StoneX (SNEX) 10-Q 7 Aug 20 2020 Q3 Quarterly report Financial data

Cover Document

Cover Document - shares	9 Months Ended
	Jun. 30, 2020	Aug. 03, 2020
Cover [Abstract]
Entity Information, Former Legal or Registered Name	INTL FCStone Inc.
Title of 12(b) Security	Common Stock, $0.01 par value
Entity Incorporation, State or Country Code	DE
Document Transition Report	false
Document Quarterly Report	true
Document Type	10-Q
Document Period End Date	Jun. 30, 2020
Entity File Number	000-23554
Entity Registrant Name	StoneX Group Inc.
Entity Address, Address Line One	155 East 44th Street
Entity Address, Address Line Two	Suite 900
Entity Address, City or Town	New York
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	10017
City Area Code	(212)
Local Phone Number	485-3500
Entity Tax Identification Number	59-2921318
Trading Symbol	SNEX
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Entity Interactive Data Current	Yes
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		19,368,297
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Central Index Key	0000913760
Current Fiscal Year End Date	--09-30
Amendment Flag	false
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Millions	Jun. 30, 2020	Sep. 30, 2019
ASSETS
Cash and cash equivalents	$ 465.2	$ 471.3
Restricted cash held in escrow	350	0
Cash, securities and other assets segregated under federal and other regulations (including $9.8 and $306.0 at fair value at June 30, 2020 and September 30, 2019, respectively)	1,145.2	1,049.9
Collateralized transactions:
Securities purchased under agreements to resell	1,757.3	1,424.5
Securities borrowed	1,467.4	1,423.2
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net (including $1261.6 and $626.9 at fair value at June 30, 2020 and September 30, 2019, respectively)	3,396.7	2,540.5
Receivables from clients, net	408.8	422.3
Notes receivable, net	4.7	2.9
Income taxes receivable	2.8	5.2
Financial instruments owned, at fair value (includes securities pledged as collateral that can be sold or repledged of $606.4 and $478.8 at June 30, 2020 and September 30, 2019, respectively)	2,831.9	2,175.2
Physical commodities inventory, net (including $173.6 and $151.9 at fair value at June 30, 2020 and September 30, 2019, respectively)	270.2	229.3
Deferred income taxes, net	13.4	18
Property and equipment, net	51.6	43.9
Operating right of use assets	75	0
Goodwill and intangible assets, net	76.3	67.9
Other assets	73	62
Total assets	12,389.5	9,936.1
Liabilities:
Accounts payable and other accrued liabilities (including $1.6 and $1.8 at fair value at June 30, 2020 and September 30, 2019, respectively)	176.4	157.5
Operating lease liabilities	87.4	0
Payables to:
Customers	4,443.7	3,589.5
Broker-dealers, clearing organizations and counterparties (including $8.8 and $5.6 at fair value at June 30, 2020 and September 30, 2019, respectively)	430	266.2
Lenders under loans	313.8	202.3
Senior secured borrowings, net	518.9	167.6
Income taxes payable	12.1	10.4
Collateralized transactions:
Securities sold under agreements to repurchase	3,530.4	2,773.7
Securities loaned	1,459.7	1,459.9
Financial instruments sold, not yet purchased, at fair value	728.3	714.8
Total liabilities	11,700.7	9,341.9
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; 21,735,636 issued and 19,313,679 outstanding at June 30, 2020 and 21,297,317 issued and 19,075,360 outstanding at September 30, 2019	0.2	0.2
Common stock in treasury, at cost - 2,421,957 shares at June 30, 2020 and 2,221,957 shares September 30, 2019	(57.6)	(50.1)
Additional paid-in capital	289.4	276.8
Total retained earnings	495	402.1
Accumulated other comprehensive loss, net	(38.2)	(34.8)
Total stockholders' equity	688.8	594.2
Total liabilities and stockholders' equity	$ 12,389.5	$ 9,936.1

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets Parentheticals - USD ($) $ in Millions	Jun. 30, 2020	Sep. 30, 2019
Balance Sheet Parentheticals [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	$ 9.8	$ 306
Dep and rec -b/d - fair value	1,261.6	626.9
Physical commodities inventory at fair value	173.6	151.9
Collateral that can be sold or repledged	606.4	478.8
Accounts pay and other accrued - fair value	1.6	1.8
Payables to b/d - fair value	$ 8.8	$ 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	21,735,636	21,297,317
Common stock - outstanding	19,313,679	19,075,360
Treasury stock - shares	2,421,957	2,221,957

Condensed Consolidated Income S

Condensed Consolidated Income Statements - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenues:
Sales of physical commodities	$ 7,944.5	$ 7,599.3	$ 38,939.4	$ 20,824.6
Principal gains, net	161	102.3	442	305.4
Commission and clearing fees	96.1	97.5	299.9	282.1
Consulting, management, and account fees	19.4	20.7	63.3	58.9
Interest income	22.4	53.2	110.1	146.4
Total revenues	8,243.4	7,873	39,854.7	21,617.4
Cost of sales of physical commodities	7,920.8	7,589.6	38,888.5	20,798.2
Operating revenues	322.6	283.4	966.2	819.2
Transaction-based clearing expenses	55.3	45.7	165.4	138.5
Introducing broker commissions	24	29.6	79.8	87
Interest expense	15.4	42.5	79.2	113.9
Net operating revenues	227.9	165.6	641.8	479.8
Compensation and other expenses:
Compensation and benefits	132.5	100.9	373.2	287.9
Trading systems and market information	11.8	9.8	33.4	28.5
Occupancy and equipment rental	5.4	5	15.3	14.4
Professional fees	6.1	5.8	16.8	16.1
Travel and business development	0.7	4	8.4	11.8
Non-trading technology and support	6.9	5.8	18.8	15
Depreciation and amortization	4.4	3.5	12.5	9.6
Communications	1.7	1.6	4.8	4.9
Bad debts	1.8	0.5	6.2	1.5
Recovery of bad debt on physical coal	0	0	0	(2.4)
Other	7.6	7.1	25.7	21
Total compensation and other expenses	178.9	144	515.1	408.3
Other gain	0	0	0.1	5.4
Income before tax	49	21.6	126.8	76.9
Income tax expense	12.4	5.3	34.6	19
Net income	$ 36.6	$ 16.3	$ 92.2	$ 57.9
Earnings per share:
Basic	$ 1.90	$ 0.85	$ 4.78	$ 3.04
Diluted	$ 1.87	$ 0.84	$ 4.71	$ 2.99
Weighted-average number of common shares outstanding:
Basic	18,807,104	18,781,401	18,809,823	18,731,203
Diluted	19,103,166	19,011,526	19,122,681	19,003,720

Condensed Consolidated Statemen

Condensed Consolidated Statement of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Condensed Consolidated Statement of Other Comprehensive Income (Loss) [Abstract]
Net income	$ 36.6	$ 16.3	$ 92.2	$ 57.9
Other comprehensive (loss) income:
Foreign currency translation adjustment	0	0.3	(2.7)	0.6
Other comprehensive (loss) income	0	0.3	(2.7)	0.6
Comprehensive income	$ 36.6	$ 16.6	$ 89.5	$ 58.5

Condensed Consolidated Cash Flo

Condensed Consolidated Cash Flows Statements - USD ($) $ in Millions	9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Cash flows from operating activities:
Net income	$ 92.2	$ 57.9
Adjustments to reconcile net income to net cash provided by (used in) operating activities:
Depreciation and amortization	12.5	9.6
Bad debts	6.2	1.5
Recovery of bad debt on physical coal	0	(2.4)
Deferred income taxes	(0.7)	0.3
Amortization of debt issuance costs	1.3	1.2
Amortization of share-based compensation	7.4	5.9
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	296.2	584.4
Securities purchased under agreements to resell	(332.8)	(662.2)
Securities borrowed	(44.2)	(948.6)
Deposits with and receivables from broker-dealers, clearing organizations, and counterparties, net	55.9	(238.7)
Receivables from clients, net	8.3	5.9
Notes receivable, net	(1.8)	(0.6)
Income taxes receivable	7.7	(0.6)
Financial instruments owned, at fair value	(656.7)	(368)
Physical commodities inventory, net	(40.9)	(115.5)
Operating right of use assets	6	0
Other assets	(7)	(7.8)
Accounts payable and other accrued liabilities	20.5	(4)
Operating lease liabilities	(6.7)	0
Payables to clients	848.4	(7.3)
Payables to broker-dealers, clearing organizations and counterparties	163.8	100.9
Income taxes payable	1.6	1.8
Securities sold under agreements to repurchase	756.7	964
Securities loaned	(0.2)	963
Financial instruments sold, not yet purchased, at fair value	13.5	(9.7)
Net cash provided by (used in) operating activities	1,207.2	325.6
Cash flows from investing activities:
Cash paid for acquisitions, net	(9.8)	(28)
Purchase of property and equipment	(5.5)	(10.3)
Net cash used in investing activities	(15.3)	(38.3)
Cash flows from financing activities:
Net change in payable to lenders under loans with maturities 90 days or less	150.4	(16.9)
Proceeds from payables to lenders under loans with maturities greater than 90 days	521.5	0
Repayments of payables to lenders under loans with maturities greater than 90 days	(560)	0
Proceeds from issuance of senior secured term loan	21.5	175
Repayments of senior secured term loan	(7.4)	(4.4)
Proceeds from issuance of senior secured notes	344.8	0
Repayments of note payable	(0.4)	(0.6)
Deferred payments on acquisitions	(0.6)	0
Repurchase of stock	(7.5)	0
Debt issuance costs	(9.2)	(3.3)
Exercise of stock options	5.2	0.8
Net cash (used in) provided by financing activities	458.3	150.6
Effect of exchange rates on cash, segregated cash, cash equivalents, and segregated cash equivalents	(2.7)	0.6
Net increase (decrease) in cash, segregated cash, cash equivalents, and segregated cash equivalents	1,647.5	438.5
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	4,098.8	2,628.6
Supplemental disclosure of cash flow information:
Cash paid for interest	78	110.1
Income taxes paid, net of cash refunds	25.7	17.5
Supplemental disclosure of non-cash investing and financing activities:
Identified intangible assets and goodwill on acquisitions	11.5	2.7
Assets acquired	357.8	40.9
Liabilities assumed	(359.5)	(7.7)
Total net assets acquired	$ (1.7)	$ 33.2

Condensed Consolidated Cash F_2

Condensed Consolidated Cash Flows Statements Reconciliation of Cash, Segregated Cash, Cash Equivalents, and Segregated Cash Equivalents - USD ($) $ in Millions	Jun. 30, 2020	Jun. 30, 2019	Mar. 31, 2019
Reconciliation of Cash, Segregated Cash, Cash Equivalents, and Segregated Cash Equivalents [Abstract]
Cash and cash equivalents	$ 465.2	$ 345
Restricted cash held in escrow	350	0
Cash segregated under federal and other regulations(1)	1,135.4	721
Securities and other assets segregated, fair value	0	299.6
Cash segregated and deposited with or pledged to exchange-clearing organizations and other futures commissions merchants	1,218.7	1,223.8
Securities segregated and pledged to exchange-clearing organizations(2)	929.5	39.2
Cash, segregated cash, cash equivalents, and segregated cash equivalents at end of period	4,098.8	$ 2,628.6
Non-cash equivalent segregated assets	9.8		$ 58.8
Non-segregated cash and other non-cash equivalent assets included within deposits and receivables from broker-dealers, clearing organizations, and counterparties	$ 1,248.5		$ 1,398.6

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	57.9				57.9
Other comprehensive income	0.6					0.6
Exercise of stock options	0.8			0.8
Share-based compensation	5.9			5.9
Repurchase of stock	0
Balance at end of period at Jun. 30, 2019	570.5	0.2	(46.3)	274.2	374.9	(32.5)
Balance at beginning of period at Mar. 31, 2019	551.8	0.2	(46.3)	272.1	358.6	(32.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	16.3				16.3
Other comprehensive income	0.3
Share-based compensation	2.1			2.1
Balance at end of period at Jun. 30, 2019	570.5	0.2	(46.3)	274.2	374.9	(32.5)
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	92.2				92.2
Other comprehensive income	(2.7)					(2.7)
Exercise of stock options	5.2			5.2
Share-based compensation	7.4			7.4
Repurchase of stock	(7.5)		7.5
Balance at end of period at Jun. 30, 2020	688.8	0.2	(57.6)	289.4	495	(38.2)
Balance at beginning of period at Mar. 31, 2020	648.6	0.2	(57.6)	285.8	458.4	(38.2)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	36.6				36.6
Other comprehensive income	0
Exercise of stock options	1.2			1.2
Share-based compensation	2.4			2.4
Balance at end of period at Jun. 30, 2020	$ 688.8	$ 0.2	$ (57.6)	$ 289.4	$ 495	$ (38.2)

