Bank Deposits (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Bank Deposits [Line Items]
Weighted average interest rate on deposits	2.48%	0.58%
Brokerage Customers Deposits [Member]
Bank Deposits [Line Items]
Deposits of related parties	$ 24,700.0	$ 25,300.0
Stifel Nicolaus [Member]
Bank Deposits [Line Items]
Interest bearing and time deposits of executive officers, directors, and affiliates	$ 10.3	$ 9.8