Amounts in Accumulated Other Comprehensive Income Expected to be Recognized as Components of Net Periodic Benefit Cost over Next Fiscal Year (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2021	Sep. 30, 2020
Retirement Plans [Line Items]
Amounts in AOCI, exclusive of tax impacts, that have not been recognized as components of net periodic benefit cost (credit)	$ 8	$ 5

Amount, before tax, after reclassification adjustment, of (increase) decrease in accumulated other comprehensive income from prior service cost (credit) of defined benefit plan.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=124509347&loc=d3e637-108580

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (j)
-URI http://asc.fasb.org/extlink&oid=124509347&loc=SL7669646-108580

Name:	us-gaap_DefinedBenefitPlanAmountsRecognizedInOtherComprehensiveIncomeNetPriorServiceCostCreditBeforeTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration