Securities and Commodity Financing Transactions - Collateral Maturities of Gross Obligations (Details) - USD ($) $ in Millions	Mar. 31, 2022	Sep. 30, 2021
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	$ 3,807.9	$ 4,340.9
Securities loaned	2,103.7	2,153.6
Gross amount of secured financing	5,911.6	6,494.5
Overnight and Open
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	2,563.4	2,949.8
Securities loaned	2,103.7	2,153.6
Gross amount of secured financing	4,667.1	5,103.4
Less than 30 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	725.6	973.4
Securities loaned	0.0	0.0
Gross amount of secured financing	725.6	973.4
30-90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	512.3	137.5
Securities loaned	0.0	0.0
Gross amount of secured financing	512.3	137.5
Over 90 Days
Assets Sold under Agreements to Repurchase [Line Items]
Securities sold under agreements to repurchase	6.6	280.2
Securities loaned	0.0	0.0
Gross amount of secured financing	$ 6.6	$ 280.2

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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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Amount, after the effects of master netting arrangements, of funds outstanding borrowed in the form of a security repurchase agreement between the entity and another party for the sale and repurchase of identical or substantially the same securities at a date certain for a specified price. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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