U.S. and Europe Retrospective Responsibility Plans - Schedule of Changes in the U.S. Litigation Escrow Account (Detail) - USD ($) $ in Millions	9 Months Ended
	Jun. 30, 2024	Jun. 30, 2023
Escrow Account [Roll Forward]
Balance as of beginning of period	$ 1,764	$ 1,449
Deposits into the U.S. litigation escrow account	0	850
Balance as of end of period	1,596	1,627
Interest Income | Opt-out Merchants
Escrow Account [Roll Forward]
Payments to opt-out merchants, net of interest earned on escrow funds	$ (168)	$ (672)