Summary of Significant Accounting Policies - Principles of Consolidation (Details)	Dec. 31, 2023
Uniti [Member]
Noncontrolling Interest [Line Items]
Equity method investment ownership percentage	50.00%
Allegheny & Tsingshan Stainless
Noncontrolling Interest [Line Items]
Equity method investment ownership percentage	50.00%
Shanghai STAL Precision Stainless Steel Co Ltd [Member] \| Allegheny Technologies Inc
Noncontrolling Interest [Line Items]
Joint venture ownership percentage	60.00%

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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 323
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147481687/323-10-50-3

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant