Loans and Leases (Delinquency Status) (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	$ 33,336.1	$ 33,822.1
Commercial
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	15,203.8	15,666.7
Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	9,246.4	9,287.4
Commercial | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	3,605.9	4,002.5
Commercial | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	1,650.8	1,877.8
Commercial | Lease Financing, net
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	235.7	293.9
Commercial | Other
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	465.0	205.1
Personal
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	18,132.3	18,155.4
Personal | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	7,394.9	8,077.5
Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	10,678.7	10,052.0
Personal | Other
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	58.7	25.9
Performing Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Current	33,141.8	33,511.4
Total Loans and Leases	33,198.8	33,661.9
Performing Financing Receivable | 30-59 Days Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	33.1	101.6
Performing Financing Receivable | 60-89 Days Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	15.2	17.9
Performing Financing Receivable | 90 Days or More Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	8.7	31.0
Performing Financing Receivable | Commercial
Financing Receivable, Recorded Investment [Line Items]
Current	15,177.6	15,620.9
Total Loans and Leases	15,186.7	15,645.9
Performing Financing Receivable | Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Current	9,229.0	9,269.8
Total Loans and Leases	9,237.6	9,278.2
Performing Financing Receivable | Commercial | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Current	3,597.1	3,974.4
Total Loans and Leases	3,597.6	3,990.9
Performing Financing Receivable | Commercial | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Current	1,650.8	1,877.7
Total Loans and Leases	1,650.8	1,877.8
Performing Financing Receivable | Commercial | Lease Financing, net
Financing Receivable, Recorded Investment [Line Items]
Current	235.7	293.9
Total Loans and Leases	235.7	293.9
Performing Financing Receivable | Commercial | Other
Financing Receivable, Recorded Investment [Line Items]
Current	465.0	205.1
Total Loans and Leases	465.0	205.1
Performing Financing Receivable | Commercial | 30-59 Days Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	3.7	16.3
Performing Financing Receivable | Commercial | 30-59 Days Past Due | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Past Due	3.2	5.3
Performing Financing Receivable | Commercial | 30-59 Days Past Due | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	0.5	10.9
Performing Financing Receivable | Commercial | 30-59 Days Past Due | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Past Due		0.1
Performing Financing Receivable | Commercial | 60-89 Days Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	3.4	2.9
Performing Financing Receivable | Commercial | 60-89 Days Past Due | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Past Due	3.4	1.9
Performing Financing Receivable | Commercial | 60-89 Days Past Due | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	0.0	1.0
Performing Financing Receivable | Commercial | 90 Days or More Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	2.0	5.8
Performing Financing Receivable | Commercial | 90 Days or More Past Due | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Past Due	2.0	1.2
Performing Financing Receivable | Commercial | 90 Days or More Past Due | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	0.0	4.6
Performing Financing Receivable | Personal
Financing Receivable, Recorded Investment [Line Items]
Current	17,964.2	17,890.5
Total Loans and Leases	18,012.1	18,016.0
Performing Financing Receivable | Personal | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Current	7,260.7	7,875.9
Total Loans and Leases	7,274.8	7,938.4
Performing Financing Receivable | Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Current	10,644.8	9,988.7
Total Loans and Leases	10,678.6	10,051.7
Performing Financing Receivable | Personal | Other
Financing Receivable, Recorded Investment [Line Items]
Current	58.7	25.9
Total Loans and Leases	58.7	25.9
Performing Financing Receivable | Personal | 30-59 Days Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	29.4	85.3
Performing Financing Receivable | Personal | 30-59 Days Past Due | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	4.0	44.5
Performing Financing Receivable | Personal | 30-59 Days Past Due | Private Client
Financing Receivable, Recorded Investment [Line Items]
Past Due	25.4	40.8
Performing Financing Receivable | Personal | 60-89 Days Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	11.8	15.0
Performing Financing Receivable | Personal | 60-89 Days Past Due | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	5.0	6.5
Performing Financing Receivable | Personal | 60-89 Days Past Due | Private Client
Financing Receivable, Recorded Investment [Line Items]
Past Due	6.8	8.5
Performing Financing Receivable | Personal | 90 Days or More Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	6.7	25.2
Performing Financing Receivable | Personal | 90 Days or More Past Due | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	5.1	11.5
Performing Financing Receivable | Personal | 90 Days or More Past Due | Private Client
Financing Receivable, Recorded Investment [Line Items]
Past Due	1.6	13.7
Nonperforming Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	137.3	160.2
Other Real Estate Owned	8.2	5.2
Total Nonperforming Assets	145.5	165.4
Nonperforming Financing Receivable | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	17.1	20.8
Nonperforming Financing Receivable | Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	8.8	9.2
Nonperforming Financing Receivable | Commercial | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	8.3	11.6
Nonperforming Financing Receivable | Personal
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	120.2	139.4
Nonperforming Financing Receivable | Personal | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	120.1	139.1
Nonperforming Financing Receivable | Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	$ 0.1	$ 0.3