Derivative Instruments and Hedging Activities Derivative Instruments and Hedging Activities - Cash Flow Hedges (Detail) - USD ($) $ in Millions	12 Months Ended
Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Derivative Instruments and Hedging Activities Disclosure [Abstract]
After-tax loss recognized in other comprehensive income (loss)	$ 11	$ 16	$ 0

The effective portion of gains and losses (net) on derivative instruments designated and qualifying as hedging instruments that was recognized in other comprehensive income during the current period.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4C
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=64837297&loc=SL5624171-113959

Name:	us-gaap_DerivativeInstrumentsGainLossRecognizedInOtherComprehensiveIncomeEffectivePortionNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration