Segment and Geographic Area Information - Schedule of Operating Results of Arconic's Reportable Segment (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Sales	$ 1,238	$ 1,134	$ 1,253	$ 1,634	$ 1,734	$ 1,794	$ 1,818	$ 1,752	$ 5,259	$ 7,098	$ 6,778
Segment operating profit									626	579	775
Restructuring and other charges (E)									182	582	163
Provision for depreciation and amortization									279	295	314
Capital expenditures									267	641	768
Total Assets	(11,443)				(17,562)				(11,443)	(17,562)
Third-party sales
Segment Reporting Information [Line Items]
Sales									5,257	7,105	6,798
Inter-segment sales
Segment Reporting Information [Line Items]
Sales									(12)	(24)	(35)
Total segment sales
Segment Reporting Information [Line Items]
Sales									5,269	7,129	6,833
Segment operating profit									890	1,390	1,105
Restructuring and other charges (E)									106	506	59
Provision for depreciation and amortization									262	269	289
Capital expenditures									158	344	407
Total Assets	(9,535)				(10,035)				(9,535)	(10,035)
Engine Products | Third-party sales
Segment Reporting Information [Line Items]
Sales									2,406	3,320	3,092
Engine Products | Inter-segment sales
Segment Reporting Information [Line Items]
Sales									(5)	(11)	(16)
Engine Products | Total segment sales
Segment Reporting Information [Line Items]
Sales									2,411	3,331	3,108
Segment operating profit									417	621	464
Restructuring and other charges (E)									36	297	47
Provision for depreciation and amortization									123	131	141
Capital expenditures									77	211	217
Total Assets	(4,756)				(5,445)				(4,756)	(5,445)
Fastening Systems | Third-party sales
Segment Reporting Information [Line Items]
Sales									1,245	1,561	1,531
Fastening Systems | Inter-segment sales
Segment Reporting Information [Line Items]
Sales									0	0	0
Fastening Systems | Total segment sales
Segment Reporting Information [Line Items]
Sales									1,245	1,561	1,531
Segment operating profit									247	396	357
Restructuring and other charges (E)									39	6	17
Provision for depreciation and amortization									48	48	48
Capital expenditures									39	36	47
Total Assets	(2,707)				(2,810)				(2,707)	(2,810)
Engineered Structures | Third-party sales
Segment Reporting Information [Line Items]
Sales									927	1,255	1,209
Engineered Structures | Inter-segment sales
Segment Reporting Information [Line Items]
Sales									(7)	(13)	(19)
Engineered Structures | Total segment sales
Segment Reporting Information [Line Items]
Sales									934	1,268	1,228
Segment operating profit									73	120	64
Restructuring and other charges (E)									28	199	(5)
Provision for depreciation and amortization									52	58	69
Capital expenditures									19	27	53
Total Assets	(1,444)				(1,151)				(1,444)	(1,151)
Forged Wheels | Third-party sales
Segment Reporting Information [Line Items]
Sales									679	969	966
Forged Wheels | Inter-segment sales
Segment Reporting Information [Line Items]
Sales									0	0	0
Forged Wheels | Total segment sales
Segment Reporting Information [Line Items]
Sales									679	969	966
Segment operating profit									153	253	220
Restructuring and other charges (E)									3	4	0
Provision for depreciation and amortization									39	32	31
Capital expenditures									23	70	$ 90
Total Assets	$ (628)				$ (629)				$ (628)	$ (629)