Statement of Consolidated Comprehensive Income (unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement of Comprehensive Income [Abstract]
Net (loss) income (H), Alcoa Corporation	$ (221)	$ (6)	$ (822)	$ 199
Net (loss) income (H), Noncontrolling interest	74	201	324	467
Net (loss) income (H)	(147)	195	(498)	666
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits, Alcoa Corporation	19	398	70	682
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits, Noncontrolling interest	(6)	4	(7)	7
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits	13	402	63	689
Foreign currency translation adjustments, Alcoa Corporation	(224)	(142)	(206)	(586)
Foreign currency translation adjustments, Noncontrolling interest	(75)	(54)	(69)	(219)
Foreign currency translation adjustments	(299)	(196)	(275)	(805)
Net change in unrecognized gains/losses on cash flow hedges, Alcoa Corporation	61	(29)	(148)	346
Net change in unrecognized gains/losses on cash flow hedges, Noncontrolling interest	(3)	5	2	(25)
Net change in unrecognized gains/losses on cash flow hedges	58	(24)	(146)	321
Total Other comprehensive income (loss), net of tax, Alcoa Corporation	(144)	227	(284)	442
Total Other comprehensive income (loss), net of tax, Noncontrolling interest	(84)	(45)	(74)	(237)
Total Other comprehensive income (loss), net of tax	(228)	182	(358)	205
Comprehensive (loss) income, Alcoa Corporation	(365)	221	(1,106)	641
Comprehensive (loss) income, Noncontrolling interest	(10)	156	250	230
Comprehensive (loss) income	$ (375)	$ 377	$ (856)	$ 871