Financial Instruments with Off-Balance Sheet Risk and Concentrations of Credit Risk - Fair Values of Derivative Instruments Designated for Hedging Held (Details) - USD ($) $ in Millions	Dec. 31, 2022	Sep. 30, 2022
Derivatives, Fair Value [Line Items]
Asset Derivatives	$ 7,120.1	$ 9,657.2
Liability Derivatives	6,984.7	9,552.4
Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset Derivatives	1.6	0.0
Liability Derivatives	54.5	70.6
Designated as Hedging Instrument \| Interest rate contracts
Derivatives, Fair Value [Line Items]
Asset Derivatives	0.3	0.0
Liability Derivatives	50.9	48.8
Designated as Hedging Instrument \| Foreign currency forward contracts
Derivatives, Fair Value [Line Items]
Asset Derivatives	1.3	0.0
Liability Derivatives	$ 3.6	$ 21.8

Fair value, before effects of master netting arrangements, of a financial liability or 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 liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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-Publisher FASB
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 5: http://www.xbrl.org/2003/role/exampleRef
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-URI https://asc.fasb.org/extlink&oid=99393222&loc=SL20226052-175313

Name:	us-gaap_DerivativeFairValueOfDerivativeLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant