StoneX (SNEX) 10-Q 7 May 20 2020 Q2 Quarterly report Financial data

DEI

DEI - shares	6 Months Ended
	Mar. 31, 2020	May 04, 2020
Document and Entity Information [Abstract]
Entity Registrant Name	INTL FCSTONE INC.
Entity Central Index Key	0000913760
Current Fiscal Year End Date	--09-30
Entity Filer Category	Accelerated Filer
Document Type	10-Q
Document Period End Date	Mar. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
Amendment Flag	false
Entity Common Stock, Shares Outstanding		19,217,710
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity Interactive Data Current	Yes

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($)	Mar. 31, 2020	Sep. 30, 2019
ASSETS
Cash and cash equivalents	$ 519,500,000	$ 471,300,000
Cash, securities and other assets segregated under federal and other regulations (including $8.1 and $306 at fair value at March 31, 2020 and September 30, 2019, respectively)	1,176,100,000	1,049,900,000
Collateralized transactions:
Securities purchased under agreements to resell	1,260,000,000	1,424,500,000
Securities borrowed	1,063,800,000	1,423,200,000
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net (including $378.7 and $626.9 at fair value at March 31, 2020 and September 30, 2019, respectively)	3,359,500,000	2,540,500,000
Receivables from clients, net	481,100,000	422,300,000
Notes receivable, net	3,900,000	2,900,000
Income taxes receivable	1,500,000	5,200,000
Financial instruments owned, at fair value (includes securities pledged as collateral that can be sold or repledged of $743.6 and $478.8 at March 31, 2020 and September 30, 2019, respectively)	2,525,700,000	2,175,200,000
Physical commodities inventory, net (including $194.1 and $151.9 at fair value at March 31, 2020 and September 30, 2019, respectively)	255,200,000	229,300,000
Deferred income taxes, net	14,000,000	18,000,000
Property and equipment, net	43,000,000	43,900,000
Operating right of use assets	31,600,000	0
Goodwill and intangible assets, net	73,100,000	67,900,000
Other assets	62,900,000	62,000,000
Total assets	10,870,900,000	9,936,100,000
Liabilities:
Accounts payable and other accrued liabilities (including $1.8 million at fair value at March 31, 2020 and September 30, 2019)	184,800,000	157,500,000
Operating lease liabilities	34,200,000	0
Payables to:
Customers	4,531,500,000	3,589,500,000
Broker-dealers, clearing organizations and counterparties (including $95.8 and $5.6 at fair value at March 31, 2020 and September 30, 2019, respectively)	429,200,000	266,200,000
Lenders under loans	275,000,000	202,300,000
Senior secured term loan, net	184,300,000	167,600,000
Income taxes payable	10,600,000	10,400,000
Collateralized transactions:
Securities sold under agreements to repurchase	2,800,300,000	2,773,700,000
Securities loaned	1,068,800,000	1,459,900,000
Financial instruments sold, not yet purchased, at fair value	703,600,000	714,800,000
Total liabilities	10,222,300,000	9,341,900,000
INTL FCStone Inc. 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; 21,638,425 issued and 19,216,468 outstanding at March 31, 2020 and 21,297,317 issued and 19,075,360 outstanding at September 30, 2019	200,000	200,000
Common stock in treasury, at cost - 2,421,957 shares at March 31, 2020 and 2,221,957 shares September 30, 2019	(57,600,000)	(50,100,000)
Additional paid-in capital	285,800,000	276,800,000
Total retained earnings	458,400,000	402,100,000
Accumulated other comprehensive loss, net	(38,200,000)	(34,800,000)
Total stockholders' equity	648,600,000	594,200,000
Total liabilities and stockholders' equity	$ 10,870,900,000	$ 9,936,100,000

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets Parentheticals - USD ($) $ in Millions	Mar. 31, 2020	Sep. 30, 2019
Balance Sheet Parentheticals [Abstract]
Securities and other assets segregated, fair value	$ 8.1	$ 306
Dep and rec -b/d - fair value	378.7	626.9
Physical commodities inventory at fair value	194.1	151.9
Collateral that can be sold or repledged	743.6	478.8
Accounts pay and other accrued - fair value	1.8	1.8
Payables to b/d - fair value	$ 95.8	$ 5.6
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	21,638,425	21,297,317
Common stock - outstanding	19,216,468	19,075,360
Treasury stock - shares	2,421,957	2,221,957

Condensed Consolidated Income S

Condensed Consolidated Income Statements - USD ($)	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Revenues:
Sales of physical commodities	$ 20,016,900,000	$ 6,929,500,000	$ 30,994,900,000	$ 13,225,300,000
Principal gains, net	168,500,000	110,300,000	281,000,000	203,100,000
Commission and clearing fees	116,600,000	85,100,000	203,800,000	184,600,000
Consulting, management, and account fees	22,600,000	19,100,000	43,900,000	38,200,000
Interest income	41,700,000	48,200,000	87,700,000	93,200,000
Total revenues	20,366,300,000	7,192,200,000	31,611,300,000	13,744,400,000
Cost of sales of physical commodities	19,999,500,000	6,921,100,000	30,967,700,000	13,208,600,000
Operating revenues	366,800,000	271,100,000	643,600,000	535,800,000
Transaction-based clearing expenses	63,800,000	42,700,000	110,100,000	92,800,000
Introducing broker commissions	29,600,000	24,800,000	55,800,000	57,400,000
Interest expense	30,000,000	38,400,000	63,800,000	71,400,000
Net operating revenues	243,400,000	165,200,000	413,900,000	314,200,000
Compensation and other expenses:
Compensation and benefits	136,700,000	97,900,000	240,700,000	187,000,000
Trading systems and market information	11,200,000	9,500,000	21,600,000	18,700,000
Occupancy and equipment rental	4,900,000	5,000,000	9,900,000	9,400,000
Professional fees	4,700,000	5,000,000	10,700,000	10,300,000
Travel and business development	3,200,000	4,000,000	7,700,000	7,800,000
Non-trading technology and support	5,900,000	5,000,000	11,900,000	9,200,000
Depreciation and amortization	4,200,000	3,200,000	8,100,000	6,100,000
Communications	1,500,000	2,000,000	3,100,000	3,300,000
Bad debts	4,400,000	700,000	4,400,000	1,000,000
Recovery of bad debt on physical coal	0	0	0	(2,400,000)
Other	10,600,000	7,400,000	18,100,000	13,900,000
Total compensation and other expenses	187,300,000	139,700,000	336,200,000	264,300,000
Other gain	0	5,400,000	100,000	5,400,000
Income before tax	56,100,000	30,900,000	77,800,000	55,300,000
Income tax expense	16,800,000	7,500,000	22,200,000	13,700,000
Net income	$ 39,300,000	$ 23,400,000	$ 55,600,000	$ 41,600,000
Earnings per share:
Basic	$ 2.03	$ 1.23	$ 2.88	$ 2.19
Diluted	$ 2	$ 1.21	$ 2.84	$ 2.15
Weighted-average number of common shares outstanding:
Basic	18,872,937	18,753,490	18,811,268	18,706,104
Diluted	19,189,953	19,004,793	19,132,497	18,999,889

Condensed Consolidated Statemen

Condensed Consolidated Statement of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Condensed Consolidated Statement of Other Comprehensive Income (Loss) [Abstract]
Net income	$ 39.3	$ 23.4	$ 55.6	$ 41.6
Other comprehensive (loss) income:
Foreign currency translation adjustment	(3.4)	0	(2.7)	0.3
Other comprehensive (loss) income	(3.4)	0	(2.7)	0.3
Comprehensive income	$ 35.9	$ 23.4	$ 52.9	$ 41.9

Condensed Consolidated Cash Flo

Condensed Consolidated Cash Flows Statements - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities:
Net income	$ 55.6	$ 41.6
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization	8.1	6.1
Bad debts	4.4	1
Recovery of bad debt on physical coal	0	(2.4)
Deferred income taxes	(1)	(0.4)
Amortization of debt issuance costs	0.7	0.8
Amortization of share-based compensation	5	3.8
Bargain purchase gain on acquisition	0	(5.4)
Changes in operating assets and liabilities, net:
Securities and other assets segregated under federal and other regulations	297.9	407.5
Securities purchased under agreements to resell	164.5	(371.6)
Securities borrowed	359.4	(1,064.3)
Deposits with and receivables from broker-dealers, clearing organizations, and counterparties, net	(52.2)	5.8
Receivables from clients, net	(63.2)	(17.2)
Notes receivable, net	(1)	1.2
Income taxes receivable	8.7	0.1
Financial instruments owned, at fair value	(350.5)	(534.8)
Physical commodities inventory, net	(25.9)	(57.3)
Operating right of use assets	3.9	0
Other assets	0	(9.6)
Accounts payable and other accrued liabilities	30.2	(19.7)
Operating lease liabilities	(4)	0
Payables to clients	942	(642.6)
Payables to broker-dealers, clearing organizations and counterparties	163	485.4
Income taxes payable	0.1	2.7
Securities sold under agreements to repurchase	26.6	448
Securities loaned	(391.1)	1,098.6
Financial instruments sold, not yet purchased, at fair value	(11.2)	85.8
Net cash provided by (used in) operating activities	1,170	(136.9)
Cash flows from investing activities:
Cash paid for acquisitions, net	(7.8)	(7.8)
Purchase of property and equipment	(4.5)	(7.3)
Net cash used in investing activities	(12.3)	(15.1)
Cash flows from financing activities:
Net change in payable to lenders under loans with maturities 90 days or less	111.6	(98)
Proceeds from payables to lenders under loans with maturities greater than 90 days	311.5	0
Repayments of payables to lenders under loans with maturities greater than 90 days	(350)	0
Proceeds from issuance of senior secured term loan	21.5	175
Repayments of senior secured term loan	(4.9)	(2.2)
Repayments of note payable	(0.4)	(0.4)
Deferred payments on acquisitions	(0.2)	0
Repurchase of stock	(7.5)	0
Debt issuance costs	(1.5)	(3.2)
Exercise of stock options	4	0.8
Net cash (used in) provided by financing activities	84.1	72
Effect of exchange rates on cash, segregated cash, cash equivalents, and segregated cash equivalents	(2.7)	0.3
Net increase (decrease) in cash, segregated cash, cash equivalents, and segregated cash equivalents	1,239.1	(79.7)
Cash, segregated cash, cash equivalents, and segregated cash equivalents at beginning of period	2,451.3	2,190.1
Cash, segregated cash, cash equivalents, and segregated cash equivalents at end of period	3,690.4	2,110.4
Supplemental disclosure of cash flow information:
Cash paid for interest	64.3	69.8
Income taxes paid, net of cash refunds	13.2	11.3
Supplemental disclosure of non-cash investing and financing activities:
Identified intangible assets and goodwill on acquisitions	7.2	2.7
Assets acquired	352.6	25.9
Liabilities assumed	(352)	(7.3)
Total net assets acquired	$ 0.6	$ 18.6

Condensed Consolidated Cash F_2

Condensed Consolidated Cash Flows Statements Reconciliation of Cash, Segregated Cash, Cash Equivalents, and Segregated Cash Equivalents - USD ($) $ in Millions	Mar. 31, 2020	Mar. 31, 2019
Reconciliation of Cash, Segregated Cash, Cash Equivalents, and Segregated Cash Equivalents [Abstract]
Cash and cash equivalents	$ 519.5	$ 274.4
Cash segregated under federal and other regulations(1)	1,168	723.3
Cash segregated and deposited with or pledged to exchange-clearing organizations and other futures commissions merchants	1,896.7	993.9
Securities segregated and pledged to exchange-clearing organizations(2)	106.2	118.8
Cash, segregated cash, cash equivalents, and segregated cash equivalents at end of period	3,690.4	2,110.4
Non-cash equivalent segregated assets	8.1	235.7
Non-segregated cash and other non-cash equivalent assets included within deposits and receivables from broker-dealers, clearing organizations, and counterparties	$ 1,356.6	$ 1,154.1

Condensed Consolidated Statem_2

Condensed Consolidated Statement of Stockholders' Equity - USD ($) $ in Millions	Total	Common Stock	Treasury Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss, net
Balance at beginning of period at Sep. 30, 2018	$ 505.3	$ 0.2	$ 46.3	$ 267.5	$ 317	$ (33.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	41.6				41.6
Other comprehensive income	0.3					0.3
Exercise of stock options	0.8			0.8
Share-based compensation	3.8			3.8
Repurchase of stock	0
Balance at end of period at Mar. 31, 2019	551.8	0.2	(46.3)	272.1	358.6	(32.8)
Balance at beginning of period at Dec. 31, 2018	526	0.2	(46.3)	269.7	335.2	(32.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	23.4				23.4
Other comprehensive income	0
Exercise of stock options	0.5			0.5
Share-based compensation	1.9			1.9
Balance at end of period at Mar. 31, 2019	551.8	0.2	(46.3)	272.1	358.6	(32.8)
ASU 2018-02 cumulative transition adjustment	0.7				0.7	(0.7)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Adjusted Balance	594.2	0.2	(50.1)	276.8	402.8	(35.5)
Balance at beginning of period at Sep. 30, 2019	594.2	0.2	(50.1)	276.8	402.1	(34.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	55.6				55.6
Other comprehensive income	(2.7)					(2.7)
Exercise of stock options	4			4
Share-based compensation	5			5
Repurchase of stock	(7.5)		7.5
Balance at end of period at Mar. 31, 2020	648.6	0.2	(57.6)	285.8	458.4	(38.2)
Balance at beginning of period at Dec. 31, 2019	614.9	0.2	(50.5)	280.9	419.1	(34.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	39.3				39.3
Other comprehensive income	(3.4)					(3.4)
Exercise of stock options	2.5			2.5
Share-based compensation	2.4			2.4
Repurchase of stock	(7.1)		7.1
Balance at end of period at Mar. 31, 2020	$ 648.6	$ 0.2	$ (57.6)	$ 285.8	$ 458.4	$ (38.2)

Basis of Presentation and Conso

Basis of Presentation and Consolidation and Recently Issued Accounting Standards (Notes)	6 Months Ended
	Mar. 31, 2020
Basis of Presentation and Consolidation [Abstract]
Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block]	Basis of Presentation and Consolidation and Accounting Standards Adopted INTL FCStone Inc. , a Delaware corporation, and its consolidated subsidiaries (collectively “INTL” or “the Company”), is a global brokerage and financial services firm providing execution, risk management and advisory services, market intelligence, and clearing services across asset classes and markets around the world. The Company’s services include comprehensive risk management advisory services for commercial clients; execution of listed futures and options on futures contracts on all major commodity exchanges; structured over-the-counter (“OTC”) products in a wide range of commodities; physical trading and hedging of precious metals and select other commodities; trading of more than 140 foreign currencies; market-making in international equities; fixed income; debt origination and asset management. The Company provides these services to a diverse group of more than 30,000 commercial and institutional clients and over 125,000 retail clients located in more than 130 countries, including producers, processors and end-users of nearly all widely-traded physical commodities to manage their risks and enhance margins; to commercial counterparties who are end-users of the Company’s products and services; to governmental and non-governmental organizations; and to commercial banks, brokers, institutional investors and major investment banks. Basis of Presentation and Consolidation The accompanying unaudited condensed consolidated balance sheet as of September 30, 2019 , which has been derived from the audited consolidated balance sheet of September 30, 2019 , and the unaudited interim condensed consolidated financial statements have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”). Certain information and disclosures normally included in annual consolidated financial statements prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) have been condensed or omitted pursuant to those rules and regulations. The Company believes that the disclosures made are adequate to make the information presented not misleading. In the opinion of management, all adjustments (consisting of normal recurring accruals) considered necessary for a fair presentation of the condensed consolidated financial statements for the interim periods presented have been reflected as required by Rule 10-01 of Regulation S-X. Operating results for interim periods are not necessarily indicative of the results that may be expected for the full year. These interim condensed consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and related notes contained in the Company’s Annual Report on Form 10-K for the fiscal year ended September 30, 2019 filed with the SEC. These condensed consolidated financial statements include the accounts of INTL FCStone Inc. and all other entities in which the Company has a controlling financial interest. All material intercompany transactions and balances have been eliminated in consolidation. The Company’s fiscal year end is September 30, and the fiscal quarters end on December 31, March 31, June 30 and September 30. Unless otherwise stated, all dates refer to fiscal years and fiscal interim periods. The preparation of condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent liabilities as of the date of the condensed consolidated financial statements and the reported amounts of revenue and expenses during the reporting period. The most significant of these estimates and assumptions relate to fair value measurement for financial instruments and investments, revenue recognition, the provision for bad debts, valuation of inventories, valuation of goodwill and intangible assets, incomes taxes, and contingencies. Although these and other estimates and assumptions are based on the best available information, actual results could be materially different from these estimates. In the condensed consolidated income statements, the total revenues reported combine gross revenues for the physical commodities business and net revenues for all other businesses. The subtotal ‘operating revenues’ in the condensed consolidated income statements is calculated by deducting cost of sales of physical commodities from total revenues. The subtotal ‘net operating revenues’ in the condensed consolidated income statements is calculated as operating revenues less transaction-based clearing expenses, introducing broker commissions and interest expense. Transaction-based clearing expenses represent variable expenses paid to executing brokers, exchanges, clearing organizations and banks in relation to transactional volumes. Introducing broker commissions include commission paid to non-employee third parties that have introduced clients 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. Accounting Standards Adopted In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2016-02, Leases (Topic 842). This update requires a lessee to recognize on the balance sheet a liability to make lease payments and a corresponding right-of-use asset. The guidance also requires certain qualitative and quantitative disclosures about the amount, timing and uncertainty of cash flows arising from leases. In July 2018, the FASB issued ASU 2018-10, Codification Improvements to Topic 842, Leases and ASU 2018-11, Leases (Topic 842) Targeted Improvements. In March 2019, the FASB issued ASU 2019-01, Leases (Topic 842) Codification Improvements. Among other things, this updated guidance provides an optional transition method, which allows for the initial application of the new accounting standard at the adoption date and the recognition of a cumulative-effect adjustment to the opening balance of retained earnings as of the beginning of the period of adoption. The Company adopted the new ASUs on October 1, 2019, using the effective date modified retrospective transition approach and has not restated comparative periods. The Company elected the package of practical expedients permitted under the transition guidance within the new standard, which among other things, allowed the Company to not reassess contracts to determine if they contain leases, lease classification and initial direct costs. The Company’s application of the new standard resulted in changes to the condensed consolidated balance sheet but did not have an impact on the condensed consolidated income statement. See Note 2 for more information. In February 2018, the FASB issued ASU 2018-02, Income Statement – Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income. The amendments in this updated standard allow a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act of 2017. The Company adopted this standard on October 1, 2019 and, as a result, recorded a $0.7 million reclassification between accumulated other comprehensive loss, net and retained earnings.

Leases (Notes)

Leases (Notes)	6 Months Ended
	Mar. 31, 2020
Leases [Abstract]
Leases of Lessee Disclosure [Text Block]	Note 2 – Leases The Company currently leases office space under non-cancelable operating leases with third parties as of March 31, 2020 . Leases with an initial term of 12 months or less are not recorded on the condensed consolidated balance sheet and the Company recognizes lease expense for these leases on a straight-line basis over the lease term. Certain office space leases include one or more options to renew, with renewal terms that can extend the lease term from three to ten years, and some of which include the Company’s option to terminate the leases within two years of the balance sheet date. The Company has not considered any renewal options in the lease terms of its office space leases as the Company does not believe it is reasonably certain that any of the rights will be exercised. In determining the term of certain office space leases, the Company has not included the periods covered by an option to terminate if the Company believes it is reasonably certain to do so. As the office space leases do not provide an implicit rate, the Company applies a collateralized incremental borrowing rate based on the information available at the lease commencement date in determining the present value of lease payments. The Company applied a collateralized incremental borrowing rate as of October 1, 2019 for operating leases that commenced prior to that date. For office space leases executed by subsidiaries, including foreign subsidiaries, the Company has applied the incremental borrowing rate of the parent company. The Company believes this is a reasonable approach as its subsidiaries either do not have their own treasury functions or the credit facilities available to its subsidiaries do not permit the financing of right-of-use assets. Additionally, in certain instances, the parent company provides a guarantee of the lease payments to the lessor under office space leases executed by its subsidiaries. As such, the Company believes that the pricing of subsidiary leases is more significantly influenced by the credit standing of the parent company than that of its subsidiaries. Certain office space leases contain variable lease payments related to fair market rent adjustments and local inflation index measures. The Company estimates variable lease payments based upon information available at the lease commencement date in determining the present value of lease payments. The Company applied information available as of October 1, 2019 for operating leases that commenced prior to that date. The Company has elected to not separate lease components from nonlease components for all office space leases. The Company does not have any financing leases as of March 31, 2020 . Operating lease expense is recognized on a straight-line basis over the lease term and is reported within ‘occupancy and equipment rental’ on the condensed consolidated statement of income. As of March 31, 2020 , the Company recorded operating lease right-of-use assets and operating lease liabilities of $31.6 million and $34.2 million , respectively. The following table presents operating lease costs and other information as of and for the three and six months ended March 31, 2020 (in millions, except as stated): Three Months Ended March 31, Six Months Ended March 31, 2020 2020 Operating lease costs (1) $ 3.5 $ 7.0 Supplemental cash flow information and non-cash activity: Cash paid for amounts included in the measurement of operating lease liabilities $ 2.8 $ 5.5 Right-of-use assets obtained in exchange for operating lease liabilities $ 0.4 $ 35.0 Lease term and discount rate information: Weighted average remaining lease term (years) 4.21 Weighted average discount rate 5.1 % (1) Includes short-term leases and variable lease costs, which are immaterial. The maturities of the lease liabilities are as follows as of March 31, 2020 (in millions): Remainder of 2020 $ 6.0 2021 10.3 2022 7.7 2023 6.1 2024 4.3 After 2024 3.5 Total lease payments (2) 37.9 Less: interest 3.7 Present value of lease liabilities $ 34.2 (2) Total lease payments excludes $80.9 million of legally binding lease payments for a lease executed for a new corporate headquarters in New York City, which was signed during the three months ended March 31, 2020, but has not yet commenced. In accordance with the disclosure requirements for the adoption of Topic 842, the Company is presenting its operating lease commitment table as of September 30, 2019, which was previously disclosed in Note 12 of the Company’s Annual Report on Form 10-K for the fiscal year ended September 30, 2019 (in millions): 2020 $ 11.2 2021 9.9 2022 7.5 2023 6.2 2024 5.8 Thereafter 2.6 $ 43.2

