Benefit Plans - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Retirement Benefits [Abstract]
Postemployment benefit costs	$ 10	$ 10	$ 30	$ 30

Period expense related to postemployment benefits.

No definition available.

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