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, 2014	$ 14,794			$ 55	$ 3	$ 1,304	$ 9,284	$ 9,379			$ (3,042)	$ (4,677)	$ 2,488
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net (loss) income	(197)							(322)					125
Other comprehensive loss (B)	(1,176)											(754)	(422)
Cash dividends declared:
Cash dividends declared, preferred		$ (2)	$ (67)						$ (2)	$ (67)
Cash dividends declared, common	(154)							(154)
Equity option on convertible notes (F)	55						55
Stock-based compensation (O)	92						92
Common stock issued: compensation plans (O)	22						(195)				217
Issuance of common stock (F and O)	870					87	783
Distributions	(106)												(106)
Contributions	2												2
Other	(2)
Balance at end 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 (loss) income	(878)							(941)					63
Other comprehensive loss (B)	(507)											(691)	184
Cash dividends declared:
Cash dividends declared, preferred		(2)	(67)						(2)	(67)
Cash dividends declared, common	(159)							(159)
Stock-based compensation (O)	86						86
Common stock issued: compensation plans (O)	(19)						(205)				186
Distributions	(226)												(226)
Contributions	51												51
Retirement of Treasury stock (O)	0					(76)	(2,563)				2,639
Reverse stock split (O)	0					(877)	877
Distribution of Alcoa Corporation	(7,271)							(8,692)				3,554	(2,133)
Other	2												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 (loss) income	(74)							(74)					0
Other comprehensive loss (B)	(74)											(76)	2
Cash dividends declared:
Cash dividends declared, preferred		$ (2)	$ (51)						$ (2)	$ (51)
Cash dividends declared, common	(109)							(109)
Stock-based compensation (O)	67						67
Common stock issued: compensation plans (O)	21						21
Issuance of common stock (F and O)	4					4
Distributions	(14)												(14)
Conversion of mandatory convertible preferred stock (O)	0				(3)	39	(36)
Other	15							15					0
Balance at end of period at Dec. 31, 2017	$ 4,924			$ 55	$ 0	$ 481	$ 8,266	$ (1,248)			$ 0	$ (2,644)	$ 14