Revenue from Contracts with Cli

Revenue from Contracts with Clients (Notes)	6 Months Ended
	Mar. 31, 2020
Revenue from Contract with Clients [Abstract]
Revenue from Contract with Customer [Text Block]	Note 3 – Revenue from Contracts with Clients The Company accounts for revenue earned from contracts with clients for services such as the execution, clearing, brokering, and custody of futures and options on futures contracts, OTC derivatives, and securities, investment management, and underwriting services under FASB Accounting Standards Codification (“ASC”) 606, Revenues from Contracts with Customers (Topic 606). As such, revenues for these services are recognized when the performance obligations related to the underlying transaction are completed. Revenues are recognized when control of the promised goods or services are transferred to clients, in an amount that reflects the consideration the Company expects to be entitled to in exchange for those goods or services. Revenues are analyzed to determine whether the Company is the principal (i.e. reports revenue on a gross basis) or agent (i.e., reports revenues on a net basis) in the contract. Principal or agent designations depend primarily on the control an entity has over the good or service before control is transferred to a client. The indicators of which party exercises control include primary responsibility over performance obligations, inventory risk before the good or service is transferred, and discretion in establishing the price. Topic 606 does not apply to revenues associated with dealing, or market-making, activities in financial instruments or contracts in the capacity of a principal, including derivative sales contracts which result in physical settlement and interest income. The Company’s revenues from contracts with clients subject to Topic 606 represent approximately 0.7% and 1.4% of the Company’s total revenues for the three months ended March 31, 2020 and 2019 , respectively. The Company’s revenues from contracts with clients subject to Topic 606 represent approximately 0.8% and 1.6% of the Company’s total revenues for the six months ended March 31, 2020 and 2019 , respectively. The Company’ revenues from contracts with clients subject to Topic 606 represent approximately 37.9% and 38.4% of the Company’s operating revenues for the three months ended March 31, 2020 and 2019 , respectively. The Company’ revenues from contracts with clients subject to Topic 606 represent approximately 38.5% and 41.6% of the Company’s operating revenues for the six months ended March 31, 2020 and 2019 , respectively. This includes all of the Company’s commission and clearing fees and consulting, management, and account fees revenues. Revenues within the scope of Topic 606 are presented within ‘Commission and clearing fees’ and ‘Consulting, management, and account fees’ on the condensed consolidated income statements. Revenues that are not within the scope of Topic 606 are presented within ‘Sales of physical commodities’, ‘Principal gains, net’, and ‘Interest income’ on the condensed consolidated income statements. The following table represents a disaggregation of the Company’s total revenues separated between revenues from contracts with clients and other sources of revenue for the three and six months ended March 31, 2020 and 2019 (in millions): Three Months Ended March 31, Six Months Ended March 31, 2020 2019 2020 2019 Revenues from contracts with clients: Commission and clearing fees: Sales-based: Exchange-traded futures and options $ 40.1 $ 31.2 $ 72.5 $ 70.3 OTC derivative brokerage 6.7 7.3 12.2 16.2 Equities and fixed income 7.1 3.6 11.4 6.8 Mutual funds 1.6 1.9 2.9 4.5 Insurance and annuity products 2.4 1.5 4.5 3.0 Other 0.5 0.5 0.8 0.7 Total sales-based commission 58.4 46.0 104.3 101.5 Trailing: Mutual funds 3.5 3.0 6.6 6.2 Insurance and annuity products 4.0 3.4 7.7 7.1 Total trailing commission 7.5 6.4 14.3 13.3 Clearing fees 41.6 26.8 71.1 59.4 Trade conversion fees 4.2 3.3 5.7 4.9 Other 4.9 2.6 8.4 5.5 Total commission and clearing fees: 116.6 85.1 203.8 184.6 Consulting, management, and account fees: Underwriting fees 0.2 0.2 0.4 0.5 Asset management fees 8.7 6.0 16.2 12.2 Advisory and consulting fees 5.7 4.7 11.3 9.7 Sweep program fees 3.6 4.1 7.6 7.9 Client account fees 3.1 2.5 6.1 5.2 Other 1.3 1.6 2.3 2.7 Total consulting, management, and account fees 22.6 19.1 43.9 38.2 Total revenues from contracts with clients $ 139.2 $ 104.2 $ 247.7 $ 222.8 Method of revenue recognition: Point-in-time $ 113.7 $ 83.0 $ 198.3 $ 179.7 Time elapsed 25.5 21.2 49.4 43.1 Total revenues from contracts with clients 139.2 104.2 247.7 222.8 Other sources of revenues Physical precious metals trading 19,694.7 6,660.9 30,352.7 12,616.4 Physical agricultural and energy product trading 322.2 268.6 642.2 608.9 Principal gains, net 168.5 110.3 281.0 203.1 Interest income 41.7 48.2 87.7 93.2 Total revenues $ 20,366.3 $ 7,192.2 $ 31,611.3 $ 13,744.4 Primary geographic region: United States $ 585.6 $ 456.6 $ 1,097.9 $ 983.6 Europe 150.0 53.8 261.6 107.1 South America 16.3 12.4 31.5 23.9 Middle East and Asia 19,613.3 6,667.3 30,218.8 12,625.9 Other 1.1 2.1 1.5 3.9 Total revenues $ 20,366.3 $ 7,192.2 $ 31,611.3 $ 13,744.4 The substantial majority of the Company’s performance obligations for revenues from contracts with clients are satisfied at a point in time and are typically collected from clients by debiting their accounts with the Company. Commission and clearing fees revenue is primarily related to the Commercial Hedging and Clearing and Execution Services reportable segments. Consulting, management, and accounts fees are primarily related to the Commercial Hedging, Clearing and Execution Services, and Securities reportable segments. Principal gains, net is primarily related to the Commercial Hedging, Global Payments, and Securities reportable segments. Interest income is primarily related to the Commercial Hedging, Securities, and Clearing and Execution Services reportable segments. Physical precious metals trading and physical agricultural and energy product trading revenues are primarily related to the Physical Commodities reportable segment. Remaining Performance Obligations Remaining performance obligations are services that the Company has committed to perform in the future in connection with its contracts with clients. The Company’s remaining performance obligations are generally related to its risk management consulting and asset management contracts with clients. Revenues associated with remaining performance obligations related to these contracts with clients are not material to the overall consolidated results of the Company. For the Company’s asset management activities, where fees are calculated based on a percentage of the fair value of eligible assets in client’s accounts, future revenue associated with remaining performance obligations cannot be determined as such fees are subject to fluctuations in the fair value of eligible assets in clients’ accounts.

Earnings per Share (Notes)

Earnings per Share (Notes)	6 Months Ended
	Mar. 31, 2020
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 income is reduced by the amount of dividends declared in the period for each class of common stock and participating security. The remaining undistributed earnings are then allocated to common stock and participating securities, based on their respective rights to receive dividends. Restricted stock awards granted to certain employees and directors contain non-forfeitable rights to dividends at the same rate as common stock and are considered participating securities. Basic EPS has been computed by dividing net income by the weighted-average number of common shares outstanding. The following is a reconciliation of the numerator and denominator of the diluted earnings per share computations for the periods presented below. Three Months Ended March 31, Six Months Ended March 31, (in millions, except share amounts) 2020 2019 2020 2019 Numerator: Net income $ 39.3 $ 23.4 $ 55.6 $ 41.6 Less: Allocation to participating securities (0.9 ) (0.4 ) (1.2 ) (0.7 ) Net income allocated to common stockholders $ 38.4 $ 23.0 $ 54.4 $ 40.9 Denominator: Weighted average number of: Common shares outstanding 18,872,937 18,753,490 18,811,268 18,706,104 Dilutive potential common shares outstanding: Share-based awards 317,016 251,303 321,229 293,785 Diluted weighted-average common shares 19,189,953 19,004,793 19,132,497 18,999,889 The dilutive effect of share-based awards is reflected in diluted earnings per share by application of the treasury stock method, which includes consideration of unamortized share-based compensation expense required under the Compensation – Stock Compensation Topic of the ASC. Options to purchase 945,211 and 1,032,077 shares of common stock for the three months ended March 31, 2020 and 2019 , respectively, and options to purchase 981,088 and 704,863 shares of common stock for the six months ended March 31, 2020 and 2019 , respectively, were excluded from the calculation of diluted earnings per share as they would have been anti-dilutive

Assets and Liabilities, at Fair

Assets and Liabilities, at Fair Value (Notes)	6 Months Ended
	Mar. 31, 2020
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 based on 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. Level 3 includes contingent liabilities that have been valued using an income approach based upon management developed discounted cash flow projections, which are an unobservable input. The Company had $1.8 million of contingent liabilities classified within Level 3 of the fair value hierarchy as of March 31, 2020 and September 30, 2019 . The Company had no Level 3 assets as of March 31, 2020 and September 30, 2019. Financial and nonfinancial assets and liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 measurements) and the lowest priority to unobservable inputs (Level 3 measurements). A market is active if there are sufficient transactions on an ongoing basis to provide current pricing information for the asset or liability, pricing information is released publicly, and price quotations do not vary substantially either over time or among market participants. Observable inputs reflect the assumptions market participants would use in pricing the asset or liability developed based on market data obtained from sources independent of the reporting entity. The guidance requires the Company to consider counterparty credit risk of all parties of outstanding derivative instruments that would be considered by a market participant in the transfer or settlement of such contracts (exit price). The Company’s exposure to credit risk on derivative financial instruments principally 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 from 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 Condensed Consolidated Balance Sheets at fair value on a recurring basis Cash and cash equivalents reported at fair value on a recurring basis includes certificates of deposit and money market mutual funds, 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 clients and broker-dealers, clearing organizations and counterparties include the value of pledged investments, primarily U.S. Treasury obligations and foreign government obligations. These balances also include the fair value of exchange-traded options on futures and OTC derivative financial instruments. Financial instruments owned and sold, not yet purchased include the fair value of equity securities, which includes common, preferred, and foreign ordinary shares, ADRs, GDRs, and exchange-traded funds (“ETFs”), corporate and municipal bonds, U.S. Treasury obligations, U.S. government agency obligations, foreign government obligations, agency mortgage-backed obligations, asset-backed obligations, derivative financial instruments, commodities 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. Cash equivalents, debt and equity 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, foreign government obligations, commodities warehouse receipts, certain equity securities traded in active markets, physical precious metals held by a regulated broker-dealer subsidiary, exchange firm common stock, investments in managed funds, as well as options on futures contracts traded on national exchanges. The fair value of exchange firm common stock 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 corporate and municipal bonds, U.S. government agency obligations, agency-mortgage backed obligations, asset-backed obligations, certain equity securities traded in less active markets, and OTC derivative contracts, which include purchase and sale commitments related to the Company’s agricultural and energy commodities. Certain derivatives without a quoted price in an active market and derivatives executed OTC are valued using internal valuation techniques, including pricing models which utilize 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. 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 exchange-quoted prices. Physical commodities inventory also includes agricultural commodities that are a part of the trading activities of a non-broker dealer subsidiary and are recorded at net realizable value using exchange-quoted prices. The fair value of precious metals physical commodities inventory is based upon unadjusted exchange-quoted prices and is, therefore, classified within Level 1 of the fair value hierarchy. The fair value of agricultural physical commodities inventory and the related OTC firm sale and purchase commitments are generally based upon exchange-quoted prices, adjusted for basis or differences in local markets, broker or dealer quotations or market transactions in either listed or OTC markets. Exchange-quoted prices are adjusted for location and quality because the exchange-quoted prices for agricultural and energy related products represent contracts that have standardized terms for commodity, quantity, future delivery period, delivery location, and commodity quality or grade. The basis or local market adjustments are observable inputs or have an insignificant impact on the measurement of fair value and, therefore, the agricultural physical commodities inventory as well as the related OTC forward firm sale and purchase commitments have been included within Level 2 of the fair value hierarchy. With the exception of certain derivative instruments where the valuation approach is disclosed above, financial instruments owned and sold are primarily valued using third-party pricing sources. Third-party pricing vendors compile prices from various sources and often apply matrix pricing for similar securities when market-observable transactions for the instruments are not observable for substantially the full term. The Company reviews the pricing methodologies used by third-party pricing vendors in order to evaluate the fair value hierarchy classification of vendor-priced financial instruments and the accuracy of vendor pricing, which typically involves the comparison of primary vendor prices to internal trader prices or secondary vendor prices. When evaluating the propriety of vendor-priced financial instruments using secondary prices, considerations include the range and quality of vendor prices, level of observable transactions for identical and similar instruments, and judgments based upon knowledge of a particular market and asset class. If the primary vendor price does not represent fair value, justification for using a secondary price, including source data used to make the determination, is subject to review and approval by authorized personnel prior to using a secondary price. 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. The fair value estimates presented herein are based on pertinent information available to management as of March 31, 2020 and September 30, 2019 . Although management is not aware of any factors that would significantly affect the estimated fair value amounts, such amounts have not been comprehensively revalued for purposes of these condensed consolidated financial statements since 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 March 31, 2020 by level in the fair value hierarchy. March 31, 2020 (in millions) Level 1 Level 2 Level 3 Netting (1) Total Assets: Certificates of deposit $ 9.2 $ — $ — $ — $ 9.2 Money market mutual funds 7.9 — — — 7.9 Cash and cash equivalents 17.1 — — — 17.1 Commodities warehouse receipts 7.9 — — — 7.9 U.S. Treasury obligations 0.2 — — — 0.2 Securities and other assets segregated under federal and other regulations 8.1 — — — 8.1 U.S. Treasury obligations 350.4 — — — 350.4 "To be announced" (TBA) and forward settling securities — 80.5 — (3.5 ) 77.0 Foreign government obligations 8.1 — — — 8.1 Derivatives 5,220.8 57.5 — (5,335.1 ) (56.8 ) Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net 5,579.3 138.0 — (5,338.6 ) 378.7 Equity securities 184.7 19.6 — — 204.3 Corporate and municipal bonds — 43.5 — — 43.5 U.S. Treasury obligations 294.2 — — — 294.2 U.S. government agency obligations — 201.6 — — 201.6 Foreign government obligations 2.6 — — — 2.6 Agency mortgage-backed obligations — 1,504.0 — — 1,504.0 Asset-backed obligations — 16.4 — — 16.4 Derivatives 0.7 1,990.8 — (1,874.9 ) 116.6 Commodities leases — 28.6 — (2.3 ) 26.3 Commodities warehouse receipts 100.5 — — — 100.5 Exchange firm common stock 10.4 — — — 10.4 Mutual funds and other 5.3 — — — 5.3 Financial instruments owned 598.4 3,804.5 — (1,877.2 ) 2,525.7 Physical commodities inventory 26.3 167.8 — — 194.1 Total assets at fair value $ 6,229.2 $ 4,110.3 $ — $ (7,215.8 ) $ 3,123.7 Liabilities: Accounts payable and other accrued liabilities - contingent liabilities — — 1.8 — 1.8 TBA and forward settling securities — 98.3 — (3.5 ) 94.8 Derivatives 5,379.7 194.5 — (5,573.2 ) 1.0 Payable to broker-dealers, clearing organizations and counterparties 5,379.7 292.8 — (5,576.7 ) 95.8 Equity securities 135.2 40.3 — — 175.5 Foreign government obligations 2.1 — — — 2.1 Corporate and municipal bonds — 28.1 — — 28.1 U.S. Treasury obligations 213.6 — — — 213.6 U.S. government agency obligations — 13.6 — — 13.6 Agency mortgage-backed obligations — 15.0 — — 15.0 Derivatives — 2,035.4 — (1,882.6 ) 152.8 Commodities leases — 102.9 — — 102.9 Financial instruments sold, not yet purchased 350.9 2,235.3 — (1,882.6 ) 703.6 Total liabilities at fair value $ 5,730.6 $ 2,528.1 $ 1.8 $ (7,459.3 ) $ 801.2 (1) Represents cash collateral and the impact of netting across the levels of the fair value hierarchy. Netting among positions classified within the same level is included in that level. The following table sets forth the Company’s financial and nonfinancial assets and liabilities accounted for at fair value, on a recurring basis, as of September 30, 2019 by level in the fair value hierarchy. September 30, 2019 (in millions) Level 1 Level 2 Level 3 Netting (1) Total Assets: Certificates of deposit $ 4.9 $ — $ — $ — $ 4.9 Money market mutual funds 8.9 — — — 8.9 Cash and cash equivalents 13.8 — — — 13.8 Commodities warehouse receipts 6.2 — — — 6.2 U.S. Treasury obligations 299.8 — — — 299.8 Securities and other assets segregated under federal and other regulations 306.0 — — — 306.0 U.S. Treasury obligations 593.9 — — — 593.9 TBA and forward settling securities — 9.8 — (1.5 ) 8.3 Foreign government obligations 9.9 — — — 9.9 Derivatives 3,131.2 43.2 — (3,159.6 ) 14.8 Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net 3,735.0 53.0 — (3,161.1 ) 626.9 Equity securities 159.5 9.0 — — 168.5 Corporate and municipal bonds — 80.0 — — 80.0 U.S. Treasury obligations 248.7 — — — 248.7 U.S. government agency obligations — 447.1 — — 447.1 Foreign government obligations 0.5 — — — 0.5 Agency mortgage-backed obligations — 1,045.0 — — 1,045.0 Asset-backed obligations — 29.1 — — 29.1 Derivatives 1.0 486.3 — (420.8 ) 66.5 Commodities leases — 28.6 — — 28.6 Commodities warehouse receipts 48.4 — — — 48.4 Exchange firm common stock 12.7 — — — 12.7 Mutual funds and other 0.1 — — — 0.1 Financial instruments owned 470.9 2,125.1 — (420.8 ) 2,175.2 Physical commodities inventory 7.1 144.8 — — 151.9 Total assets at fair value $ 4,532.8 $ 2,322.9 $ — $ (3,581.9 ) $ 3,273.8 Liabilities: Accounts payable and other accrued liabilities - contingent liabilities $ — $ — $ 1.8 $ — $ 1.8 TBA and forward settling securities — 6.8 — (1.5 ) 5.3 Derivatives 3,079.1 38.3 — (3,117.1 ) 0.3 Payable to broker-dealers, clearing organizations and counterparties 3,079.1 45.1 — (3,118.6 ) 5.6 Equity securities 147.3 10.8 — — 158.1 Corporate and municipal bonds — 39.2 — — 39.2 U.S. Treasury obligations 272.3 — — — 272.3 U.S. government agency obligations — 43.8 — — 43.8 Agency mortgage-backed obligations — 29.6 — — 29.6 Derivatives — 480.3 — (422.2 ) 58.1 Commodities leases — 113.7 — — 113.7 Financial instruments sold, not yet purchased 419.6 717.4 — (422.2 ) 714.8 Total liabilities at fair value $ 3,498.7 $ 762.5 $ 1.8 $ (3,540.8 ) $ 722.2 (1) Represents cash collateral and the impact of netting across the levels of the fair value hierarchy. Netting among positions classified within the same level is included in that level. Realized and unrealized gains and losses are included in ‘principal gains, net’, ‘interest income’, and ‘cost of sales of physical commodities’ in the condensed consolidated income statements. Additional disclosures about the fair value of financial instruments that are not carried on the Condensed Consolidated Balance Sheets at fair value Many, but not all, of the financial instruments that the Company holds are recorded at fair value in the Condensed Consolidated Balance Sheets. The following represents financial instruments in which the ending balance at March 31, 2020 and September 30, 2019 was not carried at fair value in accordance with U.S. GAAP on the Condensed Consolidated Balance Sheets: Short-term financial instruments : The carrying value of short-term financial instruments, including cash and cash equivalents, cash segregated under federal and other regulations, securities purchased under agreements to resell and securities sold under agreements to repurchase, and securities borrowed and loaned are recorded at amounts that approximate the fair value of these instruments due to their short-term nature and level of collateralization. These financial instruments generally expose the Company to limited credit risk and have no stated maturities or have short-term maturities and carry interest rates that approximate market rates. Under the fair value hierarchy, cash and cash equivalents and cash segregated under federal and other regulations are classified as Level 1. Securities purchased under agreements to resell and securities sold under agreements to repurchase, and securities borrowed and loaned are classified as Level 2 under the fair value hierarchy as they are generally overnight or short-term in nature and are collateralized by equity securities, U.S. Treasury obligations, U.S. government agency obligations, agency mortgage-backed obligations, and asset-backed obligations. Receivables and other assets : Receivables from broker-dealers, clearing organizations, and counterparties, receivables from clients, net, notes receivables, and certain other assets are recorded at amounts that approximate fair value due to their short-term nature and are classified as Level 2 under the fair value hierarchy. Payables : Payables to clients 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. Lenders under loans : Payables to lenders under loans carry variable rates of interest and are relatively short-term in duration and, thus, approximate fair value and are classified as Level 2 under the fair value hierarchy. Senior secured term loan : The senior secured term loan carries a variable rate of interest and thus approximates fair value and is classified as Level 2 under the fair value hierarchy.

