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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, 2026
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Defined contribution plans expenses | $ 22 | $ 20 | $ 19 |
Total pension plan assets | 151 | 156 |  |
U.K. Plans [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Benefit obligation | 43 |  |  |
Total pension plan assets | 51 |  |  |
Defined benefit plan settlement charge recognized amount | 3 |  |  |
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] |  |  |  |
Expected contribution |  |  |  | $ 2
U.S. Defined Benefit Plans [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Accumulated benefit obligation | 2 | 2 |  |
U.S. Defined Benefit Plans [Member] | Pension Benefits [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Benefit obligation | 2 | 2 | 2 |
U.S. Defined Benefit Plans [Member] | Postretirement Benefits [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Benefit obligation | 12 | 13 | 14 |
Foreign Plans [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Accumulated benefit obligation | $ 142 | 145 |  |
Foreign Plans [Member] | Equity [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Percentage of weighted-average target asset allocation | 30.00% |  |  |
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 | 5.00% |  |  |
Foreign Plans [Member] | Pension Benefits [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Benefit obligation | $ 152 | 155 | 139 |
Total pension plan assets | 151 | 156 | 144 |
Foreign Plans [Member] | Postretirement Benefits [Member] |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |
Benefit obligation | $ 11 | $ 12 | $ 11 |

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