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Summary of Significant Accounting Policies - Weighted-Average Useful Lives of Structures and Machinery and Equipment (Details) | 12 Months Ended
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Dec. 31, 2019
Structures | Engineered Products and Forgings |
Property, Plant and Equipment [Line Items] |
Weighted-average useful lives of assets, years | 29 years
Structures | Global Rolled Products |
Property, Plant and Equipment [Line Items] |
Weighted-average useful lives of assets, years | 31 years
Machinery and equipment | Engineered Products and Forgings |
Property, Plant and Equipment [Line Items] |
Weighted-average useful lives of assets, years | 17 years
Machinery and equipment | Global Rolled Products |
Property, Plant and Equipment [Line Items] |
Weighted-average useful lives of assets, years | 21 years

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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 Useful life of long lived, physical assets used in the normal conduct of business and not intended for resale, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. Examples include, but not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment. + References No definition available. + Details
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- Details
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- Details
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- Details
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- Details
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