Physical Commodities Inventory - Physical Commodities Inventory (Details) - USD ($) $ in Millions	Mar. 31, 2022	Sep. 30, 2021
Inventory [Line Items]
Physical Ag & Energy	$ 262.3	$ 248.6
Precious metals - held by broker-dealer subsidiary	362.4	359.9
Physical commodities inventory, net	547.4	447.5
Physical Commodities Inventory - Precious Metals
Inventory [Line Items]
Precious metals - held by broker-dealer subsidiary	100.1	111.2
Precious metals - held by non-broker-dealer subsidiaries	$ 185.0	$ 87.7

Physical commodities inventory at fair value - precious metals

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