Balances and Delinquency Status of Performing and Nonperforming Loans and Leases by Segment and Class as well as Total OREO and Nonperforming Asset Balances (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Other Real Estate Owned	$ 8.5	$ 16.6
Total Nonperforming Assets	228.1	232.3
Total Loans and Leases	32,630.2	31,640.2
Commercial
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	15,491.3	14,353.6
Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	9,030.2	8,381.9
Commercial | Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	3,500.9	3,333.3
Commercial | Lease Financing, net
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	870.6	916.3
Commercial | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	1,661.6	1,530.6
Commercial | Other
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	428.0	191.5
Personal
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	17,138.9	17,286.6
Personal | Residential Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	9,440.2	9,782.6
Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	7,615.8	7,466.9
Personal | Other
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	82.9	37.1
Performing Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Current	32,280.3	31,242.6
30-59 Days Past Due	101.7	129.6
60-89 Days Past Due	19.2	29.6
90 Days or More Past Due	9.4	22.7
Total Loans and Leases	32,410.6	31,424.5
Performing Financing Receivable | Commercial
Financing Receivable, Recorded Investment [Line Items]
Current	15,383.5	14,253.2
30-59 Days Past Due	31.4	24.1
60-89 Days Past Due	9.4	13.8
90 Days or More Past Due	6.2	10.4
Total Loans and Leases	15,430.5	14,301.5
Performing Financing Receivable | Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Current	8,980.4	8,340.5
30-59 Days Past Due	21.2	14.5
60-89 Days Past Due	4.6	4.0
90 Days or More Past Due	3.1	7.9
Total Loans and Leases	9,009.3	8,366.9
Performing Financing Receivable | Commercial | Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Current	3,442.9	3,274.3
30-59 Days Past Due	10.2	9.6
60-89 Days Past Due	4.8	9.8
90 Days or More Past Due	3.1	2.5
Total Loans and Leases	3,461.0	3,296.2
Performing Financing Receivable | Commercial | Lease Financing, net
Financing Receivable, Recorded Investment [Line Items]
Current	870.6	916.3
Total Loans and Leases	870.6	916.3
Performing Financing Receivable | Commercial | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Current	1,661.6	1,530.6
Total Loans and Leases	1,661.6	1,530.6
Performing Financing Receivable | Commercial | Other
Financing Receivable, Recorded Investment [Line Items]
Current	428.0	191.5
Total Loans and Leases	428.0	191.5
Performing Financing Receivable | Personal
Financing Receivable, Recorded Investment [Line Items]
Current	16,896.8	16,989.4
30-59 Days Past Due	70.3	105.5
60-89 Days Past Due	9.8	15.8
90 Days or More Past Due	3.2	12.3
Total Loans and Leases	16,980.1	17,123.0
Performing Financing Receivable | Personal | Residential Real Estate
Financing Receivable, Recorded Investment [Line Items]
Current	9,240.2	9,556.3
30-59 Days Past Due	37.5	49.5
60-89 Days Past Due	2.6	9.9
90 Days or More Past Due	2.2	4.5
Total Loans and Leases	9,282.5	9,620.2
Performing Financing Receivable | Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Current	7,573.7	7,396.0
30-59 Days Past Due	32.8	56.0
60-89 Days Past Due	7.2	5.9
90 Days or More Past Due	1.0	7.8
Total Loans and Leases	7,614.7	7,465.7
Performing Financing Receivable | Personal | Other
Financing Receivable, Recorded Investment [Line Items]
Current	82.9	37.1
Total Loans and Leases	82.9	37.1
Nonperforming Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	219.6	215.7
Nonperforming Financing Receivable | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	60.8	52.1
Nonperforming Financing Receivable | Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	20.9	15.0
Nonperforming Financing Receivable | Commercial | Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	39.9	37.1
Nonperforming Financing Receivable | Personal
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	158.8	163.6
Nonperforming Financing Receivable | Personal | Residential Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	157.7	162.4
Nonperforming Financing Receivable | Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	$ 1.1	$ 1.2