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Settlement Guarantee Management - Additional Information (Detail) (USD $)
Sep. 30, 2013
Sep. 30, 2012
Settlement Guarantee Management [Abstract]    
Estimated maximum settlement exposure $ 53,800,000,000 $ 49,300,000,000
Covered settlement exposure 3,000,000,000 3,500,000,000
Estimated probability-weighted value of the guarantee $ 1,000,000