StoneX (SNEX) 10-Q 10 May 21 2021 FY Quarterly report Financial data

Cover

Cover - shares	6 Months Ended
	Mar. 31, 2021	May 06, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
Document Transition Report	false
Entity File Number	000-23554
Entity Registrant Name	StoneX Group Inc.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	59-2921318
Entity Address, Address Line One	230 Park Ave
Entity Address, Address Line Two	10th Floor
Entity Address, City or Town	New York
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	10169
City Area Code	(212)
Local Phone Number	485-3500
Title of 12(b) Security	Common Stock, $0.01 par value
Trading Symbol	SNEX
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		19,825,100
Entity Central Index Key	0000913760
Current Fiscal Year End Date	--09-30
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	FY
Amendment Flag	false

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Millions	Mar. 31, 2021	Sep. 30, 2020
ASSETS
Cash and cash equivalents	$ 1,001.5	$ 952.6
Cash, securities and other assets segregated under federal and other regulations (including $102.5 million and $2.6 million at fair value at March 31, 2021 and September 30, 2020, respectively)	2,102.9	1,920.2
Collateralized transactions:
Securities purchased under agreements to resell	2,297.2	1,696.2
Securities borrowed	1,735.3	1,440
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net (including $839.8 million and $1,775.8 million at fair value at March 31, 2021 and September 30, 2020, respectively)	4,361.1	3,629.9
Receivable from clients, net (including $1.0 million and $1.5 million at fair value at March 31, 2021 and September 30, 2020, respectively)	479.4	411.4
Notes receivable, net	6.7	1.7
Income taxes receivable	14.8	16.6
Financial instruments owned, at fair value (includes securities pledged as collateral that can be sold or repledged of $564.7 million and $468.6 million at March 31, 2021 and September 30, 2020, respectively)	2,913.1	2,727.7
Physical commodities inventory, net (including $355.2 million and $215.7 million at fair value at March 31, 2021 and September 30, 2020, respectively)	450.8	281.1
Deferred income taxes, net	35.2	36.9
Property and equipment, net	86.1	62.1
Operating right of use assets	97.1	101.5
Goodwill and intangible assets, net	102.5	109.5
Other assets	116	87.5
Total assets	15,799.7	13,474.9
Liabilities:
Accounts payable and other accrued liabilities (including $1.5 million and $1.5 million at fair value at March 31, 2021 and September 30, 2020, respectively)	281.8	272.6
Operating lease liabilities	116.4	118.7
Payables to:
Clients (including $(178.2) million and $(222.7) million at fair value at March 31, 2021 and September 30, 2020, respectively)	6,544.5	5,689
Broker-dealers, clearing organizations and counterparties (including $43.7 million and $14.7 million at fair value at March 31, 2021 and September 30, 2020, respectively)	520.7	537.5
Lenders under loans	314.9	268.1
Senior secured borrowings, net	512	515.5
Income taxes payable	16.6	22.6
Collateralized transactions:
Securities sold under agreements to repurchase	3,767.2	3,155.5
Securities loaned	1,747.2	1,441.9
Financial instruments sold, not yet purchased, at fair value	1,118.2	686
Total liabilities	14,939.5	12,707.4
Commitments and contingencies (Note 11)
Stockholders' equity:
Preferred stock, $0.01 par value. Authorized 1,000,000 shares; no shares issued or outstanding	0	0
Common stock, $0.01 par value. Authorized 30,000,000 shares; 22,205,997 issued and 19,784,040 outstanding at March 31, 2021 and 21,798,551 issued and 19,376,594 outstanding at September 30, 2020	0.2	0.2
Common stock in treasury, at cost - 2,421,957 shares at March 31, 2021 and September 30, 2020, respectively	(57.6)	(57.6)
Additional paid-in-capital	304.4	292.6
Retained earnings	641	572.4
Accumulated other comprehensive loss, net	(27.8)	(40.1)
Total equity	860.2	767.5
Total liabilities and stockholders' equity	$ 15,799.7	$ 13,474.9

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2021	Sep. 30, 2020
Statement of Financial Position [Abstract]
Cash and cash equivalents, fair value	$ 102.5	$ 2.6
Deposits and receivables from bds and counterparties at fair value	839.8	1,775.8
Receivables from clients at fair value	1	1.5
Collateral that can be sold or repledged	564.7	468.6
Physical commodities inventory at fair value	355.2	215.7
Accounts payable and other accrued liabilities at fair value	1.5	1.5
Client payables at fair value	(178.2)	(222.7)
Payables to broker dealer at fair value	$ 43.7	$ 14.7
Preferred stock - par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock - authorized (in shares)	1,000,000	1,000,000
Preferred stock - issued (in shares)	0	0
Preferred stock - outstanding (in shares)	0	0
Common stock - par value (in dollar per share)	$ 0.01	$ 0.01
Common stock - authorized (in shares)	30,000,000	30,000,000
Common stock - issued (in shares)	22,205,997	21,798,551
Common stock - outstanding (in shares)	19,784,040	19,376,594
Treasury stock - shares (in shares)	2,421,957	2,421,957

Condensed Consolidated Income S

Condensed Consolidated Income Statements - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Revenues:
Sales of physical commodities	$ 10,804.3	$ 20,016.9	$ 19,687.8	$ 30,994.9
Principal gains, net	265.2	168.5	468.6	281
Commission and clearing fees	129.8	116.6	249.2	203.8
Consulting, management, and account fees	22.1	22.6	45.1	43.9
Interest income	23.4	41.7	44.6	87.7
Total revenues	11,244.8	20,366.3	20,495.3	31,611.3
Cost of sales of physical commodities	10,773.4	19,999.5	19,643.8	30,967.7
Operating revenues	471.4	366.8	851.5	643.6
Transaction-based clearing expenses	74.8	63.8	140.2	110.1
Introducing broker commissions	40.8	29.6	79	55.8
Interest expense	11.1	27.8	21	58.9
Interest expense on corporate funding	10.5	2.2	21	4.9
Net operating revenues	334.2	243.4	590.3	413.9
Compensation and other expenses:
Compensation and benefits	185	136.7	338.6	240.7
Trading systems and market information	14.8	11.2	28.5	21.6
Professional fees	9	4.7	18.3	10.7
Non-trading technology and support	10.6	5.9	21.5	11.9
Occupancy and equipment rental	7.5	4.9	16.1	9.9
Selling and marketing	6.5	4.2	15.3	5.6
Travel and business development	0.5	3.2	1.5	7.7
Communications	2.4	1.5	4.7	3.1
Depreciation and amortization	8.6	4.2	17	8.1
Bad debts	0.9	4.4	2.4	4.4
Other	12.1	6.4	23.2	12.5
Total compensation and other expenses	257.9	187.3	487.1	336.2
Other gain	0	0	0	0.1
Income before tax	76.3	56.1	103.2	77.8
Income tax expense	21	16.8	28.4	22.2
Net income	$ 55.3	$ 39.3	$ 74.8	$ 55.6
Earnings per share:
Basic (in dollar per shares)	$ 2.81	$ 2.03	$ 3.81	$ 2.88
Diluted (in dollar per shares)	$ 2.73	$ 2	$ 3.71	$ 2.84
Weighted-average number of common shares outstanding:
Basic (in shares)	19,112,216	18,872,937	19,025,604	18,811,268
Diluted (in shares)	19,670,539	19,189,953	19,570,028	19,132,497

Condensed Consolidated Statemen

Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Statement of Comprehensive Income [Abstract]
Net income	$ 55.3	$ 39.3	$ 74.8	$ 55.6
Other comprehensive (loss) income:
Foreign currency translation adjustment	(1.6)	(3.4)	12.3	(2.7)
Other comprehensive (loss) income	(1.6)	(3.4)	12.3	(2.7)
Comprehensive income	$ 53.7	$ 35.9	$ 87.1	$ 52.9

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from operating activities:
Net income	$ 74.8	$ 55.6
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	17	8.1
Amortization of right of use assets	4.8	3.9
Bad debts	2.4	4.4
Deferred income taxes	4.2	(1)
Amortization of debt issuance costs	2.1	0.7
Amortization of share-based compensation	6.5	5
Changes in operating assets and liabilities, net:
Securities and other assets segregated under federal and other regulations	(89.6)	297.9
Securities purchased under agreements to resell	(601)	164.5
Securities borrowed	(295.3)	359.4
Deposits with and receivables from broker-dealers, clearing organizations, and counterparties, net	(189.5)	(52.2)
Receivables from clients, net	(78.6)	(63.2)
Notes receivable, net	(5)	(1)
Income taxes receivable	1.3	8.7
Financial instruments owned, at fair value	(185.4)	(350.5)
Physical commodities inventory, net	(169.7)	(25.9)
Other assets	(22.5)	0
Accounts payable and other accrued liabilities	10	30.2
Operating lease liabilities	(3.2)	(4)
Payables to clients	855.3	942
Payables to broker-dealers, clearing organizations, and counterparties	(16.8)	163
Income taxes payable	(6)	0.1
Securities sold under agreements to repurchase	611.7	26.6
Securities loaned	305.3	(391.1)
Financial instruments sold, not yet purchased, at fair value	432.2	(11.2)
Net cash provided by operating activities	665	1,170
Cash flows from investing activities:
Cash paid for acquisitions, net	(0.4)	(7.8)
Purchase of property and equipment	(40)	(4.5)
Net cash used in investing activities	(40.4)	(12.3)
Cash flows from financing activities:
Net change in payables to lenders under loans with maturities 90 days or less	42.8	111.6
Proceeds from payables to lenders under loans with maturities greater than 90 days	120.4	311.5
Repayments of payables to lenders under loans with maturities greater than 90 days	(125.4)	(350)
Proceeds from issuance of senior secured term loan	0	21.5
Repayments of senior secured term loan	(4.9)	(4.9)
Issuance of note payable	9	0
Repayments of note payable	0	(0.4)
Deferred payments on acquisitions	(0.8)	(0.2)
Repurchase of common stock	0	(7.5)
Debt issuance costs	0	(1.5)
Exercise of stock options	5.3	4
Net cash provided by financing activities	46.4	84.1
Effect of exchange rates on cash, segregated cash, cash equivalents, and segregated cash equivalents	12.7	(2.7)
Net increase in cash, segregated cash, cash equivalents, and segregated cash equivalents	683.7	1,239.1
Cash, segregated cash, cash equivalents, and segregated cash equivalents at beginning of period	4,468.4	2,451.3
Cash, segregated cash, cash equivalents, and segregated cash equivalents at end of period	5,152.1	3,690.4
Supplemental disclosure of cash flow information:
Cash paid for interest	32.9	64.3
Income taxes paid, net of cash refunds	28.2	13.2
Supplemental disclosure of non-cash investing and financing activities:
Identified intangible assets and goodwill on acquisitions	0.5	7.2
Acquisition of business:
Assets acquired	0.1	352.6
Liabilities assumed	(0.2)	(352)
Total net (liabilities)/assets assumed	(0.1)	0.6
Total cash, segregated cash, cash equivalents, and segregated cash equivalents shown in the condensed consolidated statements of cash flows	$ 5,152.1	$ 3,690.4

Condensed Consolidated Statem_3

Condensed Consolidated Statement of Stockholders' Equity - USD ($) $ in Millions	Total	Cumulative Effect, Period of Adoption, Adjustment	Cumulative Effect, Period of Adoption, Adjusted Balance	Common Stock	Common StockCumulative Effect, Period of Adoption, Adjusted Balance	Treasury Stock	Treasury StockCumulative Effect, Period of Adoption, Adjusted Balance	Additional Paid-in Capital	Additional Paid-in CapitalCumulative Effect, Period of Adoption, Adjusted Balance	Retained Earnings	Retained EarningsCumulative Effect, Period of Adoption, Adjustment	Retained EarningsCumulative Effect, Period of Adoption, Adjusted Balance	Accumulated Other Comprehensive Loss, net	Accumulated Other Comprehensive Loss, netCumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Loss, netCumulative Effect, Period of Adoption, Adjusted Balance
Beginning balance at Sep. 30, 2019	$ 594.2	$ 0	$ 594.2	$ 0.2	$ 0.2	$ (50.1)	$ (50.1)	$ 276.8	$ 276.8	$ 402.1	$ 0.7	$ 402.8	$ (34.8)	$ (0.7)	$ (35.5)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	55.6									55.6
Other comprehensive income (loss)	(2.7)												(2.7)
Exercise of stock options	4							4
Share-based compensation	5							5
Repurchase of common stock	(7.5)					(7.5)
Ending balance at Mar. 31, 2020	648.6			0.2		(57.6)		285.8		458.4			(38.2)
Beginning balance at Sep. 30, 2019	594.2	0	594.2	0.2	0.2	(50.1)	(50.1)	276.8	276.8	402.1	0.7	402.8	(34.8)	$ (0.7)	(35.5)
Ending balance at Sep. 30, 2020	$ 767.5	(6.2)	761.3	0.2	0.2	(57.6)	(57.6)	292.6	292.6	572.4	(6.2)	566.2	(40.1)		(40.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Beginning balance at Dec. 31, 2019	$ 614.9			0.2		(50.5)		280.9		419.1			(34.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	39.3									39.3
Other comprehensive income (loss)	(3.4)												(3.4)
Exercise of stock options	2.5							2.5
Share-based compensation	2.4							2.4
Repurchase of common stock	(7.1)					(7.1)
Ending balance at Mar. 31, 2020	648.6			0.2		(57.6)		285.8		458.4			(38.2)
Beginning balance at Sep. 30, 2020	767.5	$ (6.2)	$ 761.3	0.2	$ 0.2	(57.6)	$ (57.6)	292.6	$ 292.6	572.4	$ (6.2)	$ 566.2	(40.1)		$ (40.1)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	74.8									74.8
Other comprehensive income (loss)	12.3												12.3
Exercise of stock options	5.3							5.3
Share-based compensation	6.5							6.5
Ending balance at Mar. 31, 2021	860.2			0.2		(57.6)		304.4		641			(27.8)
Beginning balance at Dec. 31, 2020	799.5			0.2		(57.6)		297.4		585.7			(26.2)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	55.3									55.3
Other comprehensive income (loss)	(1.6)												(1.6)
Exercise of stock options	3.6							3.6
Share-based compensation	3.4							3.4
Ending balance at Mar. 31, 2021	$ 860.2			$ 0.2		$ (57.6)		$ 304.4		$ 641			$ (27.8)

Basis of Presentation and Conso

Basis of Presentation and Consolidation and Accounting Standards Adopted	6 Months Ended
	Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation and Consolidation and Accounting Standards Adopted	Basis of Presentation and Consolidation and Accounting Standards Adopted StoneX Group Inc., a Delaware corporation, and its consolidated subsidiaries (collectively “StoneX” or “the Company”), is a global financial services network that connects companies, organizations, traders and investors to the global market ecosystem through a unique blend of digital platforms, end-to-end clearing and execution services, high touch service, and deep expertise. The Company strives to be the one trusted partner to its clients, providing its network, product and services to allow them to pursue trading opportunities, manage their market risks, make investments and improve their business performance. The Company offers a vertically integrated product suite, beginning with high-touch and electronic access to nearly all major financial markets worldwide, as well as numerous liquidity venues. It delivers its services and access through the entire lifecycle of a trade, from deep market expertise and on-the-ground intelligence, to best execution and finally post-trade clearing, custody and settlement services. The Company has created a revenue stream that is diversified by asset class, client type and geography, including commissions and spreads as clients execute transactions across its financial network, non-trading client activity including interest and fee earnings on client balances, as well as fees for market intelligence and risk management services. The Company provides its services to a diverse group of more than 35,000 commercial and institutional clients and over 340,000 retail clients, including commercial entities, asset managers, regional, national and introducing broker-dealers, insurance companies, brokers, institutional investors and professional traders, commercial and investment banks and government and non-governmental organizations (“NGOs”) located in more than 130 countries. The Company’s common stock trades on The NASDAQ Global Select Market under the symbol “SNEX”. Basis of Presentation and Consolidation The accompanying unaudited condensed consolidated balance sheet as of September 30, 2020, which has been derived from the audited consolidated balance sheet of September 30, 2020, 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 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, 2020, as filed with the SEC. These condensed consolidated financial statements include the accounts of StoneX Group Inc. and all 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 its 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. Preparing 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, income 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. 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 March 31, 2021 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 certain 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, direct non-variable expenses, as well as variable and non-variable expenses to operational and administrative employees. Reclassifications During the year ended September 30, 2020, the Company reclassified certain selling and marketing related costs in connection with the acquisition of Gain Capital Holdings, Inc. (“Gain”). In performing this reclassification, the Company has made retrospective adjustments to the condensed consolidated income statements for the three and six months ended March 31, 2020. For the three and six months ended March 31, 2020, selling and marketing related costs of $4.2 million and $5.6 million, respectively, were reclassified from ‘Other’ expense to ‘Selling and marketing’ expense. Accounting Standards Adopted In June 2016, the FASB issued ASU No. 2016-13, “Measurement of Credit Losses on Financial Instruments”, which significantly changes the ways entities recognize credit losses on financial instruments. The guidance is effective for public business entities for annual and interim periods in fiscal years beginning after December 15, 2019. In April 2019, the FASB issued ASU No. 2019-04, “Codification Improvements to Topic 326, Financial Instruments - Credit Losses, Topic 815, Derivatives and Hedging, and Topic 825, Financial Instruments”, which among other things, included several amendments to ASU No. 2016-13, changing how a company considers expected recoveries and contractual extensions or renewal options when estimating expected credit losses. The guidance replaces the previous incurred loss impairment guidance and introduces a new credit reserving model known as the Current Expected Credit Loss (“CECL”) model, which is based on expected losses over the life of an asset, and applies to financial assets carried at amortized cost, held-to-maturity debt securities and off-balance sheet credit exposures. The allowance must reflect management’s estimate of credit losses over the life of the assets taking future economic changes into consideration. The Company adopted this guidance on October 1, 2020, using the modified retrospective approach, which resulted in a recognized cumulative-effect adjustment of $6.2 million, net of tax of $2.0 million, to the opening balance of retained earnings - see notes 5 and 11. The adoption impact was attributable to an increase in allowance for credit losses on a group of approximately 300 client deficit accounts, originated in November 2018, of the FCM division of the Company’s wholly owned subsidiary, StoneX Financial Inc. Results for reporting periods beginning after October 1, 2020 are presented using the CECL model, while prior period amounts continue to be reported in accordance with previously applicable U.S. GAAP. Current Expected Credit Losses Beginning October 1, 2020, the Company estimates its allowance for credit losses on financial assets measured at amortized cost based on expected credit losses over the life of the financial asset. In determining expected credit losses, the Company considers a number of factors including, but not limited to, historical collection experience, current and forecasted economic and business conditions, internal and external credit risk ratings, collateral terms, payment terms and aging of the financial asset. The Company estimates expected credit losses primarily using a probability of default (“PD”)/loss given default (“LGD”) model (“PD/LGD model”), under which the expected credit loss is calculated as the product of PD, LGD and exposure at default.

