Income Taxes - Summary of Gross Amounts of Unrecognized Tax Benefits (Detail) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at October 1	$ 354	$ 611	$ 568
Increase due to acquisitions	2	2	1
Increase due to current year tax positions	40	23	35
Increase due to prior year tax positions	60	5	76
Decreases due to prior year tax positions	0	(4)	(49)
Decrease due to settlements with tax authorities	(77)	(183)	(4)
Decrease due to lapse of statute of limitations	(112)	(100)	(16)
Balance at September 30	267	354	611
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	$ 348	$ 447	$ 719

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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- Definition

Amount of unrecognized tax benefits.

+ References

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Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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Amount of increase in unrecognized tax benefits resulting from acquisitions.

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Amount of decrease in unrecognized tax benefits resulting from lapses of applicable statutes of limitations.

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The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate.

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