Basis of Presentation and Conso

Basis of Presentation and Consolidation and Recently Issued Accounting Standards (Notes)	9 Months Ended
	Jun. 30, 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 StoneX Group Inc. , a Delaware corporation, and its consolidated subsidiaries (collectively “SNEX” 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’s shareholders voted and approved to change the Company’s name from INTL FCStone Inc. to StoneX Group Inc. on June 24, 2020. The change in the Company’s name became effective on July 7, 2020 and the Company’s common stock began trading on The NASDAQ Global Select Market under the symbol “SNEX”. 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; commercial counterparties who are end-users of the Company’s products and services; governmental and non-governmental organizations; and 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 StoneX Group 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. These estimates and assumptions were considered and made in context with the information reasonably available to the Company and the unknown future impacts of the novel coronavirus (COVID-19) as of June 30, 2020 and through the date of this Form 10-Q. 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 loss, net 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)	9 Months Ended
	Jun. 30, 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 June 30, 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 June 30, 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 June 30, 2020 , the Company recorded operating lease right-of-use assets and operating lease liabilities of $75.0 million and $87.4 million , respectively. The following table presents operating lease costs and other related information as of and for the three and nine months ended June 30, 2020 (in millions, except as stated): Three Months Ended June 30, Nine Months Ended June 30, 2020 2020 Operating lease costs (1) $ 4.1 $ 11.1 Supplemental cash flow information and non-cash activity: Cash paid for amounts included in the measurement of operating lease liabilities $ 2.9 $ 8.4 Right-of-use assets obtained in exchange for operating lease liabilities $ 46.0 $ 81.0 Lease term and discount rate information: Weighted average remaining lease term (years) 11.64 Weighted average discount rate 3.9 % (1) Includes short-term leases and variable lease costs, which are immaterial. The maturities of the lease liabilities are as follows as of June 30, 2020 (in millions): Remainder of 2020 $ 3.8 2021 10.9 2022 11.1 2023 9.5 2024 7.7 After 2024 67.3 Total lease payments 110.3 Less: interest 22.9 Present value of lease liabilities $ 87.4 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)	9 Months Ended
	Jun. 30, 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 1.4% and 1.5% of the Company’s total revenues for the three months ended June 30, 2020 and 2019 , respectively. The Company’s revenues from contracts with clients subject to Topic 606 represent approximately 0.9% and 1.6% of the Company’s total revenues for the nine months ended June 30, 2020 and 2019 , respectively. The Company’s revenues from contracts with clients subject to Topic 606 represent approximately 35.8% and 41.7% of the Company’s operating revenues for the three months ended June 30, 2020 and 2019 , respectively. The Company’ revenues from contracts with clients subject to Topic 606 represent approximately 37.6% and 41.6% of the Company’s operating revenues for the nine months ended June 30, 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 nine months ended June 30, 2020 and 2019 (in millions): Three Months Ended June 30, Nine Months Ended June 30, 2020 2019 2020 2019 Revenues from contracts with clients: Commission and clearing fees: Sales-based: Exchange-traded futures and options $ 36.4 $ 40.4 $ 108.9 $ 110.7 OTC derivative brokerage 4.0 7.7 16.2 23.9 Equities and fixed income 5.2 4.3 16.6 11.1 Mutual funds 1.1 1.6 4.0 6.1 Insurance and annuity products 1.7 2.1 6.2 5.1 Other 0.3 0.3 1.1 1.0 Total sales-based commission 48.7 56.4 153.0 157.9 Trailing: Mutual funds 3.1 3.1 9.7 9.3 Insurance and annuity products 3.6 3.6 11.3 10.7 Total trailing commission 6.7 6.7 21.0 20.0 Clearing fees 33.3 30.3 104.4 89.7 Trade conversion fees 1.8 1.3 7.5 6.2 Other 5.6 2.8 14.0 8.3 Total commission and clearing fees: 96.1 97.5 299.9 282.1 Consulting, management, and account fees: Underwriting fees — 0.2 0.4 0.7 Asset management fees 7.0 7.2 23.2 19.4 Advisory and consulting fees 5.7 5.1 17.0 14.8 Sweep program fees 1.0 4.2 8.6 12.1 Client account fees 2.8 2.6 8.9 7.8 Other 2.9 1.4 5.2 4.1 Total consulting, management, and account fees 19.4 20.7 63.3 58.9 Total revenues from contracts with clients $ 115.5 $ 118.2 $ 363.2 $ 341.0 Method of revenue recognition: Point-in-time $ 95.1 $ 95.0 $ 293.4 $ 274.7 Time elapsed 20.4 23.2 69.8 66.3 Total revenues from contracts with clients 115.5 118.2 363.2 341.0 Other sources of revenues Physical precious metals trading 7,621.2 7,327.8 37,973.9 19,944.2 Physical agricultural and energy product trading 323.3 271.5 965.5 880.4 Principal gains, net 161.0 102.3 442.0 305.4 Interest income 22.4 53.2 110.1 146.4 Total revenues $ 8,243.4 $ 7,873.0 $ 39,854.7 $ 21,617.4 Primary geographic region: United States $ 554.2 $ 474.8 $ 1,652.1 $ 1,458.4 Europe 114.1 77.8 375.7 184.9 South America 14.6 15.3 46.1 39.2 Middle East and Asia 7,558.5 7,303.8 37,777.3 19,929.7 Other 2.0 1.3 3.5 5.2 Total revenues $ 8,243.4 $ 7,873.0 $ 39,854.7 $ 21,617.4 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)	9 Months Ended
	Jun. 30, 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 June 30, Nine Months Ended June 30, (in millions, except share amounts) 2020 2019 2020 2019 Numerator: Net income $ 36.6 $ 16.3 $ 92.2 $ 57.9 Less: Allocation to participating securities (0.9 ) (0.3 ) (2.1 ) (1.0 ) Net income allocated to common stockholders $ 35.7 $ 16.0 $ 90.1 $ 56.9 Denominator: Weighted average number of: Common shares outstanding 18,807,104 18,781,401 18,809,823 18,731,203 Dilutive potential common shares outstanding: Share-based awards 296,062 230,125 312,858 272,517 Diluted weighted-average common shares 19,103,166 19,011,526 19,122,681 19,003,720 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 947,830 and 1,209,943 shares of common stock for the three months ended June 30, 2020 and 2019 , respectively, and options to purchase 983,799 and 835,441 shares of common stock for the nine months ended June 30, 2020 and 2019

Assets and Liabilities, at Fair

Assets and Liabilities, at Fair Value (Notes)	9 Months Ended
	Jun. 30, 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 $1.6 million and $1.8 million of contingent liabilities classified within Level 3 of the fair value hierarchy as of June 30, 2020 and September 30, 2019 , respectively. The Company had no Level 3 assets as of June 30, 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 June 30, 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, particularly in light of the uncertain impacts of COVID-19. 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 June 30, 2020 by level in the fair value hierarchy. June 30, 2020 (in millions) Level 1 Level 2 Level 3 Netting (1) Total Assets: Certificates of deposit $ 2.7 $ — $ — $ — $ 2.7 Money market mutual funds 11.4 — — — 11.4 Cash and cash equivalents 14.1 — — — 14.1 Commodities warehouse receipts 9.6 — — — 9.6 U.S. Treasury obligations 0.2 — — — 0.2 Securities and other assets segregated under federal and other regulations 9.8 — — — 9.8 U.S. Treasury obligations 1,148.4 — — — 1,148.4 To be announced ("TBA") and forward settling securities — 12.2 — (5.3 ) 6.9 Foreign government obligations 8.2 — — — 8.2 Derivatives 2,876.9 13.7 — (2,792.5 ) 98.1 Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net 4,033.5 25.9 — (2,797.8 ) 1,261.6 Equity securities 248.7 12.0 — — 260.7 Corporate and municipal bonds — 75.4 — — 75.4 U.S. Treasury obligations 372.5 — — — 372.5 U.S. government agency obligations — 347.8 — — 347.8 Foreign government obligations 12.6 — — — 12.6 Agency mortgage-backed obligations — 1,558.3 — — 1,558.3 Asset-backed obligations — 19.4 — — 19.4 Derivatives 0.5 971.9 — (880.0 ) 92.4 Commodities leases — 23.2 — — 23.2 Commodities warehouse receipts 56.4 — — — 56.4 Exchange firm common stock 9.8 — — — 9.8 Mutual funds and other 3.4 — — — 3.4 Financial instruments owned 703.9 3,008.0 — (880.0 ) 2,831.9 Physical commodities inventory 19.8 153.8 — — 173.6 Total assets at fair value $ 4,781.1 $ 3,187.7 $ — $ (3,677.8 ) $ 4,291.0 Liabilities: Accounts payable and other accrued liabilities - contingent liabilities — — 1.6 — 1.6 TBA and forward settling securities — 12.6 — (5.3 ) 7.3 Derivatives 2,773.9 169.3 — (2,941.7 ) 1.5 Payable to broker-dealers, clearing organizations and counterparties 2,773.9 181.9 — (2,947.0 ) 8.8 Equity securities 202.2 15.4 — — 217.6 Foreign government obligations 2.2 — — — 2.2 Corporate and municipal bonds — 26.1 — — 26.1 U.S. Treasury obligations 354.1 — — — 354.1 U.S. government agency obligations — 6.1 — — 6.1 Agency mortgage-backed obligations — 21.1 — — 21.1 Derivatives — 937.0 — (838.3 ) 98.7 Commodities leases — 2.4 — — 2.4 Financial instruments sold, not yet purchased 558.5 1,008.1 — (838.3 ) 728.3 Total liabilities at fair value $ 3,332.4 $ 1,190.0 $ 1.6 $ (3,785.3 ) $ 738.7 (1) Represents cash collateral and the impact of netting across the levels of the fair value hierarchy. Netting among positions classified within the same level 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 June 30, 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 borrowings : Senior secured borrowings includes a senior secured term loan with a carrying value of $182.0 million as of June 30, 2020 , which carries a variable rate of interest and thus approximates fair value and is classified as Level 2 under the fair value hierarchy. Senior secured borrowings also includes the Company's 8.625% Senior Secured Notes due 2025 (the “Senior Secured Notes”) as further described in Note 11 with a carrying value of $336.9 million as of June 30, 2020 . As of June 30, 2020

Financial Instruments with Off-

Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk (Notes)	9 Months Ended
	Jun. 30, 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 June 30, 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 June 30, 2020 . The total financial instruments sold, not yet purchased of $728.3 million and $714.8 million as of June 30, 2020 and September 30, 2019 , respectively, includes $98.7 million and $58.1 million for derivative contracts, respectively, which represented a liability to the Company based on their fair values as of June 30, 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 June 30, 2020 and September 30, 2019 . Assets represent net unrealized gains and liabilities represent net unrealized losses. June 30, 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 $ 1,949.1 $ 2,085.0 $ 1,437.1 $ 1,463.4 OTC commodity derivatives 359.0 489.5 84.2 106.2 Exchange-traded foreign exchange derivatives 11.4 14.3 36.9 33.5 OTC foreign exchange derivatives 525.5 516.2 403.2 368.8 Exchange-traded interest rate derivatives 852.9 603.7 900.1 882.0 OTC interest rate derivatives 101.1 100.6 42.1 43.6 Exchange-traded equity index derivatives 64.0 70.9 758.1 700.2 TBA and forward settling securities 12.2 12.6 9.8 6.8 Gross fair value of derivative contracts 3,875.2 3,892.8 3,671.5 3,604.5 Impact of netting and collateral (3,677.8 ) (3,785.3 ) (3,581.9 ) (3,540.8 ) Total fair value included in 'Deposits with and receivables from broker-dealers, clearing organizations, and counterparties, net' $ 105.0 $ 23.1 Total fair value included in 'Financial instruments owned, at fair value $ 92.4 $ 66.5 Total fair value included in 'Payables to broker-dealers, clearing organizations and counterparties $ 8.8 $ 5.6 Fair value included in 'Financial instruments sold, not yet purchased, at fair value' $ 98.7 $ 58.1 (1) As of June 30, 2020 and September 30, 2019 , the Company’s derivative contract volume for open positions were approximately 9.3 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 June 30, 2020 and September 30, 2019 , these transactions are summarized as follows: June 30, 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, net and related notional amounts $ 7.7 $ 2,170.9 $ 3.7 $ 1,778.4 Unrealized loss on TBA securities purchased within deposits with and receivables from broker-dealers, clearing organizations and counterparties, net and related notional amounts $ (1.9 ) $ 928.5 $ (0.6 ) $ 234.5 Unrealized gain on TBA securities sold within payables to broker-dealers, clearing organizations and counterparties and related notional amounts $ 3.4 $ (1,566.8 ) $ 0.9 $ (451.6 ) Unrealized loss on TBA securities sold within payables to broker-dealers, clearing organizations and counterparties and related notional amounts $ (10.2 ) $ (2,982.1 ) $ (5.9 ) $ (2,788.0 ) Unrealized gain on forward settling securities purchased within deposits with and receivables from broker-dealers, clearing organizations and counterparties, net and related notional amounts $ 1.1 1,690.5 $ — $ — 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, net 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 $ (0.5 ) (1,268.3 ) $ — $ — (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 nine months ended June 30, 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 June 30, Nine Months Ended June 30, (in millions) 2020 2019 2020 2019 Commodities $ 28.1 $ 19.5 $ 107.9 $ 63.6 Foreign exchange 2.6 1.6 9.9 5.3 Interest rate and equity 0.7 (0.6 ) 0.3 (3.2 ) TBA and forward settling securities (5.6 ) (8.0 ) (40.9 ) (6.7 ) Net gains from derivative contracts $ 25.8 $ 12.5 $ 77.2 $ 59.0 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 June 30, 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)	9 Months Ended
	Jun. 30, 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 June 30, 2020 and September 30, 2019 , respectively. During the nine months ended June 30, 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 $19.7 million and $11.7 million as of June 30, 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 parties 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 June 30, 2020 and September 30, 2019 . During the three months ended June 30, 2020 , the Company recorded bad debt expense of $1.8 million , primarily related to $2.4 million of client trading account deficits in the Clearing and Execution Services segment and $1.1 million of OTC client account deficits in Commercial Hedging, partially offset by a recovery of a client trading account deficit of $0.6 million in the Commercial Hedging segment. During the three months ended June 30, 2019, the Company recorded bad debt expense of $0.5 million . The bad debt expense was primarily related to agricultural and metals OTC client trading account deficits in the Commercial Hedging segment. During the nine months ended June 30, 2020, the Company recorded bad debt expense of $6.2 million , primarily related to $2.7 million of client trading account deficits in the Clearing and Execution Services segment, $3.3 million of client trading account deficits in the Commercial Hedging segment, and $0.2 million in uncollected receivables in the Physical Commodities segment. During the nine months ended June 30, 2019, the Company recorded bad debt expense of $1.5 million . The bad debt expense was primarily related to agricultural and metals OTC client trading account deficits in the Company’s Commercial Hedging segment. Additionally, during the nine months ended June 30, 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 amount paid was 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)	9 Months Ended
	Jun. 30, 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) June 30, September 30, Physical Ag & Energy (1) $ 153.8 $ 144.8 Precious metals - held by broker-dealer subsidiary (2) 19.8 7.1 Precious metals - held by non-broker-dealer subsidiaries (3) 96.6 77.4 Physical commodities inventory $ 270.2 $ 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, StoneX Financial Ltd. (formerly INTL FCStone Ltd), a United Kingdom ("UK") 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 $3.7 million and $0.5 million as of June 30, 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)	9 Months Ended
	Jun. 30, 2020
Goodwill [Abstract]
Goodwill Disclosure [Text Block]	Goodwill The carrying value of goodwill is allocated to the Company’s reportable segments as follows: (in millions) June 30, September 30, Commercial Hedging $ 30.3 $ 30.3 Global Payments 11.8 7.6 Physical Commodities 4.6 4.6 Securities 8.7 8.7 Goodwill $ 55.4 $ 51.2 The Company recorded additional goodwill of $4.2 million during the nine months ended June 30, 2020 within the Global Payments reportable segment related to the initial purchase price allocation for the acquisition of GIROXX Gmbh (“GIROXX”) as further discussed in Note 18 .

