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Significant Accounting Policies - Additional Information (Detail) - USD ($) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Jun. 30, 2024 | Mar. 31, 2024 | Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2022
Significant Accounting Policies [Line Items] |  |  |  |  |
Equity affiliate investments |  |  | $ 23,000,000 | $ 20,000,000 |
Capitalized interest |  |  | 9,000,000 | 6,000,000 | $ 3,000,000
Asset retirement obligation reserve |  |  | 11,000,000 | 11,000,000 |
Changes in allowance |  |  | $ 0 | 0 | 0
Chance of utilizing the associated benefit for valuation allowances, maximum |  |  | 50.00% |  |
Equity Method Investments [Member] |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Dividends declared |  |  | $ 2,000,000 | 2,000,000 | 1,000,000
Minimum [Member] |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Payment terms |  |  | 0 days |  |
Minimum [Member] | Buildings [Member] |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Useful life of property, plant and equipment |  |  | 20 years |  |
Minimum [Member] | Machinery and Equipment [Member] |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Useful life of property, plant and equipment |  |  | 10 years |  |
Minimum [Member] | Other Fixed Assets [Member] |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Useful life of property, plant and equipment |  |  | 3 years |  |
Minimum [Member] | Cabot [Member] | Equity Affiliate Investments [Member] |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Equity method investment, ownership percentage |  |  | 20.00% |  |
Maximum [Member] |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Payment terms |  |  | 90 days |  |
Maximum [Member] | Buildings [Member] |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Useful life of property, plant and equipment |  |  | 25 years |  |
Maximum [Member] | Machinery and Equipment [Member] |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Useful life of property, plant and equipment |  |  | 25 years |  |
Maximum [Member] | Other Fixed Assets [Member] |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Useful life of property, plant and equipment |  |  | 25 years |  |
Maximum [Member] | Cabot [Member] | Equity Affiliate Investments [Member] |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Equity method investment, ownership percentage |  |  | 50.00% |  |
Other Nonoperating Income (Expense) [Member] |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Foreign currency transaction gain (loss) |  |  | $ (46,000,000) | (35,000,000) | (13,000,000)
Investment income (loss) |  |  | 17,000,000 | 16,000,000 | 5,000,000
Other Nonoperating Income (Expense) [Member] | Revaluation of Non-functional Currency [Member] |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Foreign currency transaction gain (loss) |  |  | (43,000,000) | (33,000,000) | (15,000,000)
Other Nonoperating Income (Expense) [Member] | Single Devaluation Action [Member] |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Foreign currency transaction gain (loss) |  |  | $ (33,000,000) | $ (7,000,000) | $ 0
BOPREAL Bonds [Member] |  |  |  |  |
Significant Accounting Policies [Line Items] |  |  |  |  |
Foreign currency transaction gain (loss) | $ (2,000,000) |  |  |  |
Investment income (loss) |  | $ (8,000,000) |  |  |
Purchase of bonds to settle foreign payables | $ 8,000,000 | 30,000,000 |  |  |
Proceeds from sale of bonds |  | $ 22,000,000 |  |  |

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