Loans and Leases (Borrower Ratings) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	$ 30,620.6	$ 32,490.0
1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	16,126.4	17,692.2
4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	14,090.5	14,403.2
6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	403.7	394.6
Commercial
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	13,635.5	15,175.2
Commercial | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	7,591.5	8,593.9
Commercial | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	5,901.7	6,462.4
Commercial | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	142.3	118.9
Commercial | Commercial and Institutional
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	8,532.1	8,728.1
Commercial | Commercial and Institutional | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	5,293.4	5,477.4
Commercial | Commercial and Institutional | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	3,118.6	3,159.8
Commercial | Commercial and Institutional | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	120.1	90.9
Commercial | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	3,185.0	3,228.8
Commercial | Real Estate | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	1,095.2	1,209.6
Commercial | Real Estate | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	2,068.8	1,992.2
Commercial | Real Estate | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	21.0	27.0
Commercial | Non-U.S.
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	1,648.6	2,701.6
Commercial | Non-U.S. | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	1,021.1	1,625.3
Commercial | Non-U.S. | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	626.3	1,075.3
Commercial | Non-U.S. | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	1.2	1.0
Commercial | Lease Financing, net
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	89.3	90.7
Commercial | Lease Financing, net | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	76.9	78.3
Commercial | Lease Financing, net | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	12.4	12.4
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	180.5	426.0
Commercial | Other | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	104.9	203.3
Commercial | Other | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	75.6	222.7
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	16,985.1	17,314.8
Personal | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	8,534.9	9,098.3
Personal | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	8,188.8	7,940.8
Personal | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	261.4	275.7
Personal | Real Estate
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	6,286.6	6,514.0
Personal | Real Estate | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	2,535.3	2,745.0
Personal | Real Estate | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	3,496.6	3,502.3
Personal | Real Estate | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	254.7	266.7
Personal | Private Client
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	10,669.9	10,733.3
Personal | Private Client | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	5,983.0	6,321.1
Personal | Private Client | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	4,680.2	4,403.2
Personal | Private Client | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	6.7	9.0
Personal | Other
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	28.6	67.5
Personal | Other | 1 to 3 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	16.6	32.2
Personal | Other | 4 to 5 Category
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	12.0	35.3
Personal | Other | 6 to 9 Category (Watch List)
Financing Receivable, Recorded Investment [Line Items]
Total loans and leases	$ 0.0	$ 0.0