U.S. and Europe Retrospective Responsibility Plans - Schedule of Changes in the U.S. Litigation Escrow Account (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Escrow Account [Roll Forward]
Balance as of beginning of period	$ 3,089	$ 1,764
Deposits into the U.S. litigation escrow account	875	1,500	$ 1,000
Balance as of end of period	2,990	3,089	$ 1,764
Interest Income | Opt-out Merchants
Escrow Account [Roll Forward]
Payments to opt-out merchants, net of interest earned on escrow funds	$ (974)	$ (175)