Derivatives - Summary Impact of Cross-currency Swaps to AOCI and Consolidated Statements of Operations (Detail) - Cross Currency Swaps [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Derivative Instruments Gain Loss [Line Items]
Gain/(Loss) Recognized in AOCI	$ 25	$ 1	$ 7	$ 11
(Gain)/Loss Reclassified from AOCI into Interest Expense in the Consolidated Statements of Operations	$ (1)	$ (2)	(4)	(4)
(Gain)/Loss Recognized in Interest Expense in the Consolidated Statements of Operations (Amount Excluded from Effectiveness Testing)			$ 1	$ 1