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Summary of Significant Accounting Policies - Weighted-Average Useful Lives of Software and Other Intangible Assets (Detail) | 12 Months Ended
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Dec. 31, 2017
Software | Engineered Products and Solutions |
Finite-Lived Intangible Assets [Line Items] |
Weighted-average useful lives of other intangible assets | 6 years
Software | Global Rolled Products |
Finite-Lived Intangible Assets [Line Items] |
Weighted-average useful lives of other intangible assets | 6 years
Software | Transportation and Construction Solutions |
Finite-Lived Intangible Assets [Line Items] |
Weighted-average useful lives of other intangible assets | 5 years
Other intangible assets | Engineered Products and Solutions |
Finite-Lived Intangible Assets [Line Items] |
Weighted-average useful lives of other intangible assets | 34 years
Other intangible assets | Global Rolled Products |
Finite-Lived Intangible Assets [Line Items] |
Weighted-average useful lives of other intangible assets | 9 years
Other intangible assets | Transportation and Construction Solutions |
Finite-Lived Intangible Assets [Line Items] |
Weighted-average useful lives of other intangible assets | 16 years

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- Definition Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + 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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- Details
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