Deposits - Additional Information (Detail) (USD $)	Sep. 30, 2012	Dec. 31, 2011
Deposit Liabilities [Line Items]
Brokered deposit	$ 2,600,000,000	$ 3,400,000,000
Deposit Liabilities Reclassified As Loans Receivable	$ 18,000,000	$ 13,000,000

Amount of deposits held by the entity that have been reclassified as loan balances receivable, such as overdrafts receivable, at the balance sheet date.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Statement of Position (SOP)

-Number 01-6

-Paragraph 14

-Subparagraph e

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 405

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6479006&loc=d3e64164-112818

Name:	us-gaap_DepositLiabilitiesReclassifiedAsLoansReceivable
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant