Statement of Changes in Consolidated Equity - USD ($) $ in Millions	Total	Common Stock [Member]	Additional Capital [Member]	Retained (Deficit) Earnings [Member]	Accumulated Other Comprehensive Loss [Member]	Non-controlling Interest [Member]	ParentCo [Member] Parent Company Net Investment [Member]	Alcoa Corporation [Member] Retained (Deficit) Earnings [Member]
Beginning Balance at Dec. 31, 2015	$ 11,513				$ (1,600)	$ 2,071	$ 11,042
Net (loss) income	(346)					54	(296)	$ (104)
Other comprehensive (loss) income (G)	(229)				(335)	106
Establishment of additional defined benefit plans (N)	(2,528)				(2,704)		176
Change in Parent Company net investment	(603)						(603)
Cash provided at separation to Parent Company (A)	(1,072)						(1,072)
Separation-related adjustments (A)	1,138		$ 9,521		864		$ (9,247)
Issuance of common stock (M)		$ 2	(2)
Stock-based compensation (M)	2		2
Common stock issued: compensation plans (M)	10		10
Contributions (A)	48					48
Distributions	(233)					(233)
Other	(3)					(3)
Ending Balance at Dec. 31, 2016	7,697	2	9,531	$ (104)	(3,775)	2,043
Net (loss) income	559			217		342
Other comprehensive (loss) income (G)	(1,252)				(1,407)	155
Stock-based compensation (M)	24		24
Common stock issued: compensation plans (M)	43		43
Contributions (A)	80					80
Distributions	(342)					(342)
Other	(11)		(8)			(3)
Ending Balance at Dec. 31, 2017	6,798	2	9,590	113	(5,182)	2,275
Net (loss) income	871			227		644
Other comprehensive (loss) income (G)	369				617	(248)
Stock-based compensation (M)	35		35
Common stock issued: compensation plans (M)	23		23
Repurchase of common stock (M)	(50)		(50)
Contributions (A)	149					149
Distributions	(827)					(827)
Other	26		13	1		12
Ending Balance at Dec. 31, 2018	$ 7,394	$ 2	$ 9,611	$ 341	$ (4,565)	$ 2,005