Summary of Significant Accounting Policies - Narrative (Details) $ in Millions	12 Months Ended
Jun. 30, 2020 USD ($) facility	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)
Summary of significant accounting policies
Discounts, rebates, returns and allowances	$ 25.8	$ 22.6	$ 26.5
Research and development expenditures	28.0	23.3	19.3
Inventory accounted under method other than LIFO	136.3	173.2
Capitalized software amortization expense	5.3	6.1	$ 5.1
Carrying value of computer software	$ 147.0	$ 123.8
Number of former operating facility site that the liability for future costs is discounted to present value (facility) \| facility	1
Liability for future costs discount amortization period	20 years
Environmental expenditures, discount rate	3.00%	3.00%
Environmental expenditures, liability	$ 11.2	$ 11.0
Customer \| Sales Revenue \| Howmet Aerospace Inc.
Summary of significant accounting policies
Concentration risk	10.00%	11.00%	12.00%
Customer \| Accounts Receivable \| Howmet Aerospace Inc.
Summary of significant accounting policies
Concentration risk	12.00%
Minimum \| Computer software
Summary of significant accounting policies
Estimated useful life	3 years
Minimum \| Intangible Assets
Summary of significant accounting policies
Estimated useful life	5 years
Maximum \| Computer software
Summary of significant accounting policies
Estimated useful life	12 years
Maximum \| Intangible Assets
Summary of significant accounting policies
Estimated useful life	30 years

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Total costs accrued as of the balance sheet date for environmental loss contingencies.

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Amount of expense for amortization of capitalized computer software costs.

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The carrying amount of capitalized computer software costs net of accumulated amortization as of the balance sheet date.

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The aggregate costs incurred (1) in a planned search or critical investigation aimed at discovery of new knowledge with the hope that such knowledge will be useful in developing a new product or service, a new process or technique, or in bringing about a significant improvement to an existing product or process; or (2) to translate research findings or other knowledge into a plan or design for a new product or process or for a significant improvement to an existing product or process whether intended for sale or the entity's use, during the reporting period charged to research and development projects, including the costs of developing computer software up to the point in time of achieving technological feasibility, and costs allocated in accounting for a business combination to in-process projects deemed to have no alternative future use.

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