Revenue from Contracts with Customers - Disaggregation of Revenue (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Disaggregation of Revenue [Line Items]
Revenue	$ 3,836.0	$ 2,799.8	$ 2,982.1
Percent of total revenue	100.00%	100.00%	100.00%
Nickel-based alloys and specialty alloys
Disaggregation of Revenue [Line Items]
Percent of total revenue	52.00%	43.00%	45.00%
Precision Forgings, Casting and Components [Member]
Disaggregation of Revenue [Line Items]
Percent of total revenue	15.00%	16.00%	14.00%
Titanium and Titanium-based Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of total revenue	11.00%	12.00%	17.00%
Zirconium and related alloys
Disaggregation of Revenue [Line Items]
Percent of total revenue	8.00%	10.00%	9.00%
Precision rolled strip
Disaggregation of Revenue [Line Items]
Percent of total revenue	14.00%	19.00%	15.00%
United States
Disaggregation of Revenue [Line Items]
Revenue	$ 2,218.6	$ 1,534.9	$ 1,809.1
China
Disaggregation of Revenue [Line Items]
Revenue	351.8	370.4	315.5
Germany
Disaggregation of Revenue [Line Items]
Revenue	200.9	121.3	125.4
UNITED KINGDOM
Disaggregation of Revenue [Line Items]
Revenue	217.7	153.9	126.5
Rest of World
Disaggregation of Revenue [Line Items]
Revenue	602.4	484.9	451.8
France
Disaggregation of Revenue [Line Items]
Revenue	157.2	58.5	84.9
CANADA
Disaggregation of Revenue [Line Items]
Revenue	87.4	75.9	68.9
Total Aerospace & Defense
Disaggregation of Revenue [Line Items]
Revenue	1,873.6	1,132.7	1,360.0
Total Energy
Disaggregation of Revenue [Line Items]
Revenue	753.3	591.9	618.9
Automotive
Disaggregation of Revenue [Line Items]
Revenue	302.1	305.1	263.2
Food Equipment & Appliances
Disaggregation of Revenue [Line Items]
Revenue	158.5	153.1	159.2
Construction/Mining
Disaggregation of Revenue [Line Items]
Revenue	176.4	122.2	142.0
Medical Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	163.1	131.5	119.1
Electronic Devices Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	200.0	215.1	177.7
Other
Disaggregation of Revenue [Line Items]
Revenue	209.0	148.2	142.0
Jet Engines- Commercial
Disaggregation of Revenue [Line Items]
Revenue	1,063.5	517.2	600.9
Airframes- Commercial
Disaggregation of Revenue [Line Items]
Revenue	468.9	262.7	410.8
Defense
Disaggregation of Revenue [Line Items]
Revenue	341.2	352.8	348.3
Oil & Gas
Disaggregation of Revenue [Line Items]
Revenue	476.7	332.3	365.8
Specialty Energy
Disaggregation of Revenue [Line Items]
Revenue	276.6	259.6	253.1
Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	4,249.4	3,010.7	3,182.9
Operating Segments | High Performance Materials & Components
Disaggregation of Revenue [Line Items]
Revenue	$ 1,815.7	$ 1,248.3	$ 1,235.4
Percent of total revenue	100.00%	100.00%	100.00%
Operating Segments | High Performance Materials & Components | Nickel-based alloys and specialty alloys
Disaggregation of Revenue [Line Items]
Percent of total revenue	49.00%	43.00%	38.00%
Operating Segments | High Performance Materials & Components | Precision Forgings, Casting and Components [Member]
Disaggregation of Revenue [Line Items]
Percent of total revenue	34.00%	38.00%	34.00%
Operating Segments | High Performance Materials & Components | Titanium and Titanium-based Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of total revenue	17.00%	19.00%	28.00%
Operating Segments | High Performance Materials & Components | Zirconium and related alloys
Disaggregation of Revenue [Line Items]
Percent of total revenue	0.00%	0.00%	0.00%
Operating Segments | High Performance Materials & Components | Precision rolled strip
Disaggregation of Revenue [Line Items]