Earnings per Share

Earnings per Share	6 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Earnings per Share	Earnings per Share The Company presents basic and diluted earnings per share (“EPS”) using the two-class method, which requires all outstanding unvested share-based payment awards that contain rights to non-forfeitable dividends and therefore participate in undistributed earnings with common stockholders be included in computing earnings per share. Under the two-class method, net income is reduced by the amount of dividends declared in the period for each class of common stock and participating security. The remaining undistributed earnings are then allocated to common stock and participating securities, based on their respective rights to receive dividends. Restricted stock awards granted to certain employees and directors contain non-forfeitable rights to dividends at the same rate as common stock and are considered participating securities. Basic EPS has been computed by dividing net income by the weighted-average number of common shares outstanding. The following is a reconciliation of the numerator and denominator of the diluted earnings per share computations for the periods presented below. Three Months Ended March 31, Six Months Ended March 31, (in millions, except share amounts) 2021 2020 2021 2020 Numerator: Net income $ 55.3 $ 39.3 $ 74.8 $ 55.6 Less: Allocation to participating securities (1.7) (0.9) (2.2) (1.2) Net income allocated to common stockholders $ 53.6 $ 38.4 $ 72.6 $ 54.4 Denominator: Weighted average number of: Common shares outstanding 19,112,216 18,872,937 19,025,604 18,811,268 Dilutive potential common shares outstanding: Share-based awards 558,323 317,016 544,424 321,229 Diluted weighted-average common shares 19,670,539 19,189,953 19,570,028 19,132,497 The dilutive effect of share-based awards is reflected in diluted net income per share by application of the treasury stock method, which includes consideration of unamortized share-based compensation expense. Options to purchase 212,892 and 945,211 shares of common stock for the three months ended March 31, 2021 and 2020, respectively, and options to purchase 106,368 and 981,088 shares of common stock for the six months ended March 31, 2021 and 2020, respectively, were excluded from the calculation of diluted earnings per share as they would have been anti-dilutive.

Assets and Liabilities, at Fair

Assets and Liabilities, at Fair Value	6 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Assets and Liabilities, at Fair Value	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. 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 an asset or liability at the measurement date. The Company uses prices and inputs that are current as of 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 prices. 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 $1.5 million and $1.5 million of contingent liabilities classified within Level 3 of the fair value hierarchy as of March 31, 2021 and September 30, 2020, respectively. The Company had no Level 3 assets as of March 31, 2021 and September 30, 2020. 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. Relevant guidance requires the Company to consider counterparty credit risk of all parties to 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 Over-the-counter (“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 includes the fair 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 forwards, swaps and options. Financial instruments owned and sold, not yet purchased include the fair value of equity securities, which includes common, preferred, and foreign ordinary shares, American Depository Receipts (“ADRs”), Global Depository Receipts (“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 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 instruments with such quotes 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 inventory 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 based upon observable inputs for comparable financial instruments, 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 foreign exchange, 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 significant inputs observable to market participants. The valuation techniques and inputs depend on the type of derivative and the nature of the underlying instrument. The key inputs depend upon the type of derivative and the nature of the underlying instrument and include interest yield curves, foreign exchange rates, commodity prices, volatilities and correlation. These derivative instruments are included within Level 2 of the fair value hierarchy. 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 comparing of primary vendor prices to internal trader prices or secondary vendor prices. When evaluating the propriety of vendor-priced financial instruments using secondary prices, considerations include the range and quality of vendor prices, level of observable transactions for identical and similar instruments, and judgments based upon knowledge of a particular market and asset class. If the primary vendor price does not represent fair value, justification for using a secondary price, including source data used to make the determination, is subject to review and approval by authorized personnel prior to using a secondary price. Financial instruments owned and sold that are valued using third party pricing sources are included within either Level 1 or Level 2 of the fair value hierarchy based upon the observability of the inputs used and the level of activity in the market. The fair value estimates presented herein are based on pertinent information available to management as of March 31, 2021 and September 30, 2020. 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 table sets forth the Company’s financial and nonfinancial assets and liabilities accounted for at fair value, on a recurring basis, as of March 31, 2021 by level in the fair value hierarchy. Except as disclosed in Note 6, there were no assets or liabilities that were measured at fair value on a nonrecurring basis as of March 31, 2021. March 31, 2021 (in millions) Level 1 Level 2 Level 3 Netting (1) Total Assets: Certificates of deposit $ 3.6 $ — $ — $ — $ 3.6 Money market mutual funds 12.8 — — — 12.8 Cash and cash equivalents 16.4 — — — 16.4 Commodities warehouse receipts 94.2 — — — 94.2 U.S. Treasury obligations 8.3 — — — 8.3 Securities and other assets segregated under federal and other regulations 102.5 — — — 102.5 U.S. Treasury obligations 939.2 — — — 939.2 To be announced ("TBA") and forward settling securities — 54.9 — (3.8) 51.1 Foreign government obligations 8.0 — — — 8.0 Derivatives 3,238.6 375.5 — (3,772.6) (158.5) Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net 4,185.8 430.4 — (3,776.4) 839.8 Receivables from clients - Derivatives — 334.8 (333.8) 1.0 Equity securities 408.3 14.3 — — 422.6 Corporate and municipal bonds — 71.2 — — 71.2 U.S. Treasury obligations 275.5 — — — 275.5 U.S. government agency obligations — 277.9 — — 277.9 Foreign government obligations 2.5 — — — 2.5 Agency mortgage-backed obligations — 1,552.2 — — 1,552.2 Asset-backed obligations — 46.6 — — 46.6 Derivatives 0.6 617.6 — (417.4) 200.8 Commodities leases — 23.0 — — 23.0 Commodities warehouse receipts 17.7 — — — 17.7 Exchange firm common stock 12.3 — — — 12.3 Mutual funds and other 10.8 — — — 10.8 Financial instruments owned 727.7 2,602.8 — (417.4) 2,913.1 Physical commodities inventory 93.4 261.8 — — 355.2 Total assets at fair value $ 5,125.8 $ 3,629.8 $ — $ (4,527.6) $ 4,228.0 Liabilities: Accounts payable and other accrued liabilities - contingent liabilities $ — $ — $ 1.5 $ — $ 1.5 Payables to clients - Derivatives 3,332.1 258.2 (3,768.5) (178.2) TBA and forward settling securities — 47.5 — (3.8) 43.7 Derivatives — 235.3 — (235.3) — Payable to broker-dealers, clearing organizations and counterparties — 282.8 — (239.1) 43.7 Equity securities 381.4 3.8 — — 385.2 Corporate and municipal bonds — 44.8 — — 44.8 U.S. Treasury obligations 273.3 — — — 273.3 U.S. government agency obligations — 21.2 — — 21.2 Agency mortgage-backed obligations — 2.4 — — 2.4 Derivatives — 733.4 — (343.5) 389.9 Commodities leases — 1.4 — — 1.4 Financial instruments sold, not yet purchased 654.7 807.0 — (343.5) 1,118.2 Total liabilities at fair value $ 3,986.8 $ 1,348.0 $ 1.5 $ (4,351.1) $ 985.2 (1) Represents cash collateral and the impact of netting across the levels of the fair value hierarchy. Netting among positions classified within the same level is included in that level. The following table sets forth the Company’s financial and nonfinancial assets and liabilities accounted for at fair value, on a recurring basis, as of September 30, 2020 by level in the fair value hierarchy. Except as disclosed in Note 6, there were no assets or liabilities that were measured at fair value on a nonrecurring basis as of September 30, 2020. September 30, 2020 (in millions) Level 1 Level 2 Level 3 Netting (1) Total Assets: Certificates of deposit $ 3.2 $ — $ — $ — $ 3.2 Money market mutual funds 12.8 — — — 12.8 Cash and cash equivalents 16.0 — — — 16.0 Commodities warehouse receipts 2.4 — — — 2.4 U.S. Treasury obligations 0.2 — — — 0.2 Securities and other assets segregated under federal and other regulations 2.6 — — — 2.6 U.S. Treasury obligations 1,941.3 — — — 1,941.3 TBA and forward settling securities — 31.0 — (11.8) 19.2 Foreign government obligations 8.0 — — — 8.0 Derivatives 1,949.0 395.8 — (2,537.5) (192.7) Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net 3,898.3 426.8 — (2,549.3) 1,775.8 Receivables from clients - Derivatives — 235.6 (234.1) 1.5 Equity securities 254.9 9.4 — — 264.3 Corporate and municipal bonds — 66.9 — — 66.9 U.S. Treasury obligations 419.9 — — — 419.9 U.S. government agency obligations — 293.4 — — 293.4 Foreign government obligations 2.5 — — — 2.5 Agency mortgage-backed obligations — 1,384.6 — — 1,384.6 Asset-backed obligations — 33.0 — — 33.0 Derivatives 0.7 652.3 — (535.6) 117.4 Commodities leases — 24.9 — — 24.9 Commodities warehouse receipts 103.2 — — — 103.2 Exchange firm common stock 10.1 — — — 10.1 Mutual funds and other 7.5 — — — 7.5 Financial instruments owned 798.8 2,464.5 — (535.6) 2,727.7 Physical commodities inventory 26.8 188.9 — — 215.7 Total assets at fair value $ 4,742.5 $ 3,315.8 $ — $ (3,319.0) $ 4,739.3 Liabilities: Accounts payable and other accrued liabilities - contingent liabilities $ — $ — $ 1.5 $ — $ 1.5 Payables to clients - Derivatives 2,000.8 176.4 (2,399.9) (222.7) TBA and forward settling securities — 22.0 — (11.8) 10.2 Derivatives — 306.7 — (302.2) 4.5 Payable to broker-dealers, clearing organizations and counterparties — 328.7 — (314.0) 14.7 Equity securities 218.0 14.9 — — 232.9 Corporate and municipal bonds — 22.5 — — 22.5 U.S. Treasury obligations 247.5 — — — 247.5 U.S. government agency obligations — 0.1 — — 0.1 Agency mortgage-backed obligations — 5.1 — — 5.1 Derivatives — 563.6 — (386.8) 176.8 Commodities leases — 1.1 — — 1.1 Financial instruments sold, not yet purchased 465.5 607.3 — (386.8) 686.0 Total liabilities at fair value $ 2,466.3 $ 1,112.4 $ 1.5 $ (3,100.7) $ 479.5 (1) Represents cash collateral and the impact of netting across the levels of the fair value hierarchy. Netting among positions classified within the same level is included in that level. Realized and unrealized gains and losses are included in ‘principal gains, net’, ‘interest income’, and ‘cost of sales of physical commodities’ in the condensed consolidated income statements. Additional disclosures about the fair value of financial instruments that are not carried on the Condensed Consolidated Balance Sheets at fair value Many, but not all, of the financial instruments that the Company holds are recorded at fair value in the Condensed Consolidated Balance Sheets. The following represents financial instruments in which the ending balance at March 31, 2021 and September 30, 2020 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 broker-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 thus approximate fair value and are classified as Level 2 under the fair value hierarchy.

Financial Instruments with Off-

Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk	6 Months Ended
	Mar. 31, 2021
Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk [Abstract]
Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk	Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk The Company is party to certain financial instruments with off-balance sheet risk in the normal course of its business. The Company has sold financial instruments that it does not currently own and will therefore be obliged to purchase such financial instruments at a future date. The Company has recorded these obligations in the condensed consolidated financial statements as of March 31, 2021 and September 30, 2020 at the fair values of the related financial instruments. The Company will incur losses if the fair value of the underlying financial instruments increases subsequent to March 31, 2021. The total financial instruments sold, not yet purchased of $1,118.2 million and $686.0 million as of March 31, 2021 and September 30, 2020, respectively, includes $389.9 million and $176.8 million for derivative contracts, respectively, which represented a liability to the Company based on their fair values as of March 31, 2021 and September 30, 2020. 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 Company’s derivative positions are included in the condensed consolidated balance sheets in ‘deposits with and receivables from broker-dealers, clearing organizations and counterparties’, ‘receivables from clients, net’, ‘financial instruments owned and sold, not yet purchased, at fair value’, ‘payable to clients’ and ‘payables to broker-dealers, clearing organizations and counterparties’. Listed below are the fair values of the Company’s derivative assets and liabilities as of March 31, 2021 and September 30, 2020. Assets represent net unrealized gains and liabilities represent net unrealized losses. March 31, 2021 September 30, 2020 (in millions) Assets (1) Liabilities (1) Assets (1) Liabilities (1) Derivative contracts not accounted for as hedges: Exchange-traded commodity derivatives $ 2,393.9 $ 2,325.0 $ 1,637.2 $ 1,747.3 OTC commodity derivatives 855.9 858.2 553.9 433.2 Exchange-traded foreign exchange derivatives 411.4 475.6 9.3 13.0 OTC foreign exchange derivatives 279.4 227.4 520.8 461.5 Exchange-traded interest rate derivatives 351.4 479.9 271.1 200.7 OTC interest rate derivatives 59.0 58.0 96.0 96.6 Exchange-traded equity index derivatives 82.5 51.6 32.1 39.8 OTC equity and indices derivatives 133.6 83.3 113.0 55.4 TBA and forward settling securities 54.9 47.5 31.0 22.0 Gross fair value of derivative contracts $ 4,622.0 $ 4,606.5 $ 3,264.4 $ 3,069.5 Impact of netting and collateral (4,527.6) (4,351.1) (3,319.0) (3,100.7) Total fair value included in 'Deposits with and receivables from broker-dealers, clearing organizations, and counterparties, net' $ (107.4) $ (173.5) Total fair value included in 'Receivables from clients, net' $ 1.0 $ 1.5 Total fair value included in 'Financial instruments owned, at fair value' $ 200.8 $ 117.4 Total fair value included in 'Payables to clients' $ (178.2) $ (222.7) Total fair value included in 'Payables to broker-dealers, clearing organizations and counterparties’ $ 43.7 $ 14.7 Total fair value included in 'Financial instruments sold, not yet purchased, at fair value' $ 389.9 $ 176.8 (1) As of March 31, 2021 and September 30, 2020, the Company’s derivative contract volume for open positions were approximately 10.7 million and 7.9 million contracts, respectively. The Company’s derivative contracts are principally held in its Commercial and Retail segments. The Company assists its Commercial 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 segment clients with option products, including combinations of buying and selling puts and calls. In its Retail segment, the Company provides its retail clients with access to spot foreign exchange, precious metals trading, as well as contracts for a difference (“CFDs”) and spread bets, where permitted. The Company mitigates its risk by generally offsetting the client’s transaction simultaneously with one of the Company’s trading counterparties or will offset that transaction with a similar but not identical position on the exchange. The risk mitigation of these offsetting trades is not within the documented hedging designation requirements of the Derivatives and Hedging Topic of the ASC. These derivative contracts are traded along with cash transactions because of the integrated nature of the markets for these products. The Company manages the risks associated with derivatives on an aggregate basis along with the risks associated with its proprietary trading and market-making activities in cash instruments as part of its firm-wide risk management policies. In particular, the risks related to derivative positions may be partially offset by inventory, unrealized gains in inventory or cash collateral paid or received. The Company transacts in derivative instruments, which consist of futures, mortgage-backed TBA securities and forward settling transactions, that are used to manage risk exposures in the Company’s fixed income portfolio. The fair value of these transactions is recorded in deposits with and receivables from and payables to broker-dealers, clearing organizations, and counterparties. Realized and unrealized gains and losses on securities and derivative transactions are reflected in ‘principal gains, net’. The Company enters into TBA securities transactions for the sole purpose of managing risk associated with the purchase of mortgage pass-through securities. As of March 31, 2021 and September 30, 2020, these transactions are summarized as follows: March 31, 2021 September 30, 2020 (in millions) Gain / (Loss) Notional Amounts Gain / (Loss) Notional Amounts (in millions) Gain/(Loss) Notional Amounts Gain/(Loss) Notional Amounts Unrealized gain on TBA securities purchased within deposits with and receivables from broker-dealers, clearing organizations and counterparties and related notional amounts $ — $ — $ 10.8 $ 5,389.3 Unrealized loss on TBA securities purchased within deposits with and receivables from broker-dealers, clearing organizations and counterparties and related notional amounts $ — $ — $ (1.7) $ 2,647.7 Unrealized gain on TBA securities purchased within payables to broker-dealers, clearing organizations and counterparties and related notional amounts $ 1.3 1,336.0 $ — $ — Unrealized loss on TBA securities purchased within payables to broker-dealers, clearing organizations and counterparties and related notional amounts $ (45.0) $ 7,005.0 $ — $ — Unrealized gain on TBA securities sold within deposits with and receivables from broker-dealers, clearing organizations and counterparties and related notional amounts $ 52.2 $ (8,409.0) $ — $ — Unrealized loss on TBA securities sold within deposits with and receivables from broker-dealers, clearing organizations and counterparties and related notional amounts $ (1.5) $ (1,688.0) $ — $ — Unrealized gain on TBA securities sold within payables to broker-dealers, clearing organizations and counterparties and related notional amounts $ — $ — $ 2.8 $ (2,978.7) Unrealized loss on TBA securities sold within payables to broker-dealers, clearing organizations and counterparties and related notional amounts $ — $ — $ (13.0) $ (6,549.4) Unrealized gain on forward settling securities sold within deposits with and receivables from broker-dealers, clearing organizations and counterparties and related notional amounts $ 1.4 $ (2,032.0) $ 17.4 $ (1,946.0) Unrealized loss on forward settling securities purchased within deposits with and receivables from broker-dealers, clearing organizations and counterparties and related notional amounts $ (1.0) $ 2,866.0 $ (7.3) $ 2,447.1 (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 (losses) related to derivative financial instruments for the three months ended March 31, 2021 and 2020 in accordance with the Derivatives and Hedging Topic of the ASC. The net gains (losses) set forth below are included in ‘principal gains, net’ and ‘cost of sales of physical commodities’ in the condensed consolidated income statements. Three Months Ended March 31, Six Months Ended March 31, (in millions) 2021 2020 2021 2020 Commodities $ 59.0 $ 61.6 $ 63.2 $ 79.8 Foreign exchange 25.5 5.1 61.5 7.3 Interest rate, equities, and indices 30.6 — 43.2 (0.4) TBA and forward settling securities 8.6 (34.4) 0.1 (35.3) Net gains from derivative contracts $ 123.7 $ 32.3 $ 168.0 $ 51.4 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 counterparties’ ability to satisfy 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 that margin requirements are not sufficient to fully cover losses which clients may incur. The Company controls the risks associated with these transactions by requiring clients to maintain margin deposits in compliance with individual exchange regulations and internal guidelines. The Company monitors required margin levels daily, and therefore, may require clients to deposit additional collateral or reduce positions when necessary. The Company also establishes credit limits for clients, which are monitored daily. The Company evaluates each client’s creditworthiness on a case by case basis. Clearing, financing, and settlement activities may require the Company to maintain funds with or pledge securities as collateral with other financial institutions. Generally, these exposures to both clients and exchanges are subject to master netting, or client agreements, which reduce the exposure to the Company by permitting receivables and payables with such clients to be offset in the event of a client default. Management believes that the margin deposits held as of March 31, 2021 and September 30, 2020 were adequate to minimize the risk of material loss that could be created by positions held at that time. Additionally, the Company monitors collateral fair value on a daily basis and adjusts collateral levels in the event of excess market exposure. Derivative financial instruments involve varying degrees of off-balance sheet market risk whereby changes in the fair values of underlying financial instruments may result in changes in the fair value of the financial instruments in excess of the amounts reflected in the consolidated balance sheets. Exposure to market risk is influenced by a number of factors, including the relationships between the financial instruments and the Company’s positions, as well as the volatility and liquidity in the markets in which the financial instruments are traded. The principal risk components of financial instruments include, among other things, interest rate volatility, the duration of the underlying instruments and changes in commodity pricing and foreign exchange rates. The Company attempts to manage its exposure to market risk through various techniques. Aggregate market limits have been established and market risk measures are routinely monitored against these limits.

