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Settlement Guarantee Management - Additional Information (Detail) $ in Millions	12 Months Ended
	Sep. 30, 2016 USD ($) month	Sep. 30, 2015 USD ($)
Settlement Guarantee Management [Abstract]
Number of Rolling Months of Average Chargebacks Volume Included in Settlement Risk Exposure \| month	4
Estimated maximum settlement exposure	$ 67,800	$ 43,500
Covered settlement exposure	2,900	2,200
Estimated probability-weighted value of the guarantee	$ 2	$ 1