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Revenue from Contracts with Customers - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 29, 2024	Oct. 01, 2023	Sep. 29, 2024	Oct. 01, 2023
Disaggregation of Revenue [Line Items]
Revenue	$ 1,051.2	$ 1,025.6	$ 3,189.4	$ 3,109.7
Percent of revenue	100.00%	100.00%	100.00%	100.00%
Nickel-based Alloys and Specialty Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	46.00%	47.00%	45.00%	50.00%
Precision and Engineered Strip [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	9.00%	9.00%	9.00%	9.00%
Precision Forgings, Casting and Components [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	20.00%	18.00%	19.00%	17.00%
Titanium and Titanium-based Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	17.00%	19.00%	18.00%	16.00%
Zirconium and Related Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	8.00%	7.00%	9.00%	8.00%
UNITED STATES
Disaggregation of Revenue [Line Items]
Revenue	$ 625.6	$ 556.8	$ 1,835.7	$ 1,713.4
Asia [Member]
Disaggregation of Revenue [Line Items]
Revenue	123.3	141.2	365.0	449.2
Europe [Member]
Disaggregation of Revenue [Line Items]
Revenue	243.0	267.4	783.4	757.4
CANADA
Disaggregation of Revenue [Line Items]
Revenue	31.4	23.5	84.9	76.6
South America, Middle East, and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue	27.9	36.7	120.4	113.1
Aerospace and Defense Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	653.8	625.8	1,953.4	1,808.3
Jet Engines- Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue	365.9	329.4	1,029.9	981.2
Airframes- Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue	180.8	203.6	581.7	537.7
Defense [Member]
Disaggregation of Revenue [Line Items]
Revenue	107.1	92.8	341.8	289.4
Energy
Disaggregation of Revenue [Line Items]
Revenue	142.5	148.9	443.8	538.6
Conventional energy
Disaggregation of Revenue [Line Items]
Revenue	72.6	87.0	241.2	325.8
Specialty Energy [Member]
Disaggregation of Revenue [Line Items]
Revenue	69.9	61.9	202.6	212.8
Automotive Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	63.8	48.1	190.6	160.3
Electronic Devices Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	49.1	44.8	142.8	115.2
Construction Mining Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	41.8	40.0	113.2	128.8
Food Equipment and Appliances Market
Disaggregation of Revenue [Line Items]
Revenue	12.9	16.2	41.0	58.6
Medical Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	53.1	47.5	173.9	124.4
Other Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	34.2	54.3	130.7	175.5
Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	1,201.3	1,129.9	3,582.3	3,461.5
Operating Segments | High Performance Materials & Components
Disaggregation of Revenue [Line Items]
Revenue	$ 612.9	$ 578.1	$ 1,828.6	$ 1,670.5
Percent of revenue	100.00%	100.00%	100.00%	100.00%
Operating Segments | High Performance Materials & Components | Nickel-based Alloys and Specialty Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	43.00%	42.00%	41.00%	45.00%
Operating Segments | High Performance Materials & Components | Precision and Engineered Strip [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	0.00%	1.00%	0.00%	1.00%
Operating Segments | High Performance Materials & Components | Precision Forgings, Casting and Components [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	36.00%	33.00%	36.00%	33.00%
Operating Segments | High Performance Materials & Components | Titanium and Titanium-based Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	21.00%	24.00%	23.00%	21.00%
Operating Segments | High Performance Materials & Components | Zirconium and Related Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	0.00%	0.00%	0.00%	0.00%
Operating Segments | High Performance Materials & Components | UNITED STATES
Disaggregation of Revenue [Line Items]
Revenue	$ 285.8	$ 242.6	$ 797.9	$ 661.1
Operating Segments | High Performance Materials & Components | Asia [Member]
Disaggregation of Revenue [Line Items]
Revenue	30.3	37.8	106.5	132.8
Operating Segments | High Performance Materials & Components | Europe [Member]
Disaggregation of Revenue [Line Items]
Revenue	201.4	217.7	636.9	619.7
Operating Segments | High Performance Materials & Components | CANADA
Disaggregation of Revenue [Line Items]
Revenue	16.4	13.1	45.4	41.7
Operating Segments | High Performance Materials & Components | South America, Middle East, and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue	18.5	28.3	57.6	82.4
Operating Segments | High Performance Materials & Components | Aerospace and Defense Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	474.9	456.2	1,395.0	1,287.8
Operating Segments | High Performance Materials & Components | Jet Engines- Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue	341.9	312.5	970.6	914.2
Operating Segments | High Performance Materials & Components | Airframes- Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue	84.1	104.0	263.5	242.0
Operating Segments | High Performance Materials & Components | Defense [Member]
Disaggregation of Revenue [Line Items]
Revenue	48.9	39.7	160.9	131.6
Operating Segments | High Performance Materials & Components | Energy
Disaggregation of Revenue [Line Items]
Revenue	28.7	22.7	75.3	83.6
