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Debt - Schedule of Long-Term Debt (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2014
5.25% Convertible Notes Due 2014 [Member]
Debt Instrument [Line Items]
Long-term debt, interest rate	5.25%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_LongtermDebtTypeAxis = aa_FivePointTwoFivePercentConvertibleNotesDueTwoThousandFourteenMember
Debt instrument, maturity date	2014
5.55% Notes, Due 2017 [Member]
Debt Instrument [Line Items]
Long-term debt, interest rate	5.55%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_LongtermDebtTypeAxis = aa_FivePointFiveFivePercentNotesDueTwoThousandSeventeenMember
Debt instrument, maturity date	2017
6.50% Bonds, Due 2018 [Member]
Debt Instrument [Line Items]
Long-term debt, interest rate	6.50%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_LongtermDebtTypeAxis = aa_SixPointFivePercentBondsDueTwoThousandEighteenMember
Debt instrument, maturity date	2018
6.75% Notes, Due 2018 [Member]
Debt Instrument [Line Items]
Long-term debt, interest rate	6.75%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_LongtermDebtTypeAxis = aa_SixPointSevenFivePercentNotesDueTwoThousandEighteenMember
Debt instrument, maturity date	2018
5.72% Notes, Due 2019 [Member]
Debt Instrument [Line Items]
Long-term debt, interest rate	5.72%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_LongtermDebtTypeAxis = aa_FivePointSevenTwoPercentNotesDueTwoThousandNineteenMember
Debt instrument, maturity date	2019
6.150% Notes, Due 2020 [Member]
Debt Instrument [Line Items]
Long-term debt, interest rate	6.15%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_LongtermDebtTypeAxis = aa_SixPointOneFivePercentNotesDueTwoThousandTwentyMember
Debt instrument, maturity date	2020
5.40% Notes, Due 2021 [Member]
Debt Instrument [Line Items]
Long-term debt, interest rate	5.40%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_LongtermDebtTypeAxis = aa_FivePointFourZeroPercentNotesDueTwoThousandTwentyOneMember
Debt instrument, maturity date	2021
5.87% Notes, Due 2022 [Member]
Debt Instrument [Line Items]
Long-term debt, interest rate	5.87%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_LongtermDebtTypeAxis = aa_FivePointEightSevenPercentNotesDueTwoThousandTwentyTwoMember
Debt instrument, maturity date	2022
5.125% Notes, Due 2024 [Member]
Debt Instrument [Line Items]
Long-term debt, interest rate	5.125%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_LongtermDebtTypeAxis = aa_FivePointOneTwoFivePercentNotesDueTwoThousandTwentyFourMember
Debt instrument, maturity date	2024
5.90% Notes, Due 2027 [Member]
Debt Instrument [Line Items]
Long-term debt, interest rate	5.90%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_LongtermDebtTypeAxis = aa_FivePointNinePercentNotesDueTwoThousandTwentySevenMember
Debt instrument, maturity date	2027
6.75% Bonds, Due 2028 [Member]
Debt Instrument [Line Items]
Long-term debt, interest rate	6.75%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_LongtermDebtTypeAxis = aa_SixPointSevenFivePercentBondsDueTwoThousandTwentyEightMember
Debt instrument, maturity date	2028
5.95% Notes Due 2037 [Member]
Debt Instrument [Line Items]
Long-term debt, interest rate	5.95%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_LongtermDebtTypeAxis = aa_FivePointNineFivePercentNotesDueTwoThousandThirtySevenMember
Debt instrument, maturity date	2037
BNDES Loans, Due 2015-2029 [Member]
Debt Instrument [Line Items]
Debt instrument, maturity date start	2015
Debt instrument, maturity date end	2029
Iowa Finance Authority Loan, Due 2042 (4.75%) [Member]
Debt Instrument [Line Items]
Long-term debt, interest rate	4.75%us-gaap_DebtInstrumentInterestRateStatedPercentage / us-gaap_LongtermDebtTypeAxis = aa_FourPointSevenFivePercentageIowaFinanceAuthorityLoanDueTwoThousandFortyTwoMember
Debt instrument, maturity date	2042

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Debt instrument maturity year.

+ References

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- Definition

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- Definition

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5



Reference 2: 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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