Bank Deposits (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Bank Deposits [Line Items]
Weighted average interest rate on deposits	3.33%	2.66%
Brokerage Customers Deposits [Member]
Bank Deposits [Line Items]
Deposits of related parties	$ 25,300.0	$ 24,100.0
Stifel Nicolaus [Member]
Bank Deposits [Line Items]
Interest bearing and time deposits of executive officers, directors, and affiliates	$ 5.2	$ 9.0