Intangible Assets - (Notes)

Intangible Assets - (Notes)	9 Months Ended
	Jun. 30, 2020
Intangible Assets [Abstract]
Intangible Assets Disclosure [Text Block]	Intangible Assets The Company recorded $4.2 million , $1.0 million , and $1.7 million of customer base intangible assets during the nine months ended June 30, 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): June 30, 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 $ (3.4 ) $ 1.9 $ 5.3 $ (3.0 ) $ 2.3 Customer base 29.1 (15.1 ) 14.0 22.1 (12.5 ) 9.6 Total intangible assets subject to amortization: 34.4 (18.5 ) 15.9 27.4 (15.5 ) 11.9 Intangible assets not subject to amortization: Website domains 2.1 — 2.1 2.1 — 2.1 Business licenses 2.9 — 2.9 2.7 — 2.7 Total intangible assets not subject to amortization: 5.0 — 5.0 4.8 — 4.8 Total intangible assets $ 39.4 $ (18.5 ) $ 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 June 30, 2020 and 2019 , respectively. Amortization expense related to intangible assets was $3.0 million and $1.9 million for the nine months ended June 30, 2020 and 2019 , respectively. As of June 30, 2020 , the estimated future amortization expense was as follows: (in millions) Fiscal 2020 (Remaining three months) $ 1.0 Fiscal 2021 4.2 Fiscal 2022 2.9 Fiscal 2023 2.7 Fiscal 2024 and thereafter 5.1 Total intangible assets subject to amortization $ 15.9

Credit Facilities (Notes)

Credit Facilities (Notes)	9 Months Ended
	Jun. 30, 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 $739.0 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: • $379.0 million senior facility available to StoneX Group 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, StoneX Financial Inc., for short-term funding of margin to exchange-clearing organizations. The facility is subject to annual review and guaranteed by StoneX Group 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 StoneX Group Inc. • $25.0 million facility available to the Company’s wholly owned subsidiary, StoneX Financial Ltd., for short-term funding of margin to exchange-clearing organizations. The facility is guaranteed by StoneX Group Inc. Uncommitted Credit Facilities The Company has a secured, uncommitted loan facility under which StoneX 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 June 30, 2020 , and September 30, 2019 . The Company has a secured, uncommitted loan facility under which StoneX 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 $24.4 million and zero in borrowings outstanding under this credit facility as of June 30, 2020 , and September 30, 2019 , respectively. The Company has secured, uncommitted loan facilities under which StoneX 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 June 30, 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. Senior Secured Notes On June 11, 2020, the Company completed the issuance and sale of $350 million in aggregate principal amount of the Company’s Notes at the offering price of 98.5% of the aggregate principal amount. The Company had deposited the gross proceeds from the sale of the Senior Secured Notes into a segregated escrow account until the date that certain escrow release conditions were satisfied. The escrow release conditions included, among other things, the consummation of the merger of the Company’s wholly-owned subsidiary with Gain Capital Holdings Inc. (“Gain”) as further discussed in Note 18 . Prior to the satisfaction of the escrow release conditions, the Senior Secured Notes were not guaranteed and were secured by a first-priority security interest in the escrow account. The escrow release conditions were satisfied on July 31, 2020, and the Senior Secured Notes are now fully and unconditionally guaranteed, jointly and severally, on a senior second lien secured basis, by certain subsidiaries of the Company that guarantee the Company’s senior committed credit facility and by Gain and certain of its domestic subsidiaries. The Notes will mature on June 15, 2025. Interest on the Senior Secured Notes accrues at a rate of 8.625% per annum and is payable semiannually in arrears on June 15 and December 15 of each year, commencing on December 15, 2020. The Company incurred debt issuance costs of $8.0 million in connection with the issuance of the Senior Secured Notes, which are being amortized over the term of the Senior Secured Notes under the effective interest method. The Company has the option to redeem all or a portion of the Senior Secured Notes at any time prior to June 15, 2022 at a price equal to 100% of the principal amount of the Senior Secured Notes redeemed plus accrued and unpaid interest to the redemption date plus a “make-whole” premium. At any time on or after June 15, 2022, the Company may redeem the Senior Secured Notes, in whole or in part, at the redemption prices set forth in the indenture. At any time before June 15, 2022, the Company may also redeem up to 40% of the aggregate principal amount of the Senior Secured Notes at a redemption price of 108.625% of the principal amount, plus accrued and unpaid interest, if any, to the date of redemption, with the proceeds of certain equity offerings. In addition, upon the earlier to occur of (x) a business combination between the Company’s subsidiaries that are registered in the UK and regulated by the Financial Conduct Authority and (y) the one year anniversary of the date of issuance of the Senior Secured Notes, the Company may elect to redeem up to $100.0 million in aggregate principal amount of the Senior Secured Notes at a redemption price equal to 103% of the principal amount of the Senior Secured Notes redeemed, plus accrued and unpaid interest, if any, to the date of redemption. If the Company elects not to redeem the Senior Secured Notes, the holders of the Senior Secured Notes will have the right to require the Company to repurchase up to $100.0 million in aggregate principal amount of the Senior Secured Notes (or a lesser amount equal to the difference between $100.0 million and the amounts previously redeemed by the Company) at a purchase price equal to 103% of the principal amount of the Senior Secured Notes repurchased, plus accrued and unpaid interest, if any, to the date of repurchase. The holders of the Senior Secured Notes also possess mandatory redemption rights in the event that the Gain Notes are not fully redeemed at further discussed in Note 18 . The following table sets forth a listing of credit facilities, the current committed amounts as of the report date on the facilities, and outstanding borrowings on the facilities as well as indebtedness on a promissory note and the Senior Secured Notes as of the periods indicated: (in millions) Amounts Outstanding Borrower Security Renewal/Expiration Date Total Commitment June 30, September 30, Committed Credit Facilities Term Loan (1) February 22, 2022 $ 182.5 $ 182.0 (3) $ 167.6 Revolving Line of Credit (1) February 22, 2022 196.5 127.0 70.0 Senior StoneX Group Inc. Committed Credit Facility 379.0 309.0 237.6 StoneX Financial Inc. None April 2, 2021 75.0 — — FCStone Merchants Services, LLC Certain commodities assets January 29, 2022 260.0 162.4 128.5 StoneX Financial Ltd. None September 14, 2020 25.0 — — $ 739.0 $ 471.4 $ 366.1 Uncommitted Credit Facilities StoneX Financial Inc. Commodities warehouse receipts and certain pledged securities n/a n/a 24.4 — FCStone Merchant Services, LLC Certain commodities assets n/a n/a — 3.4 StoneX Group Inc. Note Payable to Bank Certain equipment — 0.4 Senior Secured Notes (2) 336.9 (3) — Total outstanding borrowings $ 832.7 $ 369.9 (1) The StoneX Group Inc. senior committed credit facility is secured by substantially all of the assets of the Company 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) The Notes and the related guarantees are secured by liens on substantially all of the Company’s and the guarantors’ assets, subject to certain customary and other exceptions and permitted liens. The liens on the assets that secure the Senior Secured Notes and the related guarantees are contractually subordinated to the liens on the assets that secure the Company’s and the guarantors’ existing and future first lien secured indebtedness, including indebtedness under the Company’s senior committed credit facility. (3) Amounts outstanding under the Term Loan and the Senior Secured Notes is reported net of unamortized deferred financing costs and original issue discount of $0.6 million and $13.1 million , respectively. As reflected above, $100.0 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 June 30, 2020

Commodity and Other Repurchase

Commodity and Other Repurchase Agreements and Collateralized Transactions (Notes)	9 Months Ended
	Jun. 30, 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 June 30, 2020 and September 30, 2019 , financial instruments owned, at fair value of $606.4 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 June 30, 2020 and September 30, 2019 , the Company pledged financial instruments owned, at fair value of $1,590.1 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 with a fair value of $1,407.8 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 $1,448.9 million and $1,414.0 million as of June 30, 2020 , and September 30, 2019 , respectively. Additionally, the Company had also pledged financial instruments owned with a fair value of $31.1 million and zero as of June 30, 2020 , and September 30, 2019 , respectively, to collateralize uncommitted loan facilities with certain banks as discussed further in Note 11 . At June 30, 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 June 30, 2020 and September 30, 2019 , was $3,384.9 million and $3,060.2 million , respectively, of which $379.6 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 June 30, 2020 and September 30, 2019 (in millions): June 30, 2020 Overnight and Open Less than 30 Days 30-90 Days Over 90 Days Total Securities sold under agreements to repurchase $ 2,079.3 $ 899.1 $ 492.0 $ 60.0 $ 3,530.4 Securities loaned 1,459.7 — — — 1,459.7 Gross amount of secured financing $ 3,539.0 $ 899.1 $ 492.0 $ 60.0 $ 4,990.1 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 June 30, 2020 and September 30, 2019 (in millions): Securities sold under agreements to repurchase June 30, 2020 September 30, 2019 U.S. Treasury obligations $ 1,075.8 $ 108.8 U.S. government agency obligations 206.8 359.5 Asset-backed obligations 17.1 96.7 Agency mortgage-backed obligations 2,163.8 2,208.7 Corporate bonds 66.9 — Total securities sold under agreement to repurchase 3,530.4 2,773.7 Securities loaned Equity securities 1,459.7 1,459.9 Total securities loaned 1,459.7 1,459.9 Gross amount of secured financing $ 4,990.1 $ 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): June 30, 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 $ 1,757.3 $ — $ 1,757.3 Securities borrowed $ 1,467.4 $ — $ 1,467.4 Securities sold under agreements to repurchase $ 3,530.4 $ — $ 3,530.4 Securities loaned $ 1,459.7 $ — $ 1,459.7 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)	9 Months Ended
	Jun. 30, 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 client accounts of the FCM division of the Company’s wholly owned subsidiary, StoneX 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 StoneX 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 StoneX Financial Inc. acted solely as the clearing firm in its role as the FCM. StoneX Financial Inc.’s client agreements hold account holders liable for all losses in their accounts and obligate the account holders to reimburse StoneX Financial Inc. for any account deficits in their accounts. As of June 30, 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 . StoneX 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, StoneX 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. The Company does not currently believe that any potential losses related to this matter would materially and adversely 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 June 30, 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 June 30, 2020 , the Company had $1.2 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)	9 Months Ended
	Jun. 30, 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 June 30, 2020. The following table details those subsidiaries with minimum regulatory requirements in excess of $5 million along with the actual balance maintained as of June 30, 2020. (in millions) As of June 30, 2020 Subsidiary Regulatory Authority Jurisdiction Requirement Type Actual Minimum Requirement StoneX Financial Inc. SEC and CFTC United States Net capital $ 198.6 $ 126.0 StoneX Financial Inc. CFTC United States Segregated funds $ 2,705.6 $ 2,650.1 StoneX Financial Inc. CFTC United States Secured funds $ 160.6 $ 148.8 StoneX Financial Inc. (1) SEC United States Customer reserve $ 43.7 $ 46.8 StoneX Financial Ltd Financial Conduct Authority ("FCA") United Kingdom Net capital $ 264.9 $ 110.8 StoneX Financial Ltd FCA United Kingdom Segregated funds $ 471.8 $ 467.4 StoneX Financial Pte. Ltd. Monetary Authority of Singapore ("MAS") Singapore Segregated funds $ 313.8 $ 307.0 (1) As of June 30, 2020 , the Company had $43.7 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 $8.1 million to the customer SRBA on July 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 June 30, 2020 , these subsidiaries were in compliance with their local capital adequacy requirements.

Other Expenses (Notes)

Other Expenses (Notes)	9 Months Ended
	Jun. 30, 2020
Other Expenses [Abstract]
Other Expenses [Text Block]	Other Expenses Other expenses for the three and nine months ended June 30, 2020 and 2019 consisted of the following: Three Months Ended June 30, Nine Months Ended June 30, (in millions) 2020 2019 2020 2019 Contingent consideration, net $ 0.2 $ — $ 0.3 $ — Insurance 1.1 0.9 3.1 2.6 Advertising, meetings and conferences 0.5 1.2 6.1 4.1 Office supplies and printing 0.6 0.5 1.5 1.5 Other clearing related expenses 0.8 0.7 2.2 1.8 Other non-income taxes 1.2 1.1 3.8 3.2 Other 3.2 2.7 8.7 7.8 Total other expenses $ 7.6 $ 7.1 $ 25.7 $ 21.0

Accumulated Other Comprehensive

Accumulated Other Comprehensive Income (Loss) (Notes)	9 Months Ended
	Jun. 30, 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 nine months ended June 30, 2020 . (in millions) Foreign Currency Translation Adjustment Pension Benefits Adjustment Accumulated Other Comprehensive Loss, net 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 June 30, 2020 $ (34.2 ) $ (4.0 ) $ (38.2 )

Income Taxes (Notes)

Income Taxes (Notes)	9 Months Ended
	Jun. 30, 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 $12.4 million and $5.3 million for the three months ended June 30, 2020 and 2019 , respectively, and income tax expense of $34.6 million and $19.0 million for the nine months ended June 30, 2020 and 2019 , respectively, reflects estimated federal, foreign, state and local income taxes. For the three months ended June 30, 2020 and 2019 , the Company’s effective tax rate was 25% . The effective tax 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. For the nine months ended June 30, 2020 and 2019 , the Company’s effective tax rate was 27% and 25% , respectively. The effective tax 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 1.0% and 1.3% for the nine months ended June 30, 2020 and 2019 , respectively. The amount of foreign earnings taxed at higher rates increased the effective tax rate approximately 2.0% and 1.4% for nine months ended June 30, 2020 and 2019 , respectively. The estimated U.S. state and local taxes increased the effective tax rate approximately 1.7% and 1.2% for nine months ended June 30, 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 June 30, 2020 and September 30, 2019, the Company has net operating loss carryforwards for U.S. federal, state, local, and foreign income tax purposes of $6.9 million and $7.1 million , net of valuation allowances, respectively, 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. 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 partially 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 June 30, 2020 and September 30, 2019 was $8.4 million and $8.5 million , respectively. The valuation allowances as of June 30, 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 June 30, 2020 and September 30, 2019, the Company had accumulated undistributed earnings generated by its foreign subsidiaries of approximately $426.6 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 repatriated $30.0 million and $13.0 million for the nine months ended June 30, 2020 and 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.

Acquisitions Acquisitions (Note

Acquisitions Acquisitions (Notes)	9 Months Ended
	Jun. 30, 2020
Acquisitions (Notes) [Abstract]
Business Combination Disclosure [Text Block]	Note 18 - Acquisitions The Company’s condensed consolidated financial statements include the operating results of the businesses acquired during the nine months ended June 30, 2020, from the dates of acquisition. On an aggregate basis, the businesses acquired during the reporting period, contributed $5.0 million and $12.7 million of total revenues for the three and nine months ended June 30, 2020. The earnings contributed by the acquired businesses from the dates of acquisition for the three and nine months ended June 30, 2020, were not material to the Company’s condensed consolidated income statements. UOB Bullion and Futures Limited On March 19, 2019, the Company’s subsidiary StoneX Financial 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 June 30, 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 June 30, 2020, the valuation of the acquired intangible assets and property and equipment was not yet complete as the Company is completing its final review of the valuation analysis. During the three months ended June 30, 2020, the Company recorded certain measurement period adjustments, which resulted in an increase in the purchase price allocated to the property and equipment acquired and the client base intangible assets acquired of $0.1 million and $1.0 million , respectively, with a corresponding decrease to the excess purchase price assigned to goodwill. As of June 30, 2020, given the status of the valuation analysis, $0.8 million of the purchase price was preliminarily allocated to the property and equipment acquired and $4.2 million was allocated to the client base intangible assets acquired. Once the valuation analysis is complete, the Company will record additional measurement period adjustments, if any, to reflect the final determination of 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 preliminarily been assigned a useful life of 5 years . 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 to closing. FINRA approval was obtained and the other conditions to closing were fulfilled and the closing of the transaction occurred 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 involved 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 was subject to limited conditions including regulatory approval in the relevant jurisdictions. The cash purchase price was 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, and the transaction closed on April 1, 2020. The cash purchase price for the acquisition of Exotix Partners, LLP, was $4.7 million . The final allocation of the cash purchase price to the fair value of assets acquired and liabilities assumed resulted in the recognition of $1.0 million in cash and cash equivalents, $1.0 million in receivables from clients, net, $0.3 million in property and equipment, net, $3.4 million in other assets, and $1.0 million in liabilities assumed. Regulatory approval for the acquisition of Tellimer Capital Ltd was obtained during the three months ending June 30, 2020, and the transaction closed on June 1, 2020. The cash purchase price for the acquisition of Tellimer Capital Ltd was not material to the Company’s condensed consolidated financial statements. The acquired businesses have been assigned to the Company’s Securities reportable segment. 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 the equity interests 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 StoneX Financial 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. GIROXX In January 2020, the Company’s wholly owned subsidiary, StoneX Financial Ltd, executed a stock purchase agreement to acquire 100% of GIROXX based in Germany. Through its digital platform, GIROXX 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 restructurings 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 and the transaction closed on May 1, 2020. The cash purchase price was $4.4 million . The preliminary allocation of the cash purchase price to the fair value of assets acquired and liabilities assumed resulted in the recognition of cash and cash equivalents of $6.5 million , property and equipment of $0.1 million , accounts payables and other accrued liabilities of $0.6 million , and payables to clients of $5.8 million as of the acquisition date. The excess purchase price over tangible net book value on the acquisition date of $4.2 million has been preliminarily allocated to goodwill. The Company acquired certain intangible assets in connection with the acquisition of GIROXX, primarily related to a business license permitting the Company to facilitate payment transactions in the European Union. The Company is in the process of gathering the information necessary to complete a valuation analysis of the intangible assets acquired. Once the valuation analysis is complete, the Company will record measurement period adjustments to reflect the final determination of the fair value of the intangible assets acquired with any remaining excess consideration allocated to goodwill. The acquired business has been assigned to the Company’s Global Payments reportable segment. Gain Capital On February 26, 2020, the Company entered into a definitive merger agreement to acquire Gain. The Company agreed to acquire Gain for $6.00 per share in an all-cash transaction representing approximately $236.2 million in equity value. Gain is a global provider of trading services and solutions to institutional and retail investors, specializing in both 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. As discussed in Note 11 , on June 11, 2020, the Company completed the issuance and sale of $350 million in aggregate principal amount of the Company’s 8.625% Notes. The Company had deposited the gross proceeds from the sale of the Senior Secured Notes, as well as escrow agency fees and interest on the Senior Secured Notes to (but not including) the date that is two months from the date of the closing of the offering of the Senior Secured Notes, into a segregated escrow account until the date that certain escrow release conditions were satisfied, which included the consummation of the merger of the Company’s wholly-owned subsidiary with Gain. As of June 30, 2020, the total amount held in escrow was $349.8 million and is included within ‘Restricted cash held in escrow’ on the Company’s condensed consolidated balance sheet. The merger closed on July 31, 2020 subsequent to approval by Gain’s shareholders, approval by regulators, and the completion of customary closing conditions. In connection with the closing of the merger and the satisfaction of the escrow release conditions, the proceeds from the issuance of the Senior Secured Notes were released from escrow. The Company used the net proceeds from the sale of the Senior Secured Notes to fund the preliminary cash consideration for the merger of Gain on the closing date and to pay certain related transactions fees and expenses. The Company intends to utilize the remaining proceeds to fund the repayment of $92 million of Gain’s 5.00% Convertible Senior Notes due 2022 (“the Gain Notes”). The consummation of the merger with Gain constituted a fundamental change and make-whole fundamental change under the terms of the Gain Notes’ indenture. As a result, the holders of the Gain Notes are entitled to require the Company to repurchase the Gain Notes at a repurchase price equal to $1,002.36 per $1,000 principal amount on September 1, 2020. Alternatively, the holders of the Gain Notes may continue to hold such notes without exercising the repurchase right, in which case the Gain Notes will continue to bear interest at 5.00% and the notes will be convertible into the right to convert the principal amount of the Senior Secured Notes solely into cash in an amount equal to the conversion rate in effect on the conversion date multiplied by $6.00. If any holder of the Gain Notes neither exercises such holder's fundamental change repurchase right or make-whole fundamental change conversion right, such holder's Gain Notes will remain outstanding. To the extent that any Gain Notes remain outstanding following the fundamental change repurchase date, the Company will be required to redeem the Senior Secured Notes in an amount equal to the aggregate principal amount of the Gain Notes that remain outstanding after the fundamental change repurchase date, at a redemption price equal to 100% of the principal amount of the Senior Secured Notes redeemed, plus accrued and unpaid interest, if any, to the redemption date. The preliminary allocation of the cash purchase price to the fair value of assets acquired and liabilities assumed has not yet been completed. The Company incurred acquisition related costs related to the merger for the three and nine months ended June 30, 2020, of $1.4 million and $1.9 million

Segment Analysis (Notes)

Segment Analysis (Notes)	9 Months Ended
	Jun. 30, 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 June 30, Nine Months Ended June 30, (in millions) 2020 2019 2020 2019 Total revenues: Commercial Hedging $ 65.1 $ 86.4 $ 236.5 $ 226.8 Global Payments 27.4 28.9 88.2 86.0 Securities 123.0 74.2 322.0 215.8 Physical Commodities 7,960.0 7,604.3 38,971.8 20,847.0 Clearing and Execution Services 68.9 78.9 241.3 247.7 Corporate Unallocated 2.3 6.5 11.5 13.5 Eliminations (3.3 ) (6.2 ) (16.6 ) (19.4 ) Total $ 8,243.4 $ 7,873.0 $ 39,854.7 $ 21,617.4 Operating revenues: Commercial Hedging $ 65.1 $ 86.4 $ 236.5 $ 226.8 Global Payments 27.4 28.9 88.2 86.0 Securities 123.0 74.2 322.0 215.8 Physical Commodities 39.2 14.7 83.3 48.8 Clearing and Execution Services 68.9 78.9 241.3 247.7 Corporate Unallocated 2.3 6.5 11.5 13.5 Eliminations (3.3 ) (6.2 ) (16.6 ) (19.4 ) Total $ 322.6 $ 283.4 $ 966.2 $ 819.2 Net operating revenues (loss): Commercial Hedging $ 50.8 $ 66.9 $ 189.4 $ 178.0 Global Payments 26.0 27.5 83.8 81.7 Securities 97.1 30.3 218.3 94.4 Physical Commodities 35.7 9.7 71.1 35.2 Clearing and Execution Services 22.8 32.5 89.9 101.0 Corporate Unallocated (4.5 ) (1.3 ) (10.7 ) (10.5 ) Total $ 227.9 $ 165.6 $ 641.8 $ 479.8 Net contribution: (Revenues less cost of sales of physical commodities, transaction-based clearing expenses, variable compensation, introducing broker commissions and interest expense) Commercial Hedging $ 36.0 $ 48.0 $ 133.9 $ 127.9 Global Payments 20.9 22.3 67.3 66.4 Securities 64.3 17.9 142.2 59.8 Physical Commodities 24.2 6.4 49.3 25.0 Clearing and Execution Services 18.2 25.0 71.6 78.1 Total $ 163.6 $ 119.6 $ 464.3 $ 357.2 Segment income: (Net contribution less non-variable direct segment costs) Commercial Hedging $ 19.2 $ 29.7 $ 76.5 $ 73.2 Global Payments 15.9 17.0 52.0 51.4 Securities 51.6 8.2 106.7 36.0 Physical Commodities 20.3 2.8 37.5 16.5 Clearing and Execution Services 3.7 11.9 31.1 41.2 Total $ 110.7 $ 69.6 $ 303.8 $ 218.3 Reconciliation of segment income to income before tax: Segment income $ 110.7 $ 69.6 $ 303.8 $ 218.3 Net costs not allocated to operating segments 61.7 48.0 177.1 146.8 Other gain — — 0.1 5.4 Income before tax $ 49.0 $ 21.6 $ 126.8 $ 76.9 (in millions) As of June 30, 2020 As of September 30, 2019 Total assets: Commercial Hedging $ 2,112.6 $ 2,041.0 Global Payments 234.8 278.3 Securities 6,284.3 5,219.1 Physical Commodities 425.3 357.8 Clearing and Execution Services 2,546.1 1,892.1 Corporate Unallocated 786.4 147.8 Total $ 12,389.5 $ 9,936.1

Basis of Presentation and Con_2

Basis of Presentation and Consolidation and Recently Issued Accounting Standards (Policies)	9 Months Ended
	Jun. 30, 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 StoneX Group 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. These estimates and assumptions were considered and made in context with the information reasonably available to the Company and the unknown future impacts of the novel coronavirus (COVID-19) as of June 30, 2020 and through the date of this Form 10-Q
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 loss, net 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)	9 Months Ended
	Jun. 30, 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)	9 Months Ended
	Jun. 30, 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 $12.4 million and $5.3 million for the three months ended June 30, 2020 and 2019 , respectively, and income tax expense of $34.6 million and $19.0 million for the nine months ended June 30, 2020 and 2019 , respectively, reflects estimated federal, foreign, state and local income taxes. For the three months ended June 30, 2020 and 2019 , the Company’s effective tax rate was 25% . The effective tax 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. For the nine months ended June 30, 2020 and 2019 , the Company’s effective tax rate was 27% and 25% , respectively. The effective tax 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 1.0% and 1.3% for the nine months ended June 30, 2020 and 2019 , respectively. The amount of foreign earnings taxed at higher rates increased the effective tax rate approximately 2.0% and 1.4% for nine months ended June 30, 2020 and 2019 , respectively. The estimated U.S. state and local taxes increased the effective tax rate approximately 1.7% and 1.2% for nine months ended June 30, 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 June 30, 2020 and September 30, 2019, the Company has net operating loss carryforwards for U.S. federal, state, local, and foreign income tax purposes of $6.9 million and $7.1 million , net of valuation allowances, respectively, 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. 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 partially 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 June 30, 2020 and September 30, 2019 was $8.4 million and $8.5 million , respectively. The valuation allowances as of June 30, 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 June 30, 2020 and September 30, 2019, the Company had accumulated undistributed earnings generated by its foreign subsidiaries of approximately $426.6 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 repatriated $30.0 million and $13.0 million for the nine months ended June 30, 2020 and 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.

Leases Operating Lease Liabilit

Leases Operating Lease Liability Maturities (Tables)	9 Months Ended
	Jun. 30, 2020
Operating Lease Liabilities Maturities [Abstract]
Lessee, Operating Lease, Liability, Maturity [Table Text Block]	Remainder of 2020 $ 3.8 2021 10.9 2022 11.1 2023 9.5 2024 7.7 After 2024 67.3 Total lease payments 110.3 Less: interest 22.9 Present value of lease liabilities $ 87.4
Lease, Cost [Table Text Block]	Three Months Ended June 30, Nine Months Ended June 30, 2020 2020 Operating lease costs (1) $ 4.1 $ 11.1 Supplemental cash flow information and non-cash activity: Cash paid for amounts included in the measurement of operating lease liabilities $ 2.9 $ 8.4 Right-of-use assets obtained in exchange for operating lease liabilities $ 46.0 $ 81.0 Lease term and discount rate information: Weighted average remaining lease term (years) 11.64 Weighted average discount rate 3.9 %
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)	9 Months Ended
	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Disaggregation of Revenue [Table Text Block]	Three Months Ended June 30, Nine Months Ended June 30, 2020 2019 2020 2019 Revenues from contracts with clients: Commission and clearing fees: Sales-based: Exchange-traded futures and options $ 36.4 $ 40.4 $ 108.9 $ 110.7 OTC derivative brokerage 4.0 7.7 16.2 23.9 Equities and fixed income 5.2 4.3 16.6 11.1 Mutual funds 1.1 1.6 4.0 6.1 Insurance and annuity products 1.7 2.1 6.2 5.1 Other 0.3 0.3 1.1 1.0 Total sales-based commission 48.7 56.4 153.0 157.9 Trailing: Mutual funds 3.1 3.1 9.7 9.3 Insurance and annuity products 3.6 3.6 11.3 10.7 Total trailing commission 6.7 6.7 21.0 20.0 Clearing fees 33.3 30.3 104.4 89.7 Trade conversion fees 1.8 1.3 7.5 6.2 Other 5.6 2.8 14.0 8.3 Total commission and clearing fees: 96.1 97.5 299.9 282.1 Consulting, management, and account fees: Underwriting fees — 0.2 0.4 0.7 Asset management fees 7.0 7.2 23.2 19.4 Advisory and consulting fees 5.7 5.1 17.0 14.8 Sweep program fees 1.0 4.2 8.6 12.1 Client account fees 2.8 2.6 8.9 7.8 Other 2.9 1.4 5.2 4.1 Total consulting, management, and account fees 19.4 20.7 63.3 58.9 Total revenues from contracts with clients $ 115.5 $ 118.2 $ 363.2 $ 341.0 Method of revenue recognition: Point-in-time $ 95.1 $ 95.0 $ 293.4 $ 274.7 Time elapsed 20.4 23.2 69.8 66.3 Total revenues from contracts with clients 115.5 118.2 363.2 341.0 Other sources of revenues Physical precious metals trading 7,621.2 7,327.8 37,973.9 19,944.2 Physical agricultural and energy product trading 323.3 271.5 965.5 880.4 Principal gains, net 161.0 102.3 442.0 305.4 Interest income 22.4 53.2 110.1 146.4 Total revenues $ 8,243.4 $ 7,873.0 $ 39,854.7 $ 21,617.4 Primary geographic region: United States $ 554.2 $ 474.8 $ 1,652.1 $ 1,458.4 Europe 114.1 77.8 375.7 184.9 South America 14.6 15.3 46.1 39.2 Middle East and Asia 7,558.5 7,303.8 37,777.3 19,929.7 Other 2.0 1.3 3.5 5.2 Total revenues $ 8,243.4 $ 7,873.0 $ 39,854.7 $ 21,617.4

Earnings per Share (Tables)

