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, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020	Jun. 30, 2020
Net Sales:
Consolidated net sales	$ 351.9	$ 585.4	$ 1,054.0	$ 1,743.8
Operating (Loss) Income:
Consolidated operating (loss) income	(40.0)	58.7	(177.8)	173.5
Depreciation and Amortization:
Consolidated depreciation and amortization	32.0	31.2	91.6	92.2
Capital Expenditures:
Consolidated capital expenditures	18.6	49.7	78.5	144.0
Total Assets:
Consolidated total assets	3,011.0		3,011.0		$ 3,227.2
Corporate
Operating (Loss) Income:
Consolidated operating (loss) income	(26.3)	(17.8)	(123.4)	(58.8)
Depreciation and Amortization:
Consolidated depreciation and amortization	1.4	1.8	4.1	4.4
Capital Expenditures:
Consolidated capital expenditures	4.0	11.3	23.3	43.9
Total Assets:
Consolidated total assets	362.4		362.4		428.9
Intersegment
Net Sales:
Consolidated net sales	(13.4)	(11.3)	(29.1)	(42.4)
Operating (Loss) Income:
Consolidated operating (loss) income	(0.5)	0.4	(0.1)	0.6
Depreciation and Amortization:
Consolidated depreciation and amortization	0.0	(0.2)	0.0	(0.5)
Capital Expenditures:
Consolidated capital expenditures	0.0	0.0	0.0	(0.1)
Total Assets:
Consolidated total assets	(30.2)		(30.2)		(9.2)
Specialty Alloys Operations | Operating
Net Sales:
Consolidated net sales	299.6	488.1	900.8	1,462.2
Operating (Loss) Income:
Consolidated operating (loss) income	(9.9)	76.4	(40.1)	233.7
Depreciation and Amortization:
Consolidated depreciation and amortization	26.5	23.1	73.1	69.8
Capital Expenditures:
Consolidated capital expenditures	13.4	34.1	50.8	84.3
Total Assets:
Consolidated total assets	2,232.1		2,232.1		2,259.0
Performance Engineered Products | Operating
Net Sales:
Consolidated net sales	65.7	108.6	182.3	324.0
Operating (Loss) Income:
Consolidated operating (loss) income	(3.3)	(0.3)	(14.2)	(2.0)
Depreciation and Amortization:
Consolidated depreciation and amortization	4.1	6.5	14.4	18.5
Capital Expenditures:
Consolidated capital expenditures	1.2	$ 4.3	4.4	$ 15.9
Total Assets:
Consolidated total assets	$ 446.7		$ 446.7		$ 548.5