Loans and Leases (Delinquency Status) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	$ 31,354.0	$ 32,592.2
Commercial
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	13,874.1	14,558.0
Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	8,695.5	9,042.2
Commercial | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	3,288.5	3,482.7
Commercial | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	1,376.0	1,538.5
Commercial | Lease Financing, net
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	154.8	229.2
Commercial | Other
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	359.3	265.4
Personal
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	17,479.9	18,034.2
Personal | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	6,680.9	7,247.6
Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	10,764.3	10,753.1
Personal | Other
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	34.7	33.5
Performing Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Current	31,091.4	32,268.0
Total Loans and Leases	31,240.4	32,441.5
Performing Financing Receivable | 30-59 Days Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	88.9	136.7
Performing Financing Receivable | 60-89 Days Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	32.6	28.8
Performing Financing Receivable | 90 Days or More Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	27.5	8.0
Performing Financing Receivable | Commercial
Financing Receivable, Recorded Investment [Line Items]
Current	13,821.1	14,487.6
Total Loans and Leases	13,858.2	14,523.7
Performing Financing Receivable | Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Current	8,658.6	8,999.4
Total Loans and Leases	8,686.2	9,016.2
Performing Financing Receivable | Commercial | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Current	3,272.4	3,455.3
Total Loans and Leases	3,281.9	3,474.4
Performing Financing Receivable | Commercial | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Current	1,376.0	1,538.3
Total Loans and Leases	1,376.0	1,538.5
Performing Financing Receivable | Commercial | Lease Financing, net
Financing Receivable, Recorded Investment [Line Items]
Current	154.8	229.2
Total Loans and Leases	154.8	229.2
Performing Financing Receivable | Commercial | Other
Financing Receivable, Recorded Investment [Line Items]
Current	359.3	265.4
Total Loans and Leases	359.3	265.4
Performing Financing Receivable | Commercial | 30-59 Days Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	27.9	27.6
Performing Financing Receivable | Commercial | 30-59 Days Past Due | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Past Due	24.1	13.3
Performing Financing Receivable | Commercial | 30-59 Days Past Due | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	3.8	14.1
Performing Financing Receivable | Commercial | 30-59 Days Past Due | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Past Due	0.0	0.2
Performing Financing Receivable | Commercial | 60-89 Days Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	9.1	7.2
Performing Financing Receivable | Commercial | 60-89 Days Past Due | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Past Due	3.4	3.1
Performing Financing Receivable | Commercial | 60-89 Days Past Due | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	5.7	4.1
Performing Financing Receivable | Commercial | 90 Days or More Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	0.1	1.3
Performing Financing Receivable | Commercial | 90 Days or More Past Due | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Past Due	0.1	0.4
Performing Financing Receivable | Commercial | 90 Days or More Past Due | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	0.0	0.9
Performing Financing Receivable | Personal
Financing Receivable, Recorded Investment [Line Items]
Current	17,270.3	17,780.4
Total Loans and Leases	17,382.2	17,917.8
Performing Financing Receivable | Personal | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Current	6,566.2	7,059.4
Total Loans and Leases	6,583.6	7,131.2
Performing Financing Receivable | Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Current	10,669.4	10,687.5
Total Loans and Leases	10,763.9	10,753.1
Performing Financing Receivable | Personal | Other
Financing Receivable, Recorded Investment [Line Items]
Current	34.7	33.5
Total Loans and Leases	34.7	33.5
Performing Financing Receivable | Personal | 30-59 Days Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	61.0	109.1
Performing Financing Receivable | Personal | 30-59 Days Past Due | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	4.2	53.8
Performing Financing Receivable | Personal | 30-59 Days Past Due | Private Client
Financing Receivable, Recorded Investment [Line Items]
Past Due	56.8	55.3
Performing Financing Receivable | Personal | 60-89 Days Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	23.5	21.6
Performing Financing Receivable | Personal | 60-89 Days Past Due | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	12.6	11.9
Performing Financing Receivable | Personal | 60-89 Days Past Due | Private Client
Financing Receivable, Recorded Investment [Line Items]
Past Due	10.9	9.7
Performing Financing Receivable | Personal | 90 Days or More Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	27.4	6.7
Performing Financing Receivable | Personal | 90 Days or More Past Due | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	0.6	6.1
Performing Financing Receivable | Personal | 90 Days or More Past Due | Private Client
Financing Receivable, Recorded Investment [Line Items]
Past Due	26.8	0.6
Nonperforming Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	113.6	150.7
Other Real Estate Owned	11.3	4.6
Total Nonperforming Assets	124.9	155.3
Nonperforming Financing Receivable | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	15.9	34.3
Nonperforming Financing Receivable | Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	9.3	26.0
Nonperforming Financing Receivable | Commercial | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	6.6	8.3
Nonperforming Financing Receivable | Personal
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	97.7	116.4
Nonperforming Financing Receivable | Personal | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	97.3	116.4
Nonperforming Financing Receivable | Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	$ 0.4	$ 0.0