Loans (Loans) (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	$ 43,390.6	$ 47,617.0
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	20,278.8	25,412.8
Commercial | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	10,537.1	11,555.3
Commercial | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	5,314.2	5,134.2
Commercial | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	2,113.9	2,778.5
Commercial | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	2,313.6	5,944.8
Commercial | Private equity capital call finance loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	4,100.0	4,500.0
Personal
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	23,111.8	22,204.2
Personal | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	15,848.8	14,360.0
Personal | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	6,109.9	6,327.1
Personal | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	674.7	428.8
Personal | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	$ 478.4	$ 1,088.3