Loans and Allowance for Loan Losses - Changes in Accretable Balance for Purchased Credit-Impaired Loans (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended
Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Receivables [Abstract]
Accretable yield, beginning of period	$ 501	$ 441	$ 590	$ 424
Additions	31		31
Accretion	(81)	(72)	(160)	(135)
Reclassifications from nonaccretable difference during the period	28	105	18	185
Accretable yield, end of period	$ 479	$ 474	$ 479	$ 474

The aggregate excess of a loan's cash flows expected to be collected over the investor's initial investment in the loan. 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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The current period recognition due to accretion of the excess of a loan's cash flows expected to be collected over the investor's initial investment in the loan. 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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- Definition

The increases in the aggregate excess of a loan's cash flows expected to be collected over the investor's initial investment in the loan. 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, due to the acquisition of similar loans not accounted for as debt securities during the period.

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- Definition

The change in the estimate of cash flows expected to be collected, after acquisition of loans, which results in an increase in accretable yield (for example, if actual cash flows are significantly greater than previously expected). This relates to loans not accounted for as debt securities, with evidence of deterioration of credit quality since origination that was 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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