Accumulated Other Comprehensive Income (Loss) ("AOCI") - Amounts Reclassified Out of AOCI (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2023	Mar. 31, 2022
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	$ (2)	$ 33	$ (3)	$ 32
(Gains) Losses Reclassified to Interest Expense [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	(2)	(2)	(3)	(3)
(Gains) Losses Excluded from Effectiveness Testing and Amortized to Interest Expense [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	1	1	1	1
Release of Currency Translation Adjustment [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax		33		33
Release of Actuarial Losses and Prior Service Cost (Credit) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax		$ 1		$ 1
Amortization of Actuarial Losses and Prior Service Cost (Credit) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	$ (1)		$ (1)