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Settlement Guarantee Management - Additional Information (Detail) (USD $)
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3 Months Ended | |
|---|---|---|
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Mar. 31, 2015
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Sep. 30, 2014
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| Settlement Guarantee Management [Abstract] | ||
| Estimated Maximum Settlement Exposure | $ 58,600,000,000 | $ 56,900,000,000 |
| Covered settlement exposure | 2,800,000,000 | 3,200,000,000 |
| Estimated probability-weighted value of the guarantee | $ 2,000,000 | $ 2,000,000 |