Legal Matters - Additional Information (Detail) (USD $)	0 Months Ended	12 Months Ended			12 Months Ended
	Oct. 19, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2013 Class Plaintiffs		Sep. 30, 2013 Individual Plaintiffs		Sep. 30, 2013 Unsettled	Sep. 30, 2012 Unsettled
Loss Contingencies [Line Items]
Payments for legal settlements		$ 4,400,000,000			$ (4,033,000,000)	[1]	$ (350,000,000)	[1]
Provision for legal matters									3,000,000	4,100,000,000
Reserve for covered litigation			4,400,000,000	285,000,000
Takedown Money for Class Plaintiffs Settlement		$ 1,100,000,000
Distribution to Class Merchants, Rate Amount	0.10%
Distribution to Class Merchants, Period per Terms	60 days
Consecutive Months of Distribution to Class Merchants	8 months

[1] (1)These payments are associated with the interchange multidistrict litigation. The settlement with the class plaintiffs in these proceedings is subject to final court approval, which the Company cannot assure will be received, and to the adjudication of any appeals. See Note 20—Legal Matters.