Number of Loans and Leases Modified in TDRs and Total Recorded Investments and Unpaid Principal Balances (Detail) (USD $) In Millions, unless otherwise specified			3 Months Ended			3 Months Ended					3 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2012 Class of Financing Receivable Contract	Mar. 31, 2012 Commercial	Dec. 31, 2011 Commercial	Mar. 31, 2012 Commercial Class of Financing Receivable Contract	Mar. 31, 2012 Commercial Class of Financing Receivable Commercial and Institutional Contract	Mar. 31, 2012 Commercial Class of Financing Receivable Commercial Real Estates Contract	Mar. 31, 2012 Personal	Dec. 31, 2011 Personal	Mar. 31, 2012 Personal Class of Financing Receivable Contract	Mar. 31, 2012 Personal Class of Financing Receivable Residential Real Estate Contract
Financing Receivable, Modifications [Line Items]
Number of Loans and Leases			38			6	2	4			32	32
Recorded Investment			$ 10.1			$ 4.5	$ 0.7	$ 3.8			$ 5.6	$ 5.6
Unpaid Principal Balance	$ 318.9	$ 356.9	$ 11.9	$ 143.6	$ 162.6	$ 5.0	$ 1.2	$ 3.8	$ 175.3	$ 194.3	$ 6.9	$ 6.9