Revenues - Schedule of Net Revenues (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Net revenues	$ 6,130	$ 4,837	$ 17,546	$ 16,745
U.S.
Disaggregation of Revenue [Line Items]
Net revenues	2,806	2,380	8,156	7,747
International
Disaggregation of Revenue [Line Items]
Net revenues	3,324	2,457	9,390	8,998
Service revenues
Disaggregation of Revenue [Line Items]
Net revenues	2,828	2,409	8,350	7,587
Data processing revenues
Disaggregation of Revenue [Line Items]
Net revenues	3,327	2,525	9,356	8,100
International transaction revenues
Disaggregation of Revenue [Line Items]
Net revenues	1,696	1,102	4,635	4,953
Other revenues
Disaggregation of Revenue [Line Items]
Net revenues	409	314	1,185	1,071
Client incentives
Disaggregation of Revenue [Line Items]
Net revenues	$ (2,130)	$ (1,513)	$ (5,980)	$ (4,966)