Loans and Leases (Borrower Ratings) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	$ 31,354.0	$ 32,592.2
1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	17,143.5	17,763.2
4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	13,804.6	14,419.6
6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	405.9	409.4
Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	13,874.1	14,558.0
Commercial | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	7,548.7	8,067.1
Commercial | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	6,209.1	6,399.1
Commercial | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	116.3	91.8
Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	8,695.5	9,042.2
Commercial | Commercial and Institutional | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	5,389.2	5,832.9
Commercial | Commercial and Institutional | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	3,220.8	3,133.4
Commercial | Commercial and Institutional | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	85.5	75.9
Commercial | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	3,288.5	3,482.7
Commercial | Real Estate | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	1,275.9	1,280.7
Commercial | Real Estate | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	1,984.9	2,187.5
Commercial | Real Estate | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	27.7	14.5
Commercial | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	1,376.0	1,538.5
Commercial | Non-U.S. | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	591.8	606.6
Commercial | Non-U.S. | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	781.1	930.5
Commercial | Non-U.S. | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	3.1	1.4
Commercial | Lease Financing, net
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	154.8	229.2
Commercial | Lease Financing, net | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	116.4	191.4
Commercial | Lease Financing, net | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	38.4	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	359.3	265.4
Commercial | Other | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	175.4	155.5
Commercial | Other | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	183.9	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	17,479.9	18,034.2
Personal | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	9,594.8	9,696.1
Personal | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	7,595.5	8,020.5
Personal | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	289.6	317.6
Personal | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	6,680.9	7,247.6
Personal | Real Estate | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	2,839.4	2,960.5
Personal | Real Estate | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	3,564.1	3,978.8
Personal | Real Estate | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	277.4	308.3
Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	10,764.3	10,753.1
Personal | Private Client | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	6,738.4	6,716.0
Personal | Private Client | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	4,013.7	4,027.8
Personal | Private Client | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	12.2	9.3
Personal | Other
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	34.7	33.5
Personal | Other | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	17.0	19.6
Personal | Other | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	17.7	13.9
Personal | Other | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	$ 0.0	$ 0.0