Physical Commodities Inventory - Physical Commodities Inventory (Details) - USD ($) $ in Millions	Sep. 30, 2020	Sep. 30, 2019
Inventory [Line Items]
Physical Ag & Energy	$ 201.5	$ 144.8
Precious metals - held by broker -dealer subsidiary	215.7	151.9
Physical commodities inventory	281.1	229.3
Physical Commodities Inventory - Precious Metals [Member]
Inventory [Line Items]
Precious metals - held by broker -dealer subsidiary	14.2	7.1
Precious metals - held by non -broker -dealer subsidiaries	$ 65.4	$ 77.4

Physical commodities inventory at fair value - precious metals

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Carrying amount as of the balance sheet date of merchandise or supplies held which are related to plants and animals.

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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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