Concentrations of Credit Risk - Residential Real Estate Loans by Geographic Region (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Concentration Risk [Line Items]
Total Loans	$ 43,390.6	$ 47,617.0
Personal
Concentration Risk [Line Items]
Total Loans	23,111.8	22,204.2
Personal | Residential Real Estate
Concentration Risk [Line Items]
Total Loans	6,109.9	6,327.1
Florida | Personal | Residential Real Estate
Concentration Risk [Line Items]
Total Loans	1,636.5	1,648.1
California | Personal | Residential Real Estate
Concentration Risk [Line Items]
Total Loans	1,371.9	1,463.8
Illinois | Personal | Residential Real Estate
Concentration Risk [Line Items]
Total Loans	591.3	640.3
New York | Personal | Residential Real Estate
Concentration Risk [Line Items]
Total Loans	510.8	505.4
Colorado | Personal | Residential Real Estate
Concentration Risk [Line Items]
Total Loans	309.9	344.1
Texas | Personal | Residential Real Estate
Concentration Risk [Line Items]
Total Loans	308.7	318.7
All other | Personal | Residential Real Estate
Concentration Risk [Line Items]
Total Loans	$ 1,380.8	$ 1,406.7