Revenue from Contracts with Customers - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jul. 02, 2023	Jun. 30, 2024	Jul. 02, 2023
Disaggregation of Revenue [Line Items]
Revenue	$ 1,095.3	$ 1,046.0	$ 2,138.2	$ 2,084.1
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	44.00%	52.00%	44.00%	52.00%
Precision and Engineered Strip [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	9.00%	9.00%	9.00%	10.00%
Precision Forgings, Casting and Components [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	19.00%	17.00%	19.00%	16.00%
Titanium and Titanium-based Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	20.00%	14.00%	19.00%	14.00%
Zirconium and Related Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	8.00%	8.00%	9.00%	8.00%
UNITED STATES
Disaggregation of Revenue [Line Items]
Revenue	$ 638.5	$ 568.3	$ 1,210.1	$ 1,156.6
Asia [Member]
Disaggregation of Revenue [Line Items]
Revenue	125.5	154.5	241.7	308.0
Europe [Member]
Disaggregation of Revenue [Line Items]
Revenue	278.2	251.4	540.4	490.0
CANADA
Disaggregation of Revenue [Line Items]
Revenue	25.9	29.9	53.5	53.1
South America, Middle East, and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue	27.2	41.9	92.5	76.4
Aerospace and Defense Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	683.9	606.8	1,299.6	1,182.5
Jet Engines- Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue	352.8	340.9	664.0	651.8
Airframes- Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue	210.8	164.2	400.9	334.1
Defense [Member]
Disaggregation of Revenue [Line Items]
Revenue	120.3	101.7	234.7	196.6
Energy
Disaggregation of Revenue [Line Items]
Revenue	142.7	179.5	301.3	389.7
Conventional energy
Disaggregation of Revenue [Line Items]
Revenue	66.1	111.3	168.6	238.8
Specialty Energy [Member]
Disaggregation of Revenue [Line Items]
Revenue	76.6	68.2	132.7	150.9
Automotive Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	70.8	52.8	126.8	112.2
Electronic Devices Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	40.8	36.0	93.7	70.4
Construction Mining Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	44.2	48.4	71.4	88.8
Food Equipment and Appliances Market
Disaggregation of Revenue [Line Items]
Revenue	16.2	20.9	28.1	42.4
Medical Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	61.7	41.9	120.8	76.9
Other Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	35.0	59.7	96.5	121.2
Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	1,248.4	1,176.2	2,381.0	2,331.6
Operating Segments | High Performance Materials & Components
Disaggregation of Revenue [Line Items]
Revenue	$ 643.8	$ 562.8	$ 1,215.7	$ 1,092.4
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	39.00%	49.00%	39.00%	47.00%
Operating Segments | High Performance Materials & Components | Precision and Engineered Strip [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	0.00%	1.00%	1.00%	1.00%
Operating Segments | High Performance Materials & Components | Precision Forgings, Casting and Components [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	37.00%	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	24.00%	17.00%	24.00%	19.00%
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	$ 271.4	$ 222.0	$ 512.1	$ 418.5
Operating Segments | High Performance Materials & Components | Asia [Member]
Disaggregation of Revenue [Line Items]
Revenue	37.3	51.0	76.2	95.0
Operating Segments | High Performance Materials & Components | Europe [Member]
Disaggregation of Revenue [Line Items]
Revenue	224.0	207.8	435.5	402.0
Operating Segments | High Performance Materials & Components | CANADA
Disaggregation of Revenue [Line Items]
Revenue	13.7	16.6	29.0	28.6
Operating Segments | High Performance Materials & Components | South America, Middle East, and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue	15.6	29.7	39.1	54.1
Operating Segments | High Performance Materials & Components | Aerospace and Defense Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	477.5	436.2	920.1	831.6
Operating Segments | High Performance Materials & Components | Jet Engines- Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue	331.8	319.2	628.7	601.7
Operating Segments | High Performance Materials & Components | Airframes- Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue	93.7	67.0	179.4	138.0
Operating Segments | High Performance Materials & Components | Defense [Member]
Disaggregation of Revenue [Line Items]
Revenue	52.0	50.0	112.0	91.9
Operating Segments | High Performance Materials & Components | Energy
Disaggregation of Revenue [Line Items]
Revenue	24.9	33.6	46.6	60.9
