69.4 40.5 Physical Commodities (1) (31.4 ) 13.3 5.8 Clearing and Execution Services 30.4 14.8 12.9 Total $ 169.0 $ 206.0 $ 188.1 Reconciliation of segment income to income from operations, before tax: Segment income $ 169.0 $ 206.0 $ 188.1 Costs not allocated to operating segments 153.8 133.3 110.0 Income from operations, before tax $ 15.2 $ 72.7 $ 78.1 (1) During the fourth quarter of fiscal 2017, the Company recorded a charge to earnings of $47.0 million, to record an allowance for doubtful accounts related to a bad debt incurred in the physical coal business conducted solely in INTL Asia Pte. Ltd., with a coal supplier, as further discussed in Note 2 . (in millions) As of September 30, 2017 As of September 30, 2016 As of September 30, 2015 Total assets: Commercial Hedging $ 1,650.3 $ 1,637.5 $ 1,548.1 Global Payments 199.5 191.4 207.3 Securities 2,101.7 2,130.7 1,861.0 Physical Commodities 339.5 258.0 190.9 Clearing and Execution Services 1,818.9 1,617.4 1,163.8 Corporate unallocated 133.5 115.3 98.9 Total $ 6,243.4 $ 5,950.3 $ 5,070.0
Schedule of Revenue from External Customers and Long-Lived Assets, by Geographical Areas [Table Text Block]	Information regarding revenues and operating revenues for the years ended September 30, 2017, 2016, and 2015 , and information regarding long-lived assets (defined as property, equipment, leasehold improvements and software) as of September 30, 2017, 2016, and 2015 in geographic areas were as follows: Year Ended September 30, (in millions) 2017 2016 2015 Total revenues: United States $ 1,168.0 $ 817.1 $ 25,959.0 Europe 166.9 463.5 121.2 South America 53.9 64.8 49.0 Asia 28,030.3 13,405.1 8,560.0 Other 4.5 4.4 4.0 Total $ 29,423.6 $ 14,754.9 $ 34,693.2 Operating revenues: United States $ 529.4 $ 457.0 $ 424.3 Europe 166.9 120.2 125.0 South America 54.0 64.8 49.0 Asia 29.2 24.6 21.9 Other 4.5 4.4 4.1 Total $ 784.0 $ 671.0 $ 624.3 (in millions) As of September 30, 2017 As of September 30, 2016 As of September 30, 2015 Long-lived assets, as defined: United States $ 29.7 $ 23.3 $ 13.8 Europe 7.3 4.8 4.0 South America 1.5 1.2 1.7 Asia 0.2 0.1 0.2 Total $ 38.7 $ 29.4 $ 19.7

Description of Business and S52

Description of Business and Significant Accounting Policies - Accounts, Customers and Other Facts (Details)	12 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Number of different types of foreign currencies	140
Number of accounts for customers company-wide	20,000

Description of Business and S53

Description of Business and Significant Accounting Policies - Cash, Cash Equivalents, Securities (Details) - USD ($)	Sep. 30, 2017	Sep. 30, 2016
Accounting Policies [Abstract]
Cash Held at Banks and Money Market Funds - Segregated	$ 464,300,000	$ 515,200,000
US Government Obligations and other securities	33,500,000	595,500,000
Commodities Warehouse Receipts	21,000,000	23,300,000
Cash and Cash Equivalents - Deposits and Receivables	2,300,000,000	900,000,000
US Government Securities and Other Securities - Deposits and Receivables	251,354,305	500,000,000
Memberships in Exchanges Owned	12,000,000	12,100,000
Fair Value of Exchange Memberships	$ 10,200,000	$ 9,100,000

Description of Business and S54

Description of Business and Significant Accounting Policies - Notes Receivable - Participation (Details)	Sep. 30, 2017	Sep. 30, 2016
Minimum [Member]
Short Term Notes Receivable Outstanding Balance Threshold, Percentage	90.00%	90.00%
Maximum [Member]
Short Term Notes Receivable Outstanding Balance Threshold, Percentage	98.00%	98.00%

Description of Business and S55

Description of Business and Significant Accounting Policies - Additional Paid In Capital (Provident Shares Held In Escrow) (Details) - USD ($)	1 Months Ended	12 Months Ended				13 Months Ended
	Sep. 30, 2010	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2017
US Government Securities and Other Securities - Deposits and Receivables		$ 500,000,000					$ 251,354,305
Business Combination, Consideration Transferred		$ 45,000,000
Provident Group Asset Acquisition [Member]
Business Combination, Consideration Transferred					$ 5,000,000
Business Combination, Cost of Acquired Entity, Equity Interest Issued or Issuable, Total Shares Purchased and Placed In Escrow						214,325
Business Combination, Cost of Acquired Entity, Equity Interest Issued or Issuable, Period From Date of Closing Over Which Shares Will be Released from Escrow	5 years
Stock Redeemed or Called During Period, Shares			204,271
Business Combination, Cost of Acquired Entity, Equity Interest Issued or Issuable, Shares Released from Escrow			0	10,054

Description of Business and S56

Description of Business and Significant Accounting Policies - Basis of Presentation and Consolidation (Details) - USD ($)	Sep. 30, 2017	Sep. 30, 2016
Accounting Policies [Abstract]
Memberships in Exchanges Owned	$ 12,000,000	$ 12,100,000
Fair Value of Exchange Memberships	10,200,000	9,100,000
Cash and Cash Equivalents - Deposits and Receivables	$ 2,300,000,000	$ 900,000,000
Preferred Stock, Par or Stated Value Per Share	$ 0.01	$ 0.01
Preferred Stock, Shares Outstanding	0	0
US Government Securities and Other Securities - Deposits and Receivables	$ 251,354,305	$ 500,000,000

Bad Debt on Physical Coal (Deta

Bad Debt on Physical Coal (Details) - USD ($) $ in Millions	3 Months Ended				12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Bad Debt on Physical Coal [Abstract]
Unusual or Infrequent Item, or Both, Loss, Gross	$ 47	$ 0	$ 0	$ 0	$ 47	$ 0	$ 0

Earnings per Share - EPS Reconc

Earnings per Share - EPS Reconciliation (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share [Abstract]
Income from Continuing Operations	$ 6.4	$ 54.7	$ 55.7
Undistributed Earnings Allocated to Participating Securities - Continuing Operations	(0.1)	(1)	(1.3)
Income from continuing operations allocated to common shareholders	$ 6.3	$ 53.7	$ 54.4
Weighted Average Number of Shares Outstanding, Basic	18,395,987	18,410,561	18,525,374
Dilutive Securities, Effect on Basic Earnings Per Share [Abstract]
Share-based Awards For Diluted Earnings Per Share Calculation	291,367	214,811	406,861
Diluted weighted-average shares	18,687,354	18,625,372	18,932,235

Earnings per Share - Antiduliti

Earnings per Share - Antidulitive Securities (Details) - shares	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	230,135	910,060	997,459

Assets and Liabilities, at Fa60

Assets and Liabilities, at Fair Value Assets and Liabilities, at Fair Value - Financial Instruments at Fair Value Disclosure (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Assets and Liabilities, at Fair Value [Abstract]
Senior Notes	$ 0	$ 44.5	$ 45.5

