Segment Information - Schedule of Operating Results of Arconic's Reportable Segments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Total sales	$ 3,559	$ 3,524	$ 10,791	$ 10,542
Segment operating profit	524	391	1,511	1,225
Restructuring and other charges	107	17	605	27
Provision for depreciation and amortization	122	134	381	402
Operating Segments
Segment Reporting Information [Line Items]
Total sales	3,598	3,566	10,929	10,712
Intersegment sales
Segment Reporting Information [Line Items]
Total sales	41	44	142	161
Third-party sales | Operating Segments
Segment Reporting Information [Line Items]
Total sales	3,557	3,522	10,787	10,551
Engineered Products and Forgings
Segment Reporting Information [Line Items]
Segment operating profit	363	284	1,036	837
Restructuring and other charges	45	15	506	24
Provision for depreciation and amortization	65	73	206	217
Engineered Products and Forgings | Operating Segments
Segment Reporting Information [Line Items]
Total sales	1,794	1,683	5,372	5,083
Engineered Products and Forgings | Intersegment sales
Segment Reporting Information [Line Items]
Total sales	0	0	0	0
Engineered Products and Forgings | Third-party sales | Operating Segments
Segment Reporting Information [Line Items]
Total sales	1,794	1,683	5,372	5,083
Global Rolled Products
Segment Reporting Information [Line Items]
Segment operating profit	161	107	475	388
Restructuring and other charges	62	2	99	3
Provision for depreciation and amortization	57	61	175	185
Global Rolled Products | Operating Segments
Segment Reporting Information [Line Items]
Total sales	1,804	1,883	5,557	5,629
Global Rolled Products | Intersegment sales
Segment Reporting Information [Line Items]
Total sales	41	44	142	161
Global Rolled Products | Third-party sales | Operating Segments
Segment Reporting Information [Line Items]
Total sales	$ 1,763	$ 1,839	$ 5,415	$ 5,468