Loans and Leases (Delinquency Status) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	$ 30,620.6	$ 32,490.0
Commercial
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	13,635.5	15,175.2
Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	8,532.1	8,728.1
Commercial | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	3,185.0	3,228.8
Commercial | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	1,648.6	2,701.6
Commercial | Lease Financing, net
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	89.3	90.7
Commercial | Other
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	180.5	426.0
Personal
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	16,985.1	17,314.8
Personal | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	6,286.6	6,514.0
Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	10,669.9	10,733.3
Personal | Other
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	28.6	67.5
Performing Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Current	30,372.4	32,213.0
Total Loans and Leases	30,504.5	32,380.7
Performing Financing Receivable | 30-59 Days Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	93.8	112.5
Performing Financing Receivable | 60-89 Days Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	25.3	38.8
Performing Financing Receivable | 90 Days or More Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	13.0	16.4
Performing Financing Receivable | Commercial
Financing Receivable, Recorded Investment [Line Items]
Current	13,578.1	15,087.6
Total Loans and Leases	13,623.1	15,161.1
Performing Financing Receivable | Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Current	8,499.3	8,678.2
Total Loans and Leases	8,524.5	8,721.3
Performing Financing Receivable | Commercial | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Current	3,161.4	3,191.5
Total Loans and Leases	3,180.8	3,221.9
Performing Financing Receivable | Commercial | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Current	1,647.6	2,701.2
Total Loans and Leases	1,648.0	2,701.2
Performing Financing Receivable | Commercial | Lease Financing, net
Financing Receivable, Recorded Investment [Line Items]
Current	89.3	90.7
Total Loans and Leases	89.3	90.7
Performing Financing Receivable | Commercial | Other
Financing Receivable, Recorded Investment [Line Items]
Current	180.5	426.0
Total Loans and Leases	180.5	426.0
Performing Financing Receivable | Commercial | 30-59 Days Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	25.8	45.8
Performing Financing Receivable | Commercial | 30-59 Days Past Due | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Past Due	22.1	37.4
Performing Financing Receivable | Commercial | 30-59 Days Past Due | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	3.3	8.4
Performing Financing Receivable | Commercial | 30-59 Days Past Due | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Past Due	0.4	0.0
Performing Financing Receivable | Commercial | 30-59 Days Past Due | Lease Financing, net
Financing Receivable, Recorded Investment [Line Items]
Past Due	0.0	0.0
Performing Financing Receivable | Commercial | 30-59 Days Past Due | Other
Financing Receivable, Recorded Investment [Line Items]
Past Due	0.0	0.0
Performing Financing Receivable | Commercial | 60-89 Days Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	11.2	20.1
Performing Financing Receivable | Commercial | 60-89 Days Past Due | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Past Due	3.1	4.5
Performing Financing Receivable | Commercial | 60-89 Days Past Due | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	8.1	15.6
Performing Financing Receivable | Commercial | 60-89 Days Past Due | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Past Due	0.0	0.0
Performing Financing Receivable | Commercial | 60-89 Days Past Due | Lease Financing, net
Financing Receivable, Recorded Investment [Line Items]
Past Due	0.0	0.0
Performing Financing Receivable | Commercial | 60-89 Days Past Due | Other
Financing Receivable, Recorded Investment [Line Items]
Past Due	0.0	0.0
Performing Financing Receivable | Commercial | 90 Days or More Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	8.0	7.6
Performing Financing Receivable | Commercial | 90 Days or More Past Due | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Past Due	0.0	1.2
Performing Financing Receivable | Commercial | 90 Days or More Past Due | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	8.0	6.4
Performing Financing Receivable | Commercial | 90 Days or More Past Due | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Past Due	0.0	0.0
Performing Financing Receivable | Commercial | 90 Days or More Past Due | Lease Financing, net
Financing Receivable, Recorded Investment [Line Items]
Past Due	0.0	0.0
Performing Financing Receivable | Commercial | 90 Days or More Past Due | Other
Financing Receivable, Recorded Investment [Line Items]
Past Due	0.0	0.0
Performing Financing Receivable | Personal
Financing Receivable, Recorded Investment [Line Items]
Current	16,794.3	17,125.4
Total Loans and Leases	16,881.4	17,219.6
Performing Financing Receivable | Personal | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Current	6,143.2	6,376.8
Total Loans and Leases	6,183.1	6,419.0
Performing Financing Receivable | Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Current	10,622.5	10,681.1
Total Loans and Leases	10,669.7	10,733.1
Performing Financing Receivable | Personal | Other
Financing Receivable, Recorded Investment [Line Items]
Current	28.6	67.5
Total Loans and Leases	28.6	67.5
Performing Financing Receivable | Personal | 30-59 Days Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	68.0	66.7
Performing Financing Receivable | Personal | 30-59 Days Past Due | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	28.9	27.2
Performing Financing Receivable | Personal | 30-59 Days Past Due | Private Client
Financing Receivable, Recorded Investment [Line Items]
Past Due	39.1	39.5
Performing Financing Receivable | Personal | 30-59 Days Past Due | Other
Financing Receivable, Recorded Investment [Line Items]
Past Due	0.0	0.0
Performing Financing Receivable | Personal | 60-89 Days Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	14.1	18.7
Performing Financing Receivable | Personal | 60-89 Days Past Due | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	6.5	6.2
Performing Financing Receivable | Personal | 60-89 Days Past Due | Private Client
Financing Receivable, Recorded Investment [Line Items]
Past Due	7.6	12.5
Performing Financing Receivable | Personal | 60-89 Days Past Due | Other
Financing Receivable, Recorded Investment [Line Items]
Past Due	0.0	0.0
Performing Financing Receivable | Personal | 90 Days or More Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	5.0	8.8
Performing Financing Receivable | Personal | 90 Days or More Past Due | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	4.5	8.8
Performing Financing Receivable | Personal | 90 Days or More Past Due | Private Client
Financing Receivable, Recorded Investment [Line Items]
Past Due	0.5	0.0
Performing Financing Receivable | Personal | 90 Days or More Past Due | Other
Financing Receivable, Recorded Investment [Line Items]
Past Due	0.0	0.0
Nonperforming Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	116.1	109.3
Other Real Estate Owned	8.0	8.4
Total Nonperforming Assets	124.1	117.7
Nonperforming Financing Receivable | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	12.4	14.1
Nonperforming Financing Receivable | Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	7.6	6.8
Nonperforming Financing Receivable | Commercial | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	4.2	6.9
Nonperforming Financing Receivable | Commercial | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	0.6	0.4
Nonperforming Financing Receivable | Commercial | Lease Financing, net
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	0.0	0.0
Nonperforming Financing Receivable | Commercial | Other
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	0.0	0.0
Nonperforming Financing Receivable | Personal
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	103.7	95.2
Nonperforming Financing Receivable | Personal | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	103.5	95.0
Nonperforming Financing Receivable | Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	0.2	0.2
Nonperforming Financing Receivable | Personal | Other
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	$ 0.0	$ 0.0