Securities and Commodity Financing Transactions - Collateral Maturities of Gross Obligations (Details) - USD ($) $ in Millions	Sep. 30, 2023	Sep. 30, 2022
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase, gross	$ 9,196.4	$ 6,133.5
Securities loaned	1,117.3	1,189.5
Gross amount of secured financing	10,313.7	7,323.0
Overnight and Open
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase, gross	8,300.0	3,664.7
Securities loaned	1,117.3	1,189.5
Gross amount of secured financing	9,417.3	4,854.2
Less than 30 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase, gross	786.8	2,279.1
Securities loaned	0.0	0.0
Gross amount of secured financing	786.8	2,279.1
30-90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase, gross	107.0	186.3
Securities loaned	0.0	0.0
Gross amount of secured financing	107.0	186.3
Over 90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase, gross	2.6	3.4
Securities loaned	0.0	0.0
Gross amount of secured financing	$ 2.6	$ 3.4

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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