Restructuring and Other Charges - Schedule of Restructuring and Other Charges (Parenthetical) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restructuring Cost and Reserve [Line Items]
Other	$ 49	$ 47	$ 92
Alcoa Corporation [Member]
Restructuring Cost and Reserve [Line Items]
Other		$ 1	$ 32