Business Segments (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Segment Reporting Information [Line Items]
Sales	$ 1,025.6	$ 1,032.0	$ 3,109.7	$ 2,825.6
Segment EBITDA	166.1	161.6	490.2	469.9
Corporate expenses	(12.9)	(14.2)	(48.3)	(47.9)
Closed operations and other expense	(5.1)	(6.3)	(11.3)	(12.8)
Depreciation & amortization	(35.6)	(35.6)	(106.6)	(107.1)
Interest expense, net	(23.8)	(20.8)	(65.0)	(67.8)
Income (loss) from equity investments	(0.7)	0.8	(1.0)	11.2
Restructuring and other charges	(4.2)	(17.3)	(14.6)	(23.5)
Loss on asset sales and sales of businesses, net		0.0		(134.2)
Income before income taxes	84.5	67.4	243.8	76.6
Operating Segments
Segment Reporting Information [Line Items]
Sales	1,129.9	1,151.8	3,461.5	3,131.1
Depreciation & amortization	(35.6)	(35.6)	(106.6)	(107.1)
Operating Segments \| High Performance Materials & Components
Segment Reporting Information [Line Items]
Sales	578.1	505.0	1,670.5	1,325.6
Segment EBITDA	115.7	85.8	303.9	214.2
Depreciation & amortization	(16.5)	(16.7)	(51.8)	(51.5)
Operating Segments \| Advanced Alloys & Solutions
Segment Reporting Information [Line Items]
Sales	551.8	646.8	1,791.0	1,805.5
Segment EBITDA	50.4	75.8	186.3	255.7
Depreciation & amortization	(17.3)	(17.1)	(49.6)	(50.0)
Operating Segments \| Corporate Segment
Segment Reporting Information [Line Items]
Depreciation & amortization	(1.8)	(1.8)	(5.2)	(5.6)
Internal Customers \| Operating Segments
Segment Reporting Information [Line Items]
Sales	104.3	119.8	351.8	305.5
Internal Customers \| Operating Segments \| High Performance Materials & Components
Segment Reporting Information [Line Items]
Sales	38.6	47.4	132.8	130.3
Internal Customers \| Operating Segments \| Advanced Alloys & Solutions
Segment Reporting Information [Line Items]
Sales	65.7	72.4	219.0	175.2
External Customers \| Operating Segments
Segment Reporting Information [Line Items]
Sales	1,025.6	1,032.0	3,109.7	2,825.6
External Customers \| Operating Segments \| High Performance Materials & Components
Segment Reporting Information [Line Items]
Sales	539.5	457.6	1,537.7	1,195.3
External Customers \| Operating Segments \| Advanced Alloys & Solutions
Segment Reporting Information [Line Items]
Sales	$ 486.1	$ 574.4	$ 1,572.0	$ 1,630.3

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