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	3 Months Ended	12 Months Ended
Dec. 31, 2023	Sep. 30, 2023
Derivatives, Fair Value [Line Items]
Asset Derivatives	$ 7,386.6	$ 8,200.3
Liability Derivatives	7,227.7	8,017.3
Designated as Hedging Instrument
Derivatives, Fair Value [Line Items]
Asset Derivatives	10.2	1.7
Derivative assets expected to be released from Accumulated other comprehensive income into current earnings:	7.5	1.4
Liability Derivatives	8.0	27.1
Derivative liabilities expected to be released from Accumulated other comprehensive income into current earnings:	8.0	21.3
Designated as Hedging Instrument \| Foreign currency forward contracts
Derivatives, Fair Value [Line Items]
Asset Derivatives	10.2	1.7
Derivative assets expected to be released from Accumulated other comprehensive income into current earnings:	7.5	1.4
Liability Derivatives	0.0	2.5
Derivative liabilities expected to be released from Accumulated other comprehensive income into current earnings:	0.0	1.0
Designated as Hedging Instrument \| Interest rate contracts
Derivatives, Fair Value [Line Items]
Asset Derivatives	0.0	0.0
Liability Derivatives	8.0	24.6
Derivative liabilities expected to be released from Accumulated other comprehensive income into current earnings:	$ 8.0	$ 20.3

Derivative Assets, Hedge Gain (Loss) to be Reclassified within 12 Months

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- Definition

Derivative Liabilities, Hedge Gain (Loss) to be Reclassified within 12 Months

+ References

No definition available.

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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/exampleRef
-Topic 210
-SubTopic 20
-Name Accounting Standards Codification
-Section 55
-Paragraph 22
-Publisher FASB
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-Topic 210
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-Section 50
-Paragraph 3
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-Name Accounting Standards Codification
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-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481326/860-20-50-4D

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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.

+ References

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

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