Statement of Changes in Consolidated Equity - USD ($) $ in Millions	Total	Preferred Class A	Preferred Class B	Preferred stock	Mandatory convertible preferred stock	Common stock	Additional capital	Retained earnings (deficit)	Retained earnings (deficit) Preferred Class A	Retained earnings (deficit) Preferred Class B	Treasury stock	Accumulated Other Comprehensive Loss	Noncontrolling Interests
Balance at beginning of period at Dec. 31, 2015	$ 14,131			$ 55	$ 3	$ 1,391	$ 10,019	$ 8,834			$ (2,825)	$ (5,431)	$ 2,085
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(878)							(941)					63
Other comprehensive (loss) income (K)	(507)											(691)	184
Cash dividends declared:
Cash dividends declared, preferred		$ (2)	$ (67)						$ (2)	$ (67)
Cash dividends declared, common	(159)							(159)
Stock-based compensation (I)	86						86
Common stock issued: compensation plans (I)	(19)						(205)				186
Retirement of Treasury stock (I)	0					(76)	(2,563)				2,639
Reverse stock split (I)	0					(877)	877
Distribution of Alcoa Corporation	(7,271)							(8,692)				3,554	(2,133)
Distributions	(226)												(226)
Contributions	51												51
Other	2
Balance at end of period at Dec. 31, 2016	5,141			55	3	438	8,214	(1,027)			0	(2,568)	26
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(74)							(74)					0
Other comprehensive (loss) income (K)	(74)											(76)	2
Cash dividends declared:
Cash dividends declared, preferred		(2)	$ (51)						(2)	$ (51)
Cash dividends declared, common	(109)							(109)
Stock-based compensation (I)	67						67
Common stock issued: compensation plans (I)	21						21				0
Conversion of mandatory convertible preferred stock (I)	0				(3)	39	(36)
Issuance of common stock (I)	4					4
Distributions	(14)												(14)
Other	15							15
Balance at end of period at Dec. 31, 2017	4,924			55	0	481	8,266	(1,248)			0	(2,644)	14
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	642							642					0
Other comprehensive (loss) income (K)	85											85	0
Cash dividends declared:
Cash dividends declared, preferred		$ (2)							$ (2)
Cash dividends declared, common	(117)							(117)
Stock-based compensation (I)	50						50
Common stock issued: compensation plans (I)	5					2	3
Other	(2)							0					(2)
Balance at end of period at Dec. 31, 2018	$ 5,585			$ 55	$ 0	$ 483	$ 8,319	$ (358)			$ 0	$ (2,926)	$ 12