Physical Commodities Inventory - Physical Commodities Inventory by CIP and Finished (Details) - USD ($) $ in Millions	Jun. 30, 2020	Sep. 30, 2019
Inventory [Line Items]
Physical Ag & Energy(1)	$ 153.8	$ 144.8
Precious metals - held by non-broker-dealer subsidiaries(3)	173.6	151.9
Physical commodities inventory	270.2	229.3
Physical commodities inventory - precious metals [Member]
Inventory [Line Items]
Precious metals - held by non-broker-dealer subsidiaries(3)	19.8	7.1
Finished commodities	$ 96.6	$ 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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