Goodwill - Schedule of Goodwill (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Mar. 31, 2017	Mar. 31, 2016	Jun. 30, 2016	Jun. 30, 2015
Goodwill [Roll Forward]
Goodwill, Beginning Balance	$ 318.1		$ 318.1		$ 292.0	$ 292.1
Goodwill, Impairment Losses					0.0
Goodwill, Other					(0.1)
Goodwill, Acquired			26.1
Goodwill, Ending Balance	318.1		318.1		292.0
Accumulated impairment losses, Beginning Balance			(47.2)	$ (34.7)	(34.7)
Accumulated impairment losses, Impairment Losses					(12.5)
Accumulated impairment losses, Other					0.0
Accumulated impairment losses, Ending Balance	(47.2)		(47.2)		(47.2)
Total goodwill, Beginning Balance			244.8	257.4	257.4
Goodwill impairment	0.0	$ (12.5)	0.0	(12.5)	(12.5)
Other					(0.1)
Goodwill, Acquired			26.1
Total goodwill, Ending Balance	270.9		270.9		244.8
Specialty Alloys Operations
Goodwill [Roll Forward]
Goodwill, Acquired			0.0
Total goodwill, Beginning Balance			195.5	195.5	195.5
Goodwill impairment					0.0
Other					0.0
Goodwill, Acquired			0.0
Total goodwill, Ending Balance	195.5		195.5		195.5
Performance Engineered Products
Goodwill [Roll Forward]
Goodwill, Acquired			26.1
Total goodwill, Beginning Balance			49.3	$ 61.9	61.9
Goodwill impairment					(12.5)
Other					(0.1)
Goodwill, Acquired			26.1
Total goodwill, Ending Balance	$ 75.4		$ 75.4		$ 49.3