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Face (par) amount of debt instrument at time of issuance.

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Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount of consideration received or receivable for the disposal of assets and liabilities, including discontinued operation.

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Amount of gain (loss) from sale and disposal of integrated set of activities and assets capable of being conducted and managed for purpose of providing return in form of dividend, lower cost, or other economic benefit to investor, owner, member and participant.

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The cash outflow paid to third parties in connection with debt origination, which will be amortized over the remaining maturity period of the associated long-term debt.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Arconic Inc. Separation Transaction and Discontinued Operations - Narrative (Details)				3 Months Ended		6 Months Ended
	Apr. 01, 2020 company	Mar. 25, 2020 USD ($)	Feb. 01, 2020 USD ($)	Mar. 31, 2021 USD ($)	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Mar. 01, 2020 USD ($)	Feb. 07, 2020 USD ($)
Restructuring Cost and Reserve [Line Items]
Number of independent, publicly-traded companies resulting from proposed separation transaction \| company	2
Debt issuance costs incurred				$ 1,000,000	$ 45,000,000
Aluminum Rolling Mill
Restructuring Cost and Reserve [Line Items]
Consideration			$ 50,000,000
Gain (loss) on sale of business			$ (59,000,000)		6,000,000	$ 53,000,000
Hard Alloy Extrusions Plant In South Korea
Restructuring Cost and Reserve [Line Items]
Consideration							$ 62,000,000
Gain (loss) on sale of business					27,000,000
Lien Notes
Restructuring Cost and Reserve [Line Items]
Debt issuance costs incurred					$ 45,000,000
Senior Notes \| Second Lien Notes Due 2028
Restructuring Cost and Reserve [Line Items]
Aggregate principal amount								$ 600,000,000
Long-term debt, interest rate								6.125%
Line of Credit \| Senior Secured First Lien Term B Loan Facility Due 2027 \| Secured Debt
Restructuring Cost and Reserve [Line Items]
Aggregate principal amount		$ 600,000,000
Credit agreement term		7 years