Financial Instruments with Off-

Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk (Notes)	6 Months Ended
	Mar. 31, 2020
Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk [Abstract]
Derivative Instruments and Hedging Activities Disclosure [Text Block]	Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk The Company is party to certain financial instruments with off-balance sheet risk in the normal course of its business. The Company has sold financial instruments that it does not currently own and will therefore be obliged to purchase such financial instruments at a future date. The Company has recorded these obligations in the condensed consolidated financial statements as of March 31, 2020 and September 30, 2019 at the fair values of the related financial instruments. The Company will incur losses if the fair value of the underlying financial instruments increases subsequent to March 31, 2020 . The total financial instruments sold, not yet purchased of $703.6 million and $714.8 million as of March 31, 2020 and September 30, 2019 , respectively, includes $152.8 million and $58.1 million for derivative contracts, respectively, which represented a liability to the Company based on their fair values as of March 31, 2020 and September 30, 2019 . Derivatives The Company utilizes derivative products in its trading capacity as a dealer in order to satisfy client needs and mitigate risk. The Company manages risks from both derivatives and non-derivative cash instruments on a consolidated basis. The risks of derivatives should not be viewed in isolation, but in aggregate with the Company’s other trading activities. The majority of the Company’s derivative positions are included in the condensed consolidated balance sheets in ‘Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net’, ‘Financial instruments owned, at fair value’, ‘Financial instruments sold, not yet purchased, at fair value’ and ‘Payables to broker-dealers, clearing organizations and counterparties’. Listed below are the fair values of the Company’s derivative assets and liabilities as of March 31, 2020 and September 30, 2019 . Assets represent net unrealized gains and liabilities represent net unrealized losses. March 31, 2020 September 30, 2019 (in millions) Assets (1) Liabilities (1) Assets (1) Liabilities (1) Derivative contracts not accounted for as hedges: Exchange-traded commodity derivatives $ 3,201.2 $ 3,524.6 $ 1,437.1 $ 1,463.4 OTC commodity derivatives 640.1 806.0 84.2 106.2 Exchange-traded foreign exchange derivatives 15.6 18.6 36.9 33.5 OTC foreign exchange derivatives 1,306.5 1,323.3 403.2 368.8 Exchange-traded interest rate derivatives 1,613.2 1,514.7 900.1 882.0 OTC interest rate derivatives 101.7 100.6 42.1 43.6 Exchange-traded equity index derivatives 391.5 321.8 758.1 700.2 TBA and forward settling securities 80.5 98.3 9.8 6.8 Gross fair value of derivative contracts 7,350.3 7,707.9 3,671.5 3,604.5 Impact of netting and collateral (7,213.5 ) (7,459.3 ) (3,581.9 ) (3,540.8 ) Total fair value included in 'Deposits with and receivables from broker-dealers, clearing organizations, and counterparties' $ 20.2 $ 23.1 Total fair value included in 'Financial instruments owned, at fair value $ 116.6 $ 66.5 Total fair value included in 'Payables to broker-dealers, clearing organizations and counterparties $ 95.8 $ 5.6 Fair value included in 'Financial instruments sold, not yet purchased, at fair value' $ 152.8 $ 58.1 (1) As of March 31, 2020 and September 30, 2019 , the Company’s derivative contract volume for open positions were approximately 10.8 million and 10.6 million contracts, respectively. The Company’s derivative contracts are principally held in its Commercial Hedging and Clearing and Execution Services segments. The Company assists its Commercial Hedging segment clients 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 clients with option products, including combinations of buying and selling puts and calls. The Company mitigates its risk by offsetting the client’s transaction simultaneously with one of the Company’s trading counterparties or with a similar but not identical exchange-traded position. The risk mitigation of these offsetting trades is not within the documented hedging designation requirements of Topic 815. These derivative contracts are traded along with cash transactions because of the integrated nature of the markets for these products. The Company manages the risks associated with derivatives on an aggregate basis along with the risks associated with its proprietary trading and market-making activities in cash instruments as part of its firm-wide risk management policies. In particular, the risks related to derivative positions may be partially offset by inventory, unrealized gains in inventory or cash collateral paid or received. The Company has derivative instruments, which consist of TBA securities and forward settling transactions that are used to manage risk exposures in the trading inventory of the Company’s domestic institutional fixed income business. The fair value on these transactions are recorded in ‘deposits with and receivables from or payables to broker-dealers, clearing organizations and counterparties, net’. Realized and unrealized gains and losses on securities and derivative transactions are reflected in ‘principal gains, net’. As of March 31, 2020 and September 30, 2019 , these transactions are summarized as follows: March 31, 2020 September 30, 2019 (in millions) Gain / (Loss) Notional Amounts Gain / (Loss) Notional Amounts Unrealized gain on TBA securities purchased within deposits with and receivables from broker-dealers, clearing organizations and counterparties and related notional amounts $ 72.9 $ 3,335.4 $ 3.7 $ 1,778.4 Unrealized loss on TBA securities purchased within deposits with and receivables from broker-dealers, clearing organizations and counterparties and related notional amounts $ (1.5 ) $ 554.9 $ (0.6 ) $ 234.5 Unrealized gain on TBA securities sold within payables to broker-dealers, clearing organizations and counterparties and related notional amounts $ 2.0 $ (559.9 ) $ 0.9 $ (451.6 ) Unrealized loss on TBA securities sold within payables to broker-dealers, clearing organizations and counterparties and related notional amounts $ (94.8 ) $ (4,708.7 ) $ (5.9 ) $ (2,788.0 ) Unrealized gain on forward settling securities purchased within deposits with and receivables from broker-dealers, clearing organizations and counterparties and related notional amounts $ 5.6 896.9 $ — $ — Unrealized loss on forward settling securities purchased within payables to broker-dealers, clearing organizations and counterparties and related notional amounts $ — $ — $ (0.3 ) $ 1,243.5 Unrealized gain on forward settling securities sold within deposits with and receivables from broker-dealers, clearing organizations and counterparties and related notional amounts $ — $ — $ 5.2 $ (581.2 ) Unrealized loss on forward settling securities sold within payables to broker-dealers, clearing organizations and counterparties and related notional amounts $ (2.0 ) (712.4 ) $ — $ — (1) The notional amounts of these instruments reflect the extent of the Company's involvement in TBA and forward settling securities and do not represent risk of loss due to counterparty non-performance. The following table sets forth the Company’s net gains from derivative contracts for the three and six months ended March 31, 2020 and 2019 in accordance with Topic 815. The net gains set forth below are included in ‘Cost of sales of physical commodities’ and ‘principal gains, net’ in the condensed consolidated income statements. Three Months Ended March 31, Six Months Ended March 31, (in millions) 2020 2019 2020 2019 Commodities $ 61.6 $ 36.0 $ 79.8 $ 44.1 Foreign exchange 5.1 1.8 7.3 3.7 Interest rate and equity — 0.7 (0.4 ) (2.6 ) TBA and forward settling securities (34.4 ) 10.6 (35.3 ) 1.3 Net gains from derivative contracts $ 32.3 $ 49.1 $ 51.4 $ 46.5 Credit Risk In the normal course of business, the Company purchases and sells financial instruments, commodities and foreign currencies as either a principal or agent on behalf of its clients. If either the client 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, commodity, 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, clients, broker-dealers and other financial institutions. These activities primarily involve collateralized and uncollateralized arrangements and may result in credit exposure in the event that a counterparty fails to meet its contractual obligations. The Company’s exposure to credit risk can be directly impacted by volatile financial markets, which may impair the ability of counterparties to satisfy their contractual obligations. The Company seeks to control its credit risk through a variety of reporting and control procedures, including establishing credit and/or position limits based upon a review of the counterparties’ financial condition and credit ratings. The Company monitors collateral levels on a daily basis for compliance with regulatory and internal guidelines and requests changes in collateral levels as appropriate. The Company is a party to financial instruments in the normal course of its business through client and proprietary trading accounts in exchange-traded and OTC derivative instruments. These instruments are primarily the result of the execution of orders for commodity futures, options on futures, OTC swaps and options and spot and forward foreign currency contracts on behalf of its clients, 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 clients may incur. The Company controls the risks associated with these transactions by requiring clients to maintain margin deposits in compliance with individual exchange regulations and internal guidelines. The Company monitors required margin levels daily, and therefore may require clients to deposit additional collateral or reduce positions when necessary. The Company also establishes credit limits for clients, which are monitored daily. The Company evaluates each client’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 clients and exchanges are subject to master netting, or client agreements, which reduce the exposure to the Company by permitting receivables and payables with such clients to be offset in the event of a client default. Management believes that the margin deposits held as of March 31, 2020 and September 30, 2019 were adequate to minimize the risk of material loss that could be created by positions held at that time. Additionally, the Company monitors collateral fair value on a daily basis and adjusts collateral levels in the event of excess market exposure. Generally, these exposures to both clients and counterparties are subject to master netting or client agreements which reduce the exposure to the Company. Derivative financial instruments involve varying degrees of off-balance sheet market risk whereby changes in the fair values of underlying financial instruments may result in changes in the fair value of the financial instruments in excess of the amounts reflected in the condensed consolidated balance sheets. Exposure to market risk is influenced by a number of factors, including the relationships between the financial instruments and the Company’s positions, as well as the volatility and liquidity in the markets in which the financial instruments are traded. The principal risk components of financial instruments include, among other things, interest rate volatility, the duration of the underlying instruments and changes in foreign exchange rates. The Company attempts to manage its exposure to market risk through various techniques. Aggregate market limits have been established and market risk measures are routinely monitored against these limits.

Receivables From Customers, Net

Receivables From Customers, Net and Notes Receivable, Net (Notes)	6 Months Ended
	Mar. 31, 2020
Receivables from customers and notes receivable, net [Abstract]
Financing Receivables [Text Block]	Allowance for Doubtful Accounts The allowance for doubtful accounts related to deposits with and receivables from broker-dealers, clearing organizations, and counterparties was $1.3 million and $36.9 million as of March 31, 2020 and September 30, 2019 , respectively. During the three months ended March 31, 2020 , the Company charged off $35.6 million of receivables against the allowance for doubtful accounts related to the physical coal business, which the Company exited in fiscal 2018. The allowance for doubtful accounts related to receivables from clients was $17.2 million and $11.7 million as of March 31, 2020 and September 30, 2019 , respectively. The allowance increase is related to additional bad debt reserves as discussed below and recoverable amounts due from affiliated party and recorded in ‘other assets’ in the condensed consolidated balance sheets. The Company had no allowance for doubtful accounts related to notes receivable as of March 31, 2020 and September 30, 2019 . During the three months ended March 31, 2020 , the Company recorded bad debt expense of $4.4 million , primarily related to $3.9 million of OTC client account deficits in the Commercial Hedging segment, $0.3 million of client deficits in the Clearing & Execution Services segment and $0.2 million in uncollected receivables in the Physical Commodities segment. During the three months ended March 31, 2019, the Company recorded bad debt expense of $ 0.7 million , primarily related to client account deficits in the Commercial Hedging segment. During the six months ended March 31, 2020, the Company recorded bad debt expense of $4.4 million , as discussed above. During the six months ended March 31, 2019, the Company recorded bad debt expense of $1.0 million , primarily related to client account deficits in the Commercial Hedging and Clearing & Execution Services segments. Additionally, during the six months ended March 31, 2019, the Company reached settlements with clients, paying $8.4 million related to demurrage, dead freight, and other penalty charges regarding coal supplied during fiscal 2017. The settlement amounts paid were less than the accrued liability for the transactions recorded during fiscal 2017 and fiscal 2018, and accordingly the Company recorded a recovery on the bad debt on physical coal of $2.4 million .

Physical Commodities Inventory

Physical Commodities Inventory (Notes)	6 Months Ended
	Mar. 31, 2020
Physical Commodities Inventory [Abstract]
Inventory Disclosure [Text Block]	Physical Commodities Inventory The Company’s inventories consist of finished physical commodities. Inventories by component of the Company’s Physical Commodities segment are shown below. (in millions) March 31, September 30, Physical Ag & Energy (1) $ 167.8 $ 144.8 Precious metals - held by broker-dealer subsidiary (2) 26.3 7.1 Precious metals - held by non-broker-dealer subsidiaries (3) 61.1 77.4 Physical commodities inventory $ 255.2 $ 229.3 (1) Physical Ag & Energy consists of agricultural commodity inventories, including corn, soybeans, wheat, dried distillers grain, canola, sorghum, coffee, cocoa, cotton, and others. The agricultural commodity inventories are carried at net realizable value, which approximates selling prices in the ordinary course of business, less disposal costs, with changes in net realizable value included as a component of ‘cost of sales of physical commodities’ on the condensed consolidated income statements. The agricultural inventories have reliable, readily determinable and realizable market prices, have relatively insignificant costs of disposal and are available for immediate delivery. Physical Ag & Energy also maintains energy related inventory which is valued at the lower of cost or net realizable value. (2) Precious metals held by the Company’s subsidiary, INTL FCStone Ltd, a United Kingdom based broker-dealer subsidiary, is measured at fair value, with changes in fair value included as a component of ‘principal gains, net’ on the condensed consolidated income statements, in accordance with U.S. GAAP accounting requirements for broker-dealers. (3) Precious metals inventory held by subsidiaries that are not broker-dealers are valued at the lower of cost or net realizable value. The Company has recorded lower of cost or net realizable adjustments for certain precious metals inventory of $1.2 million and $0.5 million as of March 31, 2020 and September 30, 2019, respectively. The adjustments are included in ‘cost of sales of physical commodities’ in the condensed consolidated income statements.

Goodwill (Notes)

Goodwill (Notes)	6 Months Ended
	Mar. 31, 2020
Goodwill [Abstract]
Goodwill Disclosure [Text Block]	Goodwill The carrying value of goodwill is allocated to the Company’s operating segments as follows: (in millions) March 31, September 30, Commercial Hedging $ 30.2 $ 30.3 Global Payments 7.6 7.6 Securities 4.6 4.6 Physical Commodities 8.7 8.7 Clearing and Execution 1.1 — Goodwill $ 52.2 $ 51.2 The Company recorded additional goodwill of $1.1 million during the six months ended March 31, 2020 within the Clearing and Execution operating segment related to the initial purchase price allocation for the acquisition of UOB Bullion and Futures Limited as further discussed in Note 18 .

Intangible Assets - (Notes)

Intangible Assets - (Notes)	6 Months Ended
	Mar. 31, 2020
Intangible Assets [Abstract]
Intangible Assets Disclosure [Text Block]	Intangible Assets The Company recorded $3.2 million , $1.0 million , and $1.7 million of customer base intangible assets during the six months ended March 31, 2020 related to the acquisitions of UOB Bullion and Futures Limited, IFCM Commodities GmbH, and Quest Capital, respectively, as further discussed in Note 18 . The gross and net carrying values of intangible assets as of the balance sheet dates, by major intangible asset class are as follows (in millions): March 31, 2020 September 30, 2019 Gross Amount Accumulated Amortization Net Amount Gross Amount Accumulated Amortization Net Amount Intangible assets subject to amortization: Software programs/platforms $ 5.3 $ (3.2 ) $ 2.1 $ 5.3 $ (3.0 ) $ 2.3 Customer base 28.2 (14.2 ) 14.0 22.1 (12.5 ) 9.6 Total intangible assets subject to amortization: 33.5 (17.4 ) 16.1 27.4 (15.5 ) 11.9 Intangible assets not subject to amortization: Website domains 2.1 — 2.1 2.1 — 2.1 Business licenses 2.7 — 2.7 2.7 — 2.7 Total intangible assets not subject to amortization: 4.8 — 4.8 4.8 — 4.8 Total intangible assets $ 38.3 $ (17.4 ) $ 20.9 $ 32.2 $ (15.5 ) $ 16.7 Amortization expense related to intangible assets was $1.1 million and $0.6 million for the three months ended March 31, 2020 and 2019 , respectively. Amortization expense related to intangible assets was $1.9 million and $1.3 million for the six months ended March 31, 2020 and 2019 , respectively. As of March 31, 2020 , the estimated future amortization expense was as follows: (in millions) Fiscal 2020 (remaining six months) $ 2.0 Fiscal 2021 4.0 Fiscal 2022 2.7 Fiscal 2023 2.5 Fiscal 2024 and thereafter 4.9 Total intangible assets subject to amortization $ 16.1

Credit Facilities (Notes)

Credit Facilities (Notes)	6 Months Ended
	Mar. 31, 2020
Credit Facilities [Abstract]
Debt Disclosure [Text Block]	Credit Facilities Committed Credit Facilities The Company has four committed credit facilities, including a senior secured term loan, under which the Company and its subsidiaries may borrow up to $766.5 million , subject to the terms and conditions for these facilities. The amounts outstanding under these credit facilities carry variable rates of interest, thus approximating fair value. The Company’s committed credit facilities consist of the following: • $381.5 million facility available to INTL FCStone Inc. for general working capital requirements. During the three months ended December 31, 2019, additional members were added to the lending syndication increasing the committed amount to $393.0 million . The amended facility is comprised of a $196.5 million revolving credit facility and a $196.5 million Term Loan facility. The Company is required to make quarterly principal payments against the Term Loan equal to 1.25% of the original balance with the remaining balance due on the maturity date. Amounts repaid on the Term Loan may not be reborrowed. • $75.0 million facility available to the Company’s wholly owned subsidiary, INTL FCStone Financial Inc., for short-term funding of margin to exchange-clearing organizations. The facility is subject to annual review and guaranteed by INTL FCStone Inc. • $260.0 million facility available to the Company’s wholly owned subsidiary, FCStone Merchant Services, LLC, for financing traditional commodity financing arrangements and commodity repurchase agreements. The facility is guaranteed by INTL FCStone Inc. • $50.0 million facility available to the Company’s wholly owned subsidiary, INTL FCStone Ltd, for short-term funding of margin to exchange-clearing organizations. The facility is guaranteed by INTL FCStone Inc. Uncommitted Credit Facilities The Company has a secured, uncommitted loan facility under which INTL FCStone Financial Inc. may borrow up to $75.0 million , collateralized by commodities warehouse receipts, to facilitate U.S. commodity exchange deliveries of its clients, subject to certain terms and conditions of the credit agreement. There were no borrowings outstanding under this credit facility as of March 31, 2020 , and September 30, 2019 . The Company has a secured, uncommitted loan facility under which INTL FCStone Financial Inc. may borrow for short term funding of proprietary and client securities margin requirements, subject to certain terms and conditions of the agreement. The uncommitted amount available to be borrowed is not specified, and all requests for borrowing are subject to the sole discretion of the lender. The borrowings are secured by first liens on Company owned marketable securities or client owned securities which have been pledged to the Company. The amounts borrowed under the facilities are payable on demand. There were $5.0 million and zero in borrowings outstanding under this credit facility as of March 31, 2020 , and September 30, 2019 , respectively. The Company has secured, uncommitted loan facilities under which INTL FCStone Financial Inc. may borrow up to $100.0 million for short term funding of proprietary and client securities margin requirements, subject to certain terms and conditions of the agreement. The borrowings are secured by first liens on Company owned marketable securities or client owned securities which have been pledged to the Company. The amounts borrowed under the facilities are payable on demand. There were no borrowings outstanding under this credit facility as of March 31, 2020 and September 30, 2019 . The Company had a secured, uncommitted loan facility under which FCStone Merchant Services, LLC could borrow up to $20.0 million to facilitate the financing of inventory of commodities and other products or goods approved by the lender in its sole discretion, subject to certain terms and conditions of the loan facility agreement. There were $3.4 million in borrowings outstanding under this credit facility as of September 30, 2019 . The credit facility was terminated during the three months ended March 31, 2020, in connection with the refinancing and extension of FCStone Merchant Services, LLC’s committed credit facility. 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 as of the periods indicated: (in millions) Amounts Outstanding Borrower Security Renewal/Expiration Date Total Commitment March 31, September 30, Committed Credit Facilities Term Loan (1) February 22, 2022 $ 185.0 $ 184.3 (2) $ 167.6 Revolving Line of Credit (1) February 22, 2022 196.5 100.0 70.0 INTL FCStone Inc. 381.5 284.3 237.6 INTL FCStone Financial Inc. None April 2, 2021 75.0 — — FCStone Merchants Services, LLC Certain commodities assets January 29, 2022 260.0 170.0 128.5 INTL FCStone Ltd. None July 14, 2020 50.0 — — $ 766.5 $ 454.3 $ 366.1 Uncommitted Credit Facilities INTL FCStone Financial Inc. Commodities warehouse receipts and certain pledged securities n/a n/a 5.0 — FCStone Merchant Services, LLC Certain commodities assets n/a n/a — 3.4 Note Payable to Bank Monthly installments, due March 2020 and secured by certain equipment — 0.4 Total outstanding borrowings $ 459.3 $ 369.9 (1) The INTL FCStone Inc. committed credit facility is secured by substantially all of the assets of INTL FCStone Inc. and certain subsidiaries identified in the credit facility agreement as obligors, and pledged equity of certain subsidiaries identified in the credit facility as limited guarantors. (2) Amount outstanding under the Term Loan is reported net of unamortized deferred financing costs of 0.7 million . As reflected above, $125.0 million of the Company’s committed credit facilities are scheduled to expire within twelve months of this filing. The Company intends to renew or replace the facilities when they expire, and based on the Company’s liquidity position and capital structure, the Company believes it will be able to do so. The Company’s credit facility agreements contain financial covenants relating to financial measures on a consolidated basis, as well as on a certain stand-alone subsidiary basis, including minimum tangible net worth, minimum regulatory capital, minimum net unencumbered liquid assets, maximum net loss, minimum fixed charge coverage ratio and maximum funded debt to net worth ratio. Failure to comply with these covenants could result in the debt becoming payable on demand. As of March 31, 2020 , the Company was in compliance with all of its financial covenants under its credit facilities.

Commodity and Other Repurchase

Commodity and Other Repurchase Agreements and Collateralized Transactions (Notes)	6 Months Ended
	Mar. 31, 2020
Commodity and Other Repurchase Agreements [Abstract]
Commodity and Other Repurchase Agreements and Collateralized Transactions	Securities and Commodity Financing Transactions 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, fund principal debt trading, acquire securities to cover short positions, acquire securities for settlement, and to accommodate counterparties’ needs under matched-book trading strategies. These agreements are recorded as collateralized financings at their contractual amounts plus accrued interest. The related interest is recorded in the condensed consolidated income statements as interest income or interest expense, as applicable. In connection with these agreements and transactions, it is the policy of the Company to receive or pledge cash or securities to adequately collateralize such agreements and transactions in accordance with contractual agreements. The collateral is valued daily and the Company may require counterparties to deposit additional collateral or return collateral pledged. The carrying amounts of these agreements and transactions approximate fair value due to their short-term nature and the level of collateralization. The Company pledges financial instruments owned to collateralize repurchase agreements. At March 31, 2020 and September 30, 2019 , financial instruments owned, at fair value of $743.6 million and $478.8 million , respectively, were pledged as collateral under repurchase agreements. The counterparty has the right to sell or repledge the collateral in connection with these transactions. These financial instruments owned have been pledged as collateral and have been parenthetically disclosed on the condensed consolidated balance sheets. In addition, as of March 31, 2020 and September 30, 2019 , the Company pledged financial instruments owned, at fair value of $1,049.3 million and $1,228.9 million , respectively, to cover collateral requirements for tri-party repurchase agreements. These securities have not been parenthetically disclosed on the condensed consolidated balance sheets since the counterparties do not have the right to sell or repledge the collateral. The Company also repledged securities received under reverse repurchase agreements of $1,069.8 million and $1,175.1 million , respectively, to cover collateral requirements for tri-party repurchase agreements. The Company also has repledged securities borrowed and client securities held under custodial clearing arrangements to collateralize securities loaned agreements with a fair value of $1,025.9 million and $1,414.0 million as of March 31, 2020 , and September 30, 2019 , respectively. Additionally, the Company had also pledged financial instruments owned with a fair value of $21.9 million and zero as of March 31, 2020 , and September 30, 2019 , respectively, to collateralize uncommitted loan facilities with certain banks as discussed further in Note 11 . At March 31, 2020 and September 30, 2019, the Company had accepted collateral that it is permitted by contract to sell or repledge. This collateral consists primarily of securities received in reverse repurchase agreements, securities borrowed agreements, and margin securities held on behalf of correspondent brokers. The fair value of such collateral at March 31, 2020 and September 30, 2019 , was $2,449.2 million and $3,060.2 million , respectively, of which $252.2 million and $329.8 million , respectively, was used to cover securities sold short which are recorded in financial instruments sold, not yet purchased on the condensed consolidated balance sheets. 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 arrangement and matched-booked trading strategies. The following tables provide the contractual maturities of gross obligations under repurchase and securities lending agreements as of March 31, 2020 and September 30, 2019 (in millions): March 31, 2020 Overnight and Open Less than 30 Days 30-90 Days Over 90 Days Total Securities sold under agreements to repurchase $ 1,535.1 $ 737.2 $ 483.0 $ 45.0 $ 2,800.3 Securities loaned 1,068.8 — — — 1,068.8 Gross amount of secured financing $ 2,603.9 $ 737.2 $ 483.0 $ 45.0 $ 3,869.1 September 30, 2019 Overnight and Open Less than 30 Days 30-90 Days Over 90 Days Total Securities sold under agreements to repurchase $ 1,553.9 $ 565.8 $ 654.0 $ — $ 2,773.7 Securities loaned 1,459.9 — — — 1,459.9 Gross amount of secured financing $ 3,013.8 $ 565.8 $ 654.0 $ — $ 4,233.6 The following table provides the underlying collateral types of the gross obligations under repurchase and securities lending agreements as of March 31, 2020 and September 30, 2019 (in millions): Securities sold under agreements to repurchase March 31, 2020 September 30, 2019 U.S. Treasury obligations $ 32.2 $ 108.8 U.S. government agency obligations 264.1 359.5 Asset-backed obligations 76.5 96.7 Agency mortgage-backed obligations 2,402.8 2,208.7 Corporate bonds 24.7 — Total securities sold under agreement to repurchase 2,800.3 2,773.7 Securities loaned Equity securities 1,068.8 1,459.9 Total securities loaned 1,068.8 1,459.9 Gross amount of secured financing $ 3,869.1 $ 4,233.6 The following tables provide the netting of securities purchased under agreements to resell, securities sold under agreements to repurchase, securities borrowed and securities loaned as of the periods indicated (in millions): March 31, 2020 Offsetting of collateralized transactions: Gross Amounts Recognized Amounts Offset in the Condensed Consolidated Balance Sheet Net Amounts Presented in the Condensed Consolidated Balance Sheet Securities purchased under agreements to resell $ 1,260.0 $ — $ 1,260.0 Securities borrowed $ 1,063.8 $ — $ 1,063.8 Securities sold under agreements to repurchase $ 2,800.3 $ — $ 2,800.3 Securities loaned $ 1,068.8 $ — $ 1,068.8 September 30, 2019 Offsetting of collateralized transactions: Gross Amounts Recognized Amounts Offset in the Condensed Consolidated Balance Sheet Net Amounts Presented in the Condensed Consolidated Balance Sheet Securities purchased under agreements to resell $ 1,474.4 $ (49.9 ) $ 1,424.5 Securities borrowed $ 1,423.2 $ — $ 1,423.2 Securities sold under agreements to repurchase $ 2,823.6 $ (49.9 ) $ 2,773.7 Securities loaned $ 1,459.9 $ — $ 1,459.9

