Risk Ratings of the Notional Amount of Risk Participation Agreements (Detail) (Interest Rate Contract, USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Notional amount of the risk participation agreements	$ 1,207	$ 1,006
Lender Concentration Risk \| Pass
Notional amount of the risk participation agreements	1,157	993
Lender Concentration Risk \| Risk Level, Special Mention
Notional amount of the risk participation agreements	37
Lender Concentration Risk \| Risk Level, Substandard
Notional amount of the risk participation agreements	$ 13	$ 13

Nominal or face amount used to calculate payments on the derivative liability.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 1B

-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5580258-113959

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 1A

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5579245-113959

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Notional Amount

-URI http://asc.fasb.org/extlink&oid=6519104

Name:	us-gaap_DerivativeLiabilityNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant