Revenue from Contracts with Customers - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 30, 2025	Mar. 31, 2024
Disaggregation of Revenue [Line Items]
Revenue	$ 1,144.4	$ 1,042.9
Percent of revenue	100.00%	100.00%
Nickel-based Alloys and Specialty Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	48.00%	45.00%
Precision and Engineered Strip [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	5.00%	8.00%
Precision Forgings, Casting and Components [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	20.00%	19.00%
Titanium and Titanium-based Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	19.00%	18.00%
Zirconium and Related Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	8.00%	10.00%
UNITED STATES
Disaggregation of Revenue [Line Items]
Revenue	$ 643.8	$ 571.6
Asia [Member]
Disaggregation of Revenue [Line Items]
Revenue	114.3	116.2
Europe [Member]
Disaggregation of Revenue [Line Items]
Revenue	260.7	262.2
CANADA
Disaggregation of Revenue [Line Items]
Revenue	39.8	27.6
South America, Middle East, and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue	85.8	65.3
Aerospace and Defense Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	754.4	615.7
Jet Engines- Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue	421.4	311.2
Airframes- Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue	205.8	190.1
Defense [Member]
Disaggregation of Revenue [Line Items]
Revenue	127.2	114.4
Conventional energy
Disaggregation of Revenue [Line Items]
Revenue	121.8	102.5
Specialty Energy [Member]
Disaggregation of Revenue [Line Items]
Revenue	50.5	56.1
Automotive Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	60.6	56.0
Electronic Devices Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	39.6	52.9
Construction Mining Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	32.9	27.2
Medical Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	42.4	59.1
Other Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	42.2	73.4
Other Core Markets
Disaggregation of Revenue [Line Items]
Revenue	132.5	168.1
Core End Markets
Disaggregation of Revenue [Line Items]
Revenue	886.9	783.8
Industrial Markets
Disaggregation of Revenue [Line Items]
Revenue	257.5	259.1
Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	1,261.7	1,132.6
Operating Segments | HPMC
Disaggregation of Revenue [Line Items]
Revenue	$ 644.0	$ 571.9
Percent of revenue	100.00%	100.00%
Operating Segments | HPMC | Nickel-based Alloys and Specialty Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	41.00%	39.00%
Operating Segments | HPMC | Precision and Engineered Strip [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	0.00%	1.00%
Operating Segments | HPMC | Precision Forgings, Casting and Components [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	39.00%	36.00%
Operating Segments | HPMC | Titanium and Titanium-based Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	20.00%	24.00%
Operating Segments | HPMC | Zirconium and Related Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	0.00%	0.00%
Operating Segments | HPMC | UNITED STATES
Disaggregation of Revenue [Line Items]
Revenue	$ 316.4	$ 240.7
Operating Segments | HPMC | Asia [Member]
Disaggregation of Revenue [Line Items]
Revenue	33.3	38.9
Operating Segments | HPMC | Europe [Member]
Disaggregation of Revenue [Line Items]
Revenue	191.3	211.5
Operating Segments | HPMC | CANADA
Disaggregation of Revenue [Line Items]
Revenue	20.1	15.3
Operating Segments | HPMC | South America, Middle East, and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue	23.0	23.5
Operating Segments | HPMC | Aerospace and Defense Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	537.5	442.6
Operating Segments | HPMC | Jet Engines- Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue	397.3	296.9
Operating Segments | HPMC | Airframes- Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue	81.8	85.7
Operating Segments | HPMC | Defense [Member]
Disaggregation of Revenue [Line Items]
Revenue	58.4	60.0
Operating Segments | HPMC | Conventional energy
Disaggregation of Revenue [Line Items]
Revenue	1.7	3.5
Operating Segments | HPMC | Specialty Energy [Member]
Disaggregation of Revenue [Line Items]
Revenue	12.4	18.2
Operating Segments | HPMC | Automotive Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	1.4	5.0
Operating Segments | HPMC | Electronic Devices Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	0.0	1.0
Operating Segments | HPMC | Construction Mining Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	7.1	6.7
Operating Segments | HPMC | Medical Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	15.8	35.9
Operating Segments | HPMC | Other Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	8.2	17.0
Operating Segments | HPMC | Other Core Markets
Disaggregation of Revenue [Line Items]
Revenue	28.2	55.1
Operating Segments | HPMC | Core End Markets
Disaggregation of Revenue [Line Items]
Revenue	565.7	497.7
Operating Segments | AA&S
Disaggregation of Revenue [Line Items]
Revenue	$ 617.7	$ 560.7
Percent of revenue	100.00%	100.00%
Operating Segments | AA&S | Nickel-based Alloys and Specialty Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	55.00%	51.00%
Operating Segments | AA&S | Precision and Engineered Strip [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	11.00%	17.00%
Operating Segments | AA&S | Precision Forgings, Casting and Components [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	0.00%	0.00%
Operating Segments | AA&S | Titanium and Titanium-based Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	17.00%	12.00%
Operating Segments | AA&S | Zirconium and Related Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	17.00%	20.00%
Operating Segments | AA&S | UNITED STATES
Disaggregation of Revenue [Line Items]
Revenue	$ 327.4	$ 330.9
Operating Segments | AA&S | Asia [Member]
Disaggregation of Revenue [Line Items]
Revenue	81.0	77.3
Operating Segments | AA&S | Europe [Member]
Disaggregation of Revenue [Line Items]
Revenue	69.4	50.7
Operating Segments | AA&S | CANADA
Disaggregation of Revenue [Line Items]
Revenue	19.7	12.3
Operating Segments | AA&S | South America, Middle East, and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue	62.8	41.8
Operating Segments | AA&S | Aerospace and Defense Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	216.9	173.1
Operating Segments | AA&S | Jet Engines- Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue	24.1	14.3
Operating Segments | AA&S | Airframes- Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue	124.0	104.4
Operating Segments | AA&S | Defense [Member]
Disaggregation of Revenue [Line Items]
Revenue	68.8	54.4
Operating Segments | AA&S | Conventional energy
Disaggregation of Revenue [Line Items]
Revenue	120.1	99.0
Operating Segments | AA&S | Specialty Energy [Member]
Disaggregation of Revenue [Line Items]
Revenue	38.1	37.9
Operating Segments | AA&S | Automotive Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	59.2	51.0
Operating Segments | AA&S | Electronic Devices Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	39.6	51.9
Operating Segments | AA&S | Construction Mining Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	25.8	20.5
Operating Segments | AA&S | Medical Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	26.6	23.2
Operating Segments | AA&S | Other Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	34.0	56.4
Operating Segments | AA&S | Other Core Markets
Disaggregation of Revenue [Line Items]
Revenue	104.3	113.0
Operating Segments | AA&S | Core End Markets
Disaggregation of Revenue [Line Items]
Revenue	321.2	286.1
Sales to external customers | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	1,144.4	1,042.9
Sales to external customers | Operating Segments | HPMC
Disaggregation of Revenue [Line Items]
Revenue	584.1	529.9
Sales to external customers | Operating Segments | AA&S
Disaggregation of Revenue [Line Items]
Revenue	560.3	513.0
Industrial Markets | Operating Segments | HPMC
Disaggregation of Revenue [Line Items]
Revenue	18.4	32.2
Industrial Markets | Operating Segments | AA&S
Disaggregation of Revenue [Line Items]
Revenue	$ 239.1	$ 226.9