Accumulated Other Comprehensive Income (Loss) - Amounts Reclassified Out of AOCI (Detail) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2017
(Gains) Losses Reclassified to Interest Expense [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	$ (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	1	2
Amortization of Actuarial Losses [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	1	2	$ 5
Amortization of Prior Service Cost (Credit) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax		(3)	(3)
Settlement and Curtailment Gain [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	(7)
Accumulated Other Comprehensive Income (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	(13)	(4)	2
Tax impact	(2)	1
Total after tax	(15)	$ (3)	$ 2
Specialty Fluids Divestiture [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	$ (3)