Assets and Liabilities, at Fa61

Assets and Liabilities, at Fair Value - Financial Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016	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	$ 518.8	$ 1,136.3
Receivables from Brokers-Dealers and Clearing Organizations	2,625.1	1,761.4
Financial instruments owned, at fair value	1,731.8	1,606.1
Assets, Fair Value Disclosure	2,068
Accounts payable and other accrued liabilities	135.6	161.3
Payables to Broker-Dealers and Clearing Organizations	(125.7)	(260.1)
Financial Instruments Sold, Not yet Purchased, at Fair Value	717.6	839.4
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure		7.1
Cash and Securities Segregated under Federal and Other Regulations	54.5	618.8
Receivables from Exchange Clearing Organizations		853.3
Receivables from Brokers-Dealers and Clearing Organizations	204.7
Financial instruments owned, at fair value	1,731.8	1,606.1
Assets, Fair Value Disclosure	2,068	3,156.5
Payables to Broker-Dealers and Clearing Organizations	(4.8)
Financial Instruments Sold, Not yet Purchased, at Fair Value	717.6	839.4
Liabilities, Fair Value Disclosure	723.4	843.7
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	(4.8)	(3.5)
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	0	0
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	0.8
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	73.2	71.2
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	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	368.9
Financial Instruments Sold, Not yet Purchased, at Fair Value	27.9
Fair Value, Measurements, Recurring [Member] | Common stock and American Depositary Receipts (ADRs) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	34.7	36.5
Financial Instruments Sold, Not yet Purchased, at Fair Value	34.4	23.9
Fair Value, Measurements, Recurring [Member] | Exchangeable foreign ordinary equities and ADRs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	10.4	25.7
Financial Instruments Sold, Not yet Purchased, at Fair Value	10.5	25.8
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	29.1	40.8
Financial Instruments Sold, Not yet Purchased, at Fair Value	0.3	6.9
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	60	514.9
Financial Instruments Sold, Not yet Purchased, at Fair Value	285.9	509.8
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	10.2	14.6
Financial Instruments Sold, Not yet Purchased, at Fair Value		0
Fair Value, Measurements, Recurring [Member] | Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	920.9	747.5
Financial Instruments Sold, Not yet Purchased, at Fair Value	0.1	0
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	162.1	193.9
Financial Instruments Sold, Not yet Purchased, at Fair Value	317	210.9
Fair Value, Measurements, Recurring [Member] | Commodities leases and unpriced positions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	35.4	8.1
Financial Instruments Sold, Not yet Purchased, at Fair Value	41.5	62.1
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	38.5	8.9
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	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	6	8.8
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 Brokers-Dealers and Clearing Organizations	6.4
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 Brokers-Dealers and Clearing Organizations	244.7
Fair Value, Measurements, Recurring [Member] | TBA and forward settling securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Brokers-Dealers and Clearing Organizations	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	(55.2)
Fair Value, Measurements, Recurring [Member] | Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Exchange Clearing Organizations		0.3
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Exchange Clearing Organizations		512.7
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 Exchange Clearing Organizations		472.1
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		(131.8)
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	21	23.3
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	33.5	595.5
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	3.8		$ 3.8
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 Cash Equivalents, Fair Value Disclosure		7.1
Cash and Securities Segregated under Federal and Other Regulations	54.5	23.3
Receivables from Exchange Clearing Organizations		2,662.6
Receivables from Brokers-Dealers and Clearing Organizations	2,853.3
Financial instruments owned, at fair value	182.7	327.7
Assets, Fair Value Disclosure	3,167.5	3,091.9
Payables to Broker-Dealers and Clearing Organizations	(2,476.2)
Financial Instruments Sold, Not yet Purchased, at Fair Value	330.2	255.1
Liabilities, Fair Value Disclosure	2,806.4	2,216.8
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	(2,476.2)	(1,961.7)
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	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	73.2	71.2
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
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
Financial Instruments Sold, Not yet Purchased, at Fair Value	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Common stock and American Depositary Receipts (ADRs) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	31.2	34.6
Financial Instruments Sold, Not yet Purchased, at Fair Value	33.7	23.5
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Exchangeable foreign ordinary equities and ADRs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	9.2	25.2
Financial Instruments Sold, Not yet Purchased, at Fair Value	10.3	25.3
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	28.2	36.9
Financial Instruments Sold, Not yet Purchased, at Fair Value	0.3	6.9
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	60	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	285.9	0
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
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | 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
Financial Instruments Sold, Not yet Purchased, 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	1.3	206.9
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	199.4
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Commodities leases and unpriced positions [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	38.5	8.9
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	8.3	6.4
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	6	8.8
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 Brokers-Dealers and Clearing Organizations	0
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 Brokers-Dealers and Clearing Organizations	244.7
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]
Receivables from Brokers-Dealers and Clearing Organizations	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 Brokers-Dealers and Clearing Organizations	2,608.6
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Exchange Clearing Organizations		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Exchange Clearing Organizations		512.7
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 Exchange Clearing Organizations		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 Exchange Clearing Organizations		2,149.9
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	21	23.3
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]
Cash and Securities Segregated under Federal and Other Regulations	33.5	0
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	3.8		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 Cash Equivalents, Fair Value Disclosure		0
Cash and Securities Segregated under Federal and Other Regulations	0	595.5
Receivables from Exchange Clearing Organizations		480.4
Receivables from Brokers-Dealers and Clearing Organizations	304.3
Financial instruments owned, at fair value	2,940.3	2,768.1
Assets, Fair Value Disclosure	3,244.6	3,844
Payables to Broker-Dealers and Clearing Organizations	(297.7)
Financial Instruments Sold, Not yet Purchased, at Fair Value	1,647.2	2,037.8
Liabilities, Fair Value Disclosure	1,944.9	2,137.9
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	(4.9)	(2.6)
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	(292.8)	(97.5)
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	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	0	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	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	368.9
Financial Instruments Sold, Not yet Purchased, at Fair Value	27.9
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Common stock and American Depositary Receipts (ADRs) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	3.4	1.7
Financial Instruments Sold, Not yet Purchased, at Fair Value	0.7	0.4
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Exchangeable foreign ordinary equities and ADRs [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	1.2	0.5
Financial Instruments Sold, Not yet Purchased, at Fair Value	0.2	0.5
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	0.9	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	514.9
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	509.8
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	10.2	14.6
Financial Instruments Sold, Not yet Purchased, at Fair Value		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	920.9	747.5
Financial Instruments Sold, Not yet Purchased, at Fair Value	0.1	0
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	1,413.4	1,350.8
Financial Instruments Sold, Not yet Purchased, at Fair Value	1,427.2	1,319.3
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commodities leases and unpriced positions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	174.1	137.2
Financial Instruments Sold, Not yet Purchased, at Fair Value	191.1	207.8
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] | Foreign Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Brokers-Dealers and Clearing Organizations	6.4
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 Brokers-Dealers and Clearing Organizations	0
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]
Receivables from Brokers-Dealers and Clearing Organizations	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 Brokers-Dealers and Clearing Organizations	289.1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Exchange Clearing Organizations		0.3
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Exchange Clearing Organizations		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 Exchange Clearing Organizations		472.1
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 Exchange Clearing Organizations		8
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	595.5
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 Cash Equivalents, Fair Value Disclosure		0
Cash and Securities Segregated under Federal and Other Regulations	0	0
Receivables from Exchange Clearing Organizations		0
Receivables from Brokers-Dealers and Clearing Organizations	0
Financial instruments owned, at fair value	0.1	3.2
Assets, Fair Value Disclosure	0.1	3.2
Payables to Broker-Dealers and Clearing Organizations	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Liabilities, Fair Value Disclosure	1	0.8
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] | Contingent Consideration [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accounts payable and other accrued liabilities	1	0.8
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
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
Financial Instruments Sold, Not yet Purchased, at Fair Value	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Common stock and American Depositary Receipts (ADRs) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	0.1	0.2
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 and ADRs [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	3
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
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | 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
Financial Instruments Sold, Not yet Purchased, 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 and unpriced positions [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] | Foreign Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Brokers-Dealers and Clearing Organizations	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 Brokers-Dealers and Clearing Organizations	0
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]
Receivables from Brokers-Dealers and Clearing Organizations	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 Brokers-Dealers and Clearing Organizations	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Exchange Clearing Organizations		0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Exchange Clearing Organizations		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 Exchange Clearing Organizations		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 Exchange 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		(3.5)
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]
Payables to Broker-Dealers and Clearing Organizations		(1,961.7)
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]
Payables to Broker-Dealers and Clearing Organizations		(100.1)
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]
Payables to Broker-Dealers and Clearing Organizations		0
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure		0
Cash and Securities Segregated under Federal and Other Regulations	0	0
Receivables from Exchange Clearing Organizations		(2,289.7)
Receivables from Brokers-Dealers and Clearing Organizations	(2,952.9)
Financial instruments owned, at fair value	(1,391.3)	(1,492.9)
Assets, Fair Value Disclosure	(4,344.2)	(3,782.6)
Payables to Broker-Dealers and Clearing Organizations	2,769.1
Financial Instruments Sold, Not yet Purchased, at Fair Value	(1,259.8)	(1,453.5)
Liabilities, Fair Value Disclosure	(4,028.9)	(3,511.8)
Counterparty And Cash Collateral Netting Adjustment [Member] | 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	0.1	(0.9)
Counterparty And Cash Collateral Netting Adjustment [Member] | 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	2,769	2,059.2
Counterparty And Cash Collateral Netting Adjustment [Member] | 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	0	0
Counterparty And Cash Collateral Netting Adjustment [Member] | 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	0	0
Counterparty And Cash Collateral Netting Adjustment [Member] | 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	0
Counterparty And Cash Collateral Netting Adjustment [Member] | 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	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | Common stock and American Depositary Receipts (ADRs) [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
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | Exchangeable foreign ordinary equities and ADRs [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
Counterparty And Cash Collateral Netting Adjustment [Member] | 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	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Counterparty And Cash Collateral Netting Adjustment [Member] | 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	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Counterparty And Cash Collateral Netting Adjustment [Member] | 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	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value		0
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | 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
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Counterparty And Cash Collateral Netting Adjustment [Member] | 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	(1,252.6)	(1,363.8)
Financial Instruments Sold, Not yet Purchased, at Fair Value	(1,110.2)	(1,307.8)
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | Commodities leases and unpriced positions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned, at fair value	(138.7)	(129.1)
Financial Instruments Sold, Not yet Purchased, at Fair Value	(149.6)	(145.7)
Counterparty And Cash Collateral Netting Adjustment [Member] | 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	0	0
Counterparty And Cash Collateral Netting Adjustment [Member] | 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	0	0
Counterparty And Cash Collateral Netting Adjustment [Member] | 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	0	0
Counterparty And Cash Collateral Netting Adjustment [Member] | 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 Brokers-Dealers and Clearing Organizations	0
Counterparty And Cash Collateral Netting Adjustment [Member] | 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 Brokers-Dealers and Clearing Organizations	0
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | TBA and forward settling securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Brokers-Dealers and Clearing Organizations	0
Counterparty And Cash Collateral Netting Adjustment [Member] | 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	(2,952.9)
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | Mortgage Backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Exchange Clearing Organizations		0
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Exchange Clearing Organizations		0
Counterparty And Cash Collateral Netting Adjustment [Member] | 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 Exchange Clearing Organizations		0
Counterparty And Cash Collateral Netting Adjustment [Member] | Fair Value, Measurements, Recurring [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Exchange Clearing Organizations		(2,289.7)
Counterparty And Cash Collateral Netting Adjustment [Member] | 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	0	0
Counterparty And Cash Collateral Netting Adjustment [Member] | 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	0	0
Counterparty And Cash Collateral Netting Adjustment [Member] | 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	$ 0		$ 0
Counterparty And Cash Collateral Netting Adjustment [Member] | 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		$ 2,058.3

Assets and Liabilities, at Fa62

Assets and Liabilities, at Fair Value - Details of Level 3 Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Assets and Liabilities, at Fair Value [Abstract]
Total Level 3 Assets	$ 0.1	$ 3.2
Level 3 assets for which the company bears economic exposure	0.1	3.2
Assets	6,243.4	$ 5,950.3	$ 5,070
Assets, Fair Value Disclosure	$ 2,068
Total level 3 assets as a percentage of total assets	0.00%	0.10%
Level 3 assets for which the company bears economic exposure as a percertange of total assets	0.00%	0.10%
Total level 3 assets as a percentage of total financial assets at fair value	0.00%	0.10%

