Statement of Consolidated Comprehensive (Loss) Income (unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Net income (loss)	$ 169	$ 10	$ 615	$ (217)
Other comprehensive (loss) income, net of tax (G):
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits	49	19	214	21
Foreign currency translation adjustments	185	77	402	630
Net change in unrecognized gains/losses on cash flow hedges	(420)	(380)	(672)	(635)
Total Other comprehensive (loss) income, net of tax	(186)	(284)	(56)	16
Comprehensive (loss) income	(17)	(274)	559	(201)
Alcoa Corporation [Member]
Net income (loss)	113	(10)	413	(275)
Other comprehensive (loss) income, net of tax (G):
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits	44	20	190	19
Foreign currency translation adjustments	141	32	281	446
Net change in unrecognized gains/losses on cash flow hedges	(415)	(370)	(729)	(639)
Total Other comprehensive (loss) income, net of tax	(230)	(318)	(258)	(174)
Comprehensive (loss) income	(117)	(328)	155	(449)
Non-controlling Interest [Member]
Net income (loss)	56	20	202	58
Other comprehensive (loss) income, net of tax (G):
Change in unrecognized net actuarial loss and prior service cost/benefit related to pension and other postretirement benefits	5	(1)	24	2
Foreign currency translation adjustments	44	45	121	184
Net change in unrecognized gains/losses on cash flow hedges	(5)	(10)	57	4
Total Other comprehensive (loss) income, net of tax	44	34	202	190
Comprehensive (loss) income	$ 100	$ 54	$ 404	$ 248