Securities and Commodity Financing Transactions - Netting of Securities Purchased Under Agreements (Details) - USD ($) $ in Millions	Dec. 31, 2022	Sep. 30, 2022
Broker-Dealer [Abstract]
Securities purchased under agreements to resell, gross	$ 8,135.9	$ 4,609.9
Securities purchased under agreements to resell, offset	(5,382.7)	(2,937.9)
Securities purchased under agreements to resell, net	2,753.2	1,672.0
Securities borrowed, gross	484.2	1,209.8
Securities borrowed, net	484.2	1,209.8
Securities sold under agreements to repurchase, gross	10,302.3	6,133.5
Securities sold under agreements to repurchase, offset	(5,382.7)	(2,937.9)
Securities sold under agreements to repurchase, net	4,919.6	3,195.6
Securities loaned, gross	483.9	1,189.5
Securities loaned, net	$ 483.9	$ 1,189.5

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Amount, after the effects of master netting arrangements, of securities borrowed from entities in exchange for collateral. Includes assets not subject to a master netting arrangement and not elected to be offset.

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