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	6 Months Ended
	Jun. 30, 2012 Contract	Jun. 30, 2012 Contract
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases	33	71
Recorded Investment	$ 28.4	$ 37.6
Unpaid Principal Balance	32.0	43.1
Commercial
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases	3	9
Recorded Investment	24.6	28.5
Unpaid Principal Balance	27.0	31.3
Commercial | Commercial and Institutional
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases		2
Recorded Investment		0.6
Unpaid Principal Balance		1.1
Commercial | Commercial Real Estate
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases	2	6
Recorded Investment	19.4	22.7
Unpaid Principal Balance	21.8	25.0
Commercial | Lease Financing, net
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases	1	1
Recorded Investment	5.2	5.2
Unpaid Principal Balance	5.2	5.2
Personal
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases	30	62
Recorded Investment	3.8	9.1
Unpaid Principal Balance	5.0	11.8
Personal | Residential Real Estate
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases	29	61
Recorded Investment	3.0	8.3
Unpaid Principal Balance	4.2	11.0
Personal | Private Client
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases	1	1
Recorded Investment	0.8	0.8
Unpaid Principal Balance	$ 0.8	$ 0.8