Quarterly Data - Schedule of Quarterly Data (Detail) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Sales	$ 3,344	$ 3,390	$ 3,579	$ 3,090	$ 3,174	$ 2,964	$ 2,859	$ 2,655	$ 13,403	$ 11,652	$ 9,318
Net income (loss)	212	155	230	274	(56)	169	138	308	871	559	(346)
Net income (loss) attributable to Alcoa Corporation	$ 43	$ (41)	$ 75	$ 150	$ (196)	$ 113	$ 75	$ 225	$ 227	$ 217	$ (400)
Earnings per share attributable to Alcoa Corporation common shareholders(1):
Basic	$ 0.23	$ (0.22)	$ 0.40	$ 0.81	$ (1.06)	$ 0.61	$ 0.41	$ 1.23	$ 1.22	$ 1.18	$ (2.19)
Diluted	$ 0.23	$ (0.22)	$ 0.39	$ 0.80	$ (1.06)	$ 0.60	$ 0.40	$ 1.21	$ 1.20	$ 1.16	$ (2.19)