Goodwill and Other Intangible Assets, Net - Schedule of Goodwill (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2023
Changes in the carrying amount of goodwill by reportable segment
Goodwill gross, beginning balance		$ 376.0	$ 376.0
Accumulated impairment losses, beginning balance		(148.7)	(134.6)
Total goodwill net, beginning balance		227.3	241.4
Impairment	$ (14.1)	0.0	(14.1)	$ 0.0
Goodwill gross, ending balance		376.0	376.0	376.0
Accumulated impairment losses, ending balance		(148.7)	(148.7)	(134.6)
Total goodwill net, ending balance		227.3	227.3	241.4
Specialty Alloys Operations
Changes in the carrying amount of goodwill by reportable segment
Total goodwill net, beginning balance		195.5	195.5
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		31.8	45.9
Impairment			(14.1)
Total goodwill net, ending balance		$ 31.8	$ 31.8	$ 45.9