Income Taxes - Summary of Gross Amounts of Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Unrecognized Tax Benefits [Roll Forward]
Balance at October 1	$ 221	$ 269	$ 267
Increase due to current year tax positions	40	22	22
Increase due to prior year tax positions	5	0	33
Decreases due to prior year tax positions	0	0	(29)
Decrease due to settlements with tax authorities	(16)	(64)	(6)
Decrease due to lapse of statute of limitations	(10)	(6)	(18)
Balance at September 30	240	221	269
Unrecognized tax benefits that would affect the effective tax rate if recognized	$ 285	$ 257	$ 366

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

No definition available.

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- Definition

Amount of unrecognized tax benefits.

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Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

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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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