Derivative Instruments and Hedging Activities Derivative Instruments and Hedging Activities Disclosure - Gains (Losses) on Net Investment Hedges (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018
Foreign Exchange Contract
Derivative Instruments, Gain (Loss) [Line Items]
Net (losses) gains on net investment hedges	$ (18)	$ (103)	$ 41	$ (104)

Amount, before tax and reclassification, of gain (loss) from derivative designated and qualifying as net investment hedge.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4CCC
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL109998896-113959

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