Goodwill and Other Intangible Assets, Net - Schedule of Goodwill (Details) - USD ($) $ in Millions	12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Changes in the carrying amount of goodwill by reportable segment
Goodwill gross, beginning balance	$ 315.9	$ 310.6
Accumulated impairment losses, beginning balance	(47.2)	(47.2)
Total goodwill net, beginning balance	268.7	263.4
Acquisition	57.7	5.3
Goodwill gross, ending balance	373.6	315.9
Accumulated impairment losses, ending balance	(47.2)	(47.2)
Total goodwill net, ending balance	326.4	268.7
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	73.2	67.9
Acquisition	57.7	5.3
Total goodwill net, ending balance	$ 130.9	$ 73.2