Loans and Leases - Loans and Leases (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	$ 32,592.2	$ 33,822.1
Allowance for Credit Losses Assigned to Loans and Leases	(131.2)	(161.0)	$ (193.8)
Net Loans and Leases	32,461.0	33,661.1
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	14,558.0	15,666.7
Commercial | Commercial and Institutional
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	9,042.2	9,287.4
Commercial | Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	3,482.7	4,002.5
Commercial | Non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	1,538.5	1,877.8
Commercial | Lease Financing, net
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	229.2	293.9
Commercial | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	265.4	205.1
Personal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	18,034.2	18,155.4
Personal | Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	7,247.6	8,077.5
Personal | Private Client
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	10,753.1	10,052.0
Personal | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	$ 33.5	$ 25.9