Loans (Delinquency Status) (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	$ 43,334.6	$ 47,553.4
NONACCRUAL	56.0	63.6
TOTAL LOANS	43,390.6	47,617.0
NONACCRUAL WITH NO ALLOWANCE	34.6	49.4
Other Real Estate Owned	0.0	1.5
Total Nonaccrual Assets	56.0	65.1
CURRENT
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	43,110.9	47,261.1
30 – 59 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	122.6	239.5
60 – 89 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	18.8	32.7
90 DAYS OR MORE PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	82.3	20.1
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	20,242.9	25,396.5
NONACCRUAL	35.9	16.3
TOTAL LOANS	20,278.8	25,412.8
NONACCRUAL WITH NO ALLOWANCE	16.1	4.1
Commercial | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	10,507.3	11,539.0
NONACCRUAL	29.8	16.3
TOTAL LOANS	10,537.1	11,555.3
NONACCRUAL WITH NO ALLOWANCE	10.5	4.1
Commercial | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	5,308.6	5,134.2
NONACCRUAL	5.6	0.0
TOTAL LOANS	5,314.2	5,134.2
NONACCRUAL WITH NO ALLOWANCE	5.6	0.0
Commercial | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	2,113.4	2,778.5
NONACCRUAL	0.5	0.0
TOTAL LOANS	2,113.9	2,778.5
NONACCRUAL WITH NO ALLOWANCE	0.0	0.0
Commercial | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	2,313.6	5,944.8
NONACCRUAL	0.0	0.0
TOTAL LOANS	2,313.6	5,944.8
NONACCRUAL WITH NO ALLOWANCE	0.0	0.0
Commercial | CURRENT
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	20,218.4	25,221.6
Commercial | CURRENT | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	10,486.9	11,374.6
Commercial | CURRENT | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	5,304.9	5,123.7
Commercial | CURRENT | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	2,113.0	2,778.5
Commercial | CURRENT | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	2,313.6	5,944.8
Commercial | 30 – 59 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	16.1	168.1
Commercial | 30 – 59 DAYS PAST DUE | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	12.8	163.7
Commercial | 30 – 59 DAYS PAST DUE | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	3.3	4.4
Commercial | 30 – 59 DAYS PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0.0	0.0
Commercial | 30 – 59 DAYS PAST DUE | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0.0	0.0
Commercial | 60 – 89 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	1.1	6.8
Commercial | 60 – 89 DAYS PAST DUE | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0.7	0.7
Commercial | 60 – 89 DAYS PAST DUE | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0.0	6.1
Commercial | 60 – 89 DAYS PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0.4	0.0
Commercial | 60 – 89 DAYS PAST DUE | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0.0	0.0
Commercial | 90 DAYS OR MORE PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	7.3	0.0
Commercial | 90 DAYS OR MORE PAST DUE | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	6.9	0.0
Commercial | 90 DAYS OR MORE PAST DUE | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0.4	0.0
Commercial | 90 DAYS OR MORE PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0.0	0.0
Commercial | 90 DAYS OR MORE PAST DUE | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0.0	0.0
Personal
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	23,091.7	22,156.9
NONACCRUAL	20.1	47.3
TOTAL LOANS	23,111.8	22,204.2
NONACCRUAL WITH NO ALLOWANCE	18.5	45.3
Personal | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	15,846.5	14,339.7
NONACCRUAL	2.3	20.3
TOTAL LOANS	15,848.8	14,360.0
NONACCRUAL WITH NO ALLOWANCE	0.7	18.3
Personal | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	6,092.1	6,300.1
NONACCRUAL	17.8	27.0
TOTAL LOANS	6,109.9	6,327.1
NONACCRUAL WITH NO ALLOWANCE	17.8	27.0
Personal | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	674.7	428.8
NONACCRUAL	0.0	0.0
TOTAL LOANS	674.7	428.8
NONACCRUAL WITH NO ALLOWANCE	0.0	0.0
Personal | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	478.4	1,088.3
NONACCRUAL	0.0	0.0
TOTAL LOANS	478.4	1,088.3
NONACCRUAL WITH NO ALLOWANCE	0.0	0.0
Personal | CURRENT
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	22,892.5	22,039.5
Personal | CURRENT | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	15,677.6	14,240.0
Personal | CURRENT | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	6,063.4	6,283.0
Personal | CURRENT | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	673.1	428.2
Personal | CURRENT | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	478.4	1,088.3
Personal | 30 – 59 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	106.5	71.4
Personal | 30 – 59 DAYS PAST DUE | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	87.7	63.9
Personal | 30 – 59 DAYS PAST DUE | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	17.2	7.5
Personal | 30 – 59 DAYS PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	1.6	0.0
Personal | 30 – 59 DAYS PAST DUE | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0.0	0.0
Personal | 60 – 89 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	17.7	25.9
Personal | 60 – 89 DAYS PAST DUE | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	15.2	24.8
Personal | 60 – 89 DAYS PAST DUE | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	2.5	0.5
Personal | 60 – 89 DAYS PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0.0	0.6
Personal | 60 – 89 DAYS PAST DUE | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0.0	0.0
Personal | 90 DAYS OR MORE PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	75.0	20.1
Personal | 90 DAYS OR MORE PAST DUE | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	66.0	11.0
Personal | 90 DAYS OR MORE PAST DUE | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	9.0	9.1
Personal | 90 DAYS OR MORE PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0.0	0.0
Personal | 90 DAYS OR MORE PAST DUE | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	$ 0.0	$ 0.0