Derivative Instruments and Hedging Activities - Additional Information (Detail) - USD ($) $ in Millions	9 Months Ended
Jun. 30, 2018	Sep. 30, 2017
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Gain (Loss) on Derivative Used in Net Investment Hedge, after Tax	$ 53
Reclassification of terminated interest rate swaps to interest expense within the next 12 months	5
Forward exchange contracts
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount	1,500	$ 2,500
Fixed to Floating \| Fair Value Hedging
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount	1,200	$ 375
Euro Member Countries, Euro \| Debt \| Net Investment Hedging
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount	2,700
United Kingdom, Pounds \| Debt \| Net Investment Hedging
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional amount	$ 330

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

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+ References

No definition available.

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- Definition

The estimated net amount of unrealized gains or losses on interest rate cash flow hedges as of the balance sheet date expected to be reclassified to earnings within the next twelve months.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=112277219&loc=d3e80748-113994

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Amount, after tax, of reclassification from accumulated other comprehensive income (AOCI) of gain (loss) from increase (decrease) in fair value of net investment hedge.

+ References

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

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 10A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=114867106&loc=SL7669646-108580

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