Physical Commodities Inventory - Physical Commodities Inventory (Details) - USD ($) $ in Millions	Jun. 30, 2021	Sep. 30, 2020
Inventory [Line Items]
Physical Ag & Energy	$ 241.4	$ 201.5
Precious metals - held by broker-dealer subsidiary	376.3	215.7
Physical commodities inventory, net	484.8	281.1
Physical Commodities Inventory - Precious Metals
Inventory [Line Items]
Precious metals - held by broker-dealer subsidiary	135.1	14.2
Precious metals - held by non-broker-dealer subsidiaries	$ 108.3	$ 65.4

Physical commodities inventory at fair value - precious metals

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