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, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2016
Segment Reporting Information [Line Items]
Consolidated net sales	$ 618.0	$ 572.2	$ 487.8	$ 479.8	$ 507.7	$ 473.6	$ 427.4	$ 389.0	$ 2,157.7	$ 1,797.6	$ 1,813.4
Consolidated operating income	59.4	$ 45.2	$ 40.8	$ 41.7	44.6	$ 35.8	$ 15.4	$ 1.4	187.1	97.2	51.6
Consolidated depreciation and amortization									116.6	117.8	119.3
Consolidated capital expenditures									135.0	98.5	95.2
Consolidated total assets	3,007.0				2,878.1				3,007.0	2,878.1
Operating
Segment Reporting Information [Line Items]
Pension earnings, interest and deferrals									(2.1)	(23.8)	(19.3)
Corporate costs (including loss on divestiture of business, restructuring and impairment charges)
Segment Reporting Information [Line Items]
Consolidated operating income									(66.4)	(61.3)	(103.0)
Consolidated depreciation and amortization									3.9	4.0	3.8
Consolidated capital expenditures									41.6	29.7	8.6
Consolidated total assets	193.2				167.2				193.2	167.2
Intersegment
Segment Reporting Information [Line Items]
Consolidated net sales									(75.8)	(30.6)	(26.3)
Consolidated operating income									(2.9)	1.5	2.5
Consolidated depreciation and amortization									(0.8)	(0.8)	(0.8)
Consolidated capital expenditures									(1.8)	(0.4)	(0.2)
Consolidated total assets	(11.9)				(15.5)				(11.9)	(15.5)
Specialty Alloys Operations | Operating
Segment Reporting Information [Line Items]
Consolidated net sales									1,803.8	1,461.6	1,481.0
Consolidated operating income									232.4	172.3	176.9
Consolidated depreciation and amortization									93.3	94.0	94.4
Consolidated capital expenditures									63.6	52.2	67.0
Consolidated total assets	2,312.1				2,292.1				2,312.1	2,292.1
Performance Engineered Products | Operating
Segment Reporting Information [Line Items]
Consolidated net sales									429.7	366.6	358.7
Consolidated operating income									26.1	8.5	(5.5)
Consolidated depreciation and amortization									20.2	20.6	21.9
Consolidated capital expenditures									31.6	17.0	$ 19.8
Consolidated total assets	$ 513.6				$ 434.3				$ 513.6	$ 434.3