Commitments and Contingencies - Additional Information (Detail) $ in Millions	3 Months Ended
	Dec. 31, 2018 USD ($) claimants	Dec. 31, 2017 USD ($)	Sep. 30, 2018 USD ($) claimants
Respirator Liabilities [Member]
Loss Contingencies [Line Items]
Number of claimants | claimants	35,000		35,000
Cash payments for respirator reserves	$ 1	$ 1
Respirator reserve	24		$ 25
Maximum [Member] | Respirator Liabilities [Member]
Loss Contingencies [Line Items]
Cash payments for respirator reserves	1	1
Environmental Matters [Member]
Loss Contingencies [Line Items]
Reserved for environmental matters	14		$ 15
Cash payments for environmental reserves	1	1
Environmental Matters [Member] | Maximum [Member]
Loss Contingencies [Line Items]
Cash payments for environmental reserves	$ 1	$ 1