Allowance for Doubtful Accounts

Allowance for Doubtful Accounts	6 Months Ended
	Mar. 31, 2021
Receivables [Abstract]
Allowance for Doubtful Accounts	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 as of March 31, 2021 and September 30, 2020. The allowance for doubtful accounts related to receivables from clients was $33.6 million and $25.8 million as of March 31, 2021 and September 30, 2020, respectively. The Company had no allowance for doubtful accounts related to notes receivable as of March 31, 2021 and September 30, 2020. Activity in the allowance for doubtful accounts for the six months ended March 31, 2021 was as follows: (in millions) Balance as of September 30, 2020 $ 27.1 ASU 2016-13 cumulative transition adjustment 8.2 Adjusted balance as of September 30, 2020 35.3 Provision for bad debts 2.4 Allowance charge-offs (2.8) Balance as of March 31, 2021 $ 34.9

Physical Commodities Inventory

Physical Commodities Inventory	6 Months Ended
	Mar. 31, 2021
Inventory Disclosure [Abstract]
Physical Commodities Inventory	Physical Commodities Inventory The Company’s inventories consist of finished physical commodities as shown below. (in millions) March 31, September 30, Physical Ag & Energy (1) $ 261.8 $ 201.5 Precious metals - held by broker-dealer subsidiary (2) 93.4 14.2 Precious metals - held by non-broker-dealer subsidiaries (3) 95.6 65.4 Physical commodities inventory, net $ 450.8 $ 281.1 (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 consists of energy related inventories, including primarily propane, gasoline, and kerosene, which are valued at the lower of cost or net realizable value. (2) Precious metals inventory held by the Company’s subsidiary, StoneX Financial Ltd, a United Kingdom ("UK") based broker-dealer, 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 is 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 and energy inventory of $1.7 million and $0.7 million as of March 31, 2021 and September 30, 2020, respectively. The adjustments are included in ‘cost of sales of physical commodities’ in the condensed consolidated income statements.

Goodwill

Goodwill	6 Months Ended
	Mar. 31, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	Goodwill Goodwill allocated to the Company’s operating segments are as follows: (in millions) March 31, September 30, Commercial $ 32.7 $ 32.7 Institutional 9.8 9.8 Retail 2.2 2.2 Global Payments 9.8 10.0 Goodwill $ 54.5 $ 54.7

Intangible Assets

Intangible Assets	6 Months Ended
	Mar. 31, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Intangible Assets	Intangible Assets The gross and net carrying values of intangible assets as of the balance sheet dates, by major intangible asset class are as follows (in millions): March 31, 2021 September 30, 2020 Gross Amount Accumulated Net Amount Gross Amount Accumulated Net Amount Intangible assets subject to amortization Trade/domain names $ 3.7 $ (0.5) $ 3.2 $ 3.7 $ (0.2) $ 3.5 Software programs/platforms 29.0 (9.1) 19.9 29.0 (4.9) 24.1 Customer base 38.2 (19.2) 19.0 38.2 (16.3) 21.9 Total intangible assets subject to amortization 70.9 (28.8) 42.1 70.9 (21.4) 49.5 Intangible assets not subject to amortization Website domains 2.1 — 2.1 2.1 — 2.1 Business licenses 3.8 — 3.8 3.2 — 3.2 Total intangible assets not subject to amortization 5.9 — 5.9 5.3 — 5.3 Total intangible assets $ 76.8 $ (28.8) $ 48.0 $ 76.2 $ (21.4) $ 54.8 Amortization expense related to intangible assets was $3.7 million and $1.1 million for the three months ended March 31, 2021 and 2020, respectively. Amortization expense related to intangibles assets was $7.5 million and $1.9 million for the six months ended March 31, 2021 and 2020, respectively. As of March 31, 2021, the estimated future amortization expense was as follows: (in millions) Fiscal 2021 (remaining six months) $ 7.6 Fiscal 2022 13.9 Fiscal 2023 12.2 Fiscal 2024 4.7 Fiscal 2025 and thereafter 3.7 Total intangible assets subject to amortization $ 42.1

Credit Facilities

Credit Facilities	6 Months Ended
	Mar. 31, 2021
Debt Disclosure [Abstract]
Credit Facilities	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 $771.7 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: • $371.7 million senior secured syndicated loan facility available to the Company for general working capital requirements and capital expenditures. The facility was originally 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. During the six months ended March 31, 2021, the Company made scheduled quarterly principal payments against the Term Loan equal to $4.9 million. Amounts repaid on the Term Loan may not be reborrowed. • $75.0 million unsecured facility available to the Company’s wholly owned subsidiary, StoneX Financial Inc., to provide short-term funding of margin to exchange-clearing organizations, as necessary. The facility is subject to annual review and guaranteed by the Company. • $300.0 million secured syndicated facility available to the Company’s wholly owned subsidiary, FCStone Merchant Services, LLC, to finance commodity financing arrangements and commodity repurchase agreements. The facility is guaranteed by the Company. • $25.0 million unsecured syndicated 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 the Company. Uncommitted Credit Facilities The Company has a secured, uncommitted loan facility, under which StoneX Financial Ltd may borrow up to $25.0 million, collateralized by commodities warehouse receipts, to facilitate the financing of inventory of commodities, subject to certain terms and conditions of the credit agreement. 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 March 31, 2021 and September 30, 2020. 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 no borrowings outstanding under this credit facility as of March 31, 2021 and September 30, 2020. 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 March 31, 2021 and September 30, 2020. Note Payable to Bank In December 2020, the Company obtained a $9.0 million loan from a commercial bank, secured by equipment purchased with the proceeds. The note is payable in monthly installments, with the final payment due during December 2025. The note bears interest at a rate per annum equal to the Index rate, as defined in the agreement, plus 2.35%. 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 used the proceeds from the issuance of the Senior Secured Notes to fund the consideration for the acquisition of Gain Capital Holdings, Inc., to pay acquisition related costs, and to fund the redemption of the Gain Notes. The Senior Secured Notes are 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 $9.5 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 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 March 31, 2021 September 30, Committed Credit Facilities Term Loan (1) February 22, 2022 $ 175.2 (4) $ 174.9 (3) $ 179.5 Revolving Line of Credit (1) February 22, 2022 196.5 (5) 27.0 23.0 Senior StoneX Group Inc. Committed Credit Facility 371.7 201.9 202.5 StoneX Financial Inc. None April 1, 2022 75.0 — — FCStone Merchants Services, LLC Certain commodities assets January 29, 2022 300.0 (5) 254.0 200.1 StoneX Financial Ltd. None October 14, 2021 25.0 (5) — 25.0 $ 771.7 $ 455.9 $ 427.6 Uncommitted Credit Facilities StoneX Financial Inc. Commodities warehouse receipts and certain pledged securities n/a n/a — — StoneX Financial Ltd. Commodities warehouse receipts n/a n/a (5) 25.0 20.0 Note Payable to Bank Certain equipment (5) 8.9 — Senior Secured Notes (2) (4) 337.1 (3) 336.0 Total outstanding borrowings $ 826.9 $ 783.6 (1) The StoneX Group Inc. committed credit facility is secured by substantially all of the assets of StoneX Group Inc. and certain subsidiaries identified in the credit facility agreement as obligors, and pledged equity of certain subsidiaries identified in the credit facility as limited guarantors. (2) The Senior Secured 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 are reported net of unamortized deferred financing costs and original issue discount of $0.3 million and $12.8 million, respectively. (4) Included in Senior secured borrowings, net on the Condensed Consolidated Balance Sheets. (5) Included in Lenders under loans on the Condensed Consolidated Balance Sheets. As reflected above, three of the Company’s committed credit facilities are scheduled to expire during the next twelve months following the quarterly period ended March 31, 2021. The Company intends to renew or replace the facilities as they expire, and based on the Company’s liquidity position and capital structure, the Company believes it will be able to do so.

Securities and Commodity Financ

Securities and Commodity Financing Transactions	6 Months Ended
	Mar. 31, 2021
Brokers and Dealers [Abstract]
Securities and Commodity Financing 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 Company pledges financial instruments owned to collateralize repurchase agreements. At March 31, 2021 and September 30, 2020, financial instruments owned, at fair value of $564.7 million and $468.6 million, respectively, were pledged as collateral under repurchase agreements. The counterparty has the right to sell or repledge the collateral in connection with these transactions. These financial instruments owned have been pledged as collateral and have been parenthetically disclosed on the condensed consolidated balance sheets. In addition, as of March 31, 2021 and September 30, 2020, the Company had pledged financial instruments owned, at fair value of $1,327.2 million and $1,266.4 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 $1,818.8 million and $1,484.7 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 $1,698.9 million and $1,410.3 million as of March 31, 2021, and September 30, 2020, respectively. At March 31, 2021 and September 30, 2020, the Company had accepted collateral that it is permitted by contract to sell or repledge. This collateral consists primarily of securities received in reverse repurchase agreements, securities borrowed agreements, and margin securities held on behalf of correspondent brokers. The fair value of such collateral at March 31, 2021 and September 30, 2020, was $4,110.0 million and $3,303.1 million, respectively, of which $339.5 million and $285.7 million, respectively, was used to cover securities sold short which are recorded in financial instruments sold, not yet purchased on the condensed consolidated balance sheets. In the normal course of business, this collateral is used by the Company to cover financial instruments sold, not yet purchased, to obtain financing in the form of repurchase agreements, and to meet counterparties’ needs under lending arrangement and matched-booked trading strategies. The following tables provide the contractual maturities of gross obligations under repurchase and securities lending agreements as of March 31, 2021 and September 30, 2020 (in millions): March 31, 2021 Overnight and Open Less than 30 Days 30-90 Days Over 90 Days Total Securities sold under agreements to repurchase $ 2,110.2 $ 1,119.1 $ 398.9 $ 139.0 $ 3,767.2 Securities loaned 1,747.2 — — — 1,747.2 Gross amount of secured financing $ 3,857.4 $ 1,119.1 $ 398.9 $ 139.0 $ 5,514.4 September 30, 2020 Overnight and Open Less than 30 Days 30-90 Days Over 90 Days Total Securities sold under agreements to repurchase $ 1,736.3 $ 1,069.2 $ 325.0 $ 25.0 $ 3,155.5 Securities loaned 1,441.9 — — — 1,441.9 Gross amount of secured financing $ 3,178.2 $ 1,069.2 $ 325.0 $ 25.0 $ 4,597.4 The following table provides the underlying collateral types of the gross obligations under repurchase and securities lending agreements as of March 31, 2021 and September 30, 2020 (in millions): Securities sold under agreements to repurchase March 31, 2021 September 30, 2020 U.S. Treasury obligations $ 1,065.0 $ 815.8 U.S. government agency obligations 199.8 279.5 Asset-backed obligations 37.8 18.0 Agency mortgage-backed obligations 2,317.6 1,990.0 Corporate bonds 147.0 52.2 Total securities sold under agreement to repurchase 3,767.2 3,155.5 Securities loaned Equity securities 1,747.2 1,441.9 Total securities loaned 1,747.2 1,441.9 Gross amount of secured financing $ 5,514.4 $ 4,597.4 The following tables provide the netting of securities purchased under agreements to resell, securities sold under agreements to repurchase, securities borrowed and securities loaned as of the periods indicated (in millions): March 31, 2021 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 $ 2,297.2 $ — $ 2,297.2 Securities borrowed $ 1,735.3 $ — $ 1,735.3 Securities sold under agreements to repurchase $ 3,767.2 $ — $ 3,767.2 Securities loaned $ 1,747.2 $ — $ 1,747.2 September 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 $ 1,696.2 $ — $ 1,696.2 Securities borrowed $ 1,440.0 $ — $ 1,440.0 Securities sold under agreements to repurchase $ 3,155.5 $ — $ 3,155.5 Securities loaned $ 1,441.9 $ — $ 1,441.9

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Mar. 31, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	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 March 31, 2021, the aggregate receivable from these client accounts, net of collections and other allowable deductions, was $28.9 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. During the Company’s October 1, 2020 implementation of CECL, the new credit reserving model which is based on expected losses over the life of an asset and which applies to client deficits, the Company completed an assessment of the collectability of these accounts under this new guidance. As a result of the implementation, the Company recognized a cumulative-effect adjustment to record an allowance against these uncollected balances of $8.2 million. The Company continues to assess collectability of these accounts quarterly, including 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 these 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 considering information in its determination of any changes in the 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 March 31, 2021 and September 30, 2020, 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, 2020. Contractual Commitments Self-Insurance The Company self-insures its costs related to medical and dental claims. The Company is self-insured, up to a stop loss amount, for eligible participating employees and retirees, and for qualified dependent medical and dental claims, subject to deductibles and limitations. As of March 31, 2021, 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.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Loss, Net	6 Months Ended
	Mar. 31, 2021
Equity [Abstract]
Accumulated Other Comprehensive Loss, Net	Accumulated Other Comprehensive Loss, Net Comprehensive income consists of net income and other gains and losses affecting stockholders’ equity that, under U.S. GAAP, are excluded from net income. Other comprehensive income includes net actuarial losses from defined benefit pension plans and foreign currency translation adjustments. The following table summarizes the changes in accumulated other comprehensive loss, net for the six months ended March 31, 2021. (in millions) Foreign Currency Translation Adjustment Pension Benefits Adjustment Accumulated Other Comprehensive Loss, net Balances as of September 30, 2020 $ (36.0) $ (4.1) $ (40.1) Other comprehensive income 12.3 — 12.3 Balances as of March 31, 2021 $ (23.7) $ (4.1) $ (27.8)

Revenue from Contracts with Cli

Revenue from Contracts with Clients	6 Months Ended
	Mar. 31, 2021
Revenue from Contract with Customer [Abstract]
Revenue from Contracts with Clients	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 in accordance with 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 0.7% of the Company’s total revenues for the three months ended March 31, 2021 and 2020, respectively. The Company’s revenues from contracts with clients subject to Topic 606 represent approximately 1.4% and 0.8% of the Company’s total revenues for the six months ended March 31, 2021 and 2020, respectively. The Company’s revenues from contracts with clients subject to Topic 606 represent approximately 32.2% and 37.9% of the Company’s operating revenues for the three months ended March 31, 2021 and 2020, respectively. The Company’s revenues from contracts with clients subject to Topic 606 represent approximately 34.6% and 38.5% of the Company’s operating revenues for the six months ended March 31, 2021 and 2020, 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 periods indicated. Three Months Ended March 31, Six Months Ended March 31, (in millions) 2021 2020 2021 2020 Revenues from contracts with clients: Commission and clearing fees: Sales-based: Exchange-traded futures and options $ 49.4 $ 40.1 $ 95.7 $ 72.5 OTC derivative brokerage 4.6 6.7 8.4 12.2 Equities and fixed income 19.4 7.1 33.8 11.4 Mutual funds 1.5 1.6 2.7 2.9 Insurance and annuity products 2.3 2.4 4.6 4.5 Other 0.1 0.5 0.3 0.8 Total sales-based commission 77.3 58.4 145.5 104.3 Trailing: Mutual funds 3.6 3.5 6.9 6.6 Insurance and annuity products 4.2 4.0 8.1 7.7 Total trailing commission 7.8 7.5 15.0 14.3 Clearing fees 39.4 41.6 77.9 71.1 Trade conversion fees 3.6 4.2 5.7 5.7 Other 1.7 4.9 5.1 8.4 Total commission and clearing fees: 129.8 116.6 249.2 203.8 Consulting, management, and account fees: Underwriting fees 0.2 0.2 0.4 0.4 Asset management fees 9.3 8.7 18.0 16.2 Advisory and consulting fees 6.6 5.7 12.6 11.3 Sweep program fees 0.8 3.6 1.6 7.6 Client account fees 3.8 3.1 7.9 6.1 Other 1.4 1.3 4.6 2.3 Total consulting, management, and account fees 22.1 22.6 45.1 43.9 Total revenues from contracts with clients $ 151.9 $ 139.2 $ 294.3 $ 247.7 Method of revenue recognition: Point-in-time $ 127.4 $ 113.7 $ 247.1 $ 198.3 Time elapsed 24.5 25.5 47.2 49.4 Total revenues from contracts with clients 151.9 139.2 294.3 247.7 Other sources of revenues Physical precious metals trading 10,295.7 19,694.7 18,704.6 30,352.7 Physical agricultural and energy product trading 508.6 322.2 983.2 642.2 Principal gains, net 265.2 168.5 468.6 281.0 Interest income 23.4 41.7 44.6 87.7 Total revenues $ 11,244.8 $ 20,366.3 $ 20,495.3 $ 31,611.3 Primary geographic region: United States $ 853.6 $ 585.6 $ 1,612.5 $ 1,097.9 Europe 490.1 150.0 662.5 261.6 South America 14.5 16.3 29.1 31.5 Middle East and Asia 9,885.1 19,613.3 18,187.1 30,218.8 Other 1.5 1.1 4.1 1.5 Total revenues $ 11,244.8 $ 20,366.3 $ 20,495.3 $ 31,611.3 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 and consulting, management, and account fees revenues are primarily related to the Commercial and Institutional reportable segments. Principal gains, net are contributed by all of the Company’s reportable segments. Interest income is primarily related to the Commercial and Institutional reportable segments. Physical precious metals trading and physical agricultural and energy product trading revenues are primarily related to the Commercial 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.

