Legal Matters - Additional Information (Details) $ in Millions			9 Months Ended		12 Months Ended	85 Months Ended
	May 29, 2020 state	Dec. 27, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)	Jul. 30, 2020 merchant
Loss Contingencies [Line Items]
Provision for legal matters			$ 14	$ 165
Return of takedown payment to the litigation escrow account		$ 467	467	0
Number of states | state	24
Interchange Multidistrict Litigation
Loss Contingencies [Line Items]
Provision for legal matters			$ 467	$ 0
Subsequent Event | Interchange Multidistrict Litigation
Loss Contingencies [Line Items]
Settlement percentage						30.00%
Subsequent Event | U.K. Merchant Litigation
Loss Contingencies [Line Items]
Number of plaintiffs | merchant						500
Number of claims settled | merchant						100
Merchants with outstanding claims | merchant						400
Subsequent Event | U.K. Merchant Litigation | Threatened Litigation
Loss Contingencies [Line Items]
Number of plaintiffs | merchant						30
Visa, MasterCard, and Certain U.S. Financial Institutions
Loss Contingencies [Line Items]
Maximum takedown payments the defendants are entitled to					$ 700
U.S. Covered Litigation
Loss Contingencies [Line Items]
Maximum takedown payments the defendants are entitled to					467
U.S. Covered Litigation | Interchange Multidistrict Litigation
Loss Contingencies [Line Items]
Provision for legal matters					$ 600
Return of takedown payment to the litigation escrow account		$ 467