Loans with Deteriorated Credit Quality Acquired in a Transfer - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Loans That Were Acquired with Deteriorated Credit Quality [Line Items]
Provision expense for loans acquired with deteriorated credit quality	$ 7	$ 6	$ 21
Allowance for loan and lease losses	$ 2	$ 3

Reserve for loans impairments recorded after acquisition as a result of current information and events which result in it being probable that estimated cash flows will be less than previously expected or because actual cash flows are less than cash flows 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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Expense recorded to recognize an impairment of loans after acquisition. 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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