Number of Loans and Leases Modified in TDRs and Total Recorded Investments and Unpaid Principal Balances (Detail) (Class of Financing Receivable, USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014 Contract	Mar. 31, 2013 Contract
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases	36	61
Recorded Investment	$ 4.2	$ 57.1
Unpaid Principal Balance	4.5	59.1
Commercial
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases	1	8
Recorded Investment	0.7	2.6
Unpaid Principal Balance	0.7	3.2
Commercial | Commercial and Institutional
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases		7
Recorded Investment		2.5
Unpaid Principal Balance		3.1
Commercial | Commercial Real Estate Portfolio Segment
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases	1	1
Recorded Investment	0.7	0.1
Unpaid Principal Balance	0.7	0.1
Personal
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases	35	53
Recorded Investment	3.5	54.5
Unpaid Principal Balance	3.8	55.9
Personal | Residential Real Estate
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases	34	48
Recorded Investment	3.5	41.7
Unpaid Principal Balance	3.8	43.1
Personal | Private Client
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases	1	5
Recorded Investment		12.8
Unpaid Principal Balance		$ 12.8