Loans (Delinquency Status) (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	$ 41,871.6	$ 43,334.6
NONACCRUAL	76.7	56.0
TOTAL LOANS	41,948.3	43,390.6
NONACCRUAL WITH NO ALLOWANCE	48.2	34.6
CURRENT
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	41,550.2	43,110.9
30 – 59 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	258.0	122.6
60 – 89 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	38.4	18.8
90 DAYS OR MORE PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	25.0	82.3
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	20,390.7	20,242.9
NONACCRUAL	40.3	35.9
TOTAL LOANS	20,431.0	20,278.8
NONACCRUAL WITH NO ALLOWANCE	21.3	16.1
Commercial | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	9,955.3	10,507.3
NONACCRUAL	39.7	29.8
TOTAL LOANS	9,995.0	10,537.1
NONACCRUAL WITH NO ALLOWANCE	21.3	10.5
Commercial | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	5,272.2	5,308.6
NONACCRUAL	0.0	5.6
TOTAL LOANS	5,272.2	5,314.2
NONACCRUAL WITH NO ALLOWANCE	0.0	5.6
Commercial | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	2,189.5	2,113.4
NONACCRUAL	0.6	0.5
TOTAL LOANS	2,190.1	2,113.9
NONACCRUAL WITH NO ALLOWANCE	0.0	0.0
Commercial | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	2,973.7	2,313.6
NONACCRUAL	0.0	0.0
TOTAL LOANS	2,973.7	2,313.6
NONACCRUAL WITH NO ALLOWANCE	0.0	0.0
Commercial | CURRENT
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	20,250.3	20,218.4
Commercial | CURRENT | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	9,865.0	10,486.9
Commercial | CURRENT | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	5,222.1	5,304.9
Commercial | CURRENT | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	2,189.5	2,113.0
Commercial | CURRENT | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	2,973.7	2,313.6
Commercial | 30 – 59 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	117.5	16.1
Commercial | 30 – 59 DAYS PAST DUE | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	80.2	12.8
Commercial | 30 – 59 DAYS PAST DUE | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	37.3	3.3
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	4.4	1.1
Commercial | 60 – 89 DAYS PAST DUE | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0.8	0.7
Commercial | 60 – 89 DAYS PAST DUE | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	3.6	0.0
Commercial | 60 – 89 DAYS PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0.0	0.4
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	18.5	7.3
Commercial | 90 DAYS OR MORE PAST DUE | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	9.3	6.9
Commercial | 90 DAYS OR MORE PAST DUE | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	9.2	0.4
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	21,480.9	23,091.7
NONACCRUAL	36.4	20.1
TOTAL LOANS	21,517.3	23,111.8
NONACCRUAL WITH NO ALLOWANCE	26.9	18.5
Personal | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	14,543.7	15,846.5
NONACCRUAL	6.7	2.3
TOTAL LOANS	14,550.4	15,848.8
NONACCRUAL WITH NO ALLOWANCE	0.0	0.7
Personal | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	6,047.6	6,092.1
NONACCRUAL	29.7	17.8
TOTAL LOANS	6,077.3	6,109.9
NONACCRUAL WITH NO ALLOWANCE	26.9	17.8
Personal | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	657.4	674.7
NONACCRUAL	0.0	0.0
TOTAL LOANS	657.4	674.7
NONACCRUAL WITH NO ALLOWANCE	0.0	0.0
Personal | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	232.2	478.4
NONACCRUAL	0.0	0.0
TOTAL LOANS	232.2	478.4
NONACCRUAL WITH NO ALLOWANCE	0.0	0.0
Personal | CURRENT
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	21,299.9	22,892.5
Personal | CURRENT | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	14,403.3	15,677.6
Personal | CURRENT | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	6,007.0	6,063.4
Personal | CURRENT | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	657.4	673.1
Personal | CURRENT | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	232.2	478.4
Personal | 30 – 59 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	140.5	106.5
Personal | 30 – 59 DAYS PAST DUE | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	128.8	87.7
Personal | 30 – 59 DAYS PAST DUE | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	11.7	17.2
Personal | 30 – 59 DAYS PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0.0	1.6
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	34.0	17.7
Personal | 60 – 89 DAYS PAST DUE | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	8.5	15.2
Personal | 60 – 89 DAYS PAST DUE | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	25.5	2.5
Personal | 60 – 89 DAYS PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0.0	0.0
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	6.5	75.0
Personal | 90 DAYS OR MORE PAST DUE | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	3.1	66.0
Personal | 90 DAYS OR MORE PAST DUE | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	3.4	9.0
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