Loans (Loans) (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	$ 41,948.3	$ 43,390.6
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	20,431.0	20,278.8
Commercial | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	9,995.0	10,537.1
Commercial | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	5,272.2	5,314.2
Commercial | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	2,190.1	2,113.9
Commercial | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	2,973.7	2,313.6
Commercial | Private equity capital call finance loans
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	4,100.0
Personal
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	21,517.3	23,111.8
Personal | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	14,550.4	15,848.8
Personal | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	6,077.3	6,109.9
Personal | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	657.4	674.7
Personal | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans	$ 232.2	$ 478.4