Cash required to be held in escrow.

No definition available.

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- Definition

Cash required to be placed in escrow.

+ References

No definition available.

+ Details

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

- Definition

Debt Covenant As Percentage Of Assets

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

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

+ References

No definition available.

+ Details

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- Definition

Debt instrument maturity year.

+ References

No definition available.

+ Details

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- Definition

Debt instrument redemption period.

+ References

No definition available.

+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Contractual interest rate for funds borrowed, under the debt 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(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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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.

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- Definition

Description of debt redemption features under terms of the debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph e
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

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- Definition

Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

+ 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

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

+ Details

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

- Definition

The cash inflow from a debt initially having maturity due after one year or beyond 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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Balance Type:	debit
Period Type:	duration

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- Details

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Debt - Additional Information (Detail) - USD ($)	9 Months Ended	12 Months Ended
Debt - Additional Information (Detail) - USD ($)	Sep. 30, 2016	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Principal amount of debt		$ 1,404,000,000	$ 1,445,000,000
Proceeds from issuance of public debt offering		21,000,000
Alcoa Nederland Holding BV [Member]
Debt Instrument [Line Items]
Proceeds from issuance of public debt offering	$ 1,228,000,000
Cash on hand to fund redemption of senior notes		$ 81,000,000
6.75% Senior Notes Due 2024 [Member] \| Alcoa Nederland Holding BV [Member]
Debt Instrument [Line Items]
Principal amount of debt	$ 750,000,000
Senior notes, interest percentage	6.75%
6.75% Senior Notes Due 2024 [Member] \| Alcoa Nederland Holding BV [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Debt instrument redemption price percentage		105.063%
7% Senior Notes Due 2026 [Member]
Debt Instrument [Line Items]
Debt convenant percentage of assets		1.50%
7% Senior Notes Due 2026 [Member] \| Debt Covenant Terms November 1, 2016 through December 31, 2017 [Member]
Debt Instrument [Line Items]
Amount of dividend restriction		$ 38,000,000
7% Senior Notes Due 2026 [Member] \| Debt Covenant Terms 2018 [Member]
Debt Instrument [Line Items]
Amount of dividend restriction		38,000,000
7% Senior Notes Due 2026 [Member] \| Debt Covenant Terms 2019 [Member]
Debt Instrument [Line Items]
Amount of dividend restriction		0.50
7% Senior Notes Due 2026 [Member] \| Debt Covenant Terms 2020 [Member]
Debt Instrument [Line Items]
Amount of dividend restriction		0.50
7% Senior Notes Due 2026 [Member] \| Debt Covenant Terms January One Two Thousand And Twenty One Through September Thirty Two Thousand And Twenty Six [Member]
Debt Instrument [Line Items]
Amount of dividend restriction		75,000,000
7% Senior Notes Due 2026 [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Amount of dividend restriction		$ 250,000,000
7% Senior Notes Due 2026 [Member] \| Alcoa Nederland Holding BV [Member]
Debt Instrument [Line Items]
Principal amount of debt	$ 500,000,000
Senior notes, interest percentage	7.00%
Debt instrument maturity date	2026
7% Senior Notes Due 2026 [Member] \| Alcoa Nederland Holding BV [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Debt instrument redemption price percentage		103.50%
Notes 2024 and 2026 [Member] \| Alcoa Nederland Holding BV [Member]
Debt Instrument [Line Items]
Debt instrument maturity date	2024
Debt redemption description		ANBHV has the option to redeem the Notes on at least 30 days, but not more than 60 days, prior notice to the holders of the Notes under multiple scenarios, including, in whole or in part, at any time or from time to time after September 2019, in the case of the 2024 Notes, or after September 2021, in the case of the 2026 Notes, at a redemption price specified in the indenture (up to 105.063% of the principal amount for the 2024 Notes and up to 103.500% of the principal amount of the 2026 Notes, plus any accrued and unpaid interest in each case).
Debt instrument redemption price percentage		101.00%
Cash held in escrow		$ 1,228,000,000
Notes 2024 and 2026 [Member] \| Alcoa Nederland Holding BV [Member] \| Minimum [Member]
Debt Instrument [Line Items]
Debt instrument redemption period		30 days
Notes 2024 and 2026 [Member] \| Alcoa Nederland Holding BV [Member] \| Maximum [Member]
Debt Instrument [Line Items]
Debt instrument redemption period		60 days