Segment Information - Schedule of Combined Segment Adjusted EBITDA to Net Income Attributable to Arconic (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
	Jun. 19, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Segment Reporting Information [Line Items]
Combined segment adjusted EBITDA		$ 535	$ 515	$ 1,640	$ 1,607
Depreciation and amortization		(140)	(136)	(410)	(402)
Restructuring and other charges		(19)	(3)	(118)	(33)
Operating income		271	237	797	790
Other income, net		1	11	526	40
Interest expense	$ (24)	(100)	(126)	(398)	(371)
Income from continuing operations before income taxes		172	122	925	459
Provision for income taxes		(53)	(56)	(272)	(230)
Discontinued operations			100		88
Net income attributable to Arconic		119	166	653	317
Other [Member]
Segment Reporting Information [Line Items]
Depreciation and amortization		(140)	(136)	(410)	(402)
Restructuring and other charges		(19)	(3)	(118)	(33)
Impact of LIFO		(48)	(1)	(78)	(26)
Metal price lag		2	4	43	10
Corporate expense		(42)	(113)	(224)	(304)
Other		(17)	(29)	(56)	(62)
Operating income		271	237	797	790
Other income, net		1	11	526	40
Interest expense		(100)	(126)	(398)	(371)
Income from continuing operations before income taxes		172	122	925	459
Provision for income taxes		$ (53)	(56)	$ (272)	(230)
Discontinued operations			$ 100		$ 88