Share-Based Compensation Fair Value of Stock Units Vested (Details) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2016
Performance-Based Restricted Stock Units
Schedule Of Share Based Compensation, Restricted Stock Units, Fair Value of Stock Units Vested [Line Items]
Total fair value of restricted stock units	$ 31	$ 32	$ 22
Time-Vested Restricted Stock Units
Schedule Of Share Based Compensation, Restricted Stock Units, Fair Value of Stock Units Vested [Line Items]
Total fair value of restricted stock units	$ 362	$ 139	$ 114

Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (d)(2)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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