Segment Information, Geographic and Product Data - Schedule of Results of Operation, Depreciation and Amortization, Capital Expenditures and Total Assets by Reportable Segments (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2018
Segment Reporting Information [Line Items]
Consolidated net sales	$ 437.3	$ 585.4	$ 573.0	$ 585.4	$ 641.4	$ 609.9	$ 556.5	$ 572.4	$ 2,181.1	$ 2,380.2	$ 2,157.7
Consolidated operating income	(148.2)	$ 58.7	$ 55.0	$ 59.8	67.9	$ 73.2	$ 55.4	$ 45.0	25.3	241.4	189.3
Consolidated depreciation and amortization									123.9	121.5	116.6
Consolidated capital expenditures									171.4	180.3	135.0
Consolidated total assets	3,227.2				3,187.8				3,227.2	3,187.8
Corporate costs (including restructuring and asset impairment charges)
Segment Reporting Information [Line Items]
Consolidated operating income									(205.0)	(72.7)	(66.4)
Consolidated depreciation and amortization									6.2	4.9	3.9
Consolidated capital expenditures									54.9	37.1	41.6
Consolidated total assets	428.9				192.5				428.9	192.5
Intersegment
Segment Reporting Information [Line Items]
Consolidated net sales									(51.6)	(66.9)	(75.8)
Consolidated operating income									1.7	1.9	(2.8)
Consolidated depreciation and amortization									(0.6)	(0.8)	(0.8)
Consolidated capital expenditures									0.0	(1.2)	(1.8)
Consolidated total assets	(9.2)				(18.7)				(9.2)	(18.7)
Specialty Alloys Operations | Operating
Segment Reporting Information [Line Items]
Consolidated net sales									1,831.6	1,967.3	1,803.8
Consolidated operating income									239.0	282.2	232.4
Consolidated depreciation and amortization									93.5	95.2	93.3
Consolidated capital expenditures									99.3	92.7	63.6
Consolidated total assets	2,259.0				2,349.2				2,259.0	2,349.2
Performance Engineered Products | Operating
Segment Reporting Information [Line Items]
Consolidated net sales									401.1	479.8	429.7
Consolidated operating income									(10.4)	30.0	26.1
Consolidated depreciation and amortization									24.8	22.2	20.2
Consolidated capital expenditures									17.2	51.7	$ 31.6
Consolidated total assets	$ 548.5				$ 664.8				$ 548.5	$ 664.8