Loans (Delinquency Status) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	$ 43,508.2	$ 42,847.4
NONACCRUAL	68.8	45.9
TOTAL LOANS	43,577.0	42,893.3
NONACCRUAL WITH NO ALLOWANCE	56.0	28.9
Other Real Estate Owned	0.3	0.0
Total Nonaccrual Assets	69.1	45.9
CURRENT
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	43,353.7	42,504.6
30 – 59 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	101.9	243.4
60 – 89 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	16.4	45.2
90 DAYS OR MORE PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	36.2	54.2
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	21,967.8	21,608.0
NONACCRUAL	19.5	27.6
TOTAL LOANS	21,987.3	21,635.6
NONACCRUAL WITH NO ALLOWANCE	10.1	10.6
Commercial | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	12,045.0	12,397.6
NONACCRUAL	16.3	17.4
TOTAL LOANS	12,061.3	12,415.0
NONACCRUAL WITH NO ALLOWANCE	6.9	4.4
Commercial | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	5,059.9	4,762.8
NONACCRUAL	3.2	10.2
TOTAL LOANS	5,063.1	4,773.0
NONACCRUAL WITH NO ALLOWANCE	3.2	6.2
Commercial | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	2,857.8	3,131.1
NONACCRUAL	0.0	0.0
TOTAL LOANS	2,857.8	3,131.1
NONACCRUAL WITH NO ALLOWANCE	0.0	0.0
Commercial | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	2,005.1	1,316.5
NONACCRUAL	0.0	0.0
TOTAL LOANS	2,005.1	1,316.5
NONACCRUAL WITH NO ALLOWANCE	0.0	0.0
Commercial | CURRENT
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	21,952.2	21,562.8
Commercial | CURRENT | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	12,032.4	12,353.7
Commercial | CURRENT | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	5,059.9	4,761.5
Commercial | CURRENT | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	2,854.8	3,131.1
Commercial | CURRENT | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	2,005.1	1,316.5
Commercial | 30 – 59 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	10.9	41.5
Commercial | 30 – 59 DAYS PAST DUE | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	7.9	40.2
Commercial | 30 – 59 DAYS PAST DUE | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0.0	1.3
Commercial | 30 – 59 DAYS PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	3.0	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	1.6	3.0
Commercial | 60 – 89 DAYS PAST DUE | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	1.6	3.0
Commercial | 60 – 89 DAYS PAST DUE | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0.0	0.0
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	3.1	0.7
Commercial | 90 DAYS OR MORE PAST DUE | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	3.1	0.7
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	0.0	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	21,540.4	21,239.4
NONACCRUAL	49.3	18.3
TOTAL LOANS	21,589.7	21,257.7
NONACCRUAL WITH NO ALLOWANCE	45.9	18.3
Personal | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	14,048.8	14,119.0
NONACCRUAL	19.8	0.0
TOTAL LOANS	14,068.6	14,119.0
NONACCRUAL WITH NO ALLOWANCE	17.8	0.0
Personal | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	6,256.3	6,395.2
NONACCRUAL	29.5	18.3
TOTAL LOANS	6,285.8	6,413.5
NONACCRUAL WITH NO ALLOWANCE	28.1	18.3
Personal | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	432.6	510.0
NONACCRUAL	0.0	0.0
TOTAL LOANS	432.6	510.0
NONACCRUAL WITH NO ALLOWANCE	0.0	0.0
Personal | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	802.7	215.2
NONACCRUAL	0.0	0.0
TOTAL LOANS	802.7	215.2
NONACCRUAL WITH NO ALLOWANCE	0.0	0.0
Personal | CURRENT
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	21,401.5	20,941.8
Personal | CURRENT | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	13,911.3	13,843.5
Personal | CURRENT | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	6,254.9	6,373.2
Personal | CURRENT | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	432.6	509.9
Personal | CURRENT | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	802.7	215.2
Personal | 30 – 59 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	91.0	201.9
Personal | 30 – 59 DAYS PAST DUE | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	91.0	192.3
Personal | 30 – 59 DAYS PAST DUE | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0.0	9.6
Personal | 30 – 59 DAYS PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0.0	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	14.8	42.2
Personal | 60 – 89 DAYS PAST DUE | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	13.4	29.9
Personal | 60 – 89 DAYS PAST DUE | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	1.4	12.3
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	33.1	53.5
Personal | 90 DAYS OR MORE PAST DUE | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	33.1	53.3
Personal | 90 DAYS OR MORE PAST DUE | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0.0	0.1
Personal | 90 DAYS OR MORE PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	0.0	0.1
Personal | 90 DAYS OR MORE PAST DUE | Other
Financing Receivable, Credit Quality Indicator [Line Items]
TOTAL ACCRUAL	$ 0.0	$ 0.0