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Accumulated Other Comprehensive Loss - Summary of Changes in Accumulated Other Comprehensive Loss by Component (Detail) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2015 | Jun. 30, 2014 | Jun. 30, 2015 | Jun. 30, 2014
Pension and other postretirement benefits |  |  |  |
Total Other comprehensive (loss) income | $ (1) | $ 15 | $ 106 | $ 92
Foreign currency translation |  |  |  |
Other comprehensive (loss) income | 229 | 200 | (978) | 536
Available-for-sale securities |  |  |  |
Other comprehensive (loss) income | (2) | 1 |  | 1
Cash flow hedges |  |  |  |
Total Other comprehensive income (loss) | 430 | (31) | 366 | 3
Energy Contracts [Member] |  |  |  |
Cash flow hedges |  |  |  |
Total Other comprehensive income (loss) before reclassifications, net of tax | (17) |  | (11) | 5
Alcoa [Member] |  |  |  |
Pension and other postretirement benefits |  |  |  |
Balance at beginning of period | (3,496) | (3,455) | (3,601) | (3,532)
Unrecognized net actuarial loss and prior service cost/benefit | (118) | (80) | (76) | (63)
Tax benefit | 39 | 28 | 28 | 25
Total Other comprehensive (loss) income before reclassifications, net of tax | (79) | (52) | (48) | (38)
Amortization of net actuarial loss and prior service cost/benefit | 115 | 101 | 229 | 199
Tax expense | (40) | (35) | (80) | (70)
Total amount reclassified from Accumulated other comprehensive loss, net of tax | 75 | 66 | 149 | 129
Total Other comprehensive (loss) income | (4) | 14 | 101 | 91
Balance at end of period | (3,500) | (3,441) | (3,500) | (3,441)
Foreign currency translation |  |  |  |
Balance at beginning of period | (1,803) | 428 | (846) | 179
Other comprehensive (loss) income | 197 | 141 | (760) | 390
Balance at end of period | (1,606) | 569 | (1,606) | 569
Available-for-sale securities |  |  |  |
Balance at beginning of period | 2 | 2 |  | 2
Other comprehensive (loss) income | (2) | 1 |  | 1
Balance at end of period |  | 3 |  | 3
Cash flow hedges |  |  |  |
Balance at beginning of period | (294) | (276) | (230) | (308)
Net change from periodic revaluations | 614 | (32) | 504 | 4
Tax (expense) benefit | (190) | 4 | (156) | (4)
Total Other comprehensive income (loss) before reclassifications, net of tax | 424 | (28) | 348 |
Net amount reclassified to earnings | 14 | 6 | 29 | 11
Tax expense | (4) | (1) | (7) | (2)
Total amount reclassified from Accumulated other comprehensive loss, net of tax | 10 | 5 | 22 | 9
Total Other comprehensive income (loss) | 434 | (23) | 370 | 9
Balance at end of period | 140 | (299) | 140 | (299)
Alcoa [Member] | Aluminum Contracts [Member] |  |  |  |
Cash flow hedges |  |  |  |
Net amount reclassified to earnings | 10 | 6 | 23 | 11
Alcoa [Member] | Energy Contracts [Member] |  |  |  |
Cash flow hedges |  |  |  |
Net amount reclassified to earnings | 2 |  | 4 |
Alcoa [Member] | Foreign Exchange Contracts [Member] |  |  |  |
Cash flow hedges |  |  |  |
Net amount reclassified to earnings | 1 | (1) | 1 | (1)
Alcoa [Member] | Interest Rate Contracts [Member] |  |  |  |
Cash flow hedges |  |  |  |
Net amount reclassified to earnings | 1 | 1 | 1 | 1
Noncontrolling Interests [Member] |  |  |  |
Pension and other postretirement benefits |  |  |  |
Balance at beginning of period | (62) | (51) | (64) | (51)
Unrecognized net actuarial loss and prior service cost/benefit | 3 |  | 3 |
Total Other comprehensive (loss) income before reclassifications, net of tax | 3 |  | 3 |
Amortization of net actuarial loss and prior service cost/benefit | 1 | 1 | 4 | 2
Tax expense | (1) |  | (2) | (1)
Total amount reclassified from Accumulated other comprehensive loss, net of tax |  | 1 | 2 | 1
Total Other comprehensive (loss) income | 3 | 1 | 5 | 1
Balance at end of period | (59) | (50) | (59) | (50)
Foreign currency translation |  |  |  |
Balance at beginning of period | (601) | (23) | (351) | (110)
Other comprehensive (loss) income | 32 | 59 | (218) | 146
Balance at end of period | (569) | 36 | (569) | 36
Cash flow hedges |  |  |  |
Balance at beginning of period | (2) |  | (2) | (2)
Net change from periodic revaluations | (5) | (12) | (5) | (9)
Tax (expense) benefit | 1 | 4 | 1 | 3
Total Other comprehensive income (loss) before reclassifications, net of tax | (4) | (8) | (4) | (6)
Total Other comprehensive income (loss) | (4) | (8) | (4) | (6)
Balance at end of period | $ (6) | $ (8) | $ (6) | $ (8)

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- Definition Accumulated appreciation or loss, net of tax, in value of the total of available-for-sale securities at the end of an accounting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669686-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e637-108580 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14 -URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e681-108580 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669646-108580 + Details
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- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (j-k) -URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669646-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e637-108580 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14 -URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e681-108580 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669686-108580 + Details
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- Definition 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. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14 -URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e681-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669646-108580 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=36458714&loc=d3e637-108580 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 830 -SubTopic 30 -Section 45 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=6915805&loc=d3e32022-110900 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669686-108580 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 830 -SubTopic 30 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6450520&loc=d3e32583-110901 + Details
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