Other Expenses

Other Expenses	6 Months Ended
	Mar. 31, 2021
Other Expenses [Abstract]
Other Expenses	Other Expenses Other expenses consisted of the following, for the periods indicated. Three Months Ended March 31, Six Months Ended March 31, (in millions) 2021 2020 2021 2020 Insurance $ 1.9 $ 1.0 $ 3.7 $ 2.0 Office supplies and printing 0.4 0.5 0.7 0.9 Other clearing related expenses 1.0 0.6 2.0 1.4 Other non-income taxes 3.5 1.3 7.3 2.6 Contingent consideration, net 0.8 0.1 0.9 0.1 Other 4.5 2.9 8.6 5.5 Total other expenses $ 12.1 $ 6.4 $ 23.2 $ 12.5

Income Taxes

Income Taxes	6 Months Ended
	Mar. 31, 2021
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The income tax provision for interim periods is comprised of income tax on ordinary 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. 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. 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 $21.0 million and $16.8 million for the three months ended March 31, 2021 and 2020, respectively, and income tax expense of $28.4 million and $22.2 million for the six months ended March 31, 2021 and 2020, respectively, reflects estimated federal, foreign, state and local income taxes.

Capital and Other Regulatory Re

Capital and Other Regulatory Requirements	6 Months Ended
	Mar. 31, 2021
Capital and Other Regulatory Requirements [Abstract]
Capital and Other Regulatory Requirements	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. Subsidiaries of the Company were in compliance with all of their regulatory requirements as of March 31, 2021. The following table details those subsidiaries with minimum regulatory requirements in excess of $5 million along with the actual balance maintained as of that date. (in millions) As of March 31, 2021 Subsidiary Regulatory Authority Actual Minimum StoneX Financial Inc. SEC and CFTC $ 288.4 $ 163.6 StoneX Financial Ltd. Financial Conduct Authority ("FCA") $ 375.8 $ 222.4 Gain Capital Group, LLC CFTC and NFA $ 69.7 $ 31.6 Gain Capital U.K., Ltd. FCA $ 106.6 $ 31.5 Certain other subsidiaries of the Company, each with a minimum requirement less than $5.0 million, are also subject to net capital requirements promulgated by authorities in the countries in which they operate. As of March 31, 2021, all of the Company’s subsidiaries were in compliance with their local regulatory requirements.

Segment Analysis

Segment Analysis	6 Months Ended
	Mar. 31, 2021
Segment Reporting [Abstract]
Segment Analysis	Segment Analysis During the three months ended September 30, 2020, the Company completed its acquisition of Gain, which it views as a significant acquisition and which triggered a reassessment of the financial information reviewed by its executive management team, which is considered our Chief Operating Decision Maker, on a regular basis, and which is used to make resource allocation decisions. In light of this fundamental change and reassessment described above, the Company modified the operating segments it uses to evaluate its performance. Accordingly, its operating segments are now based primarily on the nature of the clients we serve (commercial, institutional, and retail), and a fourth operating segment, its global payments business. The Company manages its business in this manner due to its large global footprint, in which it has more than 3,000 employees allowing it to serve clients in more than 180 countries. Following the acquisition of Gain, the Company’s business activities are managed as operating segments and organized into reportable segments as follows: • Commercial • Institutional • Retail • Global Payments All segment information has been revised to reflect the operating segment reorganization retroactive to October 1, 2019. Commercial The Company offers commercial clients a comprehensive array of products and services, including risk management and hedging services, execution and clearing of exchange-traded and OTC products, voice brokerage, market intelligence and physical trading, as well as commodity financing and logistics services. The ability to provide these high-value-added products and services differentiates the Company from its competitors and maximizes the opportunity to retain clients. Institutional The Company provides institutional clients with a complete suite of equity trading services to help them find liquidity with best execution, consistent liquidity across a robust array of fixed income products, competitive and efficient clearing and execution in all major futures and securities exchanges globally, as well as prime brokerage in equities and major foreign currency pairs and swap transactions. In addition, the Company originates, structures and places debt instruments in the international and domestic capital markets. These instruments include asset-backed securities (primarily in Argentina) and domestic municipal securities. Retail The Company provides retail clients around the world access to over 15,000 global financial markets, including spot foreign exchange ("forex"), both financial trading and physical investment in precious metals, as well as contracts for difference (“CFDs”), which are investment products with returns linked to the performance of underlying assets. In addition, its independent wealth management business offers a comprehensive product suite to retail investors in the United States. Global Payments The Company provides customized foreign exchange and treasury services to banks and commercial businesses, as well as charities and non-governmental organizations and government organizations. The Company provides transparent pricing and offers payments services in more than 170 countries and 140 currencies, which it believes is more than any other payments solution provider. ******** The total revenues reported combine gross revenues from physical contracts 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 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. Total revenues, operating revenues and net operating revenues shown as “Corporate Unallocated” primarily consist of interest income from its centralized corporate treasury function. In the normal course of operations, the Company operates a centralized corporate treasury function in which it may sweep excess cash from certain subsidiaries, where permitted within regulatory limitations, in exchange for a short-term interest bearing intercompany payable, or provide excess cash to subsidiaries in exchange for a short-term interest bearing intercompany receivable in lieu of the subsidiary borrowing on external credit facilities. The intercompany receivables and payables are eliminated during consolidation; however, this practice may impact reported total assets between segments. Net costs not allocated to operating segments include costs and expenses of certain shared services such as information technology, accounting and treasury, credit and risk, legal and compliance, and human resources and other activities. Information for the reportable segments is shown in accordance with the Segment Reporting Topic of the ASC as follows: Three Months Ended March 31, Six Months Ended March 31, (in millions) 2021 2020 2021 2020 Total revenues: Commercial $ 10,516.4 $ 20,037.4 $ 19,381.9 $ 31,043.7 Institutional 191.6 185.7 357.1 318.1 Retail 503.5 116.5 695.7 192.8 Global Payments 33.5 29.4 67.9 60.8 Corporate Unallocated 4.2 4.0 0.7 9.2 Eliminations (4.4) (6.7) (8.0) (13.3) Total $ 11,244.8 $ 20,366.3 $ 20,495.3 $ 31,611.3 Operating revenues: Commercial $ 144.3 $ 126.2 $ 249.9 $ 219.4 Institutional 191.6 185.7 357.1 318.1 Retail 102.2 28.2 183.9 49.4 Global Payments 33.5 29.4 67.9 60.8 Corporate Unallocated 4.2 4.0 0.7 9.2 Eliminations (4.4) (6.7) (8.0) (13.3) Total $ 471.4 $ 366.8 $ 851.5 $ 643.6 Net operating revenues (loss): Commercial $ 118.2 $ 104.3 $ 200.8 $ 178.0 Institutional 123.8 104.9 229.1 169.7 Retail 70.7 9.7 122.8 14.6 Global Payments 31.7 28.0 64.4 57.8 Corporate Unallocated (10.2) (3.5) (26.8) (6.2) Total $ 334.2 $ 243.4 $ 590.3 $ 413.9 Net contribution: (Revenues less cost of sales of physical commodities, transaction-based clearing expenses, variable compensation, introducing broker commissions and interest expense) Commercial $ 81.8 $ 70.4 $ 138.6 $ 121.9 Institutional 75.3 72.5 142.4 118.5 Retail 65.5 9.4 114.1 13.9 Global Payments 25.7 22.6 51.8 46.4 Total $ 248.3 $ 174.9 $ 446.9 $ 300.7 Segment income: (Net contribution less non-variable direct segment costs) Commercial $ 55.6 $ 41.7 $ 87.7 $ 70.4 Institutional 52.0 51.4 96.8 76.7 Retail 32.0 7.0 49.9 9.9 Global Payments 19.4 17.2 39.8 36.1 Total $ 159.0 $ 117.3 $ 274.2 $ 193.1 Reconciliation of segment income to income before tax: Segment income $ 159.0 $ 117.3 $ 274.2 $ 193.1 Net costs not allocated to operating segments (82.7) (61.2) (171.0) (115.4) Other gain — — — 0.1 Income before tax $ 76.3 $ 56.1 $ 103.2 $ 77.8 (in millions) As of March 31, 2021 As of September 30, 2020 Total assets: Commercial $ 3,438.7 $ 2,753.6 Institutional 9,912.8 8,740.8 Retail 1,382.3 1,245.9 Global Payments 366.2 315.9 Corporate Unallocated 699.7 418.7 Total $ 15,799.7 $ 13,474.9

Basis of Presentation and Con_2

Basis of Presentation and Consolidation and Accounting Standards Adopted (Policies)	6 Months Ended
	Mar. 31, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	The accompanying unaudited condensed consolidated balance sheet as of September 30, 2020, which has been derived from the audited consolidated balance sheet of September 30, 2020, 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 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, 2020, as filed with the SEC.
Consolidation	These condensed consolidated financial statements include the accounts of StoneX Group Inc. and all entities in which the Company has a controlling financial interest. All material intercompany transactions and balances have been eliminated in consolidation.
Fiscal Period	The Company’s fiscal year end is September 30, and its 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	Preparing 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, income 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. 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 March 31, 2021 and through the date of this Form 10-Q.
Reclassifications	During the year ended September 30, 2020, the Company reclassified certain selling and marketing related costs in connection with the acquisition of Gain Capital Holdings, Inc. (“Gain”). In performing this reclassification, the Company has made retrospective adjustments to the condensed consolidated income statements for the three and six months ended March 31, 2020.
Accounting Standards Adopted	Accounting Standards Adopted In June 2016, the FASB issued ASU No. 2016-13, “Measurement of Credit Losses on Financial Instruments”, which significantly changes the ways entities recognize credit losses on financial instruments. The guidance is effective for public business entities for annual and interim periods in fiscal years beginning after December 15, 2019. In April 2019, the FASB issued ASU No. 2019-04, “Codification Improvements to Topic 326, Financial Instruments - Credit Losses, Topic 815, Derivatives and Hedging, and Topic 825, Financial Instruments”, which among other things, included several amendments to ASU No. 2016-13, changing how a company considers expected recoveries and contractual extensions or renewal options when estimating expected credit losses. The guidance replaces the previous incurred loss impairment guidance and introduces a new credit reserving model known as the Current Expected Credit Loss (“CECL”) model, which is based on expected losses over the life of an asset, and applies to financial assets carried at amortized cost, held-to-maturity debt securities and off-balance sheet credit exposures. The allowance must reflect management’s estimate of credit losses over the life of the assets taking future economic changes into consideration. The Company adopted this guidance on October 1, 2020, using the modified retrospective approach, which resulted in a recognized cumulative-effect adjustment of $6.2 million, net of tax of $2.0 million, to the opening balance of retained earnings - see notes 5 and 11. The adoption impact was attributable to an increase in allowance for credit losses on a group of approximately 300 client deficit accounts, originated in November 2018, of the FCM division of the Company’s wholly owned subsidiary, StoneX Financial Inc. Results for reporting periods beginning after October 1, 2020 are presented using the CECL model, while prior period amounts continue to be reported in accordance with previously applicable U.S. GAAP. Current Expected Credit Losses Beginning October 1, 2020, the Company estimates its allowance for credit losses on financial assets measured at amortized cost based on expected credit losses over the life of the financial asset. In determining expected credit losses, the Company considers a number of factors including, but not limited to, historical collection experience, current and forecasted economic and business conditions, internal and external credit risk ratings, collateral terms, payment terms and aging of the financial asset. The Company estimates expected credit losses primarily using a probability of default (“PD”)/loss given default (“LGD”) model (“PD/LGD model”), under which the expected credit loss is calculated as the product of PD, LGD and exposure at default.
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.
Income Taxes	The income tax provision for interim periods is comprised of income tax on ordinary 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.

Earnings per Share (Tables)

Earnings per Share (Tables)	6 Months Ended
	Mar. 31, 2021
Earnings Per Share [Abstract]
Schedule of Calculation of Numerator and Denominator in Earnings Per Share	The following is a reconciliation of the numerator and denominator of the diluted earnings per share computations for the periods presented below. Three Months Ended March 31, Six Months Ended March 31, (in millions, except share amounts) 2021 2020 2021 2020 Numerator: Net income $ 55.3 $ 39.3 $ 74.8 $ 55.6 Less: Allocation to participating securities (1.7) (0.9) (2.2) (1.2) Net income allocated to common stockholders $ 53.6 $ 38.4 $ 72.6 $ 54.4 Denominator: Weighted average number of: Common shares outstanding 19,112,216 18,872,937 19,025,604 18,811,268 Dilutive potential common shares outstanding: Share-based awards 558,323 317,016 544,424 321,229 Diluted weighted-average common shares 19,670,539 19,189,953 19,570,028 19,132,497

Assets and Liabilities, at Fa_2

Assets and Liabilities, at Fair Value (Tables)	6 Months Ended
	Mar. 31, 2021
Fair Value Disclosures [Abstract]
Fair Value, Assets Measured on Recurring Basis	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 March 31, 2021 by level in the fair value hierarchy. Except as disclosed in Note 6, there were no assets or liabilities that were measured at fair value on a nonrecurring basis as of March 31, 2021. March 31, 2021 (in millions) Level 1 Level 2 Level 3 Netting (1) Total Assets: Certificates of deposit $ 3.6 $ — $ — $ — $ 3.6 Money market mutual funds 12.8 — — — 12.8 Cash and cash equivalents 16.4 — — — 16.4 Commodities warehouse receipts 94.2 — — — 94.2 U.S. Treasury obligations 8.3 — — — 8.3 Securities and other assets segregated under federal and other regulations 102.5 — — — 102.5 U.S. Treasury obligations 939.2 — — — 939.2 To be announced ("TBA") and forward settling securities — 54.9 — (3.8) 51.1 Foreign government obligations 8.0 — — — 8.0 Derivatives 3,238.6 375.5 — (3,772.6) (158.5) Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net 4,185.8 430.4 — (3,776.4) 839.8 Receivables from clients - Derivatives — 334.8 (333.8) 1.0 Equity securities 408.3 14.3 — — 422.6 Corporate and municipal bonds — 71.2 — — 71.2 U.S. Treasury obligations 275.5 — — — 275.5 U.S. government agency obligations — 277.9 — — 277.9 Foreign government obligations 2.5 — — — 2.5 Agency mortgage-backed obligations — 1,552.2 — — 1,552.2 Asset-backed obligations — 46.6 — — 46.6 Derivatives 0.6 617.6 — (417.4) 200.8 Commodities leases — 23.0 — — 23.0 Commodities warehouse receipts 17.7 — — — 17.7 Exchange firm common stock 12.3 — — — 12.3 Mutual funds and other 10.8 — — — 10.8 Financial instruments owned 727.7 2,602.8 — (417.4) 2,913.1 Physical commodities inventory 93.4 261.8 — — 355.2 Total assets at fair value $ 5,125.8 $ 3,629.8 $ — $ (4,527.6) $ 4,228.0 Liabilities: Accounts payable and other accrued liabilities - contingent liabilities $ — $ — $ 1.5 $ — $ 1.5 Payables to clients - Derivatives 3,332.1 258.2 (3,768.5) (178.2) TBA and forward settling securities — 47.5 — (3.8) 43.7 Derivatives — 235.3 — (235.3) — Payable to broker-dealers, clearing organizations and counterparties — 282.8 — (239.1) 43.7 Equity securities 381.4 3.8 — — 385.2 Corporate and municipal bonds — 44.8 — — 44.8 U.S. Treasury obligations 273.3 — — — 273.3 U.S. government agency obligations — 21.2 — — 21.2 Agency mortgage-backed obligations — 2.4 — — 2.4 Derivatives — 733.4 — (343.5) 389.9 Commodities leases — 1.4 — — 1.4 Financial instruments sold, not yet purchased 654.7 807.0 — (343.5) 1,118.2 Total liabilities at fair value $ 3,986.8 $ 1,348.0 $ 1.5 $ (4,351.1) $ 985.2 (1) Represents cash collateral and the impact of netting across the levels of the fair value hierarchy. Netting among positions classified within the same level is included in that level. The following table sets forth the Company’s financial and nonfinancial assets and liabilities accounted for at fair value, on a recurring basis, as of September 30, 2020 by level in the fair value hierarchy. Except as disclosed in Note 6, there were no assets or liabilities that were measured at fair value on a nonrecurring basis as of September 30, 2020. September 30, 2020 (in millions) Level 1 Level 2 Level 3 Netting (1) Total Assets: Certificates of deposit $ 3.2 $ — $ — $ — $ 3.2 Money market mutual funds 12.8 — — — 12.8 Cash and cash equivalents 16.0 — — — 16.0 Commodities warehouse receipts 2.4 — — — 2.4 U.S. Treasury obligations 0.2 — — — 0.2 Securities and other assets segregated under federal and other regulations 2.6 — — — 2.6 U.S. Treasury obligations 1,941.3 — — — 1,941.3 TBA and forward settling securities — 31.0 — (11.8) 19.2 Foreign government obligations 8.0 — — — 8.0 Derivatives 1,949.0 395.8 — (2,537.5) (192.7) Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net 3,898.3 426.8 — (2,549.3) 1,775.8 Receivables from clients - Derivatives — 235.6 (234.1) 1.5 Equity securities 254.9 9.4 — — 264.3 Corporate and municipal bonds — 66.9 — — 66.9 U.S. Treasury obligations 419.9 — — — 419.9 U.S. government agency obligations — 293.4 — — 293.4 Foreign government obligations 2.5 — — — 2.5 Agency mortgage-backed obligations — 1,384.6 — — 1,384.6 Asset-backed obligations — 33.0 — — 33.0 Derivatives 0.7 652.3 — (535.6) 117.4 Commodities leases — 24.9 — — 24.9 Commodities warehouse receipts 103.2 — — — 103.2 Exchange firm common stock 10.1 — — — 10.1 Mutual funds and other 7.5 — — — 7.5 Financial instruments owned 798.8 2,464.5 — (535.6) 2,727.7 Physical commodities inventory 26.8 188.9 — — 215.7 Total assets at fair value $ 4,742.5 $ 3,315.8 $ — $ (3,319.0) $ 4,739.3 Liabilities: Accounts payable and other accrued liabilities - contingent liabilities $ — $ — $ 1.5 $ — $ 1.5 Payables to clients - Derivatives 2,000.8 176.4 (2,399.9) (222.7) TBA and forward settling securities — 22.0 — (11.8) 10.2 Derivatives — 306.7 — (302.2) 4.5 Payable to broker-dealers, clearing organizations and counterparties — 328.7 — (314.0) 14.7 Equity securities 218.0 14.9 — — 232.9 Corporate and municipal bonds — 22.5 — — 22.5 U.S. Treasury obligations 247.5 — — — 247.5 U.S. government agency obligations — 0.1 — — 0.1 Agency mortgage-backed obligations — 5.1 — — 5.1 Derivatives — 563.6 — (386.8) 176.8 Commodities leases — 1.1 — — 1.1 Financial instruments sold, not yet purchased 465.5 607.3 — (386.8) 686.0 Total liabilities at fair value $ 2,466.3 $ 1,112.4 $ 1.5 $ (3,100.7) $ 479.5 (1) Represents cash collateral and the impact of netting across the levels of the fair value hierarchy. Netting among positions classified within the same level is included in that level.

