Statement of Consolidated Comprehensive Income (unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Statement of Comprehensive Income [Abstract]
NET INCOME (LOSS) ATTRIBUTABLE TO ALCOA CORPORATION	$ 309	$ (197)	$ 484	$ (117)
Net income (loss), Noncontrolling interest	41	47	85	106
Net income (loss)	350	(150)	569	(11)
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits, Alcoa Corporation	253	(127)	384	(89)
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits, Noncontrolling interest	3	2	4	2
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits	256	(125)	388	(87)
Foreign currency translation adjustments, Alcoa Corporation	204	135	28	(528)
Foreign currency translation adjustments, Noncontrolling interest	51	94	(9)	(151)
Foreign currency translation adjustments	255	229	19	(679)
Net change in unrecognized gains/losses on cash flow hedges, Alcoa Corporation	(266)	(390)	(470)	311
Net change in unrecognized gains/losses on cash flow hedges, Noncontrolling interest	5	(1)	2	(21)
Net change in unrecognized gains/losses on cash flow hedges	(261)	(391)	(468)	290
Total Other comprehensive income (loss), net of tax, Alcoa Corporation	191	(382)	(58)	(306)
Total Other comprehensive income (loss), net of tax, Noncontrolling interest	59	95	(3)	(170)
Total Other comprehensive income (loss), net of tax	250	(287)	(61)	(476)
Comprehensive income (loss), Alcoa Corporation	500	(579)	426	(423)
Comprehensive income (loss), Noncontrolling interest	100	142	82	(64)
Comprehensive income (loss)	$ 600	$ (437)	$ 508	$ (487)