U.S. and Europe Retrospective Responsibility Plan - Changes in the U.S. Litigation Escrow Account (Detail) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2019	Sep. 30, 2018
Escrow Account [Roll Forward]
Beginning balance	$ 1,491	$ 1,031
Deposits into the litigation escrow account	300	600
Payments to class plaintiffs settlement funds	(600)	0
Ending balance	1,205	1,491
Interest Income \| Opt-out Merchants
Escrow Account [Roll Forward]
Payments to opt-out merchants and interest earned on escrow funds	$ 14	$ (140)

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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