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Concentrations of Credit Risk - Narrative (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2022
Dec. 31, 2021
Concentration Risk [Line Items]    
Interest bearing balances held at banks $ 1,900.0 $ 1,900.0
Credit risk to banks 4,600.0 3,000.0
Federal funds sold and securities purchased under agreements to resell 1,100.0  
Securities purchased under agreements to resell 1,070.3 686.4
Total Residential Real Estate $ 6,413.5 $ 6,319.9
Residential real estate loans as percentage of total U.S. loans 16.00% 17.00%
Residential Real Estate    
Concentration Risk [Line Items]    
Legally binding undrawn commitments to extend credit $ 783.4 $ 665.9
Residential Real Estate | Personal    
Concentration Risk [Line Items]    
Lower limit of generally required loan to collateral value for residential real estate loans 65.00%  
Upper limit of generally required loan to collateral value for residential real estate loans 80.00%  
Financing Receivable, Troubled Debt Restructuring, Subsequent Default   5.6
Financing Receivable, Troubled Debt Restructuring, Subsequent Default, Unpaid Principal Balance $ 152,551.9 5.6
Commercial Real Estate | Letter of Credit    
Concentration Risk [Line Items]    
Legally binding undrawn commitments to extend credit 449.3 357.9
Commercial Real Estate | Standby Letters of Credit    
Concentration Risk [Line Items]    
Legally binding undrawn commitments to extend credit $ 69.7 $ 30.0