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, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2015
Segment Reporting Information [Line Items]
Consolidated net sales	$ 507.7	$ 473.6	$ 427.4	$ 389.0	$ 457.7	$ 456.3	$ 443.8	$ 455.6	$ 1,797.6	$ 1,813.4	$ 2,226.7
Consolidated operating income	44.6	$ 35.8	$ 15.4	$ 1.4	29.2	$ (24.3)	$ 21.8	$ 24.8	97.2	51.6	111.5
Consolidated depreciation and amortization									117.8	119.3	122.3
Consolidated capital expenditures									98.5	95.2	170.5
Consolidated total assets	2,878.1				2,794.3				2,878.1	2,794.3
Operating
Segment Reporting Information [Line Items]
Pension earnings, interest and deferrals									(23.8)	(19.3)	(9.4)
Corporate costs (including loss on divestiture of business, restructuring and impairment charges)
Segment Reporting Information [Line Items]
Consolidated operating income									(61.3)	(103.0)	(72.0)
Consolidated depreciation and amortization									4.0	3.8	4.6
Consolidated capital expenditures									29.7	8.6	4.3
Consolidated total assets	167.2				151.3				167.2	151.3
Intersegment
Segment Reporting Information [Line Items]
Consolidated net sales									(30.6)	(26.3)	(67.6)
Consolidated operating income									1.5	2.5	(1.4)
Consolidated depreciation and amortization									(0.8)	(0.8)	(0.6)
Consolidated capital expenditures									(0.4)	(0.2)	(0.9)
Consolidated total assets	(15.5)				(29.3)				(15.5)	(29.3)
Specialty Alloys Operations | Operating
Segment Reporting Information [Line Items]
Consolidated net sales									1,461.6	1,481.0	1,796.6
Consolidated operating income									172.3	176.9	155.2
Consolidated depreciation and amortization									94.0	94.4	95.0
Consolidated capital expenditures									52.2	67.0	129.0
Consolidated total assets	2,292.1				2,256.5				2,292.1	2,256.5
Performance Engineered Products | Operating
Segment Reporting Information [Line Items]
Consolidated net sales									366.6	358.7	497.7
Consolidated operating income									8.5	(5.5)	39.1
Consolidated depreciation and amortization									20.6	21.9	23.3
Consolidated capital expenditures									17.0	19.8	$ 38.1
Consolidated total assets	$ 434.3				$ 415.8				$ 434.3	$ 415.8