Loan and Lease Segment and Class Balances Segregated by Borrower Ratings into "One to Three", "Four to Five" and "Six to Nine" (Watch List) Categories (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	$ 33,822.1	$ 33,180.9
1 TO 3 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	18,079.6	17,910.4
4 TO 5 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	15,255.1	14,688.3
6 TO 9 CATEGORY (WATCH LIST)
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	487.4	582.2
Commercial
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	15,902.3	15,156.5
Commercial | 1 TO 3 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	9,071.5	8,968.9
Commercial | 4 TO 5 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	6,664.3	5,945.5
Commercial | 6 TO 9 CATEGORY (WATCH LIST)
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	166.5	242.1
Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	9,523.0	9,431.5
Commercial | Commercial and Institutional | 1 TO 3 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	6,293.2	6,360.6
Commercial | Commercial and Institutional | 4 TO 5 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	3,108.5	2,897.2
Commercial | Commercial and Institutional | 6 TO 9 CATEGORY (WATCH LIST)
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	121.3	173.7
Commercial | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	4,002.5	3,848.8
Commercial | Real Estate | 1 TO 3 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	1,825.7	1,822.6
Commercial | Real Estate | 4 TO 5 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	2,134.8	1,992.7
Commercial | Real Estate | 6 TO 9 CATEGORY (WATCH LIST)
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	42.0	33.5
Commercial | Lease Financing, net
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	293.9	544.4
Commercial | Lease Financing, net | 1 TO 3 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	214.3	377.0
Commercial | Lease Financing, net | 4 TO 5 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	79.6	133.1
Commercial | Lease Financing, net | 6 TO 9 CATEGORY (WATCH LIST)
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	0.0	34.3
Commercial | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	1,877.8	1,137.7
Commercial | Non-U.S. | 1 TO 3 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	602.8	313.8
Commercial | Non-U.S. | 4 TO 5 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	1,273.5	823.3
Commercial | Non-U.S. | 6 TO 9 CATEGORY (WATCH LIST)
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	1.5	0.6
Commercial | Other
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	205.1	194.1
Commercial | Other | 1 TO 3 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	135.5	94.9
Commercial | Other | 4 TO 5 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	67.9	99.2
Commercial | Other | 6 TO 9 CATEGORY (WATCH LIST)
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	1.7	0.0
Personal
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	17,919.8	18,024.4
Personal | 1 TO 3 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	9,008.1	8,941.5
Personal | 4 TO 5 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	8,590.8	8,742.8
Personal | 6 TO 9 CATEGORY (WATCH LIST)
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	320.9	340.1
Personal | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	7,841.9	8,850.7
Personal | Real Estate | 1 TO 3 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	2,617.8	3,014.9
Personal | Real Estate | 4 TO 5 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	4,913.9	5,516.7
Personal | Real Estate | 6 TO 9 CATEGORY (WATCH LIST)
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	310.2	319.1
Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	10,052.0	9,136.4
Personal | Private Client | 1 TO 3 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	6,373.2	5,908.3
Personal | Private Client | 4 TO 5 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	3,668.4	3,207.1
Personal | Private Client | 6 TO 9 CATEGORY (WATCH LIST)
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	10.4	21.0
Personal | Other
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	25.9	37.3
Personal | Other | 1 TO 3 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	17.1	18.3
Personal | Other | 4 TO 5 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	8.5	19.0
Personal | Other | 6 TO 9 CATEGORY (WATCH LIST)
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	$ 0.3	$ 0.0