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Accumulated Other Comprehensive Loss - Summary of Changes in Accumulated Other Comprehensive (Loss) Income by Component (Detail) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Pension and other postretirement benefits |  |  |
Balance at beginning of period | $ (2,568) |  |
Total Other comprehensive (loss) income | (220) | $ (482) | $ (2)
Balance at end of period | (2,644) | (2,568) |
Foreign currency translation |  |  |
Other comprehensive income (loss) | 254 | 450 | (1,995)
Available-for-sale securities |  |  |
Other comprehensive income (loss) | (134) | 137 | (5)
Cash flow hedges |  |  |
Total Other comprehensive (loss) income | 26 | (612) | 826
Accumulated Other Comprehensive Loss |  |  |
Pension and other postretirement benefits |  |  |
Balance at beginning of period | (2,010) | (3,611) | (3,601)
Unrecognized net actuarial loss and prior service cost/benefit | (466) | (1,112) | (478)
Tax benefit (expense) | 102 | 380 | 170
Total Other comprehensive (loss) income before reclassifications, net of tax | (364) | (732) | (308)
Amortization of net actuarial loss and prior service cost/benefit | 222 | 389 | 458
Tax expense | (78) | (136) | (160)
Total amount reclassified from Accumulated other comprehensive loss, net of tax | 144 | 253 | 298
Total Other comprehensive (loss) income | (220) | (479) | (10)
Transfer to Alcoa Corporation | 0 | 2,080 | 0
Balance at end of period | (2,230) | (2,010) | (3,611)
Foreign currency translation |  |  |
Balance at beginning of period | (689) | (2,412) | (846)
Other comprehensive income (loss) | 252 | 268 | (1,566)
Transfer to Alcoa Corporation | 0 | 1,455 | 0
Balance at end of period | (437) | (689) | (2,412)
Available-for-sale securities |  |  |
Balance at beginning of period | 132 | (5) | 0
Other comprehensive income (loss) | (134) | 137 | (5)
Transfer to Alcoa Corporation | 0 | 0 | 0
Balance at end of period | (2) | 132 | (5)
Cash flow hedges |  |  |
Balance at beginning of period | (1) | 597 | (230)
Net change from periodic revaluations | 37 | (843) | 1,138
Tax benefit (expense) | (9) | 252 | (340)
Total Other comprehensive (loss) income before reclassifications, net of tax | 28 | (591) | 798
Net amount reclassified to earnings | (3) | (38) | 35
Tax benefit (expense) | 1 | 12 | (6)
Total amount reclassified from Accumulated other comprehensive loss, net of tax | (2) | (26) | 29
Total Other comprehensive (loss) income | 26 | (617) | 827
Transfer to Alcoa Corporation | 0 | 19 | 0
Balance at end of period | 25 | (1) | 597
Accumulated Other Comprehensive Loss | Aluminum Contracts |  |  |
Cash flow hedges |  |  |
Net amount reclassified to earnings | (2) | 1 | 21
Accumulated Other Comprehensive Loss | Energy Contracts |  |  |
Cash flow hedges |  |  |
Net amount reclassified to earnings | 0 | (49) | 6
Accumulated Other Comprehensive Loss | Foreign Exchange Contracts |  |  |
Cash flow hedges |  |  |
Net amount reclassified to earnings | 0 | 0 | 5
Accumulated Other Comprehensive Loss | Interest Rate Contracts |  |  |
Cash flow hedges |  |  |
Net amount reclassified to earnings | 0 | 9 | 1
Accumulated Other Comprehensive Loss | Nickel Contracts |  |  |
Cash flow hedges |  |  |
Net amount reclassified to earnings | (1) | 1 | 2
Noncontrolling Interests |  |  |
Pension and other postretirement benefits |  |  |
Balance at beginning of period | 0 | (56) | (64)
Unrecognized net actuarial loss and prior service cost/benefit | 0 | (9) | 5
Tax benefit (expense) | 0 | 3 | (1)
Total Other comprehensive (loss) income before reclassifications, net of tax | 0 | (6) | 4
Amortization of net actuarial loss and prior service cost/benefit | 0 | 4 | 6
Tax expense | 0 | (1) | (2)
Total amount reclassified from Accumulated other comprehensive loss, net of tax | 0 | 3 | 4
Total Other comprehensive (loss) income | 0 | (3) | 8
Transfer to Alcoa Corporation | 0 | 59 | 0
Balance at end of period | 0 | 0 | (56)
Foreign currency translation |  |  |
Balance at beginning of period | (2) | (780) | (351)
Other comprehensive income (loss) | 2 | 182 | (429)
Transfer to Alcoa Corporation | 0 | 596 | 0
Balance at end of period | 0 | (2) | (780)
Available-for-sale securities |  |  |
Balance at beginning of period | 0 | 0 | 0
Other comprehensive income (loss) | 0 | 0 | 0
Transfer to Alcoa Corporation | 0 | 0 | 0
Balance at end of period | 0 | 0 | 0
Cash flow hedges |  |  |
Balance at beginning of period | 0 | (3) | (2)
Net change from periodic revaluations | 0 | 36 | (1)
Tax benefit (expense) | 0 | (10) | 0
Total Other comprehensive (loss) income before reclassifications, net of tax | 0 | 26 | (1)
Net amount reclassified to earnings | 0 | (29) | 0
Tax benefit (expense) | 0 | 8 | 0
Total amount reclassified from Accumulated other comprehensive loss, net of tax | 0 | (21) | 0
Total Other comprehensive (loss) income | 0 | 5 | (1)
Transfer to Alcoa Corporation | 0 | (2) | 0
Balance at end of period | 0 | 0 | (3)
Noncontrolling Interests | Aluminum Contracts |  |  |
Cash flow hedges |  |  |
Net amount reclassified to earnings | 0 | 0 | 0
Noncontrolling Interests | Energy Contracts |  |  |
Cash flow hedges |  |  |
Net amount reclassified to earnings | 0 | (34) | 0
Noncontrolling Interests | Foreign Exchange Contracts |  |  |
Cash flow hedges |  |  |
Net amount reclassified to earnings | 0 | 0 | 0
Noncontrolling Interests | Interest Rate Contracts |  |  |
Cash flow hedges |  |  |
Net amount reclassified to earnings | 0 | 5 | 0
Noncontrolling Interests | Nickel Contracts |  |  |
Cash flow hedges |  |  |
Net amount reclassified to earnings | $ 0 | $ 0 | $ 0

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