Segment and Geographic Area Information Segment Information - Schedule of Operating Results of Arconic's Reportable Segments (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
Revenue, Major Customer [Line Items]
Sales (B)	$ 3,401	$ 3,559	$ 3,691	$ 3,541	$ 3,472	$ 3,524	$ 3,573	$ 3,445	$ 14,192	$ 14,014	$ 12,960
Engineered Products and Forgings
Revenue, Major Customer [Line Items]
Sales (B)									7,105	6,798	6,300
Global Rolled Products
Revenue, Major Customer [Line Items]
Sales (B)									7,082	7,223	6,540
Transportation and Construction Solutions
Revenue, Major Customer [Line Items]
Sales (B)									14,187	14,021	12,840
Aerospace | Engineered Products and Forgings
Revenue, Major Customer [Line Items]
Sales (B)									5,075	4,722	4,347
Aerospace | Global Rolled Products
Revenue, Major Customer [Line Items]
Sales (B)									1,251	1,116	1,109
Aerospace | Transportation and Construction Solutions
Revenue, Major Customer [Line Items]
Sales (B)									6,326	5,838	5,456
Transportation | Engineered Products and Forgings
Revenue, Major Customer [Line Items]
Sales (B)									1,289	1,302	1,098
Transportation | Global Rolled Products
Revenue, Major Customer [Line Items]
Sales (B)									2,418	2,550	2,072
Transportation | Transportation and Construction Solutions
Revenue, Major Customer [Line Items]
Sales (B)									3,707	3,852	3,170
Building and construction | Engineered Products and Forgings
Revenue, Major Customer [Line Items]
Sales (B)									0	0	0
Building and construction | Global Rolled Products
Revenue, Major Customer [Line Items]
Sales (B)									1,300	1,357	1,269
Building and construction | Transportation and Construction Solutions
Revenue, Major Customer [Line Items]
Sales (B)									1,300	1,357	1,269
Industrial and Other | Engineered Products and Forgings
Revenue, Major Customer [Line Items]
Sales (B)									741	774	855
Industrial and Other | Global Rolled Products
Revenue, Major Customer [Line Items]
Sales (B)									2,113	2,200	2,090
Industrial and Other | Transportation and Construction Solutions
Revenue, Major Customer [Line Items]
Sales (B)									2,854	2,974	2,945
Intersegment Eliminations
Revenue, Major Customer [Line Items]
Sales (B)									(183)	(205)	(183)
Intersegment Eliminations | Engineered Products and Forgings
Revenue, Major Customer [Line Items]
Sales (B)									0	0	0
Intersegment Eliminations | Global Rolled Products
Revenue, Major Customer [Line Items]
Sales (B)									$ (183)	$ (205)	$ (183)