Restrictions on Cash and Due from Banks, Securities, Loans and Dividends - Additional Information (Detail) (USD $)	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011
Required reserve balances	$ 412,000,000	$ 909,000,000
Loans pledged as collateral for borrowings	43,600,000,000	38,700,000,000
Federal Reserve Act restricts the amount and the terms of both credit and non-credit transactions, in percentage	10.00%
Aggregate of loan to non-bank affiliate	20.00%
Outstanding on zero bankers commercial corporation notes payable	$ 365,000,000

Reflects the aggregate value of loans, trade receivables, securities and financial instruments that serve as collateral for obligations arising from a transfer of financial assets recorded as a secured borrowing.

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

-Publisher AICPA

-Name Statement of Position (SOP)

-Number 01-6

-Paragraph 13

-Subparagraph i

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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 310

-SubTopic 10

-Section 50

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=7512638&loc=d3e5086-111524

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 30

-Section 50

-Paragraph 1A

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=7523297&loc=SL6224234-111729

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant