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Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Jan. 01, 2018
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |  |
Balance at beginning of period | $ 4,924 | $ 5,141 | $ 14,131 |
Adoption of accounting standard (A) |  |  |  | $ 0
Total Other comprehensive income (loss), net of tax | 85 | (74) | (507) |
Balance at end of period | 5,585 | 4,924 | 5,141 |
Arconic |  |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |  |
Balance at beginning of period | (2,644) | (2,568) | (5,431) |
Adoption of accounting standard (A) |  |  |  | (367)
Total Other comprehensive income (loss), net of tax | 85 | (76) | (691) |
Balance at end of period | (2,926) | (2,644) | (2,568) |
Pension and other postretirement benefits (G) |  |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |  |
Balance at beginning of period | (2,230) | (2,010) | (3,611) |
Other comprehensive income (loss), before reclassifications, before tax | 70 | (466) | (1,112) |
Other comprehensive income (loss) before reclassifications, tax benefit (expense) | (19) | 102 | 380 |
Total other comprehensive (loss) income before reclassifications, net of tax | 51 | (364) | (732) |
Reclassification from accumulated other comprehensive income, before tax | 262 | 222 | 389 |
Reclassification from AOCI, tax benefit (expense) | (58) | (78) | (136) |
Total amount reclassified from accumulated other comprehensive loss, net of tax | 204 | 144 | 253 |
Total Other comprehensive income (loss), net of tax | 255 | (220) | (479) |
Transfer to Alcoa Corporation | 0 | 0 | 2,080 |
Balance at end of period | (2,344) | (2,230) | (2,010) |
Foreign currency translation |  |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |  |
Balance at beginning of period | (437) | (689) | (2,412) |
Total Other comprehensive income (loss), net of tax | (146) | 252 | 268 |
Transfer to Alcoa Corporation | 0 | 0 | 1,455 |
Balance at end of period | (583) | (437) | (689) |
Available-for-sale securities |  |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |  |
Balance at beginning of period | (2) | 132 | (5) |
Total Other comprehensive income (loss), net of tax | (1) | (134) | 137 |
Balance at end of period | (3) | (2) | 132 |
Cash flow hedges |  |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |  |
Balance at beginning of period | 25 | (1) | 597 |
Other comprehensive income (loss), before reclassifications, before tax | (15) | 37 | (843) |
Other comprehensive income (loss) before reclassifications, tax benefit (expense) | 3 | (9) | 252 |
Total other comprehensive (loss) income before reclassifications, net of tax | (12) | 28 | (591) |
Reclassification from accumulated other comprehensive income, before tax | (14) | (3) | (38) |
Reclassification from AOCI, tax benefit (expense) | 3 | 1 | 12 |
Total amount reclassified from accumulated other comprehensive loss, net of tax | (11) | (2) | (26) |
Total Other comprehensive income (loss), net of tax | (23) | 26 | (617) |
Transfer to Alcoa Corporation | 0 | 0 | 19 |
Balance at end of period | 4 | 25 | (1) |
Cash flow hedges | Aluminum Contracts |  |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |  |
Reclassification from accumulated other comprehensive income, before tax | (8) | (2) | 1 |
Cash flow hedges | Energy Contracts |  |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |  |
Reclassification from accumulated other comprehensive income, before tax | 0 | 0 | (49) |
Cash flow hedges | Interest Rate Contracts |  |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |  |
Reclassification from accumulated other comprehensive income, before tax | (2) | 0 | 9 |
Cash flow hedges | Nickel Contracts |  |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |  |
Reclassification from accumulated other comprehensive income, before tax | (4) | (1) | 1 |
Noncontrolling Interests |  |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |  |
Balance at beginning of period | 0 | (2) |  |
Balance at end of period | 0 | 0 | (2) |
Pension and other postretirement benefits (G) |  |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |  |
Balance at beginning of period | 0 | 0 | (56) |
Other comprehensive income (loss), before reclassifications, before tax | 0 | 0 | (9) |
Other comprehensive income (loss) before reclassifications, tax benefit (expense) | 0 | 0 | 3 |
Total other comprehensive (loss) income before reclassifications, net of tax | 0 | 0 | (6) |
Reclassification from accumulated other comprehensive income, before tax | 0 | 0 | 4 |
Reclassification from AOCI, tax benefit (expense) | 0 | 0 | (1) |
Total amount reclassified from accumulated other comprehensive loss, net of tax | 0 | 0 | 3 |
Total Other comprehensive income (loss), net of tax | 0 | 0 | (3) |
Transfer to Alcoa Corporation | 0 | 0 | 59 |
Balance at end of period | 0 | 0 | 0 |
Foreign currency translation |  |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |  |
Balance at beginning of period | 0 | (2) | (780) |
Total Other comprehensive income (loss), net of tax | 0 | 2 | 182 |
Transfer to Alcoa Corporation | 0 | 0 | 596 |
Balance at end of period | 0 | 0 | (2) |
Available-for-sale securities |  |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |  |
Balance at beginning of period | 0 | 0 | 0 |
Total Other comprehensive income (loss), net of tax | 0 | 0 | 0 |
Balance at end of period | 0 | 0 | 0 |
Cash flow hedges |  |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |  |
Balance at beginning of period | 0 | 0 | (3) |
Other comprehensive income (loss), before reclassifications, before tax | 0 | 0 | 36 |
Other comprehensive income (loss) before reclassifications, tax benefit (expense) | 0 | 0 | (10) |
Total other comprehensive (loss) income before reclassifications, net of tax | 0 | 0 | 26 |
Reclassification from accumulated other comprehensive income, before tax | 0 | 0 | (29) |
Reclassification from AOCI, tax benefit (expense) | 0 | 0 | 8 |
Total amount reclassified from accumulated other comprehensive loss, net of tax | 0 | 0 | (21) |
Total Other comprehensive income (loss), net of tax | 0 | 0 | 5 |
Transfer to Alcoa Corporation | 0 | 0 | (2) |
Balance at end of period | 0 | 0 | 0 |
Cash flow hedges | Aluminum Contracts |  |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |  |
Reclassification from accumulated other comprehensive income, before tax | 0 | 0 | 0 |
Cash flow hedges | Energy Contracts |  |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |  |
Reclassification from accumulated other comprehensive income, before tax | 0 | 0 | (34) |
Cash flow hedges | Interest Rate Contracts |  |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |  |
Reclassification from accumulated other comprehensive income, before tax | 0 | 0 | 5 |
Cash flow hedges | Nickel Contracts |  |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |  |
Reclassification from accumulated other comprehensive income, before tax | $ 0 | 0 | 0 |
ASU 2017-07 | Pension and other postretirement benefits (G) |  |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |  |
Adoption of accounting standard (A) |  | 0 | 0 | (369)
ASU 2017-07 | Pension and other postretirement benefits (G) |  |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |  |
Adoption of accounting standard (A) |  | 0 | $ 0 | 0
ASU 2017-12 | Cash flow hedges |  |  |  |
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] |  |  |  |
Adoption of accounting standard (A) |  | $ 0 |  | $ 2

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