Accumulated Other Comprehensive Income (Loss) - Amounts Reclassified Out of AOCI (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018
(Gains) Losses Reclassified to Interest Expense [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	$ (5)	$ (5)	$ (5)
(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	2	1	2
Amortization of Actuarial Losses and Prior Service Cost (Credit) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	3	1	(1)
Settlement and Curtailment Loss (Gain)
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	4	(7)
Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	4	(13)	(4)
Tax impact	(1)	(2)	1
Total after tax	$ 3	(15)	$ (3)
Specialty Fluids Divestiture [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax		$ (3)