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		9 Months Ended
	Sep. 30, 2014 Contract	Sep. 30, 2013 Contract	Sep. 30, 2014 Contract	Sep. 30, 2013 Contract
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases	34	45	108	146
Recorded Investment	$ 21.3	$ 29.5	$ 29.5	$ 91.9
Unpaid Principal Balance	22.5	36.4	32.3	105.5
Commercial
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases	6	7	9	18
Recorded Investment	3.3	22.8	4.2	27.9
Unpaid Principal Balance	3.8	25.0	4.9	32.9
Commercial | Commercial and Institutional
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases	1		3	7
Recorded Investment	0.4		0.7	0.5
Unpaid Principal Balance	0.4		0.8	1.0
Commercial | Commercial Real Estate Portfolio Segment
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases	5	7	6	11
Recorded Investment	2.9	22.8	3.5	27.4
Unpaid Principal Balance	3.4	25.0	4.1	31.9
Personal
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases	28	38	99	128
Recorded Investment	18.0	6.7	25.3	64.0
Unpaid Principal Balance	18.7	11.4	27.4	72.6
Personal | Residential Real Estate
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases	28	38	96	122
Recorded Investment	18.0	6.7	25.3	51.2
Unpaid Principal Balance	18.7	11.4	27.1	59.8
Personal | Private Client
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases			3	6
Recorded Investment				12.8
Unpaid Principal Balance			$ 0.3	$ 12.8