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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
	Jun. 06, 2019 plaintiff	Mar. 31, 2020 USD ($) location	Mar. 31, 2020 EUR (€) location	Mar. 31, 2020 EUR (€)	Dec. 31, 2019 USD ($)	Mar. 31, 2019 USD ($)	Nov. 01, 2016 USD ($)
Loss Contingencies [Line Items]
Number of cleanup locations \| location		100	100
Remediation reserve balance					$ 230	$ 229
Remediation reserve balance, classified as a current liability					94	93
Payments related to remediation expenses applied against the reserve		$ 2
Income tax examination assessment outstanding		170		€ 154
Income tax reserve		59	€ 53
Tax indemnification receivable		29		€ 26
Number of plaintiffs \| plaintiff	247
Guarantees of third party related to project financing		27
Combined fair value of guarantees		10				9
Total amount committed under outstanding surety bonds		64
Surety bonds, amount outstanding		27
Bank Loan Obligations
Loss Contingencies [Line Items]
Letters of credit, total amount		138
Other Noncurrent Liabilities and Deferred Credits \| Separation Agreement
Loss Contingencies [Line Items]
Guarantees of third party related to project financing		$ 882			1,353
Massena West, NY
Loss Contingencies [Line Items]
Remediation reserve balance					$ 171	$ 169
Alcoa Corporation
Loss Contingencies [Line Items]
Tax agreement, indemnification of ultimate liability (percent)		49.00%		49.00%
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