Derivative Instruments and Hedging Activities - Additional Information (Detail) € in Millions, $ in Millions, ¥ in Billions	3 Months Ended		9 Months Ended
	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2020 EUR (€)	Jun. 30, 2020 JPY (¥)	Jun. 30, 2019 USD ($)
Derivative [Line Items]
Gains (losses) reclassified from CTA to income for the Company's outstanding net investment hedges | $	$ 0	$ 0	$ 0			$ 0
Foreign Currency Denominated Debt [Member]
Derivative [Line Items]
Notional amount | ¥					¥ 25
54 million euro net investment hedge [Member] | Foreign Currency Denominated Debt [Member]
Derivative [Line Items]
Notional amount				€ 54
One billion euro net investment hedge [Member] | Foreign Currency Denominated Debt [Member]
Derivative [Line Items]
Notional amount				888
750 million euro net investment hedge [Member] | Foreign Currency Denominated Debt [Member]
Derivative [Line Items]
Notional amount				750
423 million euro net investment hedge [Member] | Foreign Currency Denominated Debt [Member]
Derivative [Line Items]
Notional amount				€ 423