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Commitments and Contingencies - Additional Information (Detail) $ in Millions | 6 Months Ended |
--- | --- | ---
Mar. 31, 2016 USD ($) claimants | Mar. 31, 2015 USD ($) | Sep. 30, 2015 USD ($) claimants
Respirator Liabilities [Member] |  |  |
Loss Contingencies [Line Items] |  |  |
Number of claimants | claimants | 37,000 |  | 38,000
Respirator reserve | $ 9 |  | $ 11
Cash payments for respirator reserves | 2 | $ 2 |
Environmental Matters [Member] |  |  |
Loss Contingencies [Line Items] |  |  |
Reserved for environmental matters | 14 |  | $ 16
Cash payments for environmental reserves | $ 1 |  |
Maximum [Member] | Environmental Matters [Member] |  |  |
Loss Contingencies [Line Items] |  |  |
Cash payments for environmental reserves |  | $ 1 |

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