Pension, Postretirement and Other Benefits - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2015	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined contribution plan, personnel costs		$ 93	$ 58	$ 55
U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Cash balance formula contributions, rate of eligible compensation	6.00%
Pension Benefits | U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated benefit obligation—end of year		6	7
Defined Benefit Plan, Benefit Obligation		844	913	1,072
Service cost		0	0	13
Curtailment gain		0	0	(8)
Liability, Defined Benefit Plan, Noncurrent		5	6
Pension Benefits | Non-U.S. Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accumulated benefit obligation—end of year		452	5
Defined Benefit Plan, Benefit Obligation		452	433	474
Service cost		4	6	1	[1]
Curtailment gain		0	0	$ 0	[1]
Liability, Defined Benefit Plan, Noncurrent		$ 6	$ 0

[1] For fiscal 2016, the amounts represent the Visa Europe plans’ net pension benefit cost recognized from the Closing through September 30, 2016.