Goodwill and Other Intangible Assets, net - Schedule of Goodwill (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019
Changes in the carrying amount of goodwill by reportable segment
Goodwill gross, beginning balance			$ 372.2
Accumulated impairment losses, beginning balance			(81.8)
Total goodwill net, beginning balance			290.4
Impairment	$ (52.8)	$ 0.0	(52.8)	$ 0.0
Other			3.8
Goodwill gross, ending balance	376.0		376.0
Accumulated impairment losses, ending balance	(134.6)		(134.6)
Total goodwill net, ending balance	241.4		241.4
Specialty Alloy Operations
Changes in the carrying amount of goodwill by reportable segment
Total goodwill net, beginning balance			195.5
Accumulated impairment losses, ending balance	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			94.9
Impairment			(52.8)
Other			3.8
Accumulated impairment losses, ending balance	(134.6)		(134.6)
Total goodwill net, ending balance	$ 45.9		$ 45.9