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	Dec. 31, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	$ 33,180.9	$ 31,640.2
Other Real Estate Owned	8.2	16.6
Total Nonperforming Assets	188.3	232.3
Commercial
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	15,156.5	14,353.6
Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	9,431.5	8,381.9
Commercial | Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	3,848.8	3,333.3
Commercial | Lease Financing, net
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	544.4	916.3
Commercial | Other
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	194.1	191.5
Personal
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	18,024.4	17,286.6
Personal | Residential Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	8,850.7	9,782.6
Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	9,136.4	7,466.9
Personal | Other
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	37.3	37.1
Performing Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Current	32,898.5	31,242.6
Total Loans and Leases	33,000.8	31,424.5
Performing Financing Receivable | Commercial
Financing Receivable, Recorded Investment [Line Items]
Current	15,077.1	14,253.2
Total Loans and Leases	15,096.9	14,301.5
Performing Financing Receivable | Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Current	9,377.6	8,340.5
Total Loans and Leases	9,388.6	8,366.9
Performing Financing Receivable | Commercial | Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Current	3,823.3	3,274.3
Total Loans and Leases	3,832.1	3,296.2
Performing Financing Receivable | Commercial | Lease Financing, net
Financing Receivable, Recorded Investment [Line Items]
Current	544.4	916.3
Total Loans and Leases	544.4	916.3
Performing Financing Receivable | Commercial | Other
Financing Receivable, Recorded Investment [Line Items]
Current	194.1	191.5
Total Loans and Leases	194.1	191.5
Performing Financing Receivable | Personal
Financing Receivable, Recorded Investment [Line Items]
Current	17,821.4	16,989.4
Total Loans and Leases	17,903.9	17,123.0
Performing Financing Receivable | Personal | Residential Real Estate
Financing Receivable, Recorded Investment [Line Items]
Current	8,679.3	9,556.3
Total Loans and Leases	8,730.6	9,620.2
Performing Financing Receivable | Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Current	9,104.8	7,396.0
Total Loans and Leases	9,136.0	7,465.7
Performing Financing Receivable | Personal | Other
Financing Receivable, Recorded Investment [Line Items]
Current	37.3	37.1
Total Loans and Leases	37.3	37.1
Nonperforming Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	180.1	215.7
Nonperforming Financing Receivable | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	59.6	52.1
Nonperforming Financing Receivable | Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	42.9	15.0
Nonperforming Financing Receivable | Commercial | Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	16.7	37.1
Nonperforming Financing Receivable | Personal
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	120.5	163.6
Nonperforming Financing Receivable | Personal | Residential Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	120.1	162.4
Nonperforming Financing Receivable | Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	0.4	1.2
30 – 59 DAYS PAST DUE | Performing Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Past Due	62.9	129.6
30 – 59 DAYS PAST DUE | Performing Financing Receivable | Commercial
Financing Receivable, Recorded Investment [Line Items]
Past Due	10.2	24.1
30 – 59 DAYS PAST DUE | Performing Financing Receivable | Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Past Due	7.8	14.5
30 – 59 DAYS PAST DUE | Performing Financing Receivable | Commercial | Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	2.4	9.6
30 – 59 DAYS PAST DUE | Performing Financing Receivable | Personal
Financing Receivable, Recorded Investment [Line Items]
Past Due	52.7	105.5
30 – 59 DAYS PAST DUE | Performing Financing Receivable | Personal | Residential Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	35.2	49.5
30 – 59 DAYS PAST DUE | Performing Financing Receivable | Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Past Due	17.5	56.0
60 – 89 DAYS PAST DUE | Performing Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Past Due	32.3	29.6
60 – 89 DAYS PAST DUE | Performing Financing Receivable | Commercial
Financing Receivable, Recorded Investment [Line Items]
Past Due	5.8	13.8
60 – 89 DAYS PAST DUE | Performing Financing Receivable | Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Past Due	0.9	4.0
60 – 89 DAYS PAST DUE | Performing Financing Receivable | Commercial | Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	4.9	9.8
60 – 89 DAYS PAST DUE | Performing Financing Receivable | Personal
Financing Receivable, Recorded Investment [Line Items]
Past Due	26.5	15.8
60 – 89 DAYS PAST DUE | Performing Financing Receivable | Personal | Residential Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	14.5	9.9
60 – 89 DAYS PAST DUE | Performing Financing Receivable | Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Past Due	12.0	5.9
90 DAYS OR MORE PAST DUE | Performing Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Past Due	7.1	22.7
90 DAYS OR MORE PAST DUE | Performing Financing Receivable | Commercial
Financing Receivable, Recorded Investment [Line Items]
Past Due	3.8	10.4
90 DAYS OR MORE PAST DUE | Performing Financing Receivable | Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Past Due	2.3	7.9
90 DAYS OR MORE PAST DUE | Performing Financing Receivable | Commercial | Commercial Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	1.5	2.5
90 DAYS OR MORE PAST DUE | Performing Financing Receivable | Personal
Financing Receivable, Recorded Investment [Line Items]
Past Due	3.3	12.3
90 DAYS OR MORE PAST DUE | Performing Financing Receivable | Personal | Residential Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	1.6	4.5
90 DAYS OR MORE PAST DUE | Performing Financing Receivable | Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Past Due	1.7	7.8
Non-US | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	1,137.7	1,530.6
Non-US | Performing Financing Receivable | Commercial
Financing Receivable, Recorded Investment [Line Items]
Current	1,137.7	1,530.6
Total Loans and Leases	$ 1,137.7	$ 1,530.6