Commitments and Contingencies (

Commitments and Contingencies (Notes)	6 Months Ended
	Mar. 31, 2020
Commitments and Contingencies [Abstract]
Commitments and Contingencies Disclosure [Text Block]	Commitments and Contingencies Contingencies During the week ended November 16, 2018, balances in approximately 300 accounts of the FCM division of the Company’s wholly owned subsidiary, INTL FCStone Financial Inc., declined below required maintenance margin levels, primarily as a result of significant and unexpected price fluctuations in the natural gas markets. All positions in these accounts, which were managed by OptionSellers.com Inc. (“OptionSellers”), an independent Commodity Trading Advisor (“CTA”), were liquidated in accordance with the INTL FCStone Financial Inc.’s client agreements and obligations under market regulation standards. A CTA is registered with the U.S. Commodity Futures Trading Commission (“CFTC”) and a member of, and subject to audit by, the National Futures Association (“NFA”). OptionSellers is registered under a CFTC Rule 4.7 exemption for “qualified eligible persons,” which requires the account holders authorizing OptionSellers to act as their CTA to meet or exceed certain minimum financial requirements. OptionSellers, in its role as a CTA, had been granted by each of its clients full discretionary authority to manage the trading in the client accounts, while INTL FCStone Financial Inc. acted solely as the clearing firm in its role as the FCM. INTL FCStone Financial Inc.’s client agreements hold account holders liable for all losses in their accounts and obligate the account holders to reimburse INTL FCStone Financial Inc. for any account deficits in their accounts. As of March 31, 2020, the aggregate receivable from these client accounts, net of collections and other allowable deductions, was $29.0 million , with no individual account receivable exceeding $1.4 million . INTL FCStone Financial Inc. continues to pursue collection of these receivables and intends both to enforce and to defend its rights aggressively, and to claim interest and costs of collection where applicable. The Company has completed an assessment of the collectability of these accounts and has concluded that it does not have a sufficient basis to record an allowance against these uncollected balances. The assessment included the consideration of numerous arbitration proceedings the Company has initiated against these clients to recover deficit balances in their accounts. The Company believes it has a valid claim against its clients, based on the express language of the client contracts and legal precedent, and intends to pursue collection of these claims vigorously. As the Company moves through the collection and arbitration processes and additional information becomes available, the Company will continue to consider the need for an allowance against the carrying value of these uncollected balances. Additionally, INTL FCStone Financial Inc. has been named in arbitrations brought by clients seeking damages relating to the trading losses in these accounts. The Company believes that such cases are without merit and intends to defend them vigorously. The ultimate outcome of these arbitrations cannot presently be determined, however the Company believes the likelihood of a material adverse outcome is remote. Depending on future collections and arbitration proceedings, any provisions for bad debts and actual losses ultimately may or may not be material to the Company’s financial results. Currently, the Company does not believe that any potential losses related to this matter would impact its ability to comply with its ongoing liquidity, capital, and regulatory requirements. Legal Proceedings From time to time and in the ordinary course of business, the Company is involved in various legal actions and proceedings, including tort claims, contractual disputes, employment matters, workers’ compensation claims and collections. The Company carries insurance that provides protection against certain types of claims, up to the policy limits of the insurance. As of March 31, 2020 and September 30, 2019, the condensed consolidated balance sheets include loss contingency accruals which are not material, individually or in the aggregate, to the Company’s financial position or liquidity. In the opinion of management, possible exposure from loss contingencies in excess of the amounts accrued, is not likely to be material to the Company’s earnings, financial position or liquidity. There have been no material changes to the legal actions and proceedings compared to September 30, 2019. Contractual Commitments Self-Insurance The Company self-insures its costs related to medical and dental claims. The Company is self-insured, up to a stop loss amount, for eligible participating employees and retirees, and for qualified dependent medical and dental claims, subject to deductibles and limitations. As of March 31, 2020 , the Company had $1.1 million accrued for self-insured medical and dental claims included in ‘accounts payable and other accrued liabilities’ in the condensed consolidated balance sheet.

Capital and Other Regulatory Re

Capital and Other Regulatory Requirements (Notes)	6 Months Ended
	Mar. 31, 2020
Capital and Other Regulatory Requirements [Abstract]
Regulatory Capital Requirements under Banking Regulations [Text Block]	Capital and Other Regulatory Requirements The Company’s activities are subject to significant governmental regulation, both in the United States and in the international jurisdictions in which it operates. The subsidiaries of the Company were in compliance with all of their regulatory requirements as of March 31, 2020. The following table details those subsidiaries with minimum regulatory requirements in excess of $5 million along with the actual balance maintained as of March 31, 2020. (in millions) As of March 31, 2020 Subsidiary Regulatory Authority Jurisdiction Requirement Type Actual Minimum Requirement INTL FCStone Financial Inc. SEC and CFTC United States Net capital $ 175.7 $ 108.3 INTL FCStone Financial Inc. CFTC United States Segregated funds $ 2,543.6 $ 2,485.9 INTL FCStone Financial Inc. CFTC United States Secured funds $ 162.5 $ 150.0 INTL FCStone Financial Inc. (1) SEC United States Customer reserve $ 33.1 $ 66.1 INTL FCStone Ltd Financial Conduct Authority ("FCA") United Kingdom Net capital $ 270.3 $ 140.0 INTL FCStone Ltd FCA United Kingdom Segregated funds $ 437.8 $ 430.1 INTL FCStone Pte. Ltd. Monetary Authority of Singapore ("MAS") Singapore Segregated funds $ 208.2 $ 202.6 (1) As of March 31, 2020 , the Company had $33.1 million deposited in the customer special reserve bank account (“SRBA”). As a result of the reserve requirement determined through the weekly computation, the Company made an additional deposit of $38.1 million to the customer SRBA on April 2, 2020 to meet the customer segregation requirements under SEC Rule 15c3-3. Certain other non-U.S. subsidiaries of the Company are also subject to capital adequacy requirements promulgated by authorities of the countries in which they operate. As of March 31, 2020 , these subsidiaries were in compliance with their local capital adequacy requirements.

Other Expenses (Notes)

Other Expenses (Notes)	6 Months Ended
	Mar. 31, 2020
Other Expenses [Abstract]
Other Expenses [Text Block]	Other Expenses Other expenses for the three and six months ended March 31, 2020 and 2019 consisted of the following: Three Months Ended March 31, Six Months Ended March 31, (in millions) 2020 2019 2020 2019 Contingent consideration, net $ 0.1 $ — $ 0.1 $ — Insurance 1.0 0.9 2.0 1.7 Advertising, meetings and conferences 4.2 1.5 5.6 2.9 Office supplies and printing 0.5 0.5 0.9 1.0 Other clearing related expenses 0.6 0.7 1.4 1.1 Other non-income taxes 1.3 1.2 2.6 2.1 Other 2.9 2.6 5.5 5.1 Total other expenses $ 10.6 $ 7.4 $ 18.1 $ 13.9

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss) (Notes)	6 Months Ended
	Mar. 31, 2020
Accumulated Other Comprehensive Income (Loss) [Abstract]
Comprehensive Income (Loss) Note [Text Block]	Accumulated Other Comprehensive Loss, Net Comprehensive income consists of net income and other gains and losses affecting stockholders’ equity that, under U.S. GAAP, are excluded from net income. Other comprehensive income includes net actuarial losses from defined benefit pension plans and foreign currency translation adjustments. The following table summarizes the changes in accumulated other comprehensive loss, net for the six months ended March 31, 2020 . (in millions) Foreign Currency Translation Adjustment Pension Benefits Adjustment Accumulated Other Comprehensive Loss Balances as of September 30, 2019 $ (31.5 ) $ (3.3 ) $ (34.8 ) ASU 2018-02 cumulative transition adjustment — (0.7 ) (0.7 ) Adjusted Balances as of September 30, 2019 (31.5 ) (4.0 ) (35.5 ) Other comprehensive loss (2.7 ) — — (2.7 ) Balances as of March 31, 2020 $ (34.2 ) $ (4.0 ) $ (38.2 )

Income Taxes (Notes)

Income Taxes (Notes)	6 Months Ended
	Mar. 31, 2020
Income Taxes [Abstract]
Income Tax Disclosure [Text Block]	Income Taxes The income tax provision for interim periods is comprised of income tax on jurisdiction-level income (loss) figures provided at the most recent estimated annual effective income tax rate, adjusted for the income tax effect of discrete items. Management uses an estimated annual effective income tax rate based on the forecasted pretax income (loss) and statutory tax rates in the various jurisdictions in which it operates. The Company’s effective income tax rate differs from the U.S. statutory income tax rate primarily due to state and local taxes, global intangible low taxed income (“GILTI”), and differing statutory tax rates applied to the income of non-U.S. subsidiaries. The Company records the tax effect of certain discrete items, including the effects of changes in tax laws, tax rates and adjustments with respect to valuation allowances or other unusual or nonrecurring tax adjustments, in the interim period in which they occur, as an addition to, or reduction from, the income tax provision, rather than being included in the estimated effective annual income tax rate. In addition, jurisdictions with a projected loss for the year or a year-to-date loss where no income tax benefit can be recognized are excluded from the estimated annual effective income tax rate. The Company is required to assess its deferred tax assets and the need for a valuation allowance at each reporting period. This assessment requires judgment on the part of management with respect to benefits that may be realized. The Company will record a valuation allowance against deferred tax assets when it is considered more likely than not that all or a portion of the deferred tax assets will not be realized. Current and Prior Period Tax Expense Income tax expense of $16.8 million and $7.5 million for the three months ended March 31, 2020 and 2019 , respectively, and income tax expense of $22.2 million and $13.7 million for the six months ended March 31, 2020 and 2019 reflects estimated federal, foreign, state and local income taxes. For the three months ended March 31, 2020 and 2019 , the Company’s effective tax rate was 30% and 24% , respectively. For the three months ended March 31, 2020 and 2019, the effective rate was higher than the U.S. federal statutory rate of 21% due to U.S. state and local taxes, GILTI, U.S. and foreign permanent differences, and the amount of foreign earnings taxed at higher tax rates. Pre-tax income increased significantly in the three months ended March 31, 2020 as compared both to the prior quarter and the prior year. As a result of the significant increase in pre-tax income, the annual forecasted effective tax rate increased 0.6% due to state and local taxes on higher U.S.income, compared to the prior quarter ended December 31, 2019. Non-deductible compensation due to Sec. 162(m) limitations increased the effective tax rate by 0.4% as compared to the prior quarter. The amount of foreign earnings taxed at higher tax rates increased by 0.7% from the prior quarter. For the six months ended March 31, 2020 and 2019 , the Company’s effective tax rate was 29% and 25% , respectively. For the six months ended March 31, 2020 and 2019, the effective rate was higher than the U.S. federal statutory rate of 21% due to U.S. state and local taxes, GILTI, U.S. and foreign permanent differences, and the amount of foreign earnings taxed at higher tax rates. The estimated GILTI tax expense increased the effective rate approximately 1.2% and 1.3% for the six months ended March 31, 2020 and 2019 , respectively. The amount of foreign earnings taxed at higher rates increased the effective tax rate approximately 3.3% and 0.5% for six months ended March 31, 2020 and 2019 , respectively. 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 March 31, 2020 and September 30, 2019, the Company has net operating loss carryforwards for U.S. federal, state, local, and foreign income tax purposes of $7.1 million , net of valuation allowances, which are available to offset future taxable income in these jurisdictions. The state and local net operating loss carryforwards of $5.6 million , net of valuation allowance, begin to expire after September 2020. INTL Asia Pte. Ltd. has a Singapore net operating loss carryforward of $0.2 million . This Singapore net operating loss has an indefinite carryforward and, in the judgment of management, is more likely than not to be realized. As a result of the Tax Cuts and Jobs Act of 2017, the alternative minimum tax (“AMT”) credit carryforward deferred tax asset has been reclassified to income taxes receivable. As a result of the Coronavirus Aid, Relief, and Economic Security Act (CARES act), the AMT credit carryforward is refundable on the fiscal year 2019 tax return. In fiscal 2018, the Company generated $5.1 million in foreign tax credit carryforwards as part of the mandatory repatriation transition tax. These credits expire in fiscal year 2028. In the judgment of management, it is more likely than not that sufficient taxable income will be earned to utilize the foreign tax credit carryforwards during the current fiscal year. The valuation allowance for deferred tax assets as of March 31, 2020 and September 30, 2019 was $8.4 million and $8.5 million , respectively. The valuation allowances as of March 31, 2020 and September 30, 2019 were primarily related to U.S., state and local net operating loss carryforwards and foreign net operating loss carryforwards that, in the judgment of management, are not more likely than not to be realized. As of March 31, 2020 and September 30, 2019, the Company had accumulated undistributed earnings generated by its foreign subsidiaries of approximately $393.9 million and $383.5 million , respectively. The repatriation of these amounts would not be subject to U.S. federal income tax, but may be subject to applicable foreign withholding and state taxes in the relevant jurisdictions. The Company does not intend to distribute earnings in a taxable manner, and therefore intends to limit distributions to earnings previously taxed in the U.S., or earnings that would qualify for the 100 percent dividends received deduction, and earnings that would not result in any significant foreign withholding or state taxes. The Company has repatriated $30.0 million and $13.0 million as of March 31, 2020 and September 30, 2019, respectively, of earnings previously taxed in the U.S. resulting in no significant incremental taxes upon repatriation. Therefore, the Company has not recognized a deferred tax liability on its investment in foreign subsidiaries. The Company and its subsidiaries file income tax returns with the U.S. federal and various U.S. state and local, as well as foreign jurisdictions. The Company has open tax years ranging from September 30, 2012 through September 30, 2019 with U.S. federal and state and local taxing authorities. During the three months ending March 31, 2020, the Company closed their examination with the U.S. Internal Revenue Service for the 2016 tax year with no adjustments required. In the United Kingdom (“U.K.”), the Company has open tax years ending September 30, 2017 to September 30, 2019. The Company is currently under examination by HM Revenue and Customs in the UK for the 2017 tax year; however, no additional tax liability is expected. In Brazil, the Company has open tax years ranging from December 31, 2014 through December 31, 2019. In Argentina, the Company has open tax years ranging from September 30, 2012 to September 30, 2019. In Singapore, the Company has open tax years ranging from September 30, 2015 to September 30, 2019 and is currently under examination by the Inland Revenue Authority of Singapore for the year ended September 30, 2017; however, no additional tax liability is expected.

Acquisitions Acquisitions (Note

Acquisitions Acquisitions (Notes)	6 Months Ended
	Mar. 31, 2020
Acquisitions (Notes) [Abstract]
Business Combination Disclosure [Text Block]	Note 18 - Acquisitions UOB Bullion and Futures Limited On March 19, 2019, the Company’s subsidiary INTL FCStone Pte Ltd executed an asset purchase agreement to acquire the futures and options brokerage and clearing business of UOB Bullion and Futures Limited, a subsidiary of United Overseas Bank Limited. Closing was conditional upon receiving regulatory approval by the Monetary Authority of Singapore. This acquisition provides the Company access to an established institutional client base and also augments the Company’s global service capabilities in Singapore. The purchase price for the acquired assets was $5.0 million of which $2.5 million was due upon the execution of the asset purchase agreement and the remaining $2.5 million was due upon the closing of the acquisition, which occurred on October 7, 2019. The purchase price allocation resulted in the recognition of liabilities assumed related to the futures and options on futures client account balances of approximately $351.8 million as of the acquisition date, which was recorded within ‘payables to clients’ on the condensed consolidated balance sheet, and an equal and offsetting amount of assets acquired. The allocation of the purchase price to the client accounts is considered final as of March 31, 2020. The Company also acquired certain client base intangible assets and property and equipment in connection with the acquisition. The Company has engaged a third-party valuation specialist to assist with the valuation of the acquired intangible assets and property and equipment. As of March 31, 2020, the valuation of the acquired intangible assets and property and equipment was not yet complete as the Company continues to acquire the information necessary to complete the valuation analysis. As of March 31, 2020, given the status of the valuation analysis, $0.7 million of the purchase price was preliminary allocated to the net book value of the property and equipment acquired, $3.2 million was allocated to the client base intangible assets acquired, and the remaining excess purchase price of $1.1 million was allocated to goodwill. Once the valuation analysis is complete, the Company will record measurement period adjustments to reflect the fair value of the property and equipment and intangible assets acquired on the acquisition date. The business acquired has been assigned to the Company’s Clearing and Execution reportable segment. The client base intangible assets have preliminary been assigned a useful life of 5 years . The revenues and net income contributed by the acquired business during the three and six months ended March 31, 2020, were not material to the Company’s condensed consolidated financial results. Quest Capital In August 2019, the Company’s subsidiary, SA Stone Wealth Management, executed an asset purchase agreement to acquire certain client accounts of Quest Capital Strategies, Inc. The asset purchase agreement was subject to FINRA approval and other conditions of closing. FINRA approval was obtained and the other conditions of closing were fulfilled with the closing of the transaction occurring on December 9, 2019. The cash purchase price for the acquired client accounts was equal to $1.7 million . This transaction was accounted for as an asset acquisition at cost. The cash purchase price was allocated to the fair value of the client lists and relationships obtained and has been assigned, and will be amortized, over a useful life of seven years. Tellimer In December 2019, the Company executed a definitive purchase agreement to acquire the brokerage businesses of Tellimer Group. This transaction involves the stock purchase of 100% of Exotix Partners, LLP, based in the United Kingdom, and the stock purchase of 100% of Tellimer Capital Ltd based in Nigeria. The closing of this transaction is subject to limited conditions including regulatory approval in the relevant jurisdictions. The cash purchase price is equal to the net tangible book value of the acquired entities upon closing. Regulatory approval for the acquisition of Exotix Partners, LLP, was obtained during the three months ended March 31, 2020, with the transaction closing on April 1, 2020. The cash purchase price for the acquisition of Exotix Partners, LLP, was $4.7 million . The preliminary allocation of the cash purchase price to the fair value of assets acquired and liabilities assumed has not yet been completed. IFCM Commodities On January 2, 2020, the Company’s wholly owned subsidiary, INTL Netherlands B.V., executed and closed on a stock purchase agreement to acquire 100% of IFCM Commodities GmbH (“IFCM”) based in Germany. IFCM specializes in providing commodity price risk management solutions for base metals serving clients across Germany and continental Europe and historically introduced clients to INTL FCStone Ltd. This purchase is part of the Company’s overall strategic plan to expand the Company’s footprint in Germany and continental Europe in order to handle European clients and regional metals business following Brexit. The cash purchase price of $1.9 million was equal to net tangible book value upon closing plus a premium of $1.0 million . The excess of the cash consideration over the fair value of the net tangible assets acquired on the closing date was allocated to the fair value of IFCM’s client relationships. This client base intangible asset has been assigned, and will be amortized over, a useful of five years. The acquired business has been assigned to the Company’s Commercial Hedging reportable segment. The revenues and net income contributed by the acquired business during the three months ended March 31, 2020, were not material to the Company’s condensed consolidated financial results. GIROXX In January 2020, the Company’s wholly owned subsidiary, INTL FCStone Ltd, executed a stock purchase agreement to acquire 100% of GIROXX Gmbh based in Germany. Through its digital platform, GIROXX Gmbh provides online payment and foreign exchange hedging services to small and medium sized enterprises in Germany, Austria, and Switzerland. The Company offers a wide range of financial services including advisory and execution services in commodities, which will be offered to GIROXX’s institutional client base. This purchase completes a series of acquisitions and restructuring to ensure that all clients of the Company are secure with their continuity of service and market access following Brexit. The closing of the transaction was conditional upon the approval of financial services regulators in Germany, which was obtained in April 2020 with the transaction closing in May 2020. The preliminary cash purchase price was approximately $4.4 million . The preliminary allocation of the cash purchase price to the fair value of assets acquired and liabilities assumed has not yet been completed. Gain Capital On February 26, 2020, the Company entered into an definitive agreement to acquire Gain Capital Holdings, Inc. (“Gain”). The Company agreed to acquire Gain for $6.00 per share in an all-cash transaction representing approximately $236.3 million in equity value. Gain is a global provider of trading services and solutions to institutional and retail investors, specializing in both over-the-counter (“OTC”) products and exchange-traded futures and options on futures. Gain provides its clients with access to a diverse range of global OTC financial markets, including spot foreign exchange, precious metals, and contracts for a difference. As a result of the acquisition, the Company will add a new digital platform to its global financial network, significantly expand its offerings to retail clients, as well as add a complementary exchange-traded futures and options on futures business. The acquisition of Gain will also accelerate the digitization of the Company’s trading platforms. The transaction is expected to close in the second half of calendar year 2020, subject to approval by Gain’s shareholders, regulatory approvals, and customary closing conditions. In connection with the agreement, the Company has obtained commitments for up to $350.0 million in debt financing for the acquisition.

