Statement of Consolidated Comprehensive Income (unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Statement of Comprehensive Income [Abstract]
Net (loss) income, Alcoa Corporation	$ (197)	$ (402)	$ (117)	$ (601)
Net (loss) income, Noncontrolling interest	47	109	106	250
Net (loss) income	(150)	(293)	(11)	(351)
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits, Alcoa Corporation	(127)	10	(89)	51
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits, Noncontrolling interest	2	(2)	2	(1)
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits	(125)	8	(87)	50
Foreign currency translation adjustments, Alcoa Corporation	135	40	(528)	18
Foreign currency translation adjustments, Noncontrolling interest	94	4	(151)	6
Foreign currency translation adjustments	229	44	(679)	24
Net change in unrecognized gains/losses on cash flow hedges, Alcoa Corporation	(390)	79	311	(209)
Net change in unrecognized gains/losses on cash flow hedges, Noncontrolling interest	(1)	(1)	(21)	5
Net change in unrecognized gains/losses on cash flow hedges	(391)	78	290	(204)
Total Other comprehensive (loss) income, net of tax, Alcoa Corporation	(382)	129	(306)	(140)
Total Other comprehensive (loss) income, net of tax, Noncontrolling interest	95	1	(170)	10
Total Other comprehensive (loss) income, net of tax	(287)	130	(476)	(130)
Comprehensive (loss) income, Alcoa Corporation	(579)	(273)	(423)	(741)
Comprehensive (loss) income, Noncontrolling interest	142	110	(64)	260
Comprehensive (loss) income	$ (437)	$ (163)	$ (487)	$ (481)