For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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Amount of gain (loss) on sale or disposal of oil and gas property or timber property.

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Amount of gain (loss) from the difference between the sale price or salvage price and the book value of an asset that was sold or retired, and gain (loss) from the write down of assets from their carrying value to fair value.

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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

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Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

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The expected number of positions to be eliminated as a result of restructuring activities.

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Business Segments - Additional Information (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($) employee segment	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($)
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	$ 12.4
Gain on asset sales, net	$ 2.5	$ 0.0
Number of business segments \| segment	2
Goodwill	$ 520.8		$ 525.8
Gain on the sale of oil and gas rights	$ 2.5
Restructuring and Related Cost, Expected Number of Positions Eliminated \| employee	90
Aerospace and Defense Market Concentration [Member] \| High Performance Materials & Components \| Revenue from Contract with Customer, Segment Benchmark [Member]
Restructuring Cost and Reserve [Line Items]
Concentration Risk, Percentage	80.00%
Energy and Aerospace & Defense Market Concentration [Member] \| Advanced Alloys & Solutions [Member] \| Revenue from Contract with Customer, Segment Benchmark [Member]
Restructuring Cost and Reserve [Line Items]
Concentration Risk, Percentage	50.00%
Allegheny & Tsingshan Stainless
Restructuring Cost and Reserve [Line Items]
Equity method investment ownership percentage	50.00%
Uniti
Restructuring Cost and Reserve [Line Items]
Equity method investment ownership percentage	50.00%
Other Current Liabilities [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	$ 11.2
Other long-term liabilities [Member]
Restructuring Cost and Reserve [Line Items]
Restructuring Reserve	$ 1.2
Allegheny Technologies Inc \| Shanghai STAL Precision Stainless Steel Co Ltd \| Advanced Alloys & Solutions [Member]
Restructuring Cost and Reserve [Line Items]
Joint venture ownership percentage	60.00%