Statement of Consolidated Comprehensive Income (unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement of Comprehensive Income [Abstract]
NET INCOME (LOSS) ATTRIBUTABLE TO ALCOA CORPORATION	$ 337	$ (49)	$ 821	$ (166)
Net income (loss), Noncontrolling interest	33	29	118	135
Net income (loss)	370	(20)	939	(31)
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits, Alcoa Corporation	72	(32)	456	(121)
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits, Noncontrolling interest	12	(3)	16	(1)
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits	84	(35)	472	(122)
Foreign currency translation adjustments, Alcoa Corporation	(202)	5	(174)	(523)
Foreign currency translation adjustments, Noncontrolling interest	(78)	17	(87)	(134)
Foreign currency translation adjustments	(280)	22	(261)	(657)
Net change in unrecognized gains/losses on cash flow hedges, Alcoa Corporation	(111)	(240)	(581)	71
Net change in unrecognized gains/losses on cash flow hedges, Noncontrolling interest	(2)			(21)
Net change in unrecognized gains/losses on cash flow hedges	(113)	(240)	(581)	50
Total Other comprehensive (loss) income, net of tax, Alcoa Corporation	(241)	(267)	(299)	(573)
Total Other comprehensive (loss) income, net of tax, Noncontrolling interest	(68)	14	(71)	(156)
Total Other comprehensive (loss) income, net of tax	(309)	(253)	(370)	(729)
Comprehensive income (loss), Alcoa Corporation	96	(316)	522	(739)
Comprehensive income (loss), Noncontrolling interest	(35)	43	47	(21)
Comprehensive income (loss)	$ 61	$ (273)	$ 569	$ (760)