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, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	$ 32,630.2	$ 31,640.2
1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	16,168.0	16,322.9
4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	15,830.1	14,680.4
6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total Loans and Leases	632.1	636.9
Commercial
Financing Receivable, Recorded Investment [Line Items]
Commercial and Institutional	9,030.2	8,381.9
Commercial Real Estate	3,500.9	3,333.3
Lease Financing, net	870.6	916.3
Non-U.S.	1,661.6	1,530.6
Other	428.0	191.5
Total Loans and Leases	15,491.3	14,353.6
Commercial | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Commercial and Institutional	5,628.3	5,340.9
Commercial Real Estate	1,452.5	1,371.7
Lease Financing, net	510.6	552.5
Non-U.S.	513.8	636.8
Other	353.0	108.1
Total Loans and Leases	8,458.2	8,010.0
Commercial | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Commercial and Institutional	3,314.9	2,947.3
Commercial Real Estate	1,949.9	1,861.8
Lease Financing, net	324.0	360.3
Non-U.S.	1,147.6	892.9
Other	75.0	83.4
Total Loans and Leases	6,811.4	6,145.7
Commercial | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Commercial and Institutional	87.0	93.7
Commercial Real Estate	98.5	99.8
Lease Financing, net	36.0	3.5
Non-U.S.	0.2	0.9
Total Loans and Leases	221.7	197.9
Personal
Financing Receivable, Recorded Investment [Line Items]
Residential Real Estate	9,440.2	9,782.6
Private Client	7,615.8	7,466.9
Other	82.9	37.1
Total Loans and Leases	17,138.9	17,286.6
Personal | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Residential Real Estate	2,734.2	3,148.0
Private Client	4,907.1	5,143.8
Other	68.5	21.1
Total Loans and Leases	7,709.8	8,312.9
Personal | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Residential Real Estate	6,304.9	6,207.0
Private Client	2,699.4	2,311.7
Other	14.4	16.0
Total Loans and Leases	9,018.7	8,534.7
Personal | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Residential Real Estate	401.1	427.6
Private Client	9.3	11.4
Total Loans and Leases	$ 410.4	$ 439.0