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, 2018	Mar. 31, 2017	Mar. 31, 2018	Mar. 31, 2017	Jun. 30, 2017
Net Sales:
Consolidated net sales	$ 572.2	$ 473.6	$ 1,539.7	$ 1,289.9
Operating Income:
Consolidated operating income	45.2	35.8	127.7	52.6
Depreciation and Amortization:
Consolidated depreciation and amortization	29.2	30.0	87.2	88.8
Capital Expenditures:
Consolidated capital expenditures	25.2	18.0	80.9	63.1
Total Assets:
Consolidated total assets	2,991.9		2,991.9		$ 2,878.1
Corporate
Operating Income:
Consolidated operating income	(18.0)	(15.8)	(44.9)	(45.6)
Depreciation and Amortization:
Consolidated depreciation and amortization	1.0	1.3	2.8	3.0
Capital Expenditures:
Consolidated capital expenditures	7.6	6.6	24.2	21.8
Total Assets:
Consolidated total assets	164.8		164.8		167.2
Segment Reconciling Items
Operating Income:
Pension earnings, interest and deferrals	(0.5)	(5.6)	(1.6)	(18.2)
Intersegment
Net Sales:
Consolidated net sales	(18.1)	(8.4)	(59.3)	(17.5)
Operating Income:
Consolidated operating income	0.3	0.6	(2.2)	1.1
Depreciation and Amortization:
Consolidated depreciation and amortization	(0.1)	(0.2)	(0.6)	(0.5)
Capital Expenditures:
Consolidated capital expenditures	(0.4)	(0.1)	(0.9)	(0.2)
Total Assets:
Consolidated total assets	(7.4)		(7.4)		(15.5)
Specialty Alloys Operations | Operating
Net Sales:
Consolidated net sales	482.4	383.3	1,285.6	1,047.0
Operating Income:
Consolidated operating income	58.0	51.9	158.3	112.6
Depreciation and Amortization:
Consolidated depreciation and amortization	23.3	23.7	69.9	70.8
Capital Expenditures:
Consolidated capital expenditures	12.1	8.6	40.6	31.6
Total Assets:
Consolidated total assets	2,330.7		2,330.7		2,292.1
Performance Engineered Products | Operating
Net Sales:
Consolidated net sales	107.9	98.7	313.4	260.4
Operating Income:
Consolidated operating income	5.4	4.7	18.1	2.7
Depreciation and Amortization:
Consolidated depreciation and amortization	5.0	5.2	15.1	15.5
Capital Expenditures:
Consolidated capital expenditures	5.9	$ 2.9	17.0	$ 9.9
Total Assets:
Consolidated total assets	$ 503.8		$ 503.8		$ 434.3