Loans (Loans) (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	$ 42,949.4	$ 43,390.6
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	20,571.1	20,278.8
Commercial | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	10,243.5	10,537.1
Commercial | Commercial and Institutional | Private Equity Funds
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	3,900.0	4,100.0
Commercial | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	5,255.6	5,314.2
Commercial | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	2,789.5	2,113.9
Commercial | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	2,282.5	2,313.6
Personal
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	22,378.3	23,111.8
Personal | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	15,290.9	15,848.8
Personal | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	6,045.6	6,109.9
Personal | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	502.3	674.7
Personal | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	$ 539.5	$ 478.4