Segment Information - Schedule of Combined Segment Adjusted EBITDA to Net Income Attributable to Arconic (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Total segment operating profit	$ 400	$ 451
Restructuring and other charges	(7)	(73)
Operating income	333	283
Interest expense	(114)	(115)
Other (expense) income, net	(20)	316
Income before income taxes	199	484
Segment Reconciling Items
Segment Reporting Information [Line Items]
Restructuring and other charges	(7)	(73)
Corporate expense	(60)	(95)
Operating income	333	283
Interest expense	(114)	(115)
Other (expense) income, net	(20)	316
Income before income taxes	$ 199	$ 484