Employee Retirement Plans - Defined Contribution Plans (Details) - Other Pension, Postretirement and Supplemental Plans - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
Defined Contribution Plan Disclosure [Line Items]
Costs of benefits under savings plans	$ 22	$ 21	$ 21
Total fair values of grantor trust investment assets	$ 9	$ 7

Amount of asset, recognized in statement of financial position, for overfunded defined benefit pension and other postretirement plans.

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Name:	us-gaap_DefinedBenefitPlanAssetsForPlanBenefitsNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant