Intangible Assets and Goodwill - Schedule of Indefinite-Lived and Finite-Lived Intangible Assets (Details) - USD ($) $ in Millions	Sep. 30, 2025	Sep. 30, 2024
Finite-Lived Intangible Assets [Line Items]
Gross	$ 476	$ 725
Accumulated Amortization	(245)	(477)
Net	231	248
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets	27,415	26,641
Intangible Assets, Net (Excluding Goodwill) [Abstract]
Gross	27,891	27,366
Net	27,646	26,889
Customer relationships and reacquired rights
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets	23,331	22,557
Visa trade name
Indefinite-lived Intangible Assets [Line Items]
Indefinite-lived Intangible Assets	4,084	4,084
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross	476	535
Accumulated Amortization	(245)	(298)
Net	231	237
Trade names
Finite-Lived Intangible Assets [Line Items]
Gross	0	190
Accumulated Amortization	0	(179)
Net	$ 0	$ 11