Assets and Liabilities, at Fa63

Assets and Liabilities, at Fair Value - Rollforward of Level 3 (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Rollforward of Level 3 Assets [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	$ 3.2	$ 3.7
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)	(0.1)	(0.5)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	(3)	0
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	0.1	3.2	$ 3.7
Rollforward of Level 3 Liabilities [Roll Forward]
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability	(0.2)	(0.4)	1.9
Contingent Consideration [Member]
Rollforward of Level 3 Liabilities [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliations, Recurring Basis, Liability Value	0.8	3.3
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Gain (Loss) Included in Earnings	0	0
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability	0.2	0.4	1.8
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Liability, Period Increase (Decrease)		0.4
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	(2.9)
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	1	0.8	3.3
Common stock and American Depositary Receipts (ADRs) [Member]
Rollforward of Level 3 Assets [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	0.2	0.5
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)	(0.1)	(0.3)
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	0
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	0.1	0.2	0.5
Corporate Debt Securities [Member]
Rollforward of Level 3 Assets [Roll Forward]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	3	3.2
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	(0.2)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases	0	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Settlements	(3)	0
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	$ 3	$ 3.2

Assets and Liabilities, at Fa64

Assets and Liabilities, at Fair Value - Contingent Consideration (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability	$ (0.2)	$ (0.4)	$ 1.9
Contingent Consideration [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability	$ 0.2	$ 0.4	$ 1.8

Assets and Liabilities, at Fa65

Assets and Liabilities, at Fair Value - Available for Sale Securities in OCI (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Assets and Liabilities, at Fair Value [Abstract]
Equity Investments in Exchange Stock - Cost	$ 3.9	$ 3.7
Equity Investments in Exchange Stock - Fair Value	8.3	6.4
Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI for Sale of Securities, before Tax	0	0	$ 5.4
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax	$ 0	$ 0	$ 2.7

Financial Instruments with Of66

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	Sep. 30, 2017	Sep. 30, 2016
Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk [Abstract]
Financial Instruments Sold, Not yet Purchased, at Fair Value	$ 717.6	$ 839.4
Derivative, Fair Value, Net	$ 317

Financial Instruments with Of67

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	Sep. 30, 2017	Sep. 30, 2016
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 4,321.2	$ 3,715.9
Derivative Liability, Fair Value, Gross Liability	4,201	3,580.5
Derivative, Fair Value, Net	317
Exchange-traded Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	2,094.2	2,022.1
Derivative Liability, Fair Value, Gross Liability	1,975	1,920.5
Over the Counter (OTC) Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	1,084	1,217
Derivative Liability, Fair Value, Gross Liability	1,110.3	1,188.9
Foreign Exchange Forward [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	66	12.2
Derivative Liability, Fair Value, Gross Liability	52	7.5
Over the Counter (OTC) Foreign Exchange Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	618.5	346.5
Derivative Liability, Fair Value, Gross Liability	609.8	290.2
Exchange-traded interest rate contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	228.4	78.7
Derivative Liability, Fair Value, Gross Liability	203.6	120.5
Equity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	221.3	39.1
Derivative Liability, Fair Value, Gross Liability	245.4	50.3
TBA and forward settling securities [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	8.8	0.3
Derivative Liability, Fair Value, Gross Liability	4.9	2.6
TBA securities purchased [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	0
Derivative Liability, Fair Value, Gross Liability	(2.9)
Derivative Asset, Notional Amount	(51.3)
Derivative Liability, Notional Amount	(1,236.8)
TBA securities sold [Member] [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	5.8
Derivative Liability, Fair Value, Gross Liability	(0.1)
Derivative Asset, Notional Amount	(1,881.9)
Derivative Liability, Notional Amount	(404.1)
Forward settling securities purchased [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	(2)
Derivative Asset, Notional Amount	(882.9)
Forward settling securities sold [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability, Fair Value, Gross Liability	3
Derivative Liability, Notional Amount	(590.2)
Deposits and receivables from broker-dealers, clearing organizations and counterparties [Member]
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	(46.4)	(131.5)
Financial instruments owned [Member]
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	162.1	193.9
Payable to broker-dealers, clearing organizations and counterparties [Member]
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	4.8	3.5
Financial instrument sold, not yet purchased [Member]
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	317	210.9
Counterparty And Cash Collateral Netting Adjustment [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Amount Offset Against Collateral	(4,205.5)	(3,653.5)
Derivative Liability, Fair Value, Amount Offset Against Collateral	$ (3,879.2)	$ (3,366.1)

Financial Instruments with Of68

Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - Derivatives Volume (Details) number in Millions, $ in Millions	12 Months Ended
	Sep. 30, 2016USD ($)	Sep. 30, 2017
Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk [Abstract]
Derivative, Notional Amount	$ 375
Derivative, Average Remaining Maturity	15 years
Derivative, Number of Instruments Held	4	6.1

Financial Instruments with Of69

Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - Realized Gains/Losses on Derivative Contracts (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Commodity Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	$ 47.3	$ 41.8	$ 78.6
Foreign Exchange Forward [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	8.7	9.7	7.5
Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	(0.1)	0.8	3.2
TBA and forward settling securities [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	(2.5)	(14.4)	(5.1)
Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	$ 53.4	$ 37.9	$ 84.2

Receivables from customers, n70

Receivables from customers, net and notes receivable, net - Allowance for Customer Receivables (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Receivables from customers and notes receivable, net [Abstract]
Allowance for Doubtful Accounts Receivable	$ 7.6	$ 9.5

Receivables from customers, n71

Receivables from customers, net and notes receivable, net - Allowance for Notes Receivable (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Receivables from customers and notes receivable, net [Abstract]
Allowance Notes Receivable	$ 0	$ 0.2

Receivables from customers, n72

Receivables from customers, net and notes receivable, net - Bad Debt Expense and Recoveries (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Provision for Doubtful Accounts	$ 4.3	$ 4.4	$ 7.3
Allowance for Doubtful Accounts Receivable, Period Increase (Decrease)	4.2	4.2	6.6
Allowance for Doubtful Accounts Receivable, Charge-offs	0.1		6.1	$ 5.7	$ 0.6
Allowance for Doubtful Accounts Receivable, Recoveries		0.2
Commercial Hedging [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for Doubtful Accounts Receivable, Period Increase (Decrease)	3.8	3.6	2.3
Allowance for Doubtful Accounts Receivable, Charge-offs		0.4	0.7
Physical Commodities Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for Doubtful Accounts Receivable, Period Increase (Decrease)	0.2	0.4	2.8
Clearing and Execution Services Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for Doubtful Accounts Receivable, Period Increase (Decrease)	$ 0.3
Securities Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for Doubtful Accounts Receivable, Period Increase (Decrease)		$ 0.4	$ 0.5

Receivables from customers, n73

Receivables from customers, net and notes receivable, net - Allowance for Bad Debts Rollforward (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013
Allowance for Doubtful Accounts Receivable [Roll Forward]
Allowance for Doubtful Accounts - Customer and Notes Receivable	$ 54.6	$ 9.7	$ 11.2	$ 5.8
Provision for bad debts			51	4.2	$ 6
Allowance for Doubtful Accounts Receivable, Charge-offs	$ (0.1)		(6.1)	(5.7)	(0.6)
Allowance for Doubtful Accounts Receivable, Recoveries		0.2
Allowance for Doubtful Accounts - Customer and Notes Receivable		$ 54.6	$ 9.7	$ 11.2	$ 5.8

Receivables from customers, n74

Receivables from customers, net and notes receivable, net - Exim Bank Notes Receivable (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Insured short-term notes receivable		$ 2.1	$ 5
Obligations for participation rights		$ 2.1	$ 4.6
Minimum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Short Term Notes Receivable Outstanding Balance Threshold, Percentage	90.00%	90.00%
Maximum [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Short Term Notes Receivable Outstanding Balance Threshold, Percentage	98.00%	98.00%

Physical Commodities Inventor75

Physical Commodities Inventory - Physical Commodities Inventory by CIP and Finished (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Inventory [Line Items]
Agricultural Related Inventory	$ 65.1	$ 65.9
Precious Metals Inventory at fair value	13.3	5.3
Precious Metals Inventory at cost	46.4	52.6
Inventory, Net	$ 124.8	$ 123.8

Physical Commodities Inventor76

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

Property and Equipment, net (De

Property and Equipment, net (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Property, Plant and Equipment [Line Items]
Depreciation	$ 7	$ 6.6	$ 5.7
Furniture and Fixtures, Gross	7.2	6.8
Capitalized Computer Software, Gross	25.3	22.8
Machinery and Equipment, Gross	22.6	20.6
Leasehold Improvements, Gross	15.4	11.9
Property, Plant and Equipment, Gross	70.5	62.1
Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment	31.8	32.7
Property, Plant and Equipment, Net	$ 38.7	$ 29.4
Minimum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	3 years
Maximum [Member]
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Estimated Useful Lives	10 years

Goodwill - Goodwill by Segment

Goodwill - Goodwill by Segment (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Goodwill [Line Items]
Goodwill	$ 47.1	$ 47.5
Commercial Hedging [Member]
Goodwill [Line Items]
Goodwill	30.7	30.7
Global Payments [Member]
Goodwill [Line Items]
Goodwill	6.3	6.3
Physical Commodities Segment [Member]
Goodwill [Line Items]
Goodwill	2.4	2.4
Securities Segment [Member]
Goodwill [Line Items]
Goodwill	$ 7.7	$ 8.1

Intangible Assets - Gross and N

Intangible Assets - Gross and Net Intangible Assets by Major Class (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Computer Software, Gross	$ 25.3	$ 22.8
Finite-Lived Intangible Assets, Gross	22.7	17.8
Finite-Lived Intangible Assets, Accumulated Amortization	(10.4)	(8.7)
Finite-Lived Intangible Assets, Net	12.3	9.1
Trade Names [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Trade Names, Gross	0	1.1
Finite-Lived Intangible Assets, Accumulated Amortization	0	0.6
Finite-Lived Intangible Assets, Net	0	0.5
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)	(2.4)
Finite-Lived Intangible Assets, Net	0.2	0.3
Customer Relationships [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Customer Lists, Gross	20	14
Finite-Lived Intangible Assets, Accumulated Amortization	(7.9)	(5.7)
Finite-Lived Intangible Assets, Net	$ 12.1	$ 8.3