Segment Analysis (Notes)

Segment Analysis (Notes)	6 Months Ended
	Mar. 31, 2020
Segment Analysis [Abstract]
Segment Reporting Disclosure [Text Block]	Segment Analysis The Company reports its operating segments based on services provided to clients. 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 Capital Markets, Debt Capital Markets and Asset Management) • Physical Commodities (includes components Precious Metals and Physical Ag & Energy) • Clearing and Execution Services (includes components Exchange-Traded Futures & Options, FX Prime Brokerage, Correspondent Clearing, Independent Wealth Management, and Derivative Voice Brokerage) The total revenues reported combine gross revenues for the physical commodities business for subsidiaries that are not broker-dealers and net revenues for all other businesses. In order to reflect the way that the Company’s management views the results, the table below also reflects the segment contribution to ‘operating revenues’, which is shown on the face of the condensed consolidated income statements and which is calculated by deducting physical commodities cost of sales from total revenues. Segment data includes the profitability measure of net contribution by segment. Net contribution is one of the key measures used by management to assess the performance of each segment and for decisions regarding the allocation of the Company’s resources. Net contribution is calculated as revenue less direct cost of sales, transaction-based clearing expenses, variable compensation, introducing broker commissions, and interest expense. Variable compensation paid to risk management consultants/traders generally represents a fixed percentage of revenues generated, and in some cases, revenues generated less transaction-based clearing expenses, base salaries and an overhead allocation. Segment data also includes segment income which is calculated as net contribution less non-variable direct expenses of the segment. These non-variable direct expenses include trader base compensation and benefits, operational employee compensation and benefits, communication and data services, business development, professional fees, bad debt expense and other direct expenses. Inter-segment revenues, expenses, receivables and payables are eliminated upon consolidation, except revenues and expenses related to foreign currency transactions undertaken on an arm’s length basis by the foreign exchange trading business for the securities business. The foreign exchange trading business competes for this business as it does any other business. If its rates are not competitive, the securities businesses buy or sell their foreign currency through other market participants. On a recurring basis, the Company sweeps excess cash from certain U.S. operating segments to a centralized corporate treasury function in exchange for an intercompany receivable asset. The intercompany receivable asset is eliminated during consolidation, and therefore this practice may impact reported total assets between segments. Information for the reportable segments is shown in accordance with the Segment Reporting Topic of the ASC as follows Three Months Ended March 31, Six Months Ended March 31, (in millions) 2020 2019 2020 2019 Total revenues: Commercial Hedging $ 101.7 $ 80.6 $ 171.4 $ 140.4 Global Payments 29.4 27.4 60.8 57.1 Securities 117.9 72.6 199.0 141.6 Physical Commodities 20,023.5 6,940.9 31,011.8 13,242.7 Clearing and Execution Services 96.5 73.6 172.4 168.8 Corporate Unallocated 4.0 4.1 9.2 7.0 Eliminations (6.7 ) (7.0 ) (13.3 ) (13.2 ) Total $ 20,366.3 $ 7,192.2 $ 31,611.3 $ 13,744.4 Operating revenues: Commercial Hedging $ 101.7 $ 80.6 $ 171.4 $ 140.4 Global Payments 29.4 27.4 60.8 57.1 Securities 117.9 72.6 199.0 141.6 Physical Commodities 24.0 19.8 44.1 34.1 Clearing and Execution Services 96.5 73.6 172.4 168.8 Corporate Unallocated 4.0 4.1 9.2 7.0 Eliminations (6.7 ) (7.0 ) (13.3 ) (13.2 ) Total $ 366.8 $ 271.1 $ 643.6 $ 535.8 Net operating revenues (loss): Commercial Hedging $ 84.2 $ 65.8 $ 138.6 $ 111.1 Global Payments 28.0 25.8 57.8 54.2 Securities 78.1 32.0 121.2 64.1 Physical Commodities 19.5 15.1 35.4 25.5 Clearing and Execution Services 37.1 31.0 67.1 68.5 Corporate Unallocated (3.5 ) (4.5 ) (6.2 ) (9.2 ) Total $ 243.4 $ 165.2 $ 413.9 $ 314.2 Net contribution: (Revenues less cost of sales of physical commodities, transaction-based clearing expenses, variable compensation, introducing broker commissions and interest expense) Commercial Hedging $ 59.1 $ 49.3 $ 97.9 $ 79.9 Global Payments 22.6 21.0 46.4 44.1 Securities 50.5 20.1 77.9 41.9 Physical Commodities 13.8 11.5 25.1 18.6 Clearing and Execution Services 28.9 23.4 53.4 53.1 Total $ 174.9 $ 125.3 $ 300.7 $ 237.6 Segment income: (Net contribution less non-variable direct segment costs) Commercial Hedging $ 35.8 $ 30.2 $ 57.3 $ 43.5 Global Payments 17.2 15.8 36.1 34.4 Securities 38.4 11.8 55.1 27.8 Physical Commodities 9.6 7.8 17.2 13.7 Clearing and Execution Services 16.3 11.6 27.4 29.3 Total $ 117.3 $ 77.2 $ 193.1 $ 148.7 Reconciliation of segment income to income before tax: Segment income $ 117.3 $ 77.2 $ 193.1 $ 148.7 Net costs not allocated to operating segments 61.2 51.7 115.4 98.8 Other gain — 5.4 0.1 5.4 Income before tax $ 56.1 $ 30.9 $ 77.8 $ 55.3 (in millions) As of March 31, 2020 As of September 30, 2019 Total assets: Commercial Hedging $ 2,309.7 $ 2,041.0 Global Payments 298.0 278.3 Securities 5,109.4 5,219.1 Physical Commodities 458.1 357.8 Clearing and Execution Services 2,448.9 1,892.1 Corporate Unallocated 246.8 147.8 Total $ 10,870.9 $ 9,936.1

Basis of Presentation and Con_2

Basis of Presentation and Consolidation and Recently Issued Accounting Standards (Policies)	6 Months Ended
	Mar. 31, 2020
Basis of Presentation and Consolidation [Abstract]
Basis of Accounting, Policy [Policy Text Block]	The accompanying unaudited condensed consolidated balance sheet as of September 30, 2019 , which has been derived from the audited consolidated balance sheet of September 30, 2019 , and the unaudited interim condensed consolidated financial statements have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”). Certain information and disclosures normally included in annual consolidated financial statements prepared in accordance with accounting principles generally accepted in the United States of America (“U.S. GAAP”) have been condensed or omitted pursuant to those rules and regulations. The Company believes that the disclosures made are adequate to make the information presented not misleading. In the opinion of management, all adjustments (consisting of normal recurring accruals) considered necessary for a fair presentation of the condensed consolidated financial statements for the interim periods presented have been reflected as required by Rule 10-01 of Regulation S-X. Operating results for interim periods are not necessarily indicative of the results that may be expected for the full year. These interim condensed consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and related notes contained in the Company’s Annual Report on Form 10-K for the fiscal year ended September 30, 2019 filed with the SEC.
Consolidation, Policy [Policy Text Block]	These condensed consolidated financial statements include the accounts of INTL FCStone Inc. and all other entities in which the Company has a controlling financial interest. All material intercompany transactions and balances have been eliminated in consolidation.
Fiscal Period, Policy [Policy Text Block]	The Company’s fiscal year end is September 30, and the fiscal quarters end on December 31, March 31, June 30 and September 30. Unless otherwise stated, all dates refer to fiscal years and fiscal interim periods.
Use of Estimates, Policy [Policy Text Block]	The preparation of condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent liabilities as of the date of the condensed consolidated financial statements and the reported amounts of revenue and expenses during the reporting period. The most significant of these estimates and assumptions relate to fair value measurement for financial instruments and investments, revenue recognition, the provision for bad debts, valuation of inventories, valuation of goodwill and intangible assets, incomes taxes, and contingencies. Although these and other estimates and assumptions are based on the best available information, actual results could be materially different from these estimates.
Reclassification, Policy [Policy Text Block]
New Accounting Pronouncement or Change in Accounting Principle, Description	Accounting Standards Adopted In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2016-02, Leases (Topic 842). This update requires a lessee to recognize on the balance sheet a liability to make lease payments and a corresponding right-of-use asset. The guidance also requires certain qualitative and quantitative disclosures about the amount, timing and uncertainty of cash flows arising from leases. In July 2018, the FASB issued ASU 2018-10, Codification Improvements to Topic 842, Leases and ASU 2018-11, Leases (Topic 842) Targeted Improvements. In March 2019, the FASB issued ASU 2019-01, Leases (Topic 842) Codification Improvements. Among other things, this updated guidance provides an optional transition method, which allows for the initial application of the new accounting standard at the adoption date and the recognition of a cumulative-effect adjustment to the opening balance of retained earnings as of the beginning of the period of adoption. The Company adopted the new ASUs on October 1, 2019, using the effective date modified retrospective transition approach and has not restated comparative periods. The Company elected the package of practical expedients permitted under the transition guidance within the new standard, which among other things, allowed the Company to not reassess contracts to determine if they contain leases, lease classification and initial direct costs. The Company’s application of the new standard resulted in changes to the condensed consolidated balance sheet but did not have an impact on the condensed consolidated income statement. See Note 2 for more information. In February 2018, the FASB issued ASU 2018-02, Income Statement – Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income. The amendments in this updated standard allow a reclassification from accumulated other comprehensive income to retained earnings for stranded tax effects resulting from the Tax Cuts and Jobs Act of 2017. The Company adopted this standard on October 1, 2019 and, as a result, recorded a $0.7 million reclassification between accumulated other comprehensive loss, net and retained earnings.

Earnings per Share (Policies)

Earnings per Share (Policies)	6 Months Ended
	Mar. 31, 2020
Earnings Per Share [Abstract]
Earnings Per Share, Potentially Dilutive Securities	The Company presents basic and diluted earnings per share (“EPS”) using the two-class method which requires all outstanding unvested share-based payment awards that contain rights to non-forfeitable dividends and therefore participate in undistributed earnings with common stockholders be included in computing earnings per share. Under the two-class method, net income is reduced by the amount of dividends declared in the period for each class of common stock and participating security. The remaining undistributed earnings are then allocated to common stock and participating securities, based on their respective rights to receive dividends. Restricted stock awards granted to certain employees and directors contain non-forfeitable rights to dividends at the same rate as common stock and are considered participating securities. Basic EPS has been computed by dividing net income by the weighted-average number of common shares outstanding.

Income Taxes (Policies)

Income Taxes (Policies)	6 Months Ended
	Mar. 31, 2020
Income Taxes [Abstract]
Income Tax, Policy [Policy Text Block]	Note 17 – Income Taxes The income tax provision for interim periods is comprised of income tax on jurisdiction-level income (loss) figures provided at the most recent estimated annual effective income tax rate, adjusted for the income tax effect of discrete items. Management uses an estimated annual effective income tax rate based on the forecasted pretax income (loss) and statutory tax rates in the various jurisdictions in which it operates. The Company’s effective income tax rate differs from the U.S. statutory income tax rate primarily due to state and local taxes, global intangible low taxed income (“GILTI”), and differing statutory tax rates applied to the income of non-U.S. subsidiaries. The Company records the tax effect of certain discrete items, including the effects of changes in tax laws, tax rates and adjustments with respect to valuation allowances or other unusual or nonrecurring tax adjustments, in the interim period in which they occur, as an addition to, or reduction from, the income tax provision, rather than being included in the estimated effective annual income tax rate. In addition, jurisdictions with a projected loss for the year or a year-to-date loss where no income tax benefit can be recognized are excluded from the estimated annual effective income tax rate. The Company is required to assess its deferred tax assets and the need for a valuation allowance at each reporting period. This assessment requires judgment on the part of management with respect to benefits that may be realized. The Company will record a valuation allowance against deferred tax assets when it is considered more likely than not that all or a portion of the deferred tax assets will not be realized. Current and Prior Period Tax Expense Income tax expense of $16.8 million and $7.5 million for the three months ended March 31, 2020 and 2019 , respectively, and income tax expense of $22.2 million and $13.7 million for the six months ended March 31, 2020 and 2019 reflects estimated federal, foreign, state and local income taxes. For the three months ended March 31, 2020 and 2019 , the Company’s effective tax rate was 30% and 24% , respectively. For the three months ended March 31, 2020 and 2019, the effective rate was higher than the U.S. federal statutory rate of 21% due to U.S. state and local taxes, GILTI, U.S. and foreign permanent differences, and the amount of foreign earnings taxed at higher tax rates. Pre-tax income increased significantly in the three months ended March 31, 2020 as compared both to the prior quarter and the prior year. As a result of the significant increase in pre-tax income, the annual forecasted effective tax rate increased 0.6% due to state and local taxes on higher U.S.income, compared to the prior quarter ended December 31, 2019. Non-deductible compensation due to Sec. 162(m) limitations increased the effective tax rate by 0.4% as compared to the prior quarter. The amount of foreign earnings taxed at higher tax rates increased by 0.7% from the prior quarter. For the six months ended March 31, 2020 and 2019 , the Company’s effective tax rate was 29% and 25% , respectively. For the six months ended March 31, 2020 and 2019, the effective rate was higher than the U.S. federal statutory rate of 21% due to U.S. state and local taxes, GILTI, U.S. and foreign permanent differences, and the amount of foreign earnings taxed at higher tax rates. The estimated GILTI tax expense increased the effective rate approximately 1.2% and 1.3% for the six months ended March 31, 2020 and 2019 , respectively. The amount of foreign earnings taxed at higher rates increased the effective tax rate approximately 3.3% and 0.5% for six months ended March 31, 2020 and 2019 , respectively. 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 March 31, 2020 and September 30, 2019, the Company has net operating loss carryforwards for U.S. federal, state, local, and foreign income tax purposes of $7.1 million , net of valuation allowances, which are available to offset future taxable income in these jurisdictions. The state and local net operating loss carryforwards of $5.6 million , net of valuation allowance, begin to expire after September 2020. INTL Asia Pte. Ltd. has a Singapore net operating loss carryforward of $0.2 million . This Singapore net operating loss has an indefinite carryforward and, in the judgment of management, is more likely than not to be realized. As a result of the Tax Cuts and Jobs Act of 2017, the alternative minimum tax (“AMT”) credit carryforward deferred tax asset has been reclassified to income taxes receivable. As a result of the Coronavirus Aid, Relief, and Economic Security Act (CARES act), the AMT credit carryforward is refundable on the fiscal year 2019 tax return. In fiscal 2018, the Company generated $5.1 million in foreign tax credit carryforwards as part of the mandatory repatriation transition tax. These credits expire in fiscal year 2028. In the judgment of management, it is more likely than not that sufficient taxable income will be earned to utilize the foreign tax credit carryforwards during the current fiscal year. The valuation allowance for deferred tax assets as of March 31, 2020 and September 30, 2019 was $8.4 million and $8.5 million , respectively. The valuation allowances as of March 31, 2020 and September 30, 2019 were primarily related to U.S., state and local net operating loss carryforwards and foreign net operating loss carryforwards that, in the judgment of management, are not more likely than not to be realized. As of March 31, 2020 and September 30, 2019, the Company had accumulated undistributed earnings generated by its foreign subsidiaries of approximately $393.9 million and $383.5 million , respectively. The repatriation of these amounts would not be subject to U.S. federal income tax, but may be subject to applicable foreign withholding and state taxes in the relevant jurisdictions. The Company does not intend to distribute earnings in a taxable manner, and therefore intends to limit distributions to earnings previously taxed in the U.S., or earnings that would qualify for the 100 percent dividends received deduction, and earnings that would not result in any significant foreign withholding or state taxes. The Company has repatriated $30.0 million and $13.0 million as of March 31, 2020 and September 30, 2019, respectively, of earnings previously taxed in the U.S. resulting in no significant incremental taxes upon repatriation. Therefore, the Company has not recognized a deferred tax liability on its investment in foreign subsidiaries. The Company and its subsidiaries file income tax returns with the U.S. federal and various U.S. state and local, as well as foreign jurisdictions. The Company has open tax years ranging from September 30, 2012 through September 30, 2019 with U.S. federal and state and local taxing authorities. During the three months ending March 31, 2020, the Company closed their examination with the U.S. Internal Revenue Service for the 2016 tax year with no adjustments required. In the United Kingdom (“U.K.”), the Company has open tax years ending September 30, 2017 to September 30, 2019. The Company is currently under examination by HM Revenue and Customs in the UK for the 2017 tax year; however, no additional tax liability is expected. In Brazil, the Company has open tax years ranging from December 31, 2014 through December 31, 2019. In Argentina, the Company has open tax years ranging from September 30, 2012 to September 30, 2019. In Singapore, the Company has open tax years ranging from September 30, 2015 to September 30, 2019 and is currently under examination by the Inland Revenue Authority of Singapore for the year ended September 30, 2017; however, no additional tax liability is expected.

Leases Operating Lease Liabilit

Leases Operating Lease Liability Maturities (Tables)	6 Months Ended
	Mar. 31, 2020
Operating Lease Liabilities Maturities [Abstract]
Lessee, Operating Lease, Liability, Maturity [Table Text Block]	Remainder of 2020 $ 6.0 2021 10.3 2022 7.7 2023 6.1 2024 4.3 After 2024 3.5 Total lease payments (2) 37.9 Less: interest 3.7 Present value of lease liabilities $ 34.2
Lease, Cost [Table Text Block]	Three Months Ended March 31, Six Months Ended March 31, 2020 2020 Operating lease costs (1) $ 3.5 $ 7.0 Supplemental cash flow information and non-cash activity: Cash paid for amounts included in the measurement of operating lease liabilities $ 2.8 $ 5.5 Right-of-use assets obtained in exchange for operating lease liabilities $ 0.4 $ 35.0 Lease term and discount rate information: Weighted average remaining lease term (years) 4.21 Weighted average discount rate 5.1 %
Lessee, Operating Lease, Disclosure [Table Text Block]	2020 $ 11.2 2021 9.9 2022 7.5 2023 6.2 2024 5.8 Thereafter 2.6 $ 43.2

Revenue from Contracts with C_2

Revenue from Contracts with Clients Disaggregation of Revenues Table (Tables)	6 Months Ended
	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue [Table Text Block]	Three Months Ended March 31, Six Months Ended March 31, 2020 2019 2020 2019 Revenues from contracts with clients: Commission and clearing fees: Sales-based: Exchange-traded futures and options $ 40.1 $ 31.2 $ 72.5 $ 70.3 OTC derivative brokerage 6.7 7.3 12.2 16.2 Equities and fixed income 7.1 3.6 11.4 6.8 Mutual funds 1.6 1.9 2.9 4.5 Insurance and annuity products 2.4 1.5 4.5 3.0 Other 0.5 0.5 0.8 0.7 Total sales-based commission 58.4 46.0 104.3 101.5 Trailing: Mutual funds 3.5 3.0 6.6 6.2 Insurance and annuity products 4.0 3.4 7.7 7.1 Total trailing commission 7.5 6.4 14.3 13.3 Clearing fees 41.6 26.8 71.1 59.4 Trade conversion fees 4.2 3.3 5.7 4.9 Other 4.9 2.6 8.4 5.5 Total commission and clearing fees: 116.6 85.1 203.8 184.6 Consulting, management, and account fees: Underwriting fees 0.2 0.2 0.4 0.5 Asset management fees 8.7 6.0 16.2 12.2 Advisory and consulting fees 5.7 4.7 11.3 9.7 Sweep program fees 3.6 4.1 7.6 7.9 Client account fees 3.1 2.5 6.1 5.2 Other 1.3 1.6 2.3 2.7 Total consulting, management, and account fees 22.6 19.1 43.9 38.2 Total revenues from contracts with clients $ 139.2 $ 104.2 $ 247.7 $ 222.8 Method of revenue recognition: Point-in-time $ 113.7 $ 83.0 $ 198.3 $ 179.7 Time elapsed 25.5 21.2 49.4 43.1 Total revenues from contracts with clients 139.2 104.2 247.7 222.8 Other sources of revenues Physical precious metals trading 19,694.7 6,660.9 30,352.7 12,616.4 Physical agricultural and energy product trading 322.2 268.6 642.2 608.9 Principal gains, net 168.5 110.3 281.0 203.1 Interest income 41.7 48.2 87.7 93.2 Total revenues $ 20,366.3 $ 7,192.2 $ 31,611.3 $ 13,744.4 Primary geographic region: United States $ 585.6 $ 456.6 $ 1,097.9 $ 983.6 Europe 150.0 53.8 261.6 107.1 South America 16.3 12.4 31.5 23.9 Middle East and Asia 19,613.3 6,667.3 30,218.8 12,625.9 Other 1.1 2.1 1.5 3.9 Total revenues $ 20,366.3 $ 7,192.2 $ 31,611.3 $ 13,744.4

Earnings per Share (Tables)

Earnings per Share (Tables)	6 Months Ended
	Mar. 31, 2020
Earnings Per Share [Abstract]
Schedule of Calculation of Numerator and Denominator in Earnings Per Share [Table Text Block]	Basic EPS has been computed by dividing net income by the weighted-average number of common shares outstanding. The following is a reconciliation of the numerator and denominator of the diluted earnings per share computations for the periods presented below. Three Months Ended March 31, Six Months Ended March 31, (in millions, except share amounts) 2020 2019 2020 2019 Numerator: Net income $ 39.3 $ 23.4 $ 55.6 $ 41.6 Less: Allocation to participating securities (0.9 ) (0.4 ) (1.2 ) (0.7 ) Net income allocated to common stockholders $ 38.4 $ 23.0 $ 54.4 $ 40.9 Denominator: Weighted average number of: Common shares outstanding 18,872,937 18,753,490 18,811,268 18,706,104 Dilutive potential common shares outstanding: Share-based awards 317,016 251,303 321,229 293,785 Diluted weighted-average common shares 19,189,953 19,004,793 19,132,497 18,999,889

