Accrued Litigation for Both Covered and Non-Covered Litigation (Detail) (USD $)	0 Months Ended	3 Months Ended	1 Months Ended	3 Months Ended	1 Months Ended
	Jan. 14, 2015 merchant	Dec. 31, 2014	Jan. 29, 2014	Dec. 31, 2013	Jan. 29, 2015	Sep. 30, 2014	Sep. 30, 2013
Loss Contingency Accrual [Roll Forward]
Balance at October 1						$ 1,456,000,000	$ 5,000,000
Balance at December 31		1,353,000,000	4,000,000	4,000,000		1,456,000,000	5,000,000
Subsequent Event
Loss Contingency Accrual [Roll Forward]
Balance at December 31					1,174,000,000
Interchange Opt Out Litigation [Member]
Loss Contingency Accrual [Roll Forward]
Loss Contingency, Number of Cases Filed		40
Interchange Opt Out Litigation [Member] \| Subsequent Event
Loss Contingencies [Line Items]
Rejoined Opt Out Merchant	1,179
Loss Contingency Accrual [Roll Forward]
Sales Volume Of Opt Out Merchants Percent Settled					2100.00%
U.K. Merchant Litigation [Member]
Loss Contingency Accrual [Roll Forward]
Claim limitation period		6 years
Covered Litigation [Member]
Loss Contingency Accrual [Roll Forward]
Balance at October 1		1,449,000,000	0	0
Payments on litigation matters		(100,000,000)	0	0
Balance at December 31		1,349,000,000	0	0
Covered Litigation [Member] \| Subsequent Event
Loss Contingency Accrual [Roll Forward]
Payments on litigation matters					(179,000,000)
Balance at December 31					1,170,000,000
Settled [Member]
Loss Contingency Accrual [Roll Forward]
Payments on litigation matters		(103,000,000)	0	(1,000,000)
Settled [Member] \| Subsequent Event
Loss Contingency Accrual [Roll Forward]
Payments on litigation matters					$ (179,000,000)