Loans and Leases - Borrower Ratings (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	$ 32,490.0	$ 32,592.2
1 TO 3 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	17,692.2	17,763.2
4 TO 5 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	14,403.2	14,419.6
6 TO 9 CATEGORY (WATCH LIST)
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	394.6	409.4
Commercial
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	15,175.2	14,558.0
Commercial | 1 TO 3 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	8,593.9	8,067.1
Commercial | 4 TO 5 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	6,462.4	6,399.1
Commercial | 6 TO 9 CATEGORY (WATCH LIST)
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	118.9	91.8
Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	8,728.1	9,042.2
Commercial | Commercial and Institutional | 1 TO 3 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	5,477.4	5,832.9
Commercial | Commercial and Institutional | 4 TO 5 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	3,159.8	3,133.4
Commercial | Commercial and Institutional | 6 TO 9 CATEGORY (WATCH LIST)
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	90.9	75.9
Commercial | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	3,228.8	3,482.7
Commercial | Real Estate | 1 TO 3 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	1,209.6	1,280.7
Commercial | Real Estate | 4 TO 5 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	1,992.2	2,187.5
Commercial | Real Estate | 6 TO 9 CATEGORY (WATCH LIST)
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	27.0	14.5
Commercial | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	2,701.6	1,538.5
Commercial | Non-U.S. | 1 TO 3 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	1,625.3	606.6
Commercial | Non-U.S. | 4 TO 5 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	1,075.3	930.5
Commercial | Non-U.S. | 6 TO 9 CATEGORY (WATCH LIST)
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	1.0	1.4
Commercial | Lease Financing, net
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	90.7	229.2
Commercial | Lease Financing, net | 1 TO 3 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	78.3	191.4
Commercial | Lease Financing, net | 4 TO 5 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	12.4	37.8
Commercial | Lease Financing, net | 6 TO 9 CATEGORY (WATCH LIST)
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	0.0	0.0
Commercial | Other
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	426.0	265.4
Commercial | Other | 1 TO 3 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	203.3	155.5
Commercial | Other | 4 TO 5 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	222.7	109.9
Commercial | Other | 6 TO 9 CATEGORY (WATCH LIST)
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	0.0	0.0
Personal
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	17,314.8	18,034.2
Personal | 1 TO 3 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	9,098.3	9,696.1
Personal | 4 TO 5 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	7,940.8	8,020.5
Personal | 6 TO 9 CATEGORY (WATCH LIST)
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	275.7	317.6
Personal | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	6,514.0	7,247.6
Personal | Real Estate | 1 TO 3 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	2,745.0	2,960.5
Personal | Real Estate | 4 TO 5 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	3,502.3	3,978.8
Personal | Real Estate | 6 TO 9 CATEGORY (WATCH LIST)
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	266.7	308.3
Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	10,733.3	10,753.1
Personal | Private Client | 1 TO 3 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	6,321.1	6,716.0
Personal | Private Client | 4 TO 5 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	4,403.2	4,027.8
Personal | Private Client | 6 TO 9 CATEGORY (WATCH LIST)
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	9.0	9.3
Personal | Other
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	67.5	33.5
Personal | Other | 1 TO 3 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	32.2	19.6
Personal | Other | 4 TO 5 CATEGORY
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	35.3	13.9
Personal | Other | 6 TO 9 CATEGORY (WATCH LIST)
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	$ 0.0	$ 0.0