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Settlement Guarantee Management - Additional Information (Detail) - USD ($)
$ in Millions
3 Months Ended
Jun. 30, 2015
Sep. 30, 2014
Settlement Guarantee Management [Abstract]    
Estimated Maximum Settlement Exposure $ 43,900 $ 56,900
Covered settlement exposure 2,200 3,200
Estimated probability-weighted value of the guarantee $ 2 $ 2