Basis of Presentation and Consolidation and Accounting Standards Adopted (Policies)	6 Months Ended
Mar. 31, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	The accompanying unaudited Condensed Consolidated Balance Sheet as of September 30, 2021, which has been derived from the audited consolidated balance sheet of September 30, 2021, 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 included disclosures clearly and fairly present the information within. In management’s opinion, all adjustments, generally consisting of normal accruals, considered necessary to fairly present 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 relevant full year. These 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, 2021, 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, revenue recognition, valuation of inventories, and income taxes. These estimates are based on management’s best knowledge of current events and actions the Company may undertake in the future. The Company reviews all significant estimates affecting the financial statements on a recurring basis and records the effect of any necessary adjustments prior to financial statement issuance. 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, 2022 and through the date of this Form 10-Q.
Selling and marketing expenses	Selling and marketing expenses The Company generally expenses Selling and marketing costs as incurred. The Company’s policy includes expensing commercial media development costs as incurred, rather than deferring them until the related commercial airs. The Company expenses air time, such as television air-time, as used.
Derivative instruments and hedging activities	Derivative instruments and hedging activities The Company executes interest rate swaps to lessen uncertainty over interest rates and improve its interest revenue generation. The Company recognizes all derivative instruments as either assets or liabilities at fair value. All of the Company’s derivative positions that qualify for hedge accounting are cash flow hedges, for which changes in fair value generally flow through Accumulated other comprehensive income, except for the portion of a trade that is settled or the portion of the cash flow hedge that is deemed to be ineffective. All of the Company’s cash flow hedges have been deemed effective as of March 31, 2022 for both accounting and tax purposes. The Company maintains formal documentation through a periodic memo and accounting analysis that cover what is being hedged, how it is being hedged, hedge effectiveness, the nature of the risk being hedged, among other required analyses.
Accounting Standards Adopted	Accounting Standards Adopted In December 2019, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. This ASU removed certain exceptions for recognizing deferred taxes for investments, performing intraperiod allocation and calculating income taxes in interim periods. The ASU also adds guidance to reduce complexity in certain areas, including recognizing deferred taxes for tax goodwill and allocating taxes to members of a consolidated group. We adopted this standard as of October 1, 2021 on either a prospective basis or through a modified retrospective approach, as required by the standard. There was no cumulative effect adjustment recorded to retained earnings. The effects of this standard on the Company’s consolidated financial position, results of operations and cash flows are not material. In June 2016, the Financial Accounting Standards Board (“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 replaced the previous incurred loss impairment guidance and introduced 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 note 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. Current Expected Credit Losses 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. Additionally, for collateralized transactions, the Company elects to measure expected credit losses using the fair value of collateral received where the borrower is required to, and reasonably expected to, replenish the amount of collateral securing the receivable as a result of changes in the fair value of such collateral.
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 comprises 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.

Basis of Presentation and Consolidation and Accounting Standards Adopted (Policies)

6 Months Ended

Mar. 31, 2022

Organization, Consolidation and Presentation of Financial Statements [Abstract]

The accompanying unaudited Condensed Consolidated Balance Sheet as of September 30, 2021, which has been derived from the audited consolidated balance sheet of September 30, 2021, 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 included disclosures clearly and fairly present the information within. In management’s opinion, all adjustments, generally consisting of normal accruals, considered necessary to fairly present 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 relevant full year. These 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, 2021, 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, revenue recognition, valuation of inventories, and income taxes. These estimates are based on management’s best knowledge of current events and actions the Company may undertake in the future. The Company reviews all significant estimates affecting the financial statements on a recurring basis and records the effect of any necessary adjustments prior to financial statement issuance. 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, 2022 and through the date of this Form 10-Q.

Selling and marketing expenses

The Company generally expenses Selling and marketing costs as incurred. The Company’s policy includes expensing commercial media development costs as incurred, rather than deferring them until the related commercial airs. The Company expenses air time, such as television air-time, as used.

Derivative instruments and hedging activities

The Company executes interest rate swaps to lessen uncertainty over interest rates and improve its interest revenue generation. The Company recognizes all derivative instruments as either assets or liabilities at fair value. All of the Company’s derivative positions that qualify for hedge accounting are cash flow hedges, for which changes in fair value generally flow through Accumulated other comprehensive income, except for the portion of a trade that is settled or the portion of the cash flow hedge that is deemed to be ineffective. All of the Company’s cash flow hedges have been deemed effective as of March 31, 2022 for both accounting and tax purposes. The Company maintains formal documentation through a periodic memo and accounting analysis that cover what is being hedged, how it is being hedged, hedge effectiveness, the nature of the risk being hedged, among other required analyses.

Accounting Standards Adopted

In December 2019, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. This ASU removed certain exceptions for recognizing deferred taxes for investments, performing intraperiod allocation and calculating income taxes in interim periods. The ASU also adds guidance to reduce complexity in certain areas, including recognizing deferred taxes for tax goodwill and allocating taxes to members of a consolidated group. We adopted this standard as of October 1, 2021 on either a prospective basis or through a modified retrospective approach, as required by the standard. There was no cumulative effect adjustment recorded to retained earnings. The effects of this standard on the Company’s consolidated financial position, results of operations and cash flows are not material.

In June 2016, the Financial Accounting Standards Board (“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 replaced the previous incurred loss impairment guidance and introduced 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 note 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.

Current Expected Credit Losses

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. Additionally, for collateralized transactions, the Company elects to measure expected credit losses using the fair value of collateral received where the borrower is required to, and reasonably expected to, replenish the amount of collateral securing the receivable as a result of changes in the fair value of such collateral.

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 comprises 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.