Loans and Leases - Borrower Ratings (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	$ 31,409.6	$ 32,490.0
1 TO 3 CATEGORY
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	15,979.6	17,692.2
4 TO 5 CATEGORY
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	14,936.9	14,403.2
6 TO 9 CATEGORY (WATCH LIST)
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	493.1	394.6
Commercial
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	14,274.2	15,175.2
Commercial | 1 TO 3 CATEGORY
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	7,857.7	8,593.9
Commercial | 4 TO 5 CATEGORY
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	6,139.9	6,462.4
Commercial | 6 TO 9 CATEGORY (WATCH LIST)
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	276.6	118.9
Commercial | Commercial and Institutional
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	8,915.6	8,728.1
Commercial | Commercial and Institutional | 1 TO 3 CATEGORY
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	5,890.8	5,477.4
Commercial | Commercial and Institutional | 4 TO 5 CATEGORY
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	2,912.9	3,159.8
Commercial | Commercial and Institutional | 6 TO 9 CATEGORY (WATCH LIST)
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	111.9	90.9
Commercial | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	3,378.0	3,228.8
Commercial | Real Estate | 1 TO 3 CATEGORY
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	1,126.8	1,209.6
Commercial | Real Estate | 4 TO 5 CATEGORY
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	2,237.3	1,992.2
Commercial | Real Estate | 6 TO 9 CATEGORY (WATCH LIST)
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	13.9	27.0
Commercial | Non-U.S.
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	1,751.0	2,701.6
Commercial | Non-U.S. | 1 TO 3 CATEGORY
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	717.0	1,625.3
Commercial | Non-U.S. | 4 TO 5 CATEGORY
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	883.2	1,075.3
Commercial | Non-U.S. | 6 TO 9 CATEGORY (WATCH LIST)
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	150.8	1.0
Commercial | Lease Financing, net
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	65.6	90.7
Commercial | Lease Financing, net | 1 TO 3 CATEGORY
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	53.6	78.3
Commercial | Lease Financing, net | 4 TO 5 CATEGORY
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	12.0	12.4
Commercial | Lease Financing, net | 6 TO 9 CATEGORY (WATCH LIST)
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	0.0	0.0
Commercial | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	164.0	426.0
Commercial | Other | 1 TO 3 CATEGORY
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	69.5	203.3
Commercial | Other | 4 TO 5 CATEGORY
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	94.5	222.7
Commercial | Other | 6 TO 9 CATEGORY (WATCH LIST)
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	0.0	0.0
Personal
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	17,135.4	17,314.8
Personal | 1 TO 3 CATEGORY
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	8,121.9	9,098.3
Personal | 4 TO 5 CATEGORY
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	8,797.0	7,940.8
Personal | 6 TO 9 CATEGORY (WATCH LIST)
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	216.5	275.7
Personal | Real Estate
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	5,999.6	6,514.0
Personal | Real Estate | 1 TO 3 CATEGORY
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	2,638.1	2,745.0
Personal | Real Estate | 4 TO 5 CATEGORY
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	3,185.4	3,502.3
Personal | Real Estate | 6 TO 9 CATEGORY (WATCH LIST)
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	176.1	266.7
Personal | Private Client
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	11,068.7	10,733.3
Personal | Private Client | 1 TO 3 CATEGORY
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	5,455.3	6,321.1
Personal | Private Client | 4 TO 5 CATEGORY
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	5,573.0	4,403.2
Personal | Private Client | 6 TO 9 CATEGORY (WATCH LIST)
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	40.4	9.0
Personal | Other
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	67.1	67.5
Personal | Other | 1 TO 3 CATEGORY
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	28.5	32.2
Personal | Other | 4 TO 5 CATEGORY
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	38.6	35.3
Personal | Other | 6 TO 9 CATEGORY (WATCH LIST)
Financing Receivable, Credit Quality Indicator [Line Items]
Total Loans and Leases	$ 0.0	$ 0.0