Intangible Assets - Finite-Live

Intangible Assets - Finite-Lived Intangible Assets Future Amortization Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Intangible Assets [Abstract]
Amortization of Intangible Assets	$ 2.8	$ 1.6	$ 1.5
Finite-Lived Intangible Assets, Amortization Expense, Maturity Schedule [Abstract]
Fiscal 2,016	2.2
Fiscal 2,017	2.2
Fiscal 2,018	2
Fiscal 2,019	1.9
Fiscal 2020 and thereafter	4
Finite-Lived Intangible Assets, Net	$ 12.3	$ 9.1

Intangible Assets Intangible As

Intangible Assets Intangible Asset Additions (Details) $ in Millions	12 Months Ended
	Sep. 30, 2017USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
Finite-lived Intangible Assets Acquired	$ 6

Credit Facilities - Number of C

Credit Facilities - Number of Credit Facilities (Details) $ in Millions	12 Months Ended
	Sep. 30, 2017USD ($)Rate	May 05, 2015USD ($)
Line of Credit Facility [Line Items]
Number of credit facilities	4
HCO Syndicated line of credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.625%
Line of Credit Facility, Interest Rate at Period End	4.20%
Line of Credit Facility, Maximum Borrowing Capacity | $	$ 262
HCO Syndicated line of credit facility [Member] | Eurodollar Rate [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	3.00%
HCO Syndicated line of credit facility [Member] | Base Rate [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.00%
INTL FCStone, Ltd [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity | $	$ 25
INTL FCStone, Ltd [Member] | Base Rate [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.50%
INTL FCStone Financial Margin line of credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.50%
Line of Credit Facility, Interest Rate at Period End	6.25%
Line of Credit Facility, Maximum Borrowing Capacity | $	$ 75	$ 50
INTL FCStone Financial Margin line of credit facility [Member] | Base Rate [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.00%

Credit Facilities (Details)

Credit Facilities (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2013	May 05, 2015	Apr. 15, 2015
Line of Credit Facility [Line Items]
Payables to lenders under loans	$ 230.2	$ 182.8
Notes Payable to Bank	2	2.8				$ 4
Senior Notes	$ 0	$ 44.5	$ 45.5
Debt Instrument, Interest Rate, Stated Percentage	8.50%
Debt Instrument, Call Feature, Redemption Price Percentage of Principal		100.00%
Payments of Debt Issuance Costs	$ 0.3	$ 2.1	$ 0.2	$ 1.7
Debt and Capital Lease Obligations	$ 230.2	227.3
HCO Syndicated line of credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	4.20%
Line of Credit Facility, Maximum Borrowing Capacity	$ 262
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.625%
Payables to lenders under loans	$ 150	136.5
INTL FCStone Financial Margin line of credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	6.25%
Line of Credit Facility, Maximum Borrowing Capacity	$ 75				$ 50
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.50%
Payables to lenders under loans	$ 0	0
INTL FCStone Financial [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	0
Payables to lenders under loans	$ 34	0
FMS Sub-note commodity line of credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	4.00%
Line of Credit Facility, Maximum Borrowing Capacity	$ 170
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.50%
Payables to lenders under loans	$ 44.2	43.5
INTL FCStone, Ltd [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	25
Payables to lenders under loans	0	$ 0
Main line of credit facilities [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	532
Line of Credit Facility, Current Borrowing Capacity	$ 245
Base Rate [Member] | HCO Syndicated line of credit facility [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.00%
Base Rate [Member] | INTL FCStone Financial Margin line of credit facility [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.00%
Base Rate [Member] | Sterne Agee [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.00%
Base Rate [Member] | INTL FCStone, Ltd [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.50%

Commitments and Contingencies -

Commitments and Contingencies - Contingencies and Litigation (Details) $ in Millions	Sep. 30, 2017USD ($)
Commitments and Contingencies [Abstract]
Gain Contingency, Unrecorded Amount	$ 2

Commitments and Contingencies85

Commitments and Contingencies - Contigent Consideration for Acquisitions (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015	Jan. 01, 2015
Business Acquisition, Contingent Consideration [Line Items]
Business Combination, Contingent Consideration, Liability	$ 1	$ 0.8
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability	(0.2)	(0.4)	$ 1.9
G.X. Clarke (INTL FCStone Partners) [Member]
Business Acquisition, Contingent Consideration [Line Items]
Business Combination, Contingent Consideration, Liability	1
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High		1.5		$ 0.1
Business Combination, Consideration, Including Contingent Consideration	27.5
Contingent Consideration [Member]
Business Acquisition, Contingent Consideration [Line Items]
Business Combination, Contingent Consideration Arrangements, Change in Amount of Contingent Consideration, Liability	$ 0.2	$ 0.4	$ 1.8

Commitments and Contingencies86

Commitments and Contingencies - Operating Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Operating Leases [Abstract]
Operating Leases, Rent Expense	$ 11.3	$ 9.9	$ 10.1
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Operating Leases, Future Minimum Payments Due, Next Twelve Months	8.9
Operating Leases, Future Minimum Payments, Due in Two Years	8.3
Operating Leases, Future Minimum Payments, Due in Three Years	7.7
Operating Leases, Future Minimum Payments, Due in Four Years	6.7
Operating Leases, Future Minimum Payments, Due in Five Years	4.7
Operating Leases, Future Minimum Payments, Due Thereafter	10.1
Operating Leases, Future Minimum Payments Due	$ 46.4

Commitments and Contingencies87

Commitments and Contingencies - Purchase Obligations (Details) $ in Millions	Sep. 30, 2017USD ($)
Commitments and Contingencies Disclosure [Abstract]
Purchase Obligation, Due in Next Twelve Months	$ 675.7
Purchase Obligation, Due in Second and Third Year	1.8
Purchase Obligation, Due in Fourth and Fifth Year	2.1
Purchase Obligation, Due after Fifth Year	1.7
Other Commitment, Due in Next Twelve Months	$ 583.5

Commitments and Contingencies88

Commitments and Contingencies - Self-Insurance (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Commitments and Contingencies [Abstract]
Self Insurance Reserve	$ 0.8	$ 1

Regulatory Requirements and S89

Regulatory Requirements and Subsidiary Dividend Restrictions - Minimum net capital (Details)	Sep. 30, 2017USD ($)
Capital and Other Regulatory Requirements [Abstract]
Minimum Net Capital Required for Broker-Dealer Subsidiary	$ 1,000,000
Minimum Net Capital Required for Entity	$ 0.08

Regulatory Requirements and S90

Regulatory Requirements and Subsidiary Dividend Restrictions - Regulatory Capital Requirements (Details) - USD ($)	Sep. 30, 2017	Sep. 30, 2016
Minimum Net Capital Required for Entity	$ 0.08
Cash Held at Banks and Money Market Funds - Segregated	464,300,000	$ 515,200,000
INTL FCStone Financial [Member]
Net Capital	157,100,000
Cash and Securities Segregated under Commodity Exchange Act Regulation	2,248,000,000
Secured funds	165,100,000
Minimum Net Capital Required for Entity	74,000,000
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	2,195,700,000
Secured Funds Required Under Commodity Exchange Act	148,700,000
Cash Reserve Deposit Required and Made	7,200,000	0
Cash Held at Banks and Money Market Funds - Segregated	13,500,000	$ 200,000
Sterne Agee Clearing, Inc. [Member]
Net Capital	1,500,000
Minimum Net Capital Required for Entity	100,000
Sterne Agee Financial Services, Inc. [Member]
Net Capital	4,900,000
Minimum Net Capital Required for Entity	300,000
INTL FCStone, Ltd [Member]
Cash and Securities Segregated under Commodity Exchange Act Regulation	107,100,000
Net Capital under Commodity Exchange Act Computation	158,700,000
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	106,600,000
Required Net Capital under Commodity Exchange Act	88,300,000
INTL FCStone Europe [Member]
Net Capital under Commodity Exchange Act Computation	158,000,000
Required Net Capital under Commodity Exchange Act	88,300,000
INTL FCStone DTVM Ltda [Member]
Net Capital	13,000,000
Capital Required for Capital Adequacy	500,000
Gainvest S.A. Sociedad Gerente de FCI - Comision Nacional de Valores [Member]
Net Capital	5,100,000
Net Capital under Commodity Exchange Act Computation	400,000
Required Net Capital under Commodity Exchange Act	100,000
Capital Required for Capital Adequacy	200,000
INTL CIBSA S.A. - Comision Nacional de Valores [Member]
Net Capital	7,600,000
Net Capital under Commodity Exchange Act Computation	0
Required Net Capital under Commodity Exchange Act	0
Capital Required for Capital Adequacy	$ 900,000

