Revenues (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Net revenues	$ 4,837	$ 5,840	$ 16,745	$ 16,840
U.S.
Disaggregation of Revenue [Line Items]
Net revenues	2,380	2,587	7,747	7,573
International
Disaggregation of Revenue [Line Items]
Net revenues	2,457	3,253	8,998	9,267
Service revenues
Disaggregation of Revenue [Line Items]
Net revenues	2,409	2,405	7,587	7,164
Data processing revenues
Disaggregation of Revenue [Line Items]
Net revenues	2,525	2,662	8,100	7,564
International transaction revenues
Disaggregation of Revenue [Line Items]
Net revenues	1,102	1,977	4,953	5,624
Other revenues
Disaggregation of Revenue [Line Items]
Net revenues	314	342	1,071	968
Client incentives
Disaggregation of Revenue [Line Items]
Net revenues	$ (1,513)	$ (1,546)	$ (4,966)	$ (4,480)