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Settlement Guarantee Management - Additional Information (Detail) (USD $)
Mar. 31, 2014
Sep. 30, 2013
Settlement Guarantee Management [Abstract]    
Estimated maximum settlement exposure $ 56,200,000,000 $ 53,800,000,000
Covered settlement exposure 3,100,000,000 3,000,000,000
Estimated probability-weighted value of the guarantee $ 2,000,000 $ 1,000,000