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, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Sales	$ (3,401)	$ (3,559)	$ (3,691)	$ (3,541)	$ (3,472)	$ (3,524)	$ (3,573)	$ (3,445)	$ (14,192)	$ (14,014)	$ (12,960)
Capital expenditures									533	715
Goodwill	4,493				4,500				4,493	4,500	4,535
Assets	17,578				18,693				17,578	18,693
Segment operating profit									2,015	1,586	1,689
Restructuring and other charges									590
Provision for depreciation and amortization									502
Non-cash asset impairments									570	13	58
Total segment sales
Segment Reporting Information [Line Items]
Sales									(14,370)	(14,226)	(13,023)
Assets	14,941				15,339				14,941	15,339
Segment operating profit										1,586	1,689
Restructuring and other charges										(87)	113
Provision for depreciation and amortization										542	518
Total segment sales | Third-Party Sales
Segment Reporting Information [Line Items]
Sales									(14,187)	(14,021)	(12,840)
Intersegment Eliminations
Segment Reporting Information [Line Items]
Sales									183	205	183
Engineered Products and Forgings
Segment Reporting Information [Line Items]
Capital expenditures									344	407
Goodwill	4,067	7			4,186				4,067	4,186
Assets	10,034				10,494				10,034	10,494
Segment operating profit									1,390	1,105
Restructuring and other charges									509	70
Provision for depreciation and amortization									269	289
Engineered Products and Forgings | Total segment sales
Segment Reporting Information [Line Items]
Sales									(7,105)	(6,798)	(6,300)
Goodwill	4,067				4,186				4,067	4,186	4,212
Segment operating profit											1,119
Restructuring and other charges											30
Provision for depreciation and amortization											275
Engineered Products and Forgings | Total segment sales | Third-Party Sales
Segment Reporting Information [Line Items]
Sales									(7,105)	(6,798)	(6,300)
Engineered Products and Forgings | Intersegment Eliminations
Segment Reporting Information [Line Items]
Sales									0	0	0
Global Rolled Products
Segment Reporting Information [Line Items]
Sales									(7,082)	(7,223)	(6,540)
Capital expenditures									189	308
Goodwill	426	$ 68			314				426	314
Assets	4,907				4,845				4,907	4,845
Segment operating profit									625	481
Restructuring and other charges									81	(157)
Provision for depreciation and amortization									233	253
Global Rolled Products | Total segment sales
Segment Reporting Information [Line Items]
Sales									(7,265)	(7,428)	(6,723)
Goodwill	426				$ 314				426	314	323
Segment operating profit											570
Restructuring and other charges											83
Provision for depreciation and amortization											243
Global Rolled Products | Total segment sales | Third-Party Sales
Segment Reporting Information [Line Items]
Sales									(7,082)	(7,223)	(6,540)
Global Rolled Products | Intersegment Eliminations
Segment Reporting Information [Line Items]
Sales									183	$ 205	$ 183
Arconic Engines
Segment Reporting Information [Line Items]
Goodwill	$ 2,164								$ 2,164
Non-cash asset impairments			$ 428