Physical Commodities Inventory (Details) - USD ($) $ in Millions	Dec. 31, 2023	Sep. 30, 2023
Inventory [Line Items]
Physical Ag & Energy	$ 139.8	$ 146.2
Precious metals - held by broker-dealer subsidiary	314.4	386.5
Physical commodities inventory, net	518.4	537.3
Physical Commodities Inventory - Precious Metals
Inventory [Line Items]
Precious metals - held by broker-dealer subsidiary	174.6	240.3
Precious metals - held by non-broker-dealer subsidiaries	$ 204.0	$ 150.8

Physical commodities inventory at fair value - precious metals

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Carrying amount, net of valuation reserves and adjustments, as of the balance sheet date of merchandise or goods held by the company that are readily available for sale.

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Amount after valuation and LIFO reserves of inventory expected to be sold, or consumed within one year or operating cycle, if longer.

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