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Plant Closures (Details) - USD ($) | 3 Months Ended | 6 Months Ended | 12 Months Ended | 57 Months Ended
--- | --- | --- | --- | ---
Mar. 31, 2024 | Mar. 31, 2023 | Mar. 31, 2024 | Mar. 31, 2023 | Dec. 31, 2023 | Sep. 30, 2023
Property, Plant and Equipment [Line Items] |  |  |  |  |  |
Accelerated depreciation |  |  |  |  |  | $ 659,000,000
Depreciation expense | $ 450,000,000 | $ 481,000,000 | $ 902,000,000 | $ 947,000,000 |  |
Accumulated additional depreciation |  | $ 37,000,000 |  | $ 73,000,000 |  |
Cumberland |  |  |  |  |  |
Property, Plant and Equipment [Line Items] |  |  |  |  |  |
Accelerated depreciation | $ 16,000,000 |  |  |  |  |
Accumulated additional depreciation |  |  |  |  | $ 80,000,000 |

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- Definition The amount of expense recognized in the current period that reflects the allocation of the cost of tangible assets over the assets' useful lives. Includes production and non-production related depreciation. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 45 -Paragraph 28 -Subparagraph (b) -SubTopic 10 -Topic 230 -Publisher FASB -URI https://asc.fasb.org//1943274/2147482740/230-10-45-28 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 360 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org//1943274/2147482099/360-10-50-1 + Details
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