Loans and Allowance for Loan Losses - Carrying Value and Outstanding Balance for Purchased Credit Impaired Loans (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Schedule Of Outstanding Principal Balance And Related Carrying Amount Of Acquired Loans [Line Items]
Total outstanding balance	$ 1,355	$ 2,066
Carrying amount	494	902
Acquisition Date [Member]
Schedule Of Outstanding Principal Balance And Related Carrying Amount Of Acquired Loans [Line Items]
Total outstanding balance	3,153
Carrying amount	$ 1,725

The recorded balance, net of any applicable reductions (for example, unamortized accretable yield and allowance for loan losses). This relates to loans not accounted for debt securities with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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The undiscounted sum of all amounts, including amounts deemed principal, interest, fees, penalties, and other under the loan, owed to the investor at the reporting date, whether or not currently due and whether or not any such amounts have been written or charged off by the investor. This relates to loans not accounted for as debt securities, with evidence of deterioration of credit quality since origination that were acquired by completion of a transfer for which it is probable, at acquisition, that the investor will be unable to collect all contractually required payments receivable.

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