Concentrations of Credit Risk - Commercial Real Estate Loans (Detail) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Concentration Risk [Line Items]
Total Loans	$ 41,948.3	$ 43,390.6
Commercial
Concentration Risk [Line Items]
Total Loans	20,431.0	20,278.8
Commercial Real Estate | Commercial
Concentration Risk [Line Items]
Total Loans	5,272.2	5,314.2
Total Commercial Mortgages | Commercial
Concentration Risk [Line Items]
Total Loans	4,812.9	4,746.3
Apartment/ Multi-family | Commercial
Concentration Risk [Line Items]
Total Loans	1,586.4	1,599.9
Industrial/Warehouse | Commercial
Concentration Risk [Line Items]
Total Loans	960.1	906.1
Office | Commercial
Concentration Risk [Line Items]
Total Loans	948.0	944.4
Retail | Commercial
Concentration Risk [Line Items]
Total Loans	695.9	665.6
Other | Commercial
Concentration Risk [Line Items]
Total Loans	622.5	630.3
Construction, Acquisition and Development Loans | Commercial
Concentration Risk [Line Items]
Total Loans	$ 459.3	$ 567.9