Loans and Leases - Loans and Leases (Detail) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	$ 32,490.0	$ 32,592.2
Allowance for Credit Losses Assigned to Loans and Leases	(112.6)	(131.2)	$ (161.0)
Net Loans and Leases	32,377.4	32,461.0
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	15,175.2	14,558.0
Commercial | Commercial and Institutional
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	8,728.1	9,042.2
Commercial | Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	3,228.8	3,482.7
Commercial | Non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	2,701.6	1,538.5
Commercial | Lease Financing, net
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	90.7	229.2
Commercial | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	426.0	265.4
Personal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	17,314.8	18,034.2
Personal | Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	6,514.0	7,247.6
Personal | Private Client
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	10,733.3	10,753.1
Personal | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	$ 67.5	$ 33.5