Securities and Commodity Financing Transactions - Collateral Maturities of Gross Obligations (Details) - USD ($) $ in Millions	Dec. 31, 2024	Sep. 30, 2024
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	$ 17,016.7	$ 16,527.9
Securities loaned	1,826.5	1,615.9
Gross amount of secured financing	18,843.2	18,143.8
Overnight and Open
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	14,954.4	15,260.8
Securities loaned	1,826.5	1,615.9
Gross amount of secured financing	16,780.9	16,876.7
Less than 30 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	1,762.7	585.4
Securities loaned	0.0	0.0
Gross amount of secured financing	1,762.7	585.4
30-90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	218.3	631.0
Securities loaned	0.0	0.0
Gross amount of secured financing	218.3	631.0
Over 90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	81.3	50.7
Securities loaned	0.0	0.0
Gross amount of secured financing	$ 81.3	$ 50.7

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.

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The value of the collateral (typically cash) that the entity receives in a financing transaction in exchange for securities lent. This item represents a liability in the financial statements of the lender of the securities.

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Amount, after the effects of master netting arrangements, of securities loaned to entities in exchange for collateral. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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