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Income tax examination assessment outstanding.

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Letters Of Credit, Total

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Number of cleanup locations.

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Percentage of cost of goods sold.

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Tax Agreement, Indemnification of Ultimate Liability, Percent

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

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Amount of cash outflow to settle environmental loss contingencies.

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Carrying value of the obligation (known or estimated) arising from requirements to perform activities to remediate one or more sites, payable in twelve months or in the next operating cycle if longer.

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The current carrying amount of the liability for the freestanding or embedded guarantor's obligations under the guarantee or each group of similar guarantees.

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Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

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Fair value portion of guarantee, including, but not limited to, financial standby letter of credit, fair value guarantee, guarantee of collection of scheduled contractual cash flows from financial assets, and contracts that contingently require the guarantor to make payments or perform services.

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The change in the reserve for commissions, expenses and taxes recorded on the balance sheet, which is needed to adjust net income to arrive at net cash flows provided by or used in operations.

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The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

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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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Number of plaintiffs that have filed claims pertaining to a loss contingency.

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Contingencies and Commitments (Details) € in Millions, $ in Millions		3 Months Ended	9 Months Ended
	Jun. 06, 2019 plaintiff	Sep. 30, 2020 USD ($)	Sep. 30, 2020 USD ($) location	Sep. 30, 2020 EUR (€) location	Sep. 30, 2020 EUR (€)	Dec. 31, 2019 USD ($)	Sep. 30, 2018
Loss Contingencies [Line Items]
Number of cleanup locations \| location			30	30
Remediation reserve balance		$ 9	$ 9			$ 8
Remediation reserve balance, classified as a current liability		4	4			3
Payments related to remediation expenses applied against the reserve		1	1
Income tax examination assessment outstanding		181	181		€ 155
Income tax reserve			63	€ 54
Tax indemnification receivable		52	52		€ 45
Number of plaintiffs \| plaintiff	247
Guarantees of third party related to project financing		26	26
Combined fair value of guarantees		17	17			9
Total amount committed under outstanding surety bonds		43	43
Surety bonds, amount outstanding		26	26
Bank Loan Obligations
Loss Contingencies [Line Items]
Letters of credit, total amount		105	105
Other Noncurrent Liabilities and Deferred Credits \| Separation Agreement
Loss Contingencies [Line Items]
Guarantees of third party related to project financing		$ 1,183	$ 1,183			$ 1,353
Alcoa Corporation
Loss Contingencies [Line Items]
Tax agreement, indemnification of ultimate liability (percent)		49.00%	49.00%		49.00%		49.00%
Arconic Corporation
Loss Contingencies [Line Items]
Tax agreement, indemnification of ultimate liability (percent)		34.00%	34.00%		34.00%
Howmet Aerospace
Loss Contingencies [Line Items]
Tax agreement, indemnification of ultimate liability (percent)		17.00%	17.00%		17.00%
Recurring Costs of Managing Hazardous Substances and Environmental Programs \| Maximum
Loss Contingencies [Line Items]
Percentage of cost of goods sold (percent)			1.00%	1.00%
Alcoa Corporation Workers Compensation Claims
Loss Contingencies [Line Items]
Letters of credit, total amount outstanding		$ 54	$ 54
Arconic Corporation Environmental Obligations
Loss Contingencies [Line Items]
Letters of credit, total amount outstanding		29	29
Arconic Corporation Environmental Obligations \| Letters Of Credit, Pending Cancellation
Loss Contingencies [Line Items]
Letters of credit, total amount outstanding		$ 13	$ 13