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Settlement Guarantee Management - Additional Information (Detail) (USD $)
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Jun. 30, 2013
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Sep. 30, 2012
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| Settlement Guarantee Management [Abstract] | ||
| Estimated maximum settlement exposure | $ 52,100,000,000 | $ 49,300,000,000 |
| Covered settlement exposure | 3,600,000,000 | 3,500,000,000 |
| Estimated probability-weighted value of the guarantee | $ 1,000,000 | $ 1,000,000 |