Revenue - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Disaggregation of Revenue [Line Items]
Net revenue	$ 8,900	$ 8,123	$ 26,309	$ 24,044
U.S.
Disaggregation of Revenue [Line Items]
Net revenue	3,621	3,443	10,909	10,550
International
Disaggregation of Revenue [Line Items]
Net revenue	5,279	4,680	15,400	13,494
Service revenue
Disaggregation of Revenue [Line Items]
Net revenue	3,967	3,668	11,915	10,950
Data processing revenue
Disaggregation of Revenue [Line Items]
Net revenue	4,489	4,105	13,104	11,751
International transaction revenue
Disaggregation of Revenue [Line Items]
Net revenue	3,194	2,920	9,197	8,466
Other revenue
Disaggregation of Revenue [Line Items]
Net revenue	780	597	2,228	1,735
Client incentives
Disaggregation of Revenue [Line Items]
Net revenue	$ (3,530)	$ (3,167)	$ (10,135)	$ (8,858)