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Concentrations of Credit Risk - Narrative (Detail) - USD ($)
$ in Millions
Dec. 31, 2021
Dec. 31, 2020
Concentration Risk [Line Items]    
Interest bearing balances held at banks $ 1,900.0 $ 4,400.0
Credit risk to banks 3,000.0 4,300.0
Federal funds sold and securities purchased under agreements to resell 686.4  
Securities purchased under agreements to resell 686.4 1,596.5
Residential real estate $ 6,300.0 $ 6,000.0
Residential real estate loans as percentage of total U.S. loans 17.00% 19.00%
Residential Real Estate    
Concentration Risk [Line Items]    
Legally binding undrawn commitments to extend credit $ 665.9 $ 676.1
Commercial Real Estate | Letter of Credit    
Concentration Risk [Line Items]    
Legally binding undrawn commitments to extend credit 357.9 252.3
Commercial Real Estate | Standby Letters of Credit    
Concentration Risk [Line Items]    
Legally binding undrawn commitments to extend credit 30.0 $ 4.5
Florida    
Concentration Risk [Line Items]    
Residential real estate 1,600.0  
California    
Concentration Risk [Line Items]    
Residential real estate 1,400.0  
Greater Chicago Area    
Concentration Risk [Line Items]    
Residential real estate $ 700.0