Operating Segments | High Performance Materials & Components | Conventional energy
Disaggregation of Revenue [Line Items]
Revenue	2.4	2.5	8.3	8.6
Operating Segments | High Performance Materials & Components | Specialty Energy [Member]
Disaggregation of Revenue [Line Items]
Revenue	26.3	20.2	67.0	75.0
Operating Segments | High Performance Materials & Components | Automotive Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	4.6	7.2	13.4	19.5
Operating Segments | High Performance Materials & Components | Electronic Devices Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	0.0	0.6	3.0	1.8
Operating Segments | High Performance Materials & Components | Construction Mining Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	4.9	7.7	19.9	26.9
Operating Segments | High Performance Materials & Components | Food Equipment and Appliances Market
Disaggregation of Revenue [Line Items]
Revenue	0.0	0.0	0.0	0.0
Operating Segments | High Performance Materials & Components | Medical Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	28.6	28.9	97.5	70.7
Operating Segments | High Performance Materials & Components | Other Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	10.7	16.2	40.2	47.4
Operating Segments | Advanced Alloys & Solutions
Disaggregation of Revenue [Line Items]
Revenue	$ 588.4	$ 551.8	$ 1,753.7	$ 1,791.0
Percent of revenue	100.00%	100.00%	100.00%	100.00%
Operating Segments | Advanced Alloys & Solutions | Nickel-based Alloys and Specialty Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	50.00%	52.00%	50.00%	56.00%
Operating Segments | Advanced Alloys & Solutions | Precision and Engineered Strip [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	21.00%	19.00%	19.00%	18.00%
Operating Segments | Advanced Alloys & Solutions | Precision Forgings, Casting and Components [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	0.00%	0.00%	0.00%	0.00%
Operating Segments | Advanced Alloys & Solutions | Titanium and Titanium-based Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	12.00%	13.00%	13.00%	11.00%
Operating Segments | Advanced Alloys & Solutions | Zirconium and Related Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	17.00%	16.00%	18.00%	15.00%
Operating Segments | Advanced Alloys & Solutions | UNITED STATES
Disaggregation of Revenue [Line Items]
Revenue	$ 339.8	$ 314.2	$ 1,037.8	$ 1,052.3
Operating Segments | Advanced Alloys & Solutions | Asia [Member]
Disaggregation of Revenue [Line Items]
Revenue	93.0	103.4	258.5	316.4
Operating Segments | Advanced Alloys & Solutions | Europe [Member]
Disaggregation of Revenue [Line Items]
Revenue	41.6	49.7	146.5	137.7
Operating Segments | Advanced Alloys & Solutions | CANADA
Disaggregation of Revenue [Line Items]
Revenue	15.0	10.4	39.5	34.9
Operating Segments | Advanced Alloys & Solutions | South America, Middle East, and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue	9.4	8.4	62.8	30.7
Operating Segments | Advanced Alloys & Solutions | Aerospace and Defense Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	178.9	169.6	558.4	520.5
Operating Segments | Advanced Alloys & Solutions | Jet Engines- Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue	24.0	16.9	59.3	67.0
Operating Segments | Advanced Alloys & Solutions | Airframes- Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue	96.7	99.6	318.2	295.7
Operating Segments | Advanced Alloys & Solutions | Defense [Member]
Disaggregation of Revenue [Line Items]
Revenue	58.2	53.1	180.9	157.8
Operating Segments | Advanced Alloys & Solutions | Energy
Disaggregation of Revenue [Line Items]
Revenue	113.8	126.2	368.5	455.0
Operating Segments | Advanced Alloys & Solutions | Conventional energy
Disaggregation of Revenue [Line Items]
Revenue	70.2	84.5	232.9	317.2
Operating Segments | Advanced Alloys & Solutions | Specialty Energy [Member]
Disaggregation of Revenue [Line Items]
Revenue	43.6	41.7	135.6	137.8
Operating Segments | Advanced Alloys & Solutions | Automotive Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	59.2	40.9	177.2	140.8
Operating Segments | Advanced Alloys & Solutions | Electronic Devices Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	49.1	44.2	139.8	113.4
Operating Segments | Advanced Alloys & Solutions | Construction Mining Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	36.9	32.3	93.3	101.9
Operating Segments | Advanced Alloys & Solutions | Food Equipment and Appliances Market
Disaggregation of Revenue [Line Items]
Revenue	12.9	16.2	41.0	58.6
Operating Segments | Advanced Alloys & Solutions | Medical Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	24.5	18.6	76.4	53.7
Operating Segments | Advanced Alloys & Solutions | Other Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	23.5	38.1	90.5	128.1
External Customers | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	1,051.2	1,025.6	3,189.4	3,109.7
External Customers | Operating Segments | High Performance Materials & Components
Disaggregation of Revenue [Line Items]
Revenue	552.4	539.5	1,644.3	1,537.7
External Customers | Operating Segments | Advanced Alloys & Solutions
Disaggregation of Revenue [Line Items]
Revenue	$ 498.8	$ 486.1	$ 1,545.1	$ 1,572.0

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