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Bank Deposits (Narrative) (Details) - USD ($)
$ in Millions
Dec. 31, 2018
Dec. 31, 2017
Bank Deposits [Line Items]    
Weighted average interest rate on deposits 0.60% 0.10%
Brokerage Customers Deposits [Member]    
Bank Deposits [Line Items]    
Deposits of related parties $ 15,200.0 $ 13,400.0
Stifel Nicolaus [Member]    
Bank Deposits [Line Items]    
Interest bearing and time deposits of executive officers, directors, and affiliates $ 6.5 $ 0.2