Consolidated Statement of Cash Flows (Paranthetical) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
Statement of Cash Flows [Abstract]
Purchase accounting amortization	$ 4	$ 22	$ 22

Amount of increase (decrease) to assets, excluding financial assets and goodwill, lacking physical substance with a finite life for purchase accounting adjustments.

No definition available.

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