Lease Commitments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule of Finance Lease Obligations [Line Items]
Net rental expense	$ 77.9	$ 84.2	$ 68.1
One of the buildings and related land utilized for Chicago operations	In the event of sale or refinancing, the Bank would anticipate receiving full repayment of any outstanding loans plus 42% of any proceeds in excess of the original project costs.
Percentage of proceeds in excess of original project costs the bank would anticipate to receive, in addition to full repayment of outstanding loan, in the event of sale or refinancing	42.00%
Restructuring, acquisition and integration related charges
Schedule of Finance Lease Obligations [Line Items]
Net rental expense	$ 3.6	$ 6.4

A general description of the lessee's leasing arrangements including, but not limited to, the following: a) the basis on which contingent rental payments are determined; (b) the existence and terms of renewal or purchase options and escalation clauses; (c) restrictions imposed by lease agreements, such as those concerning dividends, additional debt, and further leasing.

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-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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+ Details