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Employee Benefit Plans - Additional Information (Detail) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2022
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined contribution plans expenses |  | $ 20 | $ 19 | $ 15
Pension Benefits [Member] | Scenario, Forecast [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Expected contribution | $ 5 |  |  |
Postretirement Benefits [Member] | Scenario, Forecast [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Postretirement medical benefits | $ 3 |  |  |
U.S. Defined Benefit Plans [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Accumulated benefit obligation |  | 2 | 2 |
Foreign Plans [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Accumulated benefit obligation |  | $ 145 | $ 131 |
Foreign Plans [Member] | Equity [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Percentage of weighted-average target asset allocation |  | 29.00% |  |
Foreign Plans [Member] | Fixed Income Funds [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Percentage of weighted-average target asset allocation |  | 47.00% |  |
Foreign Plans [Member] | Real Estate [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Percentage of weighted-average target asset allocation |  | 18.00% |  |
Foreign Plans [Member] | Cash and Other Securities [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Percentage of weighted-average target asset allocation |  | 6.00% |  |

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- Definition Defined benefit plan target allocation percentage plan assets. + References No definition available. + Details
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- Definition Amount of actuarial present value of benefits attributed to employee service rendered, excluding assumptions about future compensation level. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (e) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition Amount of contribution expected to be received by defined benefit plan from employer in next fiscal year following current fiscal year. + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 55 -Paragraph 18 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480482/715-20-55-18 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (g) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480506/715-20-50-1 + Details
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- Definition Amount of cost for defined contribution plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 70 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480794/715-70-50-1 + Details
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- Definition Amount of cost (reversal of cost) for other postretirement benefits. Excludes pension benefits. + References No definition available. + Details
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