Legal Matters - Accrued Litigation for Both Covered and Non-Covered Litigation (Detail) $ in Millions	9 Months Ended		73 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jul. 26, 2019 merchant	Dec. 04, 2018
Loss Contingency Accrual [Roll Forward]
Balance at beginning of period	$ 1,434	$ 982
Provision for legal matters	165	601
Balance at end of period	856	1,428
Interchange Rate, Card-Not-Present, Credit				0.0150
Interchange Rate, Card-Not-Present, Debit				0.0115
Interchange Rate, Card Present, Credit				0.0030
Interchange Rate, Card Present, Debit				0.0020
Unsettled
Loss Contingency Accrual [Roll Forward]
Provision for legal matters	37	0
Settled Litigation
Loss Contingency Accrual [Roll Forward]
Payments for legal matters	(780)	(155)
U.S. Covered Litigation
Loss Contingency Accrual [Roll Forward]
Balance at beginning of period	1,428	978
Balance at end of period	828	1,428
U.S. Covered Litigation | Interchange Multidistrict Litigation
Loss Contingency Accrual [Roll Forward]
Provision for legal matters	0	600
U.S. Covered Litigation | Settled Litigation
Loss Contingency Accrual [Roll Forward]
Payments for legal matters	(600)	(150)
VE Territory Covered Litigation
Loss Contingency Accrual [Roll Forward]
Balance at beginning of period	0	1
Provision for legal matters	165	1
Balance at end of period	9	0
VE Territory Covered Litigation | Settled Litigation
Loss Contingency Accrual [Roll Forward]
Payments for legal matters	$ (156)	$ (2)
Subsequent Event | U.K. Merchant Litigation
Loss Contingency Accrual [Roll Forward]
Number of plaintiffs | merchant			500
Number of claims settled | merchant			100
Merchants with outstanding claims | merchant			350
Subsequent Event | Threatened Litigation | U.K. Merchant Litigation
Loss Contingency Accrual [Roll Forward]
Number of plaintiffs | merchant			30