Amount of curtailment.

No definition available.

Name:	aa_AmountOfCurtailment
Namespace Prefix:	aa_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Charge related to European commission announcement.

+ References

No definition available.

+ Details

Name:	aa_ChargeRelatedToEuropeanCommissionAnnouncement
Namespace Prefix:	aa_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Due from third parties.

+ References

No definition available.

+ Details

Name:	aa_DueFromThirdParties
Namespace Prefix:	aa_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Establishment reserves.

+ References

No definition available.

+ Details

Name:	aa_EstablishmentReserves
Namespace Prefix:	aa_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Loss contingency, recovery from third party.

+ References

No definition available.

+ Details

Name:	aa_LossContingencyRecoveryFromThirdParty
Namespace Prefix:	aa_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Number of installments.

+ References

No definition available.

+ Details

Name:	aa_NumberOfInstallments
Namespace Prefix:	aa_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of plants.

+ References

No definition available.

+ Details

Name:	aa_NumberOfPlants
Namespace Prefix:	aa_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Year operating under a power supply structured.

+ References

No definition available.

+ Details

Name:	aa_NumberOfYearsOperatingUnderPowerSupplyStructured
Namespace Prefix:	aa_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Payment for litigation settlement installment amount.

+ References

No definition available.

+ Details

Name:	aa_PaymentForLitigationSettlementInstallmentAmount
Namespace Prefix:	aa_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Write-off of receivable.

+ References

No definition available.

+ Details

Name:	aa_WriteOffOfReceivable
Namespace Prefix:	aa_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Aggregate carrying amount of the estimated litigation liability for known or estimated probable loss from litigation, which may include attorneys' fees and other litigation costs.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14326-108349

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 210.5-02.25)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_LitigationReserve
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_LossContingenciesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 4

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14435-108349

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 9

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=25496072&loc=d3e14557-108349

+ Details

Name:	us-gaap_LossContingencyEstimateOfPossibleLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The estimated maximum amount of possible loss from the contingency.

+ References

+ Details

Name:	us-gaap_LossContingencyRangeOfPossibleLossMaximum
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The estimated minimum amount of possible loss from the contingency.

+ References

+ Details

Name:	us-gaap_LossContingencyRangeOfPossibleLossMinimum
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of receivable related to a loss contingency accrual. For example, an insurance recovery receivable.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 460

-SubTopic 10

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6851643&loc=d3e12053-110248

+ Details

Name:	us-gaap_LossContingencyReceivable
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of cash paid for the settlement of litigation or for other legal issues during the period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 25

-Subparagraph (g)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3536-108585

+ Details

Name:	us-gaap_PaymentsForLegalSettlements
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Cumulative provision for contract losses not offset against related costs accumulated on the balance sheet.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 605

-SubTopic 35

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6802688&loc=d3e57777-111642

+ Details

Name:	us-gaap_ProvisionForLossOnContracts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Contingencies and Commitments - Additional Information (Detail)	1 Months Ended													0 Months Ended		3 Months Ended
	Jul. 31, 2012 Plant	Jun. 12, 2012 USD ($) Installment	Jun. 12, 2012 EUR (€)	Mar. 26, 2012 USD ($)	Mar. 26, 2012 EUR (€)	Sep. 30, 2010 t	Feb. 21, 2013 Minimum [Member] USD ($)	Feb. 21, 2013 Maximum [Member] USD ($)	Feb. 21, 2013 Maximum [Member] EUR (€)	Mar. 31, 2015 Alcoa [Member] USD ($)	Mar. 31, 2015 Alcoa [Member] EUR (€)	Feb. 21, 2013 Alcoa Trasformazioni [Member] USD ($)	Feb. 21, 2013 Alcoa Trasformazioni [Member] EUR (€)	Nov. 19, 2009 Italian Government [Member] USD ($) Plant	Nov. 19, 2009 Italian Government [Member] EUR (€) Plant	Mar. 31, 2015 Italian Government [Member]	Dec. 31, 2012 Portovesme [Member] t
Loss Contingencies [Line Items]
Management estimate for maximum exposure from class action				$ 110,000,000	€ 85,000,000							$ 97,000,000	€ 76,000,000
Provision for contract losses							0	97,000,000	76,000,000
Number of years operating under a power supply structure																10 years
Charge related to European Commission announcement														250,000,000	173,000,000
Number of smelters	2aa_NumberOfPlants													2	2
Write-off of receivable														20,000,000	14,000,000
Establishment reserve														230,000,000	159,000,000
Recovery amount		375,000,000	303,000,000
Reduction in recovery amount		65,000,000aa_DueFromThirdParties	53,000,000aa_DueFromThirdParties							57,000,000	53,000,000
Payments to Italian Government		310,000,000us-gaap_PaymentsForLegalSettlements	250,000,000us-gaap_PaymentsForLegalSettlements
Payments to Italian Government, installments amount		69,000,000	50,000,000
Number of installments, litigation payment		5aa_NumberOfInstallments	5aa_NumberOfInstallments
Litigation reserve		172,000,000us-gaap_LitigationReserve	159,000,000us-gaap_LitigationReserve
Range of reasonable possible loss, minimum		172,000,000	159,000,000
Range of reasonable possible loss, maximum		329,000,000	303,000,000
Noncurrent asset										$ 99,000,000	€ 91,000,000
Amount of curtailment, metric-tons-per-year						44,000aa_AmountOfCurtailment											150,000