Revenue - Schedule of Disaggregation of Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Disaggregation of Revenue [Line Items]
Net revenue	$ 40,000	$ 35,926	$ 32,653
U.S.
Disaggregation of Revenue [Line Items]
Net revenue	15,633	14,780	14,138
International
Disaggregation of Revenue [Line Items]
Net revenue	24,367	21,146	18,515
Service revenue
Disaggregation of Revenue [Line Items]
Net revenue	17,539	16,114	14,826
Data processing revenue
Disaggregation of Revenue [Line Items]
Net revenue	19,993	17,714	16,007
International transaction revenue
Disaggregation of Revenue [Line Items]
Net revenue	14,166	12,665	11,638
Other revenue
Disaggregation of Revenue [Line Items]
Net revenue	4,053	3,197	2,479
Client incentives
Disaggregation of Revenue [Line Items]
Net revenue	$ (15,751)	$ (13,764)	$ (12,297)