Earnings per Share (Tables)	9 Months Ended
	Jun. 30, 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 June 30, Nine Months Ended June 30, (in millions, except share amounts) 2020 2019 2020 2019 Numerator: Net income $ 36.6 $ 16.3 $ 92.2 $ 57.9 Less: Allocation to participating securities (0.9 ) (0.3 ) (2.1 ) (1.0 ) Net income allocated to common stockholders $ 35.7 $ 16.0 $ 90.1 $ 56.9 Denominator: Weighted average number of: Common shares outstanding 18,807,104 18,781,401 18,809,823 18,731,203 Dilutive potential common shares outstanding: Share-based awards 296,062 230,125 312,858 272,517 Diluted weighted-average common shares 19,103,166 19,011,526 19,122,681 19,003,720

Assets and Liabilities, at Fa_2

Assets and Liabilities, at Fair Value (Tables)	9 Months Ended
	Jun. 30, 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 June 30, 2020 by level in the fair value hierarchy. June 30, 2020 (in millions) Level 1 Level 2 Level 3 Netting (1) Total Assets: Certificates of deposit $ 2.7 $ — $ — $ — $ 2.7 Money market mutual funds 11.4 — — — 11.4 Cash and cash equivalents 14.1 — — — 14.1 Commodities warehouse receipts 9.6 — — — 9.6 U.S. Treasury obligations 0.2 — — — 0.2 Securities and other assets segregated under federal and other regulations 9.8 — — — 9.8 U.S. Treasury obligations 1,148.4 — — — 1,148.4 To be announced ("TBA") and forward settling securities — 12.2 — (5.3 ) 6.9 Foreign government obligations 8.2 — — — 8.2 Derivatives 2,876.9 13.7 — (2,792.5 ) 98.1 Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net 4,033.5 25.9 — (2,797.8 ) 1,261.6 Equity securities 248.7 12.0 — — 260.7 Corporate and municipal bonds — 75.4 — — 75.4 U.S. Treasury obligations 372.5 — — — 372.5 U.S. government agency obligations — 347.8 — — 347.8 Foreign government obligations 12.6 — — — 12.6 Agency mortgage-backed obligations — 1,558.3 — — 1,558.3 Asset-backed obligations — 19.4 — — 19.4 Derivatives 0.5 971.9 — (880.0 ) 92.4 Commodities leases — 23.2 — — 23.2 Commodities warehouse receipts 56.4 — — — 56.4 Exchange firm common stock 9.8 — — — 9.8 Mutual funds and other 3.4 — — — 3.4 Financial instruments owned 703.9 3,008.0 — (880.0 ) 2,831.9 Physical commodities inventory 19.8 153.8 — — 173.6 Total assets at fair value $ 4,781.1 $ 3,187.7 $ — $ (3,677.8 ) $ 4,291.0 Liabilities: Accounts payable and other accrued liabilities - contingent liabilities — — 1.6 — 1.6 TBA and forward settling securities — 12.6 — (5.3 ) 7.3 Derivatives 2,773.9 169.3 — (2,941.7 ) 1.5 Payable to broker-dealers, clearing organizations and counterparties 2,773.9 181.9 — (2,947.0 ) 8.8 Equity securities 202.2 15.4 — — 217.6 Foreign government obligations 2.2 — — — 2.2 Corporate and municipal bonds — 26.1 — — 26.1 U.S. Treasury obligations 354.1 — — — 354.1 U.S. government agency obligations — 6.1 — — 6.1 Agency mortgage-backed obligations — 21.1 — — 21.1 Derivatives — 937.0 — (838.3 ) 98.7 Commodities leases — 2.4 — — 2.4 Financial instruments sold, not yet purchased 558.5 1,008.1 — (838.3 ) 728.3 Total liabilities at fair value $ 3,332.4 $ 1,190.0 $ 1.6 $ (3,785.3 ) $ 738.7 (1) Represents cash collateral and the impact of netting across the levels of the fair value hierarchy. Netting among positions classified within the same level 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)	9 Months Ended
	Jun. 30, 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 June 30, 2020 and September 30, 2019 . Assets represent net unrealized gains and liabilities represent net unrealized losses. June 30, 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 $ 1,949.1 $ 2,085.0 $ 1,437.1 $ 1,463.4 OTC commodity derivatives 359.0 489.5 84.2 106.2 Exchange-traded foreign exchange derivatives 11.4 14.3 36.9 33.5 OTC foreign exchange derivatives 525.5 516.2 403.2 368.8 Exchange-traded interest rate derivatives 852.9 603.7 900.1 882.0 OTC interest rate derivatives 101.1 100.6 42.1 43.6 Exchange-traded equity index derivatives 64.0 70.9 758.1 700.2 TBA and forward settling securities 12.2 12.6 9.8 6.8 Gross fair value of derivative contracts 3,875.2 3,892.8 3,671.5 3,604.5 Impact of netting and collateral (3,677.8 ) (3,785.3 ) (3,581.9 ) (3,540.8 ) Total fair value included in 'Deposits with and receivables from broker-dealers, clearing organizations, and counterparties, net' $ 105.0 $ 23.1 Total fair value included in 'Financial instruments owned, at fair value $ 92.4 $ 66.5 Total fair value included in 'Payables to broker-dealers, clearing organizations and counterparties $ 8.8 $ 5.6 Fair value included in 'Financial instruments sold, not yet purchased, at fair value' $ 98.7 $ 58.1 (1) As of June 30, 2020 and September 30, 2019 , the Company’s derivative contract volume for open positions were approximately 9.3 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 June 30, 2020 and September 30, 2019 , these transactions are summarized as follows: June 30, 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, net and related notional amounts $ 7.7 $ 2,170.9 $ 3.7 $ 1,778.4 Unrealized loss on TBA securities purchased within deposits with and receivables from broker-dealers, clearing organizations and counterparties, net and related notional amounts $ (1.9 ) $ 928.5 $ (0.6 ) $ 234.5 Unrealized gain on TBA securities sold within payables to broker-dealers, clearing organizations and counterparties and related notional amounts $ 3.4 $ (1,566.8 ) $ 0.9 $ (451.6 ) Unrealized loss on TBA securities sold within payables to broker-dealers, clearing organizations and counterparties and related notional amounts $ (10.2 ) $ (2,982.1 ) $ (5.9 ) $ (2,788.0 ) Unrealized gain on forward settling securities purchased within deposits with and receivables from broker-dealers, clearing organizations and counterparties, net and related notional amounts $ 1.1 1,690.5 $ — $ — 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, net 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 $ (0.5 ) (1,268.3 ) $ — $ — (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 nine months ended June 30, 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 June 30, Nine Months Ended June 30, (in millions) 2020 2019 2020 2019 Commodities $ 28.1 $ 19.5 $ 107.9 $ 63.6 Foreign exchange 2.6 1.6 9.9 5.3 Interest rate and equity 0.7 (0.6 ) 0.3 (3.2 ) TBA and forward settling securities (5.6 ) (8.0 ) (40.9 ) (6.7 ) Net gains from derivative contracts $ 25.8 $ 12.5 $ 77.2 $ 59.0

Physical Commodities Inventor_2

Physical Commodities Inventory Physical Commodities Table (Tables)	9 Months Ended
	Jun. 30, 2020
Inventory Disclosure [Abstract]
Schedule of Inventory, Current [Table Text Block]	(in millions) June 30, September 30, Physical Ag & Energy (1) $ 153.8 $ 144.8 Precious metals - held by broker-dealer subsidiary (2) 19.8 7.1 Precious metals - held by non-broker-dealer subsidiaries (3) 96.6 77.4 Physical commodities inventory $ 270.2 $ 229.3

Goodwill (Tables)

Goodwill (Tables)	9 Months Ended
	Jun. 30, 2020
Goodwill [Abstract]
Schedule of Goodwill [Table Text Block]	The carrying value of goodwill is allocated to the Company’s reportable segments as follows: (in millions) June 30, September 30, Commercial Hedging $ 30.3 $ 30.3 Global Payments 11.8 7.6 Physical Commodities 4.6 4.6 Securities 8.7 8.7 Goodwill $ 55.4 $ 51.2

Intangible Assets - (Tables)

Intangible Assets - (Tables)	9 Months Ended
	Jun. 30, 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): June 30, 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 $ (3.4 ) $ 1.9 $ 5.3 $ (3.0 ) $ 2.3 Customer base 29.1 (15.1 ) 14.0 22.1 (12.5 ) 9.6 Total intangible assets subject to amortization: 34.4 (18.5 ) 15.9 27.4 (15.5 ) 11.9 Intangible assets not subject to amortization: Website domains 2.1 — 2.1 2.1 — 2.1 Business licenses 2.9 — 2.9 2.7 — 2.7 Total intangible assets not subject to amortization: 5.0 — 5.0 4.8 — 4.8 Total intangible assets $ 39.4 $ (18.5 ) $ 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 June 30, 2020 and 2019 , respectively. Amortization expense related to intangible assets was $3.0 million and $1.9 million for the nine months ended June 30, 2020 and 2019 , respectively. As of June 30, 2020 , the estimated future amortization expense was as follows: (in millions) Fiscal 2020 (Remaining three months) $ 1.0 Fiscal 2021 4.2 Fiscal 2022 2.9 Fiscal 2023 2.7 Fiscal 2024 and thereafter 5.1 Total intangible assets subject to amortization $ 15.9

Credit Facilities (Tables)

Credit Facilities (Tables)	9 Months Ended
	Jun. 30, 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 and the Senior Secured Notes as of the periods indicated: (in millions) Amounts Outstanding Borrower Security Renewal/Expiration Date Total Commitment June 30, September 30, Committed Credit Facilities Term Loan (1) February 22, 2022 $ 182.5 $ 182.0 (3) $ 167.6 Revolving Line of Credit (1) February 22, 2022 196.5 127.0 70.0 Senior StoneX Group Inc. Committed Credit Facility 379.0 309.0 237.6 StoneX Financial Inc. None April 2, 2021 75.0 — — FCStone Merchants Services, LLC Certain commodities assets January 29, 2022 260.0 162.4 128.5 StoneX Financial Ltd. None September 14, 2020 25.0 — — $ 739.0 $ 471.4 $ 366.1 Uncommitted Credit Facilities StoneX Financial Inc. Commodities warehouse receipts and certain pledged securities n/a n/a 24.4 — FCStone Merchant Services, LLC Certain commodities assets n/a n/a — 3.4 StoneX Group Inc. Note Payable to Bank Certain equipment — 0.4 Senior Secured Notes (2) 336.9 (3) — Total outstanding borrowings $ 832.7 $ 369.9

Commodity and Other Repurchas_2

Commodity and Other Repurchase Agreements and Collateralized Transactions Schedule of Gross Collateralized Financings by Maturity (Tables)	9 Months Ended
	Jun. 30, 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]	June 30, 2020 Overnight and Open Less than 30 Days 30-90 Days Over 90 Days Total Securities sold under agreements to repurchase $ 2,079.3 $ 899.1 $ 492.0 $ 60.0 $ 3,530.4 Securities loaned 1,459.7 — — — 1,459.7 Gross amount of secured financing $ 3,539.0 $ 899.1 $ 492.0 $ 60.0 $ 4,990.1 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)	9 Months Ended
	Jun. 30, 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 June 30, 2020 September 30, 2019 U.S. Treasury obligations $ 1,075.8 $ 108.8 U.S. government agency obligations 206.8 359.5 Asset-backed obligations 17.1 96.7 Agency mortgage-backed obligations 2,163.8 2,208.7 Corporate bonds 66.9 — Total securities sold under agreement to repurchase 3,530.4 2,773.7 Securities loaned Equity securities 1,459.7 1,459.9 Total securities loaned 1,459.7 1,459.9 Gross amount of secured financing $ 4,990.1 $ 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): June 30, 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 $ 1,757.3 $ — $ 1,757.3 Securities borrowed $ 1,467.4 $ — $ 1,467.4 Securities sold under agreements to repurchase $ 3,530.4 $ — $ 3,530.4 Securities loaned $ 1,459.7 $ — $ 1,459.7 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)	9 Months Ended
	Jun. 30, 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 June 30, 2020. The following table details those subsidiaries with minimum regulatory requirements in excess of $5 million along with the actual balance maintained as of June 30, 2020. (in millions) As of June 30, 2020 Subsidiary Regulatory Authority Jurisdiction Requirement Type Actual Minimum Requirement StoneX Financial Inc. SEC and CFTC United States Net capital $ 198.6 $ 126.0 StoneX Financial Inc. CFTC United States Segregated funds $ 2,705.6 $ 2,650.1 StoneX Financial Inc. CFTC United States Secured funds $ 160.6 $ 148.8 StoneX Financial Inc. (1) SEC United States Customer reserve $ 43.7 $ 46.8 StoneX Financial Ltd Financial Conduct Authority ("FCA") United Kingdom Net capital $ 264.9 $ 110.8 StoneX Financial Ltd FCA United Kingdom Segregated funds $ 471.8 $ 467.4 StoneX Financial Pte. Ltd. Monetary Authority of Singapore ("MAS") Singapore Segregated funds $ 313.8 $ 307.0 (1) As of June 30, 2020 , the Company had $43.7 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 $8.1 million to the customer SRBA on July 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 June 30, 2020 , these subsidiaries were in compliance with their local capital adequacy requirements.

