Goodwill and Other Intangible Assets, Net - Schedule of Goodwill (Details) - USD ($) $ in Millions	12 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2022
Changes in the carrying amount of goodwill by reportable segment
Goodwill gross, beginning balance	$ 376.0	$ 376.0
Accumulated impairment losses, beginning balance	(134.6)	(134.6)
Total goodwill net, beginning balance	241.4	241.4
Impairment	(14.1)	0.0	$ 0.0
Goodwill gross, ending balance	376.0	376.0	376.0
Accumulated impairment losses, ending balance	(148.7)	(134.6)	(134.6)
Total goodwill net, ending balance	227.3	241.4	241.4
Specialty Alloys Operations
Changes in the carrying amount of goodwill by reportable segment
Total goodwill net, beginning balance	195.5	195.5
Impairment	0.0
Total goodwill net, ending balance	195.5	195.5	195.5
Performance Engineered Products
Changes in the carrying amount of goodwill by reportable segment
Total goodwill net, beginning balance	45.9	45.9
Impairment	(14.1)
Total goodwill net, ending balance	$ 31.8	$ 45.9	$ 45.9