Securities and Commodity Financing Transactions - Collateral Maturities of Gross Obligations (Details) - USD ($) $ in Millions	Jun. 30, 2023	Sep. 30, 2022
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	$ 11,813.4	$ 6,133.5
Securities loaned	1,093.3	1,189.5
Gross amount of secured financing	12,906.7	7,323.0
Overnight and Open
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	11,141.4	3,664.7
Securities loaned	1,093.3	1,189.5
Gross amount of secured financing	12,234.7	4,854.2
Less than 30 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	557.9	2,279.1
Securities loaned	0.0	0.0
Gross amount of secured financing	557.9	2,279.1
30-90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	69.1	186.3
Securities loaned	0.0	0.0
Gross amount of secured financing	69.1	186.3
Over 90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	45.0	3.4
Securities loaned	0.0	0.0
Gross amount of secured financing	$ 45.0	$ 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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