Operating Segments | High Performance Materials & Components | Conventional energy
Disaggregation of Revenue [Line Items]
Revenue	2.4	3.7	5.9	6.1
Operating Segments | High Performance Materials & Components | Specialty Energy [Member]
Disaggregation of Revenue [Line Items]
Revenue	22.5	29.9	40.7	54.8
Operating Segments | High Performance Materials & Components | Automotive Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	3.8	6.0	8.8	12.3
Operating Segments | High Performance Materials & Components | Electronic Devices Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	2.0	0.7	3.0	1.2
Operating Segments | High Performance Materials & Components | Construction Mining Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	8.3	11.0	15.0	19.2
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	33.0	24.3	68.9	41.8
Operating Segments | High Performance Materials & Components | Other Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	12.5	15.3	29.5	31.2
Operating Segments | Advanced Alloys & Solutions
Disaggregation of Revenue [Line Items]
Revenue	$ 604.6	$ 613.4	$ 1,165.3	$ 1,239.2
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	49.00%	55.00%	50.00%	57.00%
Operating Segments | Advanced Alloys & Solutions | Precision and Engineered Strip [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	18.00%	18.00%	18.00%	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	15.00%	11.00%	13.00%	10.00%
Operating Segments | Advanced Alloys & Solutions | Zirconium and Related Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of revenue	18.00%	16.00%	19.00%	15.00%
Operating Segments | Advanced Alloys & Solutions | UNITED STATES
Disaggregation of Revenue [Line Items]
Revenue	$ 367.1	$ 346.3	$ 698.0	$ 738.1
Operating Segments | Advanced Alloys & Solutions | Asia [Member]
Disaggregation of Revenue [Line Items]
Revenue	88.2	103.5	165.5	213.0
Operating Segments | Advanced Alloys & Solutions | Europe [Member]
Disaggregation of Revenue [Line Items]
Revenue	54.2	43.6	104.9	88.0
Operating Segments | Advanced Alloys & Solutions | CANADA
Disaggregation of Revenue [Line Items]
Revenue	12.2	13.3	24.5	24.5
Operating Segments | Advanced Alloys & Solutions | South America, Middle East, and Other [Member]
Disaggregation of Revenue [Line Items]
Revenue	11.6	12.2	53.4	22.3
Operating Segments | Advanced Alloys & Solutions | Aerospace and Defense Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	206.4	170.6	379.5	350.9
Operating Segments | Advanced Alloys & Solutions | Jet Engines- Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue	21.0	21.7	35.3	50.1
Operating Segments | Advanced Alloys & Solutions | Airframes- Commercial [Member]
Disaggregation of Revenue [Line Items]
Revenue	117.1	97.2	221.5	196.1
Operating Segments | Advanced Alloys & Solutions | Defense [Member]
Disaggregation of Revenue [Line Items]
Revenue	68.3	51.7	122.7	104.7
Operating Segments | Advanced Alloys & Solutions | Energy
Disaggregation of Revenue [Line Items]
Revenue	117.8	145.9	254.7	328.8
Operating Segments | Advanced Alloys & Solutions | Conventional energy
Disaggregation of Revenue [Line Items]
Revenue	63.7	107.6	162.7	232.7
Operating Segments | Advanced Alloys & Solutions | Specialty Energy [Member]
Disaggregation of Revenue [Line Items]
Revenue	54.1	38.3	92.0	96.1
Operating Segments | Advanced Alloys & Solutions | Automotive Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	67.0	46.8	118.0	99.9
Operating Segments | Advanced Alloys & Solutions | Electronic Devices Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	38.8	35.3	90.7	69.2
Operating Segments | Advanced Alloys & Solutions | Construction Mining Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	35.9	37.4	56.4	69.6
Operating Segments | Advanced Alloys & Solutions | Food Equipment and Appliances Market
Disaggregation of Revenue [Line Items]
Revenue	16.2	20.9	28.1	42.4
Operating Segments | Advanced Alloys & Solutions | Medical Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	28.7	17.6	51.9	35.1
Operating Segments | Advanced Alloys & Solutions | Other Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	22.5	44.4	67.0	90.0
External Customers | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	1,095.3	1,046.0	2,138.2	2,084.1
External Customers | Operating Segments | High Performance Materials & Components
Disaggregation of Revenue [Line Items]
Revenue	562.0	527.1	1,091.9	998.2
External Customers | Operating Segments | Advanced Alloys & Solutions
Disaggregation of Revenue [Line Items]
Revenue	$ 533.3	$ 518.9	$ 1,046.3	$ 1,085.9