Loans (Loans) (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	$ 41,950.3	$ 47,617.0
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	20,833.8	25,412.8
Commercial | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	10,391.3	11,555.3
Commercial | Commercial and Institutional | Private Equity Funds
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	3,800.0	4,500.0
Commercial | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	5,251.0	5,134.2
Commercial | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	2,742.6	2,778.5
Commercial | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	2,448.9	5,944.8
Personal
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	21,116.5	22,204.2
Personal | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	14,195.5	14,360.0
Personal | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	6,141.2	6,327.1
Personal | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	457.2	428.8
Personal | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Loans and leases	$ 322.6	$ 1,088.3