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, 2013 Contract	Mar. 31, 2012 Contract
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases	61	38
Recorded Investment	$ 57.1	$ 10.1
Unpaid Principal Balance	59.1	11.9
Commercial
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases	8	6
Recorded Investment	2.6	4.5
Unpaid Principal Balance	3.2	5.0
Commercial | Commercial Real Estate Portfolio Segment
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases	1	4
Recorded Investment	0.1	3.8
Unpaid Principal Balance	0.1	3.8
Commercial | Commercial and Institutional
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases	7	2
Recorded Investment	2.5	0.7
Unpaid Principal Balance	3.1	1.2
Personal
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases	53	32
Recorded Investment	54.5	5.6
Unpaid Principal Balance	55.9	6.9
Personal | Residential Real Estate
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases	48	32
Recorded Investment	41.7	5.6
Unpaid Principal Balance	43.1	6.9
Personal | Private Client
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases	5
Recorded Investment	12.8
Unpaid Principal Balance	$ 12.8