Loans (Delinquency Status) (Details) - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	$ 42,096.7	$ 47,553.4
NONACCRUAL	38.5	63.6
TOTAL LOANS	42,135.2	47,617.0
NONACCRUAL WITH NO ALLOWANCE	30.8	49.4
Other Real Estate Owned	0.0	1.5
Total Nonaccrual Assets	38.5	65.1
CURRENT
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	41,750.8	47,261.1
30 – 59 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	229.2	239.5
60 – 89 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	36.1	32.7
90 DAYS OR MORE PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	80.6	20.1
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	20,820.7	25,396.5
NONACCRUAL	13.3	16.3
TOTAL LOANS	20,834.0	25,412.8
NONACCRUAL WITH NO ALLOWANCE	7.6	4.1
Commercial | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	10,804.5	11,539.0
NONACCRUAL	7.6	16.3
TOTAL LOANS	10,812.1	11,555.3
NONACCRUAL WITH NO ALLOWANCE	7.6	4.1
Commercial | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	5,261.1	5,134.2
NONACCRUAL	5.7	0.0
TOTAL LOANS	5,266.8	5,134.2
NONACCRUAL WITH NO ALLOWANCE	0.0	0.0
Commercial | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	2,464.0	2,778.5
NONACCRUAL	0.0	0.0
TOTAL LOANS	2,464.0	2,778.5
NONACCRUAL WITH NO ALLOWANCE	0.0	0.0
Commercial | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	2,291.1	5,944.8
NONACCRUAL	0.0	0.0
TOTAL LOANS	2,291.1	5,944.8
NONACCRUAL WITH NO ALLOWANCE	0.0	0.0
Commercial | CURRENT
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	20,715.6	25,221.6
Commercial | CURRENT | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	10,721.6	11,374.6
Commercial | CURRENT | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	5,244.3	5,123.7
Commercial | CURRENT | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	2,458.6	2,778.5
Commercial | CURRENT | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	2,291.1	5,944.8
Commercial | 30 – 59 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	41.1	168.1
Commercial | 30 – 59 DAYS PAST DUE | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	19.3	163.7
Commercial | 30 – 59 DAYS PAST DUE | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	16.8	4.4
Commercial | 30 – 59 DAYS PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	5.0	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	9.4	6.8
Commercial | 60 – 89 DAYS PAST DUE | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	9.4	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	0.0	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	54.6	0.0
Commercial | 90 DAYS OR MORE PAST DUE | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	54.2	0.0
Commercial | 90 DAYS OR MORE PAST DUE | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0.0	0.0
Commercial | 90 DAYS OR MORE PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0.4	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	21,276.0	22,156.9
NONACCRUAL	25.2	47.3
TOTAL LOANS	21,301.2	22,204.2
NONACCRUAL WITH NO ALLOWANCE	23.2	45.3
Personal | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	14,414.5	14,339.7
NONACCRUAL	2.0	20.3
TOTAL LOANS	14,416.5	14,360.0
NONACCRUAL WITH NO ALLOWANCE	0.0	18.3
Personal | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	6,185.8	6,300.1
NONACCRUAL	23.2	27.0
TOTAL LOANS	6,209.0	6,327.1
NONACCRUAL WITH NO ALLOWANCE	23.2	27.0
Personal | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	437.8	428.8
NONACCRUAL	0.0	0.0
TOTAL LOANS	437.8	428.8
NONACCRUAL WITH NO ALLOWANCE	0.0	0.0
Personal | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	237.9	1,088.3
NONACCRUAL	0.0	0.0
TOTAL LOANS	237.9	1,088.3
NONACCRUAL WITH NO ALLOWANCE	0.0	0.0
Personal | CURRENT
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	21,035.2	22,039.5
Personal | CURRENT | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	14,220.5	14,240.0
Personal | CURRENT | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	6,160.1	6,283.0
Personal | CURRENT | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	416.7	428.2
Personal | CURRENT | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	237.9	1,088.3
Personal | 30 – 59 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	188.1	71.4
Personal | 30 – 59 DAYS PAST DUE | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	144.7	63.9
Personal | 30 – 59 DAYS PAST DUE | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	22.3	7.5
Personal | 30 – 59 DAYS PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	21.1	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	26.7	25.9
Personal | 60 – 89 DAYS PAST DUE | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	23.4	24.8
Personal | 60 – 89 DAYS PAST DUE | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	3.3	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	26.0	20.1
Personal | 90 DAYS OR MORE PAST DUE | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	25.9	11.0
Personal | 90 DAYS OR MORE PAST DUE | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0.1	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