Loans (Loans) (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	$ 42,505.5	$ 41,948.3
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	20,678.8	20,431.0
Commercial | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	6,569.0	6,595.3
Commercial | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	5,157.8	5,272.2
Commercial | Subscription Finance
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	4,020.1	3,603.4
Commercial | Fund Finance
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	1,483.8	1,357.7
Commercial | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	3,448.1	3,602.4
Commercial | Non-US Commercial Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	2,300.0	2,200.0
Personal
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	21,826.7	21,517.3
Personal | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	15,659.7	15,169.3
Personal | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	6,004.5	6,121.0
Personal | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	162.5	227.0
Personal | Non-US Consumer Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	$ 687.0	$ 657.4