Percent of total revenue	0.00%	0.00%	0.00%
Operating Segments | High Performance Materials & Components | United States
Disaggregation of Revenue [Line Items]
Revenue	$ 742.9	$ 571.3	$ 641.0
Operating Segments | High Performance Materials & Components | China
Disaggregation of Revenue [Line Items]
Revenue	59.8	49.5	31.0
Operating Segments | High Performance Materials & Components | Germany
Disaggregation of Revenue [Line Items]
Revenue	148.4	74.1	76.6
Operating Segments | High Performance Materials & Components | UNITED KINGDOM
Disaggregation of Revenue [Line Items]
Revenue	165.7	136.7	101.9
Operating Segments | High Performance Materials & Components | Rest of World
Disaggregation of Revenue [Line Items]
Revenue	352.5	238.5	219.3
Operating Segments | High Performance Materials & Components | France
Disaggregation of Revenue [Line Items]
Revenue	125.7	48.7	66.5
Operating Segments | High Performance Materials & Components | CANADA
Disaggregation of Revenue [Line Items]
Revenue	46.2	36.3	28.3
Operating Segments | High Performance Materials & Components | Total Aerospace & Defense
Disaggregation of Revenue [Line Items]
Revenue	1,318.0	835.5	946.9
Operating Segments | High Performance Materials & Components | Total Energy
Disaggregation of Revenue [Line Items]
Revenue	148.6	178.3	106.2
Operating Segments | High Performance Materials & Components | Automotive
Disaggregation of Revenue [Line Items]
Revenue	11.2	8.7	5.5
Operating Segments | High Performance Materials & Components | Food Equipment & Appliances
Disaggregation of Revenue [Line Items]
Revenue	0.2	0.1	0.0
Operating Segments | High Performance Materials & Components | Construction/Mining
Disaggregation of Revenue [Line Items]
Revenue	34.1	24.0	18.6
Operating Segments | High Performance Materials & Components | Medical Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	73.2	60.3	47.7
Operating Segments | High Performance Materials & Components | Electronic Devices Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	2.4	1.2	0.9
Operating Segments | High Performance Materials & Components | Other
Disaggregation of Revenue [Line Items]
Revenue	53.5	47.0	38.8
Operating Segments | High Performance Materials & Components | Jet Engines- Commercial
Disaggregation of Revenue [Line Items]
Revenue	975.7	480.9	542.7
Operating Segments | High Performance Materials & Components | Airframes- Commercial
Disaggregation of Revenue [Line Items]
Revenue	184.1	132.8	219.8
Operating Segments | High Performance Materials & Components | Defense
Disaggregation of Revenue [Line Items]
Revenue	158.2	221.8	184.4
Operating Segments | High Performance Materials & Components | Oil & Gas
Disaggregation of Revenue [Line Items]
Revenue	35.0	42.2	37.3
Operating Segments | High Performance Materials & Components | Specialty Energy
Disaggregation of Revenue [Line Items]
Revenue	113.6	136.1	68.9
Operating Segments | Advanced Alloys & Solutions [Member]
Disaggregation of Revenue [Line Items]
Revenue	$ 2,433.7	$ 1,762.4	$ 1,947.5
Percent of total revenue	100.00%	100.00%	100.00%
Operating Segments | Advanced Alloys & Solutions [Member] | Nickel-based alloys and specialty alloys
Disaggregation of Revenue [Line Items]
Percent of total revenue	54.00%	44.00%	49.00%
Operating Segments | Advanced Alloys & Solutions [Member] | Precision Forgings, Casting and Components [Member]
Disaggregation of Revenue [Line Items]
Percent of total revenue	0.00%	0.00%	0.00%
Operating Segments | Advanced Alloys & Solutions [Member] | Titanium and Titanium-based Alloys [Member]
Disaggregation of Revenue [Line Items]
Percent of total revenue	7.00%	6.00%	11.00%
Operating Segments | Advanced Alloys & Solutions [Member] | Zirconium and related alloys
Disaggregation of Revenue [Line Items]
Percent of total revenue	14.00%	17.00%	15.00%
Operating Segments | Advanced Alloys & Solutions [Member] | Precision rolled strip
Disaggregation of Revenue [Line Items]
Percent of total revenue	25.00%	33.00%	25.00%
Operating Segments | Advanced Alloys & Solutions [Member] | United States
Disaggregation of Revenue [Line Items]
Revenue	$ 1,475.7	$ 963.6	$ 1,168.1
Operating Segments | Advanced Alloys & Solutions [Member] | China
Disaggregation of Revenue [Line Items]
Revenue	292.0	320.9	284.5
Operating Segments | Advanced Alloys & Solutions [Member] | Germany
Disaggregation of Revenue [Line Items]
Revenue	52.5	47.2	48.8
Operating Segments | Advanced Alloys & Solutions [Member] | UNITED KINGDOM
Disaggregation of Revenue [Line Items]
Revenue	52.0	17.2	24.6
Operating Segments | Advanced Alloys & Solutions [Member] | Rest of World
Disaggregation of Revenue [Line Items]
Revenue	249.9	246.4	232.5
Operating Segments | Advanced Alloys & Solutions [Member] | France
Disaggregation of Revenue [Line Items]
Revenue	31.5	9.8	18.4
Operating Segments | Advanced Alloys & Solutions [Member] | CANADA
Disaggregation of Revenue [Line Items]
Revenue	41.2	39.6	40.6
Operating Segments | Advanced Alloys & Solutions [Member] | Total Aerospace & Defense
Disaggregation of Revenue [Line Items]
Revenue	555.6	297.2	413.1
Operating Segments | Advanced Alloys & Solutions [Member] | Total Energy
Disaggregation of Revenue [Line Items]
Revenue	604.7	413.6	512.7
Operating Segments | Advanced Alloys & Solutions [Member] | Automotive
Disaggregation of Revenue [Line Items]
Revenue	290.9	296.4	257.7
Operating Segments | Advanced Alloys & Solutions [Member] | Food Equipment & Appliances
Disaggregation of Revenue [Line Items]
Revenue	158.3	153.0	159.2
Operating Segments | Advanced Alloys & Solutions [Member] | Construction/Mining
Disaggregation of Revenue [Line Items]
Revenue	142.3	98.2	123.4
Operating Segments | Advanced Alloys & Solutions [Member] | Medical Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	89.9	71.2	71.4
Operating Segments | Advanced Alloys & Solutions [Member] | Electronic Devices Market [Member]
Disaggregation of Revenue [Line Items]
Revenue	197.6	213.9	176.8
Operating Segments | Advanced Alloys & Solutions [Member] | Other
Disaggregation of Revenue [Line Items]
Revenue	155.5	101.2	103.2
Operating Segments | Advanced Alloys & Solutions [Member] | Jet Engines- Commercial
Disaggregation of Revenue [Line Items]
Revenue	87.8	36.3	58.2
Operating Segments | Advanced Alloys & Solutions [Member] | Airframes- Commercial
Disaggregation of Revenue [Line Items]
Revenue	284.8	129.9	191.0
Operating Segments | Advanced Alloys & Solutions [Member] | Defense
Disaggregation of Revenue [Line Items]
Revenue	183.0	131.0	163.9
Operating Segments | Advanced Alloys & Solutions [Member] | Oil & Gas
Disaggregation of Revenue [Line Items]
Revenue	441.7	290.1	328.5
Operating Segments | Advanced Alloys & Solutions [Member] | Specialty Energy
Disaggregation of Revenue [Line Items]
Revenue	163.0	123.5	184.2
External Customers | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	3,836.0	2,799.8	2,982.1
External Customers | Operating Segments | High Performance Materials & Components
Disaggregation of Revenue [Line Items]
Revenue	1,641.2	1,155.1	1,164.6
External Customers | Operating Segments | Advanced Alloys & Solutions [Member]
Disaggregation of Revenue [Line Items]
Revenue	$ 2,194.8	$ 1,644.7	$ 1,817.5