Financial Instruments with Of_2

Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk (Tables)	6 Months Ended
	Mar. 31, 2021
Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk [Abstract]
Schedule of Derivative Instruments	Listed below are the fair values of the Company’s derivative assets and liabilities as of March 31, 2021 and September 30, 2020. Assets represent net unrealized gains and liabilities represent net unrealized losses. March 31, 2021 September 30, 2020 (in millions) Assets (1) Liabilities (1) Assets (1) Liabilities (1) Derivative contracts not accounted for as hedges: Exchange-traded commodity derivatives $ 2,393.9 $ 2,325.0 $ 1,637.2 $ 1,747.3 OTC commodity derivatives 855.9 858.2 553.9 433.2 Exchange-traded foreign exchange derivatives 411.4 475.6 9.3 13.0 OTC foreign exchange derivatives 279.4 227.4 520.8 461.5 Exchange-traded interest rate derivatives 351.4 479.9 271.1 200.7 OTC interest rate derivatives 59.0 58.0 96.0 96.6 Exchange-traded equity index derivatives 82.5 51.6 32.1 39.8 OTC equity and indices derivatives 133.6 83.3 113.0 55.4 TBA and forward settling securities 54.9 47.5 31.0 22.0 Gross fair value of derivative contracts $ 4,622.0 $ 4,606.5 $ 3,264.4 $ 3,069.5 Impact of netting and collateral (4,527.6) (4,351.1) (3,319.0) (3,100.7) Total fair value included in 'Deposits with and receivables from broker-dealers, clearing organizations, and counterparties, net' $ (107.4) $ (173.5) Total fair value included in 'Receivables from clients, net' $ 1.0 $ 1.5 Total fair value included in 'Financial instruments owned, at fair value' $ 200.8 $ 117.4 Total fair value included in 'Payables to clients' $ (178.2) $ (222.7) Total fair value included in 'Payables to broker-dealers, clearing organizations and counterparties’ $ 43.7 $ 14.7 Total fair value included in 'Financial instruments sold, not yet purchased, at fair value' $ 389.9 $ 176.8 (1) As of March 31, 2021 and September 30, 2020, the Company’s derivative contract volume for open positions were approximately 10.7 million and 7.9 million contracts, respectively.
Schedule of Derivative Instruments Included in Trading Activities	As of March 31, 2021 and September 30, 2020, these transactions are summarized as follows: March 31, 2021 September 30, 2020 (in millions) Gain / (Loss) Notional Amounts Gain / (Loss) Notional Amounts (in millions) Gain/(Loss) Notional Amounts Gain/(Loss) Notional Amounts Unrealized gain on TBA securities purchased within deposits with and receivables from broker-dealers, clearing organizations and counterparties and related notional amounts $ — $ — $ 10.8 $ 5,389.3 Unrealized loss on TBA securities purchased within deposits with and receivables from broker-dealers, clearing organizations and counterparties and related notional amounts $ — $ — $ (1.7) $ 2,647.7 Unrealized gain on TBA securities purchased within payables to broker-dealers, clearing organizations and counterparties and related notional amounts $ 1.3 1,336.0 $ — $ — Unrealized loss on TBA securities purchased within payables to broker-dealers, clearing organizations and counterparties and related notional amounts $ (45.0) $ 7,005.0 $ — $ — Unrealized gain on TBA securities sold within deposits with and receivables from broker-dealers, clearing organizations and counterparties and related notional amounts $ 52.2 $ (8,409.0) $ — $ — Unrealized loss on TBA securities sold within deposits with and receivables from broker-dealers, clearing organizations and counterparties and related notional amounts $ (1.5) $ (1,688.0) $ — $ — Unrealized gain on TBA securities sold within payables to broker-dealers, clearing organizations and counterparties and related notional amounts $ — $ — $ 2.8 $ (2,978.7) Unrealized loss on TBA securities sold within payables to broker-dealers, clearing organizations and counterparties and related notional amounts $ — $ — $ (13.0) $ (6,549.4) Unrealized gain on forward settling securities sold within deposits with and receivables from broker-dealers, clearing organizations and counterparties and related notional amounts $ 1.4 $ (2,032.0) $ 17.4 $ (1,946.0) Unrealized loss on forward settling securities purchased within deposits with and receivables from broker-dealers, clearing organizations and counterparties and related notional amounts $ (1.0) $ 2,866.0 $ (7.3) $ 2,447.1 (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	The following table sets forth the Company’s net gains (losses) related to derivative financial instruments for the three months ended March 31, 2021 and 2020 in accordance with the Derivatives and Hedging Topic of the ASC. The net gains (losses) set forth below are included in ‘principal gains, net’ and ‘cost of sales of physical commodities’ in the condensed consolidated income statements. Three Months Ended March 31, Six Months Ended March 31, (in millions) 2021 2020 2021 2020 Commodities $ 59.0 $ 61.6 $ 63.2 $ 79.8 Foreign exchange 25.5 5.1 61.5 7.3 Interest rate, equities, and indices 30.6 — 43.2 (0.4) TBA and forward settling securities 8.6 (34.4) 0.1 (35.3) Net gains from derivative contracts $ 123.7 $ 32.3 $ 168.0 $ 51.4

Allowance for Doubtful Accoun_2

Allowance for Doubtful Accounts (Tables)	6 Months Ended
	Mar. 31, 2021
Receivables [Abstract]
Financing Receivable, Allowance for Credit Loss	Activity in the allowance for doubtful accounts for the six months ended March 31, 2021 was as follows: (in millions) Balance as of September 30, 2020 $ 27.1 ASU 2016-13 cumulative transition adjustment 8.2 Adjusted balance as of September 30, 2020 35.3 Provision for bad debts 2.4 Allowance charge-offs (2.8) Balance as of March 31, 2021 $ 34.9

Physical Commodities Inventory

Physical Commodities Inventory (Tables)	6 Months Ended
	Mar. 31, 2021
Inventory Disclosure [Abstract]
Schedule of Inventory	The Company’s inventories consist of finished physical commodities as shown below. (in millions) March 31, September 30, Physical Ag & Energy (1) $ 261.8 $ 201.5 Precious metals - held by broker-dealer subsidiary (2) 93.4 14.2 Precious metals - held by non-broker-dealer subsidiaries (3) 95.6 65.4 Physical commodities inventory, net $ 450.8 $ 281.1 (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 consists of energy related inventories, including primarily propane, gasoline, and kerosene, which are valued at the lower of cost or net realizable value. (2) Precious metals inventory held by the Company’s subsidiary, StoneX Financial Ltd, a United Kingdom ("UK") based broker-dealer, 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 is valued at the lower of cost or net realizable value.

Goodwill (Tables)

Goodwill (Tables)	6 Months Ended
	Mar. 31, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill	Goodwill allocated to the Company’s operating segments are as follows: (in millions) March 31, September 30, Commercial $ 32.7 $ 32.7 Institutional 9.8 9.8 Retail 2.2 2.2 Global Payments 9.8 10.0 Goodwill $ 54.5 $ 54.7

Intangible Assets (Tables)

Intangible Assets (Tables)	6 Months Ended
	Mar. 31, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Finite and Indefinite-Lived Intangible Assets	The gross and net carrying values of intangible assets as of the balance sheet dates, by major intangible asset class are as follows (in millions): March 31, 2021 September 30, 2020 Gross Amount Accumulated Net Amount Gross Amount Accumulated Net Amount Intangible assets subject to amortization Trade/domain names $ 3.7 $ (0.5) $ 3.2 $ 3.7 $ (0.2) $ 3.5 Software programs/platforms 29.0 (9.1) 19.9 29.0 (4.9) 24.1 Customer base 38.2 (19.2) 19.0 38.2 (16.3) 21.9 Total intangible assets subject to amortization 70.9 (28.8) 42.1 70.9 (21.4) 49.5 Intangible assets not subject to amortization Website domains 2.1 — 2.1 2.1 — 2.1 Business licenses 3.8 — 3.8 3.2 — 3.2 Total intangible assets not subject to amortization 5.9 — 5.9 5.3 — 5.3 Total intangible assets $ 76.8 $ (28.8) $ 48.0 $ 76.2 $ (21.4) $ 54.8
Schedule of Expected Amortization Expense	As of March 31, 2021, the estimated future amortization expense was as follows: (in millions) Fiscal 2021 (remaining six months) $ 7.6 Fiscal 2022 13.9 Fiscal 2023 12.2 Fiscal 2024 4.7 Fiscal 2025 and thereafter 3.7 Total intangible assets subject to amortization $ 42.1

Credit Facilities (Tables)

Credit Facilities (Tables)	6 Months Ended
	Mar. 31, 2021
Debt Disclosure [Abstract]
Schedule of Debt	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 March 31, 2021 September 30, Committed Credit Facilities Term Loan (1) February 22, 2022 $ 175.2 (4) $ 174.9 (3) $ 179.5 Revolving Line of Credit (1) February 22, 2022 196.5 (5) 27.0 23.0 Senior StoneX Group Inc. Committed Credit Facility 371.7 201.9 202.5 StoneX Financial Inc. None April 1, 2022 75.0 — — FCStone Merchants Services, LLC Certain commodities assets January 29, 2022 300.0 (5) 254.0 200.1 StoneX Financial Ltd. None October 14, 2021 25.0 (5) — 25.0 $ 771.7 $ 455.9 $ 427.6 Uncommitted Credit Facilities StoneX Financial Inc. Commodities warehouse receipts and certain pledged securities n/a n/a — — StoneX Financial Ltd. Commodities warehouse receipts n/a n/a (5) 25.0 20.0 Note Payable to Bank Certain equipment (5) 8.9 — Senior Secured Notes (2) (4) 337.1 (3) 336.0 Total outstanding borrowings $ 826.9 $ 783.6 (1) The StoneX Group Inc. committed credit facility is secured by substantially all of the assets of StoneX Group Inc. and certain subsidiaries identified in the credit facility agreement as obligors, and pledged equity of certain subsidiaries identified in the credit facility as limited guarantors. (2) The Senior Secured 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 are reported net of unamortized deferred financing costs and original issue discount of $0.3 million and $12.8 million, respectively. (4) Included in Senior secured borrowings, net on the Condensed Consolidated Balance Sheets. (5) Included in Lenders under loans on the Condensed Consolidated Balance Sheets.

Securities and Commodity Fina_2

Securities and Commodity Financing Transactions (Tables)	6 Months Ended
	Mar. 31, 2021
Brokers and Dealers [Abstract]
Schedule of Underlying Assets of Repurchase Agreements when Amount of Repurchase Agreements Exceeds 10 Percent of Assets	The following tables provide the contractual maturities of gross obligations under repurchase and securities lending agreements as of March 31, 2021 and September 30, 2020 (in millions): March 31, 2021 Overnight and Open Less than 30 Days 30-90 Days Over 90 Days Total Securities sold under agreements to repurchase $ 2,110.2 $ 1,119.1 $ 398.9 $ 139.0 $ 3,767.2 Securities loaned 1,747.2 — — — 1,747.2 Gross amount of secured financing $ 3,857.4 $ 1,119.1 $ 398.9 $ 139.0 $ 5,514.4 September 30, 2020 Overnight and Open Less than 30 Days 30-90 Days Over 90 Days Total Securities sold under agreements to repurchase $ 1,736.3 $ 1,069.2 $ 325.0 $ 25.0 $ 3,155.5 Securities loaned 1,441.9 — — — 1,441.9 Gross amount of secured financing $ 3,178.2 $ 1,069.2 $ 325.0 $ 25.0 $ 4,597.4
Schedule of Financial Instruments Owned and Pledged as Collateral	The following table provides the underlying collateral types of the gross obligations under repurchase and securities lending agreements as of March 31, 2021 and September 30, 2020 (in millions): Securities sold under agreements to repurchase March 31, 2021 September 30, 2020 U.S. Treasury obligations $ 1,065.0 $ 815.8 U.S. government agency obligations 199.8 279.5 Asset-backed obligations 37.8 18.0 Agency mortgage-backed obligations 2,317.6 1,990.0 Corporate bonds 147.0 52.2 Total securities sold under agreement to repurchase 3,767.2 3,155.5 Securities loaned Equity securities 1,747.2 1,441.9 Total securities loaned 1,747.2 1,441.9 Gross amount of secured financing $ 5,514.4 $ 4,597.4 The following tables provide the netting of securities purchased under agreements to resell, securities sold under agreements to repurchase, securities borrowed and securities loaned as of the periods indicated (in millions): March 31, 2021 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 $ 2,297.2 $ — $ 2,297.2 Securities borrowed $ 1,735.3 $ — $ 1,735.3 Securities sold under agreements to repurchase $ 3,767.2 $ — $ 3,767.2 Securities loaned $ 1,747.2 $ — $ 1,747.2 September 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 $ 1,696.2 $ — $ 1,696.2 Securities borrowed $ 1,440.0 $ — $ 1,440.0 Securities sold under agreements to repurchase $ 3,155.5 $ — $ 3,155.5 Securities loaned $ 1,441.9 $ — $ 1,441.9

Accumulated Other Comprehensi_2

Accumulated Other Comprehensive Loss, Net (Tables)	6 Months Ended
	Mar. 31, 2021
Equity [Abstract]
Summary of Changes in Accumulated Other Comprehensive Loss	The following table summarizes the changes in accumulated other comprehensive loss, net for the six months ended March 31, 2021. (in millions) Foreign Currency Translation Adjustment Pension Benefits Adjustment Accumulated Other Comprehensive Loss, net Balances as of September 30, 2020 $ (36.0) $ (4.1) $ (40.1) Other comprehensive income 12.3 — 12.3 Balances as of March 31, 2021 $ (23.7) $ (4.1) $ (27.8)

Revenue from Contracts with C_2

Revenue from Contracts with Clients (Tables)	6 Months Ended
	Mar. 31, 2021
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue	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 periods indicated. Three Months Ended March 31, Six Months Ended March 31, (in millions) 2021 2020 2021 2020 Revenues from contracts with clients: Commission and clearing fees: Sales-based: Exchange-traded futures and options $ 49.4 $ 40.1 $ 95.7 $ 72.5 OTC derivative brokerage 4.6 6.7 8.4 12.2 Equities and fixed income 19.4 7.1 33.8 11.4 Mutual funds 1.5 1.6 2.7 2.9 Insurance and annuity products 2.3 2.4 4.6 4.5 Other 0.1 0.5 0.3 0.8 Total sales-based commission 77.3 58.4 145.5 104.3 Trailing: Mutual funds 3.6 3.5 6.9 6.6 Insurance and annuity products 4.2 4.0 8.1 7.7 Total trailing commission 7.8 7.5 15.0 14.3 Clearing fees 39.4 41.6 77.9 71.1 Trade conversion fees 3.6 4.2 5.7 5.7 Other 1.7 4.9 5.1 8.4 Total commission and clearing fees: 129.8 116.6 249.2 203.8 Consulting, management, and account fees: Underwriting fees 0.2 0.2 0.4 0.4 Asset management fees 9.3 8.7 18.0 16.2 Advisory and consulting fees 6.6 5.7 12.6 11.3 Sweep program fees 0.8 3.6 1.6 7.6 Client account fees 3.8 3.1 7.9 6.1 Other 1.4 1.3 4.6 2.3 Total consulting, management, and account fees 22.1 22.6 45.1 43.9 Total revenues from contracts with clients $ 151.9 $ 139.2 $ 294.3 $ 247.7 Method of revenue recognition: Point-in-time $ 127.4 $ 113.7 $ 247.1 $ 198.3 Time elapsed 24.5 25.5 47.2 49.4 Total revenues from contracts with clients 151.9 139.2 294.3 247.7 Other sources of revenues Physical precious metals trading 10,295.7 19,694.7 18,704.6 30,352.7 Physical agricultural and energy product trading 508.6 322.2 983.2 642.2 Principal gains, net 265.2 168.5 468.6 281.0 Interest income 23.4 41.7 44.6 87.7 Total revenues $ 11,244.8 $ 20,366.3 $ 20,495.3 $ 31,611.3 Primary geographic region: United States $ 853.6 $ 585.6 $ 1,612.5 $ 1,097.9 Europe 490.1 150.0 662.5 261.6 South America 14.5 16.3 29.1 31.5 Middle East and Asia 9,885.1 19,613.3 18,187.1 30,218.8 Other 1.5 1.1 4.1 1.5 Total revenues $ 11,244.8 $ 20,366.3 $ 20,495.3 $ 31,611.3

Other Expenses (Tables)

Other Expenses (Tables)	6 Months Ended
	Mar. 31, 2021
Other Expenses [Abstract]
Schedule of Other Operating Cost and Expense, by Component	Other expenses consisted of the following, for the periods indicated. Three Months Ended March 31, Six Months Ended March 31, (in millions) 2021 2020 2021 2020 Insurance $ 1.9 $ 1.0 $ 3.7 $ 2.0 Office supplies and printing 0.4 0.5 0.7 0.9 Other clearing related expenses 1.0 0.6 2.0 1.4 Other non-income taxes 3.5 1.3 7.3 2.6 Contingent consideration, net 0.8 0.1 0.9 0.1 Other 4.5 2.9 8.6 5.5 Total other expenses $ 12.1 $ 6.4 $ 23.2 $ 12.5

Capital and Other Regulatory _2

Capital and Other Regulatory Requirements (Tables)	6 Months Ended
	Mar. 31, 2021
Capital and Other Regulatory Requirements [Abstract]
Subsidiaries with Minimum Regulatory Requirements	The following table details those subsidiaries with minimum regulatory requirements in excess of $5 million along with the actual balance maintained as of that date. (in millions) As of March 31, 2021 Subsidiary Regulatory Authority Actual Minimum StoneX Financial Inc. SEC and CFTC $ 288.4 $ 163.6 StoneX Financial Ltd. Financial Conduct Authority ("FCA") $ 375.8 $ 222.4 Gain Capital Group, LLC CFTC and NFA $ 69.7 $ 31.6 Gain Capital U.K., Ltd. FCA $ 106.6 $ 31.5

Segment Analysis (Tables)

Segment Analysis (Tables)	6 Months Ended
	Mar. 31, 2021
Segment Reporting [Abstract]
Schedule of Segment Reporting Information	Information for the reportable segments is shown in accordance with the Segment Reporting Topic of the ASC as follows: Three Months Ended March 31, Six Months Ended March 31, (in millions) 2021 2020 2021 2020 Total revenues: Commercial $ 10,516.4 $ 20,037.4 $ 19,381.9 $ 31,043.7 Institutional 191.6 185.7 357.1 318.1 Retail 503.5 116.5 695.7 192.8 Global Payments 33.5 29.4 67.9 60.8 Corporate Unallocated 4.2 4.0 0.7 9.2 Eliminations (4.4) (6.7) (8.0) (13.3) Total $ 11,244.8 $ 20,366.3 $ 20,495.3 $ 31,611.3 Operating revenues: Commercial $ 144.3 $ 126.2 $ 249.9 $ 219.4 Institutional 191.6 185.7 357.1 318.1 Retail 102.2 28.2 183.9 49.4 Global Payments 33.5 29.4 67.9 60.8 Corporate Unallocated 4.2 4.0 0.7 9.2 Eliminations (4.4) (6.7) (8.0) (13.3) Total $ 471.4 $ 366.8 $ 851.5 $ 643.6 Net operating revenues (loss): Commercial $ 118.2 $ 104.3 $ 200.8 $ 178.0 Institutional 123.8 104.9 229.1 169.7 Retail 70.7 9.7 122.8 14.6 Global Payments 31.7 28.0 64.4 57.8 Corporate Unallocated (10.2) (3.5) (26.8) (6.2) Total $ 334.2 $ 243.4 $ 590.3 $ 413.9 Net contribution: (Revenues less cost of sales of physical commodities, transaction-based clearing expenses, variable compensation, introducing broker commissions and interest expense) Commercial $ 81.8 $ 70.4 $ 138.6 $ 121.9 Institutional 75.3 72.5 142.4 118.5 Retail 65.5 9.4 114.1 13.9 Global Payments 25.7 22.6 51.8 46.4 Total $ 248.3 $ 174.9 $ 446.9 $ 300.7 Segment income: (Net contribution less non-variable direct segment costs) Commercial $ 55.6 $ 41.7 $ 87.7 $ 70.4 Institutional 52.0 51.4 96.8 76.7 Retail 32.0 7.0 49.9 9.9 Global Payments 19.4 17.2 39.8 36.1 Total $ 159.0 $ 117.3 $ 274.2 $ 193.1 Reconciliation of segment income to income before tax: Segment income $ 159.0 $ 117.3 $ 274.2 $ 193.1 Net costs not allocated to operating segments (82.7) (61.2) (171.0) (115.4) Other gain — — — 0.1 Income before tax $ 76.3 $ 56.1 $ 103.2 $ 77.8 (in millions) As of March 31, 2021 As of September 30, 2020 Total assets: Commercial $ 3,438.7 $ 2,753.6 Institutional 9,912.8 8,740.8 Retail 1,382.3 1,245.9 Global Payments 366.2 315.9 Corporate Unallocated 699.7 418.7 Total $ 15,799.7 $ 13,474.9

Basis of Presentation and Con_3

Basis of Presentation and Consolidation and Accounting Standards Adopted (Details) $ in Millions	Oct. 01, 2020USD ($)	Mar. 31, 2021USD ($)countryclient	Mar. 31, 2020USD ($)	Mar. 31, 2021USD ($)countryclient	Mar. 31, 2020USD ($)	Sep. 30, 2020USD ($)
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of commercial and institutional clients (more than) | client		35,000		35,000
Number retail clients (more than) | client		340,000		340,000
Number of countries in which entity operates (more than) | country		180		180
Selling and marketing		$ 6.5	$ 4.2	$ 15.3	$ 5.6
Cumulative-effect adjustment, net of tax		641		641		$ 572.4
Income tax expense		$ 21	$ 16.8	$ 28.4	$ 22.2
Cumulative Effect, Period of Adoption, Adjustment
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Cumulative-effect adjustment, net of tax	$ (6.2)
Income tax expense	$ 2
Retail Segment
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of countries in which entity operates (more than) | country		130		130

Earnings per Share - EPS Reconc

Earnings per Share - EPS Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Numerator:
Net income	$ 55.3	$ 39.3	$ 74.8	$ 55.6
Less: Allocation to participating securities	(1.7)	(0.9)	(2.2)	(1.2)
Net income allocated to common stockholders	$ 53.6	$ 38.4	$ 72.6	$ 54.4
Denominator:
Common shares outstanding (in shares)	19,112,216	18,872,937	19,025,604	18,811,268
Dilutive potential common shares outstanding:
Share-based awards (in shares)	558,323	317,016	544,424	321,229
Diluted weighted - average common shares (in shares)	19,670,539	19,189,953	19,570,028	19,132,497

Earnings per Share - Narrative

Earnings per Share - Narrative (Details) - shares	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Earnings Per Share [Abstract]
Antidilutive securities (in shares)	212,892	945,211	106,368	981,088

Assets and Liabilities, at Fa_3

Assets and Liabilities, at Fair Value - Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2021	Sep. 30, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accounts payable and other accrued liabilities - contingent liabilities	$ 281.8	$ 272.6
Senior secured borrowings, net	512	515.5
Carrying value	$ 337.1	336
Senior Secured Notes due 2025
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt instrument, interest rate, stated percentage	8.625%
StoneX Inc. Bank of America Syndicated Credit Facility
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Senior secured borrowings, net	$ 174.9	179.5
Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term debt, fair value	370
Fair Value, Recurring | Contingent Consideration
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accounts payable and other accrued liabilities - contingent liabilities	1.5	1.5
Fair Value, Recurring | Level 3 | Contingent Consideration
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accounts payable and other accrued liabilities - contingent liabilities	1.5	1.5
Fair Value, Recurring | Level 2 | Contingent Consideration
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accounts payable and other accrued liabilities - contingent liabilities	$ 0	$ 0

Assets and Liabilities, at Fa_4

Assets and Liabilities, at Fair Value - Financial Assets and Liabilities Measured at Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2021	Sep. 30, 2020	Mar. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	$ 1,001.5	$ 952.6	$ 519.5
Cash and cash equivalents	102.5	2.6
Cash and securities segregated under federal and other regulation	2,102.9	1,920.2
Financial instruments owned	2,913.1	2,727.7
Physical commodities inventory	450.8	281.1
Accounts payable and other accrued liabilities - contingent liabilities	281.8	272.6
Payable to broker-dealers, clearing organizations and counterparties	520.7	537.5
Financial instruments sold, not yet purchased	1,118.2	686
Fair Value, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	16.4	16
Cash and securities segregated under federal and other regulation	102.5	2.6
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net	839.8	1,775.8
Receivables from clients - Derivatives	1	1.5
Financial instruments owned	2,913.1	2,727.7
Total assets at fair value	4,228	4,739.3
Payables to clients - Derivatives	(178.2)	(222.7)
Total liabilities at fair value	985.2	479.5
Fair Value, Recurring | TBA and forward settling securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payable to broker-dealers, clearing organizations and counterparties	43.7	10.2
Fair Value, Recurring | Derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payable to broker-dealers, clearing organizations and counterparties	0	4.5
Fair Value, Recurring | Payables to Broker-dealers, Clearing Organizations and Counterparties
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payable to broker-dealers, clearing organizations and counterparties	43.7	14.7
Fair Value, Recurring | Contingent Consideration
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accounts payable and other accrued liabilities - contingent liabilities	1.5	1.5
Fair Value, Recurring | Physical commodities inventory
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Physical commodities inventory	355.2	215.7
Fair Value, Recurring | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	422.6	264.3
Financial instruments sold, not yet purchased	385.2	232.9
Fair Value, Recurring | Corporate and municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	71.2	66.9
Financial instruments sold, not yet purchased	44.8	22.5
Fair Value, Recurring | U.S. Treasury obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	275.5	419.9
Financial instruments sold, not yet purchased	273.3	247.5
Fair Value, Recurring | U.S. government agency obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	277.9	293.4
Financial instruments sold, not yet purchased	21.2	0.1
Fair Value, Recurring | Foreign government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	2.5	2.5
Fair Value, Recurring | Agency mortgage-backed obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	1,552.2	1,384.6
Financial instruments sold, not yet purchased	2.4	5.1
Fair Value, Recurring | Asset-backed obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	46.6	33
Fair Value, Recurring | Derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	200.8	117.4
Financial instruments sold, not yet purchased	389.9	176.8
Fair Value, Recurring | Commodities leases
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	23	24.9
Financial instruments sold, not yet purchased	1.4	1.1
Fair Value, Recurring | Commodities warehouse receipts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	17.7	103.2
Fair Value, Recurring | Exchange firm common stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	12.3	10.1
Fair Value, Recurring | Mutual funds and other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	10.8	7.5
Fair Value, Recurring | TBA and forward settling securities
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	51.1	19.2
Fair Value, Recurring | Foreign government obligations
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	8	8
Fair Value, Recurring | U.S. Treasury obligations
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	939.2	1,941.3
Fair Value, Recurring | Derivatives
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	(158.5)	(192.7)
Fair Value, Recurring | Commodities warehouse receipts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and securities segregated under federal and other regulation	94.2	2.4
Fair Value, Recurring | U.S. Treasury obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and securities segregated under federal and other regulation	8.3	0.2
Fair Value, Recurring | Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	3.6	3.2
Fair Value, Recurring | Money market mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	12.8	12.8
Fair Value, Recurring | Netting
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0	0
Cash and securities segregated under federal and other regulation	0	0
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net	(3,776.4)	(2,549.3)
Receivables from clients - Derivatives	(333.8)	(234.1)
Financial instruments owned	(417.4)	(535.6)
Total assets at fair value	(4,527.6)	(3,319)
Payables to clients - Derivatives	(3,768.5)	(2,399.9)
Financial instruments sold, not yet purchased	(343.5)	(386.8)
Total liabilities at fair value	(4,351.1)	(3,100.7)
Fair Value, Recurring | Netting | TBA and forward settling securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payable to broker-dealers, clearing organizations and counterparties	(3.8)	(11.8)
Fair Value, Recurring | Netting | Derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payable to broker-dealers, clearing organizations and counterparties	(235.3)	(302.2)
Fair Value, Recurring | Netting | Payables to Broker-dealers, Clearing Organizations and Counterparties
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payable to broker-dealers, clearing organizations and counterparties	(239.1)	(314)
Fair Value, Recurring | Netting | Contingent Consideration
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accounts payable and other accrued liabilities - contingent liabilities	0	0
Fair Value, Recurring | Netting | Physical commodities inventory
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Physical commodities inventory	0	0
Fair Value, Recurring | Netting | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0	0
Financial instruments sold, not yet purchased	0	0
Fair Value, Recurring | Netting | Corporate and municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0	0
Financial instruments sold, not yet purchased	0	0
Fair Value, Recurring | Netting | U.S. Treasury obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0	0
Financial instruments sold, not yet purchased	0	0
Fair Value, Recurring | Netting | U.S. government agency obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0	0
Financial instruments sold, not yet purchased	0	0
Fair Value, Recurring | Netting | Foreign government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0	0
Fair Value, Recurring | Netting | Agency mortgage-backed obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0	0
Financial instruments sold, not yet purchased	0	0
Fair Value, Recurring | Netting | Asset-backed obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0	0
Fair Value, Recurring | Netting | Derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	(417.4)	(535.6)
Financial instruments sold, not yet purchased	(343.5)	(386.8)
Fair Value, Recurring | Netting | Commodities leases
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0	0
Financial instruments sold, not yet purchased	0	0
Fair Value, Recurring | Netting | Commodities warehouse receipts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0	0
Fair Value, Recurring | Netting | Exchange firm common stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0	0
Fair Value, Recurring | Netting | Mutual funds and other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0	0
Fair Value, Recurring | Netting | TBA and forward settling securities
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	(3.8)	(11.8)
Fair Value, Recurring | Netting | Foreign government obligations
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	0	0
Fair Value, Recurring | Netting | U.S. Treasury obligations
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	0	0
Fair Value, Recurring | Netting | Derivatives
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	(3,772.6)	(2,537.5)
Fair Value, Recurring | Netting | Commodities warehouse receipts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and securities segregated under federal and other regulation	0	0
Fair Value, Recurring | Netting | U.S. Treasury obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and securities segregated under federal and other regulation	0	0
Fair Value, Recurring | Netting | Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0	0
Fair Value, Recurring | Netting | Money market mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0	0
Fair Value, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	16.4	16
Cash and securities segregated under federal and other regulation	102.5	2.6
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net	4,185.8	3,898.3
Receivables from clients - Derivatives	0	0
Financial instruments owned	727.7	798.8
Total assets at fair value	5,125.8	4,742.5
Payables to clients - Derivatives	3,332.1	2,000.8
Financial instruments sold, not yet purchased	654.7	465.5
Total liabilities at fair value	3,986.8	2,466.3
Fair Value, Recurring | Level 1 | TBA and forward settling securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payable to broker-dealers, clearing organizations and counterparties	0	0
Fair Value, Recurring | Level 1 | Derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payable to broker-dealers, clearing organizations and counterparties	0	0
Fair Value, Recurring | Level 1 | Payables to Broker-dealers, Clearing Organizations and Counterparties
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payable to broker-dealers, clearing organizations and counterparties	0	0
Fair Value, Recurring | Level 1 | Contingent Consideration
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accounts payable and other accrued liabilities - contingent liabilities	0	0
Fair Value, Recurring | Level 1 | Physical commodities inventory
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Physical commodities inventory	93.4	26.8
Fair Value, Recurring | Level 1 | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	408.3	254.9
Financial instruments sold, not yet purchased	381.4	218
Fair Value, Recurring | Level 1 | Corporate and municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0	0
Financial instruments sold, not yet purchased	0	0
Fair Value, Recurring | Level 1 | U.S. Treasury obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	275.5	419.9
Financial instruments sold, not yet purchased	273.3	247.5
Fair Value, Recurring | Level 1 | U.S. government agency obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0	0
Financial instruments sold, not yet purchased	0	0
Fair Value, Recurring | Level 1 | Foreign government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	2.5	2.5
Fair Value, Recurring | Level 1 | Agency mortgage-backed obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0	0
Financial instruments sold, not yet purchased	0	0
Fair Value, Recurring | Level 1 | Asset-backed obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0	0
Fair Value, Recurring | Level 1 | Derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0.6	0.7
Financial instruments sold, not yet purchased	0	0
Fair Value, Recurring | Level 1 | Commodities leases
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0	0
Financial instruments sold, not yet purchased	0	0
Fair Value, Recurring | Level 1 | Commodities warehouse receipts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	17.7	103.2
Fair Value, Recurring | Level 1 | Exchange firm common stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	12.3	10.1
Fair Value, Recurring | Level 1 | Mutual funds and other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	10.8	7.5
Fair Value, Recurring | Level 1 | TBA and forward settling securities
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	0	0
Fair Value, Recurring | Level 1 | Foreign government obligations
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	8	8
Fair Value, Recurring | Level 1 | U.S. Treasury obligations
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	939.2	1,941.3
Fair Value, Recurring | Level 1 | Derivatives
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	3,238.6	1,949
Fair Value, Recurring | Level 1 | Commodities warehouse receipts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and securities segregated under federal and other regulation	94.2	2.4
Fair Value, Recurring | Level 1 | U.S. Treasury obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and securities segregated under federal and other regulation	8.3	0.2
Fair Value, Recurring | Level 1 | Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	3.6	3.2
Fair Value, Recurring | Level 1 | Money market mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	12.8	12.8
Fair Value, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0	0
Cash and securities segregated under federal and other regulation	0	0
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net	430.4	426.8
Receivables from clients - Derivatives	334.8	235.6
Financial instruments owned	2,602.8	2,464.5
Total assets at fair value	3,629.8	3,315.8
Payables to clients - Derivatives	258.2	176.4
Financial instruments sold, not yet purchased	807	607.3
Total liabilities at fair value	1,348	1,112.4
Fair Value, Recurring | Level 2 | TBA and forward settling securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payable to broker-dealers, clearing organizations and counterparties	47.5	22
Fair Value, Recurring | Level 2 | Derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payable to broker-dealers, clearing organizations and counterparties	235.3	306.7
Fair Value, Recurring | Level 2 | Payables to Broker-dealers, Clearing Organizations and Counterparties
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payable to broker-dealers, clearing organizations and counterparties	282.8	328.7
Fair Value, Recurring | Level 2 | Contingent Consideration
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accounts payable and other accrued liabilities - contingent liabilities	0	0
Fair Value, Recurring | Level 2 | Physical commodities inventory
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Physical commodities inventory	261.8	188.9
Fair Value, Recurring | Level 2 | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	14.3	9.4
Financial instruments sold, not yet purchased	3.8	14.9
Fair Value, Recurring | Level 2 | Corporate and municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	71.2	66.9
Financial instruments sold, not yet purchased	44.8	22.5
Fair Value, Recurring | Level 2 | U.S. Treasury obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0	0
Financial instruments sold, not yet purchased	0	0
Fair Value, Recurring | Level 2 | U.S. government agency obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	277.9	293.4
Financial instruments sold, not yet purchased	21.2	0.1
Fair Value, Recurring | Level 2 | Foreign government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0	0
Fair Value, Recurring | Level 2 | Agency mortgage-backed obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	1,552.2	1,384.6
Financial instruments sold, not yet purchased	2.4	5.1
Fair Value, Recurring | Level 2 | Asset-backed obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	46.6	33
Fair Value, Recurring | Level 2 | Derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	617.6	652.3
Financial instruments sold, not yet purchased	733.4	563.6
Fair Value, Recurring | Level 2 | Commodities leases
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	23	24.9
Financial instruments sold, not yet purchased	1.4	1.1
Fair Value, Recurring | Level 2 | Commodities warehouse receipts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0	0
Fair Value, Recurring | Level 2 | Exchange firm common stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0	0
Fair Value, Recurring | Level 2 | Mutual funds and other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0	0
Fair Value, Recurring | Level 2 | TBA and forward settling securities
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	54.9	31
Fair Value, Recurring | Level 2 | Foreign government obligations
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	0	0
Fair Value, Recurring | Level 2 | U.S. Treasury obligations
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	0	0
Fair Value, Recurring | Level 2 | Derivatives
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	375.5	395.8
Fair Value, Recurring | Level 2 | Commodities warehouse receipts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and securities segregated under federal and other regulation	0	0
Fair Value, Recurring | Level 2 | U.S. Treasury obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and securities segregated under federal and other regulation	0	0
Fair Value, Recurring | Level 2 | Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0	0
Fair Value, Recurring | Level 2 | Money market mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0	0
Fair Value, Recurring | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0	0
Cash and securities segregated under federal and other regulation	0	0
Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net	0	0
Receivables from clients - Derivatives
Financial instruments owned	0	0
Total assets at fair value	0	0
Payables to clients - Derivatives
Financial instruments sold, not yet purchased	0	0
Total liabilities at fair value	1.5	1.5
Fair Value, Recurring | Level 3 | TBA and forward settling securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payable to broker-dealers, clearing organizations and counterparties	0	0
Fair Value, Recurring | Level 3 | Derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payable to broker-dealers, clearing organizations and counterparties	0	0
Fair Value, Recurring | Level 3 | Payables to Broker-dealers, Clearing Organizations and Counterparties
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Payable to broker-dealers, clearing organizations and counterparties	0	0
Fair Value, Recurring | Level 3 | Contingent Consideration
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Accounts payable and other accrued liabilities - contingent liabilities	1.5	1.5
Fair Value, Recurring | Level 3 | Physical commodities inventory
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Physical commodities inventory	0	0
Fair Value, Recurring | Level 3 | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0	0
Financial instruments sold, not yet purchased	0	0
Fair Value, Recurring | Level 3 | Corporate and municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0	0
Financial instruments sold, not yet purchased	0	0
Fair Value, Recurring | Level 3 | U.S. Treasury obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0	0
Financial instruments sold, not yet purchased	0	0
Fair Value, Recurring | Level 3 | U.S. government agency obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0	0
Financial instruments sold, not yet purchased	0	0
Fair Value, Recurring | Level 3 | Foreign government obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0	0
Fair Value, Recurring | Level 3 | Agency mortgage-backed obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0	0
Financial instruments sold, not yet purchased	0	0
Fair Value, Recurring | Level 3 | Asset-backed obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0	0
Fair Value, Recurring | Level 3 | Derivatives
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0	0
Financial instruments sold, not yet purchased	0	0
Fair Value, Recurring | Level 3 | Commodities leases
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0	0
Financial instruments sold, not yet purchased	0	0
Fair Value, Recurring | Level 3 | Commodities warehouse receipts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0	0
Fair Value, Recurring | Level 3 | Exchange firm common stock
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0	0
Fair Value, Recurring | Level 3 | Mutual funds and other
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Financial instruments owned	0	0
Fair Value, Recurring | Level 3 | TBA and forward settling securities
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	0	0
Fair Value, Recurring | Level 3 | Foreign government obligations
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	0	0
Fair Value, Recurring | Level 3 | U.S. Treasury obligations
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	0	0
Fair Value, Recurring | Level 3 | Derivatives
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	0	0
Fair Value, Recurring | Level 3 | Commodities warehouse receipts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and securities segregated under federal and other regulation	0	0
Fair Value, Recurring | Level 3 | U.S. Treasury obligations
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and securities segregated under federal and other regulation	0	0
Fair Value, Recurring | Level 3 | Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	0	0
Fair Value, Recurring | Level 3 | Money market mutual funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets	$ 0	$ 0

Financial Instruments with Of_3

Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2021	Sep. 30, 2020
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Financial instruments sold, not yet purchased	$ 1,118.2	$ 686
Fair Value, Recurring | Derivatives
Security Owned and Sold, Not yet Purchased, at Fair Value [Line Items]
Financial instruments sold, not yet purchased	$ 389.9	$ 176.8

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) contract in Millions, $ in Millions	Mar. 31, 2021USD ($)contract	Sep. 30, 2020USD ($)contract
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset	$ 4,622	$ 3,264.4
Derivative liability, fair value, gross liability	4,606.5	3,069.5
Gross fair value of derivative contracts	(4,527.6)	(3,319)
Gross fair value of derivative contracts	$ (4,351.1)	$ (3,100.7)
Derivative, number of instruments held | contract	10.7	7.9
Deposits and Receivables from Exchange Clearing Organizations
Derivatives, Fair Value [Line Items]
Derivative, fair value, net	$ (107.4)	$ (173.5)
Receivable From Clients, Net
Derivatives, Fair Value [Line Items]
Derivative, fair value, net	1	1.5
Financial Instruments Owned
Derivatives, Fair Value [Line Items]
Derivative, fair value, net	200.8	117.4
Payables to Clients
Derivatives, Fair Value [Line Items]
Derivative, fair value, net	(178.2)	(222.7)
Payables to Broker-dealers, Clearing Organizations and Counterparties
Derivatives, Fair Value [Line Items]
Derivative, fair value, net	43.7	14.7
Financial Instrument Sold, Not Yet Purchased
Derivatives, Fair Value [Line Items]
Derivative, fair value, net	389.9	176.8
Exchange-traded commodity derivatives
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset	2,393.9	1,637.2
Derivative liability, fair value, gross liability	2,325	1,747.3
OTC commodity derivatives
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset	855.9	553.9
Derivative liability, fair value, gross liability	858.2	433.2
Exchange-traded foreign exchange derivatives
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset	411.4	9.3
Derivative liability, fair value, gross liability	475.6	13
OTC foreign exchange derivatives
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset	279.4	520.8
Derivative liability, fair value, gross liability	227.4	461.5
Exchange-traded interest rate derivatives
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset	351.4	271.1
Derivative liability, fair value, gross liability	479.9	200.7
OTC interest rate derivatives
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset	59	96
Derivative liability, fair value, gross liability	58	96.6
Exchange-traded equity index derivatives
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset	82.5	32.1
Derivative liability, fair value, gross liability	51.6	39.8
OTC equity and indices derivatives
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset	133.6	113
Derivative liability, fair value, gross liability	83.3	55.4
TBA and forward settling securities
Derivatives, Fair Value [Line Items]
Derivative asset, fair value, gross asset	54.9	31
Derivative liability, fair value, gross liability	$ 47.5	$ 22

Financial Instruments with Of_5

Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - TBAs and Forward Settling Securities (Details) - USD ($) $ in Millions	Mar. 31, 2021	Sep. 30, 2020
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative asset, fair value, gross asset	$ 4,622	$ 3,264.4
Derivative liability, fair value, gross liability	4,606.5	3,069.5
TBA Securities Purchased, Unrealized Gain | Deposits and Receivables from Broker-dealers, Clearing Organizations and Counterparties
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative asset, fair value, gross asset	0	10.8
Derivative asset, notional amount	0	5,389.3
TBA Securities Purchased, Unrealized Gain | Payables to Broker-dealers, Clearing Organizations and Counterparties
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative asset, fair value, gross asset	1.3	0
Derivative asset, notional amount	1,336	0
TBA Securities Purchased, Unrealized Loss | Deposits and Receivables from Broker-dealers, Clearing Organizations and Counterparties
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative asset, fair value, gross asset	0	(1.7)
Derivative asset, notional amount	0	2,647.7
TBA Securities Purchased, Unrealized Loss | Payables to Broker-dealers, Clearing Organizations and Counterparties
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative asset, fair value, gross asset	(45)	0
Derivative asset, notional amount	7,005	0
TBA Securities Sold, Unrealized Gain | Deposits and Receivables from Broker-dealers, Clearing Organizations and Counterparties
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative liability, fair value, gross liability	52.2	0
Derivative liability, notional amount	(8,409)	0
TBA Securities Sold, Unrealized Gain | Payables to Broker-dealers, Clearing Organizations and Counterparties
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative liability, fair value, gross liability	0	2.8
Derivative liability, notional amount	0	(2,978.7)
TBA Securities Sold, Unrealized Loss | Deposits and Receivables from Broker-dealers, Clearing Organizations and Counterparties
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative liability, fair value, gross liability	(1.5)	0
Derivative liability, notional amount	(1,688)	0
TBA Securities Sold, Unrealized Loss | Payables to Broker-dealers, Clearing Organizations and Counterparties
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative liability, fair value, gross liability	0	(13)
Derivative liability, notional amount	0	(6,549.4)
Forward Settling Securities Sold, Unrealized Gain | Deposits and Receivables from Broker-dealers, Clearing Organizations and Counterparties
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative liability, fair value, gross liability	1.4	17.4
Derivative liability, notional amount	(2,032)	(1,946)
Forward Settling Securities Purchased, Unrealized Loss | Deposits and Receivables from Broker-dealers, Clearing Organizations and Counterparties
Derivative Instruments and Hedging Activities Disclosure [Line Items]
Derivative asset, fair value, gross asset	(1)	(7.3)
Derivative asset, notional amount	$ 2,866	$ 2,447.1

Financial Instruments with Of_6

Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - Realized Gains/Losses on Derivative Contracts (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Commodities
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments, gain (loss) recognized in income, net	$ 59	$ 61.6	$ 63.2	$ 79.8
Foreign exchange
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments, gain (loss) recognized in income, net	25.5	5.1	61.5	7.3
Interest rate, equities, and indices
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments, gain (loss) recognized in income, net	30.6	0	43.2	(0.4)
TBA and forward settling securities
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments, gain (loss) recognized in income, net	8.6	(34.4)	0.1	(35.3)
Derivatives
Derivative Instruments, Gain (Loss) [Line Items]
Derivative instruments, gain (loss) recognized in income, net	$ 123.7	$ 32.3	$ 168	$ 51.4

Allowance for Doubtful Accoun_3

Allowance for Doubtful Accounts - Narrative (Details) - USD ($)	Mar. 31, 2021	Sep. 30, 2020
Receivables [Abstract]
Allowance for doubtful accounts - deposits with and receivables from broker-dealers, clearings organizations, and counterparties	$ 1,300,000	$ 1,300,000
Allowance for doubtful accounts receivable	33,600,000	25,800,000
Allowance for doubtful accounts related to notes receivable	$ 0	$ 0

Allowance for Doubtful Accoun_4

Allowance for Doubtful Accounts - Allowance for Bad Debts (Details) $ in Millions	6 Months Ended
	Mar. 31, 2021USD ($)
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance as of September 30, 2020	$ 27.1
Provision for bad debts	2.4
Allowance charge-offs	(2.8)
Balance as of March 31, 2021	34.9
Cumulative Effect, Period of Adoption, Adjustment
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance as of September 30, 2020	8.2
Cumulative Effect, Period of Adoption, Adjusted Balance
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance as of September 30, 2020	$ 35.3

Physical Commodities Inventor_2

Physical Commodities Inventory - Physical Commodities Inventory (Details) - USD ($) $ in Millions	Mar. 31, 2021	Sep. 30, 2020
Inventory [Line Items]
Physical Ag & Energy	$ 261.8	$ 201.5
Precious metals - held by broker-dealer subsidiary	355.2	215.7
Physical commodities inventory, net	450.8	281.1
Physical Commodities Inventory - Precious Metals
Inventory [Line Items]
Precious metals - held by broker-dealer subsidiary	93.4	14.2
Precious metals - held by non-broker-dealer subsidiaries	$ 95.6	$ 65.4

Physical Commodities Inventor_3

Physical Commodities Inventory - Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2021	Sep. 30, 2020
Physical Precious Metals Trading
Inventory [Line Items]
Inventory adjustments	$ 1.7	$ 0.7

Goodwill - Goodwill by Segment

Goodwill - Goodwill by Segment (Details) - USD ($) $ in Millions	Mar. 31, 2021	Sep. 30, 2020
Goodwill [Line Items]
Goodwill	$ 54.5	$ 54.7
Commercial
Goodwill [Line Items]
Goodwill	32.7	32.7
Institutional
Goodwill [Line Items]
Goodwill	9.8	9.8
Retail
Goodwill [Line Items]
Goodwill	2.2	2.2
Global Payments
Goodwill [Line Items]
Goodwill	$ 9.8	$ 10

Intangible Assets - Gross and N

Intangible Assets - Gross and Net Intangible Assets by Major Class (Details) - USD ($) $ in Millions	Mar. 31, 2021	Sep. 30, 2020
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets, gross amount	$ 70.9	$ 70.9
Finite-lived intangible assets, accumulated amortization	(28.8)	(21.4)
Total intangible assets subject to amortization	42.1	49.5
Indefinite-lived intangible assets	5.9	5.3
Intangible assets, gross amount	76.8	76.2
Total intangible assets, net amount	48	54.8
Website domains
Acquired Finite-Lived Intangible Assets [Line Items]
Indefinite-lived license agreements	2.1	2.1
Business licenses
Acquired Finite-Lived Intangible Assets [Line Items]
Indefinite-lived intangible assets	3.8	3.2
Trade/domain names
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived trade/domain names, gross amount	3.7	3.7
Finite-lived intangible assets, accumulated amortization	(0.5)	(0.2)
Total intangible assets subject to amortization	3.2	3.5
Software programs/platforms
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived software programs/platforms, gross amount	29	29
Finite-lived intangible assets, accumulated amortization	(9.1)	(4.9)
Total intangible assets subject to amortization	19.9	24.1
Customer base
Acquired Finite-Lived Intangible Assets [Line Items]
Finite-lived customer base, gross amount	38.2	38.2
Finite-lived intangible assets, accumulated amortization	(19.2)	(16.3)
Total intangible assets subject to amortization	$ 19	$ 21.9

Intangible Assets - Narrative (

Intangible Assets - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
Amortization of intangible assets	$ 3.7	$ 1.1	$ 7.5	$ 1.9

Intangible Assets - Finite-Live

Intangible Assets - Finite-Lived Intangible Assets Future Amortization Expense (Details) - USD ($) $ in Millions	Mar. 31, 2021	Sep. 30, 2020
Finite-Lived Intangible Assets, Amortization Expense, Maturity Schedule [Abstract]
Fiscal 2021 (remaining six months)	$ 7.6
Fiscal 2022	13.9
Fiscal 2023	12.2
Fiscal 2024	4.7
Fiscal 2025 and thereafter	3.7
Total intangible assets subject to amortization	$ 42.1	$ 49.5

Credit Facilities - Number of C

Credit Facilities - Number of Credit Facilities (Details)	6 Months Ended
	Mar. 31, 2021USD ($)facility	Dec. 31, 2020USD ($)	Sep. 30, 2020USD ($)	Mar. 31, 2020USD ($)
Line of Credit Facility [Line Items]
Number of credit facilities | facility	4
Maximum borrowing capacity under credit facilities	$ 771,700,000
Debt instrument, face amount	$ 196,500,000
Term loan periodic principal payment percentage	1.25%
Term loan periodic payment	$ 4,900,000
Notes payable to bank	8,900,000	$ 9,000,000	$ 0
Debt, weighted average interest rate		2.35%
Lenders under loans	314,900,000		268,100,000
StoneX Inc. Bank of America Syndicated Credit Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity under credit facilities	371,700,000
Line of credit facility borrowing	196,500,000
Long-term debt	201,900,000		202,500,000
StoneX Financial Inc.
Line of Credit Facility [Line Items]
Line of credit facility borrowing	75,000,000
Line of credit facility	0		0
FCStone Merchants Services, LLC
Line of Credit Facility [Line Items]
Line of credit facility borrowing	300,000,000
Line of credit facility	254,000,000		200,100,000
StoneX Financial Ltd.
Line of Credit Facility [Line Items]
Line of credit facility borrowing	25,000,000
Line of credit facility	0		25,000,000
StoneX Financial Inc. Uncommitted Commodities Delivery Line
Line of Credit Facility [Line Items]
Line of credit facility borrowing	25,000,000			$ 75,000,000
Long-term debt	0		0
INTL FCStone Ltd
Line of Credit Facility [Line Items]
Line of credit facility borrowing				$ 100,000,000
Lenders under loans	$ 0		$ 0

