Business Segments - Schedule of results of operation, depreciation and amortization, capital expenditures and total assets by reportable segments (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Jun. 30, 2015
Segment Data
Net sales	$ 443.8	$ 548.4	$ 899.4	$ 1,098.2
Operating income	21.8	45.0	46.7	67.2
Depreciation and amortization	30.3	30.1	60.3	60.6
Capital expenditures	19.6	68.4	49.5	127.4
Total assets	2,840.6		2,840.6		$ 2,905.9
Corporate
Segment Data
Operating income	(12.7)	(7.0)	(24.8)	(17.3)
Depreciation and amortization	0.9	1.2	1.9	2.3
Capital expenditures	0.5	0.3	1.6	1.3
Total assets	92.8		92.8		125.0
Intersegment
Segment Data
Net sales	(5.2)	(23.6)	(13.8)	(39.7)
Pension earnings, interest and deferrals	(4.8)	(2.4)	(9.6)	(4.7)
Operating income	0.7	(1.6)	1.7	(1.0)
Depreciation and amortization	(0.2)	(0.2)	(0.4)	(0.5)
Capital expenditures	(0.1)	(0.7)	(0.1)	(1.1)
Total assets	(37.7)		(37.7)		(41.3)
Specialty Alloys Operations | Operating
Segment Data
Net sales	363.6	438.3	736.2	874.2
Operating income	41.5	43.4	82.7	68.0
Depreciation and amortization	23.9	23.2	47.4	46.8
Capital expenditures	17.0	52.7	36.7	104.3
Total assets	2,309.7		2,309.7		2,323.0
Performance Engineered Products | Operating
Segment Data
Net sales	85.4	133.7	177.0	263.7
Operating income	(2.9)	12.6	(3.3)	22.2
Depreciation and amortization	5.7	5.9	11.4	12.0
Capital expenditures	2.2	$ 16.1	11.3	$ 22.9
Total assets	$ 475.8		$ 475.8		$ 499.2