Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Tax Credit Carryforward [Line Items]
US income before taxes	$ 9,536,000,000	$ 8,088,000,000	$ 8,440,000,000
U.S. federal statutory rate	21.00%	24.50%	35.00%
Tax Cuts and Jobs Act, transition tax		$ 1,100,000,000
Deferred tax assets, net	$ 698,000,000	$ 941,000,000
Income tax provision, percent	19.00%	20.00%	43.00%
Tax Cuts and Jobs Act, change in tax rate benefit		$ 1,100,000,000
Tax benefits due to various non-recurring audit settlements		161,000,000
Income tax provision	$ 2,804,000,000	2,505,000,000	$ 4,995,000,000
Income tax expense benefit charitable contributions			71,000,000
Income taxes receivable included in prepaid and other current assets	130,000,000	82,000,000
Income taxes payable included in accrued taxes as part of accrued liabilities	327,000,000	257,000,000
Accrued income taxes included in other long-term liabilities	2,500,000,000	2,400,000,000
Decreased Singapore tax as a result of the tax incentive agreement	$ (324,000,000)	$ (295,000,000)	$ (252,000,000)
Benefit of the tax incentive agreement on diluted net income per share	$ 0.14	$ 0.13	$ 0.11
Total unrecognized tax benefits exclusive of interest and penalties	$ 2,234,000,000	$ 1,658,000,000	$ 1,353,000,000	$ 1,160,000,000
Unrecognized tax benefits, if recognized, would reduce the effective tax rate in a future period	1,400,000,000	1,200,000,000	1,100,000,000
Interest expense included in interest expense and administrative and other	66,000,000	15,000,000	23,000,000
Accrued penalties related to uncertain tax positions	5,000,000	0	1,000,000
Accrued interest related to uncertain tax positions in other long term liabilities	165,000,000	99,000,000
Accrued penalties related to uncertain tax positions in other long term liabilities	26,000,000	34,000,000
Federal
Tax Credit Carryforward [Line Items]
Net operating loss carryforwards	17,000,000
State and Local Jurisdiction
Tax Credit Carryforward [Line Items]
Net operating loss carryforwards	19,000,000
Foreign Country
Tax Credit Carryforward [Line Items]
Net operating loss carryforwards	311,000,000
Other Assets
Tax Credit Carryforward [Line Items]
Deferred tax assets, net	24,000,000	14,000,000
Non-current income tax receivable	771,000,000	689,000,000
Non United States Customers
Tax Credit Carryforward [Line Items]
US income before taxes	$ 3,000,000,000.0	$ 2,700,000,000	2,900,000,000
Visa Europe
Tax Credit Carryforward [Line Items]
Income tax provision			$ 1,500,000,000