Amounts Outstanding for Loans and Leases by Segment and Class (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	$ 33,822.1	$ 33,180.9
Allowance for Credit Losses Assigned to Loans and Leases	(161.0)	(193.8)	$ (267.0)
Net Loans and Leases	33,661.1	32,987.1
Commercial
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	15,902.3	15,156.5
Allowance for Credit Losses Assigned to Loans and Leases	(83.7)	(86.3)	(143.8)
Commercial | Commercial and Institutional
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	9,523.0	9,431.5
Commercial | Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	4,002.5	3,848.8
Commercial | Lease Financing, net
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	293.9	544.4
Commercial | Non-U.S.
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	1,877.8	1,137.7
Commercial | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	205.1	194.1
Personal
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	17,919.8	18,024.4
Allowance for Credit Losses Assigned to Loans and Leases	(77.3)	(107.5)	$ (123.2)
Personal | Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	7,841.9	8,850.7
Personal | Private Client
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	10,052.0	9,136.4
Personal | Other
Accounts, Notes, Loans and Financing Receivable [Line Items]
Total Loans and Leases	$ 25.9	$ 37.3