Balances and Delinquency Status of Performing and Nonperforming Loans and Leases by Segment and Class as well as Total Other Real Estate Owned and Nonperforming Asset Balances (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Financing Receivable, Recorded Investment [Line Items]
Other Real Estate Owned	$ 16.6	$ 11.9
Total Nonperforming Assets	232.3	274.7
Total Loans and Leases	31,640.2	29,385.5
Commercial
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	14,353.6	12,620.0
Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	8,381.9	7,375.8
Commercial | Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	3,333.3	2,955.8
Commercial | Lease Financing, net
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	916.3	975.1
Commercial | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	1,530.6	954.7
Commercial | Other
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	191.5	358.6
Personal
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	17,286.6	16,765.5
Personal | Residential Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	9,782.6	10,271.3
Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	7,466.9	6,445.6
Personal | Other
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	37.1	48.6
Performing Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Current	31,242.6	28,889.0
30-59 Days Past Due	129.6	167.5
60-89 Days Past Due	29.6	49.8
90 Days or More Past Due	22.7	16.4
Total Loans and Leases	31,424.5	29,122.7
Performing Financing Receivable | Commercial
Financing Receivable, Recorded Investment [Line Items]
Current	14,253.2	12,501.8
30-59 Days Past Due	24.1	9.1
60-89 Days Past Due	13.8	26.7
90 Days or More Past Due	10.4	10.1
Total Loans and Leases	14,301.5	12,547.7
Performing Financing Receivable | Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Current	8,340.5	7,332.3
30-59 Days Past Due	14.5	5.0
60-89 Days Past Due	4.0	12.1
90 Days or More Past Due	7.9	3.3
Total Loans and Leases	8,366.9	7,352.7
Performing Financing Receivable | Commercial | Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Current	3,274.3	2,881.1
30-59 Days Past Due	9.6	4.1
60-89 Days Past Due	9.8	14.6
90 Days or More Past Due	2.5	6.8
Total Loans and Leases	3,296.2	2,906.6
Performing Financing Receivable | Commercial | Lease Financing, net
Financing Receivable, Recorded Investment [Line Items]
Current	916.3	975.1
Total Loans and Leases	916.3	975.1
Performing Financing Receivable | Commercial | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Current	1,530.6	954.7
Total Loans and Leases	1,530.6	954.7
Performing Financing Receivable | Commercial | Other
Financing Receivable, Recorded Investment [Line Items]
Current	191.5	358.6
Total Loans and Leases	191.5	358.6
Performing Financing Receivable | Personal
Financing Receivable, Recorded Investment [Line Items]
Current	16,989.4	16,387.2
30-59 Days Past Due	105.5	158.4
60-89 Days Past Due	15.8	23.1
90 Days or More Past Due	12.3	6.3
Total Loans and Leases	17,123.0	16,575.0
Performing Financing Receivable | Personal | Residential Real Estate
Financing Receivable, Recorded Investment [Line Items]
Current	9,556.3	9,934.4
30-59 Days Past Due	49.5	129.3
60-89 Days Past Due	9.9	15.6
90 Days or More Past Due	4.5	2.9
Total Loans and Leases	9,620.2	10,082.2
Performing Financing Receivable | Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Current	7,396.0	6,404.2
30-59 Days Past Due	56.0	29.1
60-89 Days Past Due	5.9	7.5
90 Days or More Past Due	7.8	3.4
Total Loans and Leases	7,465.7	6,444.2
Performing Financing Receivable | Personal | Other
Financing Receivable, Recorded Investment [Line Items]
Current	37.1	48.6
Total Loans and Leases	37.1	48.6
Nonperforming Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	215.7	262.8
Nonperforming Financing Receivable | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	52.1	72.3
Nonperforming Financing Receivable | Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	15.0	23.1
Nonperforming Financing Receivable | Commercial | Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	37.1	49.2
Nonperforming Financing Receivable | Personal
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	163.6	190.5
Nonperforming Financing Receivable | Personal | Residential Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	162.4	189.1
Nonperforming Financing Receivable | Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	$ 1.2	$ 1.4