Other Expenses (Tables)

Other Expenses (Tables)	9 Months Ended
	Jun. 30, 2020
Other Expenses [Abstract]
Schedule of Other Operating Cost and Expense, by Component [Table Text Block]	Other expenses for the three and nine months ended June 30, 2020 and 2019 consisted of the following: Three Months Ended June 30, Nine Months Ended June 30, (in millions) 2020 2019 2020 2019 Contingent consideration, net $ 0.2 $ — $ 0.3 $ — Insurance 1.1 0.9 3.1 2.6 Advertising, meetings and conferences 0.5 1.2 6.1 4.1 Office supplies and printing 0.6 0.5 1.5 1.5 Other clearing related expenses 0.8 0.7 2.2 1.8 Other non-income taxes 1.2 1.1 3.8 3.2 Other 3.2 2.7 8.7 7.8 Total other expenses $ 7.6 $ 7.1 $ 25.7 $ 21.0

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Income (Loss) (Tables)	9 Months Ended
	Jun. 30, 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 nine months ended June 30, 2020 . (in millions) Foreign Currency Translation Adjustment Pension Benefits Adjustment Accumulated Other Comprehensive Loss, net 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 June 30, 2020 $ (34.2 ) $ (4.0 ) $ (38.2 )

Segment Analysis (Tables)

Segment Analysis (Tables)	9 Months Ended
	Jun. 30, 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 June 30, Nine Months Ended June 30, (in millions) 2020 2019 2020 2019 Total revenues: Commercial Hedging $ 65.1 $ 86.4 $ 236.5 $ 226.8 Global Payments 27.4 28.9 88.2 86.0 Securities 123.0 74.2 322.0 215.8 Physical Commodities 7,960.0 7,604.3 38,971.8 20,847.0 Clearing and Execution Services 68.9 78.9 241.3 247.7 Corporate Unallocated 2.3 6.5 11.5 13.5 Eliminations (3.3 ) (6.2 ) (16.6 ) (19.4 ) Total $ 8,243.4 $ 7,873.0 $ 39,854.7 $ 21,617.4 Operating revenues: Commercial Hedging $ 65.1 $ 86.4 $ 236.5 $ 226.8 Global Payments 27.4 28.9 88.2 86.0 Securities 123.0 74.2 322.0 215.8 Physical Commodities 39.2 14.7 83.3 48.8 Clearing and Execution Services 68.9 78.9 241.3 247.7 Corporate Unallocated 2.3 6.5 11.5 13.5 Eliminations (3.3 ) (6.2 ) (16.6 ) (19.4 ) Total $ 322.6 $ 283.4 $ 966.2 $ 819.2 Net operating revenues (loss): Commercial Hedging $ 50.8 $ 66.9 $ 189.4 $ 178.0 Global Payments 26.0 27.5 83.8 81.7 Securities 97.1 30.3 218.3 94.4 Physical Commodities 35.7 9.7 71.1 35.2 Clearing and Execution Services 22.8 32.5 89.9 101.0 Corporate Unallocated (4.5 ) (1.3 ) (10.7 ) (10.5 ) Total $ 227.9 $ 165.6 $ 641.8 $ 479.8 Net contribution: (Revenues less cost of sales of physical commodities, transaction-based clearing expenses, variable compensation, introducing broker commissions and interest expense) Commercial Hedging $ 36.0 $ 48.0 $ 133.9 $ 127.9 Global Payments 20.9 22.3 67.3 66.4 Securities 64.3 17.9 142.2 59.8 Physical Commodities 24.2 6.4 49.3 25.0 Clearing and Execution Services 18.2 25.0 71.6 78.1 Total $ 163.6 $ 119.6 $ 464.3 $ 357.2 Segment income: (Net contribution less non-variable direct segment costs) Commercial Hedging $ 19.2 $ 29.7 $ 76.5 $ 73.2 Global Payments 15.9 17.0 52.0 51.4 Securities 51.6 8.2 106.7 36.0 Physical Commodities 20.3 2.8 37.5 16.5 Clearing and Execution Services 3.7 11.9 31.1 41.2 Total $ 110.7 $ 69.6 $ 303.8 $ 218.3 Reconciliation of segment income to income before tax: Segment income $ 110.7 $ 69.6 $ 303.8 $ 218.3 Net costs not allocated to operating segments 61.7 48.0 177.1 146.8 Other gain — — 0.1 5.4 Income before tax $ 49.0 $ 21.6 $ 126.8 $ 76.9 (in millions) As of June 30, 2020 As of September 30, 2019 Total assets: Commercial Hedging $ 2,112.6 $ 2,041.0 Global Payments 234.8 278.3 Securities 6,284.3 5,219.1 Physical Commodities 425.3 357.8 Clearing and Execution Services 2,546.1 1,892.1 Corporate Unallocated 786.4 147.8 Total $ 12,389.5 $ 9,936.1

Basis of Presentation and Con_3

Basis of Presentation and Consolidation and Recently Issued Accounting Standards (Details) $ in Millions	9 Months Ended
	Jun. 30, 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 ($) $ in Millions	3 Months Ended	9 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Sep. 30, 2019
Leases [Abstract]
Operating right of use assets	$ 75	$ 75	$ 0
Operating Lease, Cost	$ 4.1	$ 11.1
Operating Lease, Weighted Average Remaining Lease Term	11 years 7 months 20 days	11 years 7 months 20 days
Operating Lease, Weighted Average Discount Rate, Percent	3.90%	3.90%
Operating Lease, Payments	$ 2.9	$ 8.4
Right-of-Use Asset Obtained in Exchange for Operating Lease Liability	46	81
Operating lease liabilities	$ 87.4	$ 87.4	$ 0

Leases Maturities of Operating

Leases Maturities of Operating Lease Liabilities (Details) $ in Millions	Jun. 30, 2020USD ($)
Maturities of Operating Lease Liabilities [Abstract]
Lessee, Operating Lease, Liability, Payments, Due Next Twelve Months	$ 3.8
Lessee, Operating Lease, Liability, Payments, Due Year Two	10.9
Lessee, Operating Lease, Liability, Payments, Due Year Three	11.1
Lessee, Operating Lease, Liability, Payments, Due Year Four	9.5
Lessee, Operating Lease, Liability, Payments, Due Year Five	7.7
Lessee, Operating Lease, Liability, Payments, Due after Year Five	67.3
Lessee, Operating Lease, Liability, Payments, Due	110.3
Lessee, Operating Lease, Liability, Undiscounted Excess Amount	$ 22.9

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, 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
Operating Leases, Future Minimum Payments Due	$ 43.2

Revenue from Contracts with C_3

Revenue from Contracts with Clients (Details)	3 Months Ended		9 Months Ended
	Jun. 30, 2020Rate	Jun. 30, 2019Rate	Jun. 30, 2020Rate	Jun. 30, 2019Rate
Revenues from Contracts With Clients [Abstract]
Revenues from contracts with clients as a % of total revenues	1.40%	1.50%	0.90%	1.60%
Revenues from contracts with clients as a % of operating revenues	35.80%	41.70%	37.60%	41.60%

Revenue from Contracts with C_4

Revenue from Contracts with Clients Disaggregation of Revenues Table (Details) - USD ($)	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	$ 115,500,000	$ 118,200,000	$ 363,200,000	$ 341,000,000
Revenues	8,243,400,000	7,873,000,000	39,854,700,000	21,617,400,000
Commission and clearing fees	96,100,000	97,500,000	299,900,000	282,100,000
Consulting, management, and account fees	19,400,000	20,700,000	63,300,000	58,900,000
Transferred at Point in Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	95,100,000	95,000,000	293,400,000	274,700,000
Transferred over Time [Member]
Disaggregation of Revenue [Line Items]
Revenue from Contract with Customer, Including Assessed Tax	20,400,000	23,200,000	69,800,000	66,300,000
UNITED STATES
Disaggregation of Revenue [Line Items]
Revenues	554,200,000	474,800,000	1,652,100,000	1,458,400,000
Europe [Member]
Disaggregation of Revenue [Line Items]
Revenues	114,100,000	77,800,000	375,700,000	184,900,000
South America [Member]
Disaggregation of Revenue [Line Items]
Revenues	14,600,000	15,300,000	46,100,000	39,200,000
Middle East and Asia [Domain]
Disaggregation of Revenue [Line Items]
Revenues	7,558,500,000	7,303,800,000	37,777,300,000	19,929,700,000
Other (geographic location) [Member]
Disaggregation of Revenue [Line Items]
Revenues	2,000,000	1,300,000	3,500,000	5,200,000
Interest Income [Member]
Disaggregation of Revenue [Line Items]
Revenues	22,400,000	53,200,000	110,100,000	146,400,000
Brokerage commissions revenue [Domain] | Exhange-Traded Futures and Options [Member]
Disaggregation of Revenue [Line Items]
Revenues	36,400,000	40,400,000	108,900,000	110,700,000
Brokerage commissions revenue [Domain] | OTC Derivative Brokerage [Member]
Disaggregation of Revenue [Line Items]
Revenues	4,000,000	7,700,000	16,200,000	23,900,000
Brokerage commissions revenue [Domain] | Equities and Fixed Income Commissions [Member]
Disaggregation of Revenue [Line Items]
Revenues	5,200,000	4,300,000	16,600,000	11,100,000
Brokerage commissions revenue [Domain] | Mutual Fund Sales Based Commissions [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,100,000	1,600,000	4,000,000	6,100,000
Brokerage commissions revenue [Domain] | insurance and annuity products [Domain] [Domain]
Disaggregation of Revenue [Line Items]
Revenues	1,700,000	2,100,000	6,200,000	5,100,000
Brokerage commissions revenue [Domain] | Other Commissions [Domain]
Disaggregation of Revenue [Line Items]
Revenues	5,600,000	2,800,000	14,000,000	8,300,000
Brokerage commissions revenue [Domain] | Other Sales Based Commissions [Member]
Disaggregation of Revenue [Line Items]
Revenues	300,000	300,000	1,100,000	1,000,000
Brokerage commissions revenue [Domain] | Sales Based Commissions [Domain]
Disaggregation of Revenue [Line Items]
Sales Commissions and Fees	48,700,000	56,400,000	153,000,000	157,900,000
Brokerage commissions revenue [Domain] | Mutual Fund Trailing Commissions [Member]
Disaggregation of Revenue [Line Items]
Revenues	3,100,000	3,100,000	9,700,000	9,300,000
Brokerage commissions revenue [Domain] | Insurance and annuity product trailing commissions [Domain]
Disaggregation of Revenue [Line Items]
Revenues	3,600,000	3,600,000	11,300,000	10,700,000
Brokerage commissions revenue [Domain] | Trade Conversion Fees [Domain]
Disaggregation of Revenue [Line Items]
Revenues	1,800,000	1,300,000	7,500,000	6,200,000
Brokerage commissions revenue [Domain] | Clearing Fees [Domain]
Disaggregation of Revenue [Line Items]
Revenues	33,300,000	30,300,000	104,400,000	89,700,000
Brokerage commissions revenue [Domain] | Trailing Commissions [Domain]
Disaggregation of Revenue [Line Items]
Revenues	6,700,000	6,700,000	21,000,000	20,000,000
Consulting, management, and account fees [Domain] | Sweep Program Fees [Member]
Disaggregation of Revenue [Line Items]
Revenues	1,000,000	4,200,000	8,600,000	12,100,000
Consulting, management, and account fees [Domain] | Advisory and Consulting Fees [Member]
Disaggregation of Revenue [Line Items]
Revenues	5,700,000	5,100,000	17,000,000	14,800,000
Consulting, management, and account fees [Domain] | Asset Management [Member]
Disaggregation of Revenue [Line Items]
Revenues	7,000,000	7,200,000	23,200,000	19,400,000
Consulting, management, and account fees [Domain] | Underwriting Fees [Member]
Disaggregation of Revenue [Line Items]
Revenues	0	200,000	400,000	700,000
Consulting, management, and account fees [Domain] | Client Account Fees [Member]
Disaggregation of Revenue [Line Items]
Revenues	2,800,000	2,600,000	8,900,000	7,800,000
Consulting, management, and account fees [Domain] | Other Consulting, Management, and Account Fees [Member]
Disaggregation of Revenue [Line Items]
Revenues	2,900,000	1,400,000	5,200,000	4,100,000
Principal or Proprietary Transactions [Member]
Disaggregation of Revenue [Line Items]
Revenues	161,000,000	102,300,000	442,000,000	305,400,000
Sales of physical commodities [Member] | Precious Metals Trading Revenues [Member]
Disaggregation of Revenue [Line Items]
Revenues	7,621,200,000	7,327,800,000	37,973,900,000	19,944,200,000
Sales of physical commodities [Member] | Physical Commodity Origination and Merchandising [Member]
Disaggregation of Revenue [Line Items]
Revenues	$ 323,300,000	$ 271,500,000	$ 965,500,000	$ 880,400,000

Earnings per Share - EPS Reconc

Earnings per Share - EPS Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share [Abstract]
Net income	$ 36.6	$ 16.3	$ 92.2	$ 57.9
Less: Net income allocated to participating securities	(0.9)	(0.3)	(2.1)	(1)
Net income allocated to common shareholders	$ 35.7	$ 16	$ 90.1	$ 56.9
Weighted average number of common shares outstanding	18,807,104	18,781,401	18,809,823	18,731,203
Dilutive potential common shares outstanding:
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	296,062	230,125	312,858	272,517
Diluted weighted-average shares	19,103,166	19,011,526	19,122,681	19,003,720

Earnings per Share - Antiduliti

Earnings per Share - Antidulitive Securities (Details) - shares	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share [Abstract]
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount	947,830	1,209,943	983,799	835,441

