Segment and Geographic Area Information - Schedule of Segment EBITDA to Consolidated Net (Loss) Income Attributable to Arconic (Detail) - USD ($) $ in Millions		3 Months Ended								12 Months Ended
	Jun. 19, 2017	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Combined segment adjusted EBITDA										$ 2,144	$ 2,063	$ 1,894
Impairment of goodwill										(719)	0	(25)
Restructuring and other charges										(165)	(155)	(214)
Operating income										326	819	628
Interest expense	$ (24)									(496)	(499)	(473)
Other income, net										640	94	28
Income from continuing operations before income taxes										470	414	183
Provision for income taxes										(544)	(1,476)	(339)
Discontinued operations										0	121	(165)
Net loss attributable to Arconic		$ (727)	$ 119	$ 212	$ 322	$ (1,258)	$ 166	$ 135	$ 16	(74)	(941)	(322)
Other
Segment Reporting Information [Line Items]
Depreciation and amortization										(551)	(535)	(508)
Impairment of goodwill										(719)	0	(25)
Restructuring and other charges										(165)	(155)	(214)
Impact of LIFO										(110)	(18)	101
Metal price lag										72	27	(175)
Corporate expense										(274)	(454)	(371)
Other										(71)	(109)	(74)
Operating income										326	819	628
Interest expense										(496)	(499)	(473)
Other income, net										640	94	28
Income from continuing operations before income taxes										470	414	183
Provision for income taxes										(544)	(1,476)	(339)
Discontinued operations										0	121	(165)
Net income attributable to noncontrolling interest										$ 0	$ 0	$ (1)