Revenue - Schedule of Net Revenues (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Mar. 31, 2024	Mar. 31, 2023
Disaggregation of Revenue [Line Items]
Net revenue	$ 8,775	$ 7,985	$ 17,409	$ 15,921
U.S.
Disaggregation of Revenue [Line Items]
Net revenue	3,643	3,540	7,288	7,107
International
Disaggregation of Revenue [Line Items]
Net revenue	5,132	4,445	10,121	8,814
Service revenue
Disaggregation of Revenue [Line Items]
Net revenue	4,033	3,771	7,948	7,282
Data processing revenue
Disaggregation of Revenue [Line Items]
Net revenue	4,259	3,819	8,615	7,646
International transaction revenue
Disaggregation of Revenue [Line Items]
Net revenue	2,984	2,749	6,003	5,546
Other revenue
Disaggregation of Revenue [Line Items]
Net revenue	756	551	1,448	1,138
Client incentives
Disaggregation of Revenue [Line Items]
Net revenue	$ (3,257)	$ (2,905)	$ (6,605)	$ (5,691)