Changes in the Servicing Asset Related to Residential Mortgage Loans (Detail) (USD $) In Millions	9 Months Ended
Sep. 30, 2011	Sep. 30, 2010
Servicing Assets at Fair Value [Line Items]
Carrying amount as of the beginning of the period	$ 1,138	$ 979
Servicing obligations that result from the transfer of residential mortgage loans	155	180
Amortization	(87)	(91)
Carrying amount before valuation allowance	1,206	1,068
Valuation allowance for servicing assets:
Beginning balance	(316)	(280)
Servicing impairment	(228)	(189)
Ending balance	(544)	(469)
Carrying amount as of the end of the period	$ 662	$ 599

Carry amount of MSRs before valuation allowance.

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Carrying amount of MSR net of valuation allowance.

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Servicing obligation resulting from the transfer of residential mortgage loans.

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Decreases in the value of servicing assets due to the periodic amortization in proportion to and over the period of estimated net servicing income.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Reflects the estimated amount of impairment as of the balance sheet date of recognized servicing assets that are being amortized in proportion to and over the period of estimated net servicing income or loss.

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New provisions recoveries or charged against this account which increase or reduce the net value of servicing assets.

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A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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