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Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - Schedule of Fair Values of Derivative Instruments Designated for Hedging Held (Details) - USD ($) $ in Millions | 9 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2025 | Sep. 30, 2024
Derivatives, Fair Value [Line Items] |  |
Asset Derivatives | $ 6,732.4 | $ 7,235.9
Liability Derivatives | 6,629.6 | 7,144.1
Designated as Hedging Instrument |  |
Derivatives, Fair Value [Line Items] |  |
Asset Derivatives | 17.3 | 9.6
Derivative assets expected to be released from Other comprehensive income into current earnings: | 15.6 | 9.2
Liability Derivatives | 0.0 | 0.2
Derivative liabilities expected to be released from Other comprehensive income into current earnings: | 0.0 | 0.2
Designated as Hedging Instrument | Foreign currency forward contracts |  |
Derivatives, Fair Value [Line Items] |  |
Asset Derivatives | 17.3 | 9.6
Derivative assets expected to be released from Other comprehensive income into current earnings: | 15.6 | 9.2
Liability Derivatives | 0.0 | 0.0
Designated as Hedging Instrument | Interest rate contracts |  |
Derivatives, Fair Value [Line Items] |  |
Asset Derivatives | 0.0 | 0.0
Liability Derivatives | 0.0 | 0.2
Derivative liabilities expected to be released from Other comprehensive income into current earnings: | $ 0.0 | $ 0.2

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- Definition Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets elected not to be offset. Excludes assets not subject to a master netting arrangement. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 815 -SubTopic 10 -Name Accounting Standards Codification -Section 50 -Paragraph 7A -Publisher FASB -URI https://asc.fasb.org/1943274/2147480434/815-10-50-7A Reference 2: http://www.xbrl.org/2003/role/exampleRef -Topic 210 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 22 -Publisher FASB -URI https://asc.fasb.org/1943274/2147483444/210-20-55-22 Reference 3: http://www.xbrl.org/2003/role/exampleRef -Topic 210 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 21 -Publisher FASB -URI https://asc.fasb.org/1943274/2147483444/210-20-55-21 Reference 4: http://www.xbrl.org/2003/role/exampleRef -Topic 210 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 20 -Publisher FASB -URI https://asc.fasb.org/1943274/2147483444/210-20-55-20 Reference 5: http://www.xbrl.org/2003/role/exampleRef -Topic 210 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 15 -Publisher FASB -URI https://asc.fasb.org/1943274/2147483444/210-20-55-15 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Topic 210 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 3 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147483466/210-20-50-3 Reference 7: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 4D -Subparagraph (c)(2) -SubTopic 20 -Topic 860 -Publisher FASB -URI https://asc.fasb.org/1943274/2147481326/860-20-50-4D + Details
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