Assets and Liabilities, at Fa_3

Assets and Liabilities, at Fair Value - Financial Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Millions	9 Months Ended
	Jun. 30, 2020	Sep. 30, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Cash Equivalents, Fair Value Disclosure	$ 9.8	$ 306
Cash and Securities Segregated under Federal and Other Regulations	1,145.2	1,049.9
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net (including $1261.6 and $626.9 at fair value at June 30, 2020 and September 30, 2019, respectively)	3,396.7	2,540.5
Financial Instruments, Owned, at Fair Value	2,831.9	2,175.2
Physical commodities inventory	270.2	229.3
Accounts Payable and Other Accrued Liabilities	176.4	157.5
Broker-Dealer, Payable to Other Broker-Dealer and Clearing Organization	(430)	(266.2)
Financial Instruments Sold, Not yet Purchased, at Fair Value	$ 728.3	714.8
Document Period End Date	Jun. 30, 2020
Fair Value, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and Securities Segregated under Federal and Other Regulations	$ 9.8	306
Receivables from Clearing Organizations	1,261.6	626.9
Financial Instruments, Owned, at Fair Value	2,831.9	2,175.2
Assets, Fair Value Disclosure	4,291	3,273.8
Financial Instruments Sold, Not yet Purchased, at Fair Value	728.3
Liabilities, Fair Value Disclosure	738.7	722.2
Fair Value, Recurring [Member] | TBA and forward settling securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Broker-Dealer, Payable to Other Broker-Dealer and Clearing Organization	(7.3)	(5.3)
Fair Value, Recurring [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Broker-Dealer, Payable to Other Broker-Dealer and Clearing Organization	(1.5)	(0.3)
Fair Value, Recurring [Member] | Payable to broker-dealers, clearing organizations and counterparties [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Broker-Dealer, Payable to Other Broker-Dealer and Clearing Organization	(8.8)	(5.6)
Fair Value, Recurring [Member] | Contingent Consideration [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accounts Payable and Other Accrued Liabilities	1.6	1.8
Fair Value, Recurring [Member] | Physical commodities inventory [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Physical commodities inventory	173.6	151.9
Fair Value, 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	19.4	29.1
Fair Value, 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	347.8	447.1
Financial Instruments Sold, Not yet Purchased, at Fair Value	6.1	43.8
Fair Value, 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	372.5	248.7
Financial Instruments Sold, Not yet Purchased, at Fair Value	354.1	272.3
Fair Value, 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	12.6	0.5
Financial Instruments Sold, Not yet Purchased, at Fair Value	2.2
Fair Value, Recurring [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	92.4	66.5
Fair Value, Recurring [Member] | Commodities leases [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	23.2	28.6
Financial Instruments Sold, Not yet Purchased, at Fair Value	2.4	113.7
Fair Value, 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	56.4	48.4
Fair Value, Recurring [Member] | Exchange firm common stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	9.8	12.7
Fair Value, 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	3.4	0.1
Fair Value, Recurring [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	260.7	168.5
Financial Instruments Sold, Not yet Purchased, at Fair Value	217.6	158.1
Fair Value, Recurring [Member] | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	75.4	80
Financial Instruments Sold, Not yet Purchased, at Fair Value	26.1	39.2
Fair Value, 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	1,558.3	1,045
Financial Instruments Sold, Not yet Purchased, at Fair Value	21.1	29.6
Fair Value, Recurring [Member] | US Government Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Receivables from Clearing Organizations	1,148.4
Fair Value, 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	8.2	9.9
Fair Value, 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	6.9	8.3
Fair Value, Recurring [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Broker-Dealer, Payable to Other Broker-Dealer and Clearing Organization	98.1
Fair Value, 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	9.6	6.2
Fair Value, 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, 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	11.4	8.9
Fair Value, 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	2.7	4.9
Fair Value, 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	14.1	13.8
Fair Value, 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	(2,797.8)	(3,161.1)
Financial Instruments, Owned, at Fair Value	(880)	(420.8)
Assets, Fair Value Disclosure	(3,677.8)	(3,581.9)
Financial Instruments Sold, Not yet Purchased, at Fair Value	(838.3)	(422.2)
Liabilities, Fair Value Disclosure	(3,785.3)	(3,540.8)
Fair Value, 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]
Broker-Dealer, Payable to Other Broker-Dealer and Clearing Organization	5.3	1.5
Fair Value, Recurring [Member] | Counterparty And Cash Collateral Netting Adjustment [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Broker-Dealer, Payable to Other Broker-Dealer and Clearing Organization	2,941.7	3,117.1
Fair Value, 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]
Broker-Dealer, Payable to Other Broker-Dealer and Clearing Organization	2,947	3,118.6
Fair Value, 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, 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, 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, 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, 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, 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, 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	(880)	(420.8)
Financial Instruments Sold, Not yet Purchased, at Fair Value	(838.3)	(422.2)
Fair Value, 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	0	0
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, 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, 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, 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, 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, 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, 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, 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, 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, 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	(5.3)
Fair Value, 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	(2,792.5)
Fair Value, 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, 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, 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, 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, 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, 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	9.8	306
Receivables from Clearing Organizations	4,033.5	3,735
Financial Instruments, Owned, at Fair Value	703.9	470.9
Assets, Fair Value Disclosure	4,781.1	4,532.8
Financial Instruments Sold, Not yet Purchased, at Fair Value	558.5	419.6
Liabilities, Fair Value Disclosure	3,332.4	3,498.7
Fair Value, 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]
Broker-Dealer, Payable to Other Broker-Dealer and Clearing Organization	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Broker-Dealer, Payable to Other Broker-Dealer and Clearing Organization	(2,773.9)	(3,079.1)
Fair Value, 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]
Broker-Dealer, Payable to Other Broker-Dealer and Clearing Organization	(2,773.9)	(3,079.1)
Fair Value, 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, 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	19.8	7.1
Fair Value, 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, 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, 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	372.5	248.7
Financial Instruments Sold, Not yet Purchased, at Fair Value	354.1	272.3
Fair Value, 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	12.6	0.5
Financial Instruments Sold, Not yet Purchased, at Fair Value	2.2
Fair Value, 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	0.5	1
Financial Instruments Sold, Not yet Purchased, at Fair Value	0	0
Fair Value, 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, 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	56.4	48.4
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 1 [Member] | Exchange firm common stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial Instruments, Owned, at Fair Value	9.8	12.7
Fair Value, 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	3.4	0.1
Fair Value, 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	248.7	159.5
Financial Instruments Sold, Not yet Purchased, at Fair Value	202.2	147.3
Fair Value, 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, 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, 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	1,148.4
Fair Value, 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	8.2	9.9
Fair Value, 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, 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	2,876.9
Fair Value, 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	9.6	6.2
Fair Value, 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, 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	11.4	8.9
Fair Value, 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	2.7	4.9
Fair Value, 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	14.1	13.8
Fair Value, 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	25.9	53
Financial Instruments, Owned, at Fair Value	3,008	2,125.1
Assets, Fair Value Disclosure	3,187.7	2,322.9
Financial Instruments Sold, Not yet Purchased, at Fair Value	1,008.1	717.4
Liabilities, Fair Value Disclosure	1,190	762.5
Fair Value, 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]
Broker-Dealer, Payable to Other Broker-Dealer and Clearing Organization	(12.6)	(6.8)
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 2 [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Broker-Dealer, Payable to Other Broker-Dealer and Clearing Organization	(169.3)	(38.3)
Fair Value, 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]
Broker-Dealer, Payable to Other Broker-Dealer and Clearing Organization	(181.9)	(45.1)
Fair Value, 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, 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	153.8	144.8
Fair Value, 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	19.4	29.1
Fair Value, 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	347.8	447.1
Financial Instruments Sold, Not yet Purchased, at Fair Value	6.1	43.8
Fair Value, 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, 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, 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	971.9	486.3
Financial Instruments Sold, Not yet Purchased, at Fair Value	937	480.3
Fair Value, 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	23.2	28.6
Financial Instruments Sold, Not yet Purchased, at Fair Value	2.4	113.7
Fair Value, 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, 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, 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, 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	12	9
Financial Instruments Sold, Not yet Purchased, at Fair Value	15.4	10.8
Fair Value, 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	75.4	80
Financial Instruments Sold, Not yet Purchased, at Fair Value	26.1	39.2
Fair Value, 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	1,558.3	1,045
Financial Instruments Sold, Not yet Purchased, at Fair Value	21.1	29.6
Fair Value, 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, 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, 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	12.2	9.8
Fair Value, 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	13.7
Fair Value, 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, 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, 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, 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, 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, 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	1.6	1.8
Fair Value, 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]
Broker-Dealer, Payable to Other Broker-Dealer and Clearing Organization	0	0
Fair Value, Recurring [Member] | Fair Value, Inputs, Level 3 [Member] | Derivative [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Broker-Dealer, Payable to Other Broker-Dealer and Clearing Organization	0	0
Fair Value, 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]
Broker-Dealer, Payable to Other Broker-Dealer and Clearing Organization	0	0
Fair Value, 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	1.6	1.8
Fair Value, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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 $1261.6 and $626.9 at fair value at June 30, 2020 and September 30, 2019, respectively)		14.8
Derivative [Member] | Fair Value, 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, 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, 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, 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, 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, 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, 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, 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, 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	Jun. 30, 2020	Sep. 30, 2019
Financial Instruments Sold, Not yet Purchased, at Fair Value	$ 728.3	$ 714.8
Financial instrument sold, not yet purchased [Member]
Derivative, Fair Value, Net	$ 98.7	$ 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	Jun. 30, 2020	Sep. 30, 2019
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	$ 3,875.2	$ 3,671.5
Derivative Liability, Fair Value, Gross Liability	3,892.8	3,604.5
Impact of netting and collateral	3,677.8	3,581.9
Impact of netting and collateral	3,785.3	3,540.8
Deposits with and receivables from broker-dealers, clearing organizations, and counterparties [Member]
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	105	23.1
Financial instruments owned [Member]
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	92.4	66.5
Payable to broker-dealers, clearing organizations and counterparties [Member]
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	8.8	5.6
Financial instrument sold, not yet purchased [Member]
Derivatives, Fair Value [Line Items]
Derivative, Fair Value, Net	98.7	58.1
Exchange-traded Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	1,949.1	1,437.1
Derivative Liability, Fair Value, Gross Liability	2,085	1,463.4
Over the Counter (OTC) Commodity Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	359	84.2
Derivative Liability, Fair Value, Gross Liability	489.5	106.2
Foreign Exchange Forward [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	11.4	36.9
Derivative Liability, Fair Value, Gross Liability	14.3	33.5
Over the Counter (OTC) Foreign Exchange Contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	525.5	403.2
Derivative Liability, Fair Value, Gross Liability	516.2	368.8
Exchange-traded interest rate contracts [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	852.9	900.1
Derivative Liability, Fair Value, Gross Liability	603.7	882
Interest Rate Contract [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	101.1	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	64	758.1
Derivative Liability, Fair Value, Gross Liability	70.9	700.2
TBA and forward settling securities [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset, Fair Value, Gross Asset	12.2	9.8
Derivative Liability, Fair Value, Gross Liability	$ 12.6	$ 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	Jun. 30, 2020	Sep. 30, 2019
Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk [Abstract]
Derivative, Number of Instruments Held	9.3	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	Jun. 30, 2020	Sep. 30, 2019
Derivative Asset, Fair Value, Gross Asset	$ 3,875.2	$ 3,671.5
Derivative Liability, Fair Value, Gross Liability	(3,892.8)	(3,604.5)
TBA securities purchased [Member]
Derivative Liability, Notional Amount	(928.5)	(234.5)
Derivative Asset, Notional Amount	(2,170.9)	(1,778.4)
TBA securities sold [Member]
Derivative Liability, Notional Amount	(2,982.1)	(2,788)
Derivative Asset, Notional Amount	(1,566.8)	(451.6)
Forward settling securities purchased [Member]
Derivative Asset, Notional Amount	(1,690.5)	0
Over the Counter (OTC) Commodity Contracts [Member]
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	7.7	3.7
Derivative Liability, Fair Value, Gross Liability	1.9	0.6
Deposits and receivables from broker-dealers, clearing organizations and counterparties [Domain] | Forward settling securities purchased [Member]
Derivative Asset, Fair Value, Gross Asset	1.1	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	3.4	0.9
Derivative Liability, Fair Value, Gross Liability	10.2	5.9
Payable to broker-dealers, clearing organizations and counterparties [Member] | Forward settling securities purchased [Member]
Derivative Liability, Notional Amount	0	(1,243.5)
Derivative Liability, Fair Value, Gross Liability	0	0.3
Payable to broker-dealers, clearing organizations and counterparties [Member] | Over the Counter (OTC) Commodity Contracts [Member]
Derivative Liability, Notional Amount	(1,268.3)	0
Derivative Liability, Fair Value, Gross Liability	$ 0.5	$ 0

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		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Commodity Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	$ 28.1	$ 19.5	$ 107.9	$ 63.6
Foreign Exchange Forward [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	2.6	1.6	9.9	5.3
Interest Rate Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	0.7	(0.6)	0.3	(3.2)
TBA and forward settling securities [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	(5.6)	(8)	(40.9)	(6.7)
Derivative [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) Recognized in Income, Net	$ 25.8	$ 12.5	$ 77.2	$ 59

Receivables From Customers, N_2

Receivables From Customers, Net and Notes Receivable, Net - Allowance for Customer Receivables (Details) - USD ($) $ in Millions	9 Months Ended
	Jun. 30, 2020	Sep. 30, 2019
Receivables from customers and notes receivable, net [Abstract]
Accounts Receivable, Allowance for Credit Loss	$ 19.7	$ 11.7
Allowance for Doubtful Accounts, Premiums and Other Receivables	1.3	$ 36.9
Accounts Receivable, Allowance for Credit Loss, Writeoff	$ 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 ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Document Period End Date			Jun. 30, 2020
Bad debts	$ 1.8	$ 0.5	$ 6.2	$ 1.5
Payments for Legal Settlements				8.4
Recovery of bad debt on physical coal	0	$ 0	0	$ 2.4
Commodity and Risk Management [Member]
Bad debts	1.1		3.3
Accounts Receivable, Allowance for Credit Loss, Recovery	0.6
Clearing and Execution Services Segment
Bad debts	$ 2.4		2.7
Physical Commodities
Bad debts			$ 0.2

Physical Commodities Inventor_3

Physical Commodities Inventory - Physical Commodities Inventory by CIP and Finished (Details) - USD ($) $ in Millions	Jun. 30, 2020	Sep. 30, 2019
Inventory [Line Items]
Physical Ag & Energy(1)	$ 153.8	$ 144.8
Precious metals - held by non-broker-dealer subsidiaries(3)	173.6	151.9
Physical commodities inventory	270.2	229.3
Physical commodities inventory - precious metals [Member]
Inventory [Line Items]
Precious metals - held by non-broker-dealer subsidiaries(3)	19.8	7.1
Finished commodities	$ 96.6	$ 77.4

Physical Commodities Inventor_4

Physical Commodities Inventory - LCM Adjustments (Details) - USD ($) $ in Millions	Jun. 30, 2020	Sep. 30, 2019	Sep. 30, 2016
Physical Commodities Inventory [Abstract]
Inventory Adjustments	$ 3.7	$ 0.5	$ 0.6

Goodwill - Goodwill by Segment

Goodwill - Goodwill by Segment (Details) - USD ($) $ in Millions	Jun. 30, 2020	Sep. 30, 2019
Goodwill [Line Items]
Goodwill	$ 55.4	$ 51.2
Commodity and Risk Management [Member]
Goodwill [Line Items]
Goodwill	30.3	30.3
Global Payments
Goodwill [Line Items]
Goodwill	11.8	7.6
Physical Commodities
Goodwill [Line Items]
Goodwill	8.7	8.7
Securities
Goodwill [Line Items]
Goodwill	$ 4.6	$ 4.6

Goodwill Goodwill Adjustments (

Goodwill Goodwill Adjustments (Details) $ in Millions	9 Months Ended
	Jun. 30, 2020USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill, Acquired During Period	$ 4.2

Intangible Assets - Gross and N

Intangible Assets - Gross and Net Intangible Assets by Major Class (Details) - USD ($) $ in Millions	Jun. 30, 2020	Sep. 30, 2019
Acquired Finite-Lived Intangible Assets [Line Items]
Indefinite-Lived License Agreements	$ 2.9	$ 2.7
Indefinite-lived Intangible Assets (Excluding Goodwill)	5	4.8
Finite-Lived Intangible Assets, Accumulated Amortization	(18.5)	(15.5)
Finite-Lived Intangible Assets, Net	15.9	11.9
Other Indefinite-lived Intangible Assets	2.1	2.1
Finite-Lived Intangible Assets, Gross	34.4	27.4
Gross Finite and Indefinite-Lived Intangible Assets	39.4	32.2
Finite and Indefinited-Lived Accumulated Amortization and Impairment Charges	(18.5)	(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	(3.4)	(3)
Finite-Lived Intangible Assets, Net	1.9	2.3
Customer Relationships [Member]
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-Lived Customer Lists, Gross	29.1	22.1
Finite-Lived Intangible Assets, Accumulated Amortization	(15.1)	(12.5)
Finite-Lived Intangible Assets, Net	$ 14	$ 9.6

Intangible Assets - Indefinite-

Intangible Assets - Indefinite-Lived Intangible Assets (Details) - USD ($) $ in Millions	Jun. 30, 2020	Sep. 30, 2019
Indefinite-lived Intangible Assets [Line Items]
Gross Finite and Indefinite-Lived Intangible Assets	$ 39.4	$ 32.2
Finite and Indefinited-Lived Accumulated Amortization and Impairment Charges	(18.5)	(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	Jun. 30, 2020	Sep. 30, 2019
Finite-Lived Intangible Assets, Amortization Expense, Maturity Schedule [Abstract]
Fiscal 2020 (remaining nine months)	$ 1
Fiscal 2021	4.2
Fiscal 2022	2.9
Fiscal 2023	2.7
Fiscal 2024 and thereafter	5.1
Finite-Lived Intangible Assets, Net	$ 15.9	$ 11.9