Assets and Liabilities, at Fa_2

Assets and Liabilities, at Fair Value (Tables)	6 Months Ended
	Mar. 31, 2020
Assets and Liabilities, at Fair Value [Abstract]
Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block]	The following tables set forth the Company’s financial and nonfinancial assets and liabilities accounted for at fair value, on a recurring basis, as of March 31, 2020 by level in the fair value hierarchy. March 31, 2020 (in millions) Level 1 Level 2 Level 3 Netting (1) Total Assets: Certificates of deposit $ 9.2 $ — $ — $ — $ 9.2 Money market mutual funds 7.9 — — — 7.9 Cash and cash equivalents 17.1 — — — 17.1 Commodities warehouse receipts 7.9 — — — 7.9 U.S. Treasury obligations 0.2 — — — 0.2 Securities and other assets segregated under federal and other regulations 8.1 — — — 8.1 U.S. Treasury obligations 350.4 — — — 350.4 "To be announced" (TBA) and forward settling securities — 80.5 — (3.5 ) 77.0 Foreign government obligations 8.1 — — — 8.1 Derivatives 5,220.8 57.5 — (5,335.1 ) (56.8 ) Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net 5,579.3 138.0 — (5,338.6 ) 378.7 Equity securities 184.7 19.6 — — 204.3 Corporate and municipal bonds — 43.5 — — 43.5 U.S. Treasury obligations 294.2 — — — 294.2 U.S. government agency obligations — 201.6 — — 201.6 Foreign government obligations 2.6 — — — 2.6 Agency mortgage-backed obligations — 1,504.0 — — 1,504.0 Asset-backed obligations — 16.4 — — 16.4 Derivatives 0.7 1,990.8 — (1,874.9 ) 116.6 Commodities leases — 28.6 — (2.3 ) 26.3 Commodities warehouse receipts 100.5 — — — 100.5 Exchange firm common stock 10.4 — — — 10.4 Mutual funds and other 5.3 — — — 5.3 Financial instruments owned 598.4 3,804.5 — (1,877.2 ) 2,525.7 Physical commodities inventory 26.3 167.8 — — 194.1 Total assets at fair value $ 6,229.2 $ 4,110.3 $ — $ (7,215.8 ) $ 3,123.7 Liabilities: Accounts payable and other accrued liabilities - contingent liabilities — — 1.8 — 1.8 TBA and forward settling securities — 98.3 — (3.5 ) 94.8 Derivatives 5,379.7 194.5 — (5,573.2 ) 1.0 Payable to broker-dealers, clearing organizations and counterparties 5,379.7 292.8 — (5,576.7 ) 95.8 Equity securities 135.2 40.3 — — 175.5 Foreign government obligations 2.1 — — — 2.1 Corporate and municipal bonds — 28.1 — — 28.1 U.S. Treasury obligations 213.6 — — — 213.6 U.S. government agency obligations — 13.6 — — 13.6 Agency mortgage-backed obligations — 15.0 — — 15.0 Derivatives — 2,035.4 — (1,882.6 ) 152.8 Commodities leases — 102.9 — — 102.9 Financial instruments sold, not yet purchased 350.9 2,235.3 — (1,882.6 ) 703.6 Total liabilities at fair value $ 5,730.6 $ 2,528.1 $ 1.8 $ (7,459.3 ) $ 801.2 (1) Represents cash collateral and the impact of netting across the levels of the fair value hierarchy. Netting among positions classified within the same level is included in that level. The following table sets forth the Company’s financial and nonfinancial assets and liabilities accounted for at fair value, on a recurring basis, as of September 30, 2019 by level in the fair value hierarchy. September 30, 2019 (in millions) Level 1 Level 2 Level 3 Netting (1) Total Assets: Certificates of deposit $ 4.9 $ — $ — $ — $ 4.9 Money market mutual funds 8.9 — — — 8.9 Cash and cash equivalents 13.8 — — — 13.8 Commodities warehouse receipts 6.2 — — — 6.2 U.S. Treasury obligations 299.8 — — — 299.8 Securities and other assets segregated under federal and other regulations 306.0 — — — 306.0 U.S. Treasury obligations 593.9 — — — 593.9 TBA and forward settling securities — 9.8 — (1.5 ) 8.3 Foreign government obligations 9.9 — — — 9.9 Derivatives 3,131.2 43.2 — (3,159.6 ) 14.8 Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net 3,735.0 53.0 — (3,161.1 ) 626.9 Equity securities 159.5 9.0 — — 168.5 Corporate and municipal bonds — 80.0 — — 80.0 U.S. Treasury obligations 248.7 — — — 248.7 U.S. government agency obligations — 447.1 — — 447.1 Foreign government obligations 0.5 — — — 0.5 Agency mortgage-backed obligations — 1,045.0 — — 1,045.0 Asset-backed obligations — 29.1 — — 29.1 Derivatives 1.0 486.3 — (420.8 ) 66.5 Commodities leases — 28.6 — — 28.6 Commodities warehouse receipts 48.4 — — — 48.4 Exchange firm common stock 12.7 — — — 12.7 Mutual funds and other 0.1 — — — 0.1 Financial instruments owned 470.9 2,125.1 — (420.8 ) 2,175.2 Physical commodities inventory 7.1 144.8 — — 151.9 Total assets at fair value $ 4,532.8 $ 2,322.9 $ — $ (3,581.9 ) $ 3,273.8 Liabilities: Accounts payable and other accrued liabilities - contingent liabilities $ — $ — $ 1.8 $ — $ 1.8 TBA and forward settling securities — 6.8 — (1.5 ) 5.3 Derivatives 3,079.1 38.3 — (3,117.1 ) 0.3 Payable to broker-dealers, clearing organizations and counterparties 3,079.1 45.1 — (3,118.6 ) 5.6 Equity securities 147.3 10.8 — — 158.1 Corporate and municipal bonds — 39.2 — — 39.2 U.S. Treasury obligations 272.3 — — — 272.3 U.S. government agency obligations — 43.8 — — 43.8 Agency mortgage-backed obligations — 29.6 — — 29.6 Derivatives — 480.3 — (422.2 ) 58.1 Commodities leases — 113.7 — — 113.7 Financial instruments sold, not yet purchased 419.6 717.4 — (422.2 ) 714.8 Total liabilities at fair value $ 3,498.7 $ 762.5 $ 1.8 $ (3,540.8 ) $ 722.2 (1) Represents cash collateral and the impact of netting across the levels of the fair value hierarchy. Netting among positions classified within the same level is included in that level.

Financial Instruments with Of_2

Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk (Tables)	6 Months Ended
	Mar. 31, 2020
Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk [Abstract]
Schedule of Derivative Instruments [Table Text Block]	Listed below are the fair values of the Company’s derivative assets and liabilities as of March 31, 2020 and September 30, 2019 . Assets represent net unrealized gains and liabilities represent net unrealized losses. March 31, 2020 September 30, 2019 (in millions) Assets (1) Liabilities (1) Assets (1) Liabilities (1) Derivative contracts not accounted for as hedges: Exchange-traded commodity derivatives $ 3,201.2 $ 3,524.6 $ 1,437.1 $ 1,463.4 OTC commodity derivatives 640.1 806.0 84.2 106.2 Exchange-traded foreign exchange derivatives 15.6 18.6 36.9 33.5 OTC foreign exchange derivatives 1,306.5 1,323.3 403.2 368.8 Exchange-traded interest rate derivatives 1,613.2 1,514.7 900.1 882.0 OTC interest rate derivatives 101.7 100.6 42.1 43.6 Exchange-traded equity index derivatives 391.5 321.8 758.1 700.2 TBA and forward settling securities 80.5 98.3 9.8 6.8 Gross fair value of derivative contracts 7,350.3 7,707.9 3,671.5 3,604.5 Impact of netting and collateral (7,213.5 ) (7,459.3 ) (3,581.9 ) (3,540.8 ) Total fair value included in 'Deposits with and receivables from broker-dealers, clearing organizations, and counterparties' $ 20.2 $ 23.1 Total fair value included in 'Financial instruments owned, at fair value $ 116.6 $ 66.5 Total fair value included in 'Payables to broker-dealers, clearing organizations and counterparties $ 95.8 $ 5.6 Fair value included in 'Financial instruments sold, not yet purchased, at fair value' $ 152.8 $ 58.1 (1) As of March 31, 2020 and September 30, 2019 , the Company’s derivative contract volume for open positions were approximately 10.8 million and 10.6 million contracts, respectively. The Company’s derivative contracts are principally held in its Commercial Hedging and Clearing and Execution Services segments. The Company assists its Commercial Hedging segment clients 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 clients with option products, including combinations of buying and selling puts and calls. The Company mitigates its risk by offsetting the client’s transaction simultaneously with one of the Company’s trading counterparties or with a similar but not identical exchange-traded position. The risk mitigation of these offsetting trades is not within the documented hedging designation requirements of Topic 815. These derivative contracts are traded along with cash transactions because of the integrated nature of the markets for these products. The Company manages the risks associated with derivatives on an aggregate basis along with the risks associated with its proprietary trading and market-making activities in cash instruments as part of its firm-wide risk management policies. In particular, the risks related to derivative positions may be partially offset by inventory, unrealized gains in inventory or cash collateral paid or received. The Company has derivative instruments, which consist of TBA securities and forward settling transactions that are used to manage risk exposures in the trading inventory of the Company’s domestic institutional fixed income business. The fair value on these transactions are recorded in ‘deposits with and receivables from or payables to broker-dealers, clearing organizations and counterparties, net’. Realized and unrealized gains and losses on securities and derivative transactions are reflected in ‘principal gains, net’. As of March 31, 2020 and September 30, 2019 , these transactions are summarized as follows: March 31, 2020 September 30, 2019 (in millions) Gain / (Loss) Notional Amounts Gain / (Loss) Notional Amounts Unrealized gain on TBA securities purchased within deposits with and receivables from broker-dealers, clearing organizations and counterparties and related notional amounts $ 72.9 $ 3,335.4 $ 3.7 $ 1,778.4 Unrealized loss on TBA securities purchased within deposits with and receivables from broker-dealers, clearing organizations and counterparties and related notional amounts $ (1.5 ) $ 554.9 $ (0.6 ) $ 234.5 Unrealized gain on TBA securities sold within payables to broker-dealers, clearing organizations and counterparties and related notional amounts $ 2.0 $ (559.9 ) $ 0.9 $ (451.6 ) Unrealized loss on TBA securities sold within payables to broker-dealers, clearing organizations and counterparties and related notional amounts $ (94.8 ) $ (4,708.7 ) $ (5.9 ) $ (2,788.0 ) Unrealized gain on forward settling securities purchased within deposits with and receivables from broker-dealers, clearing organizations and counterparties and related notional amounts $ 5.6 896.9 $ — $ — Unrealized loss on forward settling securities purchased within payables to broker-dealers, clearing organizations and counterparties and related notional amounts $ — $ — $ (0.3 ) $ 1,243.5 Unrealized gain on forward settling securities sold within deposits with and receivables from broker-dealers, clearing organizations and counterparties and related notional amounts $ — $ — $ 5.2 $ (581.2 ) Unrealized loss on forward settling securities sold within payables to broker-dealers, clearing organizations and counterparties and related notional amounts $ (2.0 ) (712.4 ) $ — $ — (1) The notional amounts of these instruments reflect the extent of the Company's involvement in TBA and forward settling securities and do not represent risk of loss due to counterparty non-performance.
Schedule of Derivative Instruments, Gain (Loss) in Statement of Financial Performance [Table Text Block]	The following table sets forth the Company’s net gains from derivative contracts for the three and six months ended March 31, 2020 and 2019 in accordance with Topic 815. The net gains set forth below are included in ‘Cost of sales of physical commodities’ and ‘principal gains, net’ in the condensed consolidated income statements. Three Months Ended March 31, Six Months Ended March 31, (in millions) 2020 2019 2020 2019 Commodities $ 61.6 $ 36.0 $ 79.8 $ 44.1 Foreign exchange 5.1 1.8 7.3 3.7 Interest rate and equity — 0.7 (0.4 ) (2.6 ) TBA and forward settling securities (34.4 ) 10.6 (35.3 ) 1.3 Net gains from derivative contracts $ 32.3 $ 49.1 $ 51.4 $ 46.5

Physical Commodities Inventor_2

Physical Commodities Inventory Physical Commodities Table (Tables)	6 Months Ended
	Mar. 31, 2020
Inventory Disclosure [Abstract]
Schedule of Inventory, Current [Table Text Block]	(in millions) March 31, September 30, Physical Ag & Energy (1) $ 167.8 $ 144.8 Precious metals - held by broker-dealer subsidiary (2) 26.3 7.1 Precious metals - held by non-broker-dealer subsidiaries (3) 61.1 77.4 Physical commodities inventory $ 255.2 $ 229.3

Goodwill (Tables)

Goodwill (Tables)	6 Months Ended
	Mar. 31, 2020
Goodwill [Abstract]
Schedule of Goodwill [Table Text Block]	The carrying value of goodwill is allocated to the Company’s operating segments as follows: (in millions) March 31, September 30, Commercial Hedging $ 30.2 $ 30.3 Global Payments 7.6 7.6 Securities 4.6 4.6 Physical Commodities 8.7 8.7 Clearing and Execution 1.1 — Goodwill $ 52.2 $ 51.2

Intangible Assets - (Tables)

Intangible Assets - (Tables)	6 Months Ended
	Mar. 31, 2020
Intangible Assets [Abstract]
Schedule of Finite and Indefinite-Lived Intangible Assets [Table Text Block]	The gross and net carrying values of intangible assets as of the balance sheet dates, by major intangible asset class are as follows (in millions): March 31, 2020 September 30, 2019 Gross Amount Accumulated Amortization Net Amount Gross Amount Accumulated Amortization Net Amount Intangible assets subject to amortization: Software programs/platforms $ 5.3 $ (3.2 ) $ 2.1 $ 5.3 $ (3.0 ) $ 2.3 Customer base 28.2 (14.2 ) 14.0 22.1 (12.5 ) 9.6 Total intangible assets subject to amortization: 33.5 (17.4 ) 16.1 27.4 (15.5 ) 11.9 Intangible assets not subject to amortization: Website domains 2.1 — 2.1 2.1 — 2.1 Business licenses 2.7 — 2.7 2.7 — 2.7 Total intangible assets not subject to amortization: 4.8 — 4.8 4.8 — 4.8 Total intangible assets $ 38.3 $ (17.4 ) $ 20.9 $ 32.2 $ (15.5 ) $ 16.7
Schedule of Expected Amortization Expense [Table Text Block]	Amortization expense related to intangible assets was $1.1 million and $0.6 million for the three months ended March 31, 2020 and 2019 , respectively. Amortization expense related to intangible assets was $1.9 million and $1.3 million for the six months ended March 31, 2020 and 2019 , respectively. As of March 31, 2020 , the estimated future amortization expense was as follows: (in millions) Fiscal 2020 (remaining six months) $ 2.0 Fiscal 2021 4.0 Fiscal 2022 2.7 Fiscal 2023 2.5 Fiscal 2024 and thereafter 4.9 Total intangible assets subject to amortization $ 16.1

Credit Facilities (Tables)

Credit Facilities (Tables)	6 Months Ended
	Mar. 31, 2020
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 as of the periods indicated: (in millions) Amounts Outstanding Borrower Security Renewal/Expiration Date Total Commitment March 31, September 30, Committed Credit Facilities Term Loan (1) February 22, 2022 $ 185.0 $ 184.3 (2) $ 167.6 Revolving Line of Credit (1) February 22, 2022 196.5 100.0 70.0 INTL FCStone Inc. 381.5 284.3 237.6 INTL FCStone Financial Inc. None April 2, 2021 75.0 — — FCStone Merchants Services, LLC Certain commodities assets January 29, 2022 260.0 170.0 128.5 INTL FCStone Ltd. None July 14, 2020 50.0 — — $ 766.5 $ 454.3 $ 366.1 Uncommitted Credit Facilities INTL FCStone Financial Inc. Commodities warehouse receipts and certain pledged securities n/a n/a 5.0 — FCStone Merchant Services, LLC Certain commodities assets n/a n/a — 3.4 Note Payable to Bank Monthly installments, due March 2020 and secured by certain equipment — 0.4 Total outstanding borrowings $ 459.3 $ 369.9

Commodity and Other Repurchas_2

Commodity and Other Repurchase Agreements and Collateralized Transactions Schedule of Gross Collateralized Financings by Maturity (Tables)	6 Months Ended
	Mar. 31, 2020
Assets Sold under Agreements to Repurchase [Line Items]
Schedule of Repurchase Agreement Counterparties with Whom Repurchase Agreements Exceed 10 Percent of Stockholders' Equity [Table Text Block]	March 31, 2020 Overnight and Open Less than 30 Days 30-90 Days Over 90 Days Total Securities sold under agreements to repurchase $ 1,535.1 $ 737.2 $ 483.0 $ 45.0 $ 2,800.3 Securities loaned 1,068.8 — — — 1,068.8 Gross amount of secured financing $ 2,603.9 $ 737.2 $ 483.0 $ 45.0 $ 3,869.1 September 30, 2019 Overnight and Open Less than 30 Days 30-90 Days Over 90 Days Total Securities sold under agreements to repurchase $ 1,553.9 $ 565.8 $ 654.0 $ — $ 2,773.7 Securities loaned 1,459.9 — — — 1,459.9 Gross amount of secured financing $ 3,013.8 $ 565.8 $ 654.0 $ — $ 4,233.6

Commodity and Other Repurchas_3

Commodity and Other Repurchase Agreements and Collateralized Transactions Schedule of Collateralized Financings by Collateral Type (Tables)	6 Months Ended
	Mar. 31, 2020
Financial Instruments Owned and Pledged as Collateral [Line Items]
Schedule of Financial Instruments Owned and Pledged as Collateral [Table Text Block]	Securities sold under agreements to repurchase March 31, 2020 September 30, 2019 U.S. Treasury obligations $ 32.2 $ 108.8 U.S. government agency obligations 264.1 359.5 Asset-backed obligations 76.5 96.7 Agency mortgage-backed obligations 2,402.8 2,208.7 Corporate bonds 24.7 — Total securities sold under agreement to repurchase 2,800.3 2,773.7 Securities loaned Equity securities 1,068.8 1,459.9 Total securities loaned 1,068.8 1,459.9 Gross amount of secured financing $ 3,869.1 $ 4,233.6 The following tables provide the netting of securities purchased under agreements to resell, securities sold under agreements to repurchase, securities borrowed and securities loaned as of the periods indicated (in millions): March 31, 2020 Offsetting of collateralized transactions: Gross Amounts Recognized Amounts Offset in the Condensed Consolidated Balance Sheet Net Amounts Presented in the Condensed Consolidated Balance Sheet Securities purchased under agreements to resell $ 1,260.0 $ — $ 1,260.0 Securities borrowed $ 1,063.8 $ — $ 1,063.8 Securities sold under agreements to repurchase $ 2,800.3 $ — $ 2,800.3 Securities loaned $ 1,068.8 $ — $ 1,068.8 September 30, 2019 Offsetting of collateralized transactions: Gross Amounts Recognized Amounts Offset in the Condensed Consolidated Balance Sheet Net Amounts Presented in the Condensed Consolidated Balance Sheet Securities purchased under agreements to resell $ 1,474.4 $ (49.9 ) $ 1,424.5 Securities borrowed $ 1,423.2 $ — $ 1,423.2 Securities sold under agreements to repurchase $ 2,823.6 $ (49.9 ) $ 2,773.7 Securities loaned $ 1,459.9 $ — $ 1,459.9

Capital and Other Regulatory _2

Capital and Other Regulatory Requirements (Tables)	6 Months Ended
	Mar. 31, 2020
Capital and Other Regulatory Requirements [Abstract]
Regulatory Capital Requirements under Banking Regulations [Text Block]	Capital and Other Regulatory Requirements The Company’s activities are subject to significant governmental regulation, both in the United States and in the international jurisdictions in which it operates. The subsidiaries of the Company were in compliance with all of their regulatory requirements as of March 31, 2020. The following table details those subsidiaries with minimum regulatory requirements in excess of $5 million along with the actual balance maintained as of March 31, 2020. (in millions) As of March 31, 2020 Subsidiary Regulatory Authority Jurisdiction Requirement Type Actual Minimum Requirement INTL FCStone Financial Inc. SEC and CFTC United States Net capital $ 175.7 $ 108.3 INTL FCStone Financial Inc. CFTC United States Segregated funds $ 2,543.6 $ 2,485.9 INTL FCStone Financial Inc. CFTC United States Secured funds $ 162.5 $ 150.0 INTL FCStone Financial Inc. (1) SEC United States Customer reserve $ 33.1 $ 66.1 INTL FCStone Ltd Financial Conduct Authority ("FCA") United Kingdom Net capital $ 270.3 $ 140.0 INTL FCStone Ltd FCA United Kingdom Segregated funds $ 437.8 $ 430.1 INTL FCStone Pte. Ltd. Monetary Authority of Singapore ("MAS") Singapore Segregated funds $ 208.2 $ 202.6 (1) As of March 31, 2020 , the Company had $33.1 million deposited in the customer special reserve bank account (“SRBA”). As a result of the reserve requirement determined through the weekly computation, the Company made an additional deposit of $38.1 million to the customer SRBA on April 2, 2020 to meet the customer segregation requirements under SEC Rule 15c3-3. Certain other non-U.S. subsidiaries of the Company are also subject to capital adequacy requirements promulgated by authorities of the countries in which they operate. As of March 31, 2020 , these subsidiaries were in compliance with their local capital adequacy requirements.

Other Expenses (Tables)

Other Expenses (Tables)	6 Months Ended
	Mar. 31, 2020
Other Expenses [Abstract]
Schedule of Other Operating Cost and Expense, by Component [Table Text Block]	Other expenses for the three and six months ended March 31, 2020 and 2019 consisted of the following: Three Months Ended March 31, Six Months Ended March 31, (in millions) 2020 2019 2020 2019 Contingent consideration, net $ 0.1 $ — $ 0.1 $ — Insurance 1.0 0.9 2.0 1.7 Advertising, meetings and conferences 4.2 1.5 5.6 2.9 Office supplies and printing 0.5 0.5 0.9 1.0 Other clearing related expenses 0.6 0.7 1.4 1.1 Other non-income taxes 1.3 1.2 2.6 2.1 Other 2.9 2.6 5.5 5.1 Total other expenses $ 10.6 $ 7.4 $ 18.1 $ 13.9

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Loss) (Tables)	6 Months Ended
	Mar. 31, 2020
Accumulated Other Comprehensive Income (Loss) [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]	The following table summarizes the changes in accumulated other comprehensive loss, net for the six months ended March 31, 2020 . (in millions) Foreign Currency Translation Adjustment Pension Benefits Adjustment Accumulated Other Comprehensive Loss Balances as of September 30, 2019 $ (31.5 ) $ (3.3 ) $ (34.8 ) ASU 2018-02 cumulative transition adjustment — (0.7 ) (0.7 ) Adjusted Balances as of September 30, 2019 (31.5 ) (4.0 ) (35.5 ) Other comprehensive loss (2.7 ) — — (2.7 ) Balances as of March 31, 2020 $ (34.2 ) $ (4.0 ) $ (38.2 )

Segment Analysis (Tables)

Segment Analysis (Tables)	6 Months Ended
	Mar. 31, 2020
Segment Analysis [Abstract]
Schedule of Segment Reporting Information, by Segment [Table Text Block]	Information for the reportable segments is shown in accordance with the Segment Reporting Topic of the ASC as follows Three Months Ended March 31, Six Months Ended March 31, (in millions) 2020 2019 2020 2019 Total revenues: Commercial Hedging $ 101.7 $ 80.6 $ 171.4 $ 140.4 Global Payments 29.4 27.4 60.8 57.1 Securities 117.9 72.6 199.0 141.6 Physical Commodities 20,023.5 6,940.9 31,011.8 13,242.7 Clearing and Execution Services 96.5 73.6 172.4 168.8 Corporate Unallocated 4.0 4.1 9.2 7.0 Eliminations (6.7 ) (7.0 ) (13.3 ) (13.2 ) Total $ 20,366.3 $ 7,192.2 $ 31,611.3 $ 13,744.4 Operating revenues: Commercial Hedging $ 101.7 $ 80.6 $ 171.4 $ 140.4 Global Payments 29.4 27.4 60.8 57.1 Securities 117.9 72.6 199.0 141.6 Physical Commodities 24.0 19.8 44.1 34.1 Clearing and Execution Services 96.5 73.6 172.4 168.8 Corporate Unallocated 4.0 4.1 9.2 7.0 Eliminations (6.7 ) (7.0 ) (13.3 ) (13.2 ) Total $ 366.8 $ 271.1 $ 643.6 $ 535.8 Net operating revenues (loss): Commercial Hedging $ 84.2 $ 65.8 $ 138.6 $ 111.1 Global Payments 28.0 25.8 57.8 54.2 Securities 78.1 32.0 121.2 64.1 Physical Commodities 19.5 15.1 35.4 25.5 Clearing and Execution Services 37.1 31.0 67.1 68.5 Corporate Unallocated (3.5 ) (4.5 ) (6.2 ) (9.2 ) Total $ 243.4 $ 165.2 $ 413.9 $ 314.2 Net contribution: (Revenues less cost of sales of physical commodities, transaction-based clearing expenses, variable compensation, introducing broker commissions and interest expense) Commercial Hedging $ 59.1 $ 49.3 $ 97.9 $ 79.9 Global Payments 22.6 21.0 46.4 44.1 Securities 50.5 20.1 77.9 41.9 Physical Commodities 13.8 11.5 25.1 18.6 Clearing and Execution Services 28.9 23.4 53.4 53.1 Total $ 174.9 $ 125.3 $ 300.7 $ 237.6 Segment income: (Net contribution less non-variable direct segment costs) Commercial Hedging $ 35.8 $ 30.2 $ 57.3 $ 43.5 Global Payments 17.2 15.8 36.1 34.4 Securities 38.4 11.8 55.1 27.8 Physical Commodities 9.6 7.8 17.2 13.7 Clearing and Execution Services 16.3 11.6 27.4 29.3 Total $ 117.3 $ 77.2 $ 193.1 $ 148.7 Reconciliation of segment income to income before tax: Segment income $ 117.3 $ 77.2 $ 193.1 $ 148.7 Net costs not allocated to operating segments 61.2 51.7 115.4 98.8 Other gain — 5.4 0.1 5.4 Income before tax $ 56.1 $ 30.9 $ 77.8 $ 55.3 (in millions) As of March 31, 2020 As of September 30, 2019 Total assets: Commercial Hedging $ 2,309.7 $ 2,041.0 Global Payments 298.0 278.3 Securities 5,109.4 5,219.1 Physical Commodities 458.1 357.8 Clearing and Execution Services 2,448.9 1,892.1 Corporate Unallocated 246.8 147.8 Total $ 10,870.9 $ 9,936.1