Commodity and Other Repurchas91

Commodity and Other Repurchase Agreements (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Securities sold under agreements to repurchase	$ 1,393.1	$ 1,167.1
Fair Value of Securities Received as Collateral that Can be Resold or Repledged	631.7
Fair Value of Securities Received as Collateral that Have Been Resold or Repledged	306.9
Financial Instruments Owned and Pledged as Collateral, Amount Eligible to be Repledged by Counterparty	19.4
Securities Loaned, Fair Value of Collateral	108.4
Financial Instruments Owned and Pledged as Collateral, Amount Not Eligible to be Repledged by Counterparty	1,406.6
Securities Loaned	111.1	0
Collateralized Financings	1,504.2
Sales Repurchase Agreements	0.8	1.5
Securities Sold under Agreements to Repurchase, Fair Value of Collateral	19.4	$ 47.2
Maturity Overnight [Member]
Securities sold under agreements to repurchase	640.2
Securities Loaned	111.1
Collateralized Financings	751.3
Maturity Less than 30 Days [Member]
Securities sold under agreements to repurchase	432.9
Securities Loaned	0
Collateralized Financings	432.9
Maturity 30 to 90 Days [Member]
Securities sold under agreements to repurchase	320
Securities Loaned	0
Collateralized Financings	320
Maturity Greater than 90 Days [Member]
Securities sold under agreements to repurchase	0
Securities Loaned	0
Collateralized Financings	0
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Securities sold under agreements to repurchase	1,017.1
Asset-backed Securities [Member]
Securities sold under agreements to repurchase	36.4
US Government Debt Securities [Member]
Securities sold under agreements to repurchase	7
US Government Agencies Debt Securities [Member]
Securities sold under agreements to repurchase	332.6
Equity Securities [Member]
Securities Loaned	$ 111.1

Share-Based Compensation - Shar

Share-Based Compensation - Share-based Compensation Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Allocated Share-based Compensation Expense	$ 6.3	$ 5.1	$ 3.6

Share-Based Compensation - Stoc

Share-Based Compensation - Stock Option Plan (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	1,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	652,494	754,163
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value	$ 8.67	$ 6.40	$ 4.31
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Stock Options	$ 3.9
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition	3 years 11 months 1 day
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Total Intrinsic Value	$ 2.6	$ 1.9	$ 3.6

Share-Based Compensation - St94

Share-Based Compensation - Stock Option Plan Fair Value Weighted-Average Assumptions (Details)	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate	31.00%	28.00%	28.00%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate	0.00%	0.00%	0.00%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate	0.99%	0.83%	0.66%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term	3 years 29 days	3 years 22 days	3 years 2 months 19 days

Share-Based Compensation - Sh95

Share-Based Compensation - Share-Based Compensation Table (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized	1,000,000
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	754,163
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	1,215,821
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross	(110,000)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Period Increase (Decrease)	110,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period	(155,588)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures in Period	8,331
Share-based Compensation Arrangement by Share-based Payment Award, Options, Other Increases (Decreases) in Period	(106,996)
Share-based Compensation Arrangement by Share-based Payment Award, Options, Expirations in Period	(181,834)
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	652,494	754,163
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number	881,403	1,215,821
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number	222,116
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price	$ 27.31	$ 29.55
Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price	38.77
Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price	22.54
Share-based Compensation Arrangements by Share-based Payment Award, Options, Forfeitures in Period, Weighted Average Exercise Price	26.15
Share-based Compensation Arrangements by Share-based Payment Award, Options, Expirations in Period, Weighted Average Exercise Price	54.02
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price	24.42
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Grant Date Fair Value	11.55	12.88
Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value	8.67	$ 6.40	$ 4.31
Share-based Compensation Arrangement by Share-based Payment Award, Options, Excrecises in Period, Weighted Average Grant Date Fair Value	9.05
Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeited in Period, Weighted Average Grant Date Fair Value	13.20
Share-based Compensation Arrangement by Share-based Payment Award, Options, Expired in Period, Weighted Average Grant Date Fair Value	19.93
Share-based Compensation Arrangement by Share-based Payment Award, Options, Excercisable, Weighted Average Grant Date Fair Value	$ 10.43
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term	3 years 6 months 26 days	3 years 9 months 18 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term	2 years 6 months 7 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value	$ 9.8	$ 14.1
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value	3.1
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Stock Options	$ 3.9
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition	3 years 11 months 1 day
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Total Intrinsic Value	$ 2.6	$ 1.9	$ 3.6

Share-Based Compensation - Opti

Share-Based Compensation - Options by Exercise Price (Details)	12 Months Ended
	Sep. 30, 2017$ / sharesshares
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Number of Outstanding Options | shares	881,403
Weighted Average Exercise Price	$ 27.31
Weighted Average Remaining Term (in years)	3 years 6 months 26 days
$0 - $5,00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Range, Lower Range Limit	$ 0
Exercise Price Range, Upper Range Limit	$ 5
Number of Outstanding Options | shares	0
$5.00 - $10.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Range, Lower Range Limit	$ 5
Exercise Price Range, Upper Range Limit	$ 10
Number of Outstanding Options | shares	0
$10.00 - $15.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Range, Lower Range Limit	$ 10
Exercise Price Range, Upper Range Limit	$ 15
Number of Outstanding Options | shares	0
$15.00 - $20.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Range, Lower Range Limit	$ 15
Exercise Price Range, Upper Range Limit	$ 20
Number of Outstanding Options | shares	22,414
Weighted Average Exercise Price	$ 19.24
Weighted Average Remaining Term (in years)	3 months 18 days
$20.00 - $25.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Range, Lower Range Limit	$ 20
Exercise Price Range, Upper Range Limit	$ 25
Number of Outstanding Options | shares	97,911
Weighted Average Exercise Price	$ 21.77
Weighted Average Remaining Term (in years)	10 months 2 days
$25.00 - $30.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Range, Lower Range Limit	$ 25
Exercise Price Range, Upper Range Limit	$ 30
Number of Outstanding Options | shares	580,000
Weighted Average Exercise Price	$ 25.91
Weighted Average Remaining Term (in years)	4 years 4 months 13 days
$30.00 - $35.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Range, Lower Range Limit	$ 30
Exercise Price Range, Upper Range Limit	$ 35
Number of Outstanding Options | shares	73,578
Weighted Average Exercise Price	$ 31.37
Weighted Average Remaining Term (in years)	2 years 3 months 11 days
$35.00 - $40.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Range, Lower Range Limit	$ 35
Exercise Price Range, Upper Range Limit	$ 40
Number of Outstanding Options | shares	107,500
Weighted Average Exercise Price	$ 38.77
Weighted Average Remaining Term (in years)	3 years 3 months 7 days
$40.00 - $45.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Range, Lower Range Limit	$ 40
Exercise Price Range, Upper Range Limit	$ 45
Number of Outstanding Options | shares	0
$45.00 - $50.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Range, Lower Range Limit	$ 45
Exercise Price Range, Upper Range Limit	$ 50
Number of Outstanding Options | shares	0
$50.00 - $55.00 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise Price Range, Lower Range Limit	$ 50
Exercise Price Range, Upper Range Limit	$ 55
Number of Outstanding Options | shares	0

Share-Based Compensation - Rest

Share-Based Compensation - Restricted Stock Plan (Details) $ in Millions	12 Months Ended
	Sep. 30, 2017USD ($)shares
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period	1,500,000
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted	1,459,976
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized | $	$ 8.2
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition - Restricted Stock	1 year 3 months 4 days

Share-Based Compensation - Re98

Share-Based Compensation - Restricted Stock Plan Table (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Granted	1,459,976
Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period	1,500,000
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number	747,782
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Period Increase (Decrease)	(147,726)
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Forfeitures	459
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding, Number	1,459,976	747,782
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	357,752
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	147,726
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period	(150,545)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	(459)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	354,474	357,752
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value	$ 27.39
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value	40.98
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value	26.69
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value	37.31
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value	$ 33.34	$ 27.39
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Outstanding, Weighted Average Remaining Contractual Terms	1 year 3 months 4 days	1 year 4 months 21 days
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Aggregate Intrinsic Value, Outstanding	$ 13.6	$ 13.9
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized	$ 8.2
Employee Service Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition - Restricted Stock	1 year 3 months 4 days

Retirement Plans (Details)

Retirement Plans (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Defined Benefit Plan, Fair Value of Plan Assets	$ 36.4	$ 33.7
Defined Benefit Plan, Benefit Obligation	$ 36.5	$ 38.5
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	3.80%	3.60%
Defined Benefit Plan, Pension Plan with Accumulated Benefit Obligation in Excess of Plan Assets, Projected Benefit Obligation	$ 0.1	$ 4.8
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	$ 0.3	0.2	$ 0.1
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Rate of Return on Plan Assets	6.00%
Defined Benefit Plan, Plan Assets, Contributions by Employer	$ 2	1.8
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year	2.1
Defined Benefit Plan, Expected Future Benefit Payment, Year Two	2.1
Defined Benefit Plan, Expected Future Benefit Payment, Year Three	2
Defined Benefit Plan, Expected Future Benefit Payment, Year Four	2
Defined Benefit Plan, Expected Future Benefit Payment, Year Five	1.9
Defined Benefit Plan, Expected Future Benefit Payment, Five Fiscal Years Thereafter	9.5
Defined Contribution Plan, Employer Discretionary Contribution Amount	$ 6.1	$ 5.3	$ 5.1
Debt Securities [Member]
Defined Benefit Plan, Actual Plan Asset Allocations	80.00%
Equity Securities [Member]
Defined Benefit Plan, Actual Plan Asset Allocations	20.00%
UK Plan [Member]
Defined Contribution Plan, Employers Matching Contribution, Annual Vesting Percentage	100.00%
UK Plan [Member] | Maximum [Member]
Defined Contribution Plan, Employer Matching Contribution, Percent	10.00%
401k Plan [Member]
Defined Contribution Plan, Employer Matching Contribution, Percent	62.50%
Defined Contribution Plan, Employers Matching Contribution, Annual Vesting Percentage	8.00%
Defined Contribution Plan, Employers Matching Contribution, Annual Vesting Percentage, Two to Three Years	33.00%
Defined Contribution Plan, Employers Matching Contribution, Annual Vesting Percentage, Three to Four Years	66.00%
Defined Contribution Plan, Employers Matching Contribution, Annual Vesting Percentage, All Years	100.00%
401k Plan [Member] | Maximum [Member]
Defined Contribution Plan, Maximum Annual Contribution Per Employee, Percent	80.00%
401k Plan [Member] | Minimum [Member]
Defined Contribution Plan, Maximum Annual Contribution Per Employee, Percent	1.00%

