Income tax examination assessment outstanding.

No definition available.

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- Definition

Percentage of penalty on amount of additional taxes due.

+ References

No definition available.

+ Details

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- Definition

Percentage of share of the estimated loss.

+ References

No definition available.

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- Definition

Tax credit previously claimed and disallowed by tax authority.

+ References

No definition available.

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- Definition

Tax matters agreement, contribution percentage.

+ References

No definition available.

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- Definition

A credit or adjustment for government or taxing authority authorized decrease in taxes owed as a result of meeting certain tax policy conditions.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3602-108585

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- Definition

Estimated amount of loss resulting from an adverse tax position.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (d)(3)
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32718-109319

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- Definition

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.

+ References

No definition available.

+ Details

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Contingencies and Commitments - Additional Information - 1 (Detail)				1 Months Ended			3 Months Ended		12 Months Ended
	Jul. 06, 2018 USD ($)	Apr. 08, 2013 USD ($)	Apr. 08, 2013 BRL (R$)	Mar. 31, 2013 USD ($)	May 31, 2012 USD ($)	May 31, 2012 BRL (R$)	Sep. 30, 2018 USD ($)	Sep. 30, 2018 EUR (€)	Dec. 31, 2018 USD ($)	Dec. 31, 2018 EUR (€)	Jul. 06, 2018 EUR (€)	Jun. 30, 2018 USD ($)	Jun. 30, 2018 EUR (€)	Mar. 31, 2013 BRL (R$)
Loss Contingencies [Line Items]
Value added tax receivable									$ 107,000,000
Tax Authority, Spain [Member]
Loss Contingencies [Line Items]
Charge recorded in provision for income taxes to establish liability for estimated loss							$ 30,000,000	€ 26,000,000	$ 30,000,000	€ 26,000,000
Percentage of share of the estimated loss							49.00%	49.00%	49.00%	49.00%
Tax Authority, Spain [Member] \| Minimum [Member]
Loss Contingencies [Line Items]
Total combined assessments	$ 24,000,000										€ 21,000,000
Tax Authority, Spain [Member] \| Maximum [Member]
Loss Contingencies [Line Items]
Total combined assessments	$ 59,000,000										€ 53,000,000
Tax Authority, Spain [Member] \| Arconic Inc [Member]
Loss Contingencies [Line Items]
Tax matters agreement, contribution percentage	51.00%
Tax Authority, Spain [Member] \| Alcoa Corporation [Member]
Loss Contingencies [Line Items]
Tax matters agreement, contribution percentage	49.00%
Brazilian Federal Revenue Office [Member] \| Alcoa World Alumina Brasil [Member]
Loss Contingencies [Line Items]
Disallowed tax credits				$ 110,000,000										R$ 220,000,000
Percentage of penalty of the gross disallowed amount				50.00%
Value added tax receivable					$ 41,000,000	R$ 82,000,000
Brazilian Federal Revenue Office [Member] \| Alcoa World Alumina Brasil [Member] \| Minimum [Member]
Loss Contingencies [Line Items]
Charge recorded in provision for income taxes to establish liability for estimated loss		$ 0
Brazilian Federal Revenue Office [Member] \| Alcoa World Alumina Brasil [Member] \| Maximum [Member]
Loss Contingencies [Line Items]
Charge recorded in provision for income taxes to establish liability for estimated loss		$ 54,000,000	R$ 220,000,000
Tax Year 2006 Through 2009 [Member] \| Tax Authority, Spain [Member]
Loss Contingencies [Line Items]
Total combined assessments												$ 152,000,000	€ 131,000,000