Revenues - Schedule of Net Revenues (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Disaggregation of Revenue [Line Items]
Net revenues	$ 5,687	$ 6,054
U.S.
Disaggregation of Revenue [Line Items]
Net revenues	2,667	2,717
International
Disaggregation of Revenue [Line Items]
Net revenues	3,020	3,337
Service revenues
Disaggregation of Revenue [Line Items]
Net revenues	2,677	2,555
Data processing revenues
Disaggregation of Revenue [Line Items]
Net revenues	3,033	2,864
International transaction revenues
Disaggregation of Revenue [Line Items]
Net revenues	1,451	2,018
Other revenues
Disaggregation of Revenue [Line Items]
Net revenues	384	365
Client incentives
Disaggregation of Revenue [Line Items]
Net revenues	$ (1,858)	$ (1,748)