Benefit Plans - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended
Dec. 31, 2016	Dec. 31, 2015
Compensation and Retirement Disclosure [Abstract]
Postemployment benefit costs	$ 10	$ 10

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