Revenues - Disaggregation of Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Disaggregation of Revenue [Line Items]
Net revenues	$ 22,977	$ 20,609	$ 18,358
U.S.
Disaggregation of Revenue [Line Items]
Net revenues	10,279	9,332	8,704
International
Disaggregation of Revenue [Line Items]
Net revenues	12,698	11,277	9,654
Service revenues
Disaggregation of Revenue [Line Items]
Net revenues	9,700	8,918	7,975
Data processing revenues
Disaggregation of Revenue [Line Items]
Net revenues	10,333	9,027	7,786
International transaction revenues
Disaggregation of Revenue [Line Items]
Net revenues	7,804	7,211	6,321
Other revenues
Disaggregation of Revenue [Line Items]
Net revenues	1,313	944	841
Client incentives
Disaggregation of Revenue [Line Items]
Net revenues	$ (6,173)	$ (5,491)	$ (4,565)