Intangible Assets Definite Live

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

Intangible Assets Intangible As

Intangible Assets Intangible Assets Acquired During the Period (Details) - Customer-Related Intangible Assets [Member] $ in Millions	9 Months Ended
	Jun. 30, 2020USD ($)
UOB Bullion and Futures Limited [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-lived Intangible Assets Acquired	$ 4.2
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 ($)Rate	Jun. 30, 2020USD ($)	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	739
HCO Syndicated line of credit facility [Member]
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net		$ 0.6
Line of Credit Facility, Maximum Borrowing Capacity	196.5
Borrowing Capacity Under Credit Facilities	379
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		24.4	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	$ 25
Line of Credit, Current		$ 0	$ 0

Credit Facilities - Credit Faci

Credit Facilities - Credit Facilities (Details) - USD ($) $ in Millions	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019
Line of Credit Facility [Line Items]
Long-term Debt, Gross		$ 182.5
Senior secured borrowings, net	$ 518.9		$ 167.6
Short-term Debt	471.4		366.1
Notes Payable to Bank	0
Senior Notes	336.9		0
Debt, Long-term and Short-term, Combined Amount	832.7		369.9
Main line of credit facilities [Member]
Line of Credit Facility [Line Items]
Credit Facilities Expiring Within One Year	100
Borrowing Capacity Under Credit Facilities		739
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	24.4		0
HCO Syndicated line of credit facility [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net	0.6
Senior secured borrowings, net	182		167.6
Line of Credit Facility, Maximum Borrowing Capacity		196.5
Long-term Line of Credit, Noncurrent	127		70
Borrowing Capacity Under Credit Facilities		379
Long-term Debt	309		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	162.4		128.5
INTL FCStone Ltd [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity		25
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

Credit Facilities Senior Secure

Credit Facilities Senior Secured Notes due 2025 (Details) - USD ($) $ in Millions	9 Months Ended
	Jun. 30, 2020	Sep. 30, 2019
Debt Instrument [Line Items]
Senior Notes	$ 336.9	$ 0
Debt Instrument, Face Amount	$ 350
Debt Instrument, Interest Rate, Stated Percentage	8.625%
Debt Issuance Costs, Gross	$ 8
Debt Instrument, Redemption Price, Percentage of Principal Amount Redeemed	40.00%
Debt Instrument, Redemption Price, Percentage	108.625%
Senior Notes [Member]
Debt Instrument [Line Items]
Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net	$ 13.1

Commodity and Other Repurchas_4

Commodity and Other Repurchase Agreements Commodity and Other Repurchase Agreements (Details) - USD ($)	Jun. 30, 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	$ 3,384,900,000	$ 3,060,200,000
Financial Instruments Owned and Pledged as Collateral, Amount Eligible to be Repledged by Counterparty	606,400,000	478,800,000
Securities Loaned, Fair Value of Collateral	1,448,900,000	1,414,000,000
Securities Sold under Agreements to Repurchase, Fair Value of Collateral	606,400,000	478,800,000
Trading Securities Pledged as Collateral	1,590,100,000	1,228,900,000
Pledged Financial Instruments, Not Separately Reported, Securities for Repurchase Agreements	1,407,800,000	1,175,100,000
Fair Value of Securities Received as Collateral that Have Been Resold or Repledged	$ 379,600,000	$ 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	Jun. 30, 2020	Sep. 30, 2019
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	$ 3,530.4	$ 2,773.7
Securities Loaned	1,459.7	1,459.9
Collateralized transactions:	4,990.1	4,233.6
Maturity Overnight and on Demand [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	2,079.3	1,553.9
Securities Loaned	1,459.7	1,459.9
Collateralized transactions:	3,539	3,013.8
Maturity Less than 30 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	899.1	565.8
Securities Loaned	0	0
Collateralized transactions:	899.1	565.8
Maturity 30 to 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	492	654
Securities Loaned	0	0
Collateralized transactions:	492	654
Maturity Greater than 90 Days [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	60	0
Securities Loaned	0	0
Collateralized transactions:	$ 60	$ 0

Commodity and Other Repurchas_6

Commodity and Other Repurchase Agreements and Collateralized Transactions Gross Collateralized Financings by Collateral Type Table (Details) - USD ($)	Jun. 30, 2020	Sep. 30, 2019
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	$ 3,530,400,000	$ 2,773,700,000
Securities Loaned	1,459,700,000	1,459,900,000
Collateralized transactions:	4,990,100,000	4,233,600,000
US Government Debt Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	1,075,800,000	108,800,000
US Government Agencies Debt Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	206,800,000	359,500,000
Asset-backed Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	17,100,000	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	2,163,800,000	2,208,700,000
Equity Securities [Member]
Assets Sold under Agreements to Repurchase [Line Items]
Securities Loaned	$ 1,459,700,000	$ 1,459,900,000

Commitments and Contingencies C

Commitments and Contingencies Commitments and Contingencies - Contingencies and Litigation (Details) $ in Millions	Jun. 30, 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	$ 1.2

Capital and Other Regulatory _3

Capital and Other Regulatory Requirements - Regulatory Capital Requirements (Details) $ in Millions	Jun. 30, 2020USD ($)
FCStone LLC [Member]
Cash Reserve Deposit Required and Made	$ 43.7
Cash Reserve Deposit Required	46.8
Futures Commission Merchant, Commodity Exchange Act, Adjusted Net Capital	198.6
Futures Commission Merchant, Commodity Exchange Act, Required Net Capital	126
Cash and Securities Segregated under Commodity Exchange Act Regulation	2,705.6
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	2,650.1
Secured Funds	160.6
Secured Funds Required Under Commodity Exchange Act	148.8
INTL FCStone Ltd [Member]
Futures Commission Merchant, Commodity Exchange Act, Adjusted Net Capital	264.9
Futures Commission Merchant, Commodity Exchange Act, Required Net Capital	110.8
Cash and Securities Segregated under Commodity Exchange Act Regulation	471.8
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	467.4
INTL FCStone Pte Ltd [Member]
Cash and Securities Segregated under Commodity Exchange Act Regulation	313.8
Cash and Securities Segregated under Commodity Exchange Act Regulation, Amount Required to be Segregated	$ 307

Other Expenses - Other Expenses

Other Expenses - Other Expenses Breakout (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Other Expenses [Abstract]
Accretion Expense	$ 0.2	$ 0	$ 0.3	$ 0
Insurance	1.1	0.9	3.1	2.6
Advertising, meetings, and conferences	0.5	1.2	6.1	4.1
Office supplies and printing	0.6	0.5	1.5	1.5
Other clearing related expenses	0.8	0.7	2.2	1.8
Other non-income taxes	1.2	1.1	3.8	3.2
Other	3.2	2.7	8.7	7.8
Total other expenses	$ 7.6	$ 7.1	$ 25.7	$ 21

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Income (Loss) Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 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	0	$ 0.3	(2.7)	$ 0.6
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			$ (2.7)	$ 0.6

Effective Income Tax Rate Recon

Effective Income Tax Rate Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Taxes [Abstract]
Income Tax Expense (Benefit)	$ 12.4	$ 5.3	$ 34.6	$ 19
Effective Income Tax Rate Reconciliation, Percent	25.00%		27.00%	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			1.70%	1.20%
Effective Income Tax Rate Reconciliation, Foreign Income Tax Rate Differential, Percent			2.00%	1.40%
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent			1.00%	1.30%

Income Taxes Accumulated Foreig

Income Taxes Accumulated Foreign Undistributed Earnings (Details) - USD ($) $ in Millions	9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Undistributed Earnings of Foreign Subsidiaries	$ 426.6		$ 383.5
Foreign Earnings Repatriated	$ 30	$ 13

Income Taxes Operating Loss Car

Income Taxes Operating Loss Carryforwards (Details) - USD ($) $ in Millions	Jun. 30, 2020	Sep. 30, 2019	Sep. 30, 2016
Operating Loss Carryforwards [Line Items]
Operating Loss Carryforwards	$ 6.9	$ 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

Acquisitions UOB Acquisition (D

Acquisitions UOB Acquisition (Details) - USD ($) $ in Millions	3 Months Ended		7 Months Ended	9 Months Ended
	Dec. 31, 2019	Mar. 31, 2019	Oct. 07, 2019	Jun. 30, 2020
Business Acquisition [Line Items]
Goodwill, Acquired During Period				$ 4.2
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Property, Plant, and Equipment				0.1
Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Intangibles				$ 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			0.8
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles			4.2
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Liabilities			$ 351.8

Acquisitions Quest Capital (Det

Acquisitions Quest Capital (Details) $ in Millions	9 Months Ended
	Jun. 30, 2020USD ($)
Quest Capital Strategies, Inc. [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred	$ 1.7

Acquisitions Tellimer Acquisiti

Acquisitions Tellimer Acquisition (Details) - Tellimer [Member] - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2020	Jun. 30, 2020
Business Acquisition [Line Items]
Business Combination, Consideration Transferred	$ 4.7
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents		$ 1
Business Combination, Acquired Receivable, Fair Value		1
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment		0.3
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets		3.4
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities		$ 1

Acquisitions IFCM Commodities (

Acquisitions IFCM Commodities (Details) - IFCM Commodities Acquisition [Member] $ in Millions	9 Months Ended
	Jun. 30, 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) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	9 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Sep. 30, 2019	Jun. 30, 2019
Business Acquisition [Line Items]
Debt Instrument, Face Amount	$ 350	$ 350
Debt Instrument, Interest Rate, Stated Percentage	8.625%	8.625%
Restricted cash held in escrow	$ 350	$ 350	$ 0	$ 0
Convertible Notes Payable	$ 92	$ 92
Gain Capital Holdings Inc [Member]
Business Acquisition [Line Items]
Business Acquisition, Share Price	$ 6	$ 6
Business Combination, Consideration Transferred		$ 236.2
Restricted cash held in escrow	$ 349.8	349.8
Business Acquisition, Transaction Costs	$ 1.4	$ 1.9

Acquisitions GIROXX (Details)

Acquisitions GIROXX (Details) $ in Millions	9 Months Ended
	Jun. 30, 2020USD ($)
IFCM Commodities Acquisition [Member]
Business Acquisition [Line Items]
Business Combination, Consideration Transferred	$ 1.9
GIROXX Acquisition [Member]
Business Acquisition [Line Items]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Liabilities	5.8
Business Combination, Consideration Transferred	4.4
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents	6.5
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment	0.1
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Accounts Payable	$ 0.6

Acquisitions Overall (Details)

Acquisitions Overall (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Jun. 30, 2020	Jun. 30, 2020
Overall [Abstract]
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual	$ 5	$ 12.7

Segment Analysis (Details)

Segment Analysis (Details) - USD ($)	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Sep. 30, 2019
Segment Reporting Information [Line Items]
Revenues	$ 8,243,400,000	$ 7,873,000,000	$ 39,854,700,000	$ 21,617,400,000
Operating revenues	322,600,000	283,400,000	966,200,000	819,200,000
Net operating revenues	227,900,000	165,600,000	641,800,000	479,800,000
Net Segment Contribution	163,600,000	119,600,000	464,300,000	357,200,000
Segment Income	110,700,000	69,600,000	303,800,000	218,300,000
Net costs not allocated to operating segments	61,700,000	48,000,000	177,100,000	146,800,000
Other gain	0	0	100,000	5,400,000
Income before tax	49,000,000	21,600,000	126,800,000	76,900,000
Assets	12,389,500,000		12,389,500,000		$ 9,936,100,000
Commodity and Risk Management [Member]
Segment Reporting Information [Line Items]
Revenues	65,100,000	86,400,000	236,500,000	226,800,000
Operating revenues	65,100,000	86,400,000	236,500,000	226,800,000
Net operating revenues	50,800,000	66,900,000	189,400,000	178,000,000
Net Segment Contribution	36,000,000	48,000,000	133,900,000	127,900,000
Segment Income	19,200,000	29,700,000	76,500,000	73,200,000
Assets	2,112,600,000		2,112,600,000		2,041,000,000
Global Payments
Segment Reporting Information [Line Items]
Revenues	27,400,000	28,900,000	88,200,000	86,000,000
Operating revenues	27,400,000	28,900,000	88,200,000	86,000,000
Net operating revenues	26,000,000	27,500,000	83,800,000	81,700,000
Net Segment Contribution	20,900,000	22,300,000	67,300,000	66,400,000
Segment Income	15,900,000	17,000,000	52,000,000	51,400,000
Assets	234,800,000		234,800,000		278,300,000
Securities Segment
Segment Reporting Information [Line Items]
Revenues	123,000,000	74,200,000	322,000,000	215,800,000
Operating revenues	123,000,000	74,200,000	322,000,000	215,800,000
Net operating revenues	97,100,000	30,300,000	218,300,000	94,400,000
Net Segment Contribution	64,300,000	17,900,000	142,200,000	59,800,000
Segment Income	51,600,000	8,200,000	106,700,000	36,000,000
Assets	6,284,300,000		6,284,300,000		5,219,100,000
Physical Commodities
Segment Reporting Information [Line Items]
Revenues	7,960,000,000	7,604,300,000	38,971,800,000	20,847,000,000
Operating revenues	39,200,000	14,700,000	83,300,000	48,800,000
Net operating revenues	35,700,000	9,700,000	71,100,000	35,200,000
Net Segment Contribution	24,200,000	6,400,000	49,300,000	25,000,000
Segment Income	20,300,000	2,800,000	37,500,000	16,500,000
Assets	425,300,000		425,300,000		357,800,000
Clearing and Execution Services Segment
Segment Reporting Information [Line Items]
Revenues	68,900,000	78,900,000	241,300,000	247,700,000
Operating revenues	68,900,000	78,900,000	241,300,000	247,700,000
Net operating revenues	22,800,000	32,500,000	89,900,000	101,000,000
Net Segment Contribution	18,200,000	25,000,000	71,600,000	78,100,000
Segment Income	3,700,000	11,900,000	31,100,000	41,200,000
Assets	2,546,100,000		2,546,100,000		1,892,100,000
Corporate unallocated
Segment Reporting Information [Line Items]
Revenues	2,300,000	6,500,000	11,500,000	13,500,000
Operating revenues	2,300,000	6,500,000	11,500,000	13,500,000
Net operating revenues	(4,500,000)	(1,300,000)	(10,700,000)	(10,500,000)
Assets	786,400,000		786,400,000		$ 147,800,000
Eliminations
Segment Reporting Information [Line Items]
Revenues	(3,300,000)	(6,200,000)	(16,600,000)	(19,400,000)
Operating revenues	$ (3,300,000)	$ (6,200,000)	$ (16,600,000)	$ (19,400,000)