Goodwill and Other Intangible Assets, Net - Schedule of Goodwill (Details) - USD ($) $ in Millions	12 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Changes in the carrying amount of goodwill by reportable segment
Goodwill gross, beginning balance	$ 310.6	$ 292.0
Accumulated impairment losses, beginning balance	(47.2)	(47.2)
Total goodwill net, beginning balance	263.4	244.8
Acquisition	5.3	18.6
Goodwill gross, ending balance	315.9	310.6
Accumulated impairment losses, ending balance	(47.2)	(47.2)
Total goodwill net, ending balance	268.7	263.4
Specialty Alloys Operations
Changes in the carrying amount of goodwill by reportable segment
Total goodwill net, beginning balance	195.5	195.5
Acquisition	0.0	0.0
Total goodwill net, ending balance	195.5	195.5
Performance Engineered Products
Changes in the carrying amount of goodwill by reportable segment
Total goodwill net, beginning balance	67.9	49.3
Acquisition	5.3	18.6
Total goodwill net, ending balance	$ 73.2	$ 67.9