Revenues (Details) - USD ($) $ in Millions	3 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disaggregation of Revenue [Line Items]
Net revenues	$ 6,054	$ 5,506
U.S.
Disaggregation of Revenue [Line Items]
Net revenues	2,717	2,508
International
Disaggregation of Revenue [Line Items]
Net revenues	3,337	2,998
Service revenues
Disaggregation of Revenue [Line Items]
Net revenues	2,555	2,342
Data processing revenues
Disaggregation of Revenue [Line Items]
Net revenues	2,864	2,470
International transaction revenues
Disaggregation of Revenue [Line Items]
Net revenues	2,018	1,851
Other revenues
Disaggregation of Revenue [Line Items]
Net revenues	365	299
Client incentives
Disaggregation of Revenue [Line Items]
Net revenues	$ (1,748)	$ (1,456)