Applicable margin on base rate loans.

No definition available.

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- Definition

Applicable margin on LIBOR loans.

+ References

No definition available.

+ Details

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- Definition

Debt covenant annual share repurchase limit.

+ References

No definition available.

+ Details

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- Definition

Debt Covenant As Percentage Of Assets

+ References

No definition available.

+ Details

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- Definition

The maximum amount of dividends declarable during any four consecutive quarters.

+ References

No definition available.

+ Details

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- Definition

Debt instrument covenant interest expense coverage ratio.

+ References

No definition available.

+ Details

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- Definition

Debt instrument covenant leverage ratio.

+ References

No definition available.

+ Details

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- Definition

Debt instrument covenant leverage ratio, possible increase.

+ References

No definition available.

+ Details

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- Definition

Incremental amount of convenant, maximum.

+ References

No definition available.

+ Details

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- Definition

Investment negative covenant maximum.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Letters of credit sublimit under credit facility.

+ References

No definition available.

+ Details

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- Definition

Percentage of equity interest in foreign subsidiaries pledged as security to secured debt.

+ References

No definition available.

+ Details

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- Definition

Percentage of unused base amount used in succeeding fiscal year

+ References

No definition available.

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- Definition

Percentage of unused portion of credit facility.

+ References

No definition available.

+ Details

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- Definition

Restricted payments negative covenant maximum

+ References

No definition available.

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- Definition

Thresholds for investments negative covenants.

+ References

No definition available.

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- Definition

Thresholds for restricted payments negative covenants.

+ References

No definition available.

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- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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- Definition

Description of minimum financial levels (for example, tangible net worth and working capital) and achievement of certain financial ratios (for example, working capital ratio and debt service coverage ratio), and adherence to certain clauses which generally require or restrict certain actions (for example, entering into a debt arrangement with equal or greater seniority, and selling or discontinuing a certain business segment or material subsidiary) to be in compliance with the covenant clauses of the debt agreement. May also include a discussion of the adverse consequences that would result if the entity violates or fails to satisfy the covenants.

+ References

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- Definition

Description of the interest rate as being fixed or variable, and, if variable, identification of the index or rate on which the interest rate is based and the number of points or percentage added to that index or rate to set the rate, and other pertinent information, such as frequency of rate resets.

+ References

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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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- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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- Definition

The fee, expressed as a percentage of the line of credit facility, for the line of credit facility regardless of whether the facility has been used.

+ References

No definition available.

+ Details

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- Definition

Date the credit facility terminates, in CCYY-MM-DD format.

+ References

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

+ Details

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- Definition

Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(a)(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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-Section S99
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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- Definition

The cash inflow from a contractual arrangement with the lender, including letter of credit, standby letter of credit and revolving credit arrangements, under which borrowings can be made up to a specific amount at any point in time with maturities due beyond one year or the operating cycle, if longer.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 14
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3255-108585

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Debt (Credit Facility) - Additional Information (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Sep. 16, 2016
Debt Instrument [Line Items]
Principal amount of debt	$ 1,445,000,000	$ 1,404,000,000	$ 1,445,000,000
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Line of credit facility, outstanding borrowings	0	$ 0	$ 0	$ 1,500,000,000
Line of credit facility, maturity date		Nov. 14, 2022
Percentage of equity interest in foreign subsidiaries pledged as security to secured debt		65.00%
Revolving credit facility, covenant description		The Amended Revolving Credit Agreement also includes financial covenants requiring the maintenance of a specified interest expense coverage ratio of not less than 5.00 to 1.00, and a leverage ratio for any period of four consecutive fiscal quarters that is not greater than 2.25 to 1.00 (may be increased to a level not higher than 2.50 to 1.00). As of December 31, 2017 and 2016, Alcoa Corporation was in compliance with all such covenants.
Leverage ratio, covenants requirements		1.20%	1.30%
Incremental amount of convenant, maximum	500,000,000	$ 1,000,000,000	$ 500,000,000
Debt convenant percentage of assets		6.00%	3.00%
Restricted payments negative covenant, maximum	0	$ 100,000,000	$ 0
Investment negative covenant, maximum	250,000,000	400,000,000	250,000,000
Thresholds for restricted payments negative covenants	0	250,000,000	0
Thresholds for investments negative covenants	0	$ 200,000,000	$ 0
Percentage of unused base amount used in the succeeding fiscal year		50.00%
Percentage of unused portion of credit facility		50.00%
Annual share repurchase limit		$ 100,000,000
Amounts borrowed under the credit facility	$ 0	$ 0
Revolving Credit Facility [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Leverage ratio, covenants requirements		225.00%
Leverage ratio, maximum possible increase		250.00%
Annual share repurchase limit		$ 25,000,000
Amount of dividend restriction		$ 100,000,000
Revolving Credit Facility [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Interest expense coverage ratio required to be maintained		5.00
Revolving Credit Facility [Member] \| Debt Covenant Terms November 1, 2016 through December 31, 2017 [Member]
Debt Instrument [Line Items]
Amount of dividend restriction		$ 38,000,000
Revolving Credit Facility [Member] \| Debt Covenant Terms 2018 [Member]
Debt Instrument [Line Items]
Amount of dividend restriction		38,000,000
Revolving Credit Facility [Member] \| Debt Covenant Terms 2019 [Member]
Debt Instrument [Line Items]
Amount of dividend restriction		50,000,000
Revolving Credit Facility [Member] \| Debt Covenant Terms 2020 [Member]
Debt Instrument [Line Items]
Amount of dividend restriction		50,000,000
Revolving Credit Facility [Member] \| Debt Covenant Terms January 01, 2021 through November 01, 2021 [Member]
Debt Instrument [Line Items]
Amount of dividend restriction		$ 75,000,000
Revolving Credit Facility [Member] \| Alcoa Nederland Holding BV [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum outstanding borrowings				750,000,000
Letters of credit sublimit under credit facility				400,000,000
Credit facility, interest rate description		Loans will bear interest at a rate per annum equal to an applicable margin plus, at ANHBV’s option, either (a) an adjusted LIBOR rate or (b) a base rate determined by reference to the highest of (1) the prime rate of JPMorgan Chase Bank, N.A., (2) the greater of the federal funds effective rate and the overnight bank funding rate, plus 0.5%, and (3) the one month adjusted LIBOR rate plus 1% per annum.
Revolving Credit Facility [Member] \| Alcoa Nederland Holding BV [Member] \| Federal Funds Effective Rate [Member]
Debt Instrument [Line Items]
Debt instrument, margin over variable rate		0.50%
Revolving Credit Facility [Member] \| Alcoa Nederland Holding BV [Member] \| LIBOR [Member]
Debt Instrument [Line Items]
Debt instrument, margin over variable rate		1.00%
Revolving Credit Facility [Member] \| Alcoa Nederland Holding BV [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Principal amount of debt		$ 500,000,000		0
Commitment fee paid to maintain credit facility		0.45%
Applicable margin on LIBOR loans		2.50%
Applicable margin on base rate loans		1.50%
Revolving Credit Facility [Member] \| Alcoa Nederland Holding BV [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Commitment fee paid to maintain credit facility		0.225%
Applicable margin on LIBOR loans		1.75%
Applicable margin on base rate loans		0.75%
Revolving Credit Facility [Member] \| Alcoa Nederland Holding BV [Member] \| Letter of Credit [Member]
Debt Instrument [Line Items]
Line of credit facility, maximum outstanding borrowings				$ 750,000,000