Loans and Leases - Loans and Leases (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	$ 31,409.6	$ 32,490.0
Allowance for Credit Losses Assigned to Loans and Leases	(104.5)	(112.6)	$ (131.2)
Net Loans and Leases	31,305.1	32,377.4
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	14,274.2	15,175.2
Commercial | Commercial and Institutional
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	8,915.6	8,728.1
Commercial | Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	3,378.0	3,228.8
Commercial | Non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	1,751.0	2,701.6
Commercial | Lease Financing, net
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	65.6	90.7
Commercial | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	164.0	426.0
Personal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	17,135.4	17,314.8
Personal | Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	5,999.6	6,514.0
Personal | Private Client
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	11,068.7	10,733.3
Personal | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	$ 67.1	$ 67.5