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, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Current	$ 33,511.4	$ 32,898.5
Total Loans and Leases	33,822.1	33,180.9
Other Real Estate Owned	5.2	8.2
Total Nonperforming Assets	165.4	188.3
30 – 59 DAYS PAST DUE
Financing Receivable, Recorded Investment [Line Items]
Past Due	101.6	62.9
60 – 89 DAYS PAST DUE
Financing Receivable, Recorded Investment [Line Items]
Past Due	17.9	32.3
90 DAYS OR MORE PAST DUE
Financing Receivable, Recorded Investment [Line Items]
Past Due	31.0	7.1
Commercial
Financing Receivable, Recorded Investment [Line Items]
Current	15,821.1	15,077.1
Total Loans and Leases	15,902.3	15,156.5
Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	9,523.0	9,431.5
Commercial | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	4,002.5	3,848.8
Commercial | Lease Financing, net
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	293.9	544.4
Commercial | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	1,877.8	1,137.7
Commercial | Other
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	205.1	194.1
Commercial | 30 – 59 DAYS PAST DUE
Financing Receivable, Recorded Investment [Line Items]
Past Due	16.3	10.2
Commercial | 60 – 89 DAYS PAST DUE
Financing Receivable, Recorded Investment [Line Items]
Past Due	3.3	5.8
Commercial | 90 DAYS OR MORE PAST DUE
Financing Receivable, Recorded Investment [Line Items]
Past Due	16.3	3.8
Personal
Financing Receivable, Recorded Investment [Line Items]
Current	17,690.3	17,821.4
Total Loans and Leases	17,919.8	18,024.4
Personal | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	7,841.9	8,850.7
Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	10,052.0	9,136.4
Personal | Other
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	25.9	37.3
Personal | 30 – 59 DAYS PAST DUE
Financing Receivable, Recorded Investment [Line Items]
Past Due	85.3	52.7
Personal | 60 – 89 DAYS PAST DUE
Financing Receivable, Recorded Investment [Line Items]
Past Due	14.6	26.5
Personal | 90 DAYS OR MORE PAST DUE
Financing Receivable, Recorded Investment [Line Items]
Past Due	14.7	3.3
Performing Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	33,661.9	33,000.8
Performing Financing Receivable | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	15,857.0	15,096.9
Performing Financing Receivable | Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Current	9,470.0	9,377.6
Total Loans and Leases	9,489.3	9,388.6
Performing Financing Receivable | Commercial | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Current	3,974.4	3,823.3
Total Loans and Leases	3,990.9	3,832.1
Performing Financing Receivable | Commercial | Lease Financing, net
Financing Receivable, Recorded Investment [Line Items]
Current	293.9	544.4
Total Loans and Leases	293.9	544.4
Performing Financing Receivable | Commercial | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Current	1,877.7	1,137.7
Total Loans and Leases	1,877.8	1,137.7
Performing Financing Receivable | Commercial | Other
Financing Receivable, Recorded Investment [Line Items]
Current	205.1	194.1
Total Loans and Leases	205.1	194.1
Performing Financing Receivable | Commercial | 30 – 59 DAYS PAST DUE | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Past Due	5.3	7.8
Performing Financing Receivable | Commercial | 30 – 59 DAYS PAST DUE | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	10.9	2.4
Performing Financing Receivable | Commercial | 30 – 59 DAYS PAST DUE | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Past Due	0.1
Performing Financing Receivable | Commercial | 60 – 89 DAYS PAST DUE | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Past Due	2.3	0.9
Performing Financing Receivable | Commercial | 60 – 89 DAYS PAST DUE | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	1.0	4.9
Performing Financing Receivable | Commercial | 90 DAYS OR MORE PAST DUE | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Past Due	11.7	2.3
Performing Financing Receivable | Commercial | 90 DAYS OR MORE PAST DUE | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	4.6	1.5
Performing Financing Receivable | Personal
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	17,804.9	17,903.9
Performing Financing Receivable | Personal | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Current	7,675.7	8,679.3
Total Loans and Leases	7,727.3	8,730.6
Performing Financing Receivable | Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Current	9,988.7	9,104.8
Total Loans and Leases	10,051.7	9,136.0
Performing Financing Receivable | Personal | Other
Financing Receivable, Recorded Investment [Line Items]
Current	25.9	37.3
Total Loans and Leases	25.9	37.3
Performing Financing Receivable | Personal | 30 – 59 DAYS PAST DUE | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	44.5	35.2
Performing Financing Receivable | Personal | 30 – 59 DAYS PAST DUE | Private Client
Financing Receivable, Recorded Investment [Line Items]
Past Due	40.8	17.5
Performing Financing Receivable | Personal | 60 – 89 DAYS PAST DUE | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	6.1	14.5
Performing Financing Receivable | Personal | 60 – 89 DAYS PAST DUE | Private Client
Financing Receivable, Recorded Investment [Line Items]
Past Due	8.5	12.0
Performing Financing Receivable | Personal | 90 DAYS OR MORE PAST DUE | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Past Due	1.0	1.6
Performing Financing Receivable | Personal | 90 DAYS OR MORE PAST DUE | Private Client
Financing Receivable, Recorded Investment [Line Items]
Past Due	13.7	1.7
Nonperforming Financing Receivable
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	160.2	180.1
Nonperforming Financing Receivable | Commercial
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	45.3	59.6
Nonperforming Financing Receivable | Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	33.7	42.9
Nonperforming Financing Receivable | Commercial | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	11.6	16.7
Nonperforming Financing Receivable | Personal
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	114.9	120.5
Nonperforming Financing Receivable | Personal | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	114.6	120.1
Nonperforming Financing Receivable | Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	$ 0.3	$ 0.4