Credit Facilities - Senior Secu

Credit Facilities - Senior Secured Notes (Details) - USD ($)	Mar. 31, 2021	Jun. 11, 2020
Debt Disclosure [Abstract]
Debt instrument, face amount		$ 350,000,000
Debt instrument offering price, percentage	8.625%	98.50%
Debt issuance costs, gross	$ 9,500,000

Credit Facilities - Credit Faci

Credit Facilities - Credit Facilities and Financing Bridge Commitment (Details) - USD ($)	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020
Line of Credit Facility [Line Items]
Maximum borrowing capacity under credit facilities	$ 771,700,000
Loans payable	512,000,000		$ 515,500,000
Amount outstanding	455,900,000		427,600,000
Notes payable to bank	8,900,000	$ 9,000,000	0
Senior secured notes	337,100,000		336,000,000
Lenders under loans	826,900,000		783,600,000
StoneX Inc. Bank of America Syndicated Credit Facility
Line of Credit Facility [Line Items]
Long-term debt, gross	175,200,000
Line of credit facility borrowing	196,500,000
Maximum borrowing capacity under credit facilities	371,700,000
Loans payable	174,900,000		179,500,000
Long-term line of credit, noncurrent	27,000,000		23,000,000
Long-term debt	201,900,000		202,500,000
StoneX Financial Inc.
Line of Credit Facility [Line Items]
Line of credit facility borrowing	75,000,000
Line of credit facility	0		0
FCStone Merchants Services, LLC
Line of Credit Facility [Line Items]
Line of credit facility borrowing	300,000,000
Line of credit facility	254,000,000		200,100,000
StoneX Financial Ltd.
Line of Credit Facility [Line Items]
Line of credit facility borrowing	25,000,000
Line of credit facility	0		25,000,000
IFFI Uncommitted Lines of Credit
Line of Credit Facility [Line Items]
Short-term debt	0		0
Rabobank Uncommited Line of Credit
Line of Credit Facility [Line Items]
Short-term debt	25,000,000		$ 20,000,000
HCO Syndicated line of Credit Facility
Line of Credit Facility [Line Items]
Debt instrument, unamortized discount (premium) and debt issuance costs, net	300,000
Senior Notes
Line of Credit Facility [Line Items]
Debt instrument, unamortized discount (premium) and debt issuance costs, net	$ 12,800,000

Securities and Commodity Fina_3

Securities and Commodity Financing Transactions - Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2021	Sep. 30, 2020
Assets Sold under Agreements to Repurchase [Line Items]
Financial instruments owned and pledged as collateral, amount eligible to be repledged by counterparty	$ 564.7	$ 468.6
Pledged assets separately reported, securities Pledged for repurchase agreements, at fair value	1,818.8	1,484.7
Securities loaned, fair value of collateral	1,698.9	1,410.3
Fair value of securities received as collateral that can be resold or repledged	4,110	3,303.1
Fair value of securities received as collateral that have been resold or repledged	339.5	285.7
Tri-party Repurchase Agreements
Assets Sold under Agreements to Repurchase [Line Items]
Financial instruments owned and pledged as collateral, amount not eligible to be repledged by counterparty	$ 1,327.2	$ 1,266.4

Securities and Commodity Fina_4

Securities and Commodity Financing Transactions - Collateral Maturities of Gross Obligations (Details) - USD ($) $ in Millions	Mar. 31, 2021	Sep. 30, 2020
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	$ 3,767.2	$ 3,155.5
Securities loaned	1,747.2	1,441.9
Gross amount of secured financing	5,514.4	4,597.4
Overnight and Open
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	2,110.2	1,736.3
Securities loaned	1,747.2	1,441.9
Gross amount of secured financing	3,857.4	3,178.2
Less than 30 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	1,119.1	1,069.2
Securities loaned	0	0
Gross amount of secured financing	1,119.1	1,069.2
30-90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	398.9	325
Securities loaned	0	0
Gross amount of secured financing	398.9	325
Over 90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	139	25
Securities loaned	0	0
Gross amount of secured financing	$ 139	$ 25

Securities and Commodity Fina_5

Securities and Commodity Financing Transactions - Underlying Collateral Types of Gross Obligations (Details) - USD ($) $ in Millions	Mar. 31, 2021	Sep. 30, 2020
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	$ 3,767.2	$ 3,155.5
Securities loaned	1,747.2	1,441.9
Gross amount of secured financing	5,514.4	4,597.4
U.S. Treasury obligations
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	1,065	815.8
U.S. government agency obligations
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	199.8	279.5
Asset-backed obligations
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	37.8	18
Agency mortgage-backed obligations
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	2,317.6	1,990
Corporate bonds
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	147	52.2
Equity securities
Assets Sold under Agreements to Repurchase [Line Items]
Securities loaned	$ 1,747.2	$ 1,441.9

Securities and Commodity Fina_6

Securities and Commodity Financing Transactions - Netting of Securities Purchased Under Agreements (Details) - USD ($) $ in Millions	Mar. 31, 2021	Sep. 30, 2020
Brokers and Dealers [Abstract]
Securities purchased under agreements to resell, gross	$ 2,297.2	$ 1,696.2
Securities purchased under agreements to resell, offset	0	0
Securities purchased under agreements to resell, net	2,297.2	1,696.2
Securities borrowed, gross	1,735.3	1,440
Securities borrowed, net	1,735.3	1,440
Securities sold under agreements to repurchase, gross	3,767.2	3,155.5
Securities sold under agreements to repurchase, offset	0	0
Securities sold under agreements to repurchase, net	3,767.2	3,155.5
Securities loaned, gross	1,747.2	1,441.9
Securities loaned, net	$ 1,747.2	$ 1,441.9

Commitments and Contingencies (

Commitments and Contingencies (Details) $ in Millions	Nov. 16, 2018account	Mar. 31, 2021USD ($)	Oct. 01, 2020USD ($)
Loss Contingencies [Line Items]
Loss contingency, range of possible loss, portion not accrued		$ 28.9
Maximum amount of individual accounts receivable account		1.4
Self insurance reserve		$ 1.2
Cumulative Effect, Period of Adoption, Adjustment
Loss Contingencies [Line Items]
Retained earnings, before tax			$ 8.2
StoneX Financial
Loss Contingencies [Line Items]
Number of accounts | account	300

Accumulated Other Comprehensi_3

Accumulated Other Comprehensive Loss, Net (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 799.5	$ 614.9	$ 767.5	$ 594.2
Other comprehensive income	(1.6)	(3.4)	12.3	(2.7)
Ending balance	860.2	648.6	860.2	648.6
Foreign Currency Translation Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			(36)
Other comprehensive income			12.3
Ending balance	(23.7)		(23.7)
Pension Benefits Adjustment
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance			(4.1)
Other comprehensive income			0
Ending balance	(4.1)		(4.1)
Accumulated Other Comprehensive Loss, net
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(26.2)	(34.8)	(40.1)	(34.8)
Other comprehensive income	(1.6)	(3.4)	12.3	(2.7)
Ending balance	$ (27.8)	$ (38.2)	$ (27.8)	$ (38.2)

Revenue from Contracts with C_3

Revenue from Contracts with Clients - Narrative (Details)	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Revenues from Contracts With Clients [Abstract]
Total revenues (percentage)	1.40%	0.70%	1.40%	0.80%
Operating revenues (percentage)	32.20%	37.90%	34.60%	38.50%

Revenue from Contracts with C_4

Revenue from Contracts with Clients - Revenue from Contracts with Clients (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	$ 151.9	$ 139.2	$ 294.3	$ 247.7
Principal gains, net	265.2	168.5	468.6	281
Interest income	23.4	41.7	44.6	87.7
Total revenues	11,244.8	20,366.3	20,495.3	31,611.3
United States
Disaggregation of Revenue [Line Items]
Total revenues	853.6	585.6	1,612.5	1,097.9
Europe
Disaggregation of Revenue [Line Items]
Total revenues	490.1	150	662.5	261.6
South America
Disaggregation of Revenue [Line Items]
Total revenues	14.5	16.3	29.1	31.5
Middle East and Asia
Disaggregation of Revenue [Line Items]
Total revenues	9,885.1	19,613.3	18,187.1	30,218.8
Other
Disaggregation of Revenue [Line Items]
Total revenues	1.5	1.1	4.1	1.5
Point-in-time
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	127.4	113.7	247.1	198.3
Time elapsed
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	24.5	25.5	47.2	49.4
Exchange-traded futures and options
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	49.4	40.1	95.7	72.5
OTC derivative brokerage
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	4.6	6.7	8.4	12.2
Equities and fixed income
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	19.4	7.1	33.8	11.4
Mutual funds
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	1.5	1.6	2.7	2.9
Insurance and annuity products
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	2.3	2.4	4.6	4.5
Other
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0.1	0.5	0.3	0.8
Sales-based commission
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	77.3	58.4	145.5	104.3
Mutual funds
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	3.6	3.5	6.9	6.6
Insurance and annuity products
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	4.2	4	8.1	7.7
Trailing commissions
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	7.8	7.5	15	14.3
Clearing fees
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	39.4	41.6	77.9	71.1
Trade conversion fees
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	3.6	4.2	5.7	5.7
Other
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	1.7	4.9	5.1	8.4
Commission and clearing fees
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	129.8	116.6	249.2	203.8
Underwriting fees
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0.2	0.2	0.4	0.4
Asset management fees
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	9.3	8.7	18	16.2
Advisory and consulting fees
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	6.6	5.7	12.6	11.3
Sweep program fees
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	0.8	3.6	1.6	7.6
Client account fees
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	3.8	3.1	7.9	6.1
Other
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	1.4	1.3	4.6	2.3
Consulting, management, and account fees
Disaggregation of Revenue [Line Items]
Revenue from contract with customer	22.1	22.6	45.1	43.9
Physical precious metals trading
Disaggregation of Revenue [Line Items]
Sales of physical commodities	10,295.7	19,694.7	18,704.6	30,352.7
Physical agricultural and energy product trading
Disaggregation of Revenue [Line Items]
Sales of physical commodities	$ 508.6	$ 322.2	$ 983.2	$ 642.2

Other Expenses - Other Expenses

Other Expenses - Other Expenses Breakout (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Other Expenses [Abstract]
Insurance	$ 1.9	$ 1	$ 3.7	$ 2
Office supplies and printing	0.4	0.5	0.7	0.9
Other clearing related expenses	1	0.6	2	1.4
Other non-income taxes	3.5	1.3	7.3	2.6
Contingent consideration, net	0.8	0.1	0.9	0.1
Other	4.5	2.9	8.6	5.5
Total other expenses	$ 12.1	$ 6.4	$ 23.2	$ 12.5

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Income Tax Disclosure [Abstract]
Income tax expense	$ 21	$ 16.8	$ 28.4	$ 22.2
Effective income tax rate	28.00%	30.00%

Capital and Other Regulatory _3

Capital and Other Regulatory Requirements - Regulatory Capital Requirements (Details) $ in Millions	Mar. 31, 2021USD ($)
Capital and Other Regulatory Requirements [Abstract]
Adjusted net capital	$ 5
StoneX Financial Inc.
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Actual	288.4
Minimum Requirement	163.6
StoneX Financial Ltd.
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Actual	375.8
Minimum Requirement	222.4
Gain Capital Group, LLC
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Actual	69.7
Minimum Requirement	31.6
Gain Capital U.K., Ltd.
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Actual	106.6
Minimum Requirement	$ 31.5

Segment Analysis - Narrative (D

Segment Analysis - Narrative (Details)	6 Months Ended
	Mar. 31, 2021employeemarketcountrycurrency
Segment Reporting Information [Line Items]
Number of employees (more than) | employee	3,000
Number of countries in which entity operates (more than)	180
Retail Segment
Segment Reporting Information [Line Items]
Number of countries in which entity operates (more than)	130
Number of global financial markets (over) | market	15,000
Global Payments
Segment Reporting Information [Line Items]
Number of countries in which entity operates (more than)	170
Number of different types of foreign currencies (more than) | currency	140

Segment Analysis - Segment Repo

Segment Analysis - Segment Reporting (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Sep. 30, 2020
Segment Reporting Information [Line Items]
Revenues	$ 11,244.8	$ 20,366.3	$ 20,495.3	$ 31,611.3
Operating revenues	471.4	366.8	851.5	643.6
Net operating revenues	334.2	243.4	590.3	413.9
Net contribution	248.3	174.9	446.9	300.7
Segment income	159	117.3	274.2	193.1
Net costs not allocated to operating segments	(82.7)	(61.2)	(171)	(115.4)
Other gain	0	0	0	0.1
Income before tax	76.3	56.1	103.2	77.8
Assets	15,799.7		15,799.7		$ 13,474.9
Corporate, Non-Segment
Segment Reporting Information [Line Items]
Revenues	4.2	4	0.7	9.2
Operating revenues	4.2	4	0.7	9.2
Net operating revenues	(10.2)	(3.5)	(26.8)	(6.2)
Assets	699.7		699.7		418.7
Eliminations
Segment Reporting Information [Line Items]
Revenues	(4.4)	(6.7)	(8)	(13.3)
Operating revenues	(4.4)	(6.7)	(8)	(13.3)
Commercial
Segment Reporting Information [Line Items]
Net contribution	81.8	70.4	138.6	121.9
Segment income	55.6	41.7	87.7	70.4
Commercial | Operating Segments
Segment Reporting Information [Line Items]
Revenues	10,516.4	20,037.4	19,381.9	31,043.7
Operating revenues	144.3	126.2	249.9	219.4
Net operating revenues	118.2	104.3	200.8	178
Assets	3,438.7		3,438.7		2,753.6
Institutional
Segment Reporting Information [Line Items]
Net contribution	75.3	72.5	142.4	118.5
Segment income	52	51.4	96.8	76.7
Institutional | Operating Segments
Segment Reporting Information [Line Items]
Revenues	191.6	185.7	357.1	318.1
Operating revenues	191.6	185.7	357.1	318.1
Net operating revenues	123.8	104.9	229.1	169.7
Assets	9,912.8		9,912.8		8,740.8
Retail
Segment Reporting Information [Line Items]
Net contribution	65.5	9.4	114.1	13.9
Segment income	32	7	49.9	9.9
Retail | Operating Segments
Segment Reporting Information [Line Items]
Revenues	503.5	116.5	695.7	192.8
Operating revenues	102.2	28.2	183.9	49.4
Net operating revenues	70.7	9.7	122.8	14.6
Assets	1,382.3		1,382.3		1,245.9
Global Payments
Segment Reporting Information [Line Items]
Net contribution	25.7	22.6	51.8	46.4
Segment income	19.4	17.2	39.8	36.1
Global Payments | Operating Segments
Segment Reporting Information [Line Items]
Revenues	33.5	29.4	67.9	60.8
Operating revenues	33.5	29.4	67.9	60.8
Net operating revenues	31.7	$ 28	64.4	$ 57.8
Assets	$ 366.2		$ 366.2		$ 315.9

Uncategorized Items - intl-2021

Label	Element	Value
Cash Segregated under Commodity Exchange Act Regulation	us-gaap_CashSegregatedUnderCommodityExchangeActRegulation	$ 2,000,300,000	[1]
Cash Segregated under Commodity Exchange Act Regulation	us-gaap_CashSegregatedUnderCommodityExchangeActRegulation	1,168,000,000	[1]
Securities Segregated under Other Regulations	us-gaap_SecuritiesSegregatedUnderOtherRegulations	100,000,000	[2]
Securities Segregated under Other Regulations	us-gaap_SecuritiesSegregatedUnderOtherRegulations	106,200,000	[2]
Non-cash equivalent segregated assets	intl_Noncashequivalentsegregatedassets	8,100,000
Non-cash equivalent segregated assets	intl_Noncashequivalentsegregatedassets	102,600,000
Cash Segregated And Deposited With Or Pledged To Exchange-clearing Organizations And Other Futures Commission Merchants	intl_CashSegregatedAndDepositedWithOrPledgedToExchangeClearingOrganizationsAndOtherFuturesCommissionMerchants	1,896,700,000	[2]
Cash Segregated And Deposited With Or Pledged To Exchange-clearing Organizations And Other Futures Commission Merchants	intl_CashSegregatedAndDepositedWithOrPledgedToExchangeClearingOrganizationsAndOtherFuturesCommissionMerchants	$ 2,050,300,000	[2]
Accounting Standards Update [Extensible List]	us-gaap_AccountingStandardsUpdateExtensibleList	us-gaap:AccountingStandardsUpdate201802Member
Non-segregated cash and other non-cash equivalent assets included within deposits and receivables from broker-dealers, clearing organizations, and counterparties	intl_Nonsegregatedcashandothernoncashequivalentassetsincludedwithindepositsandreceivablesfrombrokerdealersclearingorganizationsandcounterparties	$ 1,356,600,000
Non-segregated cash and other non-cash equivalent assets included within deposits and receivables from broker-dealers, clearing organizations, and counterparties	intl_Nonsegregatedcashandothernoncashequivalentassetsincludedwithindepositsandreceivablesfrombrokerdealersclearingorganizationsandcounterparties	$ 2,210,900,000
[1]	(1) Represents segregated client cash and United States (“U.S.”) Treasury obligations held at third-party banks. Excludes segregated commodity warehouse receipts, segregated U.S. Treasury obligations with original or acquired maturities of greater than 90 days, and other assets of $102.6 million and $8.1 million as of March 31, 2021 and 2020, respectively, included within ‘Cash, securities and other assets segregated under federal and other regulations’ on the condensed consolidated balance sheets.
[2]	(2) Represents segregated client cash and U.S. Treasury obligations on deposit with, or pledged to, exchange clearing organizations and other FCMs. Excludes non-segregated cash, segregated U.S. Treasury obligations pledged to exchange-clearing organizations with original or acquired maturities greater than 90 days, and other assets of $2,210.9 million and $1,356.6 million as of March 31, 2021 and 2020, respectively, included within ‘Deposits with and receivables from broker-dealers, clearing organizations, and counterparties, net’ on the condensed consolidated balance sheets.