Business Segments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Segment Reporting Information [Line Items]
Sales	$ 1,032.0	$ 725.7	$ 2,825.6	$ 2,034.4
Segment EBITDA	161.6	94.2	469.9	241.7
Corporate expenses	(14.2)	(12.9)	(47.9)	(41.0)
Closed operations and other expense	(6.3)	(1.4)	(12.8)	(4.5)
Depreciation & amortization	(35.6)	(35.6)	(107.1)	(108.0)
Interest expense, net	(20.8)	(25.1)	(67.8)	(72.2)
Income (loss) from equity investments	0.8	0.4	11.2	0.4
Restructuring and other credits (charges)	(17.3)	2.3	(23.5)	8.5
Strike related costs	0.0	(22.9)	0.0	(63.2)
Retirement benefit settlement gain	0.0	64.9	0.0	64.9
Gain (loss) on asset sales and sale of businesses, net	0.0	13.7	(134.2)	13.7
Income before income taxes	67.4	77.2	76.6	39.9
Operating Segments
Segment Reporting Information [Line Items]
Sales	1,151.8	789.7	3,131.1	2,189.0
Depreciation & amortization	(35.6)	(35.6)	(107.1)	(108.0)
Operating Segments | High Performance Materials & Components
Segment Reporting Information [Line Items]
Sales	505.0	325.0	1,325.6	908.9
Segment EBITDA	85.8	37.4	214.2	99.2
Depreciation & amortization	(16.7)	(18.2)	(51.5)	(57.0)
Strike related costs		(1.4)		(3.5)
Operating Segments | Advanced Alloys & Solutions
Segment Reporting Information [Line Items]
Sales	646.8	464.7	1,805.5	1,280.1
Segment EBITDA	75.8	56.8	255.7	142.5
Depreciation & amortization	(17.1)	(16.3)	(50.0)	(47.9)
Strike related costs		(21.5)		(59.7)
Operating Segments | Corporate Segment
Segment Reporting Information [Line Items]
Depreciation & amortization	(1.8)	(1.1)	(5.6)	(3.1)
Internal Customers | Operating Segments
Segment Reporting Information [Line Items]
Sales	119.8	64.0	305.5	154.6
Internal Customers | Operating Segments | High Performance Materials & Components
Segment Reporting Information [Line Items]
Sales	47.4	25.0	130.3	67.4
Internal Customers | Operating Segments | Advanced Alloys & Solutions
Segment Reporting Information [Line Items]
Sales	72.4	39.0	175.2	87.2
External Customers | Operating Segments
Segment Reporting Information [Line Items]
Sales	1,032.0	725.7	2,825.6	2,034.4
External Customers | Operating Segments | High Performance Materials & Components
Segment Reporting Information [Line Items]
Sales	457.6	300.0	1,195.3	841.5
External Customers | Operating Segments | Advanced Alloys & Solutions
Segment Reporting Information [Line Items]
Sales	$ 574.4	$ 425.7	$ 1,630.3	$ 1,192.9