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		9 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015	Jun. 30, 2015
Segment Data
Net sales	$ 456.3	$ 570.6	$ 1,355.7	$ 1,668.8
Operating income	(24.3)	4.8	22.4	71.9
Depreciation and amortization	29.6	30.7	90.0	91.2
Capital expenditures	16.6	24.8	66.1	152.3
Total assets	2,786.5		2,786.5		$ 2,905.9
Corporate
Segment Data
Operating income	(64.5)	(38.6)	(89.3)	(55.9)
Depreciation and amortization	0.9	1.0	2.8	3.3
Capital expenditures	1.9	1.5	3.5	2.8
Total assets	107.6		107.6		125.0
Intersegment
Segment Data
Net sales	(5.6)	(19.6)	(19.3)	(59.3)
Pension earnings, interest and deferrals	(4.8)	(2.4)	(14.4)	(7.1)
Operating income	0.3	(0.6)	2.0	(1.9)
Depreciation and amortization	(0.2)	0.1	(0.7)	(0.5)
Capital expenditures	(0.1)	0.0	(0.2)	(1.0)
Total assets	(35.5)		(35.5)		(41.3)
Specialty Alloys Operations | Operating
Segment Data
Net sales	370.5	469.8	1,106.7	1,344.0
Operating income	45.6	37.9	128.3	106.0
Depreciation and amortization	23.4	23.9	70.9	70.7
Capital expenditures	11.2	15.2	47.9	119.5
Total assets	2,291.4		2,291.4		2,323.0
Performance Engineered Products | Operating
Segment Data
Net sales	91.4	120.4	268.3	384.1
Operating income	(0.9)	8.5	(4.2)	30.8
Depreciation and amortization	5.5	5.7	17.0	17.7
Capital expenditures	3.6	$ 8.1	14.9	$ 31.0
Total assets	$ 423.0		$ 423.0		$ 499.2