Accumulated Other Comprehensive Loss - Summary of Changes in Accumulated Other Comprehensive (Loss) Income by Component (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pension and other postretirement benefits (W)
Total Other comprehensive (loss) income	$ (82)	$ 557	$ (507)
Foreign currency translation
Other comprehensive loss	(1,266)	(1,335)	(296)
Available-for-sale-securities
Other comprehensive (loss) income	(2)	(1)	2
Cash flow hedges (X)
Total Other comprehensive income (loss)	78	184	(47)
Alcoa [Member]
Pension and other postretirement benefits (W)
Balance at beginning of period	(3,532)	(4,063)	(3,534)
Unrecognized net actuarial loss and prior service cost/benefit	(492)	281	(1,184)
Tax benefit (expense)	167	(88)	398
Total Other comprehensive (loss) income before reclassifications, net of tax	(325)	193	(786)
Amortization of net actuarial loss and prior service cost/benefit	394	520	396
Tax expense	(138)	(182)	(139)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	256	338	257
Total Other comprehensive (loss) income	(69)	531	(529)
Balance at end of period	(3,601)	(3,532)	(4,063)
Foreign currency translation
Balance at beginning of period	179	1,147	1,349
Other comprehensive loss	(1,025)	(968)	(202)
Balance at end of period	(846)	179	1,147
Available-for-sale-securities
Balance at beginning of period	2	3	1
Other comprehensive (loss) income	(2)	(1)	2
Balance at end of period		2	3
Cash flow hedges (X)
Balance at beginning of period	(308)	(489)	(443)
Net change from periodic revaluations	78	205	(2)
Tax expense	(21)	(43)	(10)
Total Other comprehensive income (loss) before reclassifications, net of tax	57	162	(12)
Net amount reclassified to earnings	25	22	(62)
Tax (expense) benefit	(4)	(3)	28
Total amount reclassified from Accumulated other comprehensive loss, net of tax	21	19	(34)
Total Other comprehensive income (loss)	78	181	(46)
Balance at end of period	(230)	(308)	(489)
Alcoa [Member] \| Aluminum Contracts [Member]
Cash flow hedges (X)
Net amount reclassified to earnings	27	18	(65)
Alcoa [Member] \| Foreign Exchange Contracts [Member]
Cash flow hedges (X)
Net amount reclassified to earnings	(3)	2
Alcoa [Member] \| Interest Rate Contracts [Member]
Cash flow hedges (X)
Net amount reclassified to earnings	1	2	3
Noncontrolling Interests [Member]
Pension and other postretirement benefits (W)
Balance at beginning of period	(51)	(77)	(99)
Unrecognized net actuarial loss and prior service cost/benefit	(22)	28	15
Tax benefit (expense)	7	(9)	(4)
Total Other comprehensive (loss) income before reclassifications, net of tax	(15)	19	11
Amortization of net actuarial loss and prior service cost/benefit	3	11	16
Tax expense	(1)	(4)	(5)
Total amount reclassified from Accumulated other comprehensive loss, net of tax	2	7	11
Total Other comprehensive (loss) income	(13)	26	22
Balance at end of period	(64)	(51)	(77)
Foreign currency translation
Balance at beginning of period	(110)	257	351
Other comprehensive loss	(241)	(367)	(94)
Balance at end of period	(351)	(110)	257
Cash flow hedges (X)
Balance at beginning of period	(2)	(5)	(4)
Net change from periodic revaluations		4	(1)
Tax expense		(1)
Total Other comprehensive income (loss) before reclassifications, net of tax		3	(1)
Total Other comprehensive income (loss)		3	(1)
Balance at end of period	$ (2)	$ (2)	$ (5)

Accumulated appreciation or loss, net of tax, in value of the total of available-for-sale securities at the end of an accounting period.

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Accumulated change, net of tax, in accumulated gains and losses from derivative instruments designated and qualifying as the effective portion of cash flow hedges. Includes an entity's share of an equity investee's Increase or Decrease in deferred hedging gains or losses.

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The total of net gain (loss), prior service cost (credit), and transition assets (obligations), as well as minimum pension liability if still remaining, included in accumulated other comprehensive income associated with a defined benefit pension or other postretirement plan(s) because they have yet to be recognized as components of net periodic benefit cost.

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Accumulated adjustment, net of tax, that results from the process of translating subsidiary financial statements and foreign equity investments into the reporting currency from the functional currency of the reporting entity, net of reclassification of realized foreign currency translation gains or losses.

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Amount after tax and reclassification adjustments, of appreciation (loss) in value of unsold available-for-sale securities. Excludes amounts related to other than temporary impairment (OTTI) loss.

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Amount after tax and reclassification adjustments, of increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

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Amount after tax and reclassification adjustments of gain (loss) on foreign currency translation adjustments, foreign currency transactions designated and effective as economic hedges of a net investment in a foreign entity and intra-entity foreign currency transactions that are of a long-term-investment nature.

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Amount before tax and reclassification adjustments of (increase) decrease in accumulated other comprehensive (income) loss related to pension and other postretirement benefit plans.

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Amount after tax, before reclassification adjustments, of (increase) decrease in accumulated other comprehensive (income) loss related to pension and other postretirement benefit plans.

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Amount after tax and reclassification adjustments, of (increase) decrease in accumulated other comprehensive (income) loss related to pension and other postretirement defined benefit plans.

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Amount of tax (expense) benefit, before reclassification adjustments, related to (increase) decrease in accumulated other comprehensive (income) loss related to pension and other postretirement benefit plans.

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Amount before tax of reclassification adjustment from accumulated other comprehensive income of accumulated gain (loss) realized from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's deferred hedging gain (loss).

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Amount after tax of reclassification adjustment from accumulated other comprehensive income of accumulated gain (loss) realized from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's deferred hedging gain (loss).

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Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income of accumulated gain (loss) realized from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's deferred hedging gain (loss).

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Amount before tax of reclassification adjustment from accumulated other comprehensive (income) loss related to net period benefit cost (credit) for pension and other postretirement defined benefit plans.

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Amount after tax of reclassification adjustment from accumulated other comprehensive (income) loss related to net period benefit cost (credit) for pension and other postretirement defined benefit plans.

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Amount of tax (expense) benefit of reclassification adjustment from accumulated other comprehensive (income) loss related to pension and other postretirement defined benefit plans.

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Amount before tax of increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

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Amount after tax of increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

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Amount of tax expense (benefit), before reclassification adjustments, related to increase (decrease) in accumulated gain (loss) from derivative instruments designated and qualifying as the effective portion of cash flow hedges and an entity's share of an equity investee's increase (decrease) in deferred hedging gain (loss).

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