| Analysis of Impaired Finance Receivables (Detail) (USD $) In Millions, unless otherwise specified | 12 Months Ended | |
|---|---|---|
| Dec. 31, 2011 | Dec. 31, 2009 | |
| Financing Receivable, Impaired [Line Items] | ||
| Recorded Investment | $ 51 | $ 13 | 
| Unpaid Principal Balance | 151 | |
| Related Allowance | 7 | |
| Average Recorded Investment | 77 | |
| Interest Income Recognized | ||
| Impaired loans with related allowance | ||
| Financing Receivable, Impaired [Line Items] | ||
| Recorded Investment | 9 | |
| Unpaid Principal Balance | 36 | |
| Related Allowance | 7 | |
| Average Recorded Investment | 14 | |
| Interest Income Recognized | ||
| Impaired loans with no related allowance | ||
| Financing Receivable, Impaired [Line Items] | ||
| Recorded Investment | 7 | |
| Unpaid Principal Balance | 80 | |
| Average Recorded Investment | 12 | |
| Interest Income Recognized | ||
| Impaired loans with U.S. government guarantee | ||
| Financing Receivable, Impaired [Line Items] | ||
| Recorded Investment | 35 | |
| Unpaid Principal Balance | 35 | |
| Average Recorded Investment | 51 | |
| Interest Income Recognized | 
| X | ||||||||||
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- Details 
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- Definition The average recorded investment related to impaired financing receivables. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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| X | ||||||||||
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- Definition The interest income recognized during the time within that period that the financing receivables were impaired. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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| X | ||||||||||
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- Definition The recorded investment related to impaired financing receivables. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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| X | ||||||||||
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- Definition Amount of allowance for credit losses related to recorded investment. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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| X | ||||||||||
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- Definition The unpaid principal balance related to impaired financing receivables. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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