Loans and Leases (Borrower Ratings) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	$ 32,473.2	$ 32,592.2
1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	17,549.8	17,763.2
4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	14,496.9	14,419.6
6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	426.5	409.4
Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	14,885.7	14,558.0
Commercial | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	8,000.0	8,067.1
Commercial | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	6,752.8	6,399.1
Commercial | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	132.9	91.8
Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	8,779.2	9,042.2
Commercial | Commercial and Institutional | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	5,822.2	5,832.9
Commercial | Commercial and Institutional | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	2,885.3	3,133.4
Commercial | Commercial and Institutional | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	71.7	75.9
Commercial | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	3,389.0	3,482.7
Commercial | Real Estate | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	1,189.7	1,280.7
Commercial | Real Estate | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	2,147.5	2,187.5
Commercial | Real Estate | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	51.8	14.5
Commercial | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	2,085.4	1,538.5
Commercial | Non-U.S. | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	609.4	606.6
Commercial | Non-U.S. | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	1,466.6	930.5
Commercial | Non-U.S. | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	9.4	1.4
Commercial | Lease Financing, net
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	156.4	229.2
Commercial | Lease Financing, net | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	118.2	191.4
Commercial | Lease Financing, net | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	38.2	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	475.7	265.4
Commercial | Other | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	260.5	155.5
Commercial | Other | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	215.2	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	17,587.5	18,034.2
Personal | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	9,549.8	9,696.1
Personal | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	7,744.1	8,020.5
Personal | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	293.6	317.6
Personal | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	6,890.5	7,247.6
Personal | Real Estate | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	2,889.2	2,960.5
Personal | Real Estate | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	3,719.6	3,978.8
Personal | Real Estate | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	281.7	308.3
Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	10,651.0	10,753.1
Personal | Private Client | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	6,635.4	6,716.0
Personal | Private Client | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	4,003.7	4,027.8
Personal | Private Client | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	11.9	9.3
Personal | Other
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	46.0	33.5
Personal | Other | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	25.2	19.6
Personal | Other | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	20.8	13.9
Personal | Other | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	$ 0.0	$ 0.0