Physical Commodities Inventory - Physical Commodities Inventory by CIP and Finished (Details) - USD ($) $ in Millions	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Inventory [Line Items]
Agricultural Related Inventory	$ 144.8	$ 114.7
Inventory, Net	229.3	222.5
Physical commodities inventory at fair value		156.9	$ 156.9
Physical commodities inventory - precious metals [Member]
Inventory [Line Items]
Physical commodities inventory at fair value	7.1	42.1
Inventory, Finished Goods, Net of Reserves	$ 77.4	$ 65.7