Loans and Allowance for Credit Losses - Schedule of Composition of Loans (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	6 Months Ended	12 Months Ended
Jun. 30, 2013	Dec. 31, 2012
Receivables [Abstract]
Direct finance leases	$ 34.8	$ 57.7

Revenue realized in the period on direct financing leases.

No definition available.

Name:	us-gaap_CapitalLeasesIncomeStatementDirectFinancingLeaseRevenue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration