Income Taxes - Summary of Changes in Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2024	Sep. 30, 2023
Balance at beginning of period	$ 59	$ 84
Decreases related to positions taken on items from prior years	(3)	(30)
Increases related to positions taken in the current year	13	8
Increases related to positions taken in the prior year	3	1
Lapse of statute of limitations	(6)	(4)
Settlements	(1)
Balance at end of period	$ 65	$ 59

Amount of unrecognized tax benefits.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 217
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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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 decrease in unrecognized tax benefits resulting from settlements with taxing authorities.

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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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