U.S. and Europe Retrospective Responsibility Plans - Changes in the U.S. Litigation Escrow Account (Detail) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2021	Sep. 30, 2020
Escrow Account [Roll Forward]
Beginning balance	$ 901	$ 1,205
Return of takedown payment to the litigation escrow account	0	467
Ending balance	894	901
Interest Income \| Opt-out Merchants
Escrow Account [Roll Forward]
Payments to opt-out merchants and interest earned on escrow funds	$ (7)	$ (771)

Amount of cash and cash equivalents restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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