Long-Term Debt - Additional Information (Detail) $ in Millions	9 Months Ended
Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)
Debt Instrument [Line Items]
Cash held in escrow	$ 72	$ 7
Proceeds from issuance of public debt offering	$ 1,313	$ 1,534
Ratio of consolidated indebtedness to consolidated EBITDDA	5.50
Alcoa Nederland Holding BV [Member]
Debt Instrument [Line Items]
Cash held in escrow	$ 1,309
Proceeds from issuance of public debt offering	1,228
Cash on hand to fund redemption of senior notes	$ 81
Amended Credit Facility [Member]
Debt Instrument [Line Items]
Revolving credit facility, term	5 years
Ratio of Indebtedness December 31, 2019 and Thereafter [Member]
Debt Instrument [Line Items]
Declining ratio of consolidated indebtedness to consolidated EBITDDA	3.50
Line of Credit Prior to Amendment [Member]
Debt Instrument [Line Items]
Replacement of existing financial covenant	$ 4,000
Post Amendment [Member]
Debt Instrument [Line Items]
Replacement of existing financial covenant	3,000
6.75% Senior Notes Due 2024 [Member] \| Alcoa Nederland Holding BV [Member]
Debt Instrument [Line Items]
Principal amount of debt	$ 750
Senior notes, interest percentage	6.75%
Debt instrument maturity date	2024
7% Senior Notes Due 2026 [Member] \| Alcoa Nederland Holding BV [Member]
Debt Instrument [Line Items]
Principal amount of debt	$ 500
Senior notes, interest percentage	7.00%
Debt instrument maturity date	2026

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