Basis of Presentation and Con_3

Basis of Presentation and Consolidation and Recently Issued Accounting Standards (Details) $ in Millions	6 Months Ended
	Mar. 31, 2020	Sep. 30, 2019USD ($)
Basis of Presentation and Consolidation [Abstract]
ASU 2018-02 cumulative transition adjustment		$ 0.7
Number of different types of foreign currencies	140
Number of accounts for customers company-wide	30,000

Leases (Details)

Leases (Details) - USD ($)	3 Months Ended	6 Months Ended
	Mar. 31, 2020	Mar. 31, 2020	Sep. 30, 2019
Leases [Abstract]
Operating right of use assets	$ 31,600,000	$ 31,600,000	$ 0
Operating Lease, Cost	$ 3,500,000	$ 7,000,000
Operating Lease, Weighted Average Remaining Lease Term	4 years 2 months 16 days	4 years 2 months 16 days
Operating Lease, Weighted Average Discount Rate, Percent	5.10%	5.10%
Operating Lease, Payments	$ 2,800,000	$ 5,500,000
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	400,000	35,000,000
Operating lease liabilities	$ 34,200,000	$ 34,200,000	$ 0

Leases Maturities of Operating

Leases Maturities of Operating Lease Liabilities (Details) - USD ($)	Mar. 31, 2020	Sep. 30, 2019
Maturities of Operating Lease Liabilities [Abstract]
Lessee, Operating Lease, Liability, Payments, Due Next Twelve Months	$ 6,000,000
Lessee, Operating Lease, Liability, Payments, Due Year Two	10,300,000
Lessee, Operating Lease, Liability, Payments, Due Year Three	7,700,000
Lessee, Operating Lease, Liability, Payments, Due Year Four	6,100,000
Lessee, Operating Lease, Liability, Payments, Due Year Five	4,300,000
Lessee, Operating Lease, Liability, Payments, Due after Year Five	3,500,000
Lessee, Operating Lease, Liability, Payments, Due	37,900,000
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	3,700,000
Operating lease liabilities	$ 34,200,000	$ 0

Leases Operating Lease Commitme

Leases Operating Lease Commitments Under ASC 840 (Details) $ in Millions	Sep. 30, 2019USD ($)
Commitments and Contingencies Disclosure [Abstract]
Operating Leases, Future Minimum Payments Due, Next Twelve Months	$ 11.2
Operating Leases, Future Minimum Payments, Remainder of Fiscal Year	43.2
Operating Leases, Future Minimum Payments, Due in Two Years	9.9
Operating Leases, Future Minimum Payments, Due in Three Years	7.5
Operating Leases, Future Minimum Payments, Due in Four Years	6.2
Operating Leases, Future Minimum Payments, Due in Five Years	5.8
Operating Leases, Future Minimum Payments, Due Thereafter	$ 2.6

Revenue from Contracts with C_3

Revenue from Contracts with Clients (Details)	3 Months Ended		6 Months Ended
	Mar. 31, 2020Rate	Mar. 31, 2019Rate	Mar. 31, 2020Rate	Mar. 31, 2019Rate
Revenues from Contracts With Clients [Abstract]
Revenues from contracts with clients as a % of total revenues	0.70%	1.40%	0.80%	1.60%
Revenues from contracts with clients as a % of operating revenues	37.90%	38.40%	38.50%	41.60%

Revenue from Contracts with C_4

Revenue from Contracts with Clients Disaggregation of Revenues Table (Details) - USD ($)	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	$ 139,200,000	$ 104,200,000	$ 247,700,000	$ 222,800,000
Revenues	20,366,300,000	7,192,200,000	31,611,300,000	13,744,400,000
Consulting, management, and account fees	22,600,000	19,100,000	43,900,000	38,200,000
Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	113,700,000	83,000,000	198,300,000	179,700,000
Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	25,500,000	21,200,000	49,400,000	43,100,000
UNITED STATES
Disaggregation of Revenue [Line Items]
Revenues	585,600,000	456,600,000	1,097,900,000	983,600,000
Europe [Member]
Disaggregation of Revenue [Line Items]
Revenues	150,000,000	53,800,000	261,600,000	107,100,000
South America [Member]
Disaggregation of Revenue [Line Items]
Revenues	16,300,000	12,400,000	31,500,000	23,900,000
Middle East and Asia [Domain]
Disaggregation of Revenue [Line Items]
Revenues	19,613,300,000	6,667,300,000	30,218,800,000	12,625,900,000
Other (geographic location) [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,100,000	2,100,000	1,500,000	3,900,000
Commission and Clearing Fees [Member]
Disaggregation of Revenue [Line Items]
Revenues	116,600,000	85,100,000	203,800,000	184,600,000
Sales Based Commissions [Domain]
Disaggregation of Revenue [Line Items]
Sales Commissions and Fees	58,400,000	46,000,000	104,300,000	101,500,000
Sales Based Commissions [Domain] | Exhange-Traded Futures and Options [Member]
Disaggregation of Revenue [Line Items]
Revenues	40,100,000	31,200,000	72,500,000	70,300,000
Sales Based Commissions [Domain] | OTC Derivative Brokerage [Member]
Disaggregation of Revenue [Line Items]
Revenues	6,700,000	7,300,000	12,200,000	16,200,000
Sales Based Commissions [Domain] | Equities and Fixed Income Commissions [Member]
Disaggregation of Revenue [Line Items]
Revenues	7,100,000	3,600,000	11,400,000	6,800,000
Sales Based Commissions [Domain] | Mutual Fund Sales Based Commissions [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,600,000	1,900,000	2,900,000	4,500,000
Sales Based Commissions [Domain] | Variable Annuity [Member]
Disaggregation of Revenue [Line Items]
Revenues	2,400,000	1,500,000	4,500,000	3,000,000
Sales Based Commissions [Domain] | Other Sales Based Commissions [Member]
Disaggregation of Revenue [Line Items]
Revenues	500,000	500,000	800,000	700,000
Trailing Commissions [Domain]
Disaggregation of Revenue [Line Items]
Revenues	7,500,000	6,400,000	14,300,000	13,300,000
Trailing Commissions [Domain] | Variable Annuity [Member]
Disaggregation of Revenue [Line Items]
Revenues	4,000,000	3,400,000	7,700,000	7,100,000
Trailing Commissions [Domain] | Mutual Fund Trailing Commissions [Member]
Disaggregation of Revenue [Line Items]
Revenues	3,500,000	3,000,000	6,600,000	6,200,000
Interest Income [Member]
Disaggregation of Revenue [Line Items]
Revenues	41,700,000	48,200,000	87,700,000	93,200,000
Clearing Fees [Domain]
Disaggregation of Revenue [Line Items]
Revenues	41,600,000	26,800,000	71,100,000	59,400,000
Trade Conversion Fees [Domain]
Disaggregation of Revenue [Line Items]
Revenues	4,200,000	3,300,000	5,700,000	4,900,000
Other Commissions [Domain]
Disaggregation of Revenue [Line Items]
Revenues	4,900,000	2,600,000	8,400,000	5,500,000
Consulting, management, and account fees [Domain] | Sweep Program Fees [Member]
Disaggregation of Revenue [Line Items]
Revenues	3,600,000	4,100,000	7,600,000	7,900,000
Consulting, management, and account fees [Domain] | Advisory and Consulting Fees [Member]
Disaggregation of Revenue [Line Items]
Revenues	5,700,000	4,700,000	11,300,000	9,700,000
Consulting, management, and account fees [Domain] | Asset Management [Member]
Disaggregation of Revenue [Line Items]
Revenues	8,700,000	6,000,000	16,200,000	12,200,000
Consulting, management, and account fees [Domain] | Underwriting Fees [Member]
Disaggregation of Revenue [Line Items]
Revenues	200,000	200,000	400,000	500,000
Consulting, management, and account fees [Domain] | Client Account Fees [Member]
Disaggregation of Revenue [Line Items]
Revenues	3,100,000	2,500,000	6,100,000	5,200,000
Consulting, management, and account fees [Domain] | Other Consulting, Management, and Account Fees [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,300,000	1,600,000	2,300,000	2,700,000
Principal or Proprietary Transactions [Member]
Disaggregation of Revenue [Line Items]
Revenues	168,500,000	110,300,000	281,000,000	203,100,000
Sales of physical commodities [Member] | Precious Metals Trading Revenues [Member]
Disaggregation of Revenue [Line Items]
Revenues	19,694,700,000	6,660,900,000	30,352,700,000	12,616,400,000
Sales of physical commodities [Member] | Physical Commodity Origination and Merchandising [Member]
Disaggregation of Revenue [Line Items]
Revenues	$ 322,200,000	$ 268,600,000	$ 642,200,000	$ 608,900,000

Earnings per Share - EPS Reconc

Earnings per Share - EPS Reconciliation (Details) - USD ($)	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Earnings Per Share [Abstract]
Net income	$ 39,300,000	$ 23,400,000	$ 55,600,000	$ 41,600,000
Less: Net income allocated to participating securities	(900,000)	(400,000)	(1,200,000)	(700,000)
Net income allocated to common shareholders	$ 38,400,000	$ 23,000,000	$ 54,400,000	$ 40,900,000
Weighted average number of common shares outstanding	18,872,937	18,753,490	18,811,268	18,706,104
Dilutive potential common shares outstanding:
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	317,016	251,303	321,229	293,785
Diluted weighted-average shares	19,189,953	19,004,793	19,132,497	18,999,889

Earnings per Share - Antiduliti

Earnings per Share - Antidulitive Securities (Details) - shares	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Earnings Per Share [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	945,211	1,032,077	981,088	704,863

Assets and Liabilities, at Fa_3

Assets and Liabilities, at Fair Value - Financial Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2020	Sep. 30, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	$ 1,176.1	$ 1,049.9
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net (including $378.7 and $626.9 at fair value at March 31, 2020 and September 30, 2019, respectively)	3,359.5	2,540.5
Financial Instruments, Owned, at Fair Value	2,525.7	2,175.2
Physical commodities inventory	255.2	229.3
Accounts Payable and Other Accrued Liabilities	184.8	157.5
Payables to Broker-Dealers and Clearing Organizations	(429.2)	(266.2)
Financial Instruments Sold, Not yet Purchased, at Fair Value	703.6	714.8
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	8.1	306
Receivables from Clearing Organizations	378.7	626.9
Financial Instruments, Owned, at Fair Value	2,525.7	2,175.2
Assets, Fair Value Disclosure	3,123.7	3,273.8
Financial Instruments Sold, Not yet Purchased, at Fair Value	703.6
Liabilities, Fair Value Disclosure	801.2	722.2
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	(94.8)	(5.3)
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	(1)	(0.3)
Fair Value, Measurements, Recurring [Member] | Payable to broker-dealers, clearing organizations and counterparties [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations	(95.8)	(5.6)
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	1.8	1.8
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	194.1	151.9
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	16.4	29.1
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	201.6	447.1
Financial Instruments Sold, Not yet Purchased, at Fair Value	13.6	43.8
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	294.2	248.7
Financial Instruments Sold, Not yet Purchased, at Fair Value	213.6	272.3
Fair Value, Measurements, Recurring [Member] | Debt Security, Government, Non-US [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	2.6	0.5
Financial Instruments Sold, Not yet Purchased, at Fair Value	2.1
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	116.6	66.5
Fair Value, Measurements, Recurring [Member] | Commodities leases [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	26.3	28.6
Financial Instruments Sold, Not yet Purchased, at Fair Value	102.9	113.7
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	100.5	48.4
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	10.4	12.7
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	5.3	0.1
Fair Value, Measurements, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	204.3	168.5
Financial Instruments Sold, Not yet Purchased, at Fair Value	175.5	158.1
Fair Value, Measurements, Recurring [Member] | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	43.5	80
Financial Instruments Sold, Not yet Purchased, at Fair Value	28.1	39.2
Fair Value, Measurements, Recurring [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	1,504	1,045
Financial Instruments Sold, Not yet Purchased, at Fair Value	15	29.6
Fair Value, Measurements, Recurring [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	350.4
Fair Value, Measurements, Recurring [Member] | Debt Security, Government, Non-US [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	8.1	9.9
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 Clearing Organizations	77	8.3
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	(56.8)
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	7.9	6.2
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	0.2	299.8
Fair Value, Measurements, Recurring [Member] | Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	7.9	8.9
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	9.2	4.9
Fair Value, Measurements, Recurring [Member] | Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	17.1	13.8
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	0	0
Receivables from Clearing Organizations	(5,338.6)	(3,161.1)
Financial Instruments, Owned, at Fair Value	(1,877.2)	(420.8)
Assets, Fair Value Disclosure	(7,215.8)	(3,581.9)
Financial Instruments Sold, Not yet Purchased, at Fair Value	(1,882.6)	(422.2)
Liabilities, Fair Value Disclosure	(7,459.3)	(3,540.8)
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | TBA and forward settling securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations	3.5	1.5
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations	5,573.2	3,117.1
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Payable to broker-dealers, clearing organizations and counterparties [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations	5,576.7	3,118.6
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Contingent Consideration [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accounts Payable and Other Accrued Liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Physical commodities inventory [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Physical commodities inventory	0	0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | US Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Debt Security, Government, Non-US [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] | Counterparty And Cash Collateral Netting Adjustment [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	(1,874.9)	(420.8)
Financial Instruments Sold, Not yet Purchased, at Fair Value	(1,882.6)	(422.2)
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Commodities leases [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	(2.3)	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Commodities warehouse receipts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Exchange firm common stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Mutual funds and other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Debt Security, Government, Non-US [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | TBA and forward settling securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	(3.5)
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	(5,335.1)
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Commodities warehouse receipts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	0	0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	0	0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Money Market Funds [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] | Counterparty And Cash Collateral Netting Adjustment [Member] | Certificates of Deposit [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	8.1	306
Receivables from Clearing Organizations	5,579.3	3,735
Financial Instruments, Owned, at Fair Value	598.4	470.9
Assets, Fair Value Disclosure	6,229.2	4,532.8
Financial Instruments Sold, Not yet Purchased, at Fair Value	350.9	419.6
Liabilities, Fair Value Disclosure	5,730.6	3,498.7
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]
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	(5,379.7)	(3,079.1)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Payable to broker-dealers, clearing organizations and counterparties [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations	(5,379.7)	(3,079.1)
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	26.3	7.1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Asset-backed Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	294.2	248.7
Financial Instruments Sold, Not yet Purchased, at Fair Value	213.6	272.3
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Debt Security, Government, Non-US [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	2.6	0.5
Financial Instruments Sold, Not yet Purchased, at Fair Value	2.1
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	0.7	1
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Commodities leases [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Commodities warehouse receipts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	100.5	48.4
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	10.4	12.7
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	5.3	0.1
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	184.7	159.5
Financial Instruments Sold, Not yet Purchased, at Fair Value	135.2	147.3
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [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] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	350.4
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Debt Security, Government, Non-US [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	8.1	9.9
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 Clearing Organizations	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	5,220.8
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	7.9	6.2
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	0.2	299.8
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]
Cash and Cash Equivalents, Fair Value Disclosure	7.9	8.9
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	9.2	4.9
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	17.1	13.8
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	0	0
Receivables from Clearing Organizations	138	53
Financial Instruments, Owned, at Fair Value	3,804.5	2,125.1
Assets, Fair Value Disclosure	4,110.3	2,322.9
Financial Instruments Sold, Not yet Purchased, at Fair Value	2,235.3	717.4
Liabilities, Fair Value Disclosure	2,528.1	762.5
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	(98.3)	(6.8)
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]
Payables to Broker-Dealers and Clearing Organizations	(194.5)	(38.3)
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Payable to broker-dealers, clearing organizations and counterparties [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations	(292.8)	(45.1)
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	167.8	144.8
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	16.4	29.1
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	201.6	447.1
Financial Instruments Sold, Not yet Purchased, at Fair Value	13.6	43.8
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Debt Security, Government, Non-US [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 2 [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	1,990.8	486.3
Financial Instruments Sold, Not yet Purchased, at Fair Value	2,035.4	480.3
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commodities leases [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	28.6	28.6
Financial Instruments Sold, Not yet Purchased, at Fair Value	102.9	113.7
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] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	19.6	9
Financial Instruments Sold, Not yet Purchased, at Fair Value	40.3	10.8
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	43.5	80
Financial Instruments Sold, Not yet Purchased, at Fair Value	28.1	39.2
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	1,504	1,045
Financial Instruments Sold, Not yet Purchased, at Fair Value	15	29.6
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Debt Security, Government, Non-US [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | TBA and forward settling securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	80.5	9.8
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	57.5
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Commodities warehouse receipts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Money Market Funds [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 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 2 [Member] | Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	0	0
Receivables from Clearing Organizations	0	0
Financial Instruments, Owned, at Fair Value	0	0
Assets, Fair Value Disclosure	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Liabilities, Fair Value Disclosure	1.8	1.8
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] | Payable to broker-dealers, clearing organizations and counterparties [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payables to Broker-Dealers and Clearing Organizations	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Contingent Consideration [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accounts Payable and Other Accrued Liabilities	1.8	1.8
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	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US Government Agencies Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | 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] | Debt Security, Government, Non-US [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] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Commodities leases [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Commodities warehouse receipts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Exchange firm common stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Mutual funds and other [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Equity 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] | 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] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Debt Security, Government, Non-US [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | TBA and forward settling securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Commodities warehouse receipts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Money Market Funds [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] | 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] | Cash Equivalents [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	$ 0	0
TBA and forward settling securities [Member] | Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		(1.5)
Debt Security, Government, Non-US [Member] | Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		0
Derivative [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net (including $378.7 and $626.9 at fair value at March 31, 2020 and September 30, 2019, respectively)		14.8
Derivative [Member] | Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		(3,159.6)
Derivative [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		3,131.2
Derivative [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		43.2
Derivative [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		0
US Government Debt Securities [Member] | Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		593.9
US Government Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		0
US Government Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		593.9
US Government Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		0
US Government Debt Securities [Member] | Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations		$ 0

Financial Instruments with Of_3

Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - Obligations to Purchase Financial Instruments at a Future Date (Details) - USD ($) $ in Millions	Mar. 31, 2020	Sep. 30, 2019
Financial Instruments Sold, Not yet Purchased, at Fair Value	$ 703.6	$ 714.8
Financial instrument sold, not yet purchased [Member]
Derivative, Fair Value, Net	$ 152.8	$ 58.1

Financial Instruments with Of_4

Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - Gross Derivative Assets and Liabilities by Type and Balance Sheet Location (Details) - USD ($) $ in Millions	Mar. 31, 2020	Sep. 30, 2019
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 7,350.3	$ 3,671.5
Derivative Liability, Fair Value, Gross Liability	7,707.9	3,604.5
Impact of netting and collateral	7,213.5	3,581.9
Impact of netting and collateral	7,459.3	3,540.8
Deposits with and receivables from broker-dealers, clearing organizations, and counterparties [Member]
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	20.2	23.1
Financial instruments owned [Member]
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	116.6	66.5
Payable to broker-dealers, clearing organizations and counterparties [Member]
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	95.8	5.6
Financial instrument sold, not yet purchased [Member]
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	152.8	58.1
Exchange-traded Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	3,201.2	1,437.1
Derivative Liability, Fair Value, Gross Liability	3,524.6	1,463.4
Over the Counter (OTC) Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	640.1	84.2
Derivative Liability, Fair Value, Gross Liability	806	106.2
Foreign Exchange Forward [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	15.6	36.9
Derivative Liability, Fair Value, Gross Liability	18.6	33.5
Over the Counter (OTC) Foreign Exchange Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	1,306.5	403.2
Derivative Liability, Fair Value, Gross Liability	1,323.3	368.8
Exchange-traded interest rate contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	1,613.2	900.1
Derivative Liability, Fair Value, Gross Liability	1,514.7	882
Interest Rate Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	101.7	42.1
Derivative Liability, Fair Value, Gross Liability	100.6	43.6
Equity Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	391.5	758.1
Derivative Liability, Fair Value, Gross Liability	321.8	700.2
TBA and forward settling securities [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	80.5	9.8
Derivative Liability, Fair Value, Gross Liability	$ 98.3	$ 6.8

Financial Instruments with Of_5

Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - Derivatives Volume (Details) number in Millions	Mar. 31, 2020	Sep. 30, 2019
Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk [Abstract]
Derivative, Number of Instruments Held	10.8	10.6