Other Expenses - Other Expenses

Other Expenses - Other Expenses Breakout (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Other Expenses [Abstract]
Accretion Expense	$ 0.1	$ 0.4	$ 1.8
General Insurance Expense	2.7	2.1	1.7
Advertising Expense	4	5.1	2.7
Technology Services Costs	11.6	7.1	4.7
Supplies and Postage Expense	2.1	1.1	1.2
Clearance Fees	2.6	1.3	1.1
Taxes, Miscellaneous	4.6	4.3	3.7
Other Expenses	9.8	8	6.6
Operating Costs and Expenses	$ 37.5	$ 29.4	$ 23.5

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Income Tax Disclosure [Abstract]
Income tax expense	$ 1.1	$ 2.3	$ 3.3	$ 2.1	$ 2.4	$ 6.8	$ 5.5	$ 3.3	$ 8.8	$ 18	$ 22.4
Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Tax									0	0	(0.4)
Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Net Unamortized (Gain) Loss Arising During Period, Tax									1	0.2	(0.8)
Adjustments to Additional Paid in Capital, Income Tax Benefit from Share-based Compensation									(0.1)	(0.8)	(0.5)
Other Comprehensive Income (Loss), Tax									9.9	17.4	20.7
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense									0
Operating Loss Carryforwards	30.1				15.7				30.1	15.7
Deferred Tax Assets, Operating Loss Carryforwards, Domestic	21.9				12.4				21.9	12.4
Deferred Tax Assets, Net of Valuation Allowance, Operating Loss Carryforwards, State and Local	4.4								4.4
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax	1.3								1.3
Deferred Tax Assets, Valuation Allowance	4				3.6				4	3.6
Valuation Allowance, Deferred Tax Asset, Change in Amount									0.4
Income (Loss) from Continuing Operations before Income Taxes, Domestic									(24.7)	(9.7)	$ 16.5
Deferred Tax Liabilities, Gross	4.9								4.9
Deferred Tax Liabilities, Unrealized Gains on Trading Securities	3.1								3.1
Undistributed Earnings of Foreign Subsidiaries	$ 321.3				$ 294.3				$ 321.3	$ 294.3

Income Taxes - Current and Defe

Income Taxes - Current and Deferred Taxes (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Income Tax Disclosure [Abstract]
Current Federal Tax Expense (Benefit)									$ 0.7	$ 1.3	$ 0.8
Current State and Local Tax Expense (Benefit)									1.2	0.8	1.2
Current Foreign Tax Expense (Benefit)									16.7	16.8	15.4
Current Income Tax Expense (Benefit)									18.6	18.9	17.4
Deferred Income Tax Expense (Benefit)									(9.8)	(0.8)	5
Other Tax Expense (Benefit)									0	(0.1)	0
Income tax expense	$ 1.1	$ 2.3	$ 3.3	$ 2.1	$ 2.4	$ 6.8	$ 5.5	$ 3.3	$ 8.8	$ 18	$ 22.4

Income Taxes - US and Internati

Income Taxes - US and International Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Income Tax Disclosure [Abstract]
Income (Loss) from Continuing Operations before Income Taxes, Domestic	$ (13.9)	$ 4.9	$ 14.5
Income (Loss) from Continuing Operations before Income Taxes, Foreign	29.1	67.9	63.7
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest	$ 15.2	$ 72.8	$ 78.2

Income Taxes - Effective Rate R

Income Taxes - Effective Rate Reconciliation (Details)	12 Months Ended
	Sep. 30, 2017Rate	Sep. 30, 2016Rate	Sep. 30, 2015Rate
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate	35.00%	35.00%	35.00%
Effective Income Tax Rate Reconciliation, State and Local Income Taxes	(2.60%)	1.30%	1.80%
Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential	11.50%	(11.00%)	(11.10%)
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Meals and Entertainment	3.60%	0.80%	0.50%
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Other	8.10%	1.90%	2.10%
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent	0.00%	(3.00%)	0.00%
Effective Income Tax Rate Reconciliation, Deductions, Other	(0.60%)	(0.30%)	(0.10%)
Effective Income Tax Rate, Continuing Operations	57.70%	25.00%	28.70%
Foreign Tax Authority [Member]
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance	(1.40%)	(0.30%)	(0.10%)
State and Local Jurisdiction [Member]
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance	4.10%	0.00%	0.60%

Income Taxes - Deferred Tax Ass

Income Taxes - Deferred Tax Assets and Liabilites (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016
Tax Credit Carryforward [Line Items]
Deferred Tax Assets, Tax Credit Carryforwards, Research	$ 0.4
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Share-based Compensation Cost	3.7	$ 4.3
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Pensions	0.1	1.9
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits, Employee Compensation	2	2
Deferred Tax Assets, Operating Loss Carryforwards, Foreign	5.6	2
Deferred Tax Assets, Operating Loss Carryforwards, State and Local	6.6	4.9
Deferred Tax Assets, Operating Loss Carryforwards, Domestic	21.9	12.4
Deferred Tax Assets, Intangible Assets	6.1	8.3
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Allowance for Doubtful Accounts	1.4	1.6
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax	1.6	1.4
Deferred Tax Assets, Tax Deferred Expense, Compensation and Benefits	3.6	3.3
Deferred Tax Assets, Other	1.9	1.8
Deferred Tax Assets, Gross	54.5	43.9
Deferred Tax Assets, Valuation Allowance	(4)	(3.6)
Deferred Tax Assets, Net of Valuation Allowance	50.5	40.3
Deferred Tax Liabilities, Unrealized Gains on Trading Securities	3.2	1.3
Deferred Tax Liabilities, Prepaid Expenses	2.5	1.9
Deferred Tax Liabilities, Property, Plant and Equipment	2.2	2.6
Deferred Tax Liabilities, Gross	7.9	5.8
Deferred tax assets, Net	$ 42.6	$ 34.5

Income Taxes - FIN 48 Analysis

Income Taxes - FIN 48 Analysis (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Income Tax Disclosure [Abstract]
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense	$ 0
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance beginning of year	0.1	$ 0	$ 0
Gross increases for tax positions related to current year	0	0	0
Gross increases for tax positions related to prior years	0	0.1	0
Gross decreases for tax positions of prior years	0	0	0
Settlements	0	0	0
Lapse of statute of limitations	0	0	0
Balance end of year	$ 0.1	$ 0.1	$ 0

Acquisitions and Disposals (Det

Acquisitions and Disposals (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended									12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Jun. 30, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015	Jan. 01, 2015
Business Acquisition [Line Items]
Gross Profit	$ 205.1	$ 197.6	$ 195.8	$ 185.5	$ 178.6	$ 175	$ 166.1	$ 151.3		$ 784	$ 671	$ 624.3
Net income	$ (23.6)	$ 12.7	$ 11	$ 6.3	$ 16.8	$ 14.6	$ 14.5	$ 8.8		6.4	54.7	55.7
Net basic earnings per share	$ (1.27)	$ 0.67	$ 0.58	$ 0.34	$ 0.91	$ 0.79	$ 0.77	$ 0.47
Net diluted earnings per share	$ (1.27)	$ 0.66	$ 0.58	$ 0.34	$ 0.90		$ 0.76	$ 0.46	$ 0.78
Business Combination, Consideration Transferred											45
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents					$ 24.9						24.9
Business Combination, Acquired Receivable, Fair Value					151.6						151.6
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Assets Noncurrent					5.7						5.7
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Prepaid Expense and Other Assets					4.8						4.8
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities					136						136
Gain on acquisition					6.2	$ 0	$ 0	$ 0		0	6.2	0
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual											8.6
Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual											0.1
Goodwill	$ 47.1				47.5					47.1	47.5
Finite-lived Intangible Assets Acquired										6
Deferred consideration payable related to acquisitions										0	0	$ 5
G.X. Clarke (INTL FCStone Partners) [Member]
Business Acquisition [Line Items]
Present Value of Estimated Total Purchase Price	27.5									27.5
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net					25.9						25.9
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill					1.5						1.5
Business Combination, Contingent Consideration Arrangements, Range of Outcomes, Value, High					1.5						1.5		$ 0.1
G.X. Clarke (INTL FCStone Partners) [Member]
Business Acquisition [Line Items]
Escrow Deposit					10						10
Adjustment Escrow					5						5
Indemnity Escrow					5						5
Deferred consideration payable related to acquisitions											5
Deposit Liability, Current	$ 4.5									$ 4.5
Business Acquisition, Contingent Consideration, Potential Cash Payment, Year One					0.5						0.5
After-tax net income over year one											5
Business Acquisition, Contingent Consideration, Potential Cash Payment Year Three					$ 1						1
After-tax net income over earn-out period											$ 30

Accumulated Other Comprehens108

Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	$ (24.5)	$ (24.6)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	(1.4)	(7.4)	$ (4)
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Reclassification Adjustment, after Tax	(1.2)	0.2	1.5
Net unrealized gain on available-for-sale securities	0	0	2.7
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax	0.4	0.5	0.3
Other Comprehensive Income (Loss), Net of Tax	0.1	(7.1)	(5.9)
Accumulated Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	(21.5)	(20.1)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax	(1.4)
Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Reclassification Adjustment from AOCI, Realized upon Sale or Liquidation, before Tax	0
Other Comprehensive Income (Loss), Net of Tax	(1.4)
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	(3)	(4.5)
Other Comprehensive (Income) Loss, Defined Benefit Plan, before Reclassification Adjustment, after Tax	1.2
Other Comprehensive (Income) Loss, Defined Benefit Plan, Reclassification Adjustment from AOCI, before Tax	0.3
Other Comprehensive Income (Loss), Net of Tax	1.5
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	(24.5)	(24.6)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	(0.2)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0.3
Other Comprehensive Income (Loss), Net of Tax	$ 0.1	$ (7.1)	$ (5.9)

Quarterly Financial Informat109

Quarterly Financial Information (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended									12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Jun. 30, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 12,382.5	$ 5,505.9	$ 5,460.8	$ 6,074.4	$ 2,777.6	$ 4,868.5	$ 3,708.9	$ 3,399.9		$ 29,423.6	$ 14,754.9	$ 34,693.2
Cost of sales of physical commodities	12,177.4	5,308.3	5,265	5,888.9	2,599	4,693.5	3,542.8	3,248.6		28,639.6	14,083.9	34,068.9
Operating revenues	205.1	197.6	195.8	185.5	178.6	175	166.1	151.3		784	671	624.3
Transaction-based clearing expenses	35.1	33.9	33.7	33.6	32	35.2	32.9	29.8		136.3	129.9	122.7
Introducing broker commissions	26.9	29.2	28.2	28.7	28.1	14.8	13.2	12.8		113	68.9	52.7
Interest expense	12	11.2	10	8.9	7.5	7.7	7.1	6		42.1	28.3	17.1
Net operating revenues	131.1	123.3	123.9	114.3	111	117.3	112.9	102.7		492.6	443.9	431.8
Compensation and benefits	73	75.5	76.6	70.6	66.2	69.4	65.2	63.1		295.7	263.9	251.1
Bad debts	0.4	0.1	1.3	2.5	(0.2)	0	2.6	2		4.3	4.4	7.3
Provision for bad debt on physical coal	47	0	0	0						47	0	0
Other	33.2	32.7	31.7	32.8	32	26.5	25.1	25.5		37.5	29.4	23.5
Total compensation and other expenses	153.6	108.3	109.6	105.9	98	95.9	92.9	90.6		477.4	377.4	353.7
Gain on acquisition					6.2	0	0	0		0	6.2	0
Income before tax	(22.5)	15	14.3	8.4	19.2	21.4	20	12.1		15.2	72.7	78.1
Income tax expense	1.1	2.3	3.3	2.1	2.4	6.8	5.5	3.3		8.8	18	22.4
Net income	$ (23.6)	$ 12.7	$ 11	$ 6.3	$ 16.8	$ 14.6	$ 14.5	$ 8.8		$ 6.4	$ 54.7	$ 55.7
Net basic earnings per share	$ (1.27)	$ 0.67	$ 0.58	$ 0.34	$ 0.91	$ 0.79	$ 0.77	$ 0.47
Net diluted earnings per share	$ (1.27)	$ 0.66	$ 0.58	$ 0.34	$ 0.90		$ 0.76	$ 0.46	$ 0.78

Segment and Geographic Infor110

Segment and Geographic Information (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Segment Reporting Information [Line Items]
Revenues	$ 12,382.5	$ 5,505.9	$ 5,460.8	$ 6,074.4	$ 2,777.6	$ 4,868.5	$ 3,708.9	$ 3,399.9	$ 29,423.6	$ 14,754.9	$ 34,693.2
Operating revenues	205.1	197.6	195.8	185.5	178.6	175	166.1	151.3	784	671	624.3
Revenues, Net of Interest Expense	131.1	123.3	123.9	114.3	111	117.3	112.9	102.7	492.6	443.9	431.8
Net Segment Contribution									387	347	320.6
Segment Income									169	206	188.1
Costs not allocated to operating segments									153.8	133.3	110
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(22.5)	$ 15	$ 14.3	$ 8.4	19.2	$ 21.4	$ 20	$ 12.1	15.2	72.7	78.1
Assets	6,243.4				5,950.3				6,243.4	5,950.3	5,070
Commercial Hedging [Member]
Segment Reporting Information [Line Items]
Revenues									244.6	236.1	262.4
Operating revenues									244.6	236.1	262.4
Revenues, Net of Interest Expense									194.3	188.2	214.7
Net Segment Contribution									141.8	134.4	151.7
Segment Income									72.8	68.7	85.6
Assets	1,650.3				1,637.5				1,650.3	1,637.5	1,548.1
Global Payments [Member]
Segment Reporting Information [Line Items]
Revenues									89.2	73.2	77.1
Operating revenues									89.2	73.2	77.1
Revenues, Net of Interest Expense									80.6	65.3	68.5
Net Segment Contribution									64.4	52.2	54.5
Segment Income									50.6	39.8	43.3
Assets	199.5				191.4				199.5	191.4	207.3
Securities Segment [Member]
Segment Reporting Information [Line Items]
Revenues									151.7	175.2	129.8
Operating revenues									151.7	175.2	129.8
Revenues, Net of Interest Expense									94.6	121.9	88.6
Net Segment Contribution									75.6	97.5	67.4
Segment Income									46.6	69.4	40.5
Assets	2,101.7				2,130.7				2,101.7	2,130.7	1,861
Physical Commodities Segment [Member]
Segment Reporting Information [Line Items]
Revenues									28,684.4	14,120.5	34,092
Operating revenues									44.8	36.6	23.1
Revenues, Net of Interest Expense									37.3	31.5	21.2
Net Segment Contribution									27.2	23.4	16.9
Segment Income									(31.4)	13.3	5.8
Assets	339.5				258				339.5	258	190.9
Clearing and Execution Services Segment [Member]
Segment Reporting Information [Line Items]
Revenues									259.8	151.1	123.4
Operating revenues									259.8	151.1	123.4
Revenues, Net of Interest Expense									102.2	48.8	38.3
Net Segment Contribution									78	39.5	30.1
Segment Income									30.4	14.8	12.9
Assets	1,818.9				1,617.4				1,818.9	1,617.4	1,163.8
Corporate [Member]
Segment Reporting Information [Line Items]
Revenues									(6.1)	(1.2)	8.5
Operating revenues									(6.1)	(1.2)	8.5
Revenues, Net of Interest Expense									(16.4)	(11.8)	0.5
Assets	$ 133.5				$ 115.3				$ 133.5	$ 115.3	$ 98.9

Segment and Geographic Infor111

Segment and Geographic Information - Total Revenues by Geographic Location (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Revenues	$ 12,382.5	$ 5,505.9	$ 5,460.8	$ 6,074.4	$ 2,777.6	$ 4,868.5	$ 3,708.9	$ 3,399.9	$ 29,423.6	$ 14,754.9	$ 34,693.2
Gross Profit	205.1	$ 197.6	$ 195.8	$ 185.5	178.6	$ 175	$ 166.1	$ 151.3	784	671	624.3
Long-Lived Assets	38.7				29.4				38.7	29.4	19.7
UNITED STATES
Revenues									1,168	817.1	25,959
Gross Profit									529.4	457	424.3
Long-Lived Assets	29.7				23.3				29.7	23.3	13.8
Europe [Member]
Revenues									166.9	463.5	121.2
Gross Profit									166.9	120.2	125
Long-Lived Assets	7.3				4.8				7.3	4.8	4
South America [Member]
Revenues									53.9	64.8	49
Gross Profit									54	64.8	49
Long-Lived Assets	1.5				1.2				1.5	1.2	1.7
Asia [Member]
Revenues									28,030.3	13,405.1	8,560
Gross Profit									29.2	24.6	21.9
Long-Lived Assets	$ 0.2				$ 0.1				0.2	0.1	0.2
Other (geographic location) [Member]
Revenues									4.5	4.4	4
Gross Profit									$ 4.5	$ 4.4	$ 4.1

Condensed Parent Only Financ112

Condensed Parent Only Financial Statements - Balance Sheet (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Cash and cash equivalents	$ 314.9	$ 316.2	$ 268.1	$ 231.3
Deposits and receivables from broker-dealers, clearing organizations and counterparties	2,625.1	1,761.4
Income taxes receivable	0.4	1.1
Financial instruments owned, at fair value	1,731.8	1,606.1
Deferred tax assets, Net	42.6	34.5
Property and equipment, net	38.7	29.4
Total assets	6,243.4	5,950.3	5,070
Liabilities:
Accounts payable and other accrued liabilities	135.6	161.3
Payables to Customers	3,072.9	2,854.2
Payables to lenders under loans	230.2	182.8
Senior unsecured notes	0	44.5	45.5
Financial Instruments Sold, Not yet Purchased, at Fair Value	717.6	839.4
Total liabilities	5,793.5	5,516.5
INTL FCStone Inc. (Parent Company Only) stockholders’ equity:
Common stock, $0.01 par value. Authorized 30,000,000 shares; 20,855,243 issued and 18,733,286 outstanding at September 30, 2017 and 20,557,175 issued and 18,435,218 outstanding at September 30, 2016	0.2	0.2
Common stock in treasury, at cost - 2,121,957 shares at September 30, 2017 and 2016	(46.3)	(46.3)
Additional Paid in Capital	259	249.4
Retained earnings	261.5	255.1
Total INTL FCStone Inc. (Parent Company Only) stockholders’ equity	449.9	433.8
Total liabilities and stockholders' equity	6,243.4	5,950.3
Parent Company [Member]
Cash and cash equivalents	2	1.3	$ 2.5	$ 3
Deposits and receivables from broker-dealers, clearing organizations and counterparties	0	2.9
Receivables from subsidiaries	3.8	3.6
Notes receivable, net	4.8	6.9
Income taxes receivable	8.6	14
Investment in subsidiaries	312.3	316.3
Financial instruments owned, at fair value	0	1.3
Deferred tax assets, Net	26.5	15.7
Property and equipment, net	24.8	12.7
Other assets	7.6	16.2
Total assets	390.4	390.9
Liabilities:
Accounts payable and other accrued liabilities	19.8	27.7
Payables to Customers	2.1	4.6
Payables to lenders under loans	152	139.3
Payable to subsidiaries, net	49.4	17.1
Senior unsecured notes	0	44.5
Financial Instruments Sold, Not yet Purchased, at Fair Value	25.3	35.9
Total liabilities	248.6	269.1
INTL FCStone Inc. (Parent Company Only) stockholders’ equity:
Preferred stock, $.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; 20,855,243 issued and 18,733,286 outstanding at September 30, 2017 and 20,557,175 issued and 18,435,218 outstanding at September 30, 2016	0.2	0.2
Common stock in treasury, at cost - 2,121,957 shares at September 30, 2017 and 2016	(46.3)	(46.3)
Additional Paid in Capital	259	249.4
Retained earnings	(71.1)	(81.5)
Total INTL FCStone Inc. (Parent Company Only) stockholders’ equity	141.8	121.8
Total liabilities and stockholders' equity	390.4	390.9
Adjustment to Investment in Subs for Equity Method Accounting	$ 332.6	$ 336.6

Condensed Parent Only Financ113

Condensed Parent Only Financial Statements - Balance Sheet (Parentheticals) (Details) - $ / shares	Sep. 30, 2017	Sep. 30, 2016
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
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	20,855,243	20,557,175
Common stock - outstanding	18,733,286	18,435,218
Treasury stock - shares	2,121,957	2,121,957

Condensed Parent Only Financ114

Condensed Parent Only Financial Statements - Income Statement (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Condensed Financial Statements, Captions [Line Items]
Trading gains, net									$ 332.2	$ 321.2	$ 328.6
Consulting fees									283.4	224.3	192.5
Interest income									69.7	55.2	39.4
Dividend income from subsidiaries									52.7	31	6
Operating revenues	$ 205.1	$ 197.6	$ 195.8	$ 185.5	$ 178.6	$ 175	$ 166.1	$ 151.3	784	671	624.3
Interest expense	12	11.2	10	8.9	7.5	7.7	7.1	6	42.1	28.3	17.1
Net operating revenues	131.1	123.3	123.9	114.3	111	117.3	112.9	102.7	492.6	443.9	431.8
Non-interest expenses:
Compensation and benefits	73	75.5	76.6	70.6	66.2	69.4	65.2	63.1	295.7	263.9	251.1
Clearing and related expenses	35.1	33.9	33.7	33.6	32	35.2	32.9	29.8	136.3	129.9	122.7
Introducing broker commissions	26.9	29.2	28.2	28.7	28.1	14.8	13.2	12.8	113	68.9	52.7
Communication and data services									39.4	32.7	28.1
Occupancy and equipment rental									15.2	13.3	13.5
Professional fees									15.2	14	12.5
Travel and business development									13.3	11.5	10.5
Depreciation and amortization									9.8	8.2	7.2
Bad debts	0.4	0.1	1.3	2.5	(0.2)	0	2.6	2	4.3	4.4	7.3
Other	33.2	32.7	31.7	32.8	32	26.5	25.1	25.5	37.5	29.4	23.5
Total non-interest expenses	153.6	108.3	109.6	105.9	98	95.9	92.9	90.6	477.4	377.4	353.7
Gain on acquisition					6.2	0	0	0	0	6.2	0
Loss from continuing operations, before tax	22.5	(15)	(14.3)	(8.4)	(19.2)	(21.4)	(20)	(12.1)	(15.2)	(72.7)	(78.1)
Income tax benefit	$ (1.1)	$ (2.3)	$ (3.3)	$ (2.1)	$ (2.4)	$ (6.8)	$ (5.5)	$ (3.3)	(8.8)	(18)	(22.4)
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Management fees from affiliates									39.1	30.1	26.6
Trading gains, net									(1)	0.7	3.2
Consulting fees									0	2.2	2.1
Interest income									1.2	1.8	4.6
Operating revenues									92	65.8	42.5
Interest expense									14.4	13.4	12.7
Net operating revenues									77.6	52.4	29.8
Non-interest expenses:
Compensation and benefits									60.3	52.8	43.5
Clearing and related expenses									1.2	1.7	1.2
Introducing broker commissions									0	0.6	0.5
Communication and data services									7.3	6.7	5.7
Occupancy and equipment rental									2.5	2.8	2.1
Professional fees									3.7	4.8	4.6
Travel and business development									2.7	1.7	1.4
Depreciation and amortization									3.3	2.5	1.8
Bad debts									0	0.2	1.6
Management services fee to affiliates									0	1.2	4.3
Other									13	11.7	10.2
Total non-interest expenses									94	86.7	76.9
Gain on acquisition									0	6.2	0
Loss from continuing operations, before tax									16.4	28.1	47.1
Income tax benefit									26.8	24.7	19.4
Net loss									10.4	(3.4)	(27.7)
Adjustment to Investment in Subs for Equity Method Accounting									$ 4	$ 58.1	$ 83.4

Condensed Parent Only Financ115

Condensed Parent Only Financial Statements - Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2013
Condensed Financial Statements, Captions [Line Items]
Depreciation and amortization									$ 9.8	$ 8.2	$ 7.2
Bad debts	$ 0.4	$ 0.1	$ 1.3	$ 2.5	$ (0.2)	$ 0	$ 2.6	$ 2	4.3	4.4	7.3
Deferred income taxes									(9.8)	(0.8)	5
Amortization and extinguishment of debt issuance costs									1.9	1.1	0.9
Amortization of share-based compensation expense									6.3	5.1	3.6
Gain on acquisition					(6.2)	$ 0	$ 0	0	0	(6.2)	0
Deposits and receivables from broker-dealers, clearing organizations, and counterparties									(889.1)	146.6	44.9
Receivables from subsidiaries, net									(0.3)	(3.1)	0
Notes receivable, net									8.3	59.5	(14.5)
Income taxes receivable									0.5	8.2	0
Financial instruments owned, at fair value									(125.6)	(192.9)	(565)
Other assets									(16)	(17.4)	(16.2)
Accounts payable and other accrued liabilities									(19.6)	7.5	23.2
Payable to customers									290.9	172.2	332.1
Financial instruments sold, not yet purchased, at fair value									(124.4)	273.9	177.5
Net cash (used in) provided by operating activities									13.9	(27.8)	37.9
Purchase of property and equipment									(16.1)	(15.4)	(9.1)
Net cash used in investing activities									(22.3)	(35.5)	(15.5)
Payable to lenders under loans									48.2	142	15.5
Proceeds from notes payable									0	0	4
Payments of notes payable									(0.8)	(0.8)	(0.4)
Payments related to earn-outs on acquisitions									0	(2.9)	(2.2)
Share repurchase									0	(19.5)	(4.7)
Debt issuance costs									(0.3)	(2.1)	(0.2)	$ (1.7)
Exercise of stock options									3.4	3.5	2.5
Income tax benefit on stock options and awards									0.7	0.8	0.5
Net cash provided by (used in) financing activities									5.7	121	15
Net (decrease) increase in cash and cash equivalents									(1.3)	48.1	36.8
Cash and cash equivalents at beginning of period				316.2				268.1	316.2	268.1	231.3
Cash and cash equivalents at end of period	314.9				316.2				314.9	316.2	268.1
Cash paid for interest									38	26	15.8
Income taxes (received) paid, net of cash refunds									17.1	8.5	15.3
Additional consideration payable related to acquisitions									(0.2)	(0.4)	1.9
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Net loss									10.4	(3.4)	(27.7)
Depreciation and amortization									3.3	2.5	1.8
Bad debts									0	0.2	1.6
Deferred income taxes									(10.7)	(3.3)	4.6
Amortization and extinguishment of debt issuance costs									1.7	1	0.8
Amortization of share-based compensation expense									5.5	5.1	3.6
Gain on acquisition									0	(6.2)	0
Deposits and receivables from broker-dealers, clearing organizations, and counterparties									(2.9)	2.8	0
Due to/from subsidiaries									27	(86.6)	33.2
Notes receivable, net									2.1	39.1	(7.8)
Income taxes receivable									5.4	10.3	(11.4)
Financial instruments owned, at fair value									1.3	1.7	(3)
Other assets									7.8	0.3	(3.9)
Accounts payable and other accrued liabilities									(7.8)	0.4	12.6
Payable to customers									(2.5)	(26.1)	4.9
Financial instruments sold, not yet purchased, at fair value									(10.6)	35.9	0
Net cash (used in) provided by operating activities									35.5	(35)	9.3
Capital contribution in affiliates									0	(48.4)	(22.4)
Capital withdrawals from affiliates									0	0	7.8
Purchase of property and equipment									(6.1)	(5.5)	(7.8)
Net cash used in investing activities									(6.1)	(53.9)	(22.4)
Payable to lenders under loans									13.5	108.5	13
Proceeds from Issuance of Senior Long-term Debt									(45.5)	0	0
Payments related to earn-outs on acquisitions									0	(2.9)	(2.2)
Share repurchase									0	(19.5)	(4.7)
Debt issuance costs									0	(1.9)	(0.1)
Exercise of stock options									3.4	3.5	2.5
Income tax benefit on stock options and awards									0.7	0.8	0.5
Net cash provided by (used in) financing activities									(28.7)	87.7	12.6
Net (decrease) increase in cash and cash equivalents									0.7	(1.2)	(0.5)
Cash and cash equivalents at beginning of period				$ 1.3				$ 2.5	1.3	2.5	3
Cash and cash equivalents at end of period	$ 2				$ 1.3				2	1.3	2.5
Cash paid for interest									8.2	9	11.9
Income taxes (received) paid, net of cash refunds									(22.3)	(33.8)	(12.9)
Additional consideration payable related to acquisitions									$ (0.2)	$ (0.4)	$ 1.9

Subsequent Events Subsequent116

Subsequent Events Subsequent Events - Redemption of Senior Notes (Details) - USD ($) $ in Millions	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2015
Subsequent Events [Abstract]
Debt Instrument, Interest Rate, Stated Percentage	8.50%
Senior Notes	$ 0	$ 44.5	$ 45.5
Debt Instrument, Call Feature, Redemption Price Percentage of Principal		100.00%

Uncategorized Items - intl-2017

Label	Element	Value
Stock Issued During Period, Value, Acquisitions	us-gaap_StockIssuedDuringPeriodValueAcquisitions	$ 0