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Contingencies and Commitments - Additional Information - 2 (Detail) € in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2017 USD ($)	Mar. 31, 2017 EUR (€)	Dec. 31, 2016 USD ($)
Loss Contingencies [Line Items]
Total combined assessments	$ 265	€ 247
Guarantees of third party related to project financing	45
Letters of credit, total amount committed	$ 107
Letters of credit, expiration date	2017
Total amount committed under outstanding surety bonds	$ 121
Surety bonds, expiration date	2017
Other Noncurrent Liabilities and Deferred Credits [Member]
Loss Contingencies [Line Items]
Combined fair value of guarantees	$ 35		$ 35
Separation Agreement [Member]
Loss Contingencies [Line Items]
Guarantees of third party related to project financing	330
Total amount committed under outstanding surety bonds	22
Supply Agreement [Member]
Loss Contingencies [Line Items]
Guarantees of third party related to project financing	1,600
Purchase Agreement [Member]
Loss Contingencies [Line Items]
Guarantees of third party related to project financing			$ 245
Alcoa Corporation Energy Supply Contracts Guarantee [Member]
Loss Contingencies [Line Items]
Guarantees of third party related to project financing	50
Alcoa Corporation Environmental Liabilities Guarantee [Member]
Loss Contingencies [Line Items]
Guarantees of third party related to project financing	53
Alcoa Corporation Workers Compensation Claims [Member]
Loss Contingencies [Line Items]
Letters of credit, total amount committed	61
Alcoa Corporation Equipment Leases And Energy Contracts [Member]
Loss Contingencies [Line Items]
Letters of credit, total amount committed	$ 103
Minimum [Member] | Separation Agreement [Member]
Loss Contingencies [Line Items]
Guarantees, expiration date	2017
Minimum [Member] | Outstanding bank guarantees [Member]
Loss Contingencies [Line Items]
Guarantees, expiration date	2017
Maximum [Member] | Separation Agreement [Member]
Loss Contingencies [Line Items]
Guarantees, expiration date	2024
Maximum [Member] | Outstanding bank guarantees [Member]
Loss Contingencies [Line Items]
Guarantees, expiration date	2026

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+ References

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- Definition

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6851643&loc=d3e12069-110248

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