Loans and Leases (Delinquency Status) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	$ 32,473.2	$ 32,592.2
Commercial
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	14,885.7	14,558.0
Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	8,779.2	9,042.2
Commercial | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	3,389.0	3,482.7
Commercial | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	2,085.4	1,538.5
Commercial | Lease Financing, net
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	156.4	229.2
Commercial | Other
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	475.7	265.4
Personal
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	17,587.5	18,034.2
Personal | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	6,890.5	7,247.6
Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	10,651.0	10,753.1
Personal | Other
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	46.0	33.5
Performing Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Current	32,213.4	32,268.0
Total Loans and Leases	32,344.8	32,441.5
Performing Financing Receivable | 30-59 Days Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	112.4	136.7
Performing Financing Receivable | 60-89 Days Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	13.8	28.8
Performing Financing Receivable | 90 Days or More Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	5.2	8.0
Performing Financing Receivable | Commercial
Financing Receivable, Recorded Investment [Line Items]
Current	14,820.5	14,487.6
Total Loans and Leases	14,864.9	14,523.7
Performing Financing Receivable | Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Current	8,754.9	8,999.4
Total Loans and Leases	8,765.1	9,016.2
Performing Financing Receivable | Commercial | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Current	3,348.1	3,455.3
Total Loans and Leases	3,382.3	3,474.4
Performing Financing Receivable | Commercial | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Current	2,085.4	1,538.3
Total Loans and Leases	2,085.4	1,538.5
Performing Financing Receivable | Commercial | Lease Financing, net
Financing Receivable, Recorded Investment [Line Items]
Current	156.4	229.2
Total Loans and Leases	156.4	229.2
Performing Financing Receivable | Commercial | Other
Financing Receivable, Recorded Investment [Line Items]
Current	475.7	265.4
Total Loans and Leases	475.7	265.4
Performing Financing Receivable | Commercial | 30-59 Days Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	43.7	27.6
Performing Financing Receivable | Commercial | 30-59 Days Past Due | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Past Due	9.5	13.3
Performing Financing Receivable | Commercial | 30-59 Days Past Due | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	34.2	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	0.7	7.2
Performing Financing Receivable | Commercial | 60-89 Days Past Due | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Past Due	0.7	3.1
Performing Financing Receivable | Commercial | 60-89 Days Past Due | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	0.0	4.1
Performing Financing Receivable | Commercial | 90 Days or More Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	0.0	1.3
Performing Financing Receivable | Commercial | 90 Days or More Past Due | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Past Due	0.0	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	17,392.9	17,780.4
Total Loans and Leases	17,479.9	17,917.8
Performing Financing Receivable | Personal | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Current	6,765.4	7,059.4
Total Loans and Leases	6,782.9	7,131.2
Performing Financing Receivable | Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Current	10,581.5	10,687.5
Total Loans and Leases	10,651.0	10,753.1
Performing Financing Receivable | Personal | Other
Financing Receivable, Recorded Investment [Line Items]
Current	46.0	33.5
Total Loans and Leases	46.0	33.5
Performing Financing Receivable | Personal | 30-59 Days Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	68.7	109.1
Performing Financing Receivable | Personal | 30-59 Days Past Due | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	3.9	53.8
Performing Financing Receivable | Personal | 30-59 Days Past Due | Private Client
Financing Receivable, Recorded Investment [Line Items]
Past Due	64.8	55.3
Performing Financing Receivable | Personal | 60-89 Days Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	13.1	21.6
Performing Financing Receivable | Personal | 60-89 Days Past Due | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	11.6	11.9
Performing Financing Receivable | Personal | 60-89 Days Past Due | Private Client
Financing Receivable, Recorded Investment [Line Items]
Past Due	1.5	9.7
Performing Financing Receivable | Personal | 90 Days or More Past Due
Financing Receivable, Recorded Investment [Line Items]
Past Due	5.2	6.7
Performing Financing Receivable | Personal | 90 Days or More Past Due | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	2.0	6.1
Performing Financing Receivable | Personal | 90 Days or More Past Due | Private Client
Financing Receivable, Recorded Investment [Line Items]
Past Due	3.2	0.6
Nonperforming Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	128.4	150.7
Other Real Estate Owned	3.8	4.6
Total Nonperforming Assets	132.2	155.3
Nonperforming Financing Receivable | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	20.8	34.3
Nonperforming Financing Receivable | Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	14.1	26.0
Nonperforming Financing Receivable | Commercial | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	6.7	8.3
Nonperforming Financing Receivable | Personal
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	107.6	116.4
Nonperforming Financing Receivable | Personal | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	107.6	116.4
Nonperforming Financing Receivable | Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	$ 0.0	$ 0.0