Statement of Combined Comprehensive (Loss) Income (unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Net (loss) income	$ 14	$ (63)	$ (203)	$ 151
Other comprehensive (loss) income, net of tax (C):
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits	19	51	21	97
Foreign currency translation adjustments	77	(1,041)	630	(1,873)
Net change in unrecognized gains/losses on cash flow hedges	(380)	200	(635)	587
Total Other comprehensive (loss) income, net of tax	(284)	(790)	16	(1,189)
Comprehensive (loss) income	(270)	(853)	(187)	(1,038)
Alcoa Corporation [Member]
Net (loss) income	(6)	(124)	(261)	(37)
Other comprehensive (loss) income, net of tax (C):
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits	20	42	19	83
Foreign currency translation adjustments	32	(743)	446	(1,357)
Net change in unrecognized gains/losses on cash flow hedges	(370)	199	(639)	590
Total Other comprehensive (loss) income, net of tax	(318)	(502)	(174)	(684)
Comprehensive (loss) income	(324)	(626)	(435)	(721)
Noncontrolling Interest [Member]
Net (loss) income	20	61	58	188
Other comprehensive (loss) income, net of tax (C):
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits	(1)	9	2	14
Foreign currency translation adjustments	45	(298)	184	(516)
Net change in unrecognized gains/losses on cash flow hedges	(10)	1	4	(3)
Total Other comprehensive (loss) income, net of tax	34	(288)	190	(505)
Comprehensive (loss) income	$ 54	$ (227)	$ 248	$ (317)