Income Taxes - Information that Causes the Income Tax Expense to Differ from the Amount of Income Tax Determined by Applying the Applicable U.S. Federal Statutory Rate of 35% to Pretax Income (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Income Tax Disclosure [Abstract]
U.S. federal income tax at statutory rate	$ 3,126	$ 3,141	$ 4,093
State income taxes, net of federal benefit	223	201	200
Non-U.S. tax effect, net of federal benefit	(527)	(465)	(641)
Transition tax on foreign earnings	0	1,147	0
Remeasurement of deferred tax balances	0	(1,133)	0
Reorganization of Visa Europe and other legal entities	0	0	1,515
Other, net	(18)	(386)	(172)
Total income tax provision	$ 2,804	$ 2,505	$ 4,995
U.S. federal income tax at statutory rate, percent	21.00%	24.50%	35.00%
State income taxes, net of federal benefit, percent	2.00%	2.00%	2.00%
Non-U.S. tax effect, net of federal benefit, percent	(4.00%)	(4.00%)	(5.00%)
Transition tax on foreign earnings, percent	0.00%	9.00%	0.00%
Remeasurement of deferred tax liability, percent	0.00%	(9.00%)	0.00%
Reorganization of Visa Europe and other legal entities, percent	0.00%	0.00%	13.00%
Other, net, percent	0.00%	(3.00%)	(2.00%)
Income tax expense, percent	19.00%	20.00%	43.00%