Loans and Leases (Delinquency Status) (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	$ 33,588.2	$ 31,230.6
TOTAL ACCRUAL	33,658.8	31,326.0
NONACCRUAL	98.5	83.6
Total Loans and Leases	33,757.3	31,409.6
NONACCRUAL WITH NO ALLOWANCE	73.3	70.6
Other Real Estate Owned	0.9	3.2
Total Nonaccrual Assets	99.4	86.8
Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	369.9
30 – 59 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	41.0	59.6
60 – 89 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	16.8	28.4
90 DAYS OR MORE PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	12.8	7.4
COMMERCIAL
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	15,723.2	13,963.8
TOTAL ACCRUAL	15,735.5	13,990.1
NONACCRUAL	34.3	11.2
Total Loans and Leases	15,769.8	14,001.3
NONACCRUAL WITH NO ALLOWANCE	9.5	3.2
COMMERCIAL | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	10,707.2	9,068.3
TOTAL ACCRUAL	10,714.1	9,083.5
NONACCRUAL	31.7	7.6
Total Loans and Leases	10,745.8	9,091.1
NONACCRUAL WITH NO ALLOWANCE	6.9	0.8
COMMERCIAL | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	3,254.7	3,089.6
TOTAL ACCRUAL	3,260.1	3,100.7
NONACCRUAL	2.6	3.6
Total Loans and Leases	3,262.7	3,104.3
NONACCRUAL WITH NO ALLOWANCE	2.6	2.4
COMMERCIAL | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	1,324.8	1,576.3
TOTAL ACCRUAL	1,324.8	1,576.3
NONACCRUAL	0.0	0.0
Total Loans and Leases	1,324.8	1,576.3
NONACCRUAL WITH NO ALLOWANCE	0.0	0.0
COMMERCIAL | Lease Financing, net
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	51.4	65.6
TOTAL ACCRUAL	51.4	65.6
NONACCRUAL	0.0	0.0
Total Loans and Leases	51.4	65.6
NONACCRUAL WITH NO ALLOWANCE	0.0	0.0
COMMERCIAL | Other
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	385.1	164.0
TOTAL ACCRUAL	385.1	164.0
NONACCRUAL	0.0	0.0
Total Loans and Leases	385.1	164.0
NONACCRUAL WITH NO ALLOWANCE	0.0	0.0
COMMERCIAL | 30 – 59 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	4.6	6.4
COMMERCIAL | 30 – 59 DAYS PAST DUE | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	3.8	4.1
COMMERCIAL | 30 – 59 DAYS PAST DUE | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	0.8	2.3
COMMERCIAL | 30 – 59 DAYS PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	0.0	0.0
COMMERCIAL | 30 – 59 DAYS PAST DUE | Lease Financing, net
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	0.0	0.0
COMMERCIAL | 30 – 59 DAYS PAST DUE | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	0.0	0.0
COMMERCIAL | 60 – 89 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	2.5	14.0
COMMERCIAL | 60 – 89 DAYS PAST DUE | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	2.5	9.9
COMMERCIAL | 60 – 89 DAYS PAST DUE | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	0.0	4.1
COMMERCIAL | 60 – 89 DAYS PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	0.0	0.0
COMMERCIAL | 60 – 89 DAYS PAST DUE | Lease Financing, net
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	0.0	0.0
COMMERCIAL | 60 – 89 DAYS PAST DUE | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	0.0	0.0
COMMERCIAL | 90 DAYS OR MORE PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	5.2	5.9
COMMERCIAL | 90 DAYS OR MORE PAST DUE | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	0.6	1.2
COMMERCIAL | 90 DAYS OR MORE PAST DUE | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	4.6	4.7
COMMERCIAL | 90 DAYS OR MORE PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	0.0	0.0
COMMERCIAL | 90 DAYS OR MORE PAST DUE | Lease Financing, net
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	0.0	0.0
COMMERCIAL | 90 DAYS OR MORE PAST DUE | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	0.0	0.0
Personal
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	17,865.0	17,266.8
TOTAL ACCRUAL	17,923.3	17,335.9
NONACCRUAL	64.2	72.4
Total Loans and Leases	17,987.5	17,408.3
NONACCRUAL WITH NO ALLOWANCE	63.8	67.4
Personal | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	11,573.4	11,027.9
TOTAL ACCRUAL	11,621.3	11,070.9
NONACCRUAL	0.0	0.5
Total Loans and Leases	11,621.3	11,071.4
NONACCRUAL WITH NO ALLOWANCE	0.0	0.5
Personal | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	5,872.2	5,997.7
TOTAL ACCRUAL	5,878.3	6,023.6
NONACCRUAL	64.2	71.4
Total Loans and Leases	5,942.5	6,095.0
NONACCRUAL WITH NO ALLOWANCE	63.8	66.4
Personal | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	365.6	174.1
TOTAL ACCRUAL	369.9	174.3
NONACCRUAL	0.0	0.5
Total Loans and Leases	369.9	174.8
NONACCRUAL WITH NO ALLOWANCE	0.0	0.5
Personal | Other
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	53.8	67.1
TOTAL ACCRUAL	53.8	67.1
NONACCRUAL	0.0	0.0
Total Loans and Leases	53.8	67.1
NONACCRUAL WITH NO ALLOWANCE	0.0	0.0
Personal | 30 – 59 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	36.4	53.2
Personal | 30 – 59 DAYS PAST DUE | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	36.0	33.2
Personal | 30 – 59 DAYS PAST DUE | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	0.4	19.8
Personal | 30 – 59 DAYS PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	0.0	0.2
Personal | 30 – 59 DAYS PAST DUE | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	0.0	0.0
Personal | 60 – 89 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	14.3	14.4
Personal | 60 – 89 DAYS PAST DUE | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	5.7	9.5
Personal | 60 – 89 DAYS PAST DUE | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	4.3	4.9
Personal | 60 – 89 DAYS PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	4.3	0.0
Personal | 60 – 89 DAYS PAST DUE | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	0.0	0.0
Personal | 90 DAYS OR MORE PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	7.6	1.5
Personal | 90 DAYS OR MORE PAST DUE | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	6.2	0.3
Personal | 90 DAYS OR MORE PAST DUE | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	1.4	1.2
Personal | 90 DAYS OR MORE PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	0.0	0.0
Personal | 90 DAYS OR MORE PAST DUE | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	$ 0.0	$ 0.0