U.S. and Europe Retrospective Responsibility Plans - Additional Information (Details) € in Millions, $ in Millions		1 Months Ended	12 Months Ended
		Sep. 30, 2020 USD ($) shares	Sep. 30, 2020 USD ($) shares	Sep. 30, 2020 EUR (€) shares	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Jun. 21, 2016 EUR (€)
Class of Stock [Line Items]
Return of takedown payment to the litigation escrow account			$ 467		$ 0
Omnibus loss sharing agreement percentage		66.6667%	66.6667%	66.6667%
Litigation loss sharing agreement, obligation threshold | €							€ 1,000
Limit of protection from VE territory covered losses							70.00%
Conversion adjustment denominator (in shares) | shares		100
VE covered loss, maximum amount of loss to allow adjustment of conversion rate during six-month period | €				€ 20
Recovery through conversion rate adjustment			$ 5
Series A convertible participating preferred stock
Class of Stock [Line Items]
Preferred stock issued		$ 7,300
Preferred stock, shares issued (in shares) | shares		374,819
Cash paid for fractional shares of series A preferred stock		$ 5
Right to Recover for Covered Losses
Class of Stock [Line Items]
Preferred stock issued			0
Recovery through conversion rate adjustment			169		8	$ 56
Preferred Stock
Class of Stock [Line Items]
Recovery through conversion rate adjustment			$ (164)		(8)	$ (56)
Preferred Stock | Series A convertible participating preferred stock
Class of Stock [Line Items]
Preferred stock, shares issued (in shares) | shares	[1]		0	0
MasterCard
Class of Stock [Line Items]
Omnibus loss sharing agreement percentage		33.3333%	33.3333%	33.3333%
Interchange Multidistrict Litigation
Class of Stock [Line Items]
Return of takedown payment to the litigation escrow account			$ 467		0
U.S. Covered Litigation | Interchange Multidistrict Litigation
Class of Stock [Line Items]
Provision for unsettled legal matters			$ 0		$ 370

[1] Increase, decrease or balance is less than one million shares.