Financial Instruments Owned and Financial Instruments Sold, But Not Yet Purchased (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Financial instruments pledged as collateral	$ 721.0	$ 796.2
Securities Owned [Member]
Schedule Of Trading Securities And Other Trading Assets [Line Items]
Financial instruments pledged as collateral	$ 418.8	$ 218.9

The aggregate fair value as of the balance sheet date of financial instruments and other positions owned by the entity including: (1) mortgages, mortgage-backed and asset backed securities; (2) US government and agency obligations; (3) state and municipal government obligations; (4) other sovereign government debt; (5) corporate obligations; (6) corporate equities; (7) principal investments; (8) derivative contracts; and (9) physical commodities. Includes both pledged and unpledged holdings.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 940
-SubTopic 320
-Section 45
-Paragraph 2
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481961/940-320-45-2

Name:	us-gaap_FinancialInstrumentsOwnedAtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant