Segment Information - Schedule of Combined Segment Adjusted EBITDA to Net Income Attributable to Arconic (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Segment Reporting Information [Line Items]
Total segment operating profit	$ 447	$ 400
Restructuring and other charges	(12)	(7)
Operating income	374	333
Interest expense	(85)	(114)
Other expense, net	(32)	(20)
Consolidated income before income taxes	257	199
Segment Reconciling Items
Segment Reporting Information [Line Items]
Restructuring and other charges	(12)	(7)
Corporate expense	(61)	(60)
Operating income	374	333
Interest expense	(85)	(114)
Other expense, net	(32)	(20)
Consolidated income before income taxes	$ 257	$ 199