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Quarterly Data - Schedule of Quarterly Data (Detail) - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended 12 Months Ended
Dec. 31, 2020
Sep. 30, 2020
Jun. 30, 2020
Mar. 31, 2020
Dec. 31, 2019
Sep. 30, 2019
Jun. 30, 2019
Mar. 31, 2019
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Quarterly Financial Information Disclosure [Abstract]                      
Sales $ 2,392 $ 2,365 $ 2,148 $ 2,381 $ 2,436 $ 2,567 $ 2,711 $ 2,719 $ 9,286 $ 10,433 $ 13,403
Net (loss) income 17 (20) (150) 139 (355) (147) (293) (58) (14) (853) 893
Net income (loss) attributable to Alcoa Corporation $ (4) $ (49) $ (197) $ 80 $ (303) $ (221) $ (402) $ (199) $ (170) $ (1,125) $ 250
Earnings per share attributable to Alcoa Corporation common shareholders:                      
Basic $ (0.02) $ (0.26) $ (1.06) $ 0.43 $ (1.63) $ (1.19) $ (2.17) $ (1.07) $ (0.91) $ (6.07) $ 1.34
Diluted $ (0.02) $ (0.26) $ (1.06) $ 0.43 $ (1.63) $ (1.19) $ (2.17) $ (1.07) $ (0.91) $ (6.07) $ 1.33