Earnings Per Share - Reconciliation of Information Used to Compute Basic and Diluted EPS (Detail) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Net loss from continuing operations attributable to Arconic	$ (74)	$ (1,062)	$ (156)
Net income from continuing operations attributable to noncontrolling interests	0	0	(1)
Less: preferred stock dividends declared	(53)	(69)	(69)
Loss from continuing operations available to Arconic common shareholders	(127)	(1,131)	(226)
Income (loss) from discontinued operations after income taxes and noncontrolling interests	0	121	(165)
Net loss available to Arconic common shareholders—basic	(127)	(1,010)	(391)
Add: interest expense related to convertible notes		0	0	$ 0
Add: dividends related to mandatory convertible preferred stock		0	0	$ 0
Net loss available to Arconic common shareholders—diluted	$ (127)	$ (1,010)	$ (391)
Average shares outstanding-basic (in shares)	451	438	420
Stock options (in shares)		0	0	0
Stock and performance awards (in shares)	0	0	0
Mandatory convertible preferred stock (in shares)		0	0	0
Convertible notes (in shares)		0	0	0
Average shares outstanding-diluted (in shares)	451	438	420