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Settlement Guarantee Management - Additional Information (Detail) (USD $)
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Dec. 31, 2013
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Sep. 30, 2013
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| Settlement Guarantee Management [Abstract] | ||
| Estimated maximum settlement exposure | $ 53,200,000,000 | $ 53,800,000,000 |
| Covered settlement exposure | 3,000,000,000 | |
| Estimated probability-weighted value of the guarantee | $ 2,000,000 | $ 1,000,000 |