Loans and Leases (Delinquency Status) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	$ 32,572.0	$ 31,230.6
TOTAL ACCRUAL	32,668.3	31,326.0
NONACCRUAL	98.0	83.6
Total Loans and Leases	32,766.3	31,409.6
NONACCRUAL WITH NO ALLOWANCE	70.9	70.6
Other Real Estate Owned	0.9	3.2
Total Nonaccrual Assets	98.9	86.8
Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	338.7
30 – 59 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	64.8	59.6
60 – 89 DAYS PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	22.9	28.4
90 DAYS OR MORE PAST DUE
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	8.6	7.4
COMMERCIAL
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	14,516.0	13,963.8
TOTAL ACCRUAL	14,547.6	13,990.1
NONACCRUAL	34.1	11.2
Total Loans and Leases	14,581.7	14,001.3
NONACCRUAL WITH NO ALLOWANCE	15.4	3.2
COMMERCIAL | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	9,470.9	9,068.3
TOTAL ACCRUAL	9,493.8	9,083.5
NONACCRUAL	30.2	7.6
Total Loans and Leases	9,524.0	9,091.1
NONACCRUAL WITH NO ALLOWANCE	11.5	0.8
COMMERCIAL | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	3,361.0	3,089.6
TOTAL ACCRUAL	3,369.7	3,100.7
NONACCRUAL	3.9	3.6
Total Loans and Leases	3,373.6	3,104.3
NONACCRUAL WITH NO ALLOWANCE	3.9	2.4
COMMERCIAL | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	1,441.0	1,576.3
TOTAL ACCRUAL	1,441.0	1,576.3
NONACCRUAL	0.0	0.0
Total Loans and Leases	1,441.0	1,576.3
NONACCRUAL WITH NO ALLOWANCE	0.0	0.0
COMMERCIAL | Lease Financing, net
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	30.1	65.6
TOTAL ACCRUAL	30.1	65.6
NONACCRUAL	0.0	0.0
Total Loans and Leases	30.1	65.6
NONACCRUAL WITH NO ALLOWANCE	0.0	0.0
COMMERCIAL | Other
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	213.0	164.0
TOTAL ACCRUAL	213.0	164.0
NONACCRUAL	0.0	0.0
Total Loans and Leases	213.0	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	22.5	6.4
COMMERCIAL | 30 – 59 DAYS PAST DUE | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	21.9	4.1
COMMERCIAL | 30 – 59 DAYS PAST DUE | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	0.6	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	8.3	14.0
COMMERCIAL | 60 – 89 DAYS PAST DUE | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	0.2	9.9
COMMERCIAL | 60 – 89 DAYS PAST DUE | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	8.1	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	0.8	5.9
COMMERCIAL | 90 DAYS OR MORE PAST DUE | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	0.8	1.2
COMMERCIAL | 90 DAYS OR MORE PAST DUE | Commercial Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	0.0	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	18,056.0	17,266.8
TOTAL ACCRUAL	18,120.7	17,335.9
NONACCRUAL	63.9	72.4
Total Loans and Leases	18,184.6	17,408.3
NONACCRUAL WITH NO ALLOWANCE	55.5	67.4
Personal | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	11,832.8	11,027.9
TOTAL ACCRUAL	11,893.0	11,070.9
NONACCRUAL	0.0	0.5
Total Loans and Leases	11,893.0	11,071.4
NONACCRUAL WITH NO ALLOWANCE	0.0	0.5
Personal | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	5,859.9	5,997.7
TOTAL ACCRUAL	5,864.4	6,023.6
NONACCRUAL	63.9	71.4
Total Loans and Leases	5,928.3	6,095.0
NONACCRUAL WITH NO ALLOWANCE	55.5	66.4
Personal | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	338.7	174.1
TOTAL ACCRUAL	338.7	174.3
NONACCRUAL	0.0	0.5
Total Loans and Leases	338.7	174.8
NONACCRUAL WITH NO ALLOWANCE	0.0	0.5
Personal | Other
Financing Receivable, Credit Quality Indicator [Line Items]
CURRENT	24.6	67.1
TOTAL ACCRUAL	24.6	67.1
NONACCRUAL	0.0	0.0
Total Loans and Leases	24.6	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	42.3	53.2
Personal | 30 – 59 DAYS PAST DUE | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	39.4	33.2
Personal | 30 – 59 DAYS PAST DUE | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	2.9	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	14.6	14.4
Personal | 60 – 89 DAYS PAST DUE | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	13.3	9.5
Personal | 60 – 89 DAYS PAST DUE | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	1.3	4.9
Personal | 60 – 89 DAYS PAST DUE | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	0.0	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	7.8	1.5
Personal | 90 DAYS OR MORE PAST DUE | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	7.5	0.3
Personal | 90 DAYS OR MORE PAST DUE | Residential Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Past Due	0.3	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