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, 2018	Sep. 30, 2017	Sep. 30, 2016
Income Tax Disclosure [Abstract]
U.S. federal income tax at statutory rate	$ 3,141	$ 4,093	$ 2,804
State income taxes, net of federal benefit	201	200	135
Non-U.S. tax effect, net of federal benefit	(465)	(641)	(553)
Transition tax on foreign earnings	1,147	0	0
Remeasurement of deferred tax balances	(1,133)	0	(88)
Revaluation of Visa Europe put option	0	0	(89)
Reorganization of Visa Europe and other legal entities	0	1,515	0
Other, net	(386)	(172)	(188)
Income tax provision	$ 2,505	$ 4,995	$ 2,021	[1]
U.S. federal income tax at statutory rate, percent	24.53%	35.00%	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%)	(5.00%)	(7.00%)
Transition tax on foreign earnings, percent	9.00%	0.00%	0.00%
Remeasurement of deferred tax liability, percent	(9.00%)	0.00%	(1.00%)
Revaluation of Visa Europe put option, percent	0.00%	0.00%	(1.00%)
Reorganization of Visa Europe and other legal entities, percent	0.00%	13.00%	0.00%
Other, net, percent	(3.00%)	(2.00%)	(3.00%)
Income tax expense, percent	20.00%	43.00%	25.00%

[1] The Company did not include Visa Europe’s financial results in the Company’s consolidated statements of operations from the acquisition date, June 21, 2016, through June 30, 2016 as the impact was immaterial. The Company’s consolidated statement of operations for the year ended September 30, 2016 includes Visa Europe’s financial results for the three months ended September 30, 2016.