Business Segments - Narrative (Details) $ in Millions	12 Months Ended
Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($) position
Segment Reporting Information [Line Items]
Gain (loss) on asset sales and sale of business, net	$ (134.2)	$ 13.8	$ 2.5
Restructuring and Related Cost, Expected Number of Positions Eliminated \| position			1,400
Restructuring and other credits (charges)	(23.7)	10.5	$ (1,132.1)
Income (loss) from equity method investments	12.6	0.1	(7.0)
Total international sales	1,617.4	1,264.9	1,173.0
Sales by U.S. operations to foreign countries	1,217.9	846.3	812.3
Inventory valuation reserves	70.9	65.4
Closed operations and other expenses	(12.1)	(4.8)	(7.4)
Net gain (loss) on sale of businesses	(134.2)	0.0	0.0
Income From Government Assistance, CARES Act	34.0
Sheffield, UK Operations
Segment Reporting Information [Line Items]
Net gain (loss) on sale of businesses	(141.0)
Pico Rivera, CA Operations
Segment Reporting Information [Line Items]
Gain (Loss) on disposition of other assets	6.8
High Performance Materials & Components
Segment Reporting Information [Line Items]
Employee Retention Credits, Aviation Manufacturing Jobs Protection Program	27.0
Advanced Alloys & Solutions [Member]
Segment Reporting Information [Line Items]
Employee retention credits	$ 7.0
Allegheny & Tsingshan Stainless
Segment Reporting Information [Line Items]
Equity method investment ownership percentage	50.00%
Revenue from related parties	$ 0.0	0.0	18.4
Income (loss) from equity method investments	9.1	(0.9)	(10.6)
Allegheny & Tsingshan Stainless \| Advanced Alloys & Solutions [Member]
Segment Reporting Information [Line Items]
Income (loss) from equity method investments	$ 8.2	(0.9)	(8.2)
Uniti [Member]
Segment Reporting Information [Line Items]
Equity method investment ownership percentage	50.00%
Revenue from related parties	$ 45.0	45.8	36.7
Uniti [Member] \| Advanced Alloys & Solutions [Member]
Segment Reporting Information [Line Items]
Income (loss) from equity method investments	$ 4.4	$ 1.0	$ 1.2
Aerospace & Defense Market Concentration Risk [Member] \| Revenue Benchmark [Member] \| High Performance Materials & Components
Segment Reporting Information [Line Items]
Percentage of sales	80.00%
Energy and Aerospace & Defense Market Concentration [Member] \| Revenue Benchmark [Member] \| Advanced Alloys & Solutions [Member]
Segment Reporting Information [Line Items]
Percentage of sales	50.00%
Commercial Jet Engines Concentration \| Revenue Benchmark [Member] \| High Performance Materials & Components
Segment Reporting Information [Line Items]
Percentage of sales	60.00%
Allegheny Technologies Inc \| STAL Precision Stainless Steel Company Limited [Member]
Segment Reporting Information [Line Items]
Joint venture ownership percentage	60.00%

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