Financial Instruments with Of_6

Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - TBAs and Forward Settling Securities (Details) - USD ($) $ in Millions	Mar. 31, 2020	Sep. 30, 2019
Derivative Asset, Fair Value, Gross Asset	$ 7,350.3	$ 3,671.5
Derivative Liability, Fair Value, Gross Liability	(7,707.9)	(3,604.5)
TBA securities purchased [Member]
Derivative Liability, Notional Amount	(554.9)	(234.5)
Derivative Asset, Notional Amount	(3,335.4)	(1,778.4)
TBA securities sold [Member]
Derivative Liability, Notional Amount	(4,708.7)	(2,788)
Derivative Asset, Notional Amount	(559.9)	(451.6)
Forward settling securities purchased [Member]
Derivative Asset, Notional Amount	(896.9)	0
Over the Counter (OTC) Commodity Contracts [Member]
Derivative Liability, Notional Amount	0	(1,243.5)
Derivative Asset, Notional Amount	0	(581.2)
Deposits and receivables from broker-dealers, clearing organizations and counterparties [Domain] | TBA securities purchased [Member]
Derivative Asset, Fair Value, Gross Asset	72.9	3.7
Derivative Liability, Fair Value, Gross Liability	1.5	0.6
Deposits and receivables from broker-dealers, clearing organizations and counterparties [Domain] | Forward settling securities purchased [Member]
Derivative Asset, Fair Value, Gross Asset	5.6	0
Deposits and receivables from broker-dealers, clearing organizations and counterparties [Domain] | Over the Counter (OTC) Commodity Contracts [Member]
Derivative Asset, Fair Value, Gross Asset	0	5.2
Payable to broker-dealers, clearing organizations and counterparties [Member] | TBA securities sold [Member]
Derivative Asset, Fair Value, Gross Asset	2	0.9
Derivative Liability, Fair Value, Gross Liability	94.8	5.9
Payable to broker-dealers, clearing organizations and counterparties [Member] | Over the Counter (OTC) Commodity Contracts [Member]
Derivative Liability, Notional Amount	(712.4)	0
Derivative Liability, Fair Value, Gross Liability	$ 2	$ 0.3

Financial Instruments with Of_7

Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - Realized Gains/Losses on Derivative Contracts (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Commodity Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	$ 61.6	$ 36	$ 79.8	$ 44.1
Foreign Exchange Forward [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	5.1	1.8	7.3	3.7
Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	0	0.7	(0.4)	(2.6)
TBA and forward settling securities [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	(34.4)	10.6	(35.3)	1.3
Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	$ 32.3	$ 49.1	$ 51.4	$ 46.5

Receivables From Customers, N_2

Receivables From Customers, Net and Notes Receivable, Net - Allowance for Customer Receivables (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Sep. 30, 2019
Receivables from customers and notes receivable, net [Abstract]
Allowance for Doubtful Accounts Receivable	$ 17.2	$ 11.7
Allowance for Doubtful Accounts, Premiums and Other Receivables	1.3	$ 36.9
Allowance for Doubtful Accounts Receivable, Write-offs	$ 35.6

Receivables From Customers, N_3

Receivables From Customers, Net and Notes Receivable, Net Receivables from Customers, Net and Notes Receivables, Net - Bad Debt Expense and Recoveries (Details) - USD ($)	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Bad debts	$ 4,400,000	$ 700,000	$ 4,400,000	$ 1,000,000
Payments for Legal Settlements				8,400,000
Recovery of bad debt on physical coal	0	0	$ 0	$ 2,400,000
Commodity and Risk Management [Member]
Bad debts	4,000,000	$ 1,000,000
Clearing and Execution Services Segment
Bad debts	0
Physical Commodities
Bad debts	$ 0

Physical Commodities Inventor_3

Physical Commodities Inventory - Physical Commodities Inventory by CIP and Finished (Details) - USD ($) $ in Millions	Mar. 31, 2020	Sep. 30, 2019
Inventory [Line Items]
Physical Ag & Energy(1)	$ 167.8	$ 144.8
Precious metals - held by non-broker-dealer subsidiaries(3)	194.1	151.9
Physical commodities inventory	255.2	229.3
Physical commodities inventory - precious metals [Member]
Inventory [Line Items]
Precious metals - held by non-broker-dealer subsidiaries(3)	26.3	7.1
Finished commodities	$ 61.1	$ 77.4

Physical Commodities Inventor_4

Physical Commodities Inventory - LCM Adjustments (Details) - USD ($) $ in Millions	Mar. 31, 2020	Sep. 30, 2019	Sep. 30, 2016
Physical Commodities Inventory [Abstract]
Inventory Adjustments	$ 1.2	$ 0.5	$ 0.6

Goodwill - Goodwill by Segment

Goodwill - Goodwill by Segment (Details) - USD ($) $ in Millions	Mar. 31, 2020	Sep. 30, 2019
Goodwill [Line Items]
Goodwill	$ 52.2	$ 51.2
Commodity and Risk Management [Member]
Goodwill [Line Items]
Goodwill	30.2	30.3
Global Payments
Goodwill [Line Items]
Goodwill	7.6	7.6
Physical Commodities
Goodwill [Line Items]
Goodwill	8.7	8.7
Securities
Goodwill [Line Items]
Goodwill	4.6	4.6
Clearing and Execution Services Segment
Goodwill [Line Items]
Goodwill	$ 1.1	$ 0

Goodwill Goodwill Adjustments (

Goodwill Goodwill Adjustments (Details) $ in Millions	6 Months Ended
	Mar. 31, 2020USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill, Acquired During Period	$ 1.1

Intangible Assets - Gross and N

Intangible Assets - Gross and Net Intangible Assets by Major Class (Details) - USD ($) $ in Millions	Mar. 31, 2020	Sep. 30, 2019
Acquired Finite-Lived Intangible Assets [Line Items]
Indefinite-Lived License Agreements	$ 2.7	$ 2.7
Indefinite-lived Intangible Assets (Excluding Goodwill)	4.8	4.8
Finite-Lived Intangible Assets, Accumulated Amortization	(17.4)	(15.5)
Finite-Lived Intangible Assets, Net	16.1	11.9
Other Indefinite-lived Intangible Assets	2.1	2.1
Finite-Lived Intangible Assets, Gross	33.5	27.4
Gross Finite and Indefinite-Lived Intangible Assets	38.3	32.2
Finite and Indefinited-Lived Accumulated Amortization and Impairment Charges	(17.4)	(15.5)
Intangible Assets, Net (Excluding Goodwill)	20.9	16.7
Computer Software, Intangible Asset [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Computer Software, Gross	5.3	5.3
Finite-Lived Intangible Assets, Accumulated Amortization	(3.2)	(3)
Finite-Lived Intangible Assets, Net	2.1	2.3
Customer Relationships [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Customer Lists, Gross	28.2	22.1
Finite-Lived Intangible Assets, Accumulated Amortization	(14.2)	(12.5)
Finite-Lived Intangible Assets, Net	$ 14	$ 9.6

Intangible Assets - Indefinite-

Intangible Assets - Indefinite-Lived Intangible Assets (Details) - USD ($) $ in Millions	Mar. 31, 2020	Sep. 30, 2019
Indefinite-lived Intangible Assets [Line Items]
Gross Finite and Indefinite-Lived Intangible Assets	$ 38.3	$ 32.2
Finite and Indefinited-Lived Accumulated Amortization and Impairment Charges	(17.4)	(15.5)
Intangible Assets, Net (Excluding Goodwill)	$ 20.9	$ 16.7

Intangible Assets - Finite-Live

Intangible Assets - Finite-Lived Intangible Assets Future Amortization Expense (Details) - USD ($) $ in Millions	Mar. 31, 2020	Sep. 30, 2019
Finite-Lived Intangible Assets, Amortization Expense, Maturity Schedule [Abstract]
Fiscal 2020 (remaining nine months)	$ 2
Fiscal 2021	4
Fiscal 2022	2.7
Fiscal 2023	2.5
Fiscal 2024 and thereafter	4.9
Finite-Lived Intangible Assets, Net	$ 16.1	$ 11.9

Intangible Assets Definite Live

Intangible Assets Definite Lived Intangible Assets Amortization (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		9 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019	Jun. 30, 2017
Definite Lived Intangible Assets Amortization [Abstract]
Amortization of Intangible Assets	$ 1.1	$ 0.6	$ 1.9	$ 1.3	$ 2.1

Intangible Assets Intangible As

Intangible Assets Intangible Assets Acquired During the Period (Details) - Customer-Related Intangible Assets [Member] $ in Millions	6 Months Ended
	Mar. 31, 2020USD ($)
UOB Bullion and Futures Limited [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired	$ 3.2
IFCM Commodities Acquisition [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired	1
Quest Capital Strategies, Inc. [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired	$ 1.7

Credit Facilities - Number of C

Credit Facilities - Number of Credit Facilities (Details) $ in Millions	6 Months Ended
	Mar. 31, 2020USD ($)Rate	Sep. 30, 2019USD ($)
Term Loan Initial Balance	$ 196.5
Term Loan Periodic Principal Payment, Percent | Rate	1.25%
Number of credit facilities	4
Maximum available under credit facility	$ 393
Main line of credit facilities [Member]
Borrowing Capacity Under Credit Facilities	766.5
HCO Syndicated line of credit facility [Member]
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net	0.7
Line of Credit Facility, Maximum Borrowing Capacity	196.5
Borrowing Capacity Under Credit Facilities	381.5
FCS Margin line of credit facility [Member]
Line of Credit Facility, Maximum Borrowing Capacity	75
Line of Credit, Current	0	$ 0
FMS Sub-note commodity line of credit facility [Member]
Line of Credit Facility, Maximum Borrowing Capacity	260
INTL FCStone Ltd [Member]
Line of Credit Facility, Maximum Borrowing Capacity	100
Line of Credit, Current	5	0
Rabobank Uncommited Line of Credit [Domain]
Line of Credit Facility, Maximum Borrowing Capacity	20
Line of Credit, Current	0	3.4
INTL FCStone Ltd [Member]
Line of Credit Facility, Maximum Borrowing Capacity	50
Line of Credit, Current	$ 0	$ 0

Credit Facilities - Credit Faci

Credit Facilities - Credit Facilities (Details) - USD ($) $ in Millions	Mar. 31, 2020	Sep. 30, 2019
Line of Credit Facility [Line Items]
Long-term Debt, Gross	$ 185
Senior secured term loan, net	184.3	$ 167.6
Short-term Debt	454.3	366.1
Notes Payable to Bank	0	0.4
Debt, Long-term and Short-term, Combined Amount	459.3	369.9
Main line of credit facilities [Member]
Line of Credit Facility [Line Items]
Credit Facilities Expiring Within One Year	125
Borrowing Capacity Under Credit Facilities	766.5
IFFI Uncommitted Lines of Credit [Member] [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	100
Line of Credit, Current	5	0
HCO Syndicated line of credit facility [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net	0.7
Senior secured term loan, net	184.3	167.6
Line of Credit Facility, Maximum Borrowing Capacity	196.5
Long-term Line of Credit, Noncurrent	100	70
Borrowing Capacity Under Credit Facilities	381.5
Long-term Debt	284.3	237.6
FCS Margin line of credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	75
Line of Credit, Current	0	0
FMS Sub-note commodity line of credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	260
Long-term Line of Credit, Noncurrent	170	128.5
INTL FCStone Ltd [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	50
Line of Credit, Current	0	0
INTL FCStone Financial Inc. Uncommitted Commodities Delivery Line [Domain]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	75
Rabobank Uncommited Line of Credit [Domain]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	20
Line of Credit, Current	$ 0	$ 3.4

Commodity and Other Repurchas_4

Commodity and Other Repurchase Agreements Commodity and Other Repurchase Agreements (Details) - USD ($)	Mar. 31, 2020	Sep. 30, 2019
Financial Instruments Owned and Pledged as Collateral [Line Items]
Fair Value of Securities Received as Collateral that Can be Resold or Repledged	$ 2,449,200,000	$ 3,060,200,000
Financial Instruments Owned and Pledged as Collateral, Amount Eligible to be Repledged by Counterparty	743,600,000	478,800,000
Securities Loaned, Fair Value of Collateral	1,025,900,000	1,414,000,000
Securities Sold under Agreements to Repurchase, Fair Value of Collateral	743,600,000	478,800,000
Trading Securities Pledged as Collateral	1,049,300,000	1,228,900,000
Pledged Financial Instruments, Not Separately Reported, Securities for Repurchase Agreements	1,069,800,000	1,175,100,000
Fair Value of Securities Received as Collateral that Have Been Resold or Repledged	$ 252,200,000	$ 329,800,000

Commodity and Other Repurchas_5

Commodity and Other Repurchase Agreements and Collateralized Transactions Gross Financings Collateral Maturities Table (Details) - USD ($) $ in Millions	Mar. 31, 2020	Sep. 30, 2019
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	$ 2,800.3	$ 2,773.7
Securities Loaned	1,068.8	1,459.9
Collateralized transactions:	3,869.1	4,233.6
Maturity Overnight and on Demand [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	1,535.1	1,553.9
Securities Loaned	1,068.8	1,459.9
Collateralized transactions:	2,603.9	3,013.8
Maturity Less than 30 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	737.2	565.8
Securities Loaned	0	0
Collateralized transactions:	737.2	565.8
Maturity 30 to 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	483	654
Securities Loaned	0	0
Collateralized transactions:	483	654
Maturity Greater than 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	45	0
Securities Loaned	0	0
Collateralized transactions:	$ 45	$ 0

Commodity and Other Repurchas_6

Commodity and Other Repurchase Agreements and Collateralized Transactions Gross Collateralized Financings by Collateral Type Table (Details) - USD ($)	Mar. 31, 2020	Sep. 30, 2019
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	$ 2,800,300,000	$ 2,773,700,000
Securities Loaned	1,068,800,000	1,459,900,000
Collateralized transactions:	3,869,100,000	4,233,600,000
US Government Debt Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	32,200,000	108,800,000
US Government Agencies Debt Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	264,100,000	359,500,000
Asset-backed Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	76,500,000	96,700,000
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	2,402,800,000	2,208,700,000
Equity Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned	$ 1,068,800,000	$ 1,459,900,000

Commitments and Contingencies C

Commitments and Contingencies Commitments and Contingencies - Contingencies and Litigation (Details) $ in Millions	Mar. 31, 2020USD ($)
Loss Contingencies [Line Items]
Loss Contingency, Estimate of Possible Loss	$ 29

Commitments and Contingencies_2

Commitments and Contingencies Commitments and Contingencies - Self Insurance (Details) $ in Millions	Mar. 31, 2020USD ($)
Commitments and Contingencies [Abstract]
Self Insurance Reserve	$ 1.1

Capital and Other Regulatory _3

Capital and Other Regulatory Requirements - Regulatory Capital Requirements (Details) $ in Millions	Mar. 31, 2020USD ($)
FCStone LLC [Member]
Cash Reserve Deposit Required and Made	$ 33.1
Cash Reserve Deposit Required	66.1
Net Capital under Commodity Exchange Act Computation	175.7
Required Net Capital under Commodity Exchange Act	108.3
Cash and Securities Segregated under Commodity Exchange Act Regulation	2,543.6
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	2,485.9
Secured Funds	162.5
Secured Funds Required Under Commodity Exchange Act	150
INTL FCStone Ltd [Member]
Net Capital under Commodity Exchange Act Computation	270.3
Required Net Capital under Commodity Exchange Act	140
Cash and Securities Segregated under Commodity Exchange Act Regulation	437.8
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	430.1
INTL FCStone Pte Ltd [Member]
Cash and Securities Segregated under Commodity Exchange Act Regulation	208.2
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	$ 202.6

Other Expenses - Other Expenses

Other Expenses - Other Expenses Breakout (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Other Expenses [Abstract]
Accretion Expense	$ 0.1	$ 0	$ 0.1	$ 0
Insurance	1	0.9	2	1.7
Advertising, meetings, and conferences	4.2	1.5	5.6	2.9
Office supplies and printing	0.5	0.5	0.9	1
Other clearing related expenses	0.6	0.7	1.4	1.1
Other non-income taxes	1.3	1.2	2.6	2.1
Other	2.9	2.6	5.5	5.1
Total other expenses	$ 10.6	$ 7.4	$ 18.1	$ 13.9

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income (Loss) Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019	Sep. 30, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	$ (38.2)		$ (38.2)		$ (34.8)
ASU 2018-02 cumulative transition adjustment					0.7
Other comprehensive (loss) income	(3.4)	$ 0	(2.7)	$ 0.3
Accumulated Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	(34.2)		(34.2)		(31.5)
ASU 2018-02 cumulative transition adjustment					0
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			(2.7)
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	(4)		(4)		(3.3)
ASU 2018-02 cumulative transition adjustment					(0.7)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			0
Accumulated Other Comprehensive Loss, net
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss, net	(38.2)		(38.2)		(34.8)
ASU 2018-02 cumulative transition adjustment					$ (0.7)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax			(2.7)
Other comprehensive (loss) income	$ (3.4)		$ (2.7)	$ 0.3

Effective Income Tax Rate Recon

Effective Income Tax Rate Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Income Taxes [Abstract]
Income Tax Expense (Benefit)	$ 16.8	$ 7.5	$ 22.2	$ 13.7
Effective Income Tax Rate Reconciliation, Percent	30.00%	24.00%	29.00%	25.00%
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate			21.00%
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent	0.60%
Effective Income Tax Rate Reconciliation, Deduction, Percent	0.40%
Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Percent	0.70%		3.30%	0.50%
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent			1.20%	1.30%

Income Taxes Accumulated Foreig

Income Taxes Accumulated Foreign Undistributed Earnings (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Mar. 31, 2020	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Undistributed Earnings of Foreign Subsidiaries	$ 393.9	$ 383.5
Foreign Earnings Repatriated	$ 30	$ 13

Income Taxes Operating Loss Car

Income Taxes Operating Loss Carryforwards (Details) - USD ($) $ in Millions	Mar. 31, 2020	Sep. 30, 2019	Sep. 30, 2016
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	$ 7.1
Deferred Tax Assets, Tax Credit Carryforwards, Foreign	5.1
Deferred Tax Assets, Valuation Allowance	8.4	$ 8.5	$ 3.6
State and Local Jurisdiction [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	5.6
Inland Revenue, Singapore (IRAS) [Member]
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	$ 0.2

Acquisitions UOB Acquisition (D

Acquisitions UOB Acquisition (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended	7 Months Ended
	Dec. 31, 2019	Mar. 31, 2019	Mar. 31, 2020	Oct. 07, 2019
Business Acquisition [Line Items]
Goodwill, Acquired During Period			$ 1.1
UOB Bullion and Futures Limited [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred	$ 2.5	$ 2.5		$ 5
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Equipment				0.7
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles				3.2
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Liabilities				$ 351.8

Acquisitions Quest Capital (Det

Acquisitions Quest Capital (Details) $ in Millions	6 Months Ended
	Mar. 31, 2020USD ($)
Quest Capital Strategies, Inc. [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred	$ 1.7

Acquisitions Tellimer Acquisiti

Acquisitions Tellimer Acquisition (Details) $ in Millions	6 Months Ended
	Mar. 31, 2020USD ($)
Tellimer [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred	$ 4.7

Acquisitions IFCM Commodities (

Acquisitions IFCM Commodities (Details) - IFCM Commodities Acquisition [Member] $ in Millions	6 Months Ended
	Mar. 31, 2020USD ($)
Business Acquisition [Line Items]
Business Combination, Consideration Transferred	$ 1.9
Purchase price in excess of net book value	$ 1

Acquisitions Gain Capital (Deta

Acquisitions Gain Capital (Details) $ / shares in Units, $ in Millions	Mar. 31, 2020USD ($)$ / shares
Business Acquisition [Line Items]
Business Acquisition, Share Price | $ / shares	$ 6
Other Commitment | $	$ 350

Acquisitions GIROXX (Details)

Acquisitions GIROXX (Details) $ in Millions	6 Months Ended
	Mar. 31, 2020USD ($)
IFCM Commodities Acquisition [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred	$ 1.9
GIROXX Acquisition [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred	$ 4.4

Segment Analysis (Details)

Segment Analysis (Details) - USD ($)	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019	Sep. 30, 2019
Segment Reporting Information [Line Items]
Revenues	$ 20,366,300,000	$ 7,192,200,000	$ 31,611,300,000	$ 13,744,400,000
Operating revenues	366,800,000	271,100,000	643,600,000	535,800,000
Net operating revenues	243,400,000	165,200,000	413,900,000	314,200,000
Net Segment Contribution	174,900,000	125,300,000	300,700,000	237,600,000
Segment Income	117,300,000	77,200,000	193,100,000	148,700,000
Net costs not allocated to operating segments	61,200,000	51,700,000	115,400,000	98,800,000
Other gain	0	5,400,000	100,000	5,400,000
Income before tax	56,100,000	30,900,000	77,800,000	55,300,000
Assets	10,870,900,000		10,870,900,000		$ 9,936,100,000
Commodity and Risk Management [Member]
Segment Reporting Information [Line Items]
Revenues	101,700,000	80,600,000	171,400,000	140,400,000
Operating revenues	101,700,000	80,600,000	171,400,000	140,400,000
Net operating revenues	84,200,000	65,800,000	138,600,000	111,100,000
Net Segment Contribution	59,100,000	49,300,000	97,900,000	79,900,000
Segment Income	35,800,000	30,200,000	57,300,000	43,500,000
Assets	2,309,700,000		2,309,700,000		2,041,000,000
Global Payments
Segment Reporting Information [Line Items]
Revenues	29,400,000	27,400,000	60,800,000	57,100,000
Operating revenues	29,400,000	27,400,000	60,800,000	57,100,000
Net operating revenues	28,000,000	25,800,000	57,800,000	54,200,000
Net Segment Contribution	22,600,000	21,000,000	46,400,000	44,100,000
Segment Income	17,200,000	15,800,000	36,100,000	34,400,000
Assets	298,000,000		298,000,000		278,300,000
Securities Segment
Segment Reporting Information [Line Items]
Revenues	117,900,000	72,600,000	199,000,000	141,600,000
Operating revenues	117,900,000	72,600,000	199,000,000	141,600,000
Net operating revenues	78,100,000	32,000,000	121,200,000	64,100,000
Net Segment Contribution	50,500,000	20,100,000	77,900,000	41,900,000
Segment Income	38,400,000	11,800,000	55,100,000	27,800,000
Assets	5,109,400,000		5,109,400,000		5,219,100,000
Physical Commodities
Segment Reporting Information [Line Items]
Revenues	20,023,500,000	6,940,900,000	31,011,800,000	13,242,700,000
Operating revenues	24,000,000	19,800,000	44,100,000	34,100,000
Net operating revenues	19,500,000	15,100,000	35,400,000	25,500,000
Net Segment Contribution	13,800,000	11,500,000	25,100,000	18,600,000
Segment Income	9,600,000	7,800,000	17,200,000	13,700,000
Assets	458,100,000		458,100,000		357,800,000
Clearing and Execution Services Segment
Segment Reporting Information [Line Items]
Revenues	96,500,000	73,600,000	172,400,000	168,800,000
Operating revenues	96,500,000	73,600,000	172,400,000	168,800,000
Net operating revenues	37,100,000	31,000,000	67,100,000	68,500,000
Net Segment Contribution	28,900,000	23,400,000	53,400,000	53,100,000
Segment Income	16,300,000	11,600,000	27,400,000	29,300,000
Assets	2,448,900,000		2,448,900,000		1,892,100,000
Corporate unallocated
Segment Reporting Information [Line Items]
Revenues	4,000,000	4,100,000	9,200,000	7,000,000
Operating revenues	4,000,000	4,100,000	9,200,000	7,000,000
Net operating revenues	(3,500,000)	(4,500,000)	(6,200,000)	(9,200,000)
Assets	246,800,000		246,800,000		$ 147,800,000
Eliminations
Segment Reporting Information [Line Items]
Revenues	(6,700,000)	(7,000,000)	(13,300,000)	(13,200,000)
Operating revenues	$ (6,700,000)	$ (7,000,000